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. Author manuscript; available in PMC: 2024 Sep 15.
Published in final edited form as: Neuropharmacology. 2023 May 23;236:109598. doi: 10.1016/j.neuropharm.2023.109598

Serotonin modulates social responses to stressed conspecifics via insular 5-HT2C receptors in rat

Alexandra J Ng 1,*, Lindsay K Vincelette 1, Jiayi Li 1, Bridget H Brady 1, John P Christianson 1
PMCID: PMC10330840  NIHMSID: NIHMS1906483  PMID: 37230216

Abstract

Behaviors associated with distress can affect the anxiety-like states in observers and this social transfer of affect shapes social interactions among stressed individuals. We hypothesized that social reactions to stressed individuals engage the serotonergic dorsal raphe nucleus (DRN) which promotes anxiety-like behavior via postsynaptic action of serotonin at serotonin 2C (5-HT2C) receptors in the forebrain. First, we inhibited the DRN by administering an agonist (8-OH-DPAT, 1μg in 0.5μL) for the inhibitory 5-HT1A autoreceptors which silences 5-HT neuronal activity. 8-OH-DPAT prevented the approach and avoidance, respectively, of stressed juvenile (PN30) or stressed adult (PN60) conspecifics in the social affective preference (SAP) test in rats. Similarly, systemic administration of a 5-HT2C receptor antagonist (SB242084, 1mg/kg, i.p.) prevented approach and avoidance of stressed juvenile or adult conspecifics, respectively. Seeking a locus of 5-HT2C action, we considered the posterior insular cortex which is critical for social affective behaviors and rich with 5-HT2C receptors. SB242084 administered directly into the insular cortex (5μM in 0.5μL bilaterally) interfered with the typical approach and avoidance behaviors observed in the SAP test. Finally, using fluorescent in situ hybridization, we found that 5-HT2C receptor mRNA (htr2c) is primarily colocalized with mRNA associated with excitatory glutamatergic neurons (vglut1) in the posterior insula. Importantly, the results of these treatments were the same in male and female rats. These data suggest that interactions with stressed others require the serotonergic DRN and that serotonin modulates social affective decision-making via action at insular 5-HT2C receptors.

Keywords: rat, insular cortex, serotonin, 5-HT2C, RNAscope, social affect

Graphical Abstract

graphic file with name nihms-1906483-f0001.jpg

1. Introduction

When encountering others in distress, observers must assess the potential risk or reward to themselves in order to determine how to interact. Specifically, the observer must recognize and integrate environmental and social cues, evaluate personal safety, and assess the potential to help the other (Staub, 1974). In rodents, social approach and avoidance behaviors are evident in a variety of experimental paradigms allowing for direct investigation of the neurobiology underlying this type of social decision-making (Baptista-de-Souza et al., 2015; Ferretti & Papaleo, 2019; Keysers et al., 2022; S.-W. Kim et al., 2021; K. Meyza & Knapska, 2018; Rogers-Carter, Varela, et al., 2018; Sterley et al., 2018; Sterley & Bains, 2021; Walsh et al., 2023). In social interactions among rodents exposed to stress, approach or avoidance behaviors appear to be influenced by several factors including internal states, familiarity with the conspecific, nature of the stressor and the safety of the interaction context. For example, social avoidance occurs when rats are presented with sick conspecifics (Rieger, Worley, et al., 2022), when rats or mice are presented with stressed adult conspecifics (Ferretti et al., 2019; Rogers-Carter, Varela, et al., 2018), and when the observer is stressed themselves (Christianson et al., 2008). On the other hand, social approach to a stressed conspecific occurs when mice are exposed to a demonstrator expressing conditioned fear (Ferretti et al., 2019; Scheggia et al., 2020), when mice or pair-bonded voles are reunited with a stressed cagemate (Burkett et al., 2016; Sterley et al., 2018), and when rats are presented with a restrained cagemate (Bartal et al., 2011) or stressed juveniles (Rogers-Carter, Varela, et al., 2018). Further, direct observation of conspecifics in distress leads to stress-related affective behaviors and vicarious learning in the observers (For review see: (Keum & Shin, 2019; K. Z. Meyza et al., 2017; Monfils & Agee, 2019).

In these experimental paradigms, the observer rat’s behavior towards a stressed conspecific can be explained by a vicarious sense of stress or anxiety in the observer. Exposure to stressed conspecifics triggers hypothalamic pituitary adrenocortical (HPA) axis stress responses (Sterley & Bains, 2021) and increases neuronal activity in brain regions associated with emotion expression such as the amygdala, anterior cingulate, prefrontal, and insular cortices (K. Meyza & Knapska, 2018). This so-called social transfer of stress, or “emotion contagion,” is thought to be a basis for social affective and empathic responding to others (de Waal, 2008; de Waal & Preston, 2017; Keysers et al., 2022; K. Z. Meyza et al., 2017; Sterley & Bains, 2021). The clearest support of this view was reported by Sterley et al., (2018) who demonstrated that exposure to stressed conspecifics potentiated excitatory drive onto paraventricular corticotropin releasing hormone (CRH) neurons, which are critical for the initiation of the stress response. Critically, inhibiting CRH activity with a CRH antagonist or direct optogenetic inhibition prevented the observer from engaging in social interactions with the stressed conspecific. These findings reinforce the hypothesis that how an individual responds to social stress cues is strongly influenced by their own vicarious experience of stress.

Stimulation of an observer’s HPA axis by social stress cues likely leads to upregulation of complementary stress and anxiety systems in the brain. Of interest to the current study is the serotonin (5-HT) system which originates from the dorsal raphe nucleus (DRN) (Fu et al., 2010) and is activated by CRH (Kirby et al., 2008). Additionally, aversive or painful stimuli (Bouwknecht et al., 2007; Hale et al., 2008), social stressors (Abumaria et al., 2006; Wood et al., 2013), drugs of abuse (Will et al., 2004), and physiological stress (Christianson et al., 2008; Rozeske et al., 2011) all augment neural activity in the DRN 5-HT neurons. Psychological (Kawahara et al., 1993) and physical stressors (Kirby et al., 1997) increase 5-HT synthesis, extracellular 5-HT at 5-HTergic cell bodies, and postsynaptic 5-HT receptor expression (Chaouloff et al., 1999; Inoue et al., 1994). The anxiogenic effects of 5-HT are mediated by action at a large and diverse family of receptors (Hoyer et al., 2002; Waselus et al., 2011) postsynaptic to its complex network of ascending axonal projections (Waselus et al., 2006). In regards to social behavior, 5-HT action at 5-HTergic receptors in the forebrain drives both approach and avoidance behavior depending on the postsynaptic targets. Prosocial interactions are mediated by DRN projections to anterior cingulate cortex (Li et al., 2021), nucleus accumbens (Waselus et al., 2006), and oxytocin-induced release of 5-HT from the DRN (Dölen et al., 2013). In fact, optogenetic stimulation of DRN neurons and 5-HTergic projections from the DRN to the nucleus accumbens can even rescue autism-like social deficits in mice (Luo et al., 2015; Walsh et al., 2018). Additionally, social behavior modifications following uncontrollable stress and aversive social situations like social defeat are mediated by 5-HT action in the DRN, basolateral amygdala, and dorsal striatum (Christianson et al., 2010; Cooper et al., 2008; Lukkes et al., 2009; Paul et al., 2011; Strong et al., 2011a).

The anxiogenic functions of 5-HT are largely attributed to 5-HT2C receptors (Drago & Serretti, 2009; Heisler et al., 2007; Marcinkiewcz et al., 2016; Millan, 2005), which are found throughout the forebrain (Clemett et al., 2000; Linley et al., 2013). For example, 5-HT2C agonist administration increases the latency to investigate novel objects (Campbell & Merchant, 2003), reduces open arm exploration in the plus maze (Pockros-Burgess et al., 2014), and mimics the effects of inescapable tail shocks on later freezing (Strong et al., 2011a). 5-HT2C receptor knockout mice exhibit an anxiolytic phenotype (Heisler et al., 2007) whereas 5-HT2C receptor overexpression results in an anxious phenotype (Kimura et al., 2009). Consistently, 5-HT2C receptor antagonists prevent anxiety-like behaviors evoked by acute 5-HT increases (Burghardt et al., 2007) and acute stress (Christianson et al., 2010) and can facilitate fear inhibition (Foilb & Christianson, 2016). Some of these actions are attributed to 5-HT2C receptors in the striatum (Strong et al., 2011b) and basolateral amygdala (Christianson et al., 2010; Pockros-Burgess et al., 2014) that receive dense innervation from the DRN.

We focused on insular 5-HT2C receptors in this study because the insula contributes to a range of motivated behaviors that are influenced by anxiety, including social cognition. The insula is a unique structure in social decision-making because it is necessary for both the approach and avoidance of stressed rats. Specifically, when an adult experimental rat is presented with a choice to interact with either a naive or stressed juvenile conspecific in a social affective preference (SAP) test, the adult experimental rat will spend more time interacting with the stressed juvenile. However, when presented with a pair of naive or stressed adult conspecifics, adult experimental rats avoid the stressed adult and spend more time interacting with the naive adult conspecific. Neurobiological treatments that inhibit insular activity prevent both of these patterns (Djerdjaj et al., 2022, 2023; Rieger, Varela, et al., 2022; Rieger, Worley, et al., 2022; Rogers-Carter, Djerdjaj, et al., 2018; Rogers-Carter, Varela, et al., 2018). Because the insula contains direct input from the DRN (Gehrlach et al., 2020; Vertes, 1991; Vertes & Kocsis, 1994) and 5-HT2C receptors (Clemett et al., 2000; Linley et al., 2013), we hypothesized that 5-HT and 5-HTergic input to insular 5-HT2C receptors may be necessary for social affective behaviors in the SAP test.

In this study, we first tested for the necessity of the DRN 5-HT neurons in SAP tests by inhibiting the DRN with a 5-HT1A agonist prior to SAP tests in male and female rats. Next, to determine if 5-HT2C receptors are needed for social affective behavior, we systemically injected test rats with a 5-HT2C receptor antagonist prior to SAP tests. Then, to determine if insular 5-HT2C receptors specifically are needed for social affective behaviors we injected test rats with 5-HT2C receptor antagonist into the posterior insula prior to SAP tests. Finally, to inform a working model for how 5-HT2C receptors may impact insular physiology, we used fluorescent in situ hybridization to investigate the cellular distribution of 5-HT2C receptors in the insula.

2. Methods

2.1. Animals

Male and female Sprague-Dawley rats were obtained from Charles River Laboratories (Wilmington, MA) at either age PN51 (test rats and adult conspecifics) or PN21 (juvenile conspecifics) and maintained in groups of 2–3. All animals were allowed to acclimate to the vivarium for a minimum of 7 days prior to any experimental or surgical procedures and given access to food and water ad libitum. Consistent with our recent experiments in female rats, on the 5 days preceding behavioral testing male and female rats were gently wrapped in a cloth towel for 1 minute to habituate the rats to experiment handling and reduce stress associated with injections (Djerdjaj et al., 2023; Rieger, Varela, et al., 2022). The vivarium maintained a 12 h light/dark cycle and all behavioral tests occurred within the first 4 h of the light cycle. All procedures and animal care were conducted in accordance with the NIH Guide for the care and use of laboratory animals and all experimental procedures were approved by the Boston College Institutional Animal Care and Use Committee.

2.2. Procedures

2.2.1. Surgical implantation of indwelling cannula

While under isoflurane anesthesia (2–5% v/v in O2), rats were surgically implanted with bilateral guide cannula (26-gauge, Plastics One, Roanoke VA) in the insular cortex (from bregma: A/P: −1.8 mm, M/L: ± 6.5 mm, D/V: −6.8 mm from skull surface) or the DRN (from bregma: A/P: −8.1, M/L: 0, D/V: −5.1) that were affixed with stainless steel screws and acrylic dental cement. Immediately following surgery, rats were injected with analgesic meloxicam (1 mg/kg, Eloxiject, Henry Schein), antibiotic penicillin (12,000 units, Combi-pen 48, Covetrus) and Ringer’s solution (10 mL, Covetrus). Rats were then returned to their homecage and allowed at least 2 weeks (males) or 3 weeks (females) for recovery prior to behavioral testing. After behavioral testing concluded, rats were overdosed with tribromoethanol (Sigma) and brains were dissected, flash frozen, and sectioned on a cryostat at 40 μm. Slices were then mounted onto gelatin-subbed slides (Fisher) and stained with cresyl-violet to verify cannula placements by comparing microinjector tip location to the rat whole brain stereotaxic atlas. Rats were included in the analyses if their cannula were in the insula (Bregma − 1.44 through Bregma −2.8) or DRN (Bregma −7.64 through Bregma −8.3). DRN cannula confirmed to be implanted in the aqueduct were included in the analyses as the injection needle protruded 1 mm beyond the cannula tip.

2.2.2. DRN 8-OH-DPAT injections:

To inhibit DRN 5-HT neurons we microinjected 8-OH-DPAT, an agonist for the inhibitory 5-HT1A autoreceptors which hyperpolarizes 5-HT neurons (Kirby et al., 2003) via G-protein coupled inward rectifying potassium channels (Hjorth & Magnusson, 1988). 8-OH-DPAT (Tocris) was first dissolved in 100% DMSO and then diluted in a vehicle of 10% DMSO and 0.9% saline. Injections were 1 μg in 0.5 μL and infused at a rate of 1.0 μL/min with an additional 1 min diffusion time. Testing occurred 30–40 mins after injection. This dose and preparation were selected based on prior use in our laboratory (Christianson et al., 2010) and others (Maier et al., 1995). Although we typically use a within-subjects design for pharmacology studies in the SAP test, a pilot study indicated that repeated DRN infusions were not viable so this experiment was conducted as a between-subjects design.

2.2.3. Systemic and insular SB242084 injections:

To determine the contribution of 5-HT2C receptors we used SB242084, a brain-penetrant, competitive and selective antagonist for the 5-HT2C receptor (Bromidge et al., 1997; Kennett et al., 1997). For systemic intraperitoneal (i.p.) injections, SB242084 (Tocris) was first dissolved in 100% DMSO prior to being diluted to 1 mg/kg in a vehicle of 10% DMSO and 0.9% saline. This dose was selected based on prior studies (Boulougouris et al., 2008; Burghardt et al., 2007; Christianson et al., 2010, 2013; Foilb & Christianson, 2016; Strong et al., 2011a). For insular microinjections, SB242084 was diluted to 5 μM in a vehicle of 10% DMSO and 0.9% saline, as used in prior studies (Christianson et al., 2010; Strong et al., 2011b). Injections were 0.5 μL/side at a rate of 1 μL/minute with an additional one-minute diffusion time. Systemic injections or insular infusions were made 30–40 mins prior to testing. Drug and vehicle treatments were administered in a counterbalanced, within-subjects design.

2.2.4. Social Affective Preference (SAP) test:

The SAP tests allow for the quantification of social interactions initiated by a test rat toward either a stressed or unstressed conspecific, providing insight into the test animal’s discrimination of socioemotional affective cues; they were conducted exactly as previously described (Djerdjaj et al., 2022, 2023; Rieger, Varela, et al., 2022; Rieger, Worley, et al., 2022; Rogers-Carter, Djerdjaj, et al., 2018; Rogers-Carter et al., 2019; Rogers-Carter, Varela, et al., 2018). Briefly, the SAP test begins when a test rat is placed in the center of an arena containing chambers for conspecifics on opposite sides of the arena. One of the conspecifics is stressed via two, 5 s 1 mA footshocks (60 s interval) immediately before testing; the other conspecific is naive to stress. The test rat is allowed to interact with the conspecifics for 5 min and time spent body sniffing and reaching for the conspecific is hand-scored by trained experimenters. In our first descriptions of the SAP test, we included analysis of a range of overt behaviors in SAP tests with male or female rats. Direct social interaction is the only objectively scorable behavior that is consistently affected by conspecific stress and age (Rogers-Carter, Djerdjaj, et al., 2018; Rogers-Carter, Varela, et al., 2018).

2.2.5. RNAScope in situ fluorescent hybridization

RNAScope was performed on posterior insular cortex (Bregma −1.8) sections according to the vendor’s instructions (ACDBio). Briefly, tissue was thawed, fixed and treated with a RNAScope cocktail including probes for vesicular glutamate transporter 1 (vglut1, catalog #317001), glutamate decarboxylase 2 (gad, catalog #435801), and htr2c (2C, catalog #469321) mRNAs, and DAPI. The total number of nuclei (DAPI) and cells colocalized with vglut1, gad, and htr2c mRNAs were determined. Effects of sex on cell counts were assessed in two-way ANOVAs with sex as a between-group factor and hemisphere side as a within-subject factor. Data were obtained for all 3 mRNAs from both hemispheres of 4 male and 4 female rats; the vglut1 and htr2c counts were replicated in a separate sample of 8 additional male and 8 female rats (both hemispheres). The mean of left and right hemisphere counts are shown.

2.3. Statistical Analysis

Data from experimental rats were only included if site-specificity criteria were met after verification of cannula placement. Interaction times during SAP tests were analyzed using 3-way ANOVA (conspecific age by conspecific affect by treatment) and percent preference data were analyzed using a 2-way ANOVA (conspecific age by treatment). Experiments were designed to be powerful enough to detect sex differences seeking N=12 for males and females. Rats were run in cohorts and data were analyzed sequentially after removal of subjects with misplaced cannulas resulting in some groups with a range of final sample sizes from 5 to 19. All dependent measures were initially analyzed with ANOVAs treating sex as a between subjects variable and in all cases, we found no significant main effect or interactions that included sex as a factor. This was consistent with visual inspection of the individual data which are provided in all of the data panels. (Readers interested in viewing male and female data separately are directed to Supplemental Figures 1, 2, and 3). Males and females exhibited a similar range of behavior, variance, and responses to drug treatment. Therefore, male and female data were combined for all subsequent analysis. Main effects and interaction effects were deemed significant at p < 0.05 and followed by Sidak post hoc tests to maintain experiment-wise type 1 error rate to ɑ < 0.05. All analyses were performed in Prism (GraphPad, version 9.5.0) and results of ANOVA’s, final sample size, and post hoc test results are presented in the figure legends and in Supplemental Table 1.

3. Results

3.1. DRN microinjection of a 5-HT1A agonist disrupts age and stress dependent social preference

To investigate the contributions of DRN 5-HT neurons to social emotional behaviors, we conducted SAP tests after infusion of 8-OH-DPAT or vehicle to the DRN (Figure 1). Only test rats that met site specificity requirements after cannula verification were included resulting in final sample sizes of n = (5–6) per group for females and n = (6–9) per group for males (Figure 1D). DRN administration of 8-OH-DPAT in male and female test rats prevented the approach to stressed juvenile and the avoidance of stressed adult conspecifics. There was a significant main effect of conspecific age (FAGE (1, 50) = 9.436, P = 0.0034, η2= 0.074) and interaction effect of conspecific age by treatment by conspecific affect (FAGE × DRUG × AFFECT (1, 50) = 45.38, P < 0.001, η2= 0.236). Post hoc comparison with juvenile conspecifics revealed a significant difference between the social investigation of naive and stressed juveniles in the vehicle condition (P = 0.0005) that was not present in the 8-OH-DPAT condition (P = 0.2981). Post hoc comparison with adult conspecifics revealed a significant difference between the social investigation of naive and stressed adults in the vehicle condition (P = 0.0208) and in the 8-OH-DPAT condition (P = 0.0129), in which the preference for conspecific interaction was opposite from the vehicle condition.

Figure 1. DRN microinjection of a 5-HT1A agonist disrupts age and stress dependent social preference.

Figure 1.

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A. Diagram of the social affective behavior test (SAP) paradigm. Rats received a DRN cannula implant and were given 2–3 weeks to recover. On the test day, rats received infusions of 5-HT1A agonist 8-OH-DPAT (DPAT) or vehicle solution into the DRN 30–40 minutes prior to a SAP test consisting of a 5-min interaction with a naive and stressed isosexual conspecific. The amount of time spent socially investigating each conspecific was recorded. B. Mean (with individual replicates) time spent interacting with naive or stressed juvenile (PN30) or adult (PN60) conspecifics in the SAP test. When tested under vehicle conditions with PN30 conspecifics, male (n = 18) and female (n = 12) test rats exhibit greater exploration of the stressed conspecific (***P = 0.0005); this pattern was blocked by 5-HT1A agonist 8-OH-DPAT (P = 0.2981). When tested under vehicle conditions with PN60 conspecifics, male (n = 13) and female (n = 11) test rats exhibit greater exploration of the naive conspecific (*P = 0.0191); this preference was blocked and reversed by 5-HT1A agonist 8-OH-DPAT (*P = 0.0117). Male test rats are shown with black lines, and female test rats are shown with red lines. C. For comparison, data from B was converted to a preference score (% preference = time investigating stressed conspecific / total investigation time * 100; mean and individual replicates shown). The effect of 8-OH-DPAT was different depending on the conspecific age (FAGE × DRUG(1, 54) = 43.99, P < 0.001, η2= 0.443). In juvenile SAP tests, 8-OH-DPAT infusions reduced the preference for stressed conspecifics whereas in adult SAP tests, 8-OH-DPAT increased preference for stressed conspecifics (****Ps < 0.0001). D. A representative cresyl violet stained DRN section showing cannula damage (scale bar = 500 μm) and cannula maps showing the placement of in-dwelling DRN cannula across all experiments related to Fig. 1. Diagram in panel A was created with BioRender.com. Atlas images recreated from Paxinos and Watson (1998).

The preference for the stressed conspecific in each experiment was calculated as a percentage of the total time spent investigating both conspecifics (Figure 1B) and analyzed with a 2-way ANOVA. There was a significant interaction effect of conspecific age by treatment (FAGE × DRUG (1, 55) = 43.99, P < 0.0001, η2= 0.443). Post hoc comparisons revealed a significant change in preference for stressed juveniles (P < 0.0001) and naïve adults (P < 0.0001) when comparing vehicle to 8-OH-DPAT (Figure 1C). In summary, test rats injected with vehicle preferred interaction with stressed juveniles and naive adults, while test rats injected with 8-OH-DPAT had no difference in interaction between stressed and naive juveniles and preferred interaction with stressed adults.

3.2. Systemic 5-HT2C receptor antagonist administration interfered with social affective preference.

To determine if social affective preference behavior involved the 5-HT2C receptor system, we conducted SAP tests after systemic injection of the highly selective antagonist SB242084 or vehicle (Figure 2). Final group sizes were n = (8–11) for females and n = (11–18) for males. There was a significant main effect of conspecific affect (FAFFECT(1, 48) = 5.254, P = 0.0263, η2= 0.015), significant conspecific age by conspecific affect interaction (FAGE × AFFECT(1, 48) = 24.49, P < 0.0001, η2= 0.074), and a significant treatment by conspecific age by conspecific affect interaction (FDRUG × AGE × AFFECT(1, 48) = 47.83, P < 0.0001, η2= 0.136). Post hoc comparison with juvenile conspecifics revealed a significant difference between the social investigation of naive and stressed juveniles in the vehicle condition (P < 0.0001) that was not present in the SB242084 condition (P = 0.1709). Post hoc comparison with adult conspecifics revealed a significant difference between the social investigation of naive and stressed adults in the vehicle condition (P < 0.0001) that was not present in the SB242084 condition (P > 0.9999).

Figure 2. Systemic 5-HT2C antagonist injections interfere with social interactions with stressed conspecifics.

Figure 2.

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A. Diagram of the social affective behavior test (SAP) paradigm. On the test day, rats received systemic injections of 5-HT2C receptor antagonist SB242084 or vehicle solution 30–40 minutes prior to a SAP test consisting of a 5-min interaction with a naive and stressed isosexual conspecific. The amount of time spent socially investigating each conspecific was recorded. B. Mean (with individual replicates) time spent interacting with naive or stressed juvenile (PN30) or adult (PN60) conspecifics in the SAP test. When tested under vehicle conditions with PN30 conspecifics, male (n = 18) and female (n = 8) test rats exhibit greater exploration of the stressed conspecific (****P < 0.0001); this pattern was blocked by 5-HT2C antagonist SB242084. When tested under vehicle conditions with PN60 conspecifics, male (n = 11) and female (n = 11) exhibit greater exploration of the naive conspecific (P < 0.0001); this pattern was blocked by 5-HT2C antagonist SB242084 (P > 0.999). Male test rats are shown with black lines, and female test rats are shown with red lines. C. For comparison, data from B was converted to a preference score (% preference = time investigating stressed conspecific / total investigation time * 100; mean and individual replicates shown). The effect of SB242084 was different depending on the conspecific age (FAGE × DRUG(1, 49) = 71.25, P < 0.0001, η2= 0.326). In juvenile SAP tests, SB242084 infusions reduced the preference for stressed conspecifics whereas in adult SAP tests, SB242084 increased preference for stressed conspecifics (****Ps < 0.0001). Diagram in panel A was created with BioRender.com.

The preference for the stressed conspecific in each experiment was calculated as a percentage of the total time spent investigating both conspecifics (Figure 2C) and analyzed with a 2-way ANOVA. There was a significant main effect of conspecific age (FAGE(1, 49) = 23.54, P < 0.0001, η2= 0.145) and significant conspecific age by treatment interaction (FAGE × DRUG(1, 49) = 71.25, P < 0.0001, η2= 0.326). Post hoc comparisons revealed a significant change in preference for stressed juveniles (P < 0.0001) and naïve adults (P < 0.0001) when comparing vehicle to SB242084 (Figure 2C). In summary, test rats injected with vehicle preferred interaction with stressed juveniles and naive adults, while test rats injected with SB242084 had no difference in interaction between stressed and naive juvenile and adult conspecifics.

3.3. Insular infusion of a 5-HT2C receptor antagonist disrupted social affective preference.

In the next experiment, we sought a locus of 5-HT2C in the posterior insular cortex. SAP tests were conducted 30–40 minutes after insular infusion of SB242084 or vehicle (Figure 3A). Only test rats with cannula found to terminate in the posterior insular cortex were included resulting in final sample sizes of n = (10–11) per group for males and n = (13–18) for females. There was a significant interaction effect of treatment by conspecific age by conspecific affect (FDRUG × AGE × AFFECT(1, 105) = 62.31, P <0.0001, η2=15.67). Post hoc comparison with juvenile conspecifics revealed a significant difference between the social investigation of naive and stressed juveniles in the vehicle condition (P < 0.0001) that was not present in the SB242084 condition (P = 0.1798). Post hoc comparison with juvenile conspecifics revealed a significant difference between the social investigation of naive and stressed adults in the vehicle condition (P = 0.0048) and in the SB242084 condition (P < 0.0001). Post hoc comparison with adult conspecifics revealed a significant difference between the social investigation of naive and stressed adults in the vehicle condition (P = 0.0048) and in the SB242084 condition (P < 0.0001), in which the preference for interaction was opposite from the vehicle condition.

Figure 3. Insular 5-HT2C antagonist injections interfere with social interactions with stressed conspecifics.

Figure 3.

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A. Diagram of the social affective behavior test (SAP) paradigm. On the test day, rats received injections of 5-HT2C receptor antagonist SB242084 or vehicle into the insular cortex 30–40 minutes prior to a SAP test consisting of a 5-min interaction with a naive and stressed isosexual conspecific. B. Mean (with individual replicates) time spent interacting with naive or stressed juvenile (PN30) or adult (PN60 conspecifics in the SAP test. When tested under vehicle with PN30 conspecifics, male (n = 11) and female (n = 14) test rats exhibit greater exploration of the stressed conspecific (****P < 0.0001); this pattern was blocked by 5-HT2C antagonist SB242084. When tested under vehicle with PN60 conspecifics, male (n = 10) and female (n = 19) test rats exhibited exhibit greater exploration of the naive conspecific (**P = 0.0048); this pattern was blocked and reversed by 5-HT2C antagonist SB242084 (****P < 0.0001). Male test rats are shown with black lines, and female test rats are shown with red lines. C. For comparison, data from B was converted to a preference score (% preference = time investigating stressed conspecific / total investigation time * 100; mean and individual replicates shown). The effect of SB242084 was different depending on the conspecific age (FAGE× DRUG(1, 52) = 74.8, P < 0.0001, η2=0.417). In juvenile SAP tests, SB242084 infusions reduced the preference for stressed conspecifics whereas in adult SAP tests, SB242084 increased preference for stressed conspecifics (****Ps < 0.0001). D. A representative cresyl violet stained IC section showing cannula damage (scale bar = 1000 μm) and cannula maps showing the placement of in-dwelling IC cannula across all experiments related to Fig. 3. Diagram in panel A was created with BioRender.com. Atlas images recreated from Paxinos and Watson (1998).

The preference for the stressed conspecific in each experiment was calculated as a percentage of the total time spent investigating both conspecifics (Figure 3C) and analyzed with a 2-way ANOVA. There was a significant interaction effect of conspecific age by treatment (FAGE × DRUG(1, 52) = 74.8, P < 0.0001, η2=0.417). Post hoc comparisons revealed a significant change in preference for stressed juveniles (P < 0.0001) and naïve adults (P < 0.0001) when comparing vehicle to SB242084. In summary, test rats injected with vehicle preferred interaction with stressed juveniles and naive adults, while test rats injected with SB242084 had no difference in interaction between stressed and naive juvenile and a preference with interaction with stressed adult conspecifics.

3.4. 5-HT2C receptor cellular distribution and colocalization in the posterior insular cortex

To begin to understand how 5-HT action at 5-HT2C receptors may impact insula function and anxiety-related behaviors, we used fluorescent in situ hybridization to visualize and colocalize mRNAs of 5-HT2C receptor (htr2c) (Drago & Serretti, 2009) expressing neurons with vesicular glutamate transporter 1 (vglut1), a putative marker for glutamatergic neurons (Juge et al., 2006), and glutamate decarboxylase 2 (gad), a putative marker for GABA neurons (Ueno, 2000), in posterior insula sections from adult male and female rats (Figure 4A). Of posterior insula cells, approximately 29% were colocalized with vglut1, 6% with gad and 4% with htr2c. A 2-way ANOVA was performed to compare the distribution of vglut1, gad, htr2c mRNAs as % of total DAPI cells and sex (male vs. female). There was a main effect of mRNA type (FmRNA(2, 47) = 140.4, ****P < 0.001, η2= 0.8468), but no sex differences (Figure 4B). Of the cells positive for htr2c, approximately 70% were colocalized with vglut1 and 20% were colocalized with gad (Figure 4C). A 2-way ANOVA was performed to compare the distribution of htr2c by cell type (vglut1 vs. gad) and sex (male vs. female), which resulted in a significant main effect of mRNA type (FmRNA(2,31) = 55.17, ****P < 0.001, η2= 0.753) but no sex differences (Figure 4C). These results suggest that htr2c mRNA is concentrated in cells that express vglut1.

Figure 4. Cellular distribution of vglut1, gad, and htr2c receptor mRNA in the insular cortex.

Figure 4.

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Fluorescent in situ hybridization was performed for vglut1, gad, htr2c receptor mRNAs. Fluorescent grains were counted in the left and right hemispheres of the posterior insular cortex. The total number of cells was determined by counting DAPI nuclei in each hemisphere. Nuclei containing 3 or more fluorescent grains were considered mRNA expressing cells. A. Representative digital photomicrographs of fluorescent visualization of DAPI and vesicular glutamate transporter 1 (vglut1), glutamate decarboxylase 2 (gad), htr2c (2C) mRNA from insular cortex coronal sections (20 μm), and all four channels merged. White arrows indicate representative mRNA expressing cells. Scale bar = 50 μm. B. Mean (with individual replicates) percent of DAPI cells colocalized with vglut1, gad, and htr2c mRNA. Data were obtained for all 3 mRNAs from 4 male and 4 female rats; the vglut1 and htr2c counts were replicated in a separate sample of 8 additional male and female rats. There was a significant main effect of cell type (****FmRNA (2, 47) = 140.4, P < 0.001, η2= 0.8468). There were no differences between male and female rats. The embedded pie chart shows the same data as a portion of the total DAPI cells. C. Mean (with individual replicates) percent of htr2c cells colocalized with vglut1 and gad mRNA, shown as a percent of the total 2C cells per subject for male and female rats. There was a significant main effect of marker (****FmRNA (2,31) = 55.17, P < 0.001, η2= 0.753). There were no differences between male and female rats. The embedded pie chart shows the same data as a portion of the total 2C cells.

4. Discussion

We investigated the neural mechanisms by which exposure to stressed conspecifics influences social affective decision-making. We focused on the role of 5-HT and 5-HT2C receptors in the insular cortex in a SAP test in which rats typically approach stressed juveniles but avoid stressed adults. We found that inhibiting 5-HTergic neurotransmission to the forebrain via a 5-HT1A agonist in the DRN and blocking systemic and insular 5-HT2C receptors via a 5-HT2C antagonist disrupted preference for a stressed juvenile and naive adult conspecific in the social affective preference test. In situ hybridization analysis revealed that 5-HT2C receptor mRNA in the posterior insula are highly colocalized with excitatory glutamatergic neurons. All of these experiments included male and female rats because sex differences in the 5-HT system may exist (Carlsson & Carlsson, 1988), but there were no sex differences in any of our observations. Together, these data suggest that interactions with stressed others drives activity in the 5-HTergic DRN and that 5-HT modulates social affective decision-making via action at insular 5-HT2C receptors on primarily glutamatergic neurons.

Previous studies in our lab found that neuromodulators like oxytocin (OT) and CRF are necessary during social affective decision-making in the SAP test (Rieger, Varela, et al., 2022; Rogers-Carter, Varela, et al., 2018). Although we have not tested it directly, we assume that in the SAP test, OT and CRF are released broadly through diffuse axonal projections including to the DRN where they could also affect DRN excitability, and thus, the 5-HT system overall. Relevant to social behavior, OT administration increases 5-HT binding potential in the DRN, insula, and amygdala in healthy humans, but not humans with autism spectrum disorders (Lefevre et al., 2018; Mottolese et al., 2014). CRF stimulates DRN output in higher doses (Kirby et al., 2003) to influence serotonergic neuron populations and stress-related behavior in rodents (Fox & Lowry, 2013). Related to our experiments with 5-HT2C receptors, CRF enhances anxiety-related behaviors through sensitization of 5-HT2C receptor signaling in cell cultures and mice (Magalhaes et al., 2010). From the perspective of the 5-HT system, 5-HT and 5-HT2C receptor activation also stimulates OT release in rodents (Bagdy & Kalogeras, 1993; Jørgensen et al., 2003) suggesting that there could be interactions between social and stress related systems at multiple levels (Walsh et al., 2023). Future investigations using direct measures of these neuromodulators during behavior are needed to untangle the exact functional relationships between these systems in social behaviors.

To gain a better understanding of how 5-HT may affect insular circuit physiology we colocalized 5-HT2C (htr2c) mRNA with putative markers for glutamatergic and GABAergic neurons in the posterior insula. Our results showed that about 70% of the neurons containing 5-HT2C mRNA were colocalized with vglut1, a marker for excitatory glutamatergic neurons and ~20% were colocalized with gad, a marker for GABAergic interneurons. Classically, 5-HT2C receptor signals via the Gɑq/11 GPCR signaling (Berg et al., 1998; Cussac et al., 2008; Gerhardt & van Heerikhuizen, 1997). Thus, 5-HT acting on 5-HT2C receptors on insular glutamatergic neurons would be expected to augment local synaptic transmission and output of the insula. Similarly, OT (Zingg, 1996) and CRF (Bangasser et al., 2010) also couple to Gɑq/11 and increase insular intrinsic excitability (Rieger, Varela, et al., 2022; Rogers-Carter, Varela, et al., 2018). Although a simple model in which the influx of 5-HT, OT, and CRF during social behavior augments insula synaptic efficacy and output is parsimonious, our prior work with CRF indicates that the circuitry is more complex. For example, CRF causes depolarization of insular pyramidal neurons which triggers the release of endocannabinoids which, via action of the cannabinoid type 1 receptor, suppresses presynaptic GABAergic inhibition (Rieger, Varela, et al., 2022). Another level of complexity may become evident when we can define the anatomical connectivity of insular 5-HT2C expressing neurons. An interesting possibility is that certain insular projection populations may be enriched with 5-HT2C receptors providing a way for social stress transfer to preferentially affect specific circuits and behaviors as recently shown in social novelty preference (S. H. Kim et al., 2022).

The current findings add to our understanding of the type of information processing and integration that occurs in the insula during social affective behaviors. Specifically, the insula integrates internal signals relating to sociability, stress, or anxiety with multimodal sensory information to augment synaptic transmission and ultimately shape the direction of behavior via outputs to prosocial or defensive subcortical systems (Rogers-Carter & Christianson, 2019). Here we speculate that the confluence of neuromodulatory signals present in the insula during social decision making may allow for greater sensory integration of multisensory inputs with motivational or affective states that is necessary to select the appropriate social behavior in a given interaction setting. The insular cortex projects to subcortical regions involved in stress and anxiety-related behaviors like the nucleus accumbens, central amygdala, and bed nucleus of the stria terminalis (Gehrlach et al., 2020; Shi & Cassell, 1998). Insula output to the NAc is necessary for prosocial approach to juveniles (Rogers-Carter et al., 2019) and 5-HT2C activation may be necessary for upregulation or selecting the insular ensembles of neurons that project to the NAc. We do not yet know what insular outputs are necessary for social avoidance, however insular projections to the BNST and central nucleus of the amygdala respond to aversive stimuli and facilitate defensive behaviors (Gehrlach et al., 2019; Luchsinger et al., 2021; Schiff et al., 2018).

There are several limitations to our findings. First, we only examined the role of one 5-HT receptor found in the insula, and it is unknown whether blocking one type of 5-HTergic receptor displaces 5-HT action to other 5-HTergic receptors. Since the insula is rich with 5-HT1A, 5-HT2A, and 5-HT2C receptors (Clemett et al., 2000; Ju et al., 2020; Linley et al., 2013), it is possible that 5-HT1A and/or 5-HT2A receptors are preferentially activated when 5-HT2C receptors are blocked. This is relevant to our experiments of social stress signals since the binding potentials of 5-HT1A and 5-HT2A receptors in the insula are correlated with anxiety in humans and non-human primates (Akimova et al., 2009), and 5-HT1A receptor binding in the insula and DRN is lower in humans with social anxiety disorder (Lanzenberger et al., 2007). Regarding cellular distribution, insular multisensory integration is associated with parvalbumin GABAergic interneurons (Gogolla et al., 2014). Our results reveal that about 20% of the htr2c mRNA colocalized with a general marker of GABAergic neurons; it would be interesting to determine if specific interneuron subtypes are enriched with 5-HT2C receptors. Finally, we had no direct measure of 5-HT release in the DRN or insula during the SAP test. Thus, important goals of future work include determining potential displacement of 5-HT action among different insular 5-HTergic receptors, the cellular mechanism by which social stress signals activate the DRN, if 5-HTergic fibers from the DRN to the insula are involved in social affective behaviors, and how different neuromodulators in the insula interact and affect synaptic excitability to influence social affective behaviors.

The insula is implicated in autonomic control, decision-making, self-awareness, social cognition, and integration of interoceptive and exteroceptive cues (Gogolla, 2017; Paulus & Stein, 2006; Rogers-Carter & Christianson, 2019). In anxiety-related disorders like PTSD and social anxiety, altered interoception and heightened sense of self-danger leads to an anxiety bias, which causes individuals to behave as if safe or ambiguous stimuli are relatively more threatening. Importantly there are noteworthy sex differences in the prevalence of these disorders, sex differences in rodent social behavior (Dumais & Veenema, 2016) and sex-specific effects of CRF and OT in the insula of the SAP test (Djerdjaj et al., 2023; Rieger, Varela, et al., 2022; Rogers-Carter, Varela, et al., 2018). Although prior reports note some sex differences in 5-HT immunoreactivity and neurochemistry (Carlsson & Carlsson, 1988), we did not find any evidence of sex differences in our behavioral, pharmacological or mRNA colocalization experiments. The current findings suggest that 5-HT contributes to insular and broader decision-making networks in response to exposure to social stress signals and encourages further investigation of insular 5-HT action in anxiety and stress-related behavioral responses.

Supplementary Material

1

  • The dorsal raphe is necessary for social behaviors with stressed conspecifics.

  • Systemic and insular 5-HT2C receptor blockade disrupted social affective behaviors.

  • 5-HT2C receptor mRNA colocalized with glutamatergic neurons in the insula.

  • Serotonin modulates social decision-making via action at insular 5-HT2C receptors.

Acknowledgements:

The authors wish to thank Nancy McGilloway and Todd Gaines, administrators of the Boston College Animal Care Facility, for outstanding animal husbandry, Bret Judson, director of the Boston College Imaging Core, for training and assistance with microscopy, Alexis Callen for assistance with behavioral testing, and Sara Barry and Shemar Joseph for assistance with RNAScope. Funding for this work was provided by Boston College Undergraduate Research Fellowship and the National Institutes of Health Grant MH119422 to JPC.

Footnotes

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Financial Disclosures:

The authors declare no direct or indirect biomedical financial interests or other potential conflicts of interest.

References:

  1. Abumaria N, Rygula R, Havemann-Reinecke U, Rüther E, Bodemer W, Roos C, & Flügge G (2006). Identification of Genes Regulated by Chronic Social Stress in the Rat Dorsal Raphe Nucleus. Cellular and Molecular Neurobiology, 26(2), 145–162. 10.1007/s10571-006-9024-1 [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Akimova E, Lanzenberger R, & Kasper S (2009). The Serotonin-1A Receptor in Anxiety Disorders. Biological Psychiatry, 66(7), 627–635. 10.1016/j.biopsych.2009.03.012 [DOI] [PubMed] [Google Scholar]
  3. Bagdy G, & Kalogeras KT (1993). Stimulation of 5-HT1A and 5-HT2/5-HT1C receptors induce oxytocin release in the male rat. Brain Research, 611(2), 330–332. 10.1016/0006-8993(93)90521-N [DOI] [PubMed] [Google Scholar]
  4. Bangasser DA, Curtis A, Reyes B. a. S., Bethea TT, Parastatidis I, Ischiropoulos H, Van Bockstaele EJ, & Valentino RJ (2010). Sex differences in corticotropin-releasing factor receptor signaling and trafficking: Potential role in female vulnerability to stress-related psychopathology. Molecular Psychiatry, 15(9), Article 9. 10.1038/mp.2010.66 [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Baptista-de-Souza D, Nunciato AC, Pereira BC, Fachinni G, Zaniboni CR, & Canto-de-Souza A (2015). Mice undergoing neuropathic pain induce anxiogenic-like effects and hypernociception in cagemates. Behavioural Pharmacology, 26(7), 664–672. 10.1097/FBP.0000000000000170 [DOI] [PubMed] [Google Scholar]
  6. Bartal IB-A, Decety J, & Mason P (2011). Empathy and Pro-Social Behavior in Rats. Science, 334(6061), 1427–1430. 10.1126/science.1210789 [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Berg KA, Maayani S, Goldfarb J, Scaramellini C, Leff P, & Clarke WP (1998). Effector Pathway-Dependent Relative Efficacy at Serotonin Type 2A and 2C Receptors: Evidence for Agonist-Directed Trafficking of Receptor Stimulus. Molecular Pharmacology, 54(1), 94–104. 10.1124/mol.54.1.94 [DOI] [PubMed] [Google Scholar]
  8. Boulougouris V, Glennon JC, & Robbins TW (2008). Dissociable effects of selective 5-HT2A and 5-HT2C receptor antagonists on serial spatial reversal learning in rats. Neuropsychopharmacology: Official Publication of the American College of Neuropsychopharmacology, 33(8), 2007–2019. 10.1038/sj.npp.1301584 [DOI] [PubMed] [Google Scholar]
  9. Bouwknecht JA, Spiga F, Staub DR, Hale MW, Shekhar A, & Lowry CA (2007). Differential effects of exposure to low-light or high-light open-field on anxiety-related behaviors: Relationship to c-Fos expression in serotonergic and non-serotonergic neurons in the dorsal raphe nucleus. Brain Research Bulletin, 72(1), 32–43. 10.1016/j.brainresbull.2006.12.009 [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Bromidge SM, Duckworth M, Forbes IT, Ham P, King FD, Thewlis KM, Blaney FE, Naylor CB, Blackburn TP, Kennett GA, Wood MD, & Clarke SE (1997). 6-Chloro-5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]- indoline (SB-242084): The first selective and brain penetrant 5-HT2C receptor antagonist. Journal of Medicinal Chemistry, 40(22), 3494–3496. 10.1021/jm970424c [DOI] [PubMed] [Google Scholar]
  11. Burghardt NS, Bush DEA, McEwen BS, & LeDoux JE (2007). Acute Selective Serotonin Reuptake Inhibitors Increase Conditioned Fear Expression: Blockade With a 5-HT2C Receptor Antagonist. Biological Psychiatry, 62(10), 1111–1118. 10.1016/j.biopsych.2006.11.023 [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Burkett JP, Andari E, Johnson ZV, Curry DC, de Waal FBM, & Young LJ (2016). Oxytocin-dependent consolation behavior in rodents. Science (New York, N.Y.), 351(6271), 375–378. 10.1126/science.aac4785 [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Campbell BM, & Merchant KM (2003). Serotonin 2C receptors within the basolateral amygdala induce acute fear-like responses in an open-field environment. Brain Research, 993(1), 1–9. 10.1016/S0006-8993(03)03384-5 [DOI] [PubMed] [Google Scholar]
  14. Carlsson M, & Carlsson A (1988). A regional study of sex differences in rat brain serotonin. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 12(1), 53–61. 10.1016/0278-5846(88)90061-9 [DOI] [PubMed] [Google Scholar]
  15. Chaouloff F, Berton O, & Mormède P (1999). Serotonin and Stress. Neuropsychopharmacology, 21(1), Article 1. 10.1016/S0893-133X(99)00008-1 [DOI] [PubMed] [Google Scholar]
  16. Christianson JP, Drugan RC, Flyer JG, Watkins LR, & Maier SF (2013). Anxiogenic effects of brief swim stress are sensitive to stress history. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 44, 17–22. 10.1016/j.pnpbp.2013.01.011 [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Christianson JP, Paul ED, Irani M, Thompson BM, Kubala KH, Yirmiya R, Watkins LR, & Maier SF (2008). The role of prior stressor controllability and the dorsal raphé nucleus in sucrose preference and social exploration. Behavioural Brain Research, 193(1), 87–93. 10.1016/j.bbr.2008.04.024 [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Christianson JP, Ragole T, Amat J, Greenwood BN, Strong PV, Paul ED, Fleshner M, Watkins LR, & Maier SF (2010). 5-Hydroxytryptamine 2C Receptors in the Basolateral Amygdala Are Involved in the Expression of Anxiety After Uncontrollable Traumatic Stress. Biological Psychiatry, 67(4), 339–345. 10.1016/j.biopsych.2009.09.011 [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Clemett DA, Punhani T, Duxon MS, Blackburn TP, & Fone KCF (2000). Immunohistochemical localisation of the 5-HT2C receptor protein in the rat CNS. Neuropharmacology, 39(1), 123–132. 10.1016/S0028-3908(99)00086-6 [DOI] [PubMed] [Google Scholar]
  20. Cooper MA, McIntyre KE, & Huhman KL (2008). Activation of 5-HT1A autoreceptors in the dorsal raphe nucleus reduces the behavioral consequences of social defeat. Psychoneuroendocrinology, 33(9), 1236–1247. 10.1016/j.psyneuen.2008.06.009 [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Cussac D, Boutet-Robinet E, Ailhaud M-C, Newman-Tancredi A, Martel J-C, Danty N, & Rauly-Lestienne I (2008). Agonist-directed trafficking of signalling at serotonin 5-HT2A, 5-HT2B and 5-HT2C-VSV receptors mediated Gq/11 activation and calcium mobilisation in CHO cells. European Journal of Pharmacology, 594(1), 32–38. 10.1016/j.ejphar.2008.07.040 [DOI] [PubMed] [Google Scholar]
  22. de Waal FBM (2008). Putting the Altruism Back into Altruism: The Evolution of Empathy. Annual Review of Psychology, 59(1), 279–300. 10.1146/annurev.psych.59.103006.093625 [DOI] [PubMed] [Google Scholar]
  23. de Waal FBM, & Preston SD (2017). Mammalian empathy: Behavioural manifestations and neural basis. Nature Reviews Neuroscience, 18(8), Article 8. 10.1038/nrn.2017.72 [DOI] [PubMed] [Google Scholar]
  24. Djerdjaj A, Ng AJ, Rieger NS, & Christianson JP (2022). The basolateral amygdala to posterior insular cortex tract is necessary for social interaction with stressed juvenile rats. Behavioural Brain Research, 435, 114050. 10.1016/j.bbr.2022.114050 [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Djerdjaj A, Rieger NS, Brady BH, Carey BN, Ng AJ, & Christianson JP (2023). Social affective behaviors among female rats involve the basolateral amygdala and insular cortex (p. 2023.02.02.526780). bioRxiv. 10.1101/2023.02.02.526780 [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Dölen G, Darvishzadeh A, Huang KW, & Malenka RC (2013). Social reward requires coordinated activity of nucleus accumbens oxytocin and serotonin. Nature, 501(7466), Article 7466. 10.1038/nature12518 [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Drago A, & Serretti A (2009). Focus on HTR2C: A possible suggestion for genetic studies of complex disorders. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics, 150B(5), 601–637. 10.1002/ajmg.b.30864 [DOI] [PubMed] [Google Scholar]
  28. Dumais KM, & Veenema AH (2016). Vasopressin and oxytocin receptor systems in the brain: Sex differences and sex-specific regulation of social behavior. Frontiers in Neuroendocrinology, 40, 1–23. 10.1016/j.yfrne.2015.04.003 [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Ferretti V, Maltese F, Contarini G, Nigro M, Bonavia A, Huang H, Gigliucci V, Morelli G, Scheggia D, Managò F, Castellani G, Lefevre A, Cancedda L, Chini B, Grinevich V, & Papaleo F (2019). Oxytocin Signaling in the Central Amygdala Modulates Emotion Discrimination in Mice. Current Biology, 29(12), 1938–1953.e6. 10.1016/j.cub.2019.04.070 [DOI] [PubMed] [Google Scholar]
  30. Ferretti V, & Papaleo F (2019). Understanding others: Emotion recognition in humans and other animals. Genes, Brain and Behavior, 18(1), e12544. 10.1111/gbb.12544 [DOI] [PubMed] [Google Scholar]
  31. Foilb AR, & Christianson JP (2016). Serotonin 2C receptor antagonist improves fear discrimination and subsequent safety signal recall. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 65, 78–84. 10.1016/j.pnpbp.2015.08.017 [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Fu W, Le Maître E, Fabre V, Bernard J-F, David Xu Z-Q, & Hökfelt T (2010). Chemical neuroanatomy of the dorsal raphe nucleus and adjacent structures of the mouse brain. Journal of Comparative Neurology, 518(17), 3464–3494. 10.1002/cne.22407 [DOI] [PubMed] [Google Scholar]
  33. Gehrlach DA, Dolensek N, Klein AS, Roy Chowdhury R, Matthys A, Junghänel M, Gaitanos TN, Podgornik A, Black TD, Reddy Vaka N, Conzelmann K-K, & Gogolla N (2019). Aversive state processing in the posterior insular cortex. Nature Neuroscience, 22(9), Article 9. 10.1038/s41593-019-0469-1 [DOI] [PubMed] [Google Scholar]
  34. Gehrlach DA, Weiand C, Gaitanos TN, Cho E, Klein AS, Hennrich AA, Conzelmann K-K, & Gogolla N (2020). A whole-brain connectivity map of mouse insular cortex. ELife, 9, e55585. 10.7554/eLife.55585 [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Gerhardt CC, & van Heerikhuizen H (1997). Functional characteristics of heterologously expressed 5-HT receptors. European Journal of Pharmacology, 334(1), 1–23. 10.1016/S0014-2999(97)01115-1 [DOI] [PubMed] [Google Scholar]
  36. Gogolla N (2017). The insular cortex. Current Biology, 27(12), R580–R586. 10.1016/j.cub.2017.05.010 [DOI] [PubMed] [Google Scholar]
  37. Gogolla N, Takesian AE, Feng G, Fagiolini M, & Hensch TK (2014). Sensory integration in mouse insular cortex reflects GABA circuit maturation. Neuron, 83(4), 894–905. 10.1016/j.neuron.2014.06.033 [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Hale MW, Hay-Schmidt A, Mikkelsen JD, Poulsen B, Bouwknecht JA, Evans AK, Stamper CE, Shekhar A, & Lowry CA (2008). Exposure to an open-field arena increases c-Fos expression in a subpopulation of neurons in the dorsal raphe nucleus, including neurons projecting to the basolateral amygdaloid complex. Neuroscience, 157(4), 733–748. 10.1016/j.neuroscience.2008.09.050 [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Heisler LK, Zhou L, Bajwa P, Hsu J, & Tecott LH (2007). Serotonin 5-HT(2C) receptors regulate anxiety-like behavior. Genes, Brain, and Behavior, 6(5), 491–496. 10.1111/j.1601-183X.2007.00316.x [DOI] [PubMed] [Google Scholar]
  40. Hjorth S, & Magnusson T (1988). The 5-HT1A receptor agonist, 8-OH-DPAT, preferentially activates cell body 5-HT autoreceptors in rat brain in vivo. Naunyn-Schmiedeberg’s Archives of Pharmacology, 338(5), 463–471. 10.1007/BF00179315 [DOI] [PubMed] [Google Scholar]
  41. Hoyer D, Hannon JP, & Martin GR (2002). Molecular, pharmacological and functional diversity of 5-HT receptors. Pharmacology Biochemistry and Behavior, 71(4), 533–554. 10.1016/S0091-3057(01)00746-8 [DOI] [PubMed] [Google Scholar]
  42. Inoue T, Tsuchiya K, & Koyama T (1994). Regional changes in dopamine and serotonin activation with various intensity of physical and psychological stress in the rat brain. Pharmacology Biochemistry and Behavior, 49(4), 911–920. 10.1016/0091-3057(94)90243-7 [DOI] [PubMed] [Google Scholar]
  43. Jørgensen H, Riis M, Knigge U, Kjær A, & Warberg J (2003). Serotonin Receptors Involved in Vasopressin and Oxytocin Secretion. Journal of Neuroendocrinology, 15(3), 242–249. 10.1046/j.1365-2826.2003.00978.x [DOI] [PubMed] [Google Scholar]
  44. Ju A, Fernandez-Arroyo B, Wu Y, Jacky D, & Beyeler A (2020). Expression of serotonin 1A and 2A receptors in molecular- and projection-defined neurons of the mouse insular cortex. Molecular Brain, 13(1), 99. 10.1186/s13041-020-00605-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Juge N, Yoshida Y, Yatsushiro S, Omote H, & Moriyama Y (2006). Vesicular Glutamate Transporter Contains Two Independent Transport Machineries *. Journal of Biological Chemistry, 281(51), 39499–39506. 10.1074/jbc.M607670200 [DOI] [PubMed] [Google Scholar]
  46. Kawahara H, Yoshida M, Yokoo H, Nishi M, & Tanaka M (1993). Psychological stress increases serotonin release in the rat amygdala and prefrontal cortex assessed by in vivo microdialysis. Neuroscience Letters, 162(1), 81–84. 10.1016/0304-3940(93)90565-3 [DOI] [PubMed] [Google Scholar]
  47. Kennett GA, Wood MD, Bright F, Trail B, Riley G, Holland V, Avenell KY, Stean T, Upton N, Bromidge S, Forbes IT, Brown AM, Middlemiss DN, & Blackburn TP (1997). SB 242084, a selective and brain penetrant 5-HT2C receptor antagonist. Neuropharmacology, 36(4–5), 609–620. 10.1016/s0028-3908(97)00038-5 [DOI] [PubMed] [Google Scholar]
  48. Keum S, & Shin H-S (2019). Neural Basis of Observational Fear Learning: A Potential Model of Affective Empathy. Neuron, 104(1), 78–86. 10.1016/j.neuron.2019.09.013 [DOI] [PubMed] [Google Scholar]
  49. Keysers C, Knapska E, Moita MA, & Gazzola V (2022). Emotional contagion and prosocial behavior in rodents. Trends in Cognitive Sciences, 26(8), 688–706. 10.1016/j.tics.2022.05.005 [DOI] [PubMed] [Google Scholar]
  50. Kim SH, An K, Namkung H, Saito A, Rannals MD, Moore JR, Mihaljevic M, Saha S, Oh S, Kondo MA, Ishizuka K, Yang K, Maher BJ, Niwa M, & Sawa A (2022). Anterior Insula-Associated Social Novelty Recognition: Pivotal Roles of a Local Retinoic Acid Cascade and Oxytocin Signaling. The American Journal of Psychiatry, appiajp21010053. 10.1176/appi.ajp.21010053 [DOI] [PubMed] [Google Scholar]
  51. Kim S-W, Kim M, & Shin H-S (2021). Affective empathy and prosocial behavior in rodents. Current Opinion in Neurobiology, 68, 181–189. 10.1016/j.conb.2021.05.002 [DOI] [PubMed] [Google Scholar]
  52. Kimura A, Stevenson PL, Carter RN, MacColl G, French KL, Paul Simons J, Al-Shawi R, Kelly V, Chapman KE, & Holmes MC (2009). Overexpression of 5-HT2C receptors in forebrain leads to elevated anxiety and hypoactivity. European Journal of Neuroscience, 30(2), 299–306. 10.1111/j.1460-9568.2009.06831.x [DOI] [PMC free article] [PubMed] [Google Scholar]
  53. Kirby LG, Chou-Green JM, Davis K, & Lucki I (1997). The effects of different stressors on extracellular 5-hydroxytryptamine and 5-hydroxyindoleacetic acid. Brain Research, 760(1), 218–230. 10.1016/S0006-8993(97)00287-4 [DOI] [PubMed] [Google Scholar]
  54. Kirby LG, Freeman-Daniels E, Lemos JC, Nunan JD, Lamy C, Akanwa A, & Beck SG (2008). Corticotropin-Releasing Factor Increases GABA Synaptic Activity and Induces Inward Current in 5-Hydroxytryptamine Dorsal Raphe Neurons. Journal of Neuroscience, 28(48), 12927–12937. 10.1523/JNEUROSCI.2887-08.2008 [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Kirby LG, Pernar L, Valentino RJ, & Beck SG (2003). Distinguishing characteristics of serotonin and non-serotonin-containing cells in the dorsal raphe nucleus: Electrophysiological and immunohistochemical studies. Neuroscience, 116(3), 669–683. 10.1016/s0306-4522(02)00584-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  56. Lanzenberger RR, Mitterhauser M, Spindelegger C, Wadsak W, Klein N, Mien L-K, Holik A, Attarbaschi T, Mossaheb N, Sacher J, Geiss-Granadia T, Kletter K, Kasper S, & Tauscher J (2007). Reduced serotonin-1A receptor binding in social anxiety disorder. Biological Psychiatry, 61(9), 1081–1089. 10.1016/j.biopsych.2006.05.022 [DOI] [PubMed] [Google Scholar]
  57. Lefevre A, Mottolese R, Redouté J, Costes N, Le Bars D, Geoffray M-M, Leboyer M, & Sirigu A (2018). Oxytocin Fails to Recruit Serotonergic Neurotransmission in the Autistic Brain. Cerebral Cortex, 28(12), 4169–4178. 10.1093/cercor/bhx272 [DOI] [PubMed] [Google Scholar]
  58. Li L, Zhang L-Z, He Z-X, Ma H, Zhang Y-T, Xun Y-F, Yuan W, Hou W-J, Li Y-T, Lv Z-J, Jia R, & Tai F-D (2021). Dorsal raphe nucleus to anterior cingulate cortex 5-HTergic neural circuit modulates consolation and sociability. ELife, 10, e67638. 10.7554/eLife.67638 [DOI] [PMC free article] [PubMed] [Google Scholar]
  59. Linley SB, Hoover WB, & Vertes RP (2013). Pattern of distribution of serotonergic fibers to the orbitomedial and insular cortex in the rat. Journal of Chemical Neuroanatomy, 48–49, 29–45. 10.1016/j.jchemneu.2012.12.006 [DOI] [PubMed] [Google Scholar]
  60. Luchsinger JR, Fetterly TL, Williford KM, Salimando GJ, Doyle MA, Maldonado J, Simerly RB, Winder DG, & Centanni SW (2021). Delineation of an insula-BNST circuit engaged by struggling behavior that regulates avoidance in mice. Nature Communications, 12(1), Article 1. 10.1038/s41467-021-23674-z [DOI] [PMC free article] [PubMed] [Google Scholar]
  61. Lukkes J, Vuong S, Scholl J, Oliver H, & Forster G (2009). Corticotropin-Releasing Factor Receptor Antagonism within the Dorsal Raphe Nucleus Reduces Social Anxiety-Like Behavior after Early-Life Social Isolation. Journal of Neuroscience, 29(32), 9955–9960. 10.1523/JNEUROSCI.0854-09.2009 [DOI] [PMC free article] [PubMed] [Google Scholar]
  62. Luo M, Zhou J, & Liu Z (2015). Reward processing by the dorsal raphe nucleus: 5-HT and beyond. Learning & Memory, 22(9), 452–460. 10.1101/lm.037317.114 [DOI] [PMC free article] [PubMed] [Google Scholar]
  63. Maier SF, Grahn RE, & Watkins LR (1995). 8-OH-DPAT microinjected in the region of the dorsal raphe nucleus blocks and reverses the enhancement of fear conditioning and interference with escape produced by exposure to inescapable shock. Behavioral Neuroscience, 109(3), 404–412. 10.1037//0735-7044.109.3.404 [DOI] [PubMed] [Google Scholar]
  64. Marcinkiewcz CA, Mazzone CM, D’Agostino G, Halladay LR, Hardaway JA, DiBerto JF, Navarro M, Burnham N, Cristiano C, Dorrier CE, Tipton GJ, Ramakrishnan C, Kozicz T, Deisseroth K, Thiele TE, McElligott ZA, Holmes A, Heisler LK, & Kash TL (2016). Serotonin engages an anxiety and fear-promoting circuit in the extended amygdala. Nature, 537(7618), Article 7618. 10.1038/nature19318 [DOI] [PMC free article] [PubMed] [Google Scholar]
  65. Meyza K, & Knapska E (2018). What can rodents teach us about empathy? Current Opinion in Psychology, 24, 15–20. 10.1016/j.copsyc.2018.03.002 [DOI] [PubMed] [Google Scholar]
  66. Meyza KZ, Bartal IB-A, Monfils MH, Panksepp JB, & Knapska E (2017). The roots of empathy: Through the lens of rodent models. Neuroscience & Biobehavioral Reviews, 76, 216–234. 10.1016/j.neubiorev.2016.10.028 [DOI] [PMC free article] [PubMed] [Google Scholar]
  67. Millan MJ (2005). Serotonin 5-HT2C Receptors as a Target for the Treatment of Depressive and Anxious States: Focus on Novel Therapeutic Strategies. Therapies, 60(5), 441–460. 10.2515/therapie:2005065 [DOI] [PubMed] [Google Scholar]
  68. Monfils MH, & Agee LA (2019). Insights from social transmission of information in rodents. Genes, Brain, and Behavior, 18(1), e12534. 10.1111/gbb.12534 [DOI] [PubMed] [Google Scholar]
  69. Mottolese R, Redouté J, Costes N, Le Bars D, & Sirigu A (2014). Switching brain serotonin with oxytocin. Proceedings of the National Academy of Sciences of the United States of America, 111(23), 8637–8642. 10.1073/pnas.1319810111 [DOI] [PMC free article] [PubMed] [Google Scholar]
  70. Paul ED, Hale MW, Lukkes JL, Valentine MJ, Sarchet DM, & Lowry CA (2011). Repeated social defeat increases reactive emotional coping behavior and alters functional responses in serotonergic neurons in the rat dorsal raphe nucleus. Physiology & Behavior, 104(2), 272–282. 10.1016/j.physbeh.2011.01.006 [DOI] [PMC free article] [PubMed] [Google Scholar]
  71. Paulus MP, & Stein MB (2006). An insular view of anxiety. Biological Psychiatry, 60(4), 383–387. 10.1016/j.biopsych.2006.03.042 [DOI] [PubMed] [Google Scholar]
  72. Pockros-Burgess LA, Pentkowski NS, Der-Ghazarian T, & Neisewander JL (2014). Effects of the 5-HT2C receptor agonist CP809101 in the amygdala on reinstatement of cocaine-seeking behavior and anxiety-like behavior. International Journal of Neuropsychopharmacology, 17(11), 1751–1762. 10.1017/S1461145714000856 [DOI] [PubMed] [Google Scholar]
  73. Rieger NS, Varela JA, Ng AJ, Granata L, Djerdjaj A, Brenhouse HC, & Christianson JP (2022). Insular cortex corticotropin-releasing factor integrates stress signaling with social affective behavior. Neuropsychopharmacology, 47(6), Article 6. 10.1038/s41386-022-01292-7 [DOI] [PMC free article] [PubMed] [Google Scholar]
  74. Rieger NS, Worley NB, Ng AJ, & Christianson JP (2022). Insular cortex modulates social avoidance of sick rats. Behavioural Brain Research, 416, 113541. 10.1016/j.bbr.2021.113541 [DOI] [PMC free article] [PubMed] [Google Scholar]
  75. Rogers-Carter MM, & Christianson JP (2019). An insular view of the social decision-making network. Neuroscience & Biobehavioral Reviews, 103, 119–132. 10.1016/j.neubiorev.2019.06.005 [DOI] [PMC free article] [PubMed] [Google Scholar]
  76. Rogers-Carter MM, Djerdjaj A, Culp AR, Elbaz JA, & Christianson JP (2018). Familiarity modulates social approach toward stressed conspecifics in female rats. PLOS ONE, 13(10), e0200971. 10.1371/journal.pone.0200971 [DOI] [PMC free article] [PubMed] [Google Scholar]
  77. Rogers-Carter MM, Djerdjaj A, Gribbons KB, Varela JA, & Christianson JP (2019). Insular Cortex Projections to Nucleus Accumbens Core Mediate Social Approach to Stressed Juvenile Rats. The Journal of Neuroscience, 39(44), 8717–8729. 10.1523/JNEUROSCI.0316-19.2019 [DOI] [PMC free article] [PubMed] [Google Scholar]
  78. Rogers-Carter MM, Varela JA, Gribbons KB, Pierce AF, McGoey MT, Ritchey M, & Christianson JP (2018). Insular cortex mediates approach and avoidance responses to social affective stimuli. Nature Neuroscience, 21(3), 404–414. 10.1038/s41593-018-0071-y [DOI] [PMC free article] [PubMed] [Google Scholar]
  79. Rozeske RR, Evans AK, Frank MG, Watkins LR, Lowry CA, & Maier SF (2011). Uncontrollable, But Not Controllable, Stress Desensitizes 5-HT1A Receptors in the Dorsal Raphe Nucleus. Journal of Neuroscience, 31(40), 14107–14115. 10.1523/JNEUROSCI.3095-11.2011 [DOI] [PMC free article] [PubMed] [Google Scholar]
  80. Scheggia D, Managò F, Maltese F, Bruni S, Nigro M, Dautan D, Latuske P, Contarini G, Gomez-Gonzalo M, Requie LM, Ferretti V, Castellani G, Mauro D, Bonavia A, Carmignoto G, Yizhar O, & Papaleo F (2020). Somatostatin interneurons in the prefrontal cortex control affective state discrimination in mice. Nature Neuroscience, 23(1), Article 1. 10.1038/s41593-019-0551-8 [DOI] [PubMed] [Google Scholar]
  81. Schiff HC, Bouhuis AL, Yu K, Penzo MA, Li H, He M, & Li B (2018). An Insula–Central Amygdala Circuit for Guiding Tastant-Reinforced Choice Behavior. Journal of Neuroscience, 38(6), 1418–1429. 10.1523/JNEUROSCI.1773-17.2017 [DOI] [PMC free article] [PubMed] [Google Scholar]
  82. Shi CJ, & Cassell MD (1998). Cortical, thalamic, and amygdaloid connections of the anterior and posterior insular cortices. The Journal of Comparative Neurology, 399(4), 440–468. 10.1002/(sici)1096-9861(19981005)399:4<440::aidcne2>3.0.co;2-1 [DOI] [PubMed] [Google Scholar]
  83. Staub E (1974). Helping a Distressed Person: Social, Personality, and Stimulus Determinants. In Berkowitz L (Ed.), Advances in Experimental Social Psychology (Vol. 7, pp. 293–341). Academic Press. 10.1016/S0065-2601(08)60040-4 [DOI] [Google Scholar]
  84. Sterley T-L, Baimoukhametova D, Füzesi T, Zurek AA, Daviu N, Rasiah NP, Rosenegger D, & Bains JS (2018). Social transmission and buffering of synaptic changes after stress. Nature Neuroscience, 21(3), Article 3. 10.1038/s41593-017-0044-6 [DOI] [PubMed] [Google Scholar]
  85. Sterley T-L, & Bains JS (2021). Social communication of affective states. Current Opinion in Neurobiology, 68, 44–51. 10.1016/j.conb.2020.12.007 [DOI] [PubMed] [Google Scholar]
  86. Strong PV, Christianson JP, Loughridge AB, Amat J, Maier SF, Fleshner M, & Greenwood BN (2011a). 5-hydroxytrptamine 2C receptors in the dorsal striatum mediate stress-induced interference with negatively-reinforced instrumental escape behavior. Neuroscience, 197, 132–144. 10.1016/j.neuroscience.2011.09.041 [DOI] [PMC free article] [PubMed] [Google Scholar]
  87. Strong PV, Christianson JP, Loughridge AB, Amat J, Maier SF, Fleshner M, & Greenwood BN (2011b). 5-hydroxytrptamine 2C receptors in the dorsal striatum mediate stress-induced interference with negatively-reinforced instrumental escape behavior. Neuroscience, 197, 132–144. 10.1016/j.neuroscience.2011.09.041 [DOI] [PMC free article] [PubMed] [Google Scholar]
  88. Ueno H (2000). Enzymatic and structural aspects on glutamate decarboxylase. Journal of Molecular Catalysis B: Enzymatic, 10(1), 67–79. 10.1016/S1381-1177(00)00114-4 [DOI] [Google Scholar]
  89. Vertes RP (1991). A PHA-L analysis of ascending projections of the dorsal raphe nucleus in the rat. Journal of Comparative Neurology, 313(4), 643–668. 10.1002/cne.903130409 [DOI] [PubMed] [Google Scholar]
  90. Vertes RP, & Kocsis B (1994). Projections of the dorsal raphe nucleus to the brainstem: PHA-L analysis in the rat. Journal of Comparative Neurology, 340(1), 11–26. 10.1002/cne.903400103 [DOI] [PubMed] [Google Scholar]
  91. Walsh JJ, Christoffel DJ, Heifets BD, Ben-Dor GA, Selimbeyoglu A, Hung LW, Deisseroth K, & Malenka RC (2018). 5-HT release in nucleus accumbens rescues social deficits in mouse autism model. Nature, 560(7720), Article 7720. 10.1038/s41586-018-0416-4 [DOI] [PMC free article] [PubMed] [Google Scholar]
  92. Walsh JJ, Christoffel DJ, & Malenka RC (2023). Neural circuits regulating prosocial behaviors. Neuropsychopharmacology, 48(1), Article 1. 10.1038/s41386-022-01348-8 [DOI] [PMC free article] [PubMed] [Google Scholar]
  93. Waselus M, Galvez JP, Valentino RJ, & Van Bockstaele EJ (2006). Differential projections of dorsal raphe nucleus neurons to the lateral septum and striatum. Journal of Chemical Neuroanatomy, 31(4), 233–242. 10.1016/j.jchemneu.2006.01.007 [DOI] [PubMed] [Google Scholar]
  94. Waselus M, Valentino RJ, & Van Bockstaele EJ (2011). Collateralized dorsal raphe nucleus projections: A mechanism for the integration of diverse functions during stress. Journal of Chemical Neuroanatomy, 41(4), 266–280. 10.1016/j.jchemneu.2011.05.011 [DOI] [PMC free article] [PubMed] [Google Scholar]
  95. Will MJ, Der-Avakian A, Bland ST, Grahn RE, Hammack SE, Sparks PD, Pepin JL, Watkins LR, & Maier SF (2004). Electrolytic lesions and pharmacological inhibition of the dorsal raphe nucleus prevent stressor potentiation of morphine conditioned place preference in rats. Psychopharmacology, 171(2), 191–198. 10.1007/s00213-003-1572-1 [DOI] [PubMed] [Google Scholar]
  96. Wood SK, Zhang X-Y, Reyes BAS, Lee CS, Van Bockstaele EJ, & Valentino RJ (2013). Cellular Adaptations of Dorsal Raphe Serotonin Neurons Associated with the Development of Active Coping in Response to Social Stress. Biological Psychiatry, 73(11), 1087–1094. 10.1016/j.biopsych.2013.01.026 [DOI] [PMC free article] [PubMed] [Google Scholar]
  97. Zingg HH (1996). Vasopressin and oxytocin receptors. Baillière’s Clinical Endocrinology and Metabolism, 10(1), 75–96. 10.1016/S0950-351X(96)80314-4 [DOI] [PubMed] [Google Scholar]

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