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[Preprint]. 2025 Oct 17:2025.07.09.663974. Originally published 2025 Jul 15. [Version 2] doi: 10.1101/2025.07.09.663974

Alcohol disrupts long-term potentiation at hippocampus-medium spiny neuron synapses in the medial shell of the nucleus accumbens

Ashley E Copenhaver 1, Jalane R Campbell 1, Tara A LeGates 1,2
PMCID: PMC12338580  PMID: 40791550

Abstract

Background:

Chronic alcohol exposure is a major driver of alcohol use disorders (AUD), in part through its ability to induce maladaptive plasticity within neural circuits that regulate reward, motivation, and affect. Excitatory projections from the hippocampus (Hipp) to the nucleus accumbens (NAc) play a pivotal role in regulating reward-related behaviors, and this pathway serves as a key locus for establishing associations between rewarding stimuli and related contextual information. Regulation of the strength of Hipp-NAc synapses is critical for supporting these behaviors, and aberrant Hipp-NAc plasticity is associated with anhedonia and disrupted reward learning.

Methods:

To examine acute ethanol effects, we used whole-cell electrophysiology to record Hipp-NAc synaptic plasticity in acute brain slices in the presence or absence of 50mM ethanol. To examine the effects of chronic ethanol administration, mice were exposed to ethanol vapor in a 3-week chronic intermittent ethanol (CIE) paradigm. Slices from ethanol and air exposed mice were used for whole-cell electrophysiology to examine Hipp-NAc synaptic plasticity.

Results:

Here, we demonstrate that acute ethanol application to ex vivo brain slices prevents long-term potentiation (LTP) at Hipp-NAc synapses, without altering presynaptic release probability. Furthermore, chronic intermittent exposure to ethanol abolishes LTP at these synapses, even during abstinence, indicating persistent synaptic dysfunction.

Conclusions:

Together, our findings demonstrate that ethanol has immediate and long-lasting effects on Hipp-NAc plasticity. Given the behavioral relevance of these synapses, this work has important implications for the mechanisms underlying ethanol-dependent effects on reward processing and negative affective states associated with AUD.

Keywords: hippocampus, nucleus accumbens, synaptic plasticity, chronic intermittent ethanol, reward

INTRODUCTION

Alcohol exerts both immediate and long-lasting effects on motivated behaviors, cognitive function, and emotional regulation (Koob and Volkow, 2010). These effects arise primarily from alcohol’s direct modulation of synaptic transmission and its influence over plasticity within key brain reward circuits (Lovinger and Abrahao, 2018). Although heightened plasticity in reward pathways may initially promote alcohol-seeking behaviors, persistent changes in circuit activation can ultimately impair the brain’s ability to respond to natural rewards and trigger prolonged activation of stress-related neural systems. As a result, disruption of normal reward processing and persistent stress signaling are thought to underlie the negative emotional states frequently associated with chronic alcohol use and dependence. AUD with comorbid anhedonia (loss of pleasure derived from previously pleasurable activities) is associated with increased risk of relapse and poorer clinical outcomes, presenting a major obstacle to recovery (Garfield, Lubman and Yücel, 2014; Destoop et al., 2019).

The nucleus accumbens (NAc) is a key mediator of motivated behaviors where both stress and rewarding experiences modulate synaptic function and plasticity to drive alterations in behavior (Carlezon and Thomas, 2009; Stuber, Britt and Bonci, 2012; Russo and Nestler, 2013). Excitatory input from several key brain regions (e.g., hippocampus, prefrontal cortex, thalamus, amygdala) has a crucial role in regulating NAc neuron activity to effectively encode reward-associated information and modulate motivated behaviors (O’Donnell and Grace, 1995; Goto and Grace, 2008; Calhoon and O’Donnell, 2013). Alterations in the strength and plasticity of these synapses as well as changes in excitability of NAc neurons have been associated with substance use disorders and depression, further demonstrating the key role of NAc activity in modulating motivated behaviors and emotional states (Volkow and Morales, 2015; Scofield et al., 2016; Francis and Lobo, 2017). For instance, chronic ethanol exposure enhances excitability and increases NMDAR activity in NAc neurons, consistently leading to increased volitional ethanol intake while also disrupting N-methyl-D-aspartate receptor (NMDAR)-dependent long-term depression (LTD) (Renteria et al., 2017; Kircher et al., 2019). This combination of effects mirrors the consequences of chronic stress, which similarly induces anhedonia and disrupts NMDAR-dependent LTD within the NAc (Lim et al., 2012). Together, this suggests that ethanol and stress may converge on overlapping mechanisms within the NAc, particularly through alterations in excitatory synaptic plasticity, to promote anhedonia and dysregulated reward processing.

Projections from the hippocampus (Hipp) provide a majority of the excitatory input to the NAc, critically modulating neuronal activity and gating the flow of information through the region (O’Donnell and Grace, 1995; Wilson and Kawaguchi, 1996; Stern, Jaeger and Wilson, 1998; Goto and O’Donnell, 2001). Hipp-NAc connectivity has been tied to several behaviors related to reward and motivation in humans and rodents including positive reinforcement learning, substance abuse, positive affect, as well as spatial- and contextual-based reward learning (Floresco and Phillips, 1999; Ito et al., 2008; Britt et al., 2012; Davidow et al., 2016; LeGates et al., 2018; Sjulson et al., 2018; Trouche et al., 2019; Zhou et al., 2019; Heller et al., 2020; Huntley et al., 2020; Sosa, Joo and Frank, 2020; Barnstedt, Mocellin and Remy, 2024). Our previous work revealed that activity-dependent strengthening of Hipp-NAc synapses drives reward-related behaviors while chronic stress disrupts this plasticity and induces anhedonia (LeGates et al., 2018). Hipp and NAc activity also influences alcohol-related behaviors, where reduced Hipp activity causes an increase in alcohol consumption, and chemogenetic activation of Hipp-NAc synapses attenuates excessive drinking (Griffin et al., 2023). Furthermore, chronic alcohol exposure induces pre- and postsynaptic changes at Hipp-NAc synapses and abolishes activity-dependent LTD (Kircher et al., 2019), again highlighting the similarly powerful effects of chronic stress and chronic alcohol on synaptic function.

Focusing on medium spiny neurons (MSNs), which represent ~95% of the neuron population in the NAc, we recently showed that LTP at Hipp-NAc synapses relies on NMDAR and L-type voltage gated calcium channels (L-type VGCCs) in males and females, respectively (Copenhaver and LeGates, 2024). Given the previously established ability of ethanol to inhibit NMDAR function within the NAc and its ability to inhibit L-type VGCCs (Lovinger, White and Weight, 1989; Zucca and Valenzuela, 2010; Mah, Fleck and Lindsley, 2011; Lee, Yeh and Yeh, 2022), we sought to determine whether ethanol exposure influenced activity-dependent potentiation of Hipp-NAc synapses similarly in both sexes. Here, we show that both acute in vitro and chronic in vivo exposure to ethanol prevents LTP at Hipp-NAc synapses in males and females. Given the link between Hipp-NAc potentiation in mediating reward-related behaviors, ethanol’s effects on these synapses may be a key mechanism driving maladaptive reward-related behaviors observed in response to alcohol use.

MATERIALS AND METHODS

Male and female C57BL/6J mice (8-10 weeks) were group housed (2-5 mice per cage) in a 12:12LD cycle with food and water ad libitum. We did not track the estrous cycle in female mice. All experiments were performed in accordance with the regulations set forth by the Institutional Animal Care and Use Committee at the University of Maryland, Baltimore County.

Ethanol Vapor Chamber Exposure

Male and female mice (8-10 weeks at the start of the experiment) were placed in acrylic inhalation chambers (60 × 59 × 35 cm) in their home cages and exposed to chronic intermittent ethanol (CIE) vapor or air 14 hours/day (ZT11-1), 4 days a week, for a total of 3 weeks. Compressed air (10–20 psi) was passed through a tube submerged in 100% ethanol to volatilize. Control vapor chambers delivered only air with no ethanol vapor. Vapor chamber ethanol concentrations were monitored daily, and air flow was adjusted to produce ethanol concentrations within 1.8-2.0% ethanol content as measured by a digital alcohol breath tester (BACTrack). After four days in the inhalation chambers, mice underwent a 72-h forced abstinence period. Whole cell electrophysiology was performed on week 4 after the 72-h abstinence period.

Brain Slice Preparation

Acute parasagittal slices (lateral 0.36-0.72) containing the fornix and nucleus accumbens were prepared for whole-cell patch-clamp electrophysiology. Animals were deeply anesthetized with isoflurane, decapitated, and brains were quickly dissected and submerged in ice-cold, bubbled (carbogen: 95% O2/5% CO2) N-methyl-D-glucamine (NMDG) recovery solution containing the following (in mM): 93 NMDG, 2.5 KCl, 1.2 NaH2PO4, 11 glucose, 25 NaHCO3, 1.2 MgCl2, and 2.4 CaCl2, pH=7.3-7.4, osmolarity=300-310 mOsm. Using a vibratome (VT1000S, Leica Microsystems), parasagittal slices (400 μm) were cut in cold, oxygenated NMDG. Slices were transferred to 32-34°C NMDG for 7-12 minutes to recover and were then transferred to room-temperature artificial cerebrospinal fluid (aCSF) containing the following (in mM): 120 NaCl, 3 KCl, 1.0 NaH2PO4, 20 glucose, 25 NaHCO3, 1.5 MgCl2·7H2O, and 2.5 CaCl2, pH=7.3-7.4. Slices were allowed to recover for 1-hour at room-temperature before beginning electrophysiological recordings.

Whole-Cell Recordings

Slices were placed in a submersion-type recording chamber and superfused with room-temperature aCSF (flow rate 0.5-1mL/min). Cells were visualized using a 60x water immersion objective on a Nikon Eclipse FN-1 or Scientifica microscope. Whole-cell patch-clamp recordings were performed using an Axopatch 200B amplifier (Axon Instruments, Molecular Devices) and a Digidata 1550B digitizer (Axon Instruments). Patch pipettes (4-8MΩ) were made from borosilicate glass (World Precision Instruments) using a Sutter Instruments P-97 model puller.

All recordings were performed in voltage-clamp conditions from MSNs in the NAc medial shell. A bipolar stimulating electrode (FHC) was placed in the fornix to electrically stimulate hippocampal axons while recording evoked excitatory postsynaptic currents (EPSC) (Figure 1a). Patch pipettes were filled with a solution containing 130 mM K-gluconate, 5 mM KCl, 2 mM MgCl6-H2O, 10 mM HEPES, 4 mM Mg-ATP, 0.3 mM Na2-GTP, 10 mM Na2-phosphocreatine, and 1 mM EGTA; pH=7.3-7.4; osmolarity=285-295mOsm. EPSCs were recorded at −70mV from paired pulses (100ms apart) elicited every 10s. After obtaining a stable 5-minute baseline EPSC recording, high-frequency stimulation (HFS: four trains of 100Hz stimulation for 1s with 15s between trains while holding the cell at −40mV) was applied, followed by a 30-minute recording of EPSCs. One cell was recorded per slice. For acute ethanol experiments, aCSF containing 50mM ethanol (Sigma) was washed onto slices for at least 20 minutes prior to recording, and experiments were done in the presence of ethanol. We used the following exclusion criteria to eliminate unhealthy cells and unreliable recordings: 1) We only proceeded with experiments on cells with series resistances <10MΩ, 2) Cells were excluded if their series resistance changed by >20% (comparing the resistance at the beginning and end of the experiment), 3) Cells in poor health or poor recording status were excluded (i.e. cell partially or fully sealed up, a decrease in holding current >100pA that is consistent with the cell dying, an increase in the variability of timing of EPSCs (jitter) post HFS, and/or an increase in response failure rate to > 50%).

Figure 1:

Figure 1:

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Ethanol interferes with LTP at Hipp-NAc synapses a) Schematic of recording strategy with stimulating electrode in the fornix and recording electrode in the NAc medial shell to record Hipp-evoked EPSCs from MSNs. The illustrated parasagittal section represents a slice from lateral +0.48mm. ac-anterior commissure f-fornix. b) Pretreatment of slices with 50mM ethanol prevents HFS-induced LTP at Hipp-NAc synapses in males and females (top). Paired-pulse ratios were not altered by HFS or ethanol (bottom). c) Summary data from the last 5 minutes of recording with representative traces below. Gray traces indicate baseline and black/blue indicate post-HFS. d) No differences in paired-pulse ratios recorded in the presence and absence of ethanol with representative traces shown below. n= 6control male, 4control female, 5ethanol male, 5ethanol female cells. Scale bar for representative traces is 20pA/10ms. * p<0.05, Scale bar for representative traces = 20pA/10ms.

Data analysis

To analyze data from HFS experiments, EPSC amplitudes were normalized to the average baseline amplitude. Normalized EPSC amplitudes were averaged over the last 5 minutes of the recording (minutes 25-30 post HFS) to examine the direction and magnitude of plasticity. Paired pulse ratio (PPR) was measured by calculating 5-minute averages of EPSC amplitudes from our paired pulses (EPSC1 and EPSC2) and dividing EPSC2 by EPSC1 (ie: EPSC2/EPSC1 = PPR). Statistical tests were performed using GraphPad Prism 9/10 software. A p-value of <0.05 was considered statistically significant, and exact p-values can be found in the results section. For acute ethanol experiments, n represents the number of cells/slices. For chronic ethanol experiments, n represents the number of mice. For line graphs, points represent the mean and error bars indicate SEM. Summary data plots display one point for each cell, with each point representing the average EPSC amplitude from the last 5 minutes of recording. For bar graphs, the bar represents the mean and error bars indicate SEM with individual data points overlayed. Statistical significance (p<0.05) was assessed by Two-way ANOVA (sex x treatment) with Šídák’s multiple comparisons. A three-way ANOVA (sex x treatment x time) was used to analyze PPR data before and after HFS.

RESULTS

Acute ethanol application to ex vivo slices prevents Hipp-NAc LTP

To determine whether ethanol acutely influences plasticity at Hipp-NAc synapses, we recorded HFS-induced LTP in the presence and absence of 50mM ethanol (Figure 1a). We found that, in the absence of ethanol, HFS induced LTP at Hipp-NAc synapses slices taken from male and female mice with no difference in magnitude between the sexes (Figure 1b–c), similar to our previous published results (LeGates et al., 2018; Copenhaver and LeGates, 2024). However, pretreatment with 50mM ethanol prevented LTP induction in slices taken from males and females (Figure 1b–c; Sex x Treatment Interaction: F(1,16) = 0.1512, p=0.7025; Main effect of Sex: F(1,16) = 0.01263, p=0.9119; Main effect of treatment: F(1,16) = 19.24, p=0.0005; Šídák’s multiple comparisons post hoc: p(Male:control vs EtOH) = 0.0175, p(Female:control vs EtOH) = 0.0107). We observed no difference in paired pulse ratio (PPR) at baseline (Figure 1d; Sex x Treatment Interaction: F(1,16) = 0.003732, p=0.9520; Main effect of Sex: F(1,16) = 1.066, p=0.3173; Main effect of treatment: F(1,16) = 0.2307, p=0.6375) suggesting that application of ethanol did not alter basal release probability. Furthermore, no change in PPR was observed following HFS irrespective of whether ethanol was present (Figure 1b, bottom; Time x Sex x Treatment Interaction: F(2.590, 41.45) = 0.5932, p=0.5992; Time x Treatment Interaction: F(2.590,41.45) = 1.814, p=0.1661; Time x Sex Interaction: F(2.590, 41.45) = 0.3843, p=0.7359), suggesting that HFS did not elicit changes in presynaptic neurotransmitter release probability.

CIE disrupts Hipp-NAc LTP

To determine whether chronic exposure to ethanol leads to changes in Hipp-NAc plasticity, we used CIE to ethanol vapor for controlled delivery and dosing of ethanol over a 3-week period (Figure 2a). Control mice were exposed to air. Following at least 72 hours of forced abstinence, slices from CIE-exposed mice demonstrated a deficit in HFS-induced LTP relative to air-exposed controls, which showed typical LTP (Figure 2b–c; Sex x Treatment Interaction: F(1,20) = 0.03737, p=0.8487; Main effect of Sex: F(1,20) = 0.1118, p=0.7415; Main effect of treatment: F(1,20) = 12.53, p=0.002; Šídák’s multiple comparisons post hoc: p(Male:control vs EtOH) = 0.0444, p(Female:control vs EtOH) = 0.0390). This effect was consistent in both male and female mice. Comparison of baseline PPRs revealed no difference between CIE mice and air exposed controls (Figure 2d; Sex x Treatment Interaction: F(1,20) = 0.2254, p=0.6401; Main effect of Sex: F(1,20) = 0.0008649, p=0.9768; Main effect of treatment: F(1,20) = 1.146, p=0.2971), suggesting that CIE did not induce changes in release probability. Similar to the data shown in Figure 1, HFS did not induce changes in PPR regardless of ethanol exposure or sex (Figure 2b bottom; Time x Sex x Treatment Interaction: F(6,20) = 1.600, p=0.1529; Time x Treatment Interaction: F(6,20) = 0.6492, p=0.6906; Time x Sex Interaction: F(6,20) = 1.067, p=3862), demonstrating a lack of effect on presynaptic function.

Figure 2:

Figure 2:

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Chronic intermittent ethanol exposure disrupts LTP at Hipp-NAc synapses. a) Schematic of experimental design to record Hipp-evoked EPSCs in the NAc shell of mice exposed to CIE or air. ac-anterior commissure f-fornix. b) Slices taken from male and female mice exposed to CIE show disrupted LTP as compared to air-exposed controls (top). Paired-pulse ratios were not altered by HFS or ethanol (bottom). c) Summary data from the last 5 minutes of recording with representative traces below. Gray traces indicate baseline and black/blue indicate post-HFS. d) No differences in paired-pulse ratios between cells recorded from air- and CIE-exposed mice with representative traces shown below. n= 7control male, 6control female, 6ethanol male, 5ethanol female mice * p<0.05, Scale bar for representative traces is 20pA/10ms.

DISCUSSION

Our data demonstrate that acute application of ethanol to ex vivo brain slices disrupts HFS-induced LTP at Hipp-NAc synapses. We also found that chronic exposure to ethanol in vivo interfered with HFS-induced LTP at Hipp-NAc synapses, an effect observed after a 72-hour abstinence period when ethanol was no longer present. Neither treatment led to a change in basal release probability, suggesting that ethanol may be acting postsynaptically to interfere with LTP. Given the previously described role for Hipp-NAc synaptic strength in mediating reward-related behaviors, ethanol’s impact on Hipp-NAc plasticity has important implications for understanding the neurobiological basis for disrupted reward processing and negative mood states associated with alcohol use disorders.

Alcohol influences affective states and cognitive function

Acute alcohol intoxication and persistent alcohol consumption have extensive effects on cognitive processing, executive function, and memory, while also influencing affective state and emotion. Chronic alcohol use contributes to the emergence of negative affective symptoms, including depression-related features such as anhedonia and sleep disturbances (McHugh and Weiss, 2019). Additionally, individuals with co-occurring alcohol use disorder (AUD) and major depressive disorder (MDD) are at elevated risk for relapse and tend to exhibit more severe symptoms (Garfield, Lubman and Yücel, 2014; Destoop et al., 2019). These behavioral results suggest key interplay between AUD and MDD that may contribute to the development and severity of these disorders.

Bidirectional regulation of the strength of Hipp-NAc connectivity plays a central role in mediating reward-based learning and memory, as well as regulating affective state and has been implicated in substance use and depression (Davidow et al., 2016; LeGates et al., 2018; Sjulson et al., 2018; Trouche et al., 2019; Heller et al., 2020; Huntley et al., 2020; Griffin et al., 2023). We previously showed that LTP of Hipp-NAc synapses facilitates reward-related behaviors while disruptions in LTP is associated with anhedonia (LeGates et al., 2018). Here, we show that both acute and chronic ethanol exposure also interferes with LTP at these synapses, mirroring the immediate and lasting effects of ethanol on synaptic plasticity previously observed within the Hipp and at other synapses in the NAc. Given the role of Hipp-NAc synapses in mediating reward-related behaviors, regulating affective state, and enduring alterations in response to ethanol, this connection may represent a key site of information convergence, providing an opportunity to identify mechanistic relationships among alcohol, mood, and cognitive processes.

Alcohol-dependent effects on synaptic function and plasticity

Alcohol has a wide range of effects on the brain, but a key factor that may underlie the ability of alcohol to influence cognitive function and emotional state across several temporal domains is its ability to impact synaptic function and plasticity in several relevant brain regions including the Hipp and NAc (Zorumski, Mennerick and Izumi, 2014; Ewin et al., 2019; Van Skike, Goodlett and Matthews, 2019; Bach, Morgan, et al., 2021). At intoxicating concentrations (~ 40–60 mM), acute ethanol application can reversibly inhibit both NMDAR responses and LTP in the Hipp (Lovinger, White and Weight, 1990; Zorumski, Mennerick and Izumi, 2014) as well as NMDAR-dependent LTD of Hipp-NAc synapses (Kircher et al., 2019). However, ethanol-mediated inhibition of NMDARs is partial at these concentrations, and partial inhibition by selective NMDAR antagonists does not fully block LTP (Schummers, Bentz and Browning, 1997; Izumi et al., 2005). This would suggest that NMDAR blockade does not completely explain ethanol’s effect on LTP, implicating potential involvement of additional signaling pathways. In line with this, ethanol has also been found to block a form of NMDAR-independent LTP that is dependent on L-type VGCCs (Izumi et al., 2005). We previously demonstrated Hipp-NAc LTP is mediated by sex-specific mechanisms: in males, LTP is NMDAR-dependent while in females, LTP is NMDAR-independent and instead relies on L-type VGCCs (Copenhaver and LeGates, 2024). Dual-effects of ethanol on NMDARs and L-type VGCCs, as observed in the Hipp (Chandler, Harris and Crews, 1998; Izumi et al., 2005), may therefore explain the deficits in LTP we observed in both males and females at Hipp-NAc synapses.

Chronic ethanol, especially with binge-like or high-dose patterns, consistently diminishes the ability of hippocampal neurons to elicit LTP, an effect that can persist for days to months after ethanol withdrawal (Roberto et al., 2002; Zorumski, Mennerick and Izumi, 2014). Similar effects on plasticity have been observed in the NAc shell where CIE-induced disruption of NMDAR-dependent LTD persists for two weeks following the last exposure (Renteria, Buske and Morrisett, 2018). Changes in glutamatergic and GABAergic receptor function and expression, which can lead to overall disruptions in excitation/inhibition balance, are thought to be key factors mediating the effects of chronic ethanol on synaptic plasticity (Nelson, Ur and Gruol, 2005; Qiang, Denny and Ticku, 2007; Obara et al., 2009). Additionally, chronic ethanol exposure induces hyperexcitability, neuron loss, and morphological alterations in the Hipp (Stragier et al., 2015; Bach, Ewin, et al., 2021), which may serve as additional factors that ultimately contribute to alterations in synaptic plasticity and produce long-lasting changes that persist into abstinence.

Our data demonstrate that chronic ethanol exposure disrupts LTP at Hipp-NAc synapses (Figure 2b–c). The absence of ethanol during recordings from slices of CIE-exposed mice indicates that ethanol produces long-lasting alterations in synaptic plasticity that persist into abstinence, consistent with previously reported effects described above. The plasticity deficits we observed are also supported by recent work demonstrating chronic ethanol exposure induces disruption to NMDAR-dependent LTD of Hipp-NAc synapses (Kircher et al., 2019). This effect coincided with synaptic alterations consistent with increased presynaptic release probability and postsynaptic incorporation of Ca2+-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), implicating both presynaptic and postsynaptic mechanisms in ethanol-related plasticity disruptions (Kircher et al., 2019). In contrast, we found no evidence of ethanol-induced changes in release probability, as measured by paired-pulse ratio (PPR) (Figure 1d and 2d) suggesting ethanol is likely acting primarily through postsynaptic mechanisms to interfere with LTP. The differences in experimental outcomes may also be due to differences in study design including the length of exposure time (3 weeks versus ~10 weeks), the method of administration in the previous study involving CIE and two-bottle choice, or the length of the abstinence period (72 versus 24 hours).

As discussed above, the mechanisms underlying LTP at Hipp-NAc synapses are sex-specific, so while previously described alterations in NMDAR function and expression may explain the effects of ethanol on LTP in males, this does not fully explain the LTP deficits we observed in females. A considerable amount of the previous work that has provided the mechanistic insight into ethanol’s influence on synaptic function and plasticity has relied on data collected from males. Growing evidence of sex differences in synaptic function suggests that focusing on only one sex may obscure key molecular mechanisms underlying alcohol’s effects. These synaptic differences may be hidden, producing similar behaviors across sexes, or manifest overtly in the well-documented disparities between males and females in alcohol sensitivity and vulnerability to AUD (Erol and Karpyak, 2015; Flores-Bonilla and Richardson, 2020). Taken together, the ability of ethanol to disrupt plasticity of synapses that rely on inherent sex-specific mechanisms highlights the complexity of mechanistically dissecting its effects on synaptic function. These findings also point to the potential for sex-specific synaptic adaptations that may contribute to differential vulnerability and dependence.

Stress and alcohol

The ethanol-induced effects on Hipp-NAc LTP observed in this study closely resemble those we reported previously in response to chronic stress (LeGates et al., 2018). In many respects, responses to alcohol closely resemble stress responses. For instance, both acute alcohol or stress exposure activate the hypothalamic-pituitary-adrenal (HPA) axis, whereas repeated or chronic exposure leads to dysregulation of HPA axis function (Richardson et al., 2008; Stephens and Wand, 2012). Chronic stress is a common precipitator of several reward-related psychiatric disorders including depression and substance use disorders, and there is a high rate of comorbidity between depression and AUD that is associated with greater severity and poorer outcomes (McHugh and Weiss, 2019). Stress-induced changes in excitatory synaptic function within key circuits involved in reward and emotion regulation are thought to be a crucial factor underlying the pathophysiology of depression (Thompson et al., 2015), and there is evidence to suggest that drugs of misuse can elicit changes in circuit function similar to those observed in response to stress (Saal et al., 2003). These overlapping neurobiological responses highlight the potential importance of interactions between stress, alcohol, and neural circuit function in depression and AUD pathophysiology, though further research is needed to fully delineate mechanisms and relevant circuits.

Hipp-NAc synapses are critical mediators of reward-related behaviors that are both stress and alcohol sensitive (LeGates et al., 2018; Kircher et al., 2019; Griffin et al., 2023; Lucantonio et al., 2025). Activation and potentiation of these synapses is rewarding and attenuates excessive alcohol consumption (Britt et al., 2012; LeGates et al., 2018; Griffin et al., 2023) while chronic stress as well as acute and chronic alcohol exposure disrupt activity-dependent synaptic plasticity and is associated with anhedonia (LeGates et al., 2018; Kircher et al., 2019) (and Figures 1 and 2). Together, this underscores the crucial interplay between Hipp-NAc circuit function and motivated behaviors, highlighting how alcohol’s influence can rapidly alter behavior and induce lasting disruptions that contribute to dependence and comorbid mental health disorders. Together, these insights position the Hipp-NAc pathway as a critical synaptic locus underlying alcohol dependence and depression, and a promising target for therapeutic intervention.

Support:

We would like to thank Dr. Yaohui Zhu and Kaela Befano for their assistance and Dr. Brian Mathur for his technical support and thoughtful comments on the manuscript. This work was supported by NSF IOS2402645, T32GM144876-02, the Meyerhoff program at UMBC, and start-up funds from UMBC.

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