Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2022 Oct 1.
Published in final edited form as: Biol Psychiatry. 2021 May 8;90(7):482–493. doi: 10.1016/j.biopsych.2021.05.002

THE RESILIENT PHENOTYPE INDUCED BY PROPHYLACTIC KETAMINE EXPOSURE DURING ADOLESCENCE IS MEDIATED BY THE VTA-NAC PATHWAY

Eric M Parise 1, Lyonna F Parise 1, Omar K Sial 2, Astrid M Cardona-Acosta 2, Trevonn M Gyles 1, Barbara Juarez 3,5, Dipesh Chaundry 3,6, Ming-Hu Han 1,3,4, Eric J Nestler 1,*, Carlos A Bolaños-Guzmán 2,*
PMCID: PMC8761260  NIHMSID: NIHMS1702165  PMID: 34247781

Abstract

Background

Major depressive disorder (MDD) is prevalent in children and adolescents and is associated with a high degree of morbidity throughout life, with potentially devastating personal consequences and public health impact. Ketamine’s (KET’s) efficacy as an antidepressant has been demonstrated in adolescent rodents; however, the neurobiological mechanisms underlying these effects are unknown. Recent evidence showed that KET reverses stress-induced (i.e., depressive-like) deficits within major mesocorticolimbic regions such as the prefrontal cortex (PFC), nucleus accumbens (NAc), and hippocampus in adult rodents. However, little is known about KET’s effect in the ventral tegmental area (VTA), which provides the majority of dopaminergic input to these brain regions.

Methods

We characterized behavioral and the biochemical and electrophysiological effects produced by KET treatment in C57BL/6J male mice during adolescence (7–10 per condition) within the VTA and its major projection regions, namely, the NAc and PFC. Subsequently, molecular targets within the VTA-NAc projection were identified for viral gene transfer manipulations to recapitulate the effects of stress or KET treatment.

Results

Repeated KET treatment produced a robust pro-resilient response to chronic social defeat stress. This effect was largely driven by Akt signaling activity within the VTA and NAc, and it could be blocked or recapitulated through direct Akt-viral-mediated manipulation. Additionally, we found that the KET-induced resilient phenotype is dependent on VTA-NAc, but not VTA-PFC, pathway activity.

Conclusions

These findings indicate that KET exposure during adolescence produces a pro-resilient phenotype mediated by changes in Akt intracellular signaling and altered neuronal activity within the VTA-NAc pathway.

Keywords: ketamine, prophylactic, adolescence, mesocorticolimbic, depression, resilience

Introduction

Major depressive disorder (MDD) during adolescence is highly debilitating and associated with a 70% increase in likelihood of relapse in adulthood (1). Although available treatments are safe in adults (2), nearly 50% of afflicted adolescents do not respond to conventional treatments (3,4). Clinical studies on childhood depression treatment have recently emerged, yet reliable evidence-based indications for antidepressant use and long term consequences of treatment in pediatric populations is critically lacking (5–7). Ketamine (KET), a non-competitive N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, has shown promise as a rapid acting and potentially long-lasting antidepressant in adults (8), and practitioners have started using KET off-label in affected youths (9–11). However, little is known about the neurobiological effects of KET treatment prior to adulthood.

The mechanisms underlying KET’s antidepressant actions are not fully elucidated. Evidence suggests that KET rapidly enhances structure and function of cortical synapses playing a role in mood regulation (12,13). Additionally, KET’s effects may depend on rapid activation of the mammalian target of rapamycin (mTOR) pathway, including increases in extracellular signal-regulated kinase (ERK), protein kinase B (PKB/Akt), and brain-derived neurotrophic factor (BDNF) within the hippocampus (HPC), and prefrontal cortex (PFC) (12,14–17).

Supporting this view, ventricular infusion of the Akt/mTOR inhibitor rapamycin (RAPA) blocks KET’s acute antidepressant-like effects (15), suggesting that other brain nuclei, besides the HPC and PFC, may be involved. The mechanisms involving KET’s sustained effects are unclear. Although evidence points to changes in AMPA glutamate receptor density and associated intracellular signaling (18,19), KET’s actions are complex, and detailed assessments of its effects on behavioral outputs, signaling pathways, and brain areas are lacking. Most efforts have centered on the HPC and PFC; however, the ventral tegmental area (VTA) is likely involved, as NMDA receptors in this brain region are highly sensitive to stress (20), and the VTA plays a role in mood regulation (20,21). VTA dopamine (DA) neurons project to, and modulate the activity of, several other brain regions such as the NAc, PFC and HPC (22–24). The VTA-NAc projection is best known for regulating goal-directed and reward-related behaviors (25,26), while the VTA-PFC projection in stress responses (27–29), and the VTA-HPC projection in emotional-related memories (22–24).

Given that the VTA appears as common modulator of these forebrain regions, it is conceivable that KET-induced effects within the PFC and HPC might be regulated through its actions in VTA, and whether the NAc also plays a role is unknown. Therefore, the overall goal was to assess neurobiological alterations within the VTA and NAc that occur following adolescent KET treatment and determine whether such adaptations can influence functional responses to stress and other mood-related stimuli.

Methods

Animals.

Detailed descriptions are provided in Supplement 1.

Experimental Design.

An initial experiment was conducted in order to determine KET’s antidepressant-like efficacy in adolescent (postnatal day [PD] PD35) mice using the social interaction (SIT) and forced swim (FST) tests. Mice were randomly assigned to receive a single injection of KET (0, 5, 10, or 20 mg/kg) 24h before the SIT and FST. Based on the results from this experiment, the 10 mg/kg KET dose was selected to assess repeated KET’s antidepressant efficacy in adolescent mice, and because it lies well within the range of sub-anesthetic doses used in clinical trials (16,30,31). Therefore, a separate group of PD35 mice received KET (0 or 10 mg/kg) daily for 15 days (last injection on PD49) and left undisturbed for 1 week (washout period) prior to exposure to 10 days of chronic social defeat stress (CSDS). Twenty-four hours later they were exposed to the SIT and FST.

Drugs.

Ketamine (KET) was obtained from Butler Schein Animal Health (Dublin, OH) in an injectable solution (100 mg/ml). KET (0, 5, 10, and 20 mg/kg) was diluted in sterile physiological saline (SAL; 0.9% sodium chloride) and administered intraperitoneally (IP) at a volume of 2 mL/kg. RAPA was obtained from Sigma-Aldrich (St. Louis, MO) in a purified powder form and reconstituted into a 0.2 nmol concentration using 100% Dimethyl sulfoxide (DMSO) as the vehicle.

Behavioral, Biochemical, Surgical, viral-mediated, and electrophysiological Assays

Details in Supplement 1.

Statistical analyses.

Data was assessed using mixed-design (between and within variables) analysis of variance (ANOVA) followed by Tukey post hoc tests. When appropriate, Student’s t-tests were used to determine statistical significance of pre-planned comparisons. Data are expressed as the mean ± SEM. Statistical significance was defined as p< 0.05.

Results

Effects of acute KET in naïve mice.

Adolescent PD35 male mice received a single KET injection 24h before behavioral assessment. KET significantly increased SI ratio (F(3,28)=6.805, p<0.005, Fig. 1B) and time spent in the interaction zone (F(3,28)=5.769, p<0.05, Fig. 1C), along with reduced total immobility (F(3,28)=4.531, p<0.05, Fig. 1D) in the FST. Post hoc analyses revealed that 10 mg/kg increased interaction ratio (p<0.05), while the 10 and 20 mg/kg decreased total immobility (p<0.05). Only 10 mg/kg KET significantly increased time spent in the interaction zone with target present when compared to no target (p<0.001; Fig. 1C), effects independent of locomotor activity as no differences in distance traveled were detected (Fig. 1E).

Figure 1.

Figure 1.

Open in a new tab

Ketamine treatment buffers responses to stress in adolescent mice. Acute treatment with KET (10 mg/kg) significantly increased interaction ratio (B) and interaction time with target present (C) when compared to saline-treated controls. (D) Acute KET treatment (10 and 20 mg/kg) significantly reduced total immobility in the FST when compared to SAL-treated controls. (E) Acute KET treatment did not influence locomotor activity. (F) Schematic timeline of stress exposure, KET treatment, and subsequent behavioral testing. (G-J) CSDS significantly reduced social interaction in CSDS-exposed mice pretreated with SAL, whereas KET (10 mg/kg, IP) pre-treatment blocks this stress-induced deficit. (I) SAL-pretreated CSDS-exposed mice also demonstrated significantly increased total immobility in the FST, while those pre-treated with KET showed the opposite effect. (J) KET pre-treatment had no effect on locomotor activity. Data are presented as mean ± SEM. For acute treatment, n=8 per condition. For repeated treatment, CON-SAL (n=10 ), CON-KET (n=10), CSDS-SAL (n=9), CSDS-KET (n=9). *Significantly different from SAL treated controls (p<0.05). #Significantly different from SAL treated in the CSDS condition (p<0.05). Data for the acute KET treatment were analyzed using one-way ANOVA followed by Tukey correction while the data for the repeated KET treatment were analyzed using a two-way ANOVA followed by Tukey correction.

Effects of repeated KET prior to CSDS.

Mice received KET (10 mg/kg) from PD35–49 and a week after exposed to ten days CSDS, followed by SIT and FST (Fig. 1F). KET produced robust antidepressant-like responses in the SIT. ANOVA revealed main effects of stress (F(1,34)=5.464, p<0.05), drug-pretreatment (F(1,34)=5.516, p<0.05), and interaction (F(1,34)=8.163, p<0.005; Fig. 1G). Post hoc indicated that SAL+CSDS-exposed mice had reduced interaction ratio when compared to controls (CON), while KET+CSDS resulted in increased SI ratio compared to the SAL+CSDS-exposed mice (p<0.05, respectively).

Similarly, analysis of time in the interaction zone revealed main effects of stress (F(3,34)=3.011, p<0.05), drug-pretreatment (F(1,34)=12.68, p<0.005), and interaction (F(3,34)=7.056, p<0.005; Fig. 1H). Post hoc showed that KET blocked the CSDS-induced reduction in time spent in the interaction zone in the KET+CSDS-exposed mice (p<0.05), and the mice assigned to KET+CON condition (p<0.05).

Repeated KET produced antidepressant-like responses in the FST (Fig. 1I), revealed by main effects of stress (F(1,34)=4.771, p<0.05) and drug-pretreatment (F(1,34)=6.237, p<0.05). SAL+CSDS-exposed mice displayed greater total immobility when compared to all other conditions (p<0.05). In contrast, KET+CSDS-exposed mice displayed lower total immobility when compared to the respective SAL+CSDS-exposed controls (p<0.05). While there was an overall main effect of stress on locomotor activity (F(1,34)=15.65, p<0.005), the behavioral effects were independent of general locomotion as no within-group differences were detected (Fig. 1J).

Effects of intra-VTA KET in adolescent mice.

To determine whether KET effects could be mediated within the VTA, adolescent mice were cannulated and microinfused with KET (1 μg) before the SIT and FST (Fig. 2A–B). KET dose was selected based on previous study showing that intra-VTA infusion of KET blocked heroin self-administration (32). Direct KET infusion into VTA had no effect on social interaction (p>0.05; Fig. 2C) or distance traveled (p>0.05; Fig. 2E) but significantly reduced total immobility in the FST (t(22)=2.633, p<0.05; Fig. 2D).

Figure 2.

Figure 2.

Open in a new tab

Intra-VTA bilateral ketamine infusion (1 μg/side) produces antidepressant-like effects in adolescent mice. (A) Schematic timeline of cannulation surgeries, intra-VTA infusions and behavioral testing. (B) Injection sites of the intra-VTA KET infusion are represented schematically along with a representative image of VTA infused with methylene blue. (C) Intra-VTA KET treatment had no influence on social interaction, but (D) significantly reduced total immobility in the FST without influencing distance traveled (E). Data are presented as mean ± SEM; n=12 per condition. *Significantly different from SAL treated mice (p<0.05). Data were analyzed using Student’s t-tests.

Effects of acute and repeated KET on VTA and NAc gene expression.

(see Supplement 1 and SF1).

Inhibition of Akt/mTOR within the VTA blocks KET effects.

Given KET’s effects on Akt and mTOR mRNA expression, intra-VTA infusions of Akt/mTOR inhibitor RAPA (0.5 μl/side; 0.2 nmol) were used to further examine KET’s antidepressant-like efficacy (Fig. 3A,B). Two-way ANOVA, with VTA-RAPA-infusion and KET (10 mg/kg; IP) as independent variables, indicated that total immobility in FST (Fig. 3D) was dependent on VTA-RAPA-infusion (F(1,24)=13.60, p<0.005), KET treatment (F(1,24)=10.25, p<0.05), and their interaction (F(1,24)=5.107, p<0.05). VEH-infused+KET-pretreated mice spent less time immobile than all other conditions (p<0.05). In contrast, RAPA completely blocked the effects of KET. No significant differences were apparent on SI or distance traveled (Figure 3C,E).

Figure 3.

Figure 3.

Open in a new tab

Pharmacological inhibition of Akt/mTOR with rapamycin (RAPA; 0.2 nmol) within the VTA blocks the antidepressant like effects of systemic ketamine (10 mg/kg, IP). (A) Schematic time-line of cannulation surgeries, intra-VTA infusions, and behavioral testing. (B) Injection sites of the intra-VTA infusion are represented schematically along with a representative image of VTA infused with methylene blue. (C) Intra-VTA RAPA had no effect on social interaction but blocked the antidepressant-like effects of acute KET in the FST (D) without influencing distance traveled (E). Data are presented as mean ± SEM. SAL-VEH (n=7), KET-VEH (n=7), SAL-RAPA (n=7), KET-RAPA (n=7). *Significantly different from SAL-VEH-treated mice (p<0.05). #Significantly different KET-VEH-treated mice. Data were analyzed using two-way ANOVA followed by Tukey correction.

Repeated KET and CSDS influence Akt signaling in the NAc.

(see Supplement 1 and SF2).

Viral-mediated downregulation of Akt within the VTA blocks repeated KET’s effects.

Based on the ability of acute and repeated KET to increase Akt/mTOR, and of RAPA within the VTA to block acute KET’s effects, the consequences of Akt/mTOR activity within VTA on KET-induced antidepressant-related efficacy was assessed. Decreased Akt function was induced in SAL- and KET-pretreated adolescent mice by local VTA microinfusion of HSV–Aktdn, using HSV-GFP as control (Fig. 4A,B). We have shown that overexpression HSV–Aktdn reduces Akt activity (33,34). Three-way ANOVA (independent variables: stress, KET, HSV) indicated that SI was dependent on stress (F(1,57)=164.8, p<0.005), KET treatment (F(1,57)=8.666, p<0.005), HSV (F(1,57)=8.858, p<0.005), stress by HSV (F(1,57)=7.789, p<0.05), and KET treatment by HSV (F(1,57)=6.383, p<0.05), with a three-way interaction (F(1,57)=5.677, p<0.05). Total immobility in the FST (Fig. 4D) was dependent on stress (F(1,57)=10.57, p<0.005), stress by KET (F(1,57)=27.84, p<0.005), stress by HSV (F(1,57)=19.14, p<0.005), with a three-way interaction (F(1,57)=14.04, p<0.005). Post hoc revealed that exposure to CSDS produced deficits in SI and forced-swimming behavior as the SAL-CSDS-HSV-GFP-exposed mice had lower SI ratio (p<0.05; Fig. 4C) and spent more time immobile (p<0.05; Fig. 4D) in the FST, when compared to SAL-CON-HSV-GFP-exposed mice. KET blocked the effects of CSDS on SI and forced-swimming as the KET-CSDS-HSV-GFP-exposed mice showed higher interaction ratio (p<0.005; Fig. 4C) and less time immobile (p<0.005; Fig. 4D) when compared to the SAL-CSDS-HSV-GFP-exposed mice. Downregulation of Akt in the VTA blocked KET’s effects in the SIT as KET-CSDS-HSV-Aktdn-treated mice had lower interaction ratio when compared to SAL-CSDS-HSV-GFP- (p<0.005; Fig. 4C) and KET-CSDS-HSV-GFP-exposed (p<0.005; Fig. 4C) mice. Decreasing Akt activity in the VTA blocked KET’s effects in the FST (Fig. 4D) as the KET-CSDS-HSV-Aktdn-exposed mice spent more time immobile when compared to the SAL-CON-HSV-GFP- (p<0.05) and KET-CSDS-HSV-GFP-exposed mice (p<0.005). Interestingly, KET-CON-HSV-GFP-exposed mice spent more time immobile when compared to the SAL-CON-HSV-GFP- (p<0.005), SAL-CON-HSV-Aktdn (p<0.005) and KET-CON-HSV-Aktdn-exposed mice (p<0.05); effects independent of viral-induced changes in locomotion (Fig. 4E).

Figure 4.

Figure 4.

Open in a new tab

Viral-mediated downregulation of Akt activity within the VTA blocks the antidepressant-like effects of repeated ketamine (10 mg/kg, IP). (A) Schematic timeline of KET pretreatment, CSDS exposure, viral surgeries, and behavioral testing. (B) Injection sites of the intra-VTA infusion are represented schematically along with a representative immunofluorescent image of viral transgene expression in the VTA. (C) Downregulation of Akt—achieved by expression of a dominant negative Akt mutant (Aktdn)—within the VTA blocks the KET-induced antidepressant-like effects in social interaction and (D) forced swimming behavior (E) without influencing distance traveled. Data are presented as mean ± SEM. CON-SAL-GFP (n=8), CSDS-SAL-GFP (n=7), CON-SAL-Aktdn (n=8), CSDS-SAL- Aktdn (n=10), CON-KET-GFP (n=7), CSDS-KET-GFP (n=9), CON-KET- Aktdn (n=8), CSDS-KET-Aktdn (n=8). *Significantly different from CON-SAL-GFP-exposed mice (p<0.05). #Significantly different from CSDS-SAL-GFP-exposed mice. αSignificantly different from CSDS-KET-Aktdn-exposed mice. $Significantly different from CON-SAL-GFP, CON-SAL-Aktdn, and CON-KET- Aktdn. Data were analyzed using three-way ANOVA followed by Tukey correction.

Viral-mediated overexpression of Akt in the NAc induces a susceptible phenotype.

We assessed functional consequences of increasing Akt activity within the NAc using HSV-Aktca (Fig. 5A–E). Aktca is a constitutively active Akt mutant that enhances Akt activity (33,34). Following viral manipulation, mice were exposed to a microdefeat, an adaptation of CSDS (i.e., subthreshold defeat) considered a submaximal CSDS procedure insufficient for producing a susceptible phenotype in naïve mice with high validity and reproducibility (35–40). A two-way ANOVA (independent variables: virus and microdefeat) indicated that SI ratio (F(1,24)=5.107, p<0.05; Fig. 5C) and immobility in the FST (F(1,24)=5.107, p<0.05; Fig. 5D) were dependent on an interaction between them. Mice overexpressing HSV-Aktca+micro-defeat displayed lower SI ratio when compared to CON-HSV-GFP- (t(26)=3.065, p<0.05; Fig. 5C) and CON-HSV-Aktca-exposed mice (t(26)=4.45, p<0.05; Fig. 5C). When assessing immobility in the FST (Fig. 5D), increased stress susceptibility was observed: HSV-Aktca+microdefeat-exposed mice exhibited higher immobility when compared to CON-HSV-GFP- (p<0.05) and CON-HSV-Aktca-exposed mice (p<0.05). No differences in locomotor activity observed due to virus treatment (Fig. 5E).

Figure 5.

Figure 5.

Open in a new tab

Viral-induced overexpression of Akt in the NAc induces a susceptible phenotype in adolescent mice. (A) Schematic timeline of the submaximal social defeat procedure (micro-defeat), where c57BL/6 mice were defeated three times within a single day, three days after viral infusions into the NAc. (B) Injection sites of the intra-NAc infusion are represented schematically along with a representative immunofluorescent image of viral transgene expression in the NAc. (C) Overexpression of constitutively active Akt (Aktca) in the NAc produced a susceptible phenotype only in mice exposed to a micro-defeat, as characterized by a reduced interaction ratio, and (D) increased total immobility in the FST, (E) without influencing distance traveled. Data are presented as mean ± SEM. *Significantly different from CON-GFP-exposed mice (p<0.05). #Significantly different from micro-defeat-Aktca-exposed mice (p<0.05). Data were analyzed using two-way ANOVA followed by Tukey correction.

Viral-mediated downregulation of Akt in the NAc reverses the susceptible phenotype induced by CSDS.

The effects of downregulating Akt activity within the NAc in response to a full CSDS were assessed (Fig. 7). Interaction ratio (Fig. 6C) was dependent on stress (F(1,27)=5.537, p<0.05) and virus main effects (F(1,27)=5.877, p<0.05). Post hoc showed that CSDS-HSV-GFP-exposed mice had lower SI ratio when compared to all other groups (p<0.05). Downregulation of Akt in NAc of CSDS-exposed mice increased SI ratio as compared to CSDS-HSV-GFP group (p<0.05). Similarly, immobility in the FST (Fig. 6D) was dependent on stress (F(1,27)=5.791, p<0.05) and virus main effects (F(1,27)= 5.178, p<0.05), with post hoc indicating that CSDS-HSV-GFP-exposed mice spent more time immobile when compared to all other groups (p<0.05). CSDS-HSV-Aktdn-exposed mice showed reduced immobility when compared to CSDS-HSV-GFP-exposed group (p<0.05). These effects were not a function of viral exposure as no differences in locomotor activity were observed (Fig. 6E).

Figure 7.

Figure 7.

Open in a new tab

Repeated ketamine (10 mg/kg, IP) treatment in adolescent mice influences VTA-NAc neuronal activity. (A) Repeated treatment with KET during adolescence has no effect on VTA-PFC neuronal activity. (B) KET treatment produced a robust reduction in VTA-NAc neuronal activity. Data are presented as mean ± SEM. VTA-PFC-SAL (n=16 cells), VTA-PFC-KET (n=33 cells), VTA-NAC-SAL (n=35 cells), VTA-NAC-KET (n=28 cells). *Significantly different from SAL-treated mice (p<0.05). Data were analyzed using Student’s t tests.

Figure 6.

Figure 6.

Open in a new tab

Viral-mediated downregulation of Akt in the NAc reverses the susceptible phenotype induced by CSDS in adolescent mice. (A) Schematic time-line of the social defeat procedure, viral infusions into the NAc, and subsequent behavioral testing. (B) Injection sites of the intra-NAc infusion are represented schematically along with a representative immunofluorescent image of viral transgene expression in the NAc. (C) Downregulation of Akt—achieved by expressing Aktdn—reversed the significant reduction in social interaction observed in CSDS-GFP-exposed mice and (D) blocked the CSDS-induced increases in total immobility seen in CSDS-GFP-exposed mice, (E) without influencing distance traveled. Data are presented as mean ± SEM. CON-GFP (n=8), CSDS-GFP (n=7), CON-Aktdn (n=8), CSDS-Aktdn (n=8). *Significantly different from CON-GFP-exposed mice (p<0.05). #Significantly different from CSDS-GFP-exposed mice (p<0.05). Data were analyzed using two-way ANOVA followed by Tukey correction.

Effects of repeated KET on VTA-NAc neuronal activity.

After verifying the VTA’s involvement in KET’s effects, we determined whether the PFC or NAc, major VTA efferent projection regions, play a role in repeated KET’s effects (Fig. 7). Repeated KET during adolescence had no effect on PFC-projecting VTA cells (Fig. 7A, p>0.005), while producing a robust decrease in activity of NAc-projecting VTA cells (t(61)=3.273, p<0.005; Fig. 7B).

Optogenetic stimulation of the VTA-NAc pathway blocks the antidepressant-like effects of repeated KET.

We investigated the contribution of VTA-NAc projection on KET’s behavioral effects by optogenetically manipulating this pathway (Fig. 8A–E). Optical stimulation blocked repeated KET’s effects in KET-CSDS-exposed mice, which show lower SI ratio when compared to SAL-CON-exposed in the stimulated (t(12)=2.916, p<0.05; Fig. 8D) and KET-CSDS-exposed mice in non-stimulated condition (t(14)=2.767, p<0.05). Optical stimulation of VTA-NAc pathway did not influence SI in CSDS-exposed mice, as both SAL-CSDS-exposed no-stimulation (t(13)=2.503, p<0.05) and the SAL-CSDS-exposed stimulated (t(13)=4.707, p<0.005; Fig. 10D) mice exhibited reduced SI ratios when compared to their CON-counterparts; effects independent of changes in locomotor activity (Fig. 8E).

Figure 8.

Figure 8.

Open in a new tab

Optogenetic stimulation of the VTA-NAc pathway blocks the antidepressant-like effects induced by repeated ketamine (10 mg/kg, IP) in adolescent mice. (A) Schematic time-line surgeries, KET treatment, exposure to stress, and subsequent behavioral testing. (B) Injection sites of the intra-NAc infusion are represented schematically along with a representative immunofluorescent image of viral transgene expression. (C) A representative immunofluorescent image of viral transgene expression as well as fiber optic cannula placement within the VTA. (D) Optogenetic stimulation of the VTA-NAc neuronal circuit blocked the antidepressant-like effects of adolescent repeated KET treatment in social interaction, (E) without influencing distance traveled. Data are presented as mean ± SEM. CON-NO-STIM-SAL (n=8), CON-STIM-SAL (n=6), CON-NO-STIM-KET (n=10), CON-STIM-KET (n=7), CSDS-NO-STIM-SAL (n=6), CSDS-STIM-SAL (n=9), CSDS-NO-STIM-KET (n=8), CSDS-STIM-KET (n=8). *Significantly different from the CON-exposed counterpart (p<0.05). #Significantly different from CSDS-KET-STIM group (p<0.05). Data were analyzed as pre-planned comparisons using Student’s t-tests.

Discussion

Pediatric depression can have life-long devastating outcomes, yet reliable evidence-based indications for antidepressant use and its long-term neurobiological consequences are severely lacking (5–7,31). To start bridging this gap in our knowledge, we assessed KET’s antidepressant-like activity in adolescent mice. The mice received acute KET (0–20 mg/kg) and time spent interacting with a social target and immobility time in the FST were assessed. Only those mice receiving 10 mg/kg KET showed reliable antidepressant-like effects (i.e., increased social interaction and decreased total immobility in the FST). This is in line with findings showing no antidepressant-like effects at 3 mg/kg KET in adolescent mice (41), further supporting our use of 10 mg/kg dose. To our knowledge, our studies are the first to perform a dose-response assessment of KET’s antidepressant-like efficacy in adolescent mice, findings in agreement with studies showing antidepressant-like effects in adult rodents at 3–30 mg/kg KET doses (14,15,42).

We determined whether repeated KET (10 mg/kg) would buffer the effects of stress. Repeated KET blocked behavioral dysregulation induced by CSDS as measured in the SIT and FST, indicating that repeated KET produces a stress-resistant phenotype in adolescent male mice, as we have reported in rats (43), highlighting the importance of understanding the mechanisms underlying repeated KET treatment to develop treatments against stress (44). While these effects could potentially be explained by KET or its active metabolites still present in the system at time of stress exposure (45,46), this is unlikely as mice were subjected to CSDS after a week washout period, at a time when all traces of KET should have been fully metabolized (47–51). Our findings are not the first to suggest KET produces prophylactic effects against stress, as acute KET in adult mice produces a stress-resistant phenotype (44). This previous study also incorporated a week-long washout period before CSDS, further supporting the idea that KET may induce neurobiological changes that promote resilience to stress. We now expand these findings to include adolescent mice.

Although much of the work examining KET’s antidepressant mechanisms have focused on the PFC and HPC (13,14,52,53), both of these brain regions receive input from the VTA as part of the mesocorticolimbic reward pathway (20,22,54). Optogenetic studies have demonstrated that VTA manipulation can profoundly influence behavioral responsivity to stress (25,40,55,56). The VTA contains NMDA receptors (57,58) and KET influences the activity of dopaminergic neurons within this region (59,60). Therefore, it is plausible that KET may exert its effects, at least partly, via the VTA, which would then influence the PFC and HPC resulting in antidepressant-like effects. Unfortunately, the VTA’s role in KET’s antidepressant effects is poorly understood. Therefore, we assessed the effects of direct KET administration into the VTA of adolescent mice and examined behavioral reactivity to stress. Intra-VTA KET produced antidepressant-like responses by reducing total immobility in the FST, demonstrating that VTA plays a significant role in the antidepressant-like actions of KET during adolescence. Interestingly, intra-VTA KET had no effect on SI, suggesting that a higher dose of KET may be required before influencing SI. Alternatively, it is possible that other brain areas, beside the VTA, mediate systemic KET’s observed effects in the SIT, and studies are needed to better understand this phenomenon. Our findings are not the first to assign importance to the VTA in KET’s antidepressant effects, as others have shown KET increases the number of spontaneously active VTA-dopamine neurons in mice, and reverses stress-induced deficits on dopaminergic transmission in the VTA of adult rats (61,62). While these studies demonstrated possible VTA’s involvement in KET’s antidepressant effects through electrophysiological measures, our study is the first to demonstrate it behaviorally through direct pharmacological manipulation.

KET’s antidepressant actions are hypothesized to be mediated by transient increases in Akt/mTOR signaling within the PFC (13). We found that both acute and repeated systemic KET produced robust increases in Akt and mTOR gene expression as well as pAkt and pMTOR within the VTA. These findings are important because Akt signaling within the VTA is known to regulate responses to stress (12), and elevated levels of pAkt within the VTA have been observed in MDD patients treated chronically with fluoxetine (29). Combined, this evidence suggests that KET’s antidepressant effects may be driven by changes in Akt/mTOR signaling within the VTA. This is further supported by our findings with the Akt/mTOR inhibitor RAPA, as its microinfusion into the VTA blocked the effects of acute systemic KET in the FST. Neither microinfusion of KET nor RAPA influenced SI, a surprising finding given our initial results showing that acute KET increases SI. The cause of this discrepancy is unknown. Additionally, a clinical study found that oral RAPA pretreatment failed to block KET’s antidepressant effects (63), highlighting the importance in targeted versus systemic blockade of mTORC1. Nevertheless, our findings indicate that Akt/mTOR signaling within the VTA plays a role in KET’s effects, implicating this brain region as a key mediator in KET’s antidepressant/pro-resilience actions during adolescence.

Akt’s involvement in acute KET’s effects led us to explore its role within the VTA after repeated exposure. Adolescent mice received KET (10 mg/kg) for 15 days, followed by CSDS before receiving bilateral microinfusions of HSV-Aktdn within the VTA. Repeated KET blocked CSDS-induced behavioral deficits in the SIT and FST in the HSV-GFP-infused mice, whereas downregulating Akt completely reversed antidepressant-like responses, effect independent of basal locomotion. Importantly, CSDS decreases pAkt levels within the VTA, and viral-mediated downregulation of Akt increases the excitability of DA neurons, inducing a stress-vulnerability phenotype (33). Given the opposing effects of stress and KET on Akt signaling and dopaminergic neuronal activity, we hypothesize that Akt signaling within the VTA plays an important role in driving KET’s effects.

The brain circuitry and mechanisms underlying KET’s antidepressant effects continue to be elucidated, with much focus placed on the PFC and HPC. However, structural changes within multiple brain regions likely underlie the maintenance of KET’s actions (13,19,53). Acute KET influences mTOR signaling, promoting synaptogenesis and spine formation in the PFC (53), along with enhancement of PFC-NAc functional connectivity (64). Importantly, both the PFC and NAc receive input from the VTA (20,65). Studies have confirmed the VTA and its connections to the PFC and NAc as important mediators of addiction- and depression-related behaviors (25,40,55,56). However, whether the VTA-PFC and/or VTA-NAc circuits are influenced by KET is unknown. We assessed these possibilities by measuring the effects of repeated KET on activity of VTA neurons projecting to either the PFC or NAc. Repeated KET produced no changes in VTA activity within the VTA-PFC connection. This was surprising given work showing that KET influences activity of PFC neurons (15) and that there is increased activity within the VTA-PFC pathway in stress-resilient mice, which can be reversed by optogenetic inhibition (40). Conversely, repeated KET produced a robust reduction in neuronal activity within the VTA-NAc pathway. This is particularly exciting because optogenetic stimulation of this projection produces a stress-susceptibility phenotype, while inhibition reverses CSDS-induced depressive-like symptomatology (40). These data suggest that repeated KET produces its antidepressant effects, at least partially, by reducing DA neuronal activity projecting from VTA to the NAc, thereby buffering the effects of CSDS. However, for the electrophysiological experiments conducted herein, DA cells were identified by the presence of a large Ih current, which was evoked by holding cells at −70 mV and stepping to −120 mV in 10 mV increments. While Ih is present in >90% of DA neurons (66,67), its presence does not unequivocally identify DA cells in midbrain slices (68). Therefore, it is possible that the observed reduction in activity within the VTA and VTA-NAc connection were not solely driven by changes in DA neuronal activity. It will thus be important to replicate these findings utilizing a cell-type specific approach.

We found that both acute and repeated ketamine treatment reduced the expression of Akt and mTOR mRNA in the NAc of adolescent mice, while only repeated KET treatment produced a significant reduction in pAkt and pmTOR protein. Importantly, exposure to CSDS produced increased Akt mRNA and pAkt protein in the NAc of adolescent mice, while repeated KET prior to CSDS completely blocked these effects. These data suggest that NAc Akt/mTOR signaling is disrupted after CSDS and KET pretreatment opposes these adaptations. These findings are in agreement with work demonstrating that CSDS increases Akt signaling within the NAc of adult mice (69), and we now extend these findings to adolescence, further demonstrating that KET can buffer CSDS-induced increase in Akt/mTOR activity. These findings set the stage to determine the significance of increased Akt activity within the NAc on stress-induced behavioral responding during adolescence. We delivered viral vectors overexpressing a constitutively active form of Akt (HSV-Aktca), a dominant negative inhibitor of Akt (HSV-Aktdn), or GFP (HSV-GFP) into the NAc and assessed behavioral reactivity to stress. Adolescent mice receiving HSV-Aktca into the NAc displayed increased social avoidance after exposure to subthreshold CSDS, while blocking Akt activity with HSV-Aktdn was sufficient to block the social avoidance induced by 10 days of CSDS. These results confirm our earlier findings, supporting the hypothesis that Akt signaling within the NAc plays a crucial role in gating sensitivity to stress and may, in conjunction with decreased Akt activity within the VTA, modulate the depressive-like phenotype induced by CSDS. The results are in agreement with evidence that the Akt/mTOR pathway plays an important role in mediating complex emotional behavior, including responses to antidepressants (33,53,69–71). These findings establish a novel role for elevated Akt levels within the NAc in increasing sensitivity to stress, whereas blockade of Akt activity results in a stress-resistant phenotype, and point directly to Akt and its downstream signaling molecules as potential therapeutic targets for stress-induced and related mood disorders (72).

Optogenetic stimulation of the VTA-NAc pathway was sufficient to block the behavioral phenotype observed after repeated KET exposure. Optical stimulation of the VTA-NAc pathway prevented increases in SI induced by repeated KET in the CSDS-exposed mice, thus demonstrating, for the first time, that KET’s effects in adolescent mice are dependent on a decrease in VTA-NAc neuronal activity. This finding provides a link to understand the neural network involved in KET’s antidepressant effects. However, the viral vector used to express channel rhodopsin in this study does not solely infect DA neurons, making it likely that other, non-dopaminergic neurons (e.g., GABA) were also stimulated. Additionally, the investigation of the VTA-NAc pathway’s role in repeated KET’s antidepressant effects was limited to one behavioral output (social interaction). It will be important to replicate these findings using additional behavioral assays. A previous study using learned helplessness in rats found that bilateral injections of R-ketamine into NAc shell and core were insufficient to produce antidepressant-like effects (73), suggesting that KET may not produce its antidepressant effects through direct action in the NAc. Nevertheless, the present results further substantiate the influence of the VTA-NAc circuit on mood regulation and underscore the need for a clearer understanding of the mechanisms downstream of Akt within the VTA that regulate depression-like behavior in adolescents.

Here we provide crucial evidence on KET’s antidepressant mechanism of action: pretreatment with repeated KET during adolescence produces a lasting pro-resilient phenotype that is mediated by increases in Akt/mTOR signaling within the VTA and decreases in the NAc, along with a reduction in the activity of VTA neurons projecting to NAc. Our findings establish a novel role for Akt activity within the NAc regulating responses to stress, and our ability to enhance resistance to stress by reducing Akt activity within the NAc provides novel insight into the development of therapeutic agents that promote resilience.

Supplementary Material

2

KEY RESOURCES TABLE

Resource Type Specific Reagent or Resource Source or Reference Identifiers Additional Information
Add additional rows as needed for each resource type Include species and sex when applicable. Include name of manufacturer, company, repository, individual, or research lab. Include PMID or DOI for references; use “this paper” if new. Include catalog numbers, stock numbers, database IDs or accession numbers, and/or RRIDs. RRIDs are highly encouraged; search for RRIDs at https://scicrunch.org/resources. Include any additional information or notes if necessary.
Organism/Strain c57BL/6J mice, male Jackson Labs Stock No.000664
Organism/Strain CD-1 retired breeders, male Charles River strain code:022
Other Precast 4%–20% gradient gels Biorad cat#:5671094
Antibody Akt Cell signaling cat#: 9272S
Antibody Phospho-Akt (Ser473) Cell signaling cat#: 4060S
Antibody mTOR Cell signaling cat#: 2972S
Antibody Phospho-mTOR (Ser2448) Cell signaling cat#: 2971S
Antibody GAPDH Cell signaling cat#: 5174S
Antibody Goat Anti-Rabbit IgG Antibody (H+L), Peroxidase Vector Laboratories cat#: PI-1000–1
Viral vector HSV-GFP Rachael L Neve; PMID: 18639865 N/A
Viral vector HSV-Aktdn Rachael L Neve; PMID: 18639865 N/A
Viral vector HSV-Aktca Rachael L Neve; PMID: 18639865 N/A
Viral vector HSV-Aktwt Rachael L Neve; PMID: 18639865 N/A
Viral vector AAV2/5-ChR2–eYFP University of Pennsylvania vector core facility N/A
Drugs Ketamine HCL Butler Schein Animal Health (Dublin, OH) cat#: 1049007
Drugs AnaSeD (Xylazine) Santa Cruz Animal Health cat#: sc-362949Rx
Reagent Rapamyacin Sigma Aldrich cat#: R8781
Open in a new tab

FUNDING

This work was supported by Texas A&M University, College of Liberal Arts, and by R01DA046794 from the National Institute on Drug Abuse (NIDA); R01MH051399 (EJN) and R01 MH120637 (MHH) from the National Institute of Mental Health.

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Disclosure

The authors report no biomedical financial interests or potential conflicts of interest.

References

  • 1.Richmond TK, Rosen DS (2005): The treatment of adolescent depression in the era of the black box warning. Current opinion in pediatrics 17: 466–472. [DOI] [PubMed] [Google Scholar]
  • 2.Trivedi MH, Rush AJ, Wisniewski SR, Nierenberg AA, Warden D, Ritz L, et al. (2006): Evaluation of outcomes with citalopram for depression using measurement-based care in STAR*D: implications for clinical practice. American Journal of Psychiatry 163: 28–40. [DOI] [PubMed] [Google Scholar]
  • 3.Hazell P (2011): Depression in children and adolescents. Clinical evidence 2011. [Google Scholar]
  • 4.Maalouf FT, Atwi M, Brent DA (2011): Treatment-resistant depression in adolescents: review and updates on clinical management. Depression and anxiety 28: 946–954. [DOI] [PubMed] [Google Scholar]
  • 5.Zito JM, Safer DJ, DosReis S, Gardner JF, Soeken K, Boles M, Lynch F (2002): Rising prevalence of antidepressants among US youths. Pediatrics 109: 721–727. [DOI] [PubMed] [Google Scholar]
  • 6.Coyle JT, Pine DS, Charney DS, Lewis L, Nemeroff CB, Carlson GA, et al. (2003): Depression and bipolar support alliance consensus statement on the unmet needs in diagnosis and treatment of mood disorders in children and adolescents. Undefined, vol. 42 42: 1494–1503. [DOI] [PubMed] [Google Scholar]
  • 7.Birmaher B (1998): Should we use antidepressant medications for children and adolescents with depressive disorders? Psychopharmacol Bull 34: 35–39. [PubMed] [Google Scholar]
  • 8.Molero P, Ramos-Quiroga JA, Martin-Santos R, Calvo-Sánchez E, Gutiérrez-Rojas L, Meana JJ (2018): Antidepressant Efficacy and Tolerability of Ketamine and Esketamine: A Critical Review. CNS Drugs 32: 411–420. [DOI] [PubMed] [Google Scholar]
  • 9.Papolos DF, Teicher MH, Faedda GL, Murphy P, Mattis S (2013): Clinical experience using intranasal ketamine in the treatment of pediatric bipolar disorder/fear of harm phenotype. J Affect Disord 147: 431–436. [DOI] [PubMed] [Google Scholar]
  • 10.Cullen KR, Amatya P, Roback MG, Albott CS, Schreiner MW, Ren Y, et al. (2018): Intravenous Ketamine for Adolescents with Treatment-Resistant Depression: An Open-Label Study. Journal of child and adolescent psychopharmacology 28: 437–444. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Kim S, Rush BS, Rice TR (2020): A systematic review of therapeutic ketamine use in children and adolescents with treatment-resistant mood disorders. European child & adolescent psychiatry 206: 256–17. [DOI] [PubMed] [Google Scholar]
  • 12.Murrough JW (2012): Ketamine as a novel antidepressant: from synapse to behavior. Clinical Pharmacology & Therapeutics 91: 303–309. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 13.Duman RS, Li N, Liu R-J, Duric V, Aghajanian G (2011): Signaling pathways underlying the rapid antidepressant actions of ketamine. Neuropharmacology 62: 35–41. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 14.Autry AE, Adachi M, Nosyreva E, Na ES, Los MF, Cheng P, et al. (2011): NMDA receptor blockade at rest triggers rapid behavioural antidepressant responses. Nature 475: 91–95. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Li N, Lee B, Liu R-J, Banasr M, Dwyer JM, Iwata M, et al. (2010): mTOR-dependent synapse formation underlies the rapid antidepressant effects of NMDA antagonists. Science 329: 959–964. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Abdallah CG, Adams TG, Kelmendi B, Esterlis I, Sanacora G, Krystal JH (2016): KETAMINE’S MECHANISM OF ACTION: A PATH TO RAPID-ACTING ANTIDEPRESSANTS. Depression and anxiety. 10.1002/da.22501 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Sial OK, Parise EM, Parise LF, Gnecco T, Bolaños-Guzmán CA (2020): Ketamine_ The final frontier or another depressing end? Behavioural Brain Research 383: 112508. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Koike H, Iijima M, Chaki S (2011): Involvement of AMPA receptor in both the rapid and sustained antidepressant-like effects of ketamine in animal models of depression. Behavioural Brain Research 224: 107–111. [DOI] [PubMed] [Google Scholar]
  • 19.Machado-Vieira R, Yuan P, Brutsche N, Diazgranados N, Luckenbaugh D, Manji HK, Zarate CAJ (2009): Brain-derived neurotrophic factor and initial antidepressant response to an N-methyl-D-aspartate antagonist. The Journal of clinical psychiatry 70: 1662–1666. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20.Nestler EJ, Carlezon WA (2006): The mesolimbic dopamine reward circuit in depression. BPS 59: 1151–1159. [DOI] [PubMed] [Google Scholar]
  • 21.Iñiguez SD, Vialou V, Warren BL, Cao J-L, Alcantara LF, Davis LC, et al. (2010): Extracellular signal-regulated kinase-2 within the ventral tegmental area regulates responses to stress. Journal of Neuroscience 30: 7652–7663. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Lisman JE, Grace AA (2005): The hippocampal-VTA loop: controlling the entry of information into long-term memory. Neuron 46: 703–713. [DOI] [PubMed] [Google Scholar]
  • 23.Luo AH, Tahsili-Fahadan P, Wise RA, Lupica CR, Aston-Jones G (2011): Linking Context with Reward: A Functional Circuit from Hippocampal CA3 to Ventral Tegmental Area. Science 333: 353–357. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Lammel S, Lim BK, Ran C, Huang KW, Betley MJ, Tye KM, et al. (2012): Input-specific control of reward and aversion in the ventral tegmental area. Nature 491: 1–8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Britt JP, Bonci A (2013): Optogenetic interrogations of the neural circuits underlying addiction. Current Opinion in Neurobiology 23: 539–545. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Wise RA (1996): Neurobiology of addiction. Current Opinion in Neurobiology 6: 243–251. [DOI] [PubMed] [Google Scholar]
  • 27.Nestler EJ, Barrot M, Dileone RJ, Eisch AJ, Gold SJ, Monteggia LM (2002): Neurobiology of depression. Neuron 34: 13–25. [DOI] [PubMed] [Google Scholar]
  • 28.Berton O, Nestler EJ (2006): New approaches to antidepressant drug discovery: beyond monoamines. Nat Rev Neurosci 7: 137–151. [DOI] [PubMed] [Google Scholar]
  • 29.Krishnan V, Nestler EJ (2008): The molecular neurobiology of depression. Nature 455: 894–902. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 30.Kratochvil CJ, Vitiello B, Walkup J, Emslie G, Waslick BD, Weller EB, et al. (2006): Selective serotonin reuptake inhibitors in pediatric depression: is the balance between benefits and risks favorable? Journal of child and adolescent psychopharmacology 16: 11–24. [DOI] [PubMed] [Google Scholar]
  • 31.Emslie GJ, Mayes TL (2001): Mood disorders in children and adolescents: psychopharmacological treatment. BPS 49: 1082–1090. [DOI] [PubMed] [Google Scholar]
  • 32.Xi ZX, Stein EA (2002): Blockade of ionotropic glutamatergic transmission in the ventral tegmental area reduces heroin reinforcement in rat. Psychopharmacology 164: 144–150. [DOI] [PubMed] [Google Scholar]
  • 33.Krishnan V, Han M-H, Mazei-Robison M, Iñiguez SD, Ables JL, Vialou V, et al. (2008): AKT Signaling within the Ventral Tegmental Area Regulates Cellular and Behavioral Responses to Stressful Stimuli. Biological Psychiatry 64: 691–700. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 34.Russo SJ, Bolaños CA, Theobald DE, DeCarolis NA, Renthal W, Kumar A, et al. (2007): IRS2-Akt pathway in midbrain dopamine neurons regulates behavioral and cellular responses to opiates. Nature Neuroscience 10: 93–99. [DOI] [PubMed] [Google Scholar]
  • 35.Golden SA, Covington HE, Berton O, Russo SJ (2011): A standardized protocol for repeated social defeat stress in mice. Nature Protocols 6: 1183–1191. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 36.Terrillion CE, Francis TC, Puche AC, Lobo MK, Gould TD (2017): Decreased Nucleus Accumbens Expression of Psychiatric Disorder Risk Gene Cacna1c Promotes Susceptibility to Social Stress. Int J Neuropsychoph 20: 428–433. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 37.Menard C, Pfau ML, Hodes GE, Kana V, Wang VX, Bouchard S, et al. (2017): Social stress induces neurovascular pathology promoting depression. Nat Neurosci 20: 1752–1760. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 38.Wang J, Hodes GE, Zhang H, Zhang S, Zhao W, Golden SA, et al. (2018): Epigenetic modulation of inflammation and synaptic plasticity promotes resilience against stress in mice. Nat Commun 9: 477. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 39.Krishnan V, Han M-H, Graham DL, Berton O, Renthal W, Russo SJ, et al. (2007): Molecular adaptations underlying susceptibility and resistance to social defeat in brain reward regions. Cell 131: 391–404. [DOI] [PubMed] [Google Scholar]
  • 40.Chaudhury D, Walsh JJ, Friedman AK, Juarez B, Ku SM, Koo JW, et al. (2013): Rapid regulation of depression-related behaviours by control of midbrain dopamine neurons. Nature 493: 532–536. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 41.Nosyreva E, Autry AE, Kavalali ET, Monteggia LM (2014): Age dependence of the rapid antidepressant and synaptic effects of acute NMDA receptor blockade. Front Mol Neurosci 7: 94. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 42.Li Y, Zhu ZR, Ou BC, Wang YQ, Tan ZB, Deng CM, et al. (2015): Dopamine D2/D3 but not dopamine D1 receptors are involved in the rapid antidepressant-like effects of ketamine in the forced swim test. Behavioural Brain Research 279: 100–105. [DOI] [PubMed] [Google Scholar]
  • 43.Parise EM, Alcantara LF, Warren BL, Wright KN, Hadad R, Sial OK, et al. (2013): Repeated ketamine exposure induces an enduring resilient phenotype in adolescent and adult rats. Biological Psychiatry 74: 750–759. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 44.Brachman RA, McGowan JC, Perusini JN, Lim SC, Pham TH, Faye C, et al. (2015): Ketamine as a Prophylactic Against Stress-Induced Depressive-Like Behavior. Biological Psychiatry. 10.1016/j.biopsych.2015.04.022 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 45.Yao N, Skiteva O, Zhang X, Svenningsson P, Chergui K (2017): Ketamine and its metabolite (2R,6R)-hydroxynorketamine induce lasting alterations in glutamatergic synaptic plasticity in the mesolimbic circuit. Molecular Psychiatry 15: 1–12. [DOI] [PubMed] [Google Scholar]
  • 46.Zanos P, Moaddel R, Morris PJ, Georgiou P, Fischell J, Elmer GI, et al. (2016): NMDAR inhibition-independent antidepressant actions of ketamine metabolites. Nature 1–18. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 47.Zarate CAJ, Singh JB, Carlson PJ, Brutsche NE, Ameli R, Luckenbaugh DA, et al. (2006): A randomized trial of an N-methyl-D-aspartate antagonist in treatment-resistant major depression. Archives of General Psychiatry 63: 856–864. [DOI] [PubMed] [Google Scholar]
  • 48.Clements JA, Nimmo WS, Grant IS (1982): Bioavailability, pharmacokinetics, and analgesic activity of ketamine in humans. J Pharm Sci 71: 539–542. [DOI] [PubMed] [Google Scholar]
  • 49.Williams ML, Mager DE, Parenteau H, Gudi G, Tracy TS, Mulheran M, Wainer IW (2004): Effects of protein calorie malnutrition on the pharmacokinetics of ketamine in rats. Drug metabolism and disposition: the biological fate of chemicals 32: 786–793. [DOI] [PubMed] [Google Scholar]
  • 50.Shiue CY, Vallabhahosula S, Wolf AP, Dewey SL, Fowler JS, Schlyer DJ, et al. (1997): Carbon-11 labelled ketamine-synthesis, distribution in mice and PET studies in baboons. Nuclear Medicine and Biology 24: 145–150. [DOI] [PubMed] [Google Scholar]
  • 51.Sato Y (2004): Chronopharmacological studies of ketamine in normal and NMDA 1 receptor knockout mice. British journal of anaesthesia 92: 859–864. [DOI] [PubMed] [Google Scholar]
  • 52.da Silva FCC, do C de O Cito M, MIG da Silva, Moura BA, de A Neto MR, Feitosa ML, et al. (2010): Behavioral alterations and pro-oxidant effect of a single ketamine administration to mice. Brain Research Bulletin 83: 9–15. [DOI] [PubMed] [Google Scholar]
  • 53.Duman RS, Voleti B (2012): Signaling pathways underlying the pathophysiology and treatment of depression: novel mechanisms for rapid-acting agents. Trends in Neurosciences 35: 47–56. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 54.Yadid G, Overstreet DH, Zangen A (2001): Limbic dopaminergic adaptation to a stressful stimulus in a rat model of depression. Brain Research 896: 43–47. [DOI] [PubMed] [Google Scholar]
  • 55.Jennings JH, Sparta DR, Stamatakis AM, Ung RL, Pleil KE, Kash TL, Stuber GD (2013): Distinct extended amygdala circuits for divergent motivational states. Nature 496: 224–228. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 56.Friedman AK, Walsh JJ, Juarez B, Ku SM, Chaudhury D, Wang J, et al. (2014): Enhancing depression mechanisms in midbrain dopamine neurons achieves homeostatic resilience. Science 344: 313–319. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 57.Rodriguez JJ, Doherty MD, Pickel VM (2000): N-methyl-D-aspartate (NMDA) receptors in the ventral tegmental area: subcellular distribution and colocalization with 5-hydroxytryptamine(2A) receptors. J Neurosci Res 60: 202–211. [DOI] [PubMed] [Google Scholar]
  • 58.Monaghan DT, Cotman CW (1985): Distribution of N-methyl-D-aspartate-sensitive L-[3H]glutamate-binding sites in rat brain. The Journal of neuroscience : the official journal of the Society for Neuroscience 5: 2909–2919. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 59.Erhardt S, Engberg G (2002): Increased phasic activity of dopaminergic neurones in the rat ventral tegmental area following pharmacologically elevated levels of endogenous kynurenic acid. Acta Physiologica Scandinavica 175: 45–53. [DOI] [PubMed] [Google Scholar]
  • 60.French ED, Ceci A (1990): Non-competitive N-methyl-D-aspartate antagonists are potent activators of ventral tegmental A10 dopamine neurons. Neuroscience Letters 119: 159–162. [DOI] [PubMed] [Google Scholar]
  • 61.Belujon P, Grace AA (2014): Restoring Mood Balance in Depression_Ketamine Reverses Deficit in Dopamine-Dependent Synaptic Plasticity. BPS 76: 927–936. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 62.Witkin JM, Monn JA, Schoepp DD, Li X, Overshiner CD, Mitchell SN, et al. (2016): The Rapidly-Acting Antidepressant Ketamine and the mGlu2/3 Receptor Antagonist LY341495 Rapidly Engage Dopaminergic Mood Circuits. Journal of Pharmacology and Experimental Therapeutics 1–48. [DOI] [PubMed] [Google Scholar]
  • 63.Abdallah CG, Averill LA, Gueorguieva R, Goktas S, Purohit P, Ranganathan M, et al. (2020): Modulation of the antidepressant effects of ketamine by the mTORC1 inhibitor rapamycin. Neuropsychopharmacol 45: 990–997. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 64.Dawson N, Morris BJ, Pratt JA (2013): Subanaesthetic ketamine treatment alters prefrontal cortex connectivity with thalamus and ascending subcortical systems. Schizophrenia bulletin 39: 366–377. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 65.Cao J-L, Covington HE, Friedman AK, Wilkinson MB, Walsh JJ, Cooper DC, et al. (2010): Mesolimbic dopamine neurons in the brain reward circuit mediate susceptibility to social defeat and antidepressant action. Journal of Neuroscience 30: 16453–16458. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 66.Cameron DL, Wessendorf MW, Williams JT (1997): A subset of ventral tegmental area neurons is inhibited by dopamine, 5-hydroxytryptamine and opioids. NSC 77: 155–166. [DOI] [PubMed] [Google Scholar]
  • 67.Neuhoff H, Neu A, Liss B, Roeper J (2002): I(h) channels contribute to the different functional properties of identified dopaminergic subpopulations in the midbrain. Journal of Neuroscience 22: 1290–1302. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 68.Margolis EB, Lock H, Hjelmstad GO, Fields HL (2006): The ventral tegmental area revisited: is there an electrophysiological marker for dopaminergic neurons? The Journal of physiology 577: 907–924. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 69.Dwyer JM, Duman RS (2013): Activation of Mammalian target of rapamycin and synaptogenesis: role in the actions of rapid-acting antidepressants. Biological Psychiatry 73: 1189–1198. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 70.Kitagishi Y, Kobayashi M, Kikuta K, Matsuda S (2012): Roles of PI3K/AKT/GSK3/mTOR Pathway in Cell Signaling of Mental Illnesses. Depression research and treatment 2012: 752563. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 71.Huang W, Zhao Y, Zhu X, Cai Z, Wang S, Yao S, et al. (2013): Fluoxetine upregulates phosphorylated-AKT and phosphorylated-ERK1/2 proteins in neural stem cells: evidence for a crosstalk between AKT and ERK1/2 pathways. Journal of Molecular Neuroscience 49: 244–249. [DOI] [PubMed] [Google Scholar]
  • 72.Manji HK, Drevets WC, Charney DS (2001): The cellular neurobiology of depression. Nature Medicine 7: 541–547. [DOI] [PubMed] [Google Scholar]
  • 73.Shirayama Y, Hashimoto K (2017): Effects of a single bilateral infusion of R-ketamine in the rat brain regions of a learned helplessness model of depression. Eur Arch Psy Clin N 267: 177–182. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

2
NIHMS1702165-supplement-2.pdf (200.4KB, pdf)

RESOURCES