Influence of Chronic Electroconvulsive Seizures on Plasticity-Associated Gene Expression and Perineuronal Nets Within the Hippocampi of Young Adult and Middle-Aged Sprague-Dawley Rats.

BACKGROUND: Electroconvulsive seizure therapy is often used in both treatment-resistant and geriatric depression. However, preclinical studies identifying targets of chronic electroconvulsive seizure (ECS) are predominantly focused on animal models in young adulthood. Given that putative transcriptional, neurogenic, and neuroplastic mechanisms implicated in the behavioral effects of chronic ECS themselves exhibit age-dependent modulation, it remains unknown whether the molecular and cellular targets of chronic ECS vary with age. METHODS: We subjected young adult (2-3 months) and middle-aged (12-13 months), male Sprague Dawley rats to sham or chronic ECS and assessed for despair-like behavior, hippocampal gene expression, hippocampal neurogenesis, and neuroplastic changes in the extracellular matrix, reelin, and perineuronal net numbers. RESULTS: Chronic ECS reduced despair-like behavior at both ages, accompanied by overlapping and unique changes in activity-dependent and trophic factor gene expression. Although chronic ECS had a similar impact on quiescent neural progenitor numbers at both ages, the eventual increase in hippocampal progenitor proliferation was substantially higher in young adulthood. We noted a decline in reelin⁺ cell numbers following chronic ECS only in young adulthood. In contrast, an age-invariant, robust dissolution of perineuronal net numbers that encapsulate parvalbumin⁺ neurons in the hippocampus were observed following chronic ECS. CONCLUSION: Our findings indicate that age is a key variable in determining the nature of chronic ECS-evoked molecular and cellular changes in the hippocampus. This raises the intriguing possibility that chronic ECS may recruit distinct, as well as overlapping, mechanisms to drive antidepressant-like behavioral changes in an age-dependent manner.

Evaluation of real-world outcomes associated with use of a prescription digital therapeutic to treat substance use disorders.

BACKGROUND AND OBJECTIVES: Digital therapeutics can expand the reach and fidelity of behavioral treatment for substance use disorders (SUDs). This analysis evaluated real-world engagement and clinical outcomes in patients diagnosed with SUD who were prescribed reSET®, an FDA-authorized prescription digital therapeutic (PDT). METHODS: Patients were prescribed a 12-week PDT comprising 61 therapy lessons (31 "core" and 30 "keep learning" lessons) and contingency management rewards (positive reinforcement message or monetary gift cards) based on lesson completion and negative urine drug screens. Engagement (defined as any activity in the PDT), retention (any activity in Weeks 9-12), and substance use data were collected automatically by the PDT and analyzed descriptively. Associations between early lesson completion and end-of-treatment outcomes were assessed. RESULTS: Six hundred and fifty-eight patients filled their prescription. Evaluated were 602 patients who were exposed to therapeutic content by completing at least one lesson (median age 37 years, 33% female, 41% male, 26% unreported sex). Median lessons completed was 33 (out of 61 possible), and 52% of patients completed all core modules. Retention in treatment during the last 4 weeks of treatment was 74%, and 62% were abstinent (missing data considered positive). [Correction added on 13 December 2022, after first online publication: In the preceding sentence, the treatment percentage values were revised from 74.6% to 74%.] DISCUSSION AND CONCLUSIONS: Patients with SUD exhibited robust engagement with a PDT, high rates of retention through 12 weeks, and substantial rates of abstinence at end of treatment when the therapeutic was used in a real-world setting. PDT's hold promise as a new way to access effective SUD treatment. SCIENTIFIC SIGNIFICANCE: This study is the first to report real-world PDT engagement and clinical outcomes data from a large, geographically diverse population of patients with SUDs.

Exercise reduces the anxiogenic effects of meta-chlorophenylpiperazine: The role of 5-HT2C receptors in the bed nucleus of the stria terminalis.

Introduction: Two weeks of voluntary exercise in group-housed mice produces a reduction in anxiety-like behaviors across a number of different measures, including a reduction in the anxiety levels typically produced by the anxiogenic serotonergic drug m-chlorophenylpiperazine (mCPP), an agonist at 5-HT2C/2b receptors. We have previously demonstrated that 2-weeks of voluntary exercise blunted the anxiogenic effects of systemic mCPP, and we have also shown that mCPP infused into the bed nucleus of the stria terminalis (BNST) is anxiogenic. Here we follow up on these reports. Methods: In Experiment 1 we infused several doses of mCPP into the BNST with or without the 5-HT2C antagonist SB242084. In Experiment 2, we administered mCPP into amygdala subregions and the dorsal hippocampus to investigate site specificity. In Experiment 4 we lesioned the BNST and subsequently infused mCPP systemically, and in Experiment 4 we used RNAscope® to assess BNST 5-HT2C transcripts following wheel running. Results: BNST mCPP infusion increased acoustic startle responding, which was by 5-HT2C antagonism, while neither mCPP infused into the amygdala nor hippocampus was anxiogenic. Lesions of the BNST prevented the anxiogenic effect of systemically administered mCPP. Lastly, exercise reduced 5-HT2C transcripts in the BNST. Discussion: These results suggest that the BNST is a critical site of action for the effects of exercise on mCPP. Together these data suggest that exercise may reduce 5-HT2C receptor function in the BNST, which may, in part, explain some of the anxiolytic effects associated with wheel running.

The impact of introducing nurse-led analgesia and sedation guidelines in ventilated infants following cardiac surgery.

INTRODUCTION: Enhanced clinical outcomes in the Paediatric Intensive Care Unit following standardisation of analgesia and sedation practice are reported. Little is known about the impact of standardisation of analgesia and sedation practice including incorporation of a validated distress assessment instrument on infants post cardiac surgery, a subset of whom have Trisomy 21. This study investigated whether the parallel introduction of nurse-led analgesia and sedation guidelines including regular distress assessment would impact on morphine administered to infants post cardiac surgery, and whether any differences observed would be amplified within the Trisomy 21 population. METHODOLOGY: A retrospective single centre before/after study design was used. Patients aged between 44 weeks postconceptual age and one year old who had open cardiothoracic surgery were included. RESULTS: 61 patients before and 64 patients after the intervention were included. After the intervention, a reduction in the amount of morphine administered was not evident, while greater use of adjuvant sedatives and analgesics was observed. Patients with Trisomy 21 had a shorter duration of mechanical ventilation after the change in practice. CONCLUSION: The findings from this study affirm the importance of the nurses' role in managing prescribed analgesia and sedation supported by best available evidence. A continued education and awareness focus on analgesia and sedation management in the pursuit of best patient care is imperative.

Rapastinel, an NMDAR positive modulator, produces distinct behavioral, sleep, and EEG profiles compared with ketamine.

Rapastinel, a positive NMDAR modulator, produces rapid-acting and long-lasting antidepressant-like effects; however, unlike ketamine, the abuse potential for rapastinel is minimal. Ketamine has also been shown to induce psychotomimetic/dissociative side effects, aberrant gamma oscillations, and effects similar to sleep deprivation, which may potentially limit its clinical use. In this study, we compared the side effect profile and potential sleep-altering properties of rapastinel (3, 10, and 30 mg/kg) to ketamine (30 mg/kg) in rodents. In addition, we investigated corresponding changes in transcriptomics and proteomics. Rapastinel exhibited no effect on locomotor activity and prepulse inhibition in mice, while ketamine induced a significant increase in locomotor activity and a significant decrease in prepulse inhibition, which are indications of a psychosis-like state. The effects of rapastinel on sleep architecture were minimal, and rapastinel did not alter gamma frequency oscillations. In contrast, ketamine administration resulted in a greater latency to slow wave and REM sleep, disrupted duration of sleep, and affected duration of wakefulness during sleep. Further, ketamine increased cortical oscillations in the gamma frequency range, which is a property associated with psychosis. Rapastinel induced similar plasticity-related changes in transcriptomics to ketamine in rats but differed in several gene ontology classes, some of which may be involved in the regulation of sleep. In conclusion, rapastinel demonstrated a lower propensity than ketamine to induce CNS-related adverse side effects and sleep disturbances.

Prefrontal cortex circuits in depression and anxiety: contribution of discrete neuronal populations and target regions.

Our understanding of depression and its treatment has advanced with the advent of ketamine as a rapid-acting antidepressant and the development and refinement of tools capable of selectively altering the activity of populations of neuronal subtypes. This work has resulted in a paradigm shift away from dysregulation of single neurotransmitter systems in depression towards circuit level abnormalities impacting function across multiple brain regions and neurotransmitter systems. Studies on the features of circuit level abnormalities demonstrate structural changes within the prefrontal cortex (PFC) and functional changes in its communication with distal brain structures. Treatments that impact the activity of brain regions, such as transcranial magnetic stimulation or rapid-acting antidepressants like ketamine, appear to reverse depression associated circuit abnormalities though the mechanisms underlying the reversal, as well as development of these abnormalities remains unclear. Recently developed optogenetic and chemogenetic tools that allow high-fidelity control of neuronal activity in preclinical models have begun to elucidate the contributions of the PFC and its circuitry to depression- and anxiety-like behavior. These tools offer unprecedented access to specific circuits and neuronal subpopulations that promise to offer a refined view of the circuit mechanisms surrounding depression and potential mechanistic targets for development and reversal of depression associated circuit abnormalities.

Ketamine increases vmPFC activity: Effects of (R)- and (S)-stereoisomers and (2R,6R)-hydroxynorketamine metabolite.

Ketamine, an NMDA receptor antagonist and fast acting antidepressant, produces a rapid burst of glutamate in the ventral medial prefrontal cortex (mPFC). Preclinical studies have demonstrated that pyramidal cell activity in the vmPFC is necessary for the rapid antidepressant response to ketamine in rodents. We sought to characterize the effects of ketamine and its stereoisomers (R and S), as well as a metabolite, (2R,6R)-hydroxynorketamine (HNK), on vmPFC activity using a genetically encoded calcium indicator (GCaMP6f). Ratiometric fiber photometry was utilized to monitor GCaMP6f fluorescence in pyramidal cells of mouse vmPFC prior to and immediately following administration of compounds. GCaMP6f signal was assessed to determine correspondance of activity between compounds. We observed dose dependent effects with (R,S)-ketamine (3-100 mg/kg), with the greatest effects on GCaMP6f activity at 30 mg/kg and lasting up to 20 min. (S)-ketamine (15 mg/kg), which has high affinity for the NMDA receptor channel produced similar effects to (R,S)-ketamine, but compounds with low NMDA receptor affinity, including (R)-ketamine (15 mg/kg) and (2R,6R)-HNK (30 mg/kg) had little or no effect on GCaMP6f activity. The initial response to administration of (R,S)-ketamine as well as (S)-ketamine is characterized by a brief period of robust GCaMP6f activation, consistent with increased activity of vmPFC pyramidal neurons. Because (2R,6R)-HNK and (R)-ketamine are reported to have antidepressant activity in rodent models the current results indicate that different initiating mechanisms lead to similar brain adaptive consequences that underlie the rapid antidepressant responses.

Ketamine rapidly reverses stress-induced impairments in GABAergic transmission in the prefrontal cortex in male rodents.

Dysfunction of medial prefrontal cortex (mPFC) in association with imbalance of inhibitory and excitatory neurotransmission has been implicated in depression. However, the precise cellular mechanisms underlying this imbalance, particularly for GABAergic transmission in the mPFC, and the link with the rapid acting antidepressant ketamine remains poorly understood. Here we determined the influence of chronic unpredictable stress (CUS), an ethologically validated model of depression, on synaptic markers of GABA neurotransmission, and the influence of a single dose of ketamine on CUS-induced synaptic deficits in mPFC of male rodents. The results demonstrate that CUS decreases GABAergic proteins and the frequency of inhibitory post synaptic currents (IPSCs) of layer V mPFC pyramidal neurons, concomitant with depression-like behaviors. In contrast, a single dose of ketamine can reverse CUS-induced deficits of GABA markers, in conjunction with reversal of CUS-induced depressive-like behaviors. These findings provide further evidence of impairments of GABAergic synapses as key determinants of depressive behavior and highlight ketamine-induced synaptic responses that restore GABA inhibitory, as well as glutamate neurotransmission.

Neurobiology of rapid-acting antidepressants: convergent effects on GluA1-synaptic function.

Efforts to develop efficacious antidepressant agents with novel mechanisms have been largely unsuccessful since the 1950's until the discovery of ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist that produces rapid and sustained antidepressant actions even in treatment-resistant patients. This finding has ushered in a new era for the development of novel rapid-acting antidepressants that act at the NMDA receptor complex, but without dissociative and psychotomimetic side effects of ketamine. Here, we review the current state of rapid-acting antidepressant drug development, including NMDA channel blockers, glycine site agents, and allosteric modulators, as well as ketamine stereoisomers and metabolites. In addition, we focus on the neurobiological mechanisms underlying the actions of these diverse agents and discuss evidence of convergent mechanisms including increased brain-derived neurotrophic factor signaling, increased synthesis of synaptic proteins, and most notably increased GluR1 and synaptic connectivity in the medial prefrontal cortex. These convergent mechanisms provide insight for potential additional novel targets for drug development (e.g., agents that increase synaptic protein synthesis and plasticity). Importantly, the convergent effects on synapse formation and plasticity also reverse the well-documented neuronal and synaptic deficits associated with stress and depression, and thereby target the underlying pathophysiology of major depressive disorder.

Optogenetic stimulation of medial prefrontal cortex Drd1 neurons produces rapid and long-lasting antidepressant effects.

Impaired function in the medial prefrontal cortex (mPFC) contributes to depression, and the therapeutic response produced by novel rapid-acting antidepressants such as ketamine are mediated by mPFC activity. The mPFC contains multiple types of pyramidal cells, but it is unclear whether a particular subtype mediates the rapid antidepressant actions of ketamine. Here we tested two major subtypes, Drd1 and Drd2 dopamine receptor expressing pyramidal neurons and found that activating Drd1 expressing pyramidal cells in the mPFC produces rapid and long-lasting antidepressant and anxiolytic responses. In contrast, photostimulation of Drd2 expressing pyramidal cells was ineffective across anxiety-like and depression-like measures. Disruption of Drd1 activity also blocked the rapid antidepressant effects of ketamine. Finally, we demonstrate that stimulation of mPFC Drd1 terminals in the BLA recapitulates the antidepressant effects of somatic stimulation. These findings aid in understanding the cellular target neurons in the mPFC and the downstream circuitry involved in rapid antidepressant responses.

Two Weeks of Variable Stress Increases Gamma-H2AX Levels in the Mouse Bed Nucleus of the Stria Terminalis.

Recent reports demonstrate that DNA damage is induced, and rapidly repaired, in circuits activated by experience. Moreover, stress hormones are known to slow DNA repair, suggesting that prolonged stress may result in persistent DNA damage. Prolonged stress is known to negatively impact physical and mental health; however, DNA damage as a factor in stress pathology has only begun to be explored. Histone H2A-X phosphorylated at serine 139 (γH2AX) is a marker of DNA double-strand breaks (DSB), a type of damage that may lead to cell death if unrepaired. We hypothesized that a 14-day period of variable stress exposure sufficient to alter anxiety-like behavior in male C57BL/6J mice would produce an increase in γH2AX levels in the bed nucleus of the stria terminalis (BNST), a region implicated in anxiety and stress regulation. We observed that 14 days of variable stress, but not a single stress exposure, was associated with increased levels of γH2AX 24 h after termination of the stress paradigm. Further investigation found that phosphorylation levels of a pair of kinases associated with the DNA damage response, glycogen synthase kinase 3 ß (GSK3ß) and p38 mitogen-activated protein kinase (MAPK) were also elevated following variable stress. Our results suggest that unrepaired DNA DSBs and/or repetitive attempted repair may represent an important component of the allostatic load that stress places on the brain.

Persistent Increase in Microglial RAGE Contributes to Chronic Stress-Induced Priming of Depressive-like Behavior.

BACKGROUND: Chronic stress-induced inflammatory responses occur in part via danger-associated molecular pattern (DAMP) molecules, such as high mobility group box 1 protein (HMGB1), but the receptor(s) underlying DAMP signaling have not been identified. METHODS: Microglia morphology and DAMP signaling in enriched rat hippocampal microglia were examined during the development and expression of chronic unpredictable stress (CUS)-induced behavioral deficits, including long-term, persistent changes after CUS. RESULTS: The results show that CUS promotes significant morphological changes and causes robust upregulation of HMGB1 messenger RNA in enriched hippocampal microglia, an effect that persists for up to 6 weeks after CUS exposure. This coincides with robust and persistent upregulation of receptor for advanced glycation end products (RAGE) messenger RNA, but not toll-like receptor 4 in hippocampal microglia. CUS also increased surface expression of RAGE protein on hippocampal microglia as determined by flow cytometry and returned to basal levels 5 weeks after CUS. Importantly, exposure to short-term stress was sufficient to increase RAGE surface expression as well as anhedonic behavior, reflecting a primed state that results from a persistent increase in RAGE messenger RNA expression. Further evidence for DAMP signaling in behavioral responses is provided by evidence that HMGB1 infusion into the hippocampus was sufficient to cause anhedonic behavior and by evidence that RAGE knockout mice were resilient to stress-induced anhedonia. CONCLUSIONS: Together, the results provide evidence of persistent microglial HMGB1-RAGE expression that increases vulnerability to depressive-like behaviors long after chronic stress exposure.

Activity-Dependent Brain-Derived Neurotrophic Factor Release Is Required for the Rapid Antidepressant Actions of Scopolamine.

BACKGROUND: Brain-derived neurotrophic factor (BDNF) plays a key role in the pathophysiology and treatment of depression. Recent clinical studies demonstrate that scopolamine, a nonselective muscarinic acetylcholine receptor antagonist, produces rapid antidepressant effects in patients with depression. Rodent studies demonstrate that scopolamine increases glutamate transmission and synaptogenesis in the medial prefrontal cortex (mPFC). Here we tested the hypothesis that activity-dependent BDNF release within the mPFC is necessary for the antidepressant actions of scopolamine. METHODS: Behavioral effects of scopolamine were assessed in BDNF Val/Met knock-in mice, in which BDNF processing and release are impaired. In addition, intra-mPFC infusion of a BDNF-neutralizing antibody was performed to test the necessity of BDNF release in driving scopolamine-induced behavioral responses. Further in vivo and in vitro experiments were performed to delineate BDNF-dependent mechanisms underlying the effects of scopolamine. RESULTS: We found that BDNF Met/Met mice have attenuated responses to scopolamine and that anti-BDNF antibody infusions into the mPFC prevented the antidepressant-like behavioral effects of scopolamine. In vitro experiments show that scopolamine rapidly stimulates BDNF release and tropomyosin receptor kinase B-extracellular signal-regulated kinase signaling. Moreover, these effects require alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor activation and are blocked by neuronal silencing. Importantly, pretreatment with verapamil prevented scopolamine-induced behavioral responses and BDNF-tropomyosin receptor kinase B signaling, suggesting that these effects are dependent on activation of voltage-dependent calcium channels. CONCLUSIONS: The results identify an essential role for activity-dependent BDNF release in the rapid antidepressant effects of scopolamine. Attenuation of responses in BDNF Met mice indicates that patients with the Met allele may be less responsive to scopolamine.

Failure to Inactivate Nuclear GSK3ß by Ser389-Phosphorylation Leads to Focal Neuronal Death and Prolonged Fear Response.

GSK3ß plays an essential role in promoting cell death and is emerging as a potential target for neurological diseases. Understanding the mechanisms that control neuronal GSK3ß is critical. A ubiquitous mechanism to repress GSK3ß involves Akt-mediated phosphorylation of Ser9. Here we show that phosphorylation of GSK3ß on Ser389 mediated by p38 MAPK specifically inactivates nuclear GSK3ß in the cortex and hippocampus. Using GSK3ß Ser389 to Ala mutant mice, we show that failure to inactivate nuclear GSK3ß by Ser389 phosphorylation causes neuronal cell death in subregions of the hippocampus and cortex. Although this focal neuronal death does not impact anxiety/depression-like behavior or hippocampal-dependent spatial learning, it leads to an amplified and prolonged fear response. This phenotype is consistent with some aspects of post-traumatic stress disorder (PTSD). Our studies indicate that inactivation of nuclear GSK3ß by Ser389 phosphorylation plays a key role in fear response, revealing new potential therapeutic approaches to target PTSD.

Suitability of the forearm for non-invasive blood pressure measurement in children.

BACKGROUND: Measurement of forearm blood pressure (BP) in pediatric patients during general anesthesia is periodically employed despite a lack of evidence for this practice. Upper arm BP measurement may be impossible to perform for either patient or surgical reasons, and the forearm has theoretical benefits over the lower leg when an alternate site is required. We hypothesize that forearm BP measurement provides an accurate and reliable alternative to the upper arm. Published adult data do not support this hypothesis, and the little pediatric data published contain methodological shortcomings. METHODS: A dedicated, externally calibrated noninvasive oscillometer was used to compare BP measurements in the upper arm and ipsilateral forearm of pediatric patients undergoing general anesthesia prior to application of a surgical stimulus. Both upper arm BP and ipsilateral forearm BP were sequentially measured 20 seconds apart on 3 separate occasions with an appropriately sized cuff. The systolic, diastolic, and mean blood pressures were recorded under steady-state conditions. RESULTS: Thirty-five elective surgical patients aged 1 to 10 years were studied. The bias (±limits of agreement) for forearm minus upper arm blood pressures were as follows: mean BP -1.3 mm Hg (±7.2), diastolic BP -3.3 (±5.3), and systolic BP +3.2 mm Hg (±8.3). Differences greater than ±5 mm Hg occurred in 59% (systolic BP), 42% (diastolic BP), and 46% (mean BP) of all observations and greater than ±10 mm Hg in 17% (systolic BP), 8.6% (diastolic BP), and 15% (mean BP). CONCLUSION: The differences within mean ±1.96 standard deviations reside considerably outside the clinically accepted tolerance of ±5 mm Hg. Thus, the forearm may not be used interchangeably with upper limb BP readings in anesthetized healthy children. Future use of the forearm for BP measurement requires a validated anthropomorphically appropriate forearm cuff.

Molecular and Cellular Effects of Traumatic Stress: Implications for PTSD.

PURPOSE OF REVIEW: Posttraumatic stress disorder (PTSD) is characterized by hyperarousal and recurrent stressful memories after an emotionally traumatic event. Extensive research has been conducted to identify the neurobiological determinants that underlie the pathophysiology of PTSD. In this review, we examine evidence regarding the molecular and cellular pathophysiology of PTSD focusing on two primary brain regions: the vmPFC and the amygdala. RECENT FINDINGS: This discussion includes a review of the molecular alterations related to PTSD, focusing mainly on changes to glucocorticoid receptor signaling. We also examine postmortem gene expression studies that have been conducted to date and the molecular changes that have been observed in peripheral blood studies of PTSD patients. Causal, mechanistic evidence is difficult to obtain in human studies, so we also review preclinical models of PTSD. Integration of peripheral blood and postmortem studies with preclinical models of PTSD has begun to reveal the molecular changes occurring in patients with PTSD. These findings indicate that the pathophysiology of PTSD includes disruption of glucocorticoid signaling and inflammatory systems and occurs at the level of altered gene expression. We will assess the impact of these findings on the future of PTSD molecular research.

Rapid Acting Antidepressants in Chronic Stress Models: Molecular and Cellular Mechanisms.

Stress-associated disorders, including depression and anxiety, impact nearly 20% of individuals in the United States. The social, health, and economic burden imposed by stress-associated disorders requires in depth research efforts to identify suitable treatment strategies. Traditional medications (e.g., selective serotonin reuptake inhibitors, monoamine oxidase inhibitors) have significant limitations, notably a time lag for therapeutic response that is compounded by low rates of efficacy. Excitement over ketamine, a rapid acting antidepressant effective in treatment resistant patients, is tempered by transient dissociative and psychotomimetic effects, as well as abuse potential. Rodent stress models are commonly used to produce behavioral abnormalities that resemble those observed in stress-associated disorders. Stress models also produce molecular and cellular morphological changes in stress sensitive brain regions, including the prefrontal cortex and hippocampus that resemble alterations observed in depression. Rapid acting antidepressants such as ketamine can rescue stress-associated morphological and behavioral changes in rodent models. Here, we review the literature supporting a role for rapid acting antidepressants in opposing the effects of stress, and summarize research efforts seeking to elucidate the molecular, cellular, and circuit level targets of these agents.

GLYX-13 Produces Rapid Antidepressant Responses with Key Synaptic and Behavioral Effects Distinct from Ketamine.

GLYX-13 is a putative NMDA receptor modulator with glycine-site partial agonist properties that produces rapid antidepressant effects, but without the psychotomimetic side effects of ketamine. Studies were conducted to examine the molecular, cellular, and behavioral actions of GLYX-13 to further characterize the mechanisms underlying the antidepressant actions of this agent. The results demonstrate that a single dose of GLYX-13 rapidly activates the mTORC1 pathway in the prefrontal cortex (PFC), and that infusion of the selective mTORC1 inhibitor rapamycin into the medial PFC (mPFC) blocks the antidepressant behavioral actions of GLYX-13, indicating a requirement for mTORC1 similar to ketamine. The results also demonstrate that GLYX-13 rapidly increases the number and function of spine synapses in the apical dendritic tuft of layer V pyramidal neurons in the mPFC. Notably, GLYX-13 significantly increased the synaptic responses to hypocretin, a measure of thalamocortical synapses, compared with its effects on 5-HT responses, a measure of cortical-cortical responses mediated by the 5-HT2A receptor. Behavioral studies further demonstrate that GLYX-13 does not influence 5-HT2 receptor induced head twitch response or impulsivity in a serial reaction time task (SRTT), whereas ketamine increased responses in both tests. In contrast, both GLYX-13 and ketamine increased attention in the SRTT task, which is linked to hypocretin-thalamocortical responses. The differences in the 5-HT2 receptor synaptic and behavioral responses may be related to the lack of psychotomimetic side effects of GLYX-13 compared with ketamine, whereas regulation of the hypocretin responses may contribute to the therapeutic benefits of both rapid acting antidepressants.