Ketamine ameliorates post-traumatic social avoidance by erasing the traumatic memory encoded in VTA-innervated BLA engram cells

Windows of change: Revisiting temporal and molecular dynamics of memory reconsolidation and persistence

Retrieval can bring memories to a labile state, creating a window to modify its content during reconsolidation. Numerous studies have investigated this period to elucidate reconsolidation mechanisms, understand long-term memory persistence, and develop therapeutic strategies for memory-related psychiatric disorders. However, the temporal dynamics of post-retrieval memory processes have been largely overlooked, leading to mixed findings and hindering the development of targeted interventions. This review discusses retrieval-related cellular and molecular events and how they develop in series and parallel across time. Emerging evidence suggests that some mechanisms triggered after fear memory retrieval can influence either reconsolidation or persistence in different time windows. The temporal boundaries of these post-retrieval processes are still unclear. Further research integrating behavioral and molecular approaches to a deeper understanding of reconsolidation and persistence temporal dynamics is essential to address current debates, including which system/pathway offers the most effective therapeutic window of opportunity.

Molecular pathways of ketamine: A systematic review of immediate and sustained effects on PTSD

RATIONALE

Existing studies predominantly focus on the molecular and neurobiological mechanisms underlying Ketamine's acute treatment effects on post-traumatic stress disorder (PTSD). This emphasis has largely overlooked its sustained therapeutic effects, which hold significant potential for the development of targeted interventions.

OBJECTIVES

This systematic review examines the pharmacokinetic and pharmacodynamic effects of ketamine on PTSD, differentiating between immediate and sustained molecular effects.

METHOD

A comprehensive search across databases (Web of Science, Scopus, Global Health, PubMed) and grey literature yielded 317 articles, where 29 studies met the inclusion criteria. These studies included preclinical models and clinical trials, through neurotransmitter regulation, gene expression, synaptic plasticity, and neural pathways (PROSPERO ID: CRD42024582874).

RESULTS

We found accumulating evidence that the immediate effects of ketamine, which involve changes in GABA, glutamate, and glutamine levels, trigger the re-regulation of BDNF, enhancing synaptic plasticity via pathways such as TrkB and PSD-95. Other molecular influences also include c-Fos, GSK-3, HDAC, HCN1, and the modulation of hormones like CHR and ACTH, alongside immune responses (IL-6, IL-1β, TNF-α). Sustained effects arise from neurotransmitter remodulations and involve prolonged changes in gene expression. These include mTOR-mediated BDNF expression, alterations in GSK-3β, FkBP5, GFAP, ERK phosphorylation, and epigenetic modifications (DNMT3, MeCP2, H3K27me3, mir-132, mir-206, HDAC).

CONCLUSION

These molecular changes promote long-term synaptic stability and re-regulation in key brain regions, contributing to prolonged therapeutic benefits. Understanding the sustained molecular and epigenetic mechanisms behind ketamine's effects is critical for developing safe and effective personalised treatments, potentially leading to more effective recovery.

Effects of ketamine on fear memory extinction: a review of preclinical literature

Introduction

Ketamine, a multimodal dissociative anesthetic, is widely used as a trauma analgesic in emergency situations. Ketamine is also used to treat psychiatric disorders due to its broad application potential, including treatment-resistant major depression. However, its impacts on the development of post-traumatic stress disorder (PTSD) and its potential as a treatment for PTSD are controversial. PTSD is marked by persistent and intrusive memories of traumatic event(s) and re-experiencing of the traumatic memories when exposed to trauma-related stimuli. Individuals with PTSD are often treated with prolonged exposure therapy (PE), in which they are gradually exposed to stimuli that remind them of the previous traumatic memory. If successful, they may learn that the previously traumatic stimuli are no longer threatening, a process known as fear extinction. Although fear extinction can be studied in laboratory animals, previous preclinical literature on the effects of ketamine on fear extinction has been inconsistent.

Methods

Thus, we summarized the existing preclinical literature examining effects of ketamine on fear extinction and its potential molecular mechanisms.

Results

Studies found that ketamine may enhance, impair, have no effect, or have mixed effects on fear extinction. These discrepancies may be attributed to differences in dosage, route, and timing of ketamine administration.

Discussion

We conclude the review with recommendations for future research on ketamine and PTSD such as the inclusion of more female subjects, clinically relevant doses and routes of ketamine administration, and more comprehensive behavioral assays that are relevant to PTSD in humans to enhance translation between preclinical and clinical research.

Brain circuits that regulate social behavior

Social interactions are essential for the survival of individuals and the reproduction of populations. Social stressors, such as social defeat and isolation, can lead to emotional disorders and cognitive impairments. Furthermore, dysfunctional social behaviors are hallmark symptoms of various neuropsychiatric disorders, including autism spectrum disorder (ASD) and post-traumatic stress disorder (PTSD). Consequently, understanding the neural circuit mechanisms underlying social behaviors has become a major focus in neuroscience. Social behaviors, which encompass a wide range of expressions and phases, are regulated by complex neural networks. In this review, we summarize recent progress in identifying the circuits involved in different types of social behaviors, including general social investigation, social preference, mating, aggression, parenting, prosocial behaviors, and dominance behaviors. We also outline the circuit mechanisms associated with social deficits in neuropsychiatric disorders, such as ASD, schizophrenia, and PTSD. Given the pivotal role of rodents in social behavior research, our review primarily focuses on neural circuits in these animals. Finally, we propose future research directions, including the development of specific behavioral paradigms, the identification of circuits involved in motor output, the integration of activity, transcriptome, and connectome data, the multifunctional roles of neurons with multiple targets, and the interactions among multiple brain regions.

Mesoscale brain-wide fluctuation analysis: revealing ketamine's rapid antidepressant across multiple brain regions

Depression has been linked to cortico-limbic brain regions, and ketamine is known for its rapid antidepressant effects. However, how these brain regions encode depression collaboratively and how ketamine regulates these regions to exert its prompt antidepressant effects through mesoscale brain-wide fluctuations remain elusive. In this study, we used a multidisciplinary approach, including multi-region in vivo recordings in mice, chronic social defeat stress (CSDS), and machine learning, to construct a Mesoscale Brain-Wide Fluctuation Analysis platform (MBFA-platform). This platform analyzes the mesoscale brain-wide fluctuations of multiple brain regions from the perspective of local field potential oscillations and network dynamics. The decoder results demonstrate that our MBFA platform can accurately classify the Control/CSDS and ketamine/saline-treated groups based on neural oscillation and network activities among the eight brain regions. We found that multiple-region LFPs patterns are disrupted in CSDS-induced social avoidance, with the basolateral amygdala playing a key role. Ketamine primarily exerts the compensatory effects through network dynamics, contributing to its rapid antidepressant effect. These findings highlight the MBFA platform as an interdisciplinary tool for revealing mesoscale brain-wide fluctuations underlying complex emotional pathologies, providing insights into the etiology of psychiatry. Furthermore, the platform's evaluation capabilities present a novel approach for psychiatric therapeutic interventions.

Ketamine Reduces Avoidance Responses During Re-Exposition to Aversive Stimulus: Comparison Between (S)-Isomer and Racemic Mixture

BACKGROUND/OBJECTIVES

Recent studies have investigated the effects of ketamine on fear memory in animals. However, it is unclear if ketamine might affect avoidance memory and emotional behaviors concomitantly. In this study, we compared the effects of (R,S)- and (S)-ketamine in modulating avoidance responses, depression- and anxiety-related behaviors in stressed mice.

METHODS

Mice were previously exposed to inescapable footshock stress, and 24 h later, they were trained in the active avoidance task. (R,S)-ketamine or (S)-isomer was administered 1 h prior to re-exposition to the active avoidance task. Three hours after drug administration, mice were tested in the tail suspension, followed by the open field test.

RESULTS

Neither form of ketamine affected avoidance memory retrieval, while (S)-ketamine, and tangentially, (R,S) reduced avoidance responses during re-exposition to aversive stimulus. In the tail suspension test, (R,S)- and (S)-ketamine equally evoked antidepressant effects. In the open field test, the racemic mixture, but not (S)-ketamine, induced anxiolytic actions.

CONCLUSIONS

These findings reinforce the therapeutic potential of ketamine for the treatment of stress-related disorders, with (R,S)-ketamine being more effective in simultaneously inducing antidepressant and anxiolytic responses and reducing avoidance responses in stressed mice.

A small population of stress-responsive neurons in the hypothalamus-habenula circuit mediates development of depression-like behavior in mice

Accumulating evidence has shown that various brain functions are associated with experience-activated neuronal ensembles. However, whether such neuronal ensembles are engaged in the pathogenesis of stress-induced depression remains elusive. Utilizing activity-dependent viral strategies in mice, we identified a small population of stress-responsive neurons, primarily located in the middle part of the lateral hypothalamus (mLH) and the medial part of the lateral habenula (LHbM). These neurons serve as "starter cells" to transmit stress-related information and mediate the development of depression-like behaviors during chronic stress. Starter cells in the mLH and LHbM form dominant connections, which are selectively potentiated by chronic stress. Silencing these connections during chronic stress prevents the development of depression-like behaviors, whereas activating these connections directly elicits depression-like behaviors without stress experience. Collectively, our findings dissect a core functional unit within the LH-LHb circuit that mediates the development of depression-like behaviors in mice.