Ketamine increases activity of a fronto-striatal projection that regulates compulsive behavior in SAPAP3 knockout mice

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

Erasing traumatic memory during memory reconsolidation is a promising retrieval-extinction strategy for post-traumatic stress disorder (PTSD). Here, we developed an acute social defeat stress (SDS) mouse model with short-term and re-exposure-evoked long-term social avoidance. SDS-associated traumatic memories were identified to be stored in basolateral amygdala (BLA) engram cells. A single intraperitoneal administration of subanesthetic-dose ketamine within, but not beyond, the re-exposure time window significantly alleviates SDS-induced social avoidance, which reduces the activity and quantity of reactivated BLA engram cells. Furthermore, activation or inhibition of dopaminergic projections from the ventral tegmental area to the BLA effectively mimics or blocks the therapeutic effect of re-exposure with ketamine and is dopamine D2 receptor dependent. Single-cell RNA sequencing reveals that re-exposure with ketamine triggered significant changes in memory-related pathways in the BLA. Together, our research advances the understanding of how ketamine mitigates PTSD symptoms and offers promising avenues for developing more effective treatments for trauma-related disorders.

New horizons for obsessive-compulsive disorder drug discovery: is targeting glutamate receptors the answer?

INTRODUCTION

Over the past decade, glutamate has emerged as a prominent focus in the field of obsessive-compulsive disorder (OCD) pathophysiology. A convergence of evidence from genetic, preclinical, and clinical studies points to glutamatergic dysfunction as a key feature of this condition. In light of these findings, there has been a growing interest in exploring the potential of glutamatergic agents in the treatment of OCD.

AREAS COVERED

This paper reviews the literature on glutamate transmission in OCD. In addition, the authors examine the results of clinical trials investigating the efficacy of glutamatergic agents in the treatment of OCD patients.

EXPERT OPINION

Along with the recognition of neuroinflammation in the brain in OCD, the evidence of glutamate dysfunction represents one of the most promising recent discoveries for understanding the mechanisms involved in OCD. The importance of this discovery lies primarily in its pharmacological implications and has led to intense research activity in the field of glutamatergic agents. While this research has not yet had a substantial clinical impact, targeting glutamate receptors remains a promising horizon for the successful treatment of OCD patients.

The genetics of trichotillomania and excoriation disorder: A systematic review

BACKGROUND

Trichotillomania (TTM) and excoriation disorder (ED) are impairing obsessive-compulsive related disorders that are common in the general population and for which there are no clear first-line medications, highlighting the need to better understand the underlying biology of these disorders to inform treatments. Given the importance of genetics in obsessive-compulsive disorder (OCD), evaluating genetic factors underlying TTM and ED may advance knowledge about the pathophysiology of these body-focused repetitive behaviors.

AIM

In this systematic review, we summarize the available evidence on the genetics of TTM and ED and highlight gaps in the field warranting further research.

METHOD

We systematically searched Embase, PsycInfo, PubMed, Medline, Scopus, and Web of Science for original studies in genetic epidemiology (family or twin studies) and molecular genetics (candidate gene and genome-wide) published up to June 2023.

RESULTS

Of the 3536 records identified, 109 studies were included in this review. These studies indicated that genetic factors play an important role in the development of TTM and ED, some of which may be shared across the OCD spectrum, but there are no known high-confidence specific genetic risk factors for either TTM or ED.

CONCLUSIONS

Our review underscores the need for additional genome-wide research conducted on the genetics of TTM and ED, for instance, genome-wide association and whole-genome/whole-exome DNA sequencing studies. Recent advances in genomics have led to the discovery of risk genes in several psychiatric disorders, including related conditions such as OCD, but to date, TTM and ED have remained understudied.

Striking Long Term Beneficial Effects of Single Dose Psilocybin and Psychedelic Mushroom Extract in the SAPAP3 Rodent Model of OCD-Like Excessive Self-Grooming

Obsessive compulsive disorder (OCD) is a highly prevalent disorder that causes serious disability. Available treatments leave 40% or more of people with OCD significantly symptomatic. There is an urgent need for novel therapeutic approaches. Mice that carry a homozygous deletion of the SAPAP3 gene (SAPAP3 KO) manifest a phenotype of excessive self-grooming, tic-like head-body twitches and anxiety. These behaviors closely resemble pathological self-grooming behaviors observed in humans in conditions that overlap with OCD. Following a preliminary report that the tryptaminergic psychedelic, psilocybin, may reduce symptoms in patients with OCD, we undertook a randomized controlled trial of psilocybin in 50 SAPAP3 KO mice (28 male, 22 female). Mice that fulfilled inclusion criteria were randomly assigned to a single intraperitoneal injection of psilocybin (4.4 mg/kg), psychedelic mushroom extract (encompassing the same psilocybin dose) or vehicle control and were evaluated after 2, 4 and 21 days by a rater blind to treatment allocation for grooming characteristics, head-body twitches, anxiety and other behavioral features. Mice treated with vehicle (n=18) manifested a 118.71±95.96 % increase in total self-grooming (the primary outcome measure) over the 21-day observation period. In contrast, total self-grooming decreased by 14.60%±17.90% in mice treated with psilocybin (n=16) and by 19.20±20.05% in mice treated with psychedelic mushroom extract (n=16) (p=.001 for effect of time; p=.0001 for time × treatment interaction). 5 mice were dropped from the vehicle group because they developed skin lesions; 4 from the psilocybin group and none from the psychedelic mushroom extract group. Secondary outcome measures such as head-body twitches and anxiety all showed a significant improvement over 21 days. Notably, in mice that responded to psilocybin (n=12) and psychedelic mushroom extract (n=13), the beneficial effect of a single treatment persisted up to 7 weeks. Mice initially treated with vehicle and non-responsive, showed a clear and lasting therapeutic response when treated with a single dose of psilocybin or psychedelic mushroom extract and followed for a further 3 weeks. While equivalent to psilocybin in overall effect on self-grooming, psychedelic mushroom extract showed superior effects in alleviating head-body twitches and anxiety. These findings strongly justify clinical trials of psilocybin in the treatment of OCD and further studies aimed at elucidating mechanisms that underlie the long-term effects to alleviate excessive self-grooming observed in this study.

Closed-loop recruitment of striatal interneurons prevents compulsive-like grooming behaviors

Compulsive behaviors have been associated with striatal hyperactivity. Parvalbumin-positive striatal interneurons (PVIs) in the striatum play a crucial role in regulating striatal activity and suppressing prepotent inappropriate actions. To investigate the potential role of striatal PVIs in regulating compulsive behaviors, we assessed excessive self-grooming-a behavioral metric of compulsive-like behavior-in male Sapap3 knockout mice (Sapap3-KO). Continuous optogenetic activation of PVIs in striatal areas receiving input from the lateral orbitofrontal cortex reduced self-grooming events in Sapap3-KO mice to wild-type levels. Aiming to shorten the critical time window for PVI recruitment, we then provided real-time closed-loop optogenetic stimulation of striatal PVIs, using a transient power increase in the 1-4 Hz frequency band in the orbitofrontal cortex as a predictive biomarker of grooming onsets. Targeted closed-loop stimulation at grooming onsets was as effective as continuous stimulation in reducing grooming events but required 87% less stimulation time, paving the way for adaptive stimulation therapeutic protocols.

Hyperactivity of indirect pathway-projecting spiny projection neurons promotes compulsive behavior

Compulsive behaviors are a hallmark symptom of obsessive compulsive disorder (OCD). Striatal hyperactivity has been linked to compulsive behavior generation in correlative studies in humans and causal studies in rodents. However, the contribution of the two distinct striatal output populations to the generation and treatment of compulsive behavior is unknown. These populations of direct and indirect pathway-projecting spiny projection neurons (SPNs) have classically been thought to promote or suppress actions, respectively, leading to a long-held hypothesis that increased output of direct relative to indirect pathway promotes compulsive behavior. Contrary to this hypothesis, here we find that indirect pathway hyperactivity is associated with compulsive grooming in the Sapap3-knockout mouse model of OCD-relevant behavior. Furthermore, we show that suppression of indirect pathway activity using optogenetics or treatment with the first-line OCD pharmacotherapy fluoxetine is associated with reduced grooming in Sapap3-knockouts. Together, these findings highlight the striatal indirect pathway as a potential treatment target for compulsive behavior.

Informational Analysis and Prediction of Obsessive-Compulsive Disorder Pathogenesis

OBJECTIVE

We aimed to predict the possible mechanism of obsessive-compulsive disorder (OCD) by integrating and analyzing mRNA sequencing results from two datasets and to provide direction for future studies into the pathogenesis of OCD.

METHODS

Two OCD datasets, GSE78104 and GSE60190, were obtained, and the intersection of the two gene sets with differential expression in OCD samples was selected. Kyoto Encyclopedia of Genes and Genomes (KEGG) signal pathway enrichment and Gene Ontology (GO) analyses were performed using the Database for Annotation, Visualization, and Integrated Discovery (DAVID) online analysis website for the genes at the intersection, and the data were mapped using http://www.bioinformatics.com.cn. After genes with p≤0.05 had been screened out, protein-protein interaction (PPI) interaction analysis was conducted using Metascape to screen the key Molecular Complex Detection (MCODE) genes. MCODE genes were then enriched using the KEGG signaling pathway and GO classification.

RESULTS

A total of 3,449 differentially expressed genes (DEGs) were obtained from the GSE78104 and GSE60190 datasets. KEGG, GO, and Gene Set Enrichment Analysis analyses of DEGs showed that the onset of OCD was related to oxidative phosphorylation and other metabolic processes, which may have a similar pathogenesis to other neurodegenerative diseases. Single-gene PPI analysis of SAPAP3 revealed that the mechanism by which SAPAP3 knockout induces OCD may also be caused by affecting oxidative phosphorylation.

CONCLUSION

The mechanism of SAPAP3 knockout-induced OCD in mice may be due to the oxidative phosphorylation process in the body. Future studies on the neural circuit mechanism of OCD should be conducted.

Acute administration of the NMDA receptor antagonists ketamine and MK-801 reveals dysregulation of glutamatergic signalling and sensorimotor gating in the Sapap3 knockout mouse model of compulsive-like behaviour

Obsessive-compulsive disorder (OCD) is characterised by excessive intrusive thoughts that may cause an individual to engage in compulsive behaviours. Frontline pharmacological treatments (i.e., selective serotonin reuptake inhibitors (SSRIs)) leave approximately 40% of patients refractory to treatment. To investigate the possibility of novel pharmacological therapies for OCD, as well as the potential mechanisms underlying its pathology, we used the Sapap3 knockout (KO) mouse model of OCD, which exhibits increased anxiety and compulsive grooming behaviours. Firstly, we investigated whether administration of the NMDA receptor (NMDAR) antagonist ketamine (30 mg/kg), would reduce anxiety and grooming behaviour in Sapap3 KO mice. Anxiety-like behaviour was measured via time spent in the light component of the light-dark box test. Grooming behaviour was recorded and scored in freely moving mice. In line with previous works conducted in older animals (i.e. typically between 6 and 9 months of age), we confirmed here that Sapap3 KO mice exhibit an anxious, compulsive grooming, hypolocomotive and reduced body weight phenotype even at a younger age (i.e., 2-3 months of age). However, we found that acute administration of ketamine did not cause a reduction in anxiety or grooming behaviour. We then investigated in vivo glutamatergic function via the administration of a different NMDAR antagonist, MK-801 (0.25 mg/kg), prior to locomotion and prepulse inhibition assays. We found evidence of altered functional NMDAR activity, as well as sexually dimorphic prepulse inhibition, a measure of sensorimotor gating, in Sapap3 KO mice. These results are suggestive of in vivo glutamatergic dysfunction and their functional consequences, enabling future research to further investigate novel treatments for OCD.

Unraveling the mechanisms of deep-brain stimulation of the internal capsule in a mouse model

Deep-brain stimulation (DBS) is an effective treatment for patients suffering from otherwise therapy-resistant psychiatric disorders, including obsessive-compulsive disorder. Modulation of cortico-striatal circuits has been suggested as a mechanism of action. To gain mechanistic insight, we monitored neuronal activity in cortico-striatal regions in a mouse model for compulsive behavior, while systematically varying clinically-relevant parameters of internal-capsule DBS. DBS showed dose-dependent effects on both brain and behavior: An increasing, yet balanced, number of excited and inhibited neurons was recruited, scattered throughout cortico-striatal regions, while excessive grooming decreased. Such neuronal recruitment did not alter basic brain function such as resting-state activity, and only occurred in awake animals, indicating a dependency on network activity. In addition to these widespread effects, we observed specific involvement of the medial orbitofrontal cortex in therapeutic outcomes, which was corroborated by optogenetic stimulation. Together, our findings provide mechanistic insight into how DBS exerts its therapeutic effects on compulsive behaviors.

Mechanisms of pathogenesis and environmental moderators in preclinical models of compulsive-like behaviours

Obsessive-compulsive and related disorders (OCRD) is an emergent class of psychiatric illnesses that contributes substantially to the global mental health disease burden. In particular, the prototypical illness, obsessive-compulsive disorder (OCD), has a profoundly deleterious effect on the quality of life of those with lived experience. Both clinical and preclinical studies have investigated the genetic and environmental influences contributing to the pathogenesis of obsessive-compulsive and related disorders. Significant progress has been made in recent years in our understanding of the genetics of OCD, along with the critical role of common environmental triggers (e.g., stress). Some of this progress can be attributed to the sophistication of rodent models used in the field, particularly genetic mutant models, which demonstrate promising construct, face, and predictive validity. However, there is a paucity of studies investigating how these genetic and environmental influences interact to precipitate the behavioural, cellular, and molecular changes that occur in OCD. In this review, we assert that preclinical studies offer a unique opportunity to carefully manipulate environmental and genetic factors, and in turn to interrogate gene-environment interactions and relevant downstream sequelae. Such studies may serve to provide a mechanistic framework to build our understanding of the pathogenesis of complex neuropsychiatric disorders such as OCD. Furthermore, understanding gene-environment interactions and pathogenic mechanisms will facilitate precision medicine and other future approaches to enhance treatment, reduce side-effects of therapeutic interventions, and improve the lives of those suffering from these devastating disorders.

Treatment-resistant OCD: Pharmacotherapies in adults

Serotonin reuptake inhibitor (SRI) medications are well established as first-line pharmacotherapeutic treatment for Obsessive-Compulsive Disorder (OCD). However, despite the excellent safety profile and demonstrated efficacy of these medications, a substantial proportion of individuals with OCD fail to attain sufficient benefit from SRIs. In this narrative review, we discuss clinical features of OCD that have been associated with poorer response to SRIs, and we present pharmacotherapeutic interventions that have been explored as augmenting or alternative treatments for treatment-resistant OCD. We additionally highlight non-SRI interventions for OCD that are currently under investigation. Pharmacotherapeutic interventions were identified via expert consensus. To assess the evidence base for individual pharmacotherapies, targeted searches for relevant English-language publications were performed on standard biomedical research databases, including MEDLINE. Information relevant to ongoing registered clinical trials in OCD was obtained by search of ClinicalTrials.gov. Pharmacotherapies are grouped for review in accordance with the general principles of Neuroscience-based Nomenclature (NbN). Clinical features of OCD that may suggest poorer response to SRI treatment include early age of onset, severity of illness, duration of untreated illness, and the presence of symmetry/ordering or hoarding-related symptoms. Based on evolving pathophysiologic models of OCD, diverse agents engaging serotonin, dopamine, norepinephrine, glutamate, and anti-inflammatory pathways have been explored as alternative or adjunctive therapies for treatment-resistant OCD and have at least preliminary evidence of efficacy. Medications with dopamine antagonist activity remain the most robustly evidence-based of augmenting interventions, yet dopamine antagonists benefit only a minority of those who try them and carry elevated risks of adverse effects. Interventions targeting glutamatergic and anti-inflammatory pathways are less well evidenced, but may offer more favorable benefit to risk profiles. Ongoing research should explore whether specific interventions may benefit individuals with particular features of treatment-resistant OCD.

SAPAP Scaffold Proteins: From Synaptic Function to Neuropsychiatric Disorders

Excitatory (glutamatergic) synaptic transmission underlies many aspects of brain activity and the genesis of normal human behavior. The postsynaptic scaffolding proteins SAP90/PSD-95-associated proteins (SAPAPs), which are abundant components of the postsynaptic density (PSD) at excitatory synapses, play critical roles in synaptic structure, formation, development, plasticity, and signaling. The convergence of human genetic data with recent in vitro and in vivo animal model data indicates that mutations in the genes encoding SAPAP1-4 are associated with neurological and psychiatric disorders, and that dysfunction of SAPAP scaffolding proteins may contribute to the pathogenesis of various neuropsychiatric disorders, such as schizophrenia, autism spectrum disorders, obsessive compulsive disorders, Alzheimer's disease, and bipolar disorder. Here, we review recent major genetic, epigenetic, molecular, behavioral, electrophysiological, and circuitry studies that have advanced our knowledge by clarifying the roles of SAPAP proteins at the synapses, providing new insights into the mechanistic links to neurodevelopmental and neuropsychiatric disorders.

Acute (R,S)-Ketamine Administration Induces Sex-Specific Behavioral Effects in Adolescent but Not Aged Mice

(R,S)-ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist that was originally developed as an anesthetic. Most recently, (R,S)-ketamine has been used as a rapid-acting antidepressant, and we have reported that (R,S)-ketamine can also be a prophylactic against stress in adult mice. However, most pre-clinical studies have been performed in adult mice. It is still unknown how an acute (R,S)-ketamine injection influences behavior across the lifespan (e.g., to adolescent or aged populations). Here, we administered saline or (R,S)-ketamine at varying doses to adolescent (5-week-old) and aged (24-month-old) 129S6/SvEv mice of both sexes. One hour later, behavioral despair, avoidance, locomotion, perseverative behavior, or contextual fear discrimination (CFD) was assessed. A separate cohort of mice was sacrificed 1 h following saline or (R,S)-ketamine administration. Brains were processed to quantify the marker of inflammation Cyclooxygenase 2 (Cox-2) expression to determine whether the acute effects of (R,S)-ketamine were partially mediated by changes in brain inflammation. Our findings show that (R,S)-ketamine reduced behavioral despair and perseverative behavior in adolescent female, but not male, mice and facilitated CFD in both sexes at specific doses. (R,S)-ketamine reduced Cox-2 expression specifically in ventral CA3 (vCA3) of male mice. Notably, (R,S)-ketamine was not effective in aged mice. These results underscore the need for sex- and age-specific approaches to test (R,S)-ketamine efficacy across the lifespan.