Role ofNMDAandAMPAglutamatergic receptors in the effects of social defeat on the rewarding properties ofMDMAin mice

The effects of different types of social interactions on the electrophysiology of neurons in the nucleus accumbens in rodents

BORLAND, J.M., The effects of different types of social interactions on the electrophysiology of neurons in the nucleus accumbens in rodents, NEUROSCI BIOBEH REV 21(1) XXX-XXX, 2024.-Sociality shapes an organisms' life. The nucleus accumbens is a critical brain region for mental health. In the following review, the effects of different types of social interactions on the physiology of neurons in the nucleus accumbens is synthesized. More specifically, the effects of sex behavior, aggression, social defeat, pair-bonding, play behavior, affiliative interactions, parental behaviors, the isolation from social interactions and maternal separation on measures of excitatory synaptic transmission, intracellular signaling and factors of transcription and translation in neurons in the nucleus accumbens in rodent models are reviewed. Similarities and differences in effects depending on the type of social interaction is then discussed. This review improves the understanding of the molecular and synaptic mechanisms of sociality.

The therapeutic effects of saikosaponins on depression through the modulation of neuroplasticity: From molecular mechanisms to potential clinical applications

Depression is a major global health issue that urgently requires innovative and precise treatment options. In this context, saikosaponin has emerged as a promising candidate, offering a variety of therapeutic benefits that may be effective in combating depression. This review delves into the multifaceted potential of saikosaponins in alleviating depressive symptoms. We summarized the effects of saikosaponins on structural and functional neuroplasticity, elaborated the regulatory mechanism of saikosaponins in modulating key factors that affect neuroplasticity, such as inflammation, the hypothalamic-pituitary-adrenal (HPA) axis, oxidative stress, and the brain-gut axis. Moreover, this paper highlights existing gaps in current researches and outlines directions for future studies. A detailed plan is provided for the future clinical application of saikosaponins, advocating for more targeted researches to speed up its transition from preclinical trials to clinical practice.

Exposure to anandamide on young rats causes deficits in learning, temporal perception and induces changes in NMDA receptor expression

Human use of marijuana at an early age has been reported to lead to cognitive impairment. However, researchers have not yet clearly determined whether this impairment is due to marijuana-induced alterations in the developing nervous system and whether this deficit persists into adulthood after marijuana use has ceased. We administered anandamide to developing rats to assess the effect of cannabinoids on development. We subsequently evaluated learning and performance on a temporal bisection task in adulthood and assessed the expression of genes encoding principal subunits of NMDA receptors (Grin1, Grin2A, and Grin2B) in the hippocampus and prefrontal cortex. Rats in two age groups, namely, 21-day-old and 150-day-old rats, received intraperitoneal injections of anandamide or the vehicle for 14 days. Both groups performed a temporal bisection test, which included listening to tones of different durations and classifying them as short or long. The expression of the Grin1, Grin2A and Grin2B mRNAs was evaluated using quantitative PCR in both age groups after extracting mRNA from the hippocampus and prefrontal cortex. We observed a learning impairment in the temporal bisection task (p < 0.05) and changes in the response latency (p < 0.05) in rats that received anandamide. Furthermore, these rats exhibited decreased expression of Grin2b (p = 0.001) compared to those that received the vehicle. In human subjects, the use of cannabinoids during development induces a long-term deficit, but this deficit is not observed in subjects who use cannabinoids in adulthood. Rats treated with anandamide earlier in development took longer to learn the task, suggesting that anandamide exerts a harmful effect on cognition in developing rats. Administration of anandamide during early stages of development induced deficits in learning and other cognitive processes that depend on an adequate estimation of time. The cognitive demands of the environment must be considered when evaluating the cognitive effects of cannabinoids on developing or mature brains. High cognitive demands might induce differential expression of NMDA receptors that improves cognitive capacity, overcoming altered glutamatergic function.

Pharmacological Strategies for Suicide Prevention Based on the Social Pain Model: A Scoping Review

Suicidal behaviour is a public health problem whose magnitude is both substantial and increasing. Since many individuals seek medical treatment following a suicide attempt, strategies aimed at reducing further attempts in this population are a valid and feasible secondary prevention approach. An evaluation of the available evidence suggests that existing treatment approaches have a limited efficacy in this setting, highlighting the need for innovative approaches to suicide prevention. Existing research on the neurobiology of social pain has highlighted the importance of this phenomenon as a risk factor for suicide, and has also yielded several attractive targets for pharmacological strategies that could reduce suicidality in patients with suicidal ideation or a recent attempt. In this paper, the evidence related to these targets is synthesized and critically evaluated. The way in which social pain is related to the “anti-suicidal” properties of recently approved treatments, such as ketamine and psilocybin, is examined. Such strategies may be effective for the short-term reduction in suicidal ideation and behaviour, particularly in cases where social pain is identified as a contributory factor. These pharmacological approaches may be effective regardless of the presence or absence of a specific psychiatric diagnosis, but they require careful evaluation.

Resilience to the effects of social stress on vulnerability to developing drug addiction

We review the still scarce but growing literature on resilience to the effects of social stress on the rewarding properties of drugs of abuse. We define the concept of resilience and how it is applied to the field of drug addiction research. We also describe the internal and external protective factors associated with resilience, such as individual behavioral traits and social support. We then explain the physiological response to stress and how it is modulated by resilience factors. In the subsequent section, we describe the animal models commonly used in the study of resilience to social stress, and we focus on the effects of chronic social defeat (SD), a kind of stress induced by repeated experience of defeat in an agonistic encounter, on different animal behaviors (depression- and anxiety-like behavior, cognitive impairment and addiction-like symptoms). We then summarize the current knowledge on the neurobiological substrates of resilience derived from studies of resilience to the effects of chronic SD stress on depression- and anxiety-related behaviors in rodents. Finally, we focus on the limited studies carried out to explore resilience to the effects of SD stress on the rewarding properties of drugs of abuse, describing the current state of knowledge and suggesting future research directions.

Hypericum perforatum L. prevents the acquisition of and promotes resilience against stress-induced reinstatement of the conditioned place preference induced by cocaine

Cocaine use disorder is a serious problem worldwide, and there are no approved medications for its treatment. A novel approach to the treatment of drug addiction is the use of natural products, and, in this context, preclinical evidence suggests that Hypericum perforatum L. (Hypericum) is effective against alcohol and other substance use disorders. We hypothesised that Hypericum could also be useful as a treatment for cocaine use disorder, and so we set out to test its effectiveness in a mice model of cocaine addiction. In the first experiment we evaluated its effects on the acquisition of cocaine-induced conditioned place preference (CPP). Adult male mice were conditioned with cocaine (25 mg/kg), cocaine with Hypericum (75, 150 or 300 mg/kg) or the plant extract alone (300 mg/kg). In the second experiment, we tested the effects of Hypericum on stress-induced reinstatement of cocaine CPP. All the mice were conditioned with cocaine (25 mg/kg) and, after extinction of CPP, the reinstating effects of social defeat (alone or with 75, 150 or 300 mg/kg of Hypericum) were evaluated. All the doses of Hypericum prevented the acquisition of cocaine-induced CPP. Furthermore, the plant extract dose-dependently reduced the reinstating effects of social defeat. Therefore, Hypericum is effective in reducing the rewarding effects of cocaine and prevents the stress-induced reinstatement of cocaine CPP in mice. The mechanisms underlying these positive effects of Hypericum perforatum L. need to be determined by future research. Our results endorse Hypericum as a natural treatment for cocaine dependence.

The gabapentinoid drugs and their abuse potential

The gabapentinoid drugs, gabapentin and pregabalin, are first-line treatments for neuropathic pain. The epidemics of chronic pain and opioid misuse have given rise to the widespread use of non-opioid drugs such as the gabapentinoids for treatment. Unfortunately, the widespread use of gabapentinoid drugs has resulted in reports of misuse and abuse. Here we summarize the clinical reports of gabapentinoid abuse in different patient populations to help inform clinical practice of chronic pain management.

Role of acute social stress in the rewarding effects of MDMA in adolescent mice

Drug use among adolescents is a serious problem in our society, as some individuals develop dependence and addiction. MDMA/Esctasy is one of the most typically used substances by this age group. It is well known that environmental factors can alter the rewarding properties of drugs and the propensity to drug-related disorders. In this sense, exposure to social stress induces long-term effects in mice, enhancing the rewarding effects of MDMA in the conditioned place preference (CPP) paradigm. On the other hand, previous research has not provided conclusive results regarding the short-term effects of social defeat on MDMA reward in adolescent animals, probably due to the use of very low or very high doses. Thus, in the present study, we set out to evaluate whether exposure to social defeat immediately before each conditioning session with an intermediate dose of MDMA (2.25 mg/kg) modulates the rewarding effect of this drug in adolescent animals. Our results indicate that both control and socially defeated mice acquired CPP, but only stressed mice showed reinstatement. These findings indicate that social defeat induces an increase in the rewarding effect of MDMA, suggesting that this type of stress is a potential factor in the development of MDMA addiction.

Psychedelics in Psychiatry: Neuroplastic, Immunomodulatory, and Neurotransmitter Mechanisms

Mounting evidence suggests safety and efficacy of psychedelic compounds as potential novel therapeutics in psychiatry. Ketamine has been approved by the Food and Drug Administration in a new class of antidepressants, and 3,4-methylenedioxymethamphetamine (MDMA) is undergoing phase III clinical trials for post-traumatic stress disorder. Psilocybin and lysergic acid diethylamide (LSD) are being investigated in several phase II and phase I clinical trials. Hence, the concept of psychedelics as therapeutics may be incorporated into modern society. Here, we discuss the main known neurobiological therapeutic mechanisms of psychedelics, which are thought to be mediated by the effects of these compounds on the serotonergic (via 5-HT_2A and 5-HT_1A receptors) and glutamatergic [via N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors] systems. We focus on 1) neuroplasticity mediated by the modulation of mammalian target of rapamycin-, brain-derived neurotrophic factor-, and early growth response-related pathways; 2) immunomodulation via effects on the hypothalamic-pituitary-adrenal axis, nuclear factor ĸB, and cytokines such as tumor necrosis factor-α and interleukin 1, 6, and 10 production and release; and 3) modulation of serotonergic, dopaminergic, glutamatergic, GABAergic, and norepinephrinergic receptors, transporters, and turnover systems. We discuss arising concerns and ways to assess potential neurobiological changes, dependence, and immunosuppression. Although larger cohorts are required to corroborate preliminary findings, the results obtained so far are promising and represent a critical opportunity for improvement of pharmacotherapies in psychiatry, an area that has seen limited therapeutic advancement in the last 20 years. Studies are underway that are trying to decouple the psychedelic effects from the therapeutic effects of these compounds. SIGNIFICANCE STATEMENT: Psychedelic compounds are emerging as potential novel therapeutics in psychiatry. However, understanding of molecular mechanisms mediating improvement remains limited. This paper reviews the available evidence concerning the effects of psychedelic compounds on pathways that modulate neuroplasticity, immunity, and neurotransmitter systems. This work aims to be a reference for psychiatrists who may soon be faced with the possibility of prescribing psychedelic compounds as medications, helping them assess which compound(s) and regimen could be most useful for decreasing specific psychiatric symptoms.

Effect of Aggressive Experience in Female Syrian Hamsters on Glutamate Receptor Expression in the Nucleus Accumbens

Our social relationships determine our health and well-being. In rodent models, there is now strong support for the rewarding properties of aggressive or assertive behaviors to be critical for the expression and development of adaptive social relationships, buffering from stress and protecting from the development of psychiatric disorders such as depression. However, due to the false belief that aggression is not a part of the normal repertoire of social behaviors displayed by females, almost nothing is known about the neural mechanisms mediating the rewarding properties of aggression in half the population. In the following study, using Syrian hamsters as a well-validated and translational model of female aggression, we investigated the effects of aggressive experience on the expression of markers of postsynaptic structure (PSD-95, Caskin I) and excitatory synaptic transmission (GluA1, GluA2, GluA4, NR2A, NR2B, mGluR1a, and mGluR5) in the nucleus accumbens (NAc), caudate putamen and prefrontal cortex. Aggressive experience resulted in an increase in PSD-95, GluA1 and the dimer form of mGluR5 specifically in the NAc 24 h following aggressive experience. There was also an increase in the dimer form of mGluR1a 1 week following aggressive experience. Aggressive experience also resulted in an increase in the strength of the association between these postsynaptic proteins and glutamate receptors, supporting a common mechanism of action. In addition, 1 week following aggressive experience there was a positive correlation between the monomer of mGluR5 and multiple AMPAR and NMDAR subunits. In conclusion, we provide evidence that aggressive experience in females results in an increase in the expression of postsynaptic density, AMPARs and group I metabotropic glutamate receptors, and an increase in the strength of the association between postsynaptic proteins and glutamate receptors. This suggests that aggressive experience may result in an increase in excitatory synaptic transmission in the NAc, potentially encoding the rewarding and behavioral effects of aggressive interactions.

Plasticity of the Reward Circuitry After Early-Life Adversity: Mechanisms and Significance

Disrupted operation of the reward circuitry underlies many aspects of affective disorders. Such disruption may manifest as aberrant behavior including risk taking, depression, anhedonia, and addiction. Early-life adversity is a common antecedent of adolescent and adult affective disorders involving the reward circuitry. However, whether early-life adversity influences the maturation and operations of the reward circuitry, and the potential underlying mechanisms, remain unclear. Here, we present novel information using cutting-edge technologies in animal models to dissect out the mechanisms by which early-life adversity provokes dysregulation of the complex interactions of stress and reward circuitries. We propose that certain molecularly defined pathways within the reward circuitry are particularly susceptible to early-life adversity. We examine regions and pathways expressing the stress-sensitive peptide corticotropin-releasing factor (CRF), which has been identified in critical components of the reward circuitry and interacting stress circuits. Notably, CRF is strongly modulated by early-life adversity in several of these brain regions. Focusing on amygdala nuclei and their projections, we provide evidence suggesting that aberrant CRF expression and function may underlie augmented connectivity of the nucleus accumbens with fear/anxiety regions, disrupting the function of this critical locus of pleasure and reward.