Ketamine metabolite alleviates morphine withdrawal-induced anxiety via modulating nucleus accumbens parvalbumin neurons in male mice

Estrogen receptor alpha (ERα) partially modulates ketamine's sustained anxiolytic effects without altering its antidepressant properties in female rats

Ketamine is a rapid-acting antidepressant with sexually dimorphic effects. Female animals exhibit a higher sensitivity to its antidepressant properties, which has been associated with their ovarian hormone levels. One factor contributing to this sex difference is the faster rate of ketamine metabolism observed in females, potentially regulated by estrogen receptor alpha (ERα) through modulation of enzymatic activity. In this study, we explored the role of ERα in mediating the therapeutic effects of ketamine in adult female Wistar rats. To inhibit ERα, we administered its antagonist, methyl-piperidino-pyrazole (MPP; 1 mg/kg, IP), 24 h and 1 h prior to a single antidepressant dose of ketamine (10 mg/kg, IP) or saline (vehicle). We tested the animals in the forced swim test (FST), open field test (OFT), elevated plus maze (EPM), and auditory fear conditioning. Ketamine administration ameliorated behavioral despair observed in the vehicle group, and ERα antagonism did not affect this outcome. An interaction between MPP and ketamine was observed in anxiety-like behaviors assessed in the OFT and EPM; however, this effect did not reach significance in post-hoc analyses. Neither MPP nor ketamine affected fear memory, as measured in cued fear conditioning. These findings suggest that the sexually dimorphic antidepressant effects of ketamine occur independently of ERα activity, although ERα may influence neural circuits related to anxiety.

(2R,6R)-hydroxynorketamine prevents opioid abstinence-related negative affect and stress-induced reinstatement in mice

BACKGROUND AND PURPOSE

Opioid use disorder (OUD) is a pressing public health concern marked by frequent relapse during periods of abstinence, perpetuated by negative affective states. Classical antidepressants or the currently prescribed opioid pharmacotherapies have limited efficacy to reverse the negative affect or prevent relapse.

EXPERIMENTAL APPROACH

Using mouse models, we investigated the effects of ketamine's metabolite (2R,6R)-hydroxynorketamine (HNK) on reversing conditioning to sub-effective doses of morphine in stress-susceptible mice, preventing conditioned-place aversion and alleviating acute somatic abstinence symptoms in opioid-dependent mice. Additionally, we evaluated its effects on anhedonia, anxiety-like behaviours and cognitive impairment during protracted opioid abstinence, while mechanistic studies examined cortical EEG oscillations and synaptic plasticity markers.

KEY RESULTS

(2R,6R)-HNK reversed conditioning to sub-effective doses of morphine in stress-susceptible mice and prevented conditioned-place aversion and acute somatic abstinence symptoms in opioid-dependent mice. In addition, (2R,6R)-HNK reversed anhedonia, anxiety-like behaviours and cognitive impairment emerging during protracted opioid abstinence plausibly via a restoration of impaired cortical high-frequency EEG oscillations, through a GluN2A-NMDA receptor-dependent mechanism. Notably, (2R,6R)-HNK facilitated the extinction of opioid conditioning, prevented stress-induced reinstatement of opioid-seeking behaviours and reduced the propensity for enhanced morphine self-consumption in mice previously exposed to opioids.

CONCLUSIONS AND IMPLICATIONS

These findings emphasize the therapeutic potential of (2R,6R)-HNK, which is currently in Phase II clinical trials, in addressing stress-related opioid responses. Reducing the time and cost required for development of new medications for the treatment of OUDs via drug repurposing is critical due to the opioid crisis we currently face.

Ketamine and Hydroxynorketamine as Novel Pharmacotherapies for the Treatment of Opioid Use Disorders

Opioid use disorder (OUD) has reached epidemic proportions, with many countries facing high levels of opioid use and related fatalities. Although currently prescribed medications for OUD are considered lifesaving, they inadequately address negative affect and cognitive impairment, resulting in high relapse rates to nonmedical opioid use even years after drug cessation (protracted abstinence). Evidence supports the notion that ketamine, an anesthetic and rapid-acting antidepressant drug, holds promise as a candidate for OUD treatment, including the management of acute withdrawal somatic symptoms, negative affect during protracted opioid abstinence, and prevention of retaking nonmedical opioids. In this review, we comprehensively discuss preclinical and clinical research that has evaluated ketamine and its metabolites as potential novel therapeutic strategies for treating OUD. Furthermore, we examine evidence that supports the relevance of the molecular targets of ketamine and its metabolites in relation to their potential effects and therapeutic outcomes in OUD. Overall, existing evidence demonstrates that ketamine and its metabolites can effectively modulate pathophysiological processes affected in OUD, suggesting a promising therapeutic role in the treatment of OUD and the prevention of return to opioid use during abstinence.

Endogenous opiates and behavior: 2023

This paper is the forty-sixth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2023 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug and alcohol abuse (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Occurrence, ecotoxicity and ecological risks of psychoactive substances in surface waters

Psychoactive substances (PSs) represent a subset of emerging contaminants. Their widespread production and utilization contribute to a growing ecological burden and risk on a global scale. Conventional wastewater treatment methods have proven insufficient in adequately removing psychoactive substances, leading to their occurrence in surface water ecosystems worldwide. As of present, however, a thorough understanding of their geographical prevalence and distribution patterns remains elusive. Further, in the existing literature, there is a scarcity of comprehensive overviews that systematically summarize the toxicity of various psychoactive substances towards aquatic organisms. Through summarizing almost 140 articles, the present study provides an overview of the sources, pollution status, and biotoxicity of psychoactive substances in surface waters, as well as an assessment of their ecological risks. Concentrations of several psychoactive substances in surface waters were found to be as high as hundreds or even thousands of ng·L-1. In parallel, accumulation of psychoactive substances in the tissues or organs of aquatic organisms was found to potentially cause certain adverse effects, including behavioral disorders, organ damage, and DNA changes. Oxidative stress was found to be a significant factor in the toxic effects of psychoactive substances on organisms. The application of the risk quotient approach indicated that psychoactive substances posed a medium to high risk in certain surface water bodies, as well as the need for sustained long-term attention and management strategies.