Opioid modulation of depression: A focus on imaging studies

Different drugs come with different motives: Examining motives for substance use among people who engage in polysubstance use undergoing methadone maintenance therapy (MMT)

BACKGROUND

Substance use motives (i.e., reasons for using a substance) are thought to be the most proximal variable leading to substance use. These motives have been described by various typologies, the most well known being the four-factor drinking motives model which separates motives into enhancement, social, coping, and conformity (Cooper, 1994). Although extensively studied in adult community samples, motives for use have less commonly been investigated among populations at a later stage of addiction, where polysubstance use is more common. Moreover, because the motives literature has largely focused on drinking motives, it is not clear whether existing findings can also be applied to other substances (Cooper et al., 2016).

METHODS

Using Zero-inflated beta Bayesian linear mixed modeling, we investigated the stability of seven distinct substance use motives (enhancement, social, expansion, coping with anxiety, coping with depression, coping with withdrawal, and conformity) across six different drug categories (tobacco, alcohol, cannabis, opioids, stimulants, and tranquilisers) to determine the extent to which drug class can influence motive endorsement. One-hundred-and-thirty-eight methadone maintenance therapy (MMT) clients (F = 34.1%; M = 65.9%; age = 40.18 years) completed a novel short-form polysubstance motives questionnaire.

RESULTS

External motives (i.e., conformity and social motives) were the most stable across drug categories, while all internal motives (i.e., enhancement, expansion, and all three coping motives) demonstrated varying levels of inter-drug variability.

CONCLUSIONS

These findings have important implications for prevention and intervention strategies among people who engage in polysubstance use, highlighting the importance of both universal and substance-specific programming.

Ketamine: The final frontier or another depressing end?

Two decades ago, the observation of a rapid and sustained antidepressant response after ketamine administration provided an exciting new avenue in the search for more effective therapeutics for the treatment of clinical depression. Research elucidating the mechanism(s) underlying ketamine's antidepressant properties has led to the development of several hypotheses, including that of disinhibition of excitatory glutamate neurons via blockade of N-methyl-d-aspartate (NMDA) receptors. Although the prominent understanding has been that ketamine's mode of action is mediated solely via the NMDA receptor, this view has been challenged by reports implicating other glutamate receptors such as AMPA, and other neurotransmitter systems such as serotonin and opioids in the antidepressant response. The recent approval of esketamine (Spravato™) for the treatment of depression has sparked a resurgence of interest for a deeper understanding of the mechanism(s) underlying ketamine's actions and safe therapeutic use. This review aims to present our current knowledge on both NMDA and non-NMDA mechanisms implicated in ketamine's response, and addresses the controversy surrounding the antidepressant role and potency of its stereoisomers and metabolites. There is much that remains to be known about our understanding of ketamine's antidepressant properties; and although the arrival of esketamine has been received with great enthusiasm, it is now more important than ever that its mechanisms of action be fully delineated, and both the short- and long-term neurobiological/functional consequences of its treatment be thoroughly characterized.