Chronic Loss of Muscarinic M5 Receptor Function Manifests Disparate Impairments in Exploratory Behavior in Male and Female Mice despite Common Dopamine Regulation

Abstract

There are five cloned muscarinic acetylcholine receptors (M1-M5). Of these, the muscarinic type 5 receptor (M5) is the only one localized to dopamine neurons in the ventral tegmental area and substantia nigra. Unlike M1-M4, the M5 receptor has relatively restricted expression in the brain, making it an attractive therapeutic target. Here, we performed an in-depth characterization of M5-dependent potentiation of dopamine transmission in the nucleus accumbens and accompanying exploratory behaviors in male and female mice. We show that M5 receptors potentiate dopamine transmission by acting directly on the terminals within the nucleus accumbens. Using the muscarinic agonist oxotremorine, we revealed a unique concentration-response curve and a sensitivity to repeated forced swim stress or restraint stress exposure. We found that constitutive deletion of M5 receptors reduced exploration of the center of an open field while at the same time impairing normal habituation only in male mice. In addition, M5 deletion reduced exploration of salient stimuli, especially under conditions of high novelty, yet had no effect on hedonia assayed using the sucrose preference test or on stress-coping strategy assayed using the forced swim test. We conclude that M5 receptors are critical for both engaging with the environment and updating behavioral output in response to environment cues, specifically in male mice. A cardinal feature of mood and anxiety disorders is withdrawal from the environment. These data indicate that boosting M5 receptor activity may be a useful therapeutic target for ameliorating these symptoms of depression and anxiety.

Corticotropin releasing factor alters the functional diversity of accumbal cholinergic interneurons

“…The nucleus accumbens is composed of important microdomains or functional units that can control different circuit outputs and behavioral repertoires ( The spontaneous activity of cholinergic interneurons ensures an ambient level of acetylcholine, which can in turn bind nicotinic and muscarinic receptors. Focusing on muscarinic receptors, all five cloned receptors are present in the striatum, either on striatal neurons themselves or cortical and/or dopamine terminals (Benarroch, 2012;Razidlo et al, 2022). How and when these receptors are differentially or cooperatively activated in the intact circuit is poorly understood.…”

Local and long-distance inputs dynamically regulate striatal acetylcholine during decision making

“…For behavior experiments, males at 6-8 weeks of age were used. Only males were used to avoid any behavioral variation due to the estrous cycle in female mice and because of recent findings that only male behavior is affected by loss of muscarinic Ach receptors 73 . All animal care and experimental manipulations were performed in accordance with protocols approved by the Harvard Standing Committee on Animal Care, following guidelines described in the US NIH Guide for the Care and Use of Laboratory Animals.…”

Characterization of Selective M5Acetylcholine Muscarinic Receptor Modulators on Dopamine Signaling in the Striatum

“…To refine our knowledge of midbrain M 5 expression pattern and its modulatory role on DA release, we first used fluorescent in situ hybridization to confirm and supplement previous findings showing prominent expression of M 5 not only in DA neurons (Gould et al, 2019;Razidlo et al, 2022), but also in glutamate and dual DA/glutamate neurons. Then, utilizing ex vivo fast-scan cyclic voltammetry (FSCV), we demonstrated that enhancement of M 5 activity can increase DA release while reduction of M 5 activity can diminish DA release in the striatum.…”

“…Thus, they may afford relevant therapeutic targets for neuropsychiatric diseases as illustrated by the antidepressant effects of the non-selective antagonist scopolamine (Drevets et al, 2020) or the antipsychotic effects of M 1 /M 4 agonists (Foster et al, 2021). G i/o -coupled M 2 and M 4 receptors are expressed by CINs (Zhang et al, 2002) and can directly modulate DA release (Shin et al, 2015), while the G q/11coupled M 5 receptor is highly expressed in midbrain DA neurons (Weiner et al, 1990) and their terminals in the striatum (Razidlo et al, 2022;Shin et al, 2015). Unlike other mAChRs subtypes, the function of M 5 remains elusive and conflicting experimental results across studies confound the existing literature.…”