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.…”

Cholinergic interneurons in the nucleus accumbens are a site of cellular convergence for corticotropin release factor and estrogen regulation

“…Acetylcholine transmission, via ionotropic nicotinic acetylcholine receptors (nAChRs) and metabotropic muscarinic acetylcholine receptors (mAChRs), modulates the excitability and fast synaptic transmission of the two major classes of GABAergic projection neurons: direct, or dopamine D1 receptor-containing spiny projection neurons, and indirect, or dopamine D2 receptor-containing spiny projection neurons [14][15][16] . In addition, ChIs have been shown to modulate dopamine transmission through the activation of either mAChRs [17][18][19][20][21][22] or nAChRs, with nAChR activation on dopaminergic varicosities capable of generating action potential-mediated dopamine release that is independent of somatic firing 17-22 . This relationship between acetylcholine and dopamine transmission is critical to maintaining striatal function.…”