M1 muscarinic receptor activation decreases alcohol consumption via a reduction in consummatory behavior.

Muscarinic acetylcholine receptors (mAChRs) have been shown to mediate alcohol consumption and seeking. Both M4 and M5 mAChRs have been highlighted as potential novel treatment targets for alcohol use disorders (AUD). Similarly, M1 mAChRs are expressed throughout reward circuitry, and their signaling has been implicated in cocaine consumption. However, whether the same effects are seen for alcohol consumption, or whether natural reward intake is inadvertently impacted is still unknown. To determine the role of M1 mAChRs in alcohol consumption, we tested operant self-administration of alcohol under both fixed ratio (FR3) and progressive ratio (PR3-4) schedules. Enhancing M1 mAChR signaling (via the M1 PAM-Agonist PF-06767832, 1 mg/kg, i.p.) reduced operant alcohol consumption on a fixed schedule but had no effect on motivation to acquire alcohol. To determine whether these actions were specific to alcohol, we examined the effects of M1 enhancement on natural reward (sucrose) self-administration. Systemic administration of PF-06767832 (1 mg/kg, i.p.) also reduced operant sucrose self-administration, suggesting the actions of the M1 receptor may be non-selective across drug and natural rewards. Finally, to understand whether this reduction extended to natural consummatory behaviors, we assessed home cage standard chow and water consumption. M1 enhancement via systemic PF-06767832 administration reduced food and water consumption. Together our results suggest the M1 PAM-agonist, PF-06767832, non-specifically reduces consummatory behaviors that are not associated with motivational strength for the reward. These data highlight the need to further characterize M1 agonists, PAMs, and PAM-agonists, which may have varying degrees of utility in the treatment of neuropsychiatric disorders including AUD.

Muscarinic M4 and M5 receptors in the ventral subiculum differentially modulate alcohol seeking versus consumption in male alcohol-preferring rats.

BACKGROUND AND PURPOSE: Muscarinic acetylcholine receptors mediate alcohol consumption and seeking in rats. While M4 and M5 receptors have recently been implicated to mediate these behaviours in the striatum, their role in other brain regions remain unknown. The ventral tegmental area (VTA) and ventral subiculum (vSub) both densely express M4 and M5 receptors and modulate alcohol-seeking, via their projections to the nucleus accumbens shell (AcbSh). EXPERIMENTAL APPROACH: In Indiana alcohol-preferring (iP) male rats, we examined Chrm4 (M4 ) and Chrm5 (M5 ) expression in the VTA and vSub following long-term alcohol consumption and abstinence using RT-qPCR. Using a combination of retrograde tracing and RNAscope, we examined the localisation of Chrm4 and Chrm5 on vSub cells that project to the AcbSh. Using selective allosteric modulators, we examined the functional role of M4 and M5 receptors within the vSub in alcohol consumption, context-induced alcohol-seeking, locomotor activity, and food/water consumption. KEY RESULTS: Long-term alcohol and abstinence dysregulated the expression of genes for muscarinic receptors in the vSub, not in the VTA. Chrm4 was down-regulated following long-term alcohol and abstinence, while Chrm5 was up-regulated following long-term alcohol consumption. Consistent with these data, a positive allosteric modulator (VU0467154) of intra-vSub M4 receptors reduced context-induced alcohol-seeking, but not motivation for alcohol self-administration, while M5 receptor negative allosteric modulator (ML375) reduced initial motivation for alcohol self-administration, but not context-induced alcohol-seeking. CONCLUSION AND IMPLICATIONS: Collectively, our data highlight alcohol-induced cholinergic dysregulation in the vSub and distinct roles for M4 and M5 receptor allosteric modulators to reduce alcohol consumption or seeking.

Cocaine and amphetamine regulated transcript (CART) signalling in the central nucleus of the amygdala modulates stress-induced alcohol seeking.

The central nucleus of the amygdala (CeA) is a key hub of the neural circuitry regulating alcohol and stress interactions. However, the exact neuronal populations that govern this interaction are not well defined. Here we examined the role of the neuropeptide cocaine and amphetamine regulated transcript (CART) within the CeA in stress-induced alcohol seeking. We found that CART-containing neurons are predominantly expressed in the capsular/lateral division of the CeA and are a subpopulation of protein kinase Cδ (PKCδ) cells, distinct from corticotrophin releasing factor (CRF)-expressing cells. Both stress (yohimbine) and stress-induced alcohol seeking activated CART cells within the CeA, while neutralisation of endogenous CeA CART signalling (via antibody administration) attenuated stress-induced alcohol, but not sucrose seeking. Further, blocking CART signalling within the CeA did not alter the motivation to obtain and consume alcohol but did attenuate stressor-induced anxiety-like behaviour during abstinence from alcohol. Together, these data identify CeA CART cells as a subpopulation of PKCδ cells that influence stress × alcohol interactions and mediate stress-induced alcohol seeking behaviours.