Influence of nonsynaptic α1 glycine receptors on ethanol consumption and place preference

Abstract

Alcohol abuse leads to great medical, social, and economic burdens throughout the world. It is believed that the rewarding actions of alcohol are mediated by alterations in the mesolimbic dopaminergic system leading to increased levels of dopamine in the nucleus accumbens (NAc). Little is known about the role that ligand-gated ion channels (LGICs), such as glycine receptors (GlyRs), have in regulating levels of ethanol intake and place preference. In this study, we used knock-in (KI) mice that have ethanol-insensitive α1 GlyRs (KK385/386AA) and a combination of electrophysiological and behavioral approaches to examine how expression of ethanol-resistant α1GlyRs in brain neurons might affect binge drinking and conditioned place preference.Data show that tonic α1 GlyR-mediated currents that modulate accumbal excitability were exclusively sensitive to ethanol only in wild-type (WT) mice. Behavioral studies showed that the KI mice have a higher intake of ethanol upon first exposure to drinking and greater conditioned place preference to ethanol, suggesting that α1 GlyRs in the brain have a protective role against abuse. This study suggests that nonsynaptic α1-containing GlyRs have a role in motivational and early reinforcing effects of ethanol and open a novel opportunity for pharmacotherapy development to treat alcohol use disorders.

Ethanol consumption and sedation are altered in mice lacking the glycine receptor α2 subunit

“…This test is a form of Pavlovian conditioning used to measure the rewarding and motivational effects of abused drugs (Cunningham, Gremel, & Groblewski, 2006). It was previously reported that KI mice for the α1 glycine receptor subunit showed increased preference for the ethanol side compared to WT mice, demonstrating the relevance of glycine receptors in the regulation of behaviours related with alcohol seeking (Muñoz et al, 2019). The WT and Glra2 − /Y mice used in the conditioned place preference test did not show preference for either side of the cage during the 15‐min pre‐conditioning session (Figure 7a,c).…”

“…Previous studies demonstrated that nucleus accumbens expresses glycine receptor α and β subunits (Jonsson et al, 2012; Muñoz et al, 2019). Analysis of glycine receptor subunit relative expression in the nucleus accumbens using real‐time PCR revealed high levels of α2 and β subunits in WT mice, while in the Glra2 − /Y mice, the expression of α2 was completely abolished, as expected (Figure 1a).…”

“…The conditioned place preference was performed as previously described (Muñoz et al, 2019). This paradigm is based on a Pavlovian conditioning behaviour.…”

“…After ANOVA, Bonferroni post hoc test was run only if F achieved the necessary level of statistical significance ( P < 0.05) and there was no significant variance inhomogeneity. As in previous studies (Aguayo et al, 2014; Muñoz et al, 2019), in order to obtain statistical power above 95% ( α = 0.05, power = 0.95) to determine existence of statistically significant differences ( P < 0.05), we used a sample size of 6–8 measurements for experimental group. For behaviour studies, we considered at least 10–12 animals per group; however, there were some small variations in group size due to unreliable intraperitoneal injections or problems with the bottles.…”

“…Our laboratory recently characterized the properties of glycine receptors in the nucleus accumbens (Forstera et al, 2017) and determined that accumbal medium spiny neurons express functional, ethanol‐sensitive glycine receptors, primarily α1 and α2 subunits. A genetically modified knock‐in (KI) mouse for the glycine receptor α1 subunit (K385/386A) that has an impaired interaction with G proteins demonstrated reduced ethanol sensitivity in the nucleus accumbens, a higher ethanol intake and increased conditioned place preference (CPP) to ethanol (Aguayo et al, 2014; Muñoz et al, 2019). Since glycine receptor α2 subunits are also known to be regulated by ethanol (Yevenes et al, 2010) and they are expressed in nucleus accumbens (Forstera et al, 2017; Jonsson et al, 2012), glycine receptor α2 subunits might also play an important role in regulating the mesolimbic dopaminergic reward circuitry and addictive behaviours.…”