Cerebellar GABAA receptor contributions to EtOH intoxication and EtOH intake

Oregon Health & Science University, Portland OR

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Abstract

DESCRIPTION (provided by applicant): There is substantial heritable risk for developing alcohol dependence. One established risk factor associated with enhanced alcohol consumption is a behavioral insensitivity to alcohol-induced impairment on a cerebellar- dependent measure, such as body sway. However, the cellular mechanisms underlying this behavioral insensitivity are poorly understood. One potential site of differential alcohol action that contributes to this behavioral phenotype is on tonic GABAA receptor (GABAAR)-mediated transmission of cerebellar granule cells (GCs) which powerfully regulates the transmission of afferent information from the periphery through the cerebellar cortex. Previous research in low-alcohol consuming Sprague-Dawley (SD) rats identified that alcohol enhances the magnitude of tonic GABAAR inhibition of GCs, which may impair behavior by dampening transmission through the cerebellar cortex. In my preliminary experiments, I investigated whether the alcohol- induced enhancement of tonic GABAAR inhibition of GCs differed across rodents with divergent sensitivities to alcohol-induced cerebellar ataxia and alcohol consumption phenotypes. I found that in DBA/2J (D2) mice, which like SD rats, express a behaviorally sensitive and low-alcohol consuming phenotype, alcohol greatly enhanced tonic GABAAR inhibition of GCs. However, intriguingly, alcohol suppressed tonic GABAAR inhibition in C57BL/6J (B6) mice, which more closely model the human cerebellar low LR phenotype. These experiments illuminated a potentially significant role that alcohol action on tonic GABAAR inhibition of GCs plays in alcohol- induced ataxia and alcohol intake. The research goals of the current application are to determine if genotypic differences in alcohol-induced modulation of tonic GABAAR-mediated inhibition of GCs differentially impacts signal transmission through the cerebellar cortex and establish its relationship to cerebellar ataxia and EtOH consumption. The broad overall hypothesis is that the suppressive actions of alcohol on tonic GABAAR currents in B6 mouse GCs is less disruptive (compared to enhancement observed in D2 mice and SD rats) of transmission through the cerebellar cortex, and thus is less disruptive of cerebellar dependent behaviors. In particular, I propose that the novel suppressive action of EtOH on GC tonic GABAAR currents contributes to the B6's reduced sensitivity to EtOH-induced motor impairment, which in turn contributes to their high EtOH consumption phenotype. I will test these hypotheses with pharmacological and electrophysiological studies of GC tonic GABAAR modulation of signal transmission through the cerebellar cortex (Aim 1) and behavioral studies designed to determine how manipulations of tonic GABAAR currents impacts cerebellar-dependent rotarod performance and EtOH intake (Aim 2). The information gained from this proposal will add substantially to our understanding of the cellular correlates that underlie a known behavioral risk factor for developing an alcohol use disorder and can be applied to the development of novel pharmacological interventions to combat this destructive condition.