Alpha1 GlyRs are important for ethanol-induced sedation. Implications for drug development.

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Aguayo LG1, Muñoz B1, San Martin, L1, Lovinger DM2, Homanics GE3, and Jose L. Guzman1.

1University of Concepcion, Concepcion, Chile
2National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD, USA
3University of Pittsburgh, Pittsburgh, PA 15261 USA

Alcohol abuse affects many millions of people worldwide causing significant social, medical and economic burdens. The available pharmacotherapeutic tools are limited, have low adherence and cause side effects, which emphasizes the search for novel, mechanistically oriented therapies.
We previously reported that basic amino acids in the intracellular loop of the α1 subunit (316-320 and 385/386) are important to regulate the sensitivity of glycine receptors (GlyR) to low concentrations of ethanol. The pharmacological effects of the mutations are specific for ethanol, since the sensitivity to neurosteroids, isoflurane, propofol and Zn2+ are unchanged. Therefore, we generated and studied a Knock In (KI) mouse for the α1 GlyR with mutations in residues 385/386 of the receptor. The KI mice had normal behavior and most importantly did not display a hyperexcitable phenotype indicating that the mutation is primarily silent. The study of spinal and brain stem neurons with electrophysiological techniques showed that native GlyRs were less affected by ethanol- and Gβγ- mediated modulations. Interestingly, the mice exhibited a reduced loss of righting reflex (LORR) time when compared with wild type mice. Using the DID protocol, we found that the KI mice went into binge drinking from day 1 of exposure drinking three times more than the WT.
Our search for inhibitory molecules acting at the site of Gβγ/GlyR site identified a small peptide that reduced the ethanol-induced potentiation of GlyR activated currents and miniature inhibitory synaptic currents (mIPSCs). Using in silico screening and patch clamp techniques, we discovered a small, indol derivative molecule that was able to reduce ethanol potentiation of a1 GlyR. The i.p. administration of this compound reduced the ethanol-induced LORR by ≈25% at the highest dose tested in WT mice. In conclusion, we identified important amino acids that participate in the modulation of GlyRs by ethanol. These findings could lead to the development of new therapy for alcohol related disorders.

Supported by NIH RO1 and Fondecyt DPI 20140008 grants