Gene knockout of the alpha6 subunit of the gamma-aminobutyric acid type A receptor: lack of effect on responses to ethanol, pentobarbital, and general anesthetics.

Abstract

The alpha6 subunit of the gamma-aminobutyric acid type A receptor (GABA(A)-R) has been implicated in mediating the intoxicating effects of ethanol and the motor ataxic effects of general anesthetics. To test this hypothesis, we used gene targeting in embryonic stem cells to create mice lacking a functional alpha6 gene. Homozygous mice are viable and fertile and have grossly normal cerebellar cytoarchitecture. Northern blot and reverse transcriptase-polymerase chain reaction analyses demonstrated that the targeting event disrupted production of functional alpha6 mRNA. Autoradiography of histological sections of adult brains demonstrated that diazepam-insensitive binding of [3H]Ro15-4513 to the cerebellar granule cell layer of wild-type mice was completely absent in homozygous mice. Cerebellar GABA(A)-R density was unchanged in the mutant mice; however, the apparent affinity for muscimol was markedly reduced. Sleep time response to injection of ethanol after pretreatment with vehicle or Ro15-4513 did not differ between genotypes. Sleep time response to injection of pentobarbital and loss of righting reflex and response to tail clamp stimulus in mice anesthetized with volatile anesthetics also did not differ between genotypes. Thus, the alpha6 subunit of the GABA(A)-R is not required for normal development, viability, and fertility and does not seem to be a critical or unique component of the neuronal pathway mediating the hypnotic effect of ethanol and its antagonism by Ro15-4513 in mice. Similarly, the alpha6 subunit does not seem to be involved in the behavioral responses to general anesthetics or pentobarbital.