GENE KNOCKOUT OF THE ALPHA-6 SUBUNIT OF THE GAMMA-AMINOBUTYRIC-ACID TYPE-A RECEPTOR - LACK OF EFFECT ON RESPONSES TO ETHANOL, PENTOBARBITAL, AND GENERAL-ANESTHETICS

The alpha 6 subunit of the gamma-aminobutyric acid type A receptor (GA BA(A)-R) has been implicated in mediating the intoxicating effects of ethanol and the motor ataxic effects of general anesthetics. To test t his hypothesis, we used gene targeting in embryonic stem cells to crea te mice lacking a functional alpha 6 gene. Homozygous mice are viable and fertile and have grossly normal cerebellar cytoarchitecture. North ern blot and reverse transcriptase-polymerase chain reaction analyses demonstrated thai the targeting event disrupted production oi function al alpha 6 mRNA. Autoradiography of histological sections of adult bra ins demonstrated that diazepam-insensitive binding of [H-3]Ro15-4513 t o the cerebellar granule cell layer of wild-type mice was completely a bsent in homozygous mice. Cerebellar GABA(A)-R density was unchanged i n the mutant mice; however, the apparent affinity for muscimol was mar kedly reduced. Sleep time response to injection of ethanol after pretr eatment with vehicle or Ro15-4513 did not differ between genotypes. Sl eep time response to injection of pentobarbital and loss of righting r eflex and response to tail clamp stimulus in mice anesthetized with vo latile anesthetics also did not differ between genotypes. Thus, the al pha 6 subunit of the GABA(A)-R is not required far 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 et hanol and its antagonism by Ro15-4513 in mice. Similarly, the alpha 6 subunit does not seem to be involved in the behavioral responses to ge neral anesthetics or pentobarbital.