BENZODIAZEPINE-INSENSITIVE MICE GENERATED BY TARGETED DISRUPTION OF THE GAMMA(2) SUBUNIT GENE OF GAMMA-AMINOBUTYRIC-ACID TYPE-A RECEPTORS

Vigilance, anxiety, epileptic activity, and muscle tone can be modulat ed by drugs acting at the benzodiazepine (BZ) site of gamma-aminobutyr ic acid type A (GABA(A)) receptors, In vivo, BZ sites are potential ta rgets for endogenous ligands regulating the corresponding central nerv ous system states, To assess the physiological relevance of BZ sites, mice were generated containing GABA(A) receptors devoid of BZ sites, F ollowing targeted disruption of the gamma(2) subunit gene, 94% of the BZ sites were absent in brain of neonatal mice, while the number of GA BA sites was only slightly reduced. Except for the gamma(2) subunit, t he level of expression and the regional and cellular distribution of t he major GABA(A) receptor subunits were unaltered, The single channel main conductance level and the Hill coefficient were reduced to values consistent with recombinant GABA(A), receptors composed of alpha and beta subunits, The GABA response was potentiated by pentobarbital but not by flunitrazepam. Diazepam was inactive behaviorally, Thus, the ga mma(2) subunit is dispensable for the assembly of functional GABA(A) r eceptors but is required for normal channel conductance and the format ion of BZ sites in vivo, BZ sites are not essential for embryonic deve lopment, as suggested by the normal body weight and histology of newbo rn mice. Postnatally, however, the reduced GABA(A) receptor function i s associated with retarded growth, sensorimotor dysfunction, and drast ically reduced life-span, The lack of postnatal GABA(A) receptor regul ation by endogenous ligands of BZ sites might contribute to this pheno type.