Effects of whisker trimming on GABA A receptor binding in the barrel cortex of developing and adult rats

Both sensory deprivation and blockade of γ‐aminobutyric acid A (GABA A ) receptors result in signs of cortical disinhibition. To investigate whether down‐regulation of GABA A receptors could underlie effects of sensory deprivation, [ 3 H]muscimol binding was assessed in rat whisker barrels after chronic whisker trimming. Vibrissae in row C or rows A,B,D, and E were trimmed during certain developmental periods. When whiskers were trimmed for the first 6 postnatal weeks, [ 3 H]muscimol binding was 8.3% lower in deprived barrel rows than in adjacent nondeprived rows ( P < 0.001). The effect may be somewhat selective for GABA A receptors because there was no evident change in N ‐methyl‐D‐aspartate (NMDA) receptors as indicated by [ 3 H]MK‐801 binding. Ten weeks after whiskers were allowed to regrow, the decrease in [ 3 H]muscimol binding was partly reversed ( P < 0.002), leaving a 3.3% decrease ( P < 0.001). These declines in GABA A receptors could contribute to persisting electrophysiological signs of reduced inhibition in similarly deprived barrel neurons (Simons and Land [1987] Nature 326 :694–697). A 6‐week deprivation beginning in adulthood resulted in a 7.7% decrease ( P < 0.001), indicating that the effect is not restricted to an early critical period. In rats trimmed for the first 10 postnatal days, [ 3 H]muscimol binding declined 2.3% ( P < 0.05), which is a small change compared with the magnitude of the developmental peak; thus, normal whisker input apparently is not required for the developmental increase in GABA A receptors. The present study suggests that sensory input can regulate cortical GABA A receptors in adulthood and during ontogeny. Down‐regulation of cortical GABA A receptors may be a compensatory mechanism that serves to disinhibit the reduced sensory input. J. Comp. Neurol. 395:209–216, 1998. © 1998 Wiley‐Liss, Inc.