In anesthetized kittens (< 1 to 24 days old), the effects of GABA(A) r
eceptor antagonism on phrenic, hypoglossal and cervical sympathetic di
scharges were examined by i.v. bicuculline infusions during hyperoxia
and hypoxia. Administration of bicuculline during hyperoxia produced m
arked increases in the amplitudes of inspiratory nerve discharges. Dur
ing hypoxic stimulation (10% O2), the amplitudes of inspiratory activi
ties decreased towards or below those observed during hyperoxia; bicuc
ulline reversed this depression and restored inspiratory discharges. O
ur results indicated that GABA(A) receptors were functional shortly af
ter birth, acting to mediate influences shaping inspiratory activity d
uring hyperoxic breathing and during conditions of increased chemical
drive.