We examined the effects of GABA(B) receptor activation in the dentate
gyrus of hippocampal slices prepared from 6-8-day-old rat pups. Baclof
en (0.25-1.0 mu M), a GABA(B) agonist, rapidly and potently disinhibit
ed the developing dentate, similar to its effect in the mature organis
m. CGP 35348, a GABA(B) antagonist, quickly reversed the baclofen-indu
ced disinhibition. However, GABA(B) antagonists did not reverse long-l
atency (500-1000 ms IPI) paired-pulse depression, suggesting that it i
s not caused by a late GABA(B)-mediated IPSP. GABA(B)-mediated disinhi
bition of the dentate gyrus can occur by postnatal day 6, providing a
powerful mechanism for altering excitability in the developing hippoca
mpus.