THE DEVELOPMENT OF GABA(B)-MEDIATED ACTIVITY IN THE RAT DENTATE GYRUS

We examined the effects of GABA(B) receptor activation in the dentate gyrus of hippocampal slices prepared from 6-8-day-old rat pups. Baclofen (0.25-1.0 mu M), a GABA(B) agonist, rapidly and potently disinhibited the developing dentate, similar to its effect in the mature organism. CGP 35348, a GABA(B) antagonist, quickly reversed the baclofen-induced disinhibition. However, GABA(B) antagonists did not reverse long-latency (500-1000 ms IPI) paired-pulse depression, suggesting that it is not caused by a late GABA(B)-mediated IPSP. GABA(B)-mediated disinhibition of the dentate gyrus can occur by postnatal day 6, providing a powerful mechanism for altering excitability in the developing hippocampus.