THE DENSITY OF GABA-B BINDING-SITES IN THE SUBSTANTIA-NIGRA IS GREATER IN RAT PUPS THAN IN ADULTS

Baclofen-displaced [H-3]GABA (gamma-aminobutyric acid) binding to GABA(B) sites was assayed in brain regions obtained from adult and 14- to 17-day-old rats. Thc substantia nigra of rat pups exhibited a 3- to 5-fold higher density (B(max)) of GABA(B) binding sites than thc nigra of adult rats. In contrast, the density of GABA(B) sites was lower in hippocampal and cerebellar tissue from pups. both approximately two-thirds the density in corresponding adult structures. This anatomically selective overproduction of GABA(B) receptors in immature substantia nigra is consistent with the increased anticonvulsant efficacy of the GABA(B) agonist baclofen observed in rat pups.