POSTNATAL MATURATION OF GAMMA-AMINOBUTYRIC ACID(A AND B)-MEDIATED INHIBITION IN THE CA3 HIPPOCAMPAL REGION OF THE RAT

In the adult central nervous system, GABAergic synaptic inhibition is known to play a crucial role in preventing the spread of excitatory glutamatergic activity, This inhibition is achieved by a membrane hyperpolarization through the activation of postsynaptic gamma-aminobutyric acid(A) (GABA(A)) and GABA(B) receptors, In addition, GABA also depress transmitter release acting through presynaptic GABA(B) receptors, Despite the wealth of data regarding the role of GABA in regulating the degree of synchronous activity in the adult, little is known about GABA transmission during early stages of development. In the following we report that GABA mediates most of the excitatory drive at early stages of development in the hippocampal CA3 region, Activation of GABA(A) receptors induces a depolarization and excitation of immature CA3 pyramidal neurons and increases intracellular Ca2+ ([Ca2+](i))] during the first postnatal week of life, During the same developmental period, the postsynaptic GABA(B)-mediated inhibition is poorly developed, In contrast, the presynaptic GABAB-mediated inhibition is well developed at birth and plays a crucial role in modulating the postsynaptic activity by depressing transmitter release at early postnatal stages, We have also shown that GABA plays a trophic role in the neuritic outgrowth of cultured hippocampal neurons. (C) 1995 John Wiley & Sons, Inc.