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 gl utamatergic activity, This inhibition is achieved by a membrane hyperp olarization through the activation of postsynaptic gamma-aminobutyric acid(A) (GABA(A)) and GABA(B) receptors, In addition, GABA also depres s transmitter release acting through presynaptic GABA(B) receptors, De spite the wealth of data regarding the role of GABA in regulating the degree of synchronous activity in the adult, little is known about GAB A transmission during early stages of development. In the following we report that GABA mediates most of the excitatory drive at early stage s of development in the hippocampal CA3 region, Activation of GABA(A) receptors induces a depolarization and excitation of immature CA3 pyra midal neurons and increases intracellular Ca2+ ([Ca2+](i))] during the first postnatal week of life, During the same developmental period, t he postsynaptic GABA(B)-mediated inhibition is poorly developed, In co ntrast, the presynaptic GABAB-mediated inhibition is well developed at birth and plays a crucial role in modulating the postsynaptic activit y by depressing transmitter release at early postnatal stages, We have also shown that GABA plays a trophic role in the neuritic outgrowth o f cultured hippocampal neurons. (C) 1995 John Wiley & Sons, Inc.