NMDA-DEPENDENT GABA(A)-MEDIATED POLYSYNAPTIC POTENTIALS IN THE NEONATAL RAT HIPPOCAMPAL CA3 REGION

Evoked inhibitory postsynaptic potentials (IPSPs) were studied in CA3 hippocampal neurons from brain slice preparations of rats ranging from 5 to 18 days of age (P5-18) using intracellular recording techniques. With KMeSO(4)-filled electrodes the evoked inhibitory response consisted of fast and slow IPSPs mediated by GABAA and GABAB receptors respectively. In recordings obtained with electrodes filled with 2-(triethylamino)-N(2,6-dimethylphenyl) acetamide and KMeSO(4), electrical stimulation evoked monophasic IPSPs in mature slices (P10-18) and biphasic IPSPs with an early and a late phase in neonatal slices (P4-7). In neonates both the early and late phases of the IPSP were mediated by GABA(A) receptors. Pharmacological investigation revealed that the early phase arose from both direct and feedforward activation of GABAergic interneurons involving non-NMDA receptors, while the late phase resulted from polysynaptic activation of GABAergic interneurons mediated by NMDA receptors.