EXCITATORY SYNAPTIC RESPONSES MEDIATED BY GABA(A) RECEPTORS IN THE HIPPOCAMPUS

Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the cortex. Activation of postsynaptic GABA(A) receptors hyperpolarizes cells and inhibits neuronal activity. Synaptic responses mediated by GABA(A) receptors also strongly excited hippocampal neurons. This excitatory response was recorded in morphologically identified interneurons in the presence of 4-aminopyridine or after elevation of extracellular potassium concentrations. The synaptic excitation sustained by GABA(A) receptors synchronized the activity of inhibitory interneurons. This synchronized discharge of interneurons in turn elicited large-amplitude inhibitory postsynaptic potentials in pyramidal and granule cells. Excitatory synaptic responses mediated by GABA(A) receptors may thus provide a mechanism for the recruitment of GABAergic interneurons through their recurrent connections.