Mechanisms of Induction and Expression of Long-Term Depression at GABAergic Synapses in the Neonatal Rat Hippocampus

Abstract

Synaptic plasticity at excitatory glutamatergic synapses is believed to be instrumental in the maturation of neuronal networks. Using whole-cell patch-clamp recordings, we have studied the mechanisms of induction and expression of long-term depression at excitatory GABAergic synapses in the neonatal rat hippocampus (LTD_GABA-A). We report that the induction of LTD_GABA-A requires a GABA_A receptor-mediated membrane depolarization, which is necessary to remove the Mg²⁺ block from postsynaptic NMDA receptors. LTD_GABA-A is associated with an increase in the coefficient of variation of evoked GABA_A receptor-mediated synaptic currents and a decrease in the frequency, but not amplitude, of Sr²⁺-induced asynchronous GABA_A quantal events. We conclude that LTD_GABA-A induction requires the activation of both GABA_A and NMDA postsynaptic receptors and that its expression is likely presynaptic.