Whole-cell patch study of GABAergic inhibition in CA1 neurons of immature rat hippocampal slices

Abstract

Inhibitory processes mediated by γ-aminobutyric acid (GABA) were studied in immature rat hippocampal slices using the whole-cell patch clamp technique. Orthodromically evoked hyperpolarizing inhibitory postsynaptic potentials (IPSPs) were observed in CA1 neurons of postnatal 2–5 (P2–5) and 7–13 (P7–13) day old rats under conditions of low internal [Cl −]. In the whole-cell voltage-clamp mode, applications of GABA evoked outward currents which reversed at −55 mV and −62 mV in P2–5 and P7–13 CA1 neurons, respectively, with comparable reversal potentials for the IPSPs for each age. An increase of internal [Cl −] caused a depolarizing shift of the GABA reversal potential which followed the Nernst equation. In both groups of neurons, the IPSPs and GABA currents were blocked with the bath applications of bicuculline (10 μM) and picrotoxin (100 μM). We conclude that the GABA A-mediated inhibitory synaptic process exists in P2–5 CA1 neurons and hypothesize that the absence of such IPSPs noted in previous studies of immature CA1 neurons was likely due to higher internal [Cl −] in the more immature neurons.