CORTICOSTERONE-INDUCED DECREASE OF INHIBITORY POSTSYNAPTIC POTENTIALSIN RAT HIPPOCAMPAL PYRAMIDAL NEURONS IN-VITRO DEPENDS ON CYTOSOLIC FACTORS

Previous studies using high-resistance sharp electrodes demonstrated t hat corticosterone (CORT) reduced GABAergic synaptic inhibition in CA1 neurons of the rat hippocampus in vitro. In the present study we used whole-cell gigaseal recordings to investigate the possible role of cy tosolic factors in the transduction mechanism underlying this action. The perturbation of the intracellular milieu that occurs under these r ecording conditions abolished the CORT-induced decrease in inhibitory postsynaptic conductance. CORT actually increased GABA(A) receptor-med iated conductances in about 50% of the neurons rested when the whole-c ell recording mode was employed. As in the high-resistance microelectr ode studies, CORT did not change the resting membrane potential, actio n potential amplitude or input resistance. The results suggest that th e reduction of GABAergic synaptic inhibition in hippocampal CA1 pyrami dal neurons induced by CORT critically depends on the presence of cyto solic factors, which wash out during whole-cell gigaseal recordings.