Corticosteroid actions on amino acid-mediated transmission in rat CA1 hippocampal cells

We here describe actions mediated by mineralo- and glucocorticoid receptors (MRs and GRs, respectively) on intracellularly recorded synaptic responses, evoked in rat CA1 pyramidal cells in vitro by stimulation of the Schaffer collaterals. Neurons in slices from adrenalectomized (ADX) rats, that is, where MRs and GRs are unoccupied, showed a synaptic response consisting of an EPSP, followed by a fast and a slow IPSP; the responses were apparently similar to those in slices from sham-operated rats. However, in the ADX rats, repeated electrical stimulation over a period of 80 min resulted in a gradual decline of the firing probability for synaptically driven action potentials and of the slow IPSP amplitude. Nonsynaptic responses (e.g., membrane potential, accommodation, and afterhyperpolarization) were stable during the 80 min period. Application of 3 nM aldosterone between 20 and 40 min after impalement of cells in slices from ADX rats, thus activating predominantly MRs, yielded stable synaptic and nonsynaptic responses for at least 1 hr after the onset of the steroid application. By contrast, corticosterone (30 nM), which occupies GRs in addition to MRs, reduced the amplitude of both the EPSP and slow IPSP, and the firing probability of synaptically driven action potentials, within 20 min; nonsynaptic properties remained stable. Similar results were obtained with the selective glucocorticoid RU 28362. The EPSP and fast and slow IPSPs of neurons in slices from ADX rats impaled with a time lag of 1-4 hr after the steroid application did not differ significantly from the responses of neurons impaled before steroid application.(ABSTRACT TRUNCATED AT 250 WORDS)