Effects of corticosteroids on synaptic transmission in rat dorsolateral septal nucleus

The effects of corticosteroids on synaptic transmission in the rat dorsolateral septal nucleus (DLSN) were examined, in vitro, by using intracellular and voltage-clamp recording methods. Prednisolone (100 microM) increased the amplitude of excitatory postsynaptic potential (EPSP) and depressed both fast and slow inhibitory postsynaptic potentials (IPSP). Under voltage-clamp conditions, prednisolone (100 microM) increased the amplitude of excitatory postsynaptic current (EPSC) and depressed the fast and slow inhibitory postsynaptic currents (IPSCs). Corticosterone (100 microM) mimicked the effects of prednisolone on the postsynaptic currents (PSCs). To examine the direct effects of prednisolone on the EPSC and slow IPSC, the fast IPSC was blocked by bicuculline (20 microM). Under these experimental conditions, prednisolone (100 microM) did not alter the isolated EPSC but depressed slow IPSC by 22 +/- 3% (n = 10). The fast IPSC was isolated by pretreatment with kynurenic acid and CGP55845A, where the EPSC and slow IPSC were blocked. Prednisolone (100 microM) depressed the isolated fast IPSC in DLSN neurons. Prednisolone (100 microM) did not change either the inward current produced by glutamate or the outward current produced by gamma-aminobutyric acid (GABA). The results suggest that corticosteroids facilitate excitatory synaptic transmission in the DLSN by reducing the release of GABA from the presynaptic nerve terminals of interneurons.