Corticosteroid modulation of hippocampal potentials: increased effect with aging.

Adrenal steroids bind specifically to hippocampal neurons under normal conditions and may contribute to hippocampal cell loss during aging, but little is known about the neurophysiological mechanisms by which they may change hippocampal cell functions. In the present studies, adrenal steroids have been shown to modulate a well-defined membrane conductance in hippocampal pyramidal cells. The calcium-dependent slow afterhyperpolarization is reduced in hippocampal slices from adrenalectomized rats, and it is increased after in vivo or in vitro administration of the adrenal steroid, corticosterone. Calcium action potentials are also reduced in adrenalectomized animals, indicating that the primary effect of corticosteroids may be on calcium conductance. The afterhyperpolarization component reduced by adrenalectomy is greater in aged rats than in young rats, suggesting that, with aging, there is an increased effect of corticosteroids on some calcium-mediated brain processes. Because elevated concentrations of intracellular calcium can be cytotoxic, these observations may increase the understanding of glucocorticoid involvement in brain aging as well as of the normal functions of these steroids in the brain.