Antagonistic effects of aldosterone on corticosterone-mediated changes in exploratory behavior of adrenalectomized rats.

The effect of aldosterone administration on exploratory activity of chronic adrenalectomized (10 days) male rats was investigated. Aldosterone (30 micrograms/100 g body wt sc) administered 1 hr or 30 min prior to the behavioral test failed to normalize disturbed exploratory activity of adrenalectomized rats, in contrast to the restoration observed after corticosterone, the naturally occurring glucocorticoid of the rat. Administration of the mineralocorticoid 30 min prior to corticosterone prevented the normalization of the behavioral response by the latter steroid. Administration of the same dose of aldosterone 30 min prior to a tracer amount of [3H]corticosterone effectively blocked cell nuclear uptake of radioactive-labeled hormone in the hippocampus. The specific action of corticosterone on exploratory behavior corresponds with the stringent specificity of the neuronal hippocampal corticosterone receptor system. Mineralocorticoid receptors do not seem to be involved in effects on this behavior. The antagonistic action of aldosterone is probably exerted by competitive binding to the corticosterone receptor.