MINERALOCORTICOID RECEPTOR-MEDIATED ENHANCEMENT OF NEURONAL EXCITABILITY AND SYNAPTIC PLASTICITY IN THE DENTATE GYRUS IN-VIVO IS DEPENDENT ON THE BETA-ADRENERGIC ACTIVITY

The dentate gyrus neurons in the hippocampus contain a high density of both mineralocorticoid and adrenergic receptors, By in vivo extracell ular recording from adrenalectomized rats we investigated the possible relationships between the two systems with regard to neuronal excitab ility and activity-dependent synaptic plasticity, Pretreatment with al dosterone significantly enhanced both basal neuronal excitability and tetanically evoked synaptic plasticity in adrenalectomized, but not sh am-operated rats, The enhancement was blocked by spironolactone, indic ating a mineralocorticoid receptor-dependent effect. The adrenomedulla ry hormone epinephrine also significantly enhanced synaptic plasticity via activation of beta-adrenergic receptors, P-Adrenergic antagonist propranolol, infused directly into the dentate gyrus granule cell laye r, significantly reduced the effect of aldosterone on neuronal excitab ility and partly canceled the aldosterone-enhanced synaptic plasticity , No effect of propranolol was found after its amygdaloid infusion, Th e mineralocorticoid receptor antagonist spironolactone did not affect the epinephrine-induced effects. These results indicate that the pretr eated adrenal steroids interact with the catecholaminergic system in t he dentate gyrus of adrenalectomized rats and that the functional beta -adrenergic pathway is involved in the mechanism of mineralocorticoid- induced cellular effects in vivo. (C) 1998 Wiley-Liss, Inc.