Corticosterone time-dependently modulates β-adrenergic effects on long-term potentiation in the hippocampal dentate gyrus

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Abstract
Previous experiments in the hippocampal CA1 area have shown that corticosterone can facilitate long-term potentiation (LTP) in a rapid non-genomic fashion, while the same hormone suppresses LTP that is induced several hours after hormone application. Here, we elaborated on this finding by examining whether corticosterone exerts opposite effects on LTP depending on the timing of hormone application in the dentate gyrus as well. Moreover, we tested rapid and delayed actions by corticosterone on β-adrenergic-dependent changes in LTP. Unlike the CA1 region, our in vitro field potential recordings show that rapid effects of corticosterone do not influence LTP induced by mild tetanization in the hippocampal dentate gyrus, unless GABAA receptors are blocked. In contrast, the β-adrenergic agonist isoproterenol does initiate a slow-onset, limited amount of potentiation. When corticosterone was applied concurrently with isoproterenol, a further enhancement of synaptic strength was identified, especially during the early stage of potentiation. Yet, treatment with corticosterone several hours in advance of isoproterenol fully prevented any effect of isoproterenol on LTP. This emphasizes that corticosterone can regulate β-adrenergic modulation of synaptic plasticity in opposite directions, depending on the timing of hormone application.