Intracerebroventricular norepinephrine potentiation of the perforant path-evoked potential in dentate gyrus of anesthetized and awake rats:: A role for both α- and β-adrenoceptor activation

Norepinephrine (NE) applied iontophoretically to the dentate gyrus in vivo, and bath applied to hippocampal slices in vitro, produces potentiation of the perforant path-evoked potential. beta-receptors mediate exogenous NE potentiation in vitro, while alpha-receptors are implicated in exogenous effects in vivo. The present study uses intracerebroventricular (i.c.v.) NE to mimic in vitro bath conditions in vivo. Short-term NE potentiation was reliably seen with 10 mu g[+/-]NE in 2 mu l of 0.9% saline i.c.v. Long-term potentiation occurred with higher doses of NE. The beta-agonist isoproterenol and the alpha-agonist phenylephrine also produced potentiation. Long-term effects were common with isoprote-renol. The beta-antagonist metoprolol and the a-antagonist phentolamine attenuated NE potentiation. The results suggest that both alpha- and beta-receptors could play a role in NE potentiation in dentate gyrus in vivo. In awake animals, 10 mu g NE i.c.v. reproduced the potentiation pattern seen in anesthetized rats. NE potentiation in awake rats was independent of behavioral variation. (C) 1998 Elsevier Science B.V.