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

Abstract

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. β-receptors mediate exogenous NE potentiation in vitro, while α-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 μg [±] NE in 2 μl of 0.9% saline i.c.v. Long-term potentiation occurred with higher doses of NE. The β-agonist isoproterenol and the α-agonist phenylephrine also produced potentiation. Long-term effects were common with isoproterenol. The β-antagonist metoprolol and the α-antagonist phentolamine attenuated NE potentiation. The results suggest that both α- and β-receptors could play a role in NE potentiation in dentate gyrus in vivo. In awake animals, 10 μg NE i.c.v. reproduced the potentiation pattern seen in anesthetized rats. NE potentiation in awake rats was independent of behavioral variation.