INTRACEREBROVENTRICULAR NOREPINEPHRINE POTENTIATION OF THE PERFORANT PATH-EVOKED POTENTIAL IN DENTATE GYRUS OF ANESTHETIZED AND AWAKE RATS - A ROLE FOR BOTH ALPHA-ADRENOCEPTOR AND BETA-ADRENOCEPTOR ACTIVATION

Norepinephrine (NE) applied iontophoretically to the dentate gyrus in vivo, and bath applied to hippocampal slices in vitro, produces potent iation of the perforant path-evoked potential. beta-receptors mediate exogenous NE potentiation in vitro, while alpha-receptors are implicat ed in exogenous effects in vivo. The present study uses intracerebrove ntricular (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 dose s of NE. The beta-agonist isoproterenol and the alpha-agonist phenylep hrine also produced potentiation. Long-term effects were common with i soprote-renol. The beta-antagonist metoprolol and the a-antagonist phe ntolamine attenuated NE potentiation. The results suggest that both al pha- and beta-receptors could play a role in NE potentiation in dentat e gyrus in vivo. In awake animals, 10 mu g NE i.c.v. reproduced the po tentiation pattern seen in anesthetized rats. NE potentiation in awake rats was independent of behavioral variation. (C) 1998 Elsevier Scien ce B.V.