The effect of intracerebroventricular norepinephrine on dentate gyrus evoked potentials in anaesthetized and awake, behaving rats

Chaulk, Paul Cyril (1994) The effect of intracerebroventricular norepinephrine on dentate gyrus evoked potentials in anaesthetized and awake, behaving rats. Masters thesis, Memorial University of Newfoundland.

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Abstract

Exogenous application of norepinephrine (NE) or stimulation of endogenous NE release has been shown to potentiate the perforant path-evoked dentate gyrus population spike (popspike). In vitro studies (Lacaille and Harley, 1985) suggest beta receptor mediation of the enhancement. In contrast, an in vivo study (Winson and Dahl, 1985) implicates alpha receptors. The present study utilizes intracerebroventricular (icv) administration of NE (1, 10, 50, 100 μg) as well as alpha and beta agonists and antagonists in urethane-anaesthetized rats in order to examine in vitro-like bath application conditions in the intact preparation. The effect of icv NE was also assessed in awake, behaving animals. In the anaesthetized rat, NE as well as the beta agonist isoproterenol reliably potentiated the population spike (popspike) amplitude. The alpha agonist phenylephrine potentiated the popspike in a majority of experiments. The icv-induced enhancement was frequently long-lasting for the beta agonist isoproterenol and higher doses of NE (50, 100 μg). Both alpha (phentolamine) and beta (metoprolol) antagonists blocked the NE induced potentiation in a majority of experiments. However, only the alpha antagonism was significant. EPSP slope changes were inconsistent. NE (10 μg) produced a potentiation in the awake, behaving rat which was virtually indistinguishable from that obtained with the same dose in the anaesthetized preparation. These results suggest that the icv methodology is a reliable method of producing popspike potentiation by exogenous NE applicaiton in vivo. Secondly, the results suggest a possible role for alpha as well as beta receptors in the NE potentiation effect in the dentate gyrus. Finally, the results extend the finding of NE induced potentiation to exogenously applied NE in the awake animal.

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