Actions of norepinephrine in the rat hippocampus

Acting at postsynaptic α₁- and β₁-receptors, norepinephrine (NE) exerts a complex action in rat hippocampus. It is currently believed that β₁-receptor activation enhances excitability of recorded neurons, whereas α₁ activation suppresses reactivity to afferent stimulation. These reported effects of α-agonists are not consistent with α₁ effects found elsewhere in the brain. We have conducted experiments in the anesthetized rat and found that an amphetamine-induced increase in the dentate gyrus population spike can be blocked by a β-antagonist but also by an α₁-antagonist. We have conducted experiments in the brain slide preparation and found that an α-agonist, phenylephrine (PHE), selectively enhances responses to N-methyl-D-aspartate (NMDA) but not to quisqualate. We propose that the product of activation of both α- and β-receptor types will enhance reactivity of hippocampal cells to afferent stimulation.