Orexin‐A increases the firing activity of hippocampal CA1 neurons through orexin‐1 receptors

Orexins including two peptides, orexin‐A and orexin‐B, are produced in the posterior lateral hypothalamus. Much evidence has indicated that central orexinergic systems play numerous functions including energy metabolism, feeding behavior, sleep/wakefulness, and neuroendocrine and sympathetic activation. Morphological studies have shown that the hippocampal CA1 regions receive orexinergic innervation originating from the hypothalamus. Positive orexin‐1 (OX1) receptors are detected in the CA1 regions. Previous behavioral studies have shown that microinjection of OX1 receptor antagonist into the hippocampus impairs acquisition and consolidation of spatial memory. However, up to now, little has been known about the direct electrophysiological effects of orexin‐A on hippocampal CA1 neurons. Employing multibarrel single‐unit extracellular recordings, the present study showed that micropressure administration of orexin‐A significantly increased the spontaneous firing rate from 2.96 ± 0.85 to 8.45 ± 1.86 Hz (P