Behavioral role of orexin-A in the amygdaloid body

Abstract

Lateral hypothalamic orexin neurons project widely through the neuroaxis. One of their target areas is the extended amygdala. We studied the effects of intraamygdalar orexin-A (OXA) microinjections on food and water intake, and emotion- and learning-related behaviors in rats. Bilateral administration of OXA into the intraamygdaloid division of the bed nucleus of stria terminalis (BSTIA) enhanced food and water intake which were blocked by a selective orexin-1 receptor (OX1R) antagonist. In elevated plus maze test (EPM) the time spent on open arms was increased after OXA administration. In EPM and open field tests general motor activity was not changed. In the passive avoidance test OXA increased the transfer latency indicating its enhancing effect on avoidance learning. Analgesic effects of OXA were not found in the hot plate test. We provided evidences for the complex functions of OXA in the BSTIA on food and water intake mediated via OX1Rs, on decrease of anxiety, and on avoidance learning which is supposed to be due to anxiolysis. These data indicate the functional heterogeneity of OXA on feeding behavior, emotion- and learning-related mechanisms. Supported by 21st Century COE program and Grants-in-Aid for Scientific Research (S.A.), NKTH-RET-008/2005 MEDIPOLIS, ETT317/2006, NKTH-OTKA K68431 and HAS (L.L.). [J Physiol Sci. 2008;58 Suppl:S148]