Abstract
The orexins are lateral hypothalamic neurotransmitters acting in various sites of the central nervous system. The aim of the present series of experiments was to reveal whether orexin-A (OXA) in the bed nucleus of stria terminalis (BST) is involved in learning, anxiety, reinforcement and nociception. Bilateral OXA microinjections into the BST of male Wistar rats were performed in the doses of 250ng (70pmol) and 500ng (140pmol) 30 min prior to 1) open field (OPF), 2) elevated plus maze (EPM), 3) conditioned place preference (CPP), 4) passive avoidance (PAV) or 5) hot plate (HP) tests. In the EPM 500ng OXA increased the total time spent on the open arms and on the end of the open arms. Higher dose slightly increased the general motor activity in EPM and OPF. In the CPP, microinjection of lower dose increased the frequency of entering into the treatment quadrant. In the PAV, both doses decreased the retention time to enter the dark room dose-dependently. OXA did not alter pain sensation in HP. Our data show the functional heterogeneity of OXA in the BST, especially its effect on avoidance learning, which is supposed to be due to anxiolysis rather than analgesia. Supported by 21st Century COE program and Grants-in-Aid for Scientific Research (S.A.), NKTH-RET-008/2005 MEDIPOLIS, ETT 317/2006 and the HAS (L.L.). [J Physiol Sci. 2007;57 Suppl:S163]
