Nonselective, high-affinity receptor for both orexin-A and orexin-B neuropeptides. Triggers an increase in cytoplasmic Ca(2+) levels in response to orexin-A binding. Expressed in the brain in the cerebral cortex, septal nuclei, hippocampus, medial thalamic groups, dorsal and median raphe nuclei, and many hypothalamic nuclei including the tuberomammillary nucleus, dorsomedial hypothalamus, paraventricular hypothalamic nucleus, and ventral premammillary nucleus. Not detected in the spleen, lung, liver, skeletal muscle, kidney and testis. Orexin receptor mRNA expression has also been reported in the adrenal gland, enteric nervous system, and pancreas. The N-terminal region is required for orexin signaling. Belongs to the G-protein coupled receptor 1 family.