Orexin and psychiatric disorders

Orexin-A and Orexin-B (also known as hypocretin 1 and 2) are, respectively, 33and 28-amino acid residue peptides that activate a G-protein-coupled ‘orphan’ receptor, i.e. which has no known ligand.1 Immuno-cytochemical studies show that orexin-positive neurons are located in the lateral hypothalamic area and arcuate and perifornical nuclei.2 They are also found in various sites beyond the hypothalamus such as the thalamic paraventricular and reuniens nuclei, locus coeruleus, nucleus of the solitary tract, raphe and septal nuclei.