Small synthetic molecules called growth-hormone secretagogues (GHSs) stimulate the release of growth hormone (GH) from the pituitary. They act through GHS-R, a G-protein-coupled receptor for which the ligand is unknown. Recent cloning of GHS-R strongly suggests that an endogenous ligand for the receptor does exist and that there is a mechanism for regulating GH release that is distinct from its regulation by hypothalamic growth-hormone-releasing hormone (GHRH). We now report the purification and identification in rat stomach of an endogenous ligand specific for GHS-R. The purified ligand is a peptide of 28 amino acids, in which the serine 3 residue is n-octanoylated. The acylated peptide specifically releases GH both in vivo and in vitro, and O-n-octanoylation at serine 3 is essential for the activity. We designate the GH-releasing peptide 'ghrelin' (ghre is the Proto-Indo-European root of the word 'grow'). Human ghrelin is homologous to rat ghrelin apart from two amino acids. The occurrence of ghrelin in both rat and human indicates that GH release from the pituitary may be regulated not only by hypothalamic GHRH, but also by ghrelin.

were unable to use this method for one of 41 sites, since the responses were too small. For this site, the onset of eye movements was detected visually.For each condition and each stimulation site, the gain of the responses to the perturbations was computed as the square root of E divided by T, where E is the area within the polygon de®ned by the polar plot for each set of eight perturbations in different directions, and T is the area within the polygon de®ned by the peak target velocity, always 282.84.

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We determined the immunohistochemical distributions of orexin-A and orexin-B, hypothalamic peptides that function in the regulation of feeding behavior and energy homeostasis. Orexin-A and -B neurons were restricted to the lateral and posterior hypothalamus, whereas both orexin-A and -B nerve fibers projected widely into the olfactory bulb, cerebral cortex, thalamus, hypothalamus, and brainstem. Dense populations of orexin-containing fibers were present in the paraventricular thalamic nucleus, central gray, raphe nuclei, and locus coeruleus. Moderate numbers of these fibers were found in the olfactory bulb, insular, infralimbic and prelimbic cortex, amygdala, ventral, and dorsolateral parts of the suprachiasmatic nucleus, paraventricular nucleus except the lateral magnocellular division, arcuate nucleus, supramammillary nucleus, nucleus of the solitary tract, and dorsal motor nucleus of the vagus. Small numbers of orexin fibers were present in the perirhinal, motor and sensory cortex, hippocampus, and supraoptic nucleus, and a very small number in the lateral magnocellular division of the paraventricular nucleus. Intracerebroventricular injections of orexins induced c-fos expression in the paraventricular thalamic nucleus, locus coeruleus, arcuate nucleus, central gray, raphe nuclei, nucleus of the solitary tract, dorsal motor nucleus of the vagus, suprachiasmatic nucleus, supraoptic nucleus, and paraventricular nucleus except the lateral magnocellular division. The unique neuronal distribution of orexins and their functional activation of neural circuits suggest specific complex roles of the peptides in autonomic and neuroendocrine control.The lateral hypothalamus (LH) is a region classically implicated in the central regulation of feeding behavior and energy homeostasis (1-3). Feeding behavior is regulated by a large number of substances, including peptides, whereas, until the discovery of orexins, melanin-concentrating hormone (MCH) was the only neuropeptide known to be synthesized specifically in the LH and zona incerta and to stimulate food intake (4, 5). Very recently, two novel hypothalamic peptides named orexin-A and orexin-B (from the Greek word for appetite, orexis) were discovered in an intracellular calcium influx assay on multiple cells expressing individual ''orphan'' G proteincoupled receptors (6). Orexin-A is a 33-residue peptide with two intramolecular disulfide bonds in the N-terminal region, and orexin-B is a linear 28-residue peptide. These peptides, encoded by a single mRNA transcript, have a 46% amino acid sequence identity. This mRNA also was found in rat hypothalamus by another group of researchers using the directional tag PCR subtraction method (7). Bolus injections of orexin-A and -B to rat lateral ventricle stimulated food intake dose dependently (6). prepro-orexin mRNA was restricted to the LH and adjacent areas, and its mRNA level up-regulated on fasting (6). Orexins therefore are thought to participate in the hypothalamic regulation of feeding behavior. Better understanding...