Orexins/hypocretins in the ob/ob mouse: hypothalamic gene expression, peptide content and metabolic effects.
Orexins (forms A and B) belong to a new family of peptides that, as neuropeptide Y (NPY), stimulate food intake when centrally injected. The ob/ob mouse is a well-characterized model of hyperphagia and obesity associated with strong metabolic disturbances and a central dysregulation of peptides involved in the control of feeding. In the present report, we investigated the hypocretin (Hcrt)/orexin (OX) peptide pathway in lean and ob/ob mice. Prepro-Hcrt/OX mRNA expression, measured by in situ hybridization was restricted to the lateral hypothalamus area. It was significantly decreased in ob/ob mice (-18%; p<0.01). When estimated by real time RT-PCR in the whole hypothalamus, this decrease amounted to 65% (p<0.001). Hcrt-1/OX-A peptide concentrations, measured by RIA in microdissected hypothalamic nuclei were high in the lateral hypothalamus (LH) and lower in the arcuate (ARC) and paraventricular nuclei (PVN). In ob/ob mice, OX-A levels were significantly lower than in lean mice in the LH (-34%; p<0.02) and in the PVN (-72%; p<0.005). Acute intracerebroventricular injection of Hcrt-1/OX-A (1-10 nmol) stimulated feeding in lean, but not in ob/ob mice, whereas Hcrt-2/OX-B (1-10 nmol) had the opposite effect. Acute third ventricle (i3vt) injections of Hcrt/OX peptides in ob/ob mice transiently increased their metabolic rate and stimulated lipid substrate utilization. These findings provide direct evidence that Hcrt/OX peptides are down-regulated in the hypothalamus of ob/ob mice, contrary to the NPY system. The present data argues that Hcrt/OX peptides are not primarily responsible for the metabolic syndrome of the ob/ob mice. The diminution in the OX tone might participate in a counterregulatory system necessary to limit the adverse effects of NPY on food intake and body weight.
Stricker-Krongrad
Alain
A
Metabolic Diseases Physiology Department, Millennium Pharmaceuticals 75 Sidney Street, MA 02139, USA.
Richy
Sébastien
S
Beck
Bernard
B
D000818:Animals; D002352:Carrier Proteins / Q000032:analysis* / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D004435:Eating; D004734:Energy Metabolism; D005247:Feeding Behavior; D015870:Gene Expression; D007026:Hypothalamic Area, Lateral / Q000378:metabolism*; D017403:In Situ Hybridization; D007276:Injections, Intraventricular / Q000379:methods; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D009478:Neuropeptide Y / Q000032:analysis; D009479:Neuropeptides / Q000032:analysis* / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D009765:Obesity / Q000378:metabolism*; D000068797:Orexins; D012333:RNA, Messenger / Q000096:biosynthesis; D011863:Radioimmunoassay / Q000379:methods; D020133:Reverse Transcriptase Polymerase Chain Reaction
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009478:Neuropeptide Y; D009479:Neuropeptides; D000068797:Orexins; D012333:RNA, Messenger