Insulin-induced hypoglycemia increases preprohypocretin (orexin) mRNA in the rat lateral hypothalamic area

The recent identification of two peptides named hypocretins (Hcrt), and exp ressed in neurons of the rat tuberal lateral hypothalamus (LHA) previously detected by an ovine prolactin antiserum, led us to revisit some experiment al procedures intented to understand the physiological roles of these neuro ns. In the present study, rats received intraperitoneal injections of insul in and/or glucose. Immunocytochemical observations and quantitation of in s itu hybridization signals pointed out a clear stimulation of Hcrt neurons f ollowing the sole injection of insulin in hypoglycemic but not in hyperglyc emic conditions. This result, together with the robust appetite boosting ef fect of Hcrt reported elsewhere, suggests the involvement of Hcrt neurons i n the control of food intake. (C) 1999 Elsevier Science Ireland Ltd. All ri ghts reserved.