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

The recent identification of two peptides named hypocretins (Hcrt), and expressed in neurons of the rat tuberal lateral hypothalamus (LHA) previously detected by an ovine prolactin antiserum, led us to revisit some experimental procedures intented to understand the physiological roles of these neurons. In the present study, rats received intraperitoneal injections of insulin and/or glucose. Immunocytochemical observations and quantitation of in situ hybridization signals pointed out a clear stimulation of Hcrt neurons following the sole injection of insulin in hypoglycemic but not in hyperglycemic conditions. This result, together with the robust appetite boosting effect of Hcrt reported elsewhere, suggests the involvement of Hcrt neurons in the control of food intake.