Neurons containing orexin in the lateral hypothalamic area of the adult rat brain are activated by insulin-induced acute hypoglycemia

Orexin-A and -B (also known as hypocretin-1 and -2) are neuropeptides which stimulate food intake when administered intracerebroventricularly. Orexins are specifically localized in neurons within and around the lateral hypoth alamic area (LHA). Previous electrophysiological studies have demonstrated that some neurons in the LHA are activated by hypoglycemia, and are therefo re termed 'glucose-sensitive neurons'. In the present study, we examined wh ether orexin-containing neurons are activated in the hypoglycemic states, u sing Fos-like immunoreactivity (FLI) as a marker of neuronal activation. We observed that FLI was induced in the LHA by acute insulin treatment. Doubl e staining with anti-fos and anti-orexin antibodies revealed that up to 33% of the orexin-containing neurons in the LHA also expressed FLI under the h ypoglycemic condition. These results suggest that some populations of neuro ns which contain orexins are activated under hypoglycemic conditions. (C) 1 999 Published by Elsevier Science Ireland Ltd. All rights reserved.