Orexin A immunoreactivity and prepro-orexin mRNA in the brain of Zucker and WKY rats

The primary role of the orexins was originally believed to be appetite regu lation. but is now believed to be the regulation of sleep, arousal and loco motor activity. Orexin A immunoreactivity (orexin A-IR) and prepro-orexin m RNA were measured in the CNS of obese and lean Zucker rats. There were no d ifferences in orexin A-IR or prepro-orexin mRNA levels between obese and le an Zucker rats. The orexins are therefore unlikely to be important in this model of obesity. Levels of orexin A-IR and prepro-orexin mRNA were measure d in the CNS of Wistar-Kyoto (WKY) rats, which are hypoactive and have abno rmal sleep architecture. Compared to Wistar rats, WKY rats had significantl y lower orexin A-IR (with differences of up to 100% in some brain regions) and prepro-orexin mRNA levels. These observations suggest that the sleep an d activity phenotype of the WKY strain may be related to orexin deficiency and that this strain may be a useful model of partial orexin deficiency. Ne uroReport 12:459-464 (C) 2001 Lippincott Williams & Wilkins.