The effect of food deprivation and experimental diabetes on orexin and NPY mRNA levels.

Although exogenous orexin can induce feeding, reports of increased orexin gene expression after caloric manipulations have been inconsistent. We hypothesized that orexin gene expression is increased only by extreme negative energy balance challenges. We measured hypothalamic orexin and NPY mRNA by in situ hybridization and orexin-A immunoreactivity in rats after food deprivation, streptozotocin-induced diabetes, and combined deprivation and diabetes. Neither food deprivation, nor diabetes, nor the combination affected orexin mRNA levels, although orexin-A immunoreactivity was increased by diabetes. NPY mRNA levels were increased by either treatment. These results suggest that increased orexin gene expression is not a consistent correlate of negative energy balance challenges.