Hypothalamic control of feeding behavior in the thirteen-lined ground squirrel

Abstract

The thirteen-lined ground squirrel (Ictidomys tridecemlineatus) undergoes natural, extreme changes in feeding behavior, including a six-month fast during hibernation. In the spring and summer, ground squirrels become hyperphagic by increasing food intake for fat storage during hibernation. Immediately before hibernation, they decrease food intake and become hypophagic. The reverse process occurs after hibernation. mRNA expression in the hypothalamus of the brain during the fall feeding transition in the ground squirrel showed increased orexigenic expression during hyperphagia and decreased expression during hypophagia (Schwartz, Hampton, & Andrews, 2015). However, protein expression is not known. Orexigenic protein expression of mRNA targets that are interesting to human health include neuropeptide Y (NPY) and orexin A. We used immunohistochemistry to detect NPY and orexin A protein expression levels over hyperphagic, fall hypophagic, interbout arousal (during hibernation), and spring hypophagic transitions. c-fos, a marker for neuronal activity, was used to determine active areas of the hypothalamus during feeding transitions. Coverage and cell count revealed increased NPY and orexin A expression during periods of hyperphagia and complementary to this, increased c-fos expression in lateral hypothalamic neurons during hyperphagia. This suggested that orexin A is a key player in feeding control of the ground squirrel, particularly during hyperphagia.