Sex differences in feeding behavior

Because there are sex differences in feeding behavior in rats, we looked for a possible sex difference in the activity of melanin-concentrating hormone (MCH) and orexin neurons in the lateral hypothalamic area using phosphorylated cyclic AMP response element-binding protein (pCREB) as a marker of neural activity. Under free feeding condition, the activity of MCH neurons was increased and decreased in association with a meal initiation and meal termination, respectively. The activity of orexin neurons did not correlate with feeding states. Though fasting activated MCH neurons in both male and female rats, while the activation of orexin neurons was only observed in female rats. In fasted rats, glucose injection decreased the activity of MCH neurons more promptly in females than in males. The magnitude of decrease caused by glucose was greater at proestrus and estrus than at diestrus 2. Gonadectomy in males enhanced and in females attenuated the response of MCH neurons to glucose. Testosterone and estrogen replacement in males and females, respectively, restored the response of MCH neurons to glucose. Sex differences in the response of MCH neurons to glucose correlated well with the gonadal steroid milieu; thus, MCH neurons may play an important role in sex differences in feeding behavior. On the other hand, orexin neurons may responsed to stress induced by fasting only in female rats. Sex differences in MCH and orexin neurons may be the neural basis for the fact that females are more suspectable to eating disorder. [J Physiol Sci. 2007;57 Suppl:S52]