Abstract
We have shown that there are sex differences in the response of melanin-concentrating hormone (MCH) neurons to glucose using phosphorylated cyclic AMP response element-binding protein (pCREB) as a marker of neural activity. That is, glucose injection in 48 h-fasted rats decreased the number of MCH neurons expressing pCREB more promptly in females than in males. We therefore suggest that MCH neurons play a role in sex differences in feeding behavior. In the present study, we examined changes in the activity of MCH neurons under normal (free) feeding condition. Male and female rats were killed at various time point and preparations were subjected to immunohistochemical processing for the double staining of MCH and pCREB. Approximately 10% of MCH neurons expressed pCREB between meals irrespective of sex. Next, we found that approximately 40% of MCH neurons expressed pCREB 10 sec after meal initiation irrespective of sex. Five min after meal termination, on the other hand, the number of MCH neurons expressing pCREB was significantly decreased only in females but not in males. No changes in the activity of orexin, cocaine and amphetamine-related transcript, and neuropeptide Y neurons were observed. The results further suggest MCH neurons play an important role not only in sex differences in feeding behavior but also in controlling feeding behavior per se. [J Physiol Sci. 2006;56 Suppl:S220]
