Long-term alteration in bodyweight and food restriction does not affect the gene expression of either preproorexin or prodynorphin in the sheep

Various hypothalamic neuropeptides are involved in central regulation of food intake and expression of genes encoding these peptides changes with alterations in the bodyweight/metabolic status/nutritional status. Orexin(s) and dynorphin have been implicated in the regulation of appetite and neuroendocrine systems, but the function of these peptides is not well understood. We have employed in situ hybridization to examine the effects of long-term alterations in the bodyweight on expression of mRNA for preproorexin and prodynorphin in the putative feeding centers of the ovine hypothalamus. Expression of preproorexin was localized to the dorsomedial hypothalamic nucleus, perifornical area and lateral hypothalamic area. Cells expressing prodynorphin were localized to the periventricular, supraoptic, paraventricular, ventromedial hypothalamic nuclei and the thalamus. Small numbers of single scattered cells were seen in other brain areas. A few scattered prodynorphin-expressing cells were found in the lateral hypothalamic area but, in contrast to observations in the rat, there was no colocalization with preproorexin. Long-term alterations in the bodyweight did not influence the level of expression of preproorexin or prodynorphin. These findings suggest that orexin and dynorphin may not play a direct role in appetite regulation in sheep, although regulation at the level of the receptors for these peptides remains a possibility.