Hypothalamic gene expression in sheep for cocaine- and amphetamine-regulated transcript, pro-opiomelanocortin, neuropeptide Y, agouti-related peptide and leptin receptor and responses to negative energy balance.

Hypothalamic pathways involved in the regulation of energy balance have not been widely studied in ruminants to date. Here, we used in situ hybridisation to study the gene expression of a number of leptin-sensitive receptors and neuropeptides in the ovine hypothalamus. Gene expression was first localised for cocaine- and amphetamine-regulated transcript (CART) and agouti-related peptide (AGRP). We then examined in adult male castrated sheep the effects of acute negative energy balance induced by a 4-day fast on the amounts of these mRNAs and those for leptin receptor (OB-Rb), neuropeptide Y (NPY) and pro-opiomelanocortin (POMC). CART mRNA was localised in the arcuate nucleus (ARC), paraventricular nucleus, median eminence and ventromedial hypothalamic nucleus, and extensive co-localisation with POMC mRNA was demonstrated in the ARC. AGRP mRNA was localised in the ARC. Fasting up-regulated gene expression for OB-Rb and for the orexigenic neuropeptides NPY and AGRP in the ARC. There was a trend towards down-regulation of gene expression for the anorexigenic neuropeptide CART and no effect on POMC in the ARC, although these results are inconclusive. The presence or absence of oestradiol-containing subcutaneous implants did not influence gene expression or the effects of fasting. The hypothalamic changes were consistent with responses to the observed reduction in circulation leptin and suggest that the peripheral feedback and central mechanisms for restoring the energy balance may be largely conserved across monogastric and ruminant species.