Expression of orexin receptors in the brain and peripheral tissues of the male sheep.

Orexins exert their effects through two specific receptors (OX1R and OX2R) that have been found mainly in the brain and also in peripheral tissues of rats and humans. Here, we demonstrate expression of mRNA encoding for ovine OX1R and OX2R in central and peripheral tissues of sheep. Gene expression for orexin receptors in the hypothalamus and the preoptic area was localised by in situ hybridisation. OX1R was detected in arcuate nuclei (ARC), median eminence (ME), the lateral hypothalamic nuclei and preoptic area (POA) and it was scattered along the third ventricle from the paraventricular (PVN) to the ventromedial hypothalamic nuclei (VMH). OX2R was localised in the PVN, ARC, ME, ventral VMH and a small region of the ventral POA. Gene expression for OX1R and OX2R in central and peripheral tissues was analysed using quantitative real time RT-PCR. Both orexin receptor genes were expressed in the hypothalamus, POA, hippocampus, amygdala, olfactory bulb, pineal gland and recess and pituitary gland, whereas only OX1R mRNA was detected in the testis, kidney and adrenal gland. The expression of the genes for orexin receptors in this range of ovine tissues suggests roles for orexins in multiple physiological functions, with actions at both central and peripheral levels.