It has been reported that there are two orexin (from the Greek word for appetite
orexis) peptides derived from pre-pro-orexin
designated as orexin A and B. Orexin A is a 33-residue peptite with two intramolecular disulfide bonds in the N-terminal region
and orexin B is a linear 28-residue peptide. These peptides
encoded by a single mRNA transcript
has a 46% amino acid sequence identity (Sakurai T et al. 1998). Their effects are mediated by receptors
orexin 1 and 2 receptor. Orexin-A has ha similar affinity for both receptors
whereas orexin-B has a higher affinity for the orexin 2 receptor subtype.It has been also reported that orexin-A and -B mRNA and their cell bodies were mainly detedted in the hypothalamic area
particularly in the lateral hypothalamic area and the perifornical nucleus. Recently
it has been reported that the distribution of immunoreactive fibers overlaps with the luteinizing hormone-releasing hormone(LHRH) neuronal system in the septopreoptic area and the arcuate nucleus median eminence region
suggesting that orexins are involved with the sex hormone secretion. However
the sex difference of the expression of orexin-A and -B has not been elucidated. In the project
we investigated the sex difference of the distribution pattern of the feeding related neurons
particularly orexin neuorns and the effect of estrogen for the expression of orexin peptides in the male
female and ovariectomized (OVX) rats.Orexin neurons are distributed in the perifornical and lateral hypothalamic area
a region classically implicated in the control of feeding behavior
and project their axons within the hypothalamus and throughout the central nervous system to be involved in the control of feeding. In the project
we investigated the sexual difference of orexin neurons using specific orexin-A and orexin-B antibodies. The density of both orexin-A and orexin-B immunopositive neurons in male was preferentially higher than those in female rats. On the other hand
ovariectomy in female rats induced the change to the male pattern. Colocalization of orexin and estrogen receptor was not observed. These results suggested that orexin neurons were indirectly regulated by estrogen through the other estrogen dependent neurons.
