Orexins and their receptors in the human retina.

OBJECTIVES Orexins A and B are neuropeptides involved in the regulation of feeding behavior, energy homeostasis and arousal. In the human retina, however, immunohistochemical localization of orexins and their receptors, OX-R1 and OX-R2, has not been ascertained. METHODS We localized orexins A and B, OX-R1 and OX-R2 in the human retina using immunohistochemistry. Retinae from 2 Alzheimer's disease (AD) patients provided preliminary evidence for possible orexin alterations. RESULTS Orexin A, orexin B and OX-R1 were localized in ganglion and amacrine cells, cellular processes in the inner and outer plexiform layer and in the inner segments of photoreceptor cells. There was no OX-R2 immunoreactivity in the retina. The staining intensity for both orexins was decreased in the AD patients. CONCLUSION This immunohistochemical study provides the first evidence for the distribution of orexin A, orexin B and OX-R1 in the human retina. The localization pattern suggests a modulatory role for orexins in the interactions of those retinal cells which transmit light information to the suprachiasmatic nuclei, and thus may be involved in circadian rhythm entrainment.