The Maintenance of Reproductive Status in Pekin Drakes Requires Both Red and Blue Wavelengths of Light: Relationship to Opsin-Related Proteins in the Hypothalamus
Dr. Gregory Fraley, Hope College
In birds there is compelling evidence that photoresponsiveness is mediated—at least in part—by neurons that express photosensitive chemicals. These neurons have been referred to as deep encephalic photoreceptors. Photo-responsive pigments all consist of an opsin protein that is a transmembrane, G-couple receptor that transduces light energy into a neuronal signal. Two of these opsin-related proteins, opsin and melanopsin, have been identified in avian brains. Pekin ducks are seasonal breeders and as such, very sensitive to artificial and natural light. The purpose of these studies was to determine if specific wavelengths of light are necessary to maintain plasma luteinizing hormone secretion and to determine the hypothalamic circuitry underlying this effect. First, drakes were exposed to full spectrum, white light or red (~625 nm) or blue (~400 nm) specific wavelengths and blood samples take at intervals around lights on (0300 hrs). We found that neither the read nor blue wavelengths of light could maintain circulating LH levels compared to that of drakes housed under white light. Second, drakes housed under white lights were euthanized and brains processed for immunocytochemstry for opsin and melanopsin. As in other species, opsin-ir (RET-P1) was found in the lateral septal area (LS) and infundibular nuclei (INF) and were colocalized with vasoactive intestinal polypeptide. Melanopsin-ir was observed in the premammillary nucleus (PMM) and colocalized with tyrosine hydroxylase. Immunoreactive fibers for both opsin- and melanopsin were observed throughout the diencephalon and found to be in close contact with GnRH cell bodies. Third, a significant (p<0.01) increase in fos-ir was observed in all three nuclei in drakes exposed to white light compared to dark conditions. These data suggest that multiple opsin-related peptides within the diencepahlon are necessary to maintain photoresponsiveness in Pekin drakes.
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