Seasonal cycles of reproduction are regulated by environmental cues of light levels, called photic cues. The eyes are not the only detectors of light; many animals also have light sensitivity in the pineal glad within the head. However, in many vertebrates other than mammals, the receptors for these regulatory cues are actually light-sensitive cells within the brain itself. These "deep brain photoreceptors" are known to exist, but they have not yet been positively localized and identified. This work will use biochemical, electrophysiological and anatomical approaches to localize and identify these cells in the brains of birds that show cyclic seasonal breeding. Specific antibody-binding tests can label cells that contain compounds resembling the protein opsin, part of a known photopigment. Electrophysiological recording determines the responses of these identified cells to light stimuli. Electron microscopy shows the detailed connections from these cells to nerve cells in the hypothalamus controlling hormone secretions. Results from this study will have impact beyond sensory neuroscience, to issues of circadian regulation of behavior and the ecological relationship of breeding cycles to environmental cues.
