A central property of living systems is rhythmic periodic activity, particularly circadian rhythms which are daily cycles. It is not yet clear what mechanisms entrain and regulate the occurrence and timing of these oscillations. The primary environmental signal for circadian rhythms is the change in light intensity associated with dawn and dusk, but the "circadian photoreceptors" that mediate these responses are still poorly understood. This project is pilot work to try to get information on this mechanism by using a new marking technique that labels pathways in the brain. This marker will allow visualizing the circuit that connects the cells that receive the important light stimulus to the cells in the brain that regulate the circadian rhythm. One particular strain of mutant mice has been found to be missing key cellular elements in the eye, yet still showing a photically driven rhythm. The pathway in this mutant will be compared to that in normal mice to clarify how the light information gets to the brain. If this novel marking technique can be made to work well, the results will be very important to visual science, chronobiology, and neuroscience in general.
