The investigators conducting this project have been studying properties of the visual system of the horseshoe crab, Limulus, for some time. This is a favorite model system for investigations of visual mechanisms and principles of neural organization. Among their important recent discoveries is the observation that the structure and function of the eyes are modified by signals from the brain recurring with a twenty-four hour (circadian) cycle. This observation is an example of a newly emerging principle in sensory physiology: feedback from the brain alters the nature of sensory receptors and the information they transmit to the brain. That is, sensory receptors and the brain are two-way communication systems, not unidirectional systems as had been thought previously. In this project they will obtain long term recordings of electrical signals in the Limulus retina and optic nerve in intact animals. The potential for doing such studies is one of the advantages to using this organism as an experimental model. This will permit better analysis of the circadian regulation of retinal sensitivity. They will also conduct anatomical, neurochemical and behavioral studies of the system. The goals are to increase our understanding of the mechanisms by which the brain can influence retinal structure and function; the neural characteristics of the "clock" controlling circadian rhythms; the course of development of circadian rhythms in retinal sensitivity; and the role of such rhythms in visual behavior. They also plan to explore other possible animal models for studying control of visual sensitivity by the brain. We expect significant advances in our understanding of vision, neural organization, and general principles of sensory receptor modulation by the brain to emerge from this project.
