Stony Brook Researcher, Lawrence Morin, PhD, Advances Understanding of Circadian Rhythms Through Study of Photoreceptors

Lawrence Morin, PhDStony Brook Professor, Lawrence Morin, PhD, is an expert in circadian rhythms—the daily ebb and flow of life that involves the timing of sleep and wakefulness, digestion, circulation and almost every other biological function. Circadian rhythms are self-sustaining in that their patterns continue day after day, but they are adjusted in response to changes in light through a process known as entrainment.

In a study published in the October issue of Neuroscience, Dr. Morin described a series of experiments that advance the scientific understanding of how light signals are processed to affect non-image forming visual responses, including adjustments to the timing of circadian rhythms.

Dr. Morin’s experiments focused on two pathways in the eye through which light is processed. One involves the classical photoreceptors—rods and cones—that react to light and send signals to the brain, enabling animals to see and adjust to changes in light. The second involves cells known as intrinsically photoreceptive retinal ganglion cells that contain a photosensitive protein called melanopsin. Dr. Morin studied how these pathways are involved in reactions to changes in light intensity.

In two experiments, Dr. Morin demonstrated that the classical photoreceptors and not the photoreceptive retinal ganglion cells enable mice to adjust to gradual changes in very dim light, such as those that occur at dawn or dusk. In another, he showed that locomotor quiescence (reduction in activity) and photosomnolence (induction of sleep) occurred in nocturnally active rodents exposed to brief flashes of light even if they lacked the classical photoreceptors, so long as their intrinsically photoreceptive retinal ganglion cells were intact.

Dr. Morin noted in an interview that these studies will help scientists understand the mechanisms through which light signals are translated into biological adjustments that affect activity levels and sleep. They are particularly important for understanding the circadian rhythm phase responses that are normal parts of the daily cycle. In addition, the ability to induce sleep in nocturnal rodents by controlling the ambient light may facilitate the study of how animals transition from wakefulness to sleep. 

Dr. Morin is a Professor in the Department of Psychiatry and Behavioral Science at Stony Brook University. The paper, titled Separation of Function for Classical and Ganglion Cell Photoreceptors with Respect to Circadian Rhythm Entrainment and Induction of Photosomnolence, was co-authored by Keith M. Studholme.