Samer Hattar, Ph.D.

For many years, it was assumed that rods and cones are the only photoreceptors capable of detecting light in the mammalian retina. However, research from several laboratories uncovered a third type of photoreceptor cell in the mammalian retina, called intrinsically photosensitive retinal ganglion cells (ipRGCs) that express their own photopigment called melanopsin (Hattar et al., Science (2002); Berson et al., Science (2002)). Our main goals are to understand how ipRGCs detect light and send light information to the brain to regulate physiology and behavior. We have shown that ipRGCs target many visual centers in the brain including the circadian pacemaker and the area responsible for pupil constriction, among many others, and are critical for the influence of light on circadian rhythms, sleep, mood and pupil constriction. More recently we have found that ipRGCs are more abundant than previously appreciated and that there are at least 5 different subtypes (M1–M5). Some of these subtypes target regions of the brain involved in image formation, which allows mice lacking rod and cone function to have rudimentary pattern vision. More recently, we have found that ipRGCs also mediate the negative effects of light on mood and learning and enhance the ability to detect contrast in an image. Many questions still remain about the function of these cells and the circuits that are critical for ipRGCs-mediated behaviors. We are continuing to explore them using a variety of techniques including mouse genetics, anatomy, in vivo calcium imaging, viral circuit tracing, and animal behavior.

Dr. Samer Hattar is a Senior Investigator and Chief of the Section on Light and Circadian Rhythms (SLCR). He received his PhD from the University of Houston in Texas under the mentorship of Arnold Eskin. From 2000-2004, Dr. Hattar was a postdoctoral fellow at Johns Hopkins University School of Medicine and the Howard Hughes Medical Institute with Dr. King-Wai Yau.

In 2004 Dr. Hattar joined the faculty of the Biology department at Johns Hopkins University with a joint appointment in the Department of Neuroscience at the Johns Hopkins University School of Medicine. In 2017 Dr. Hattar joined the faculty of the Intramural Research Program at the National Institute of Mental Health. His research focuses on light effects on circadian rhythms, sleep, mood and learning.