A turf battle in the retina helps internal clocks see the light

With every sunrise and sunset, our eyes make note of the light as it waxes and wanes, a process that is critical to aligning our circadian rhythms to match the solar day so we are alert during the day and restful at night.

Watching the sun come and go sounds like a peaceful process, but Johns Hopkins scientists have discovered that behind the scenes, millions of specialised cells in our eyes are fighting for their lives to help the retina set the stage to keep our internal clocks ticking.

In a study that appeared in a recent issue of Neuron, a team led by biologist Samer Hattar has found that there is a kind of turf war going on behind our eyeballs, where intrinsically photosensitive retinal ganglion cells (ipRGCs) are jockeying for the best position to receive information from rod and cone cells about light levels.

By studying these specialised cells in mice, Hattar and his team found that the cells actually kill each other to seize more space and find the best position to do their job.

Understanding this fight could one day lead to victories against several conditions, including autism and some psychiatric disorders, where neural circuits influence our behaviour. The results could help scientists have a better idea about how the circuits behind our eyes assemble to influence our physiological functions, said Hattar, an associate professor of biology in the Krieger School of Arts and Sciences.

''In a nutshell, death in our retina plays a vital role in assembling the retinal circuits that influence crucial physiological functions such as circadian rhythms and sleep-wake cycles,'' Hattar said. ''Once we have a greater understanding of the circuit formation underlying all of our neuronal abilities, this could be applied to any neurological function.''