About Johns Hopkins

Recent news from The Johns Hopkins University

This section contains regularly updated highlights of the news from around The Johns Hopkins University. Links to the complete news reports from the nine schools, the Applied Physics Laboratory and other centers and institutes are to the left, as are links to help news media contact the Johns Hopkins communications offices.

 

Tick, Tock: Rods Help Set Internal Clocks, Johns Hopkins Biologist Says

We run our modern lives largely by the clock, from the alarms that startle us out of our slumbers and herald each new workday to the watches and clocks that remind us when it’s time for meals, after-school pick-up and the like. In addition to those ubiquitous timekeepers, though, we have internal “clocks” that are part of our biological machinery and which help set our circadian rhythms, regulating everything from our sleep-wake cycles to our appetites and hormone levels. Light coming into our brains via our eyes set those clocks, though no one is sure exactly how this happens. Johns Hopkins biologist Samer Hattar, in collaboration with scientists at the University of Southern California and Cornell University, however, has unlocked part of that mystery recently in a study that found that rod cells – one of three kinds of exquisitely photosensitive cells found in the retina of the eye – are the only ones responsible for “setting” those clocks in low light conditions. What’s more, the study found that rods – which take their name from their cylindrical shape – also contribute (along with cones and other retinal cells) to setting internal clocks in bright light conditions. The study appeared in a recent issue of Nature Neuroscience.

Blind Mice Can “See” Thanks To Special Retinal Cells

It would make the perfect question for the popular television show “Are You Smarter than a 5th Grader:” What parts of the eye allow us to see? The conventional wisdom: rods and cones. The human retina contains about 120 million rods, which detect light and darkness, shape and movement, and about 7 million cones, which in addition detect color. Without them, or so we are taught, our eyesight simply would not exist. But that might not be true, according to a study — published July 15 in the journal Neuron and led by Johns Hopkins biologist Samer Hattar — that provides new hope to people who have severe vision impairments or who are blind.