An 'eye catching' vision discovery

Jul 26, 2009
This is a goldfish. Credit: Johns Hopkins Medicine

Nearly all species have some ability to detect light. At least three types of cells in the retina allow us to see images or distinguish between night and day. Now, researchers at the Johns Hopkins School of Medicine have discovered in fish yet another type of cell that can sense light and contribute to vision.

Reporting in this week's Nature, the team of neuroscientists shows that retinal horizontal cells, which are once thought only to talk to neighboring nerve cells and not even to the brain, are light sensitive themselves.

"This is mind-boggling," says King-Wai Yau, Ph.D., a professor of neuroscience at the Solomon H. Snyder Department of at Johns Hopkins.

"For more than 100 years, it's been known that rod cells and cone cells are responsible for sensing light, and therefore, vision," says Yau. "Then, about seven years ago, another light sensor was discovered in the , revealing a third type of light-sensitive cells in mammals, so we set out to look at whether this was true in other vertebrates as well."

This is a channel catfish. Credit: Johns Hopkins Medicine

Focusing their efforts on the melanopsin light sensor, which is responsible for sensing day and night but barely involved — in mammals, at least — in seeing images, Yau's team looked for melanopsin-containing cells in other , and found some in the retinal horizontal cells in goldfish and catfish.

Catfish contain two flavors of retinal horizontal cells: those that connect to cone cells, which respond to bright light, and those that connect to rod cells, which respond to dim light. The team took electrical readings from single isolated retinal horizontal cells. They found that light caused a change in electrical current in cone horizontal cells but not in rod horizontal cells.

Horizontal cells, says Yau, allow cross-talk between neighboring , allowing these cells to compare the light they sense, a process necessary for the brain to see images. "The brain processes what it sees in context to the surroundings," says Yau. "This allows our brain to see borders and contours—horizontal cells are the reason why we can recognize and see a face, for example."

Testing light at different wavelengths, the team found that these fish horizontal cells are thousands of times less light sensitive than their partner cone cells.

"The bottom line is that the light effect on the horizontal cells is subtle, perhaps to allow the eyes of these animals to fine-tune their functions to different ambient light conditions," says Yau. "But that these horizontal cells are light sensitive at all is a very surprising finding and changes how we think about retinas as a whole."

Learning more about how the light sensitivity of horizontal cells contributes to image vision will require studying whole retinas, not just single cells. Yau, whose goal is to understand vision, is hooked. "Maybe," he says, "there are still other photosensitive cells in the eye that we don't know about yet."

Source: Johns Hopkins Medical Institutions

Explore further: Proteases help nerve cells to navigate

add to favorites email to friend print save as pdf

Related Stories

Bright lights, not-so-big pupils

Dec 31, 2008

A team of Johns Hopkins neuroscientists has worked out how some newly discovered light sensors in the eye detect light and communicate with the brain. The report appears online this week in Nature.

The difference between eye cells is... sumo?

Mar 09, 2009

Researchers at the Johns Hopkins University School of Medicine and Washington University School of Medicine have identified a key to eye development — a protein that regulates how the light-sensing nerve cells in the retina ...

Lizard’s ‘third eye’ sheds light on how vision evolved

Mar 30, 2006

A primitive third eye found in many types of lizards, used to detect changes in light and dark and to regulate the production of certain hormones, may help explain how vision evolved and how signals are transmitted from the ...

Perfect Vision But Blind To Light

Jun 11, 2008

Mammals have two types of light-sensitive detectors in the retina. Known as rod and cone cells, they are both necessary to picture their environment. However, researchers at the Salk Institute for Biological ...

Recommended for you

Proteases help nerve cells to navigate

1 hour ago

Our ability to move relies on the correct formation of connections between different nerve cells and between nerve and muscle cells. Growing axons of nerve cells are guided to their targets by signposts expressed ...

New test to help brain injury victims recover

Oct 21, 2014

A dynamic new assessment for helping victims of trauma to the brain, including those suffering from progressive conditions such as dementia, has been developed by a clinical neuropsychologist at the University ...

See-through sensors open new window into the brain

Oct 21, 2014

(Medical Xpress)—Developing invisible implantable medical sensor arrays, a team of University of Wisconsin-Madison engineers has overcome a major technological hurdle in researchers' efforts to understand ...

User comments : 0