New Look at Vision
Another Light-Sensitive Cell Discovered
all species have some ability to detect light. At least three types of
cells in the human retina allow us to see images or distinguish
between night and day. Now, researchers at the Johns Hopkins
School of Medicine have discovered yet another type of cell that can
sense light and contribute to vision.
In the journal Nature, the team of Johns Hopkins neuroscientists report their discovery that retinal horizontal cells - nerve cells once thought only to talk to neighboring nerve cells - are light sensitive themselves.
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 vertebrates, and found some in the retinal horizontal cells in goldfish and catfish.
Catfish contain two types 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.
Testing light at different wavelengths, the team found that the 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. 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."
Source: The Solomon H. Snyder Department of Neuroscience
at Johns Hopkins School of Medicine