Evidence for both local and central regulation of rat rod outer segment disc shedding.

Rats entrained to a 7 A.M.:7 P.M. lighting cycle had one eye patched and then were placed in either constant light or in a 2 A.M.:2 P.M. lighting cycle. In both cases, the patched eyes maintained the original pattern of rod outer segment (ROS) disc shedding, whereas the open eyes responded to the ambient lighting conditions. When the optic nerves were severed at the optic chiasm, the shedding rhythm persisted, but it was no longer possible to shift the rhythm to a new lighting cycle. From these experiments we conclude that ROS disc shedding is regulated both by local oscillators within the orbit as well as by central elements.