Fixed interval feeding does not entrain the circadian pacemaker in blind rats.

Male and female rats were blinded by orbital enucleation at 1 or 21 days of age and were housed along with intact controls in a temperature- and light-controlled room (22 +/- 2 degrees C, LD 12:12). At 40 days of age the rats were transferred to running wheel cages connected to an event recorder and their activity patterns were monitored for the next 11--16 wk. After 4--6 wk in the running wheels, the rats were subjected to a fixed interval feeding (FIF) schedule lasting 23 days followed by 4--6 wk of ad libitum feeding and watering. Of 19 blind rats with interpretable activity records, 14 showed no change in their activity patterns associated with the FIF other than the addition of a large component of activity before and after the feeding period every day. It was concluded that, in contrast to the squirrel monkey, FIF is not an important zeitgeber for blind rats.