Nonphotic entrainment of activity and temperature rhythms in anophthalmic mice.

Although it is more common to study the effects of light on circadian systems, nonphotic stimuli can also influence and entrain circadian clocks. Because anophthalmic mice (ZRDCT-AN) have a genetic mutation that prevents the development of the eyes, they do not respond to light or entrain to light-dark cycles. Thus, entrainment of anophthalmic mice requires a nonphotic zeitgeber (entraining stimulus). In the current study we attempted to entrain sighted and anophthalmic mice of the same strain, using restricted access to an unlocked running wheel as the zeitgeber. First, free-running rhythms were established. The running wheels were then locked, and unlocked only from 0930-1130 h each day. Finally, a postentrainment free run was measured. In one group of animals, body temperature and general activity were measured using a Minimitter telemetry system. In another, general activity was measured by a sensitive force plate beneath the cage. Running-wheel activity was recorded in both groups. The force plate proved satisfactory for observing the behavior of the circadian system during wheel locking, and preferable to the temperature transmitters for long-term studies because the battery life of the mouse temperature transmitters was limited. Both sighted and anophthalmic mice were able to entrain to restricted wheel access, although not all animals responded. Mice that did not entrain showed either no effect of wheel locking or exhibited masking.