Ethanol and circadian rhythms in the Syrian hamster: effects on entrained phase, reentrainment rate, and period.

Wheel-running rhythms were examined in male hamsters with access to 28% ethanol in lieu of water. One group was recorded in a light-dark (LD) cycle that was phase advanced by 8 h on three occasions separated by 23-27 days. On two of the three occasions, hamsters were subjected to a 2- to 3-h cage change procedure designed to stimulate wheel running, which accelerates the rate of reentrainment to 8-h advances. Ethanol and control hamsters showed no group differences in rhythm amplitude, entrained phase, or reentrainment rate. Both groups showed faster reentrainment in the cage change condition. A second group of hamsters recorded in constant dim showed a small but significant lengthening of the free-running period of their wheel-running rhythm when provided with a 28% ethanol solution. Wheel running decreased during ethanol access in this group. Voluntary ethanol consumption evidently can slow the circadian pacemaker regulating activity rhythms in hamsters but has no measurable effect on photic entrainment or pacemaker response to LD shifts or nonphotic manipulations (stimulated activity). Period lengthening may be secondary to decreased activity, but other period-activity correlations obtained did not reveal a strong association between these two variables.