Anticipatory activity and entrainment of circadian rhythms in Syrian hamsters exposed to restricted palatable diets.

Activity rhythms were recorded from hamsters in three conditions: during timed feedings of an attractive diet with free access to regular food, during restriction to 70% of normal food consumption, and during moderate food deprivation with limited temporal access to an attractive diet. An attractive diet given to intact animals did not induce anticipatory activity or entrainment, but damage to the suprachiasmatic nuclei (SCN) led to the development of anticipatory activity. Food restriction to 70% of normal intake led to anticipatory components in some intact animals, without entraining the dominant circadian pacemaker. The combination of a palatable diet and food restriction led to anticipatory activity before the daily feeding times and entrainment of a previously free-running circadian rhythm in some animals. Ablation of the SCN did not eliminate anticipatory activity in experimental animals, but did eliminate the free-running component of the rhythms. These results indicate that hamsters have a mechanism separate from the SCN that can anticipate daily feeding times, as rats do, and that they may show entrainment of the SCN-based pacemaker to such feeding schedules.