Anticipation and entrainment to feeding time in intact and SCN-ablated C57BL/6j mice.

To characterize properties and mechanisms of non-photic entrainment of circadian rhythms, the effects of scheduled feeding were assessed in intact and suprachiasmatic nuclei (SCN) ablated C57BL/6j mice. During ad libitum food access, mice with no or partial SCN damage exhibited free-running activity and drinking rhythms, whereas mice with complete ablations were arrhythmic. When food was restricted to 4 h/day for 5-9 weeks, intact and partial SCN-ablated mice exhibited anticipatory activity to mealtime, concurrent with free-running rhythms. In some cases, free-running rhythms became entrained to feeding time; this was more prevalent in intact than partial ablated mice and was related to free-running period. Free-running phase or period were modified in other cases, revealing a phase-response profile consistent with other non-photic zeitgebers. Five of 12 mice with complete or near complete SCN ablations showed anticipatory activity. Mice that failed to anticipate were less active generally and sustained larger lesions. Sites of damage unique to non-anticipators were not evident. The results indicate that the SCN is not necessary for anticipatory rhythms in mice, but that cell populations distributed across several hypothalamic areas may be important for at least some behavioral markers of this circadian function.