Circadian properties of anticipatory activity to restricted water access in suprachiasmatic-ablated hamsters.

This study provides evidence that anticipation of daily water access in hamsters is regulated by nonphotically entrainable circadian oscillators located outside of the suprachiasmatic nuclei (SCN). Intact and SCN-ablated hamsters receiving 2 h/day water access ate large meals (representing 17-55% of daily food intake) during the 2-h access time. Two of nine SCN-intact hamsters, five of five hamsters with partial SCN ablations, and seven of nine hamsters with total SCN ablations showed anticipatory wheel-running rhythms synchronized to water access time. These anticipation rhythms usually disappeared during subsequent ad libitum water access but reappeared when the hamsters were water deprived for 2 days. When the water restriction schedule was shortened to an 18-h interval in six SCN-ablated hamsters, an 18-h activity rhythm emerged that usually did not persist during water deprivation. When the schedule was lengthened to 30-h intervals, several hamsters showed 27- to 29-h rhythms that did not stably synchronize to water access time. These results indicate that hamsters, like rats, possess a non-SCN-based water- and/or food-entrainable, self-sustaining oscillator with circadian limits to entrainment.