Food-entrained circadian rhythms in rats are insensitive to deuterium oxide

Rats anticipate a scheduled daily meat by entrainment of a circadian pacema ker separate from the light-entrainable circadian pacemaker located in the suprachiasmatic nuclei (SCN). The site and molecular mechanisms of the food -entrainable pacemaker are unknown. The intrinsic period (tau) of the SCN p acemaker is significantly lengthened by deuteriation. Sensitivity of food-e ntrained circadian rhythms to D2O (25% in drinking water) was evaluated in intact and SCN-ablated rats entrained to daily feeding schedules. In intact rats fed ad-libitum, D2O lengthened tau sufficiently to drive activity rhy thms out of entrainment to the light-dark cycle. By contrast, food-entraine d rhythms were surprisingly resistant to modulation by D2O. The mean daily onset time of food anticipatory activity in rats with complete SCN-ablation s was not affected by up to 28 days of D2O intake. Transient delays and dis ruption of anticipatory activity were evident in intact and one partial SCN -ablated rat during D2O treatment, but these are interpretable as effects o f coupling and/or masking interactions between a D2O-sensitive light-entrai nable pacemaker, and a D2O-resistant food-entrained pacemaker. Differential sensitivity to D2O suggests diversity in the molecular mechanisms of food- and light-entrainable circadian pacemakers in mammals. D2O may have utilit y as a screening., test to identify putative food-entrainable pacemakers fr om among those central and peripheral tissues that can express circadian os cillations of clock genes independent of the SCN. (C) 2001 Elsevier Science B.V. All rights reserved.