ENTRAINMENT IN CALORIE-RESTRICTED MICE - CONFLICTING ZEITGEBERS AND FREE-RUNNING CONDITIONS

Phase-shifting effects of timed calorie restriction were investigated in mice during exposure to a 12:12-h light-dark cycle. Food-anticipato ry activity (FAA), the output of a food-entrainable pacemaker, was exp ressed before the time of feeding whether mice received daily hypocalo ric food (3.3 g of chow/day) or normocaloric food (5 g of chow/day) at zeitgeber time (ZT) 2 (ZT12 = lights off). Subsequently, mice were pl aced in constant darkness and fed ad libitum. The onset of the nocturn al period of locomotor activity was phase advanced by 1 h in calorie-r estricted mice compared with normocalorie-fed controls. The phase adva nce still occurred when FAA was prevented by restraining calorie-restr icted mice. Giving hypocaloric food at ZT2, ZT10, ZT14, or ZT22 phase advanced the nocturnal pattern of activity by 1, 3, 1, and 1 h, respec tively. After transfer to constant darkness, FAA free ran in parallel with the normal nocturnal period of locomotor activity. A light pulse during the early subjective night phase delayed both components. These results indicate that 1) timed calorie restriction under a light-dark cycle can phase advance the light-entrainable pacemaker with a phase- dependent magnitude, 2) FAA feedback is not crucial for the observed p hase advance, and 3) the light-entrainable pacemaker may control the p eriod of the food-entrainable pacemaker in mice fed ad libitum.