Food anticipatory activity and photic entrainment in food-restricted BALB/c mice

The BALB/c mouse was evaluated as a model for the study of entrainment of c ircadian rhythms by feeding schedules. Mice were housed in a 12:12-h light- dark (LD) environment with food available for 3-5 h/day (5 h before dark on set). Food anticipatory activity (FAA) rhythms were evident in all mice, ra nging from robust in some to weak and variable in others. Advancing transie nts of the end of nocturnal activity were evident in many cases, culminatin g in a significant shortening of the main bout of nocturnal activity. Trans ients and contraction of nocturnal activity were not dependent on the expre ssion of FAA. Following restricted feeding, nocturnal activity expanded by a series of delaying transients. On the first day of constant dark (DD) wit h ad libitum food access following restricted feeding in LD, the phase from which activity free-ran was advanced by comparison with control tests. Tra nsients, compressed nocturnal activity, and advanced phase of free-run sugg est that feeding schedules cause phase advancement of light-entrained rhyth ms in BALB/c mice. When restricted feeding was imposed in DD, several mice expressed robust FAA concurrent with a free-running activity component. In some cases. free-running rhythms entrained to feeding time, and in other ca ses, the period of the free run lengthened toward 24 h. These data show tha t restricted feeding in BALB/c mice can engage a circadian mechanism drivin g FAA rhythms and can also modulate the phase of photic entrainment, possib ly by a direct entraining effect on the light-entrained rhythm. The BALB/c mouse strain, in several respects, appears to be a useful model for the stu dy of scheduled feeding and circadian rhythms. (C) 2000 Elsevier Science In c. All rights reserved.