Natural food intake patterns do not synchronize peripheral clocks

Food is thought to synchronize circadian clocks in the body, but this is based on time-restricted feeding (TRF) protocols. To test whether naturalistic feeding patterns are sufficient to phase-shift and entrain peripheral tissues, we measured circadian rhythms of the liver, kidney, and submandibular gland in mPer2Luc mice under different feeding schedules. In ad lib feeding as well as in a schedule designed to mimic the ad lib pattern, PER2::LUC bioluminescence peaked during the night as expected. Surprisingly, shifting the scheduled feeding by 12h caused only small advances (<3h). To isolate the effects of feeding from the light-dark cycle, clock phase was then measured in mice acclimated to scheduled feeding and housed in constant darkness. In these conditions, peripheral clock phases were better predicted by the rest-activity cycle than the food schedule. Under natural feeding patterns, the master pacemaker in the brain sets the phase of peripheral organs independent of feeding behavior.

Effects of Sucrose Concentrations upon Schedule-Induced Polydipsia on a Ffi-60-Sec. Dry-Food Reinforcement Schedule

Food-deprived female albino rats were tested under a free-food schedule (FFI-60-sec.) in which water was freely available in both the test chamber and the home cage. 5 groups of 4 Ss each received different formulae of Noyes 45-mg. dry-food pellets. Group 1 received standard formula pellets containing 7.5% glucose. Group 2 received “no glucose” formula pellets. Groups 3, 4, and 5 received “no glucose” formula pellets with 4.0%, 16.0%, and 32 0% sucrose added, respectively, by weight. An inverse relationship between sucrose concentration of the pellets and water intake levels was obtained and all groups receiving sucrose or glucose pellets drank less than the group that received the “no-glucose” pellet.

Infantile Handling and the Extinction of Responses Acquired under Food Reward

A comparison was made of the runway behaviour of rats which had been handled from Days 1–21 and their non-handled litter mates. The training began on Day 70 after the animals were habituated to a restricted food schedule for 10 days. The subjects were given six trials each day in the runway and were rewarded with a 0.045 g. Noyes pellet. After 10 days of rewarded training trials, subjects were given 6 extinction trials a day for 10 days. Results showed that handled rats ran faster than non-handled rats during acquisition and during the first 3 days of extinction. The extinction data suggested that the relationship between emotionality and effects of frustrative non-reward should be re-evaluated.

Effect on Food Intake by Rats of Day-Night Cycle Control and Increment in Deprivation

Additional data on the relation between food intake and deprivation were provided by incorporating Siegel's day-night cycle control and extending the small increments in deprivation. Ten male hooded rats were housed in individual translucen cages and exposed to a constant illumination from a 25-w light. on the last day of a 10-day base period 10 Ss were assigned to 10 deprivation levels: 0, 8, 16, 24, 36, 48, 60, 72, 84, and 96 hr., but each S began a sequence at each of the 10 levels and then began another at the next level so that each level preceded and followed each other level an equal number of times. Before each deprivation Ss were weighed, deprived, and then given a 3-hr. food-intake period. At the end of this period remaining food pellets were removed and weighed. Ss were maintained on a continuous food schedule for at least twice as long as the last deprivation in order to regain lost weight. Food intake increased steadily and reached constant maximum after 16 hr., not the usual 24 hr.

Effects of Alternating Weak and Strong Shock during Blocks of Variable-Interval Punishment

12 naive rats were run on a variable-interval punishment schedule (superimposed on a variable-interval food schedule) during 4 punishment periods, alternated with 4 no-punishment periods. Punishment intensity for the 4 punishment periods was varied in two sequences: 0.4 ma., 1.0 ma., 0.4 ma., and 1.0 ma., or vice versa. Two effects of punishment were observed: (1) an immediate, but reversible, suppressive effect during punishment and (2) a permanent, gradual decremental effect which was observed during post-punishment sessions. The two effects appeared to function reciprocally. When strong suppression during the weaker punishment (first effect) occurred in some Ss, there was better recovery following punishment to pre-punishment levels (no second effect); however, if little suppression (no first effect) occurred and S continued to respond, there was more eventual response decrement (second effect).