Behavioral and neurochemical investigation of circadian time-place learning in the rat.

The ability to form an association between the time and the place of food availability, namely time-place learning, is presumably important for survival. The present study was designed to examine time-place learning and to identify exogenous and endogenous factors that may affect this behavior in rats. In an initial experiment, rats displayed poor time-place behavior and appeared to prefer the feeder that was closer to the center aisle and water supply. When these cues were minimized in a subsequent experiment, rats consistently displayed the time-place discrimination by exhibiting food anticipatory activity (FAA) at the correct location prior to each meal time. These rats also showed significant correlations between the level of FAA and the amount of dopamine turnover (the dihydroxyphenylacetic acid/dopamine ratio) in the nucleus accumbens and paraventricular nucleus of the hypothalamus, indicating possible involvement of regional dopaminergic activity in time-place behavior. No correlation was found for norepinephrine, epinephrine, or serotonin. In addition, the correlation between FAA and dopamine turnover was not found when rats were entrained to only one meal per day. Together, the data suggest that rats can learn the time-place discrimination under proper experimental conditions and that dopamine may play a role in the expression of this behavior.