The ontogeny of feeding in rats: III. Thermal determinants of early ingestive responding.

Abstract

High ambient temperatures (38.degree. C) stimulated high spontaneous levels of activity and high frequencies of behaviors normally associated with ingestion (mouthing and probing), particularly in young, 3 and 6 day old rat pups. The level of spontaneous behavior was highly correlated with body temperature and depended on deprivation condition. Temperature played an important role in determining pups'' responses to food stimuli as well. When pups were fed by oral infusion or by placing milk on the floor beneath them, warm ambient temperatures were required for active ingestion. Body temperature and ambient temperature were manipulated independently to assess their relative importance for pups'' feeding behavior. Pups with a low (29.degree. C) or normal (34.degree. C) core temperature at the start of testing were fed in a 24 or 34.degree. C ambience. Regardless of body temperature, the pups'' levels of intake, activity, mouthing and probing were higher in a warm ambience than in a cool ambience. The suppressed ingestive behavior of pups fed at cool temperatuers occurred not simply because pups became hypothermic and inactive. Perceived warmth (independent of core temperature) appears to be a significant contextual cue that regulates pups'' responses to food stimuli.