Thermoregulatory behavior in rat pups from birth to weaning.

One-19 day old rat pups were placed individually in a thermal gradient (floor temperatures 17-45 degrees C) at either 45 degrees, 30 degrees, or 20 degrees C. From the first day of life, pups placed at 45 degrees or 30 degrees C and given sufficient time (up to 2 hrs) oriented and moved along the gradient to an area of moderate temperatures (35 degrees-40 degrees C). The pups regulated their body temperatures by remaining in appropriate positions in the gradient. Most pups under a week old were immobilized when placed in the cold area. During the next two weeks, pups placed at 20 degrees C moved up the gradient to the 35 degrees-40 degrees C area. Response latency was related to both starting temperature and age. Observations of the pups' behavior in different temperatures are discussed.