Adaptation to novel environments by the rat: effects of age, stimulus intensity, group testing, and temperature.

Adaptation of operant bar pressing in a dark 2-bar test box was determined during 2-hr tests for singly tested rats 16-18, 24-32, and 750-800 days old. Rats 16-18 days old failed to adapt during the test, although all other age groups did. Adaptation occurred more slowly for the 120-150 day-old group than for the remaining 2 age groups. Experiments with the 2 youngest groups showed that bright light lowered response levels of both age groups, compared with controls, but failed to alter the course of adaptation. In contrast, group testing resulted in lowered response levels and faster adaptation for 16-18 day-old rats, but higher response levels for 24-32 day-old rats compared with singly tested controls. High temperature (32.5 degrees C) resulted in adaptation for the 2 younger groups. The failure of 16-18 day-old rats to adapt may have been due to lower body temperature while in the test chamber than while in the home cage nest area.