Effects of early separation of young rats from the mother on their open-field behavior.

Changes were studied in the open-field behavior of young rats prematurely separated from their mothers at different ages. Premature separation from the mother on days 15 and 18 of life increased their fear or emotional behavior, as measured by the amount of defecation and locomotor activity. The changes in rats' open-field behavior were due to the absence of the mother rather than to an inadequate food supply after the day of separation.