Programming life histories: An experimental design and initial results

The life experiences of rats were experimentally programmed through the systematic manipulation of several social and stress variables. These were (1) infantile handling vs. no handling of the mothers of the subjects, (2) infantile handling vs. no handling of the subjects, (3)rearing of the subjects in either a maternity cage or a free environment between birth and weaning, (4) rearing of the subjects in either a laboratory cage or a free environment between weaning and 42 days of age, and (5) presence or absence of a stress experience (shuttlebox avoidance learning at 70 days of age, or food and water deprivation at 100 days) in adulthood. Test measures included open-field performance and shuttlebox learning at 70 and 190 days of age. Open-field activity was increased by handling pups in infancy and by rearing pups in a free environment between birth and weaning, whereas it was decreased by food and water deprivation at 100 days. Postweaning free-environment experience improved avoidance learning performance. A number of interactions were significant, most of which involved the three preweaning variables of Mother Handling, Offspring Handling, and Preweaning Housing.