Neonatal Chronic Stress Induces Subsensitivity to Chronic Stress in Adult Rats. I. Effects on Forced Swim Behavior and Endocrine Responses 1

A. S. GONZALEZ,; E. L. RODRIGUEZ ECHANDÍA; R. CABRERA; M. R. FOSCOLO; L. N. FRACCHIA

PHYSIOLOGY AND BEHAVIOR

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 1989 vol. 47 p. 735 - 741

0031-9384

Received 7 February 1989GONZ.~EZ, A. S., E. L. RODR.[GUEZ ECHAND~A, R. CABRERA, M. R. FOSCOLO AND L. N. FRACCHIA. Neonatalchronic stress induces subsensitivity to chronic stress in adult rats. 1. Effects on forced swim behavior and endocrine responses.PHYSIOL BEHAV 47(4) 735-741, 1990.--An influence of early stimulation on sensitivity to acute stress in adulthood has been reported. The purpose of the present work was to determine the effect of exposure of male and female rats to three models of chronic stress (unpredictable stress, cold stress and handling) from day 2 to day 15 of life on behavioral and endocrine sensitivity to chronic stresses in adulthood. The chronic stresses applied in adulthood were a model of intermittent cold stress (daily 30-min sessions at -20°C for 15 days) and the Katz´s model of unpredictable chronic stress (15 days). Forced swim behavior and serum concentrationof the stress-sensitive hormones, corticosterone and prolactin, were chosen to investigate stress sensitivity. It was found that all neonatal treatments stimulated body weight gain, did not cause infant mortality and did not affect forced swim behavior as adult. The repetitive exposure to cold stress in adulthood did not cause major impairment of forced swim behavior and did not affect basal levels of serum corticosterone and prolactin in either control or experimental rats. These findings support the view that repeated stressors can induce behavioral and endocrine adaptation in rats. The neonatal treatments did not affect this characteristic. The exposure of controlrats to the unpredictable stress model severely impaired forced swim behavior and increased basal levels of serum corticosterone and prolactin. This observation conforms to the view that standard laboratory rats cannot adapt to unpredictable chronic stress. This has been reported to cause a behavioral depression syndrome comprising forced swim deficit and endocrine alterations. The exposure of rats to the neonatal stress models provided protection to these behavioral and endocrine effects of the unpredictable chronic stress in adulthood. Though minor between-sex and between-treatment differences were apparent, all neonatal treatments were effective. Theresults suggest that mild neonatal stresses might increase resistance of rats to some behavioral and endocrine effects of chronic aleatory stress in adulthood.