NEONATAL CHRONIC STRESS INDUCES SUBSENSITIVITY TO CHRONIC STRESS IN ADULT-RATS .2. EFFECTS ON ESTROUS-CYCLE IN FEMALES

The purpose of the present report was to determine the effect of expos ure of females rats to the unpredictable chronic stress model and two models of predictable chronic stress (cold and handling), from day 2-1 5 of life, on the estrous cycle alterations caused by the unpredictabl e chronic stress in adulthood. Adult control and neonatally stressed r ats were submitted to estrous cycle analysis for 8 days through micros copic observations of vaginal smears. They were then exposed to chroni c aleatory stress, and vaginal smears were analyzed daily throughout t he stress period (17 days) up to day 5 after completion of the treatme nt. It was found that this treatment caused constant diestrus in a maj ority of control females. Such diestrus started at day 5.75 +/- 0.96 o f stress administration and was maintained up to day 20.0 +/- 0.49 (i. e., about 3 days after interruption of stress). This effect was preven ted by the neonatal aleatory stress and the neonatal cold stress. Neon atal handling only attenuated the estrous cycle alterations; this grou p showed a period of diestrus no longer than 4 days during the 17-day exposure to stress. The increased resistance of neonatally stressed ra ts to the estrous cycle effects of chronic aleatory stress in adulthoo d supports the speculation that neonatal manipulation can increase res istance of rats to stress-induced reactions throughout life.