Neonatal handling induces anovulatory estrous cycles in rats

Since previous work has shown that stimulation early in life decreases sexu al receptiveness as measured by the female lordosis quotient, we suggested that neonatal handling could affect the function of the hypothalamus-pituit ary-gonadal axis. The effects of neonatal handling on the estrous cycle and ovulation were analyzed in adult rats. Two groups of animals were studied: intact (no manipulation, N = 10) and handled (N = 11). Pups were either ha ndled daily for 1 min during the first 10 days of life or left undisturbed. At the age of 90 days, a vaginal smear was collected daily at 9:00 a.m. an d analyzed for 29 days; at 9:00 a.m. on the day of estrus, animals were ane sthetized with thiopental (40 mg/kg, ip), the ovaries were removed and the oviduct was dissected and squashed between 2 glass slides. The number of oo cytes of both oviductal ampullae was counted under the microscope. The aver age numbers for each phase of the cycle (diestrus I, diestrus II, proestrus and estrus) during the period analyzed were compared between the two group s. There were no significant differences between intact and handled females during any of the phases. However, the number of handled females that show ed anovulatory cycles (8 out of 11) was significantly higher than in the in tact group (none out of 10). Neonatal stimulation may affect not only the h ypothalamus-pituitary-adrenal axis, as previously demonstrated, but also th e hypothalamus-pituitary-gonadal axis in female rats.