PERINATAL AND POSTNATAL EXPOSURE TO 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN - EFFECTS ON PHYSIOLOGICAL DEVELOPMENT, REFLEXES, LOCOMOTOR-ACTIVITY AND LEARNING-BEHAVIOR IN WISTAR RATS

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the developme nt of rat offspring were studied after administration of a loading dos e of 300 or 1000 ng TCDD/kg body wt on day 19 of pregnancy, followed b y weekly maintenance doses of 120 or 400 ng TCDD/kg body wt. The dose regimens led to a fluctuation of average TCDD concentrations in the li ver of the offspring of 4.9-14.9 ng/g (TCDD1000/400 group) or 1.4-6.3 ng/g (TCDD300/120 group) during the course of the experiment. In both TCDD-exposed groups the body weight of the offspring was significantly lower on postnatal day 7 (PND 7); in the high dose group from PND 7 t o PND 31. Some landmarks of postnatal development were retarded in the exposed groups; in particular, the vaginal opening was delayed for se veral days in both TC-DD-exposed groups. The TCDD-exposed animals reve aled a reduced ability to remain on a rotating rod. During reflex test ing, the rate of successfully responding animals was higher in the exp osed groups. No statistically significant differences in the locomotor activity between controls and TCDD-exposed offspring were detectable under our experimental conditions. In a discrimination learning test n o effects on the learning ability were found. However, TCDD-exposed of fspring showed an increase in unanswered trials during critical phases of the task. They also exhibited increased locomotor activity in a no vel environment; prior to an amphetamine challenge dose of 1 mg/kg bod y weight. Amphetamine-induced activity was decreased in a dose-depende nt manner.