Evidence from animal studies suggests that a period of anoxia to the fetus, a consequence common to many birth complications, results in long-term alterations in ventral mesencephalic dopamine function. Long-term functional changes in these dopamine neurons, in particular those that innervate the nucleus accumbens, also occur when animals are repeatedly stressed. In the present study, we examined the possibility that a period of anoxia during a Cesarean section birth can later alter the development of stress-induced sensitization of dopamine transmission in the nucleus accumbens. Dams were decapitated on the last day of gestation and the entire uterus was removed by Cesarean section. Pups were then delivered either immediately (Cesarean section group) or were immersed in a 37 degrees C saline bath for 3.5 or 13.5 min (Cesarean section+anoxia groups) before delivery of the pups. A fourth group of pups that were born vaginally served as controls (Vaginal group). Three to four months postnatally, animals from each group were implanted with monoamine-selective carbon-fiber electrodes into the nucleus accumbens. Voltammetry was used to monitor the dopamine response to each of five consecutive, once daily, 15-min exposures to tail-pinch stress. The results show that the first exposure to stress elicited dopamine signal increases of comparable amplitudes and durations in all animals. However, when compared to the initial stress response, the fourth and fifth exposures to tail-pinch elicited significantly longer-lasting dopamine responses in animals born by Cesarean section, either with or without added anoxia. In contrast, there was no significant day-to-day enhancement of the stress response in control, vaginally born animals. The findings reported here provide experimental support for the idea that birth complications may contribute to the pathophysiology of psychiatric disorders, in particular those that involve central dopamine dysfunction, such as schizophrenia. Specifically, our results suggest that subtle alterations in birth procedure may be sufficient to increase the sensitivity of mesolimbic dopamine neurons to the effects of repeated stress in the adult animal.