Neurobehavioral changes produced in rats by prenatal exposure to carbon monoxide

Wistar female rats were exposed to relatively mild concentrations of carbon monoxide (75 and 150 ppm) from day 0 to day 20 of pregnancy. The results show that prenatal exposure to CO (150 ppm) produced a significant reduction in the minimum frequency of ultrasonic calls emitted by rat pups removed from their nest. Moreover, a significant decrease in the responsiveness (rate of calling) to a challenge dose of diazepam (0.25 mg/kg) was found in male pups exposed to CO (150 ppm) during gestation. Prenatal CO (75 and 150 ppm) did not significantly affect locomotor activity or D-amphetamine-induced hyperactivity in both 14- and 21-day-old animals. Furthermore, adult male rats exposed to this chemical (150 ppm) during gestation exhibited significant alterations in the acquisition of an active avoidance task. CO-induced learning disruption does not seem to be linked to changes in the emotionality of animals. These findings suggest that gestational exposure to CO induces in rat offspring both short- and long-term behavioral changes characterized by altered ontogeny of emotional responsiveness to environmental challenges and by learning impairment.