Abuse pattern of gestational toluene exposure alters behavior in rats in a "waiting-for-reward" task

Toluene abuse during pregnancy is a world-wide public health concern although the neurobehavioral teratogenic effects of toluene at the high concentrations and binge-like exposure patterns typical of abuse remain understudied. We assessed the effects of binge prenatal toluene exposure on behavior reflective of impulsivity in rat offspring using a "waiting-for-reward" operant task. Timed-pregnant Sprague-Dawley rats were exposed for 15 min, twice daily, from gestational day (GD) 8 through GD20 to either air, 8000 ppm, 12,000 ppm or 16,000 ppm toluene in a static exposure system. At postnatal day 60, male and female offspring were trained to stable lever pressing in a standard fixed-ratio 50 (FR50) paradigm. A wait requirement was then introduced such that after each FR completion, a "free" pellet was delivered at increasing time intervals (2 s, 4 s, 6 s, etc.) until the rat pressed another lever which reinstated the FR50 component ("FR Reset"). A pattern of increased FR Resets and fewer total pellets received overall and during the wait component is interpretable as "impulsivity." The "wait" component assessment was repeated after the rats had been injected with varying doses of amphetamine. Consistent with our hypotheses, repeated binge prenatal toluene exposure appeared to increase impulsivity based upon decreases in the total number of free pellets received and mean waiting time. However, a toluene dose-dependent decrease in the number of FR Resets and in response rates under all conditions indicated there was a general impairment in performance in rats exposed prenatally to higher doses of toluene. Also, prenatal exposure to 12,000 ppm and 16,000 ppm toluene resulted in a hyposensitivity to the stimulatory effects of the amphetamine challenge in male rats. For female rats, amphetamine further interfered with performance on the task. These results suggest that acute binge prenatal toluene exposure alters performance in this task but the results are not consistent with increased impulsivity or impaired behavioral inhibition. These outcomes in young adult rats also suggest that there may be long-term behavioral deficits due to prenatal toluene exposure.