Immediate-early gene expression in concurrent prenatal ethanol- and/or cocaine-exposed rat pups: intrauterine differences in cocaine levels and Fos expression.

Concurrent use of cocaine and ethanol is a common mode of abuse. Cocaine and ethanol have distinctive pharmacologies but both have been shown to cause uterine vasoconstriction and fetal hypoxia. We developed a paradigm of chronic ethanol exposure via liquid diet coupled with binge cocaine exposure on the last day of gestation. Lipton et al. demonstrated unequal segregation of cocaine in rat fetuses as a function of proximal-distal location in the uterus, indicating a differential vasoconstriction of the two main arteries supplying the uterus in rats receiving cocaine. By performing C-sections after exposure to cocaine, we were able to measure the cocaine content and immediate-early gene (IEG) induction in the brains of fetuses according to their intrauterine position and assess the potentially vasoconstrictive effect of ethanol. HPLC analysis of fetal brains exposed to cocaine supported the study of Lipton et al.: fetuses from the proximal (lower) end of the uterus had more cocaine than fetuses from the distal (upper) end. Concurrent ethanol decreased the amount of cocaine reaching the fetuses and diminished the proximal-distal gradient. There were increased numbers of Fos-immunoreactive cells in fetuses exposed to both ethanol and cocaine compared to cocaine binge only. Additionally, the gradient of c-fos induction observed as a function of intrauterine position in cocaine-treated rats was in the opposite direction: most distal fetuses generally had the most Fos-immunoreactive cells. These results indicate that IEG induction in fetal brains exposed to cocaine and ethanol may be more related to hypoxic consequences of prenatal drug exposure.