Effects of postnatal cocaine on differentiation of the rat corpus callosum.

We investigated the effects of cocaine on the development of the corpus callosum. Pregnant Wistar strain rats (Thirteenth day of gestation) were used in this study. On the day following birth, litters were culled to 8 pups (4 males and 4 females), and rats were assigned to either a control or drug treatment group. From postnatal day 1 (P1, at birth = P0) to P5, cocaine (50 mg/kg) was subcutaneously injected to the cocaine-treated pups, and saline in the same volume to the control pups. Animals were sacrificed in 110 days and a mid-sagittal section of the callosum was obtained. From this section the morphometric measurement of the corpus callosum was performed. In the control group the rat corpus callosum has a sex difference with the male corpus callosum being larger than the female's. But this sex difference disappeared in the cocaine group. This was attributed to the fact that cocaine-treated male rats indicated a significant reduction of callosal area. These findings suggest that the early postnatal cocaine can abolish the sexual differentiation of the corpus callosum.