The effects of in utero cocaine exposure on CNS development is still unclear. In previous studies we have demonstrated that cocaine has direct, dose-dependent inhibitory effects on nerve growth factor (NGF)-induced PC12 neuronal differentiation. Cocaine binds with high affinity to the dopamine transporter, resulting in a large elevation in dopamine at nerve endings. When different neurotransmitters were applied to PC12 cells, only dopamine inhibited NGF-induced neuronal differentiation in a dose-dependent pattern. In this study, we further examined the role of dopamine receptors in mediating inhibition of differentiation. We used PC12 cells, a well-characterized neuronal model, which differentiate into neurons on exposure to NGF. Differentiation was quantified by counting cells bearing neurites greater than one cell diameter after 72 hr exposure to NGF 20 ng/ml alone or with dopamine receptor agonists. D1 agonist, R(+) SKF-38393, and D2 agonist, (-) quinpirole, 10 μg/ml of each were used. Only the D1 agonist had a significant inhibitory effect on neurite outgrowth. Specifically, D1 receptor agonist had dose-dependent inhibitory effects on NGF-induced differentiation (see table). Cells were treated with dopamine, 6.75 μg/ml, and D1 receptor antagonist, R(+) SCH-23390, in a range of doses. Full recovery of neurite outgrowth was observed in cells treated with the D1 antagonist in concentrations of 2-8 μg/ml, but not in higher doses. The dopamine transporter inhibitor, GBR 12909, which mimics cocaine's effects on this transporter, produced dose-dependent inhibited differentiation similar to that with cocaine. Numerous studies have linked cocaine behavioral and cognitive effects to activation of D1 dopamine receptor and subsequent induction of c-fos and other genes. Our previous studies linked the prolonged c-fos induction mediated by cocaine to altered differentiation. This study suggests that activation of D1 receptors has a major role in altering the neuronal phenotype probably by interfering with NGF signaling, perhaps, through the effects of D1 activation on c-fos expression.

Table 1 No caption available.