Cocaine is a major drug of abuse in women of child bearing age. 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. Cocaine also blocks uptake of serotonin and norepinephrine (NE) and is involved in modulating acetylcholine (ACh) activity. In this study we examined the effects of high doses of the above neurotransmitters on NGF-induced differentiation to understand more directly how cocaine works at the cellular level. 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, serotonin, norepinephrine or acetylcholine, each in concentration of 50 μM. Results of three experiments revealed the following percentages of neurite outgrowth: NGF-53%, NE-47%, dopamine- 5%, serotonin-65% and Ach- 55%. NE and ACh did not affect NGF-induced differentiation significantly. Serotonin enhanced neurite outgrowth significantly in comparison to NGF alone (Dunnet's T <3.24). Dopamine completely inhibited neurite extension (Dunnet's T< 3.24) showing a morphological pattern similar to that seen with cocaine. Further, dopamine exerts its effect on NGF-induced differentiation in a dose- dependent pattern (see table). Numerous studies link behavioral and cognitive effects of cocaine to activation of dopamine receptors. This study reinforces the significance of dopamine in mediating cocaine inhibitory effects on NGF-induced neuronal differentiation.

Table 1 No caption available.
Full size table