Effects of a novel dopamine uptake inhibitor upon extracellular dopamine from superfused murine striatal tissue

The dopamine transporter (DAT) plays an important role in substance abuse, schizophrenia, and dopaminergic toxicity associated with the Parkinsonian animal model toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Accordingly, the DAT serves as a critical component in regulating dopaminergic function in health and disease states. We have been working with a novel cage compound, 8-phenylethyl-pentacycloundecane (1), and found that this compound can inhibit dopamine uptake and serve as a neuroprotectant against MPTP-induced dopaminergic toxicity. The current study was aimed at investigating additional mechanistic features of DAT function that interact with our compound (1). Extracellular dopamine levels were analyzed from superfused striatal tissue in response to various conditions of compound 1 infusion. The results showed that compound 1: (1) significantly increased spontaneous dopamine; (2) significantly decreased methamphetamine-stimulated dopamine; (3) significantly increased dopamine when co-infused with 30 mM potassium chloride; (4) lost the stimulatory effect of potassium chloride-evoked dopamine when calcium-free buffer was used and (5) exhibited moderate voltage-gated calcium channel blocking activity with an IC50 of 22 μM. These data demonstrate that compound 1 modulates dopaminergic function as determined by effects upon extracellular dopamine responses. It appears that compound 1 exerts these effects primarily through interaction with the DAT by blocking dopamine uptake via a calcium-dependent mechanism, and does not lead to extracellular efflux via the DAT. In conclusion, the findings suggest that compound 1 may have the potential to serve as a lead candidate for therapeutics designed to treat drug abuse and possibly disorders like Parkinson's disease.