Use of in vitro superfusion to assess the dynamics of striatal dopamine clearance: influence of estrogen

To determine the feasibility of assessing dopamine uptake using in vitro superfusion, striatal tissue from ovariectomized female rats was infused with dopamine (1 μM), nomifensine (1 mM), or a combination of dopamine and nomifensine. Treatment with nomifensine or dopamine/nomifensine increased the recovery of dopamine in the effluent samples as compared to treatment with dopamine alone. In Experiment 2, the striatal tissue was treated with varying concentrations (0, 3, 30 or 300 nM) estradiol throughout the superfusion and subsequently given a dopamine (1 μM) challenge. The recovery of dopamine was enhanced in the presence of 3 and 30 nM estradiol. These results show that (1) in vitro superfusion can be used to dynamically evaluate dopamine recovery, and (2) estradiol, like nomifensine, increases the recovery of exogenously applied dopamine from the striata of ovariectomized female rats. Such increases in dopamine recovery with estrogen and similarities to that obtained with nomifensine suggest that estrogen may be inhibiting dopamine uptake from these striatal tissue fragments. Moreover, the doses at which estrogen can exert these effects insinuates a physiological role for this process. Our data provide a clear functional demonstration for one of the mechanisms by which estradiol can modulate striatal dopamine neurons, that of an uptake inhibitor. Such a mechanism has important implications with regard to estradiol's capacity to function as a neuroprotectant of the nigrostriatal dopaminergic system through inhibition of uptake of neurotoxins which can produce neurodegeneration of striatal dopamine neurons.