The effects of selected drugs on monoamine neurons in brain has been examined. Fenfluramine, in high doses, has been found to decrease monoamine uptake sites in rat brain suggesting a neurotoxic effect at these high doses. The pharmacokinetics, and regional specificity as well as the time course of these effects have been examined. Also, DSP-4 has been shown to have different effects on norepinephrine uptake in the cerebral cortex versus the hypothalamus. These studies provide evidence for a heterogeneity of norepinephrine sites.