Toward development of an in vitro model of methamphetamine-induced dopamine nerve terminal toxicity

To develop an in vitro model of methamphetamine (METH) induced dopamine (DA ) neurotoxicity, striatal synaptosomes were incubated at 37 degrees C with METH for different periods of time (10-80 min), washed once, then tested fo r DA transporter function at 37 degrees C. METH produced time- and dose-dep endent reductions in the V-max of DA uptake, without producing any change i n K-m. Incubation of synaptosomes with the DA neurotoxins 1-methyl-4-phenyl -pyridinium ion, 6-hydroxydopamine, and amphetamine under similar condition s produced comparable effects. In contrast, incubation with fenfluramine, a serotonin neurotoxin, did not. METH-induced decreases in DA uptake were se lective, insofar as striatal glutamate uptake was unaffected. Various DA tr ansporter blockers (cocaine, methylphenidate, and bupropion) afforded compl ete protection against METH-induced decreases in DA uptake, without produci ng any effect themselves. METH's effects were also temperature dependent, w ith greater decreases in DA uptake occurring at higher temperatures. Tests for residual drug revealed small amounts (0.1-0.2 mu M) of remaining METH, but kinetic studies indicated that decreases in DA uptake were not likely t o be due to METH acting as a competitive inhibitor of DA uptake. Decreases in the V-max of DA uptake were not accompanied by decreases in B-max of [H- 3]WIN 35,428 binding, possibly because there is no mechanism for removing d amaged DA nerve endings from the in vitro preparation Collectively, these r esults give good support to the development of a valid in vitro model that may prove helpful for elucidating the mechanisms underlying METH-induced DA neurotoxicity.