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Vol. 304, Issue 3, 1181-1187, March 2003
Department of Pharmacology and Toxicology, University of Utah, Salt
Lake City, Utah
It has been hypothesized that high-dose methamphetamine treatment
rapidly redistributes cytoplasmic dopamine within nerve terminals,
leading to intraneuronal reactive oxygen species formation and well
characterized persistent dopamine deficits. We and others have reported
that in addition to this persistent damage, methamphetamine treatment
rapidly decreases vesicular dopamine uptake, as assessed in purified
vesicles prepared from treated rats; a phenomenon that may contribute
to aberrant intraneuronal dopamine redistribution proposedly caused by
the stimulant. Interestingly, post-treatment with dopamine transporter
inhibitors protect against the persistent dopamine deficits caused by
methamphetamine; however, mechanisms underlying this phenomenon have
not been elucidated. Also of interest are findings that dopamine
transporter inhibitors, including methylphenidate, rapidly increase 1)
vesicular dopamine uptake, 2) vesicular monoamine transporter-2
(VMAT-2) ligand binding, and 3) VMAT-2 immunoreactivity in a vesicular
subcellular fraction prepared from treated rats. Therefore, we
hypothesized that methylphenidate post-treatment might protect against
the persistent striatal dopamine deficits caused by methamphetamine by
rapidly affecting VMAT-2 and vesicular dopamine content. Results reveal
that methylphenidate post-treatment both prevents the persistent
dopamine deficits and reverses the acute decreases in vesicular
dopamine uptake and VMAT-2 ligand binding caused by methamphetamine
treatment. In addition, methylphenidate post-treatment reverses the
acute decreases in vesicular dopamine content caused by methamphetamine
treatment. Taken together, these findings suggest that methylphenidate
prevents persistent methamphetamine-induced dopamine deficits by
redistributing vesicles and the associated VMAT-2 protein and
presumably affecting dopamine sequestration. These findings not only
provide insight into the neurotoxic effects of methamphetamine but also
mechanisms underlying dopamine neurodegenerative disorders, including
Parkinson's disease.
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