Abstract:The neurotoxic effect of 1 -methyl-4-phenyl-1 2,3,6-tetrahydropyridine (MPTP) was tested on mice lacking the dopamine (DA) transporter (DAT-/-mice). Striatal tissue DA content and glial fibrillary acidic protein (GFAP) mRNA expression were assessed as markers of MPTP neurotoxicity. MPTP (30 mg/kg, s.c., bid.) produced an 87% decrease in tissue DA levels and a 29-fold increase in the level of GFAP mRNA in the striatum of wild-type animals 48 h after administration. Conversely, there were no significant changes in either parameter in DAT-I--mice. Heterozygotes demonstrated partial sensitivity to MPTP administration as shown by an intermediate value (48%) of tissue DA loss. Direct intrastriatal infusion of the active metabolite of MPTP, 1 -methyl-4-phenylpyridinium (MPP t; 10 mM), via a microdialysis probe produced a massive efflux of DA in wild-type mice (>320-fold). In the DAT-/ -mice the same treatment produced a much smaller increase in extracellular DA (sixfold), which is likely secondary to tissue damage due to the implantation of the dialysis probe. These observations show that the DAT is a mandatory component for expression of MPTP toxicity in vivo. Key Words: Dopamine transporter-MPTP neurotoxicity-MPP+ -Glial fibrillary acidic protein-Microdialysis. J. Neurochem. 69, 1322-1325 (1997).1 -Methyl-4-phenyl-1 ,2,3,6-tetrahydropyridine (MPTP) is a potent neurotoxin that produces selective damage of midbrain dopaminergic neurons in humans and animals and therefore elicits neurochemical and neuropathological changes that are similar to idiopathic Parkinson's disease (for reviews, see Snyder and D'Amato, 1986;Kopin, 1992;Tipton and Singer, 1993). Many studies have attempted to elucidate the critical steps in MPTP neurotoxicity. Metabolic conversion of MPTP to a toxic metabolite, 1-methyl-4-phenylpyridinium (MPP~) mediated by monoamine oxidase B in glial cells (Heikkila et al., 1984), and selective uptake of MPP ± by dopaminergic neurons via the plasma membrane dopamine (DA) transporter (DAT) (Javitch et al., 1985) have been suggested as important steps in determining accessibility of the toxin into the neuron. Cellular neurotoxicity of MPP + is believed to be mainly mediated by inhibition of mitochondrial respiration by blockade of NADH oxidation (Ramsay and Singer, 1986), but generation of free radicals as well as other possible mechanisms have also been suggested (Chiueh et al., 1992;Tipton and Singer, 1993). Accumulation of the neurotoxin into synaptic vesicles via the vesicular monoamine transporter has been demonstrated as an important intraneuronal mechanism conferring MPP~resistance (Liu et al., 1992).This study focuses on elucidating the role of the DAT in MPTP toxicity in vivo in the mouse. The importance of the DAT in MPP + transport has been well documented in vitro (Javitch et al., 1985;Pifi et al., 1993), but the role of the DAT in MPTP neurotoxicity in vivo has been exclusively inferred from the protective effect of DAT inhibitors (Kopin, 1992). The recent availability of genetically altered...