Free radical production induced by methamphetamine in rat striatal synaptosomes


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Abstract

The pro-oxidative effect of methamphetamine (METH) in dopamine terminals was studied in rat striatal synaptosomes. Flow cytometry analysis showed increased production of reactive oxygen species (ROS) in METH-treated synaptosomes, without reduction in the density of dopamine transporters.In synaptosomes from dopamine (DA)-depleted animals, METH did not induce ROS production. Reserpine, in vitro, completely inhibited METH-induced ROS production. These results point to endogenous DA as the main source of ROS induced by METH. Antioxidants and inhibitors of neuronal nitric oxide synthase and protein kinase C (PKC) prevented the METH-induced oxidative effect.EGTA and the specific antagonist methyllycaconitine (MLA, 50 μM) prevented METH-induced ROS production, thus implicating calcium and α7 nicotinic receptors in such effect. Higher concentrations of MLA (>100 μM) showed nonspecific antioxidant effect.Preincubation of synaptosomes with METH (1 μM) for 30 min reduced [3H]DA uptake by 60%. The METH effect was attenuated by MLA and EGTA and potentiated by nicotine, indicating that activation of α7 nicotinic receptors and Ca2+ entry are necessary and take place before DAT inhibition.From these findings, it can be postulated that, in our model, METH induces DA release from synaptic vesicles to the cytosol. Simultaneously, METH activates α7 nicotinic receptors, probably inducing depolarization and an increase in intrasynaptosomal Ca2+. This would lead to DAT inhibition and NOS and PKC activation, initiating oxidation of cytosolic DA.[]

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