This laboratory has demonstrated that a single methamphetamine (METH) injection rapidly and reversibly decreases the activity of the dopamine transporter (DAT), as assessed ex vivo in synaptosomes prepared from treated rats. This decrease does not occur because of residual drug introduced by the original injection or nor is it associated with a change in binding of the DAT ligand WIN35428. The purpose of this study was to elucidate the mechanism or mechanisms of this METH effect by determining whether direct application of this stimulant to synaptosomes causes changes in DAT similar to those observed ex vivo. Similar to the ex vivo effect, incubation of striatal synaptosomes with METH decreased DAT activity, but not WIN35428 binding: the effect on activity was not eliminated by repeated washing of synaptosomes. Also, as observed ex vivo, incubation with 3,4-methylenedioxymethamphetamine, but not cocaine or methylphenidate, caused a METH-like reduction in DAT function. The rapid and reversible METH-induced diminution in DAT activity did not occur because of a change in membrane potential, as assessed in vitro and ex vivo by [(3)H]tetraphenylphosphonium accumulation. However, the METH-related decline in DAT function may be attributed to phosphorylation because NPC15437, a protein kinase C inhibitor, attenuated the METH-induced decline in DAT function. Similarities between previously reported effects ex vivo of a single METH injection on serotonin and norepinephrine transporter function and effects of direct METH application in vitro were also found. Together, these data demonstrate that the in vitro incubation model mimics the rapid and reversible effects observed after a single METH injection.

Recent studies demonstrated that vesicular dopamine (DA) uptake can be rapidly altered in synaptic vesicles purified from the striata of stimulant-treated rats. Specifically, a single administration of the plasmalemmal DA transporter inhibitor, cocaine, or the DA D 2 agonist, quinpirole, increases vesicular DA uptake in vesicles purified from the striata of treated rats. These effects of cocaine are prevented by pretreatment with a D 2 , but not D 1 , DA receptor antagonist. The purpose of the present study was to characterize the effect of a mechanistically different psychostimulant, methamphetamine (METH), on vesicular DA uptake. Results demonstrated that a single administration of this DA-releasing agent rapidly and reversibly decreased vesicular DA uptake. The METH-related decrease in vesicular DA uptake was attenuated by pretreatment with the D 2 antagonist, eticlopride, but not the D 1 antagonist, SCH23390 (R-[ϩ]-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine). Core body temperature did not contribute to the effects of METH on vesicular DA uptake. Neither quinpirole nor cocaine increased vesicular DA uptake when rats were concurrently treated with METH. These studies provide further evidence that psychostimulants rapidly and differentially modify vesicular DA uptake. In addition, these studies demonstrate a complex role for D 2 DA receptors in altering vesicular DA transport.Sequestration of monoamines, such as dopamine (DA), into synaptic vesicles for storage and subsequent release, is mediated by the vesicular monoamine transporter-2 (VMAT-2). Recent studies demonstrate a novel mechanism whereby this sequestration is rapidly regulated by both psychostimulant and D 2 DA receptor agonist treatment. Specifically, Brown et al. (2001b) demonstrated that a single injection of cocaine or quinpirole increases vesicular [ 3 H]DA uptake, as assessed in synaptic vesicles purified from the striata of treated rats sacrificed 1 h after treatment. The cocaine-induced effect was not attributable to residual drug in the vesicular preparation, and was associated with an increase in B max of binding of the VMAT-2 ligand, Brown et al., 2001a). In addition, this increase was: 1) reversed within 6 h after drug treatment; 2) mimicked by administration of other DA transporter inhibitors (GBR-12935 and amfonelic acid); and 3) dependent on D 2 , but not D 1 , receptor activation (Brown et al., 2001a,b).Recent evidence suggests that not only do cocaine or D 2 receptor agonists rapidly alter vesicular DA uptake, but methamphetamine (METH) administration does as well.Specifically, multiple high-dose administrations of METH produce a rapid (within 1 h; Brown et al., 2000Brown et al., , 2001a and prolonged (persisting at least 24 h; Brown et al., 2000;Hogan et al., 2000) (Brown et al., 2001a). The purpose of the present study was to characterize and determine the role, if any, of DA receptors in this latter effect. Results demonstrated that a single METH administration rapidly and reversibly decreased...

No abstract

No abstract