Depletion of striatal dopamine transporter does not affect psychostimulant-induced locomotor activity

The effect of neurotoxin-induced depletion of striatal dopamine transporter (DAT) binding sites on animals' responses to psychostimulants was investigated. Multiple 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or methamphetamine (METH) injections but not a single METH injection to Swiss Webster mice resulted in > 60% depletion of striatal DAT. MPTP-induced depletion of DAT did not affect METH- and cocaine-stimulated locomotor activity compared with the response of control mice. Pre-exposure to either the neurotoxic or the single non-neurotoxic dose of METH resulted in a marked locomotor sensitization in response to METH or cocaine challenge injections. The present results indicate that > 60% loss in striatal DAT binding sites has no effect on animals' responses to psychostimulants, and suggest that neural systems other than striatal DAT may contribute to the induction of locomotor sensitization to METH and cocaine.     

Modulation of cocaine- and methamphetamine-induced behavioral sensitization by inhibition of brain nitric oxide synthase

Evidence suggests the existence of multiple interactions between dopamine, glutamate and nitric oxide (NO) in brain structures associated with psychomotor stimulation. The present study was undertaken to investigate the effect of the relatively selective inhibitor of the neuronal nitric oxide synthase (NOS) isoform, 7-nitroindazole (7-NI), on the development of sensitization to the locomotor stimulating effect of cocaine and methamphetamine (METH). Male Swiss Webster mice that received 15 mg/kg cocaine once a day for 5 days developed a marked locomotor sensitization to a challenge cocaine (15 mg/kg) or cross-sensitization to a challenge METH (0.5 mg/kg) injection given after a 10-day drug-free period. This treatment also produced a context-dependent sensitization as evident by the sensitized response to a challenge saline injection. Pretreatment with 7-NI (25 mg/kg) 30 min before cocaine administration (5 days) completely blocked the induction of sensitization to cocaine, the cross-sensitization to METH and the conditioned locomotion induced by cocaine. 7-NI when given alone, either acutely or for 5 days, had no significant effect on the locomotor activity of animals. Animals treated with METH (1.0 mg/kg) for 5 days developed marked sensitization to challenge METH (0.5 mg/kg), cross-sensitization to challenge cocaine (15 mg/kg) and context-dependent locomotion. Pretreatment with 7-NI (25 mg/kg) attenuated the sensitized response to METH and the cross-sensitization to cocaine as revealed after a 10-day drug-free period. However, the METH-induced conditioned locomotion was unaffected by the pretreatment with 7-NI. The present study supports the role of brain NO in the development of sensitization to both psychostimulants, cocaine and METH. However, it appears that the inability of 7-NI to completely abolish the sensitized responses induced after METH administration is the result of the resistible conditioned locomotion caused by METH, but not by cocaine.     

Role of nitric oxide in methamphetamine neurotoxicity: protection by 7-nitroindazole, an inhibitor of neuronal nitric oxide synthase

The role of nitric oxide (NO.) in the neurotoxic effects of methamphetamine (METH) was evaluated using 7-nitroindazole (7-NI), a potent inhibitor of neuronal nitric oxide synthase. Treatment of mice with 7-NI (50 mg/kg) almost completely counteracted the loss of dopamine, 3,4-dihydroxyphenylacetic acid, and tyrosine hydroxylase immunoreactivity observed 5 days after four injections of 10 or 7.5 mg/kg METH. With the higher dose of METH, this protection at 5 days occurred despite the fact that combined administration of METH and 7-NI significantly increased lethality and exacerbated METH-induced dopamine release (as indicated by a greater dopamine depletion at 90 min and 1 day). Combined treatment with 4 x 10 mg/kg METH and 7-NI also slightly increased the body temperature of mice as compared with METH alone. Thus, the neuroprotective effects of 7-NI are independent from lethality, are not likely to be related to a reduction of METH-induced dopamine release, and are not due to a decrease in body temperature. These results indicate that NO. formation is an important step leading to METH neurotoxicity, and suggest that the cytotoxic properties of NO. may be directly involved in dopaminergic terminal damage.     

Rapid ATP loss caused by methamphetamine in the mouse striatum: relationship between energy impairment and dopaminergic neurotoxicity

To study the relationship between energy impairment and the effects of d-methamphetamine (METH) on dopaminergic neurons, ATP and dopamine levels were measured in the brain of C57BL/6 mice treated with either a single or four injections of METH (10 mg/kg, i.p.) at 2-h intervals. Neither striatal ATP nor dopamine concentrations changed after a single injection of METH, but both were significantly decreased 1.5 h after the multiple-dose regimen. The effects of METH on ATP levels appear to be selective for the striatum, as ATP concentrations were not affected in the cerebellar cortex and hippocampus after either a single or multiple injections of METH. In a second set of experiments, an intraperitoneal injection of 2-deoxyglucose (2-DG; 1 g/kg), an inhibitor of glucose uptake and utilization, was given 30 min before the third and fourth injections of METH. 2-DG significantly potentiated METH-induced striatal ATP loss at 1.5 h and dopamine depletions at 1.5 h and 1 week. These results indicate that a toxic regimen of METH selectively causes striatal energy impairment and raise the possibility that perturbations of energy metabolism play a role in METH-induced dopaminergic neurotoxicity.     

Lowering ambient or core body temperature elevates striatal MPP+ levels and enhances toxicity to dopamine neurons in MPTP-treated mice

The neuroprotective effects of lowering body temperature have been well documented in various models of neuronal injury. The present study investigated the effects a lower ambient or core body temperature would have on damage to striatal dopamine (DA) neurons produced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Mice received systemic MPTP treatment at two different temperatures, 4 degrees C and 22 degrees C. MPTP-treated mice maintained at 4 degrees C demonstrated (1) a greater hypothermic response, (2) a significant reduction in striatal DA content and tyrosine hydroxylase (TH) activity, and (3) significantly greater striatal 1-methyl-4-phenylpyridinium (MPP+) levels, as compared to mice dosed with MPTP at room temperature. Parallel studies with methamphetamine (METH) were conducted since temperature appears to play a pivotal role in the mediation of damage to DA neurons by this CNS stimulant in rodents. As previously reported, METH-induced hyperthermia and the subsequent loss of striatal DA content were attenuated in animals dosed at 4 degrees C. We also evaluated the effects a hypothermic state induced by pharmacological agents would have on striatal neurochemistry and MPP+ levels following MPTP treatment. Concurrent administration of MK-801 or 8-OHDPAT increased the striatal MPP+ levels following MPTP treatment. However, only 8-OHDPAT potentiated the MPTP-induced decrements of striatal DA content and TH activity; MK-801 did not affect MPTP decreases in these striatal markers of dopaminergic damage. Altogether, these findings indicate that temperature has a profound effect on striatal MPP+ levels and MPTP-induced damage to DA neurons in mice.     

A new concept of cotreatment with human growth hormone and menotropins in ovulation induction protocols

Inhibition of Na+/K+ ATPase by cardiac glycosides has been shown to potentiate toxic effects of excitatory amino acids and mitochondrial poisons in neurons in vitro. The present study tested the hypothesis that the systemic administration of the cardiac glycoside, digoxin, potentiates effects of the dopamine neurotoxin 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) in vivo. Mice were injected with digoxin (1 mg/kg) or vehicle followed by MPTP (20 mg/kg) or saline 1 h later. After 1 or 8 days, mice were euthanized and dopamine levels in the striatum were measured by high-performance liquid chromatography with electrochemical detection. MPTP caused a significant 35-45% reduction in striatal dopamine levels compared to those in control mice. However, pretreatment with digoxin completely prevented the MPTP-induced dopamine depletion. This result was unexpected and suggests that cardiac glycosides may protect against MPTP neurotoxicity.     

Exacerbation of methamphetamine-induced neurochemical deficits by melatonin

Methamphetamine (METH), administered in large, repeated doses, compromises the dopaminergic and serotonergic systems as indicated by prolonged suppression of tyrosine hydroxylase and tryptophan hydroxylase activity and concurrent decreases in the content of dopamine and 5-hydroxytryptamine. Because dopamine is necessary for these dopaminergic and serotonergic deficits we postulated that dopamine and/or its reactive metabolites are responsible for these degenerative alterations. Because we previously demonstrated that in vitro reducing conditions reverse the decrease in tryptophan hydroxylase activity, we reasoned that melatonin, a purported endogenous antioxidant, may alter this response. Rats were treated with METH and/or melatonin and trytophan hydroxylase activity and 5-hydroxytryptamine content were assessed; tyrosine hydroxylase activity and dopamine content were also measured. Not only did melatonin not prevent METH-induced deficits in serotonergic and dopaminergic parameters, but coadministration of melatonin with METH actually enhanced most of the monoaminergic effects of METH. This enhancing effect could not be attributed to alteration of body temperature. Because METH abuse causes insomnia and melatonin is promoted in some countries for insomnia, the implications of the interaction between these two drugs could be clinically important.     

Delta opioid peptide [D-Ala2,D-leu5]enkephalin blocks the long-term loss of dopamine transporters induced by multiple administrations of methamphetamine: involvement of opioid receptors and reactive oxygen species

Delta opioid peptide [D-Ala2,D-leu5]enkephalin (DADLE) can prolong organ preservation and increases myocardial tolerance to ischemia. Our study examined the protective property of DADLE against methamphetamine- (METH) induced dopaminergic terminal damage in the central nervous system. Because the neurotoxicity of METH involves reactive oxygen species, we also examined if DADLE might be an antioxidative agent in vitro. DADLE at 2 and 4 mg/kg (i.p.), given 30 min before each METH administration (5 or 10 mg/kg, i.p., four injections in a day at 2-hr intervals), dose-dependently blocked the METH-induced long-term dopamine transporter loss. The opioid antagonist naltrexone blocked this action of DADLE in both aspects of striata but tends not to affect the effects of DADLE in the nucleus accumbens. DADLE did not alter changes in body temperature induced by METH. The reduction of striatal dopaminergic content and tyrosine hydroxylase activity caused by METH, however, were not blocked by DADLE. In vitro, DADLE was approximately equipotent to glutathione in inhibiting both superoxide anion formation induced by xanthine oxidase and hydroxyl radical formation evoked by ferrous/citrate complex. DADLE was only slightly less potent than glutathione in inhibiting the iron/ascorbate-induced brain lipid peroxidation. These results suggest that DADLE can protect the terminal membranes of dopaminergic neurons against METH-induced insult but not the loss of dopaminergic content and tyrosine hydroxylase activity and that this action of DADLE might involve opioid receptors as well as the sequestration of free radical.     

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyride neurotoxicity is attenuated in mice overexpressing Bcl-2

The proto-oncogene Bcl-2 rescues cells from a wide variety of insults. Recent evidence suggests that Bcl-2 protects against free radicals and that it increases mitochondrial calcium-buffering capacity. The neurotoxicity of 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyride (MPTP) is thought to involve both mitochondrial dysfunction and free radical generation. We therefore investigated MPTP neurotoxicity in both Bcl-2 overexpressing mice and littermate controls. MPTP-induced depletion of dopamine and loss of [3H]mazindol binding were significantly attenuated in Bcl-2 overexpressing mice. Protection was more profound with an acute dosing regimen than with daily MPTP administration over 5 d. 1-Methyl-4-phenylpyridinium (MPP+) levels after MPTP administration were similar in Bcl-2 overexpressing mice and littermates. Bcl-2 blocked MPP+-induced activation of caspases. MPTP-induced increases in free 3-nitrotyrosine levels were blocked in Bcl-2 overexpressing mice. These results indicate that Bcl-2 overexpression protects against MPTP neurotoxicity by mechanisms that may involve both antioxidant activity and inhibition of apoptotic pathways.     

Substrates of energy metabolism attenuate methamphetamine-induced neurotoxicity in striatum

High doses of methamphetamine (METH) produce a long-term depletion in striatal tissue dopamine content. The mechanism mediating this toxicity has been associated with increased concentrations of dopamine and glutamate and altered energy metabolism. In vivo microdialysis was used to assess and alter the metabolic environment of the brain during high doses of METH. METH significantly increased extracellular concentrations of lactate in striatum and prefrontal cortex. This increase was significantly greater in striatum and coincided with the greater vulnerability of this brain region to the toxic effects of METH. To examine the effect of supplementing energy metabolism on METH-induced dopamine content depletions, the striatum was perfused directly with decylubiquinone or nicotinamide to enhance the energetic capacity of the tissue during or after a neurotoxic dosing regimen of METH. When decylubiquinone or nicotinamide was perfused into striatum during the administration of METH, there was no significant effect on METH-induced striatal dopamine efflux, glutamate efflux, or the long-term dopamine depletions measured 7 days later. However, a delayed perfusion with decylubiquinone or nicotinamide for 6 h beginning immediately after the last METH injection attenuated the METH-induced striatal dopamine depletions measured 1 week later. These results support the hypothesis that the compromised metabolic state produced by METH administration predisposes dopamine terminals to the neurotoxic effects of glutamate, dopamine, and/or free radicals.     

Effects of testosterone upon MPTP-induced neurotoxicity of the nigrostriatal dopaminergic system of C57/B1 mice

We have recently reported that treatment of gonadectomized female and male C57/B1 mice with the gonadal steroid hormone, estrogen, reduced nigrostriatal dopaminergic neurotoxicity resulting from the Parkinson's-like inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In the present report we examined whether the predominantly male gonadal steroid hormone, testosterone, would similarly modulate MPTP-induced neurotoxicity. Male C57/B1 mice were assigned to one of the following five treatment conditions: (1) Intact, (2) Orchidectomized, (3) Intact + MPTP, (4) Orchidectomized + Testosterone + MPTP and (5) Orchidectomized + MPTP. Corpus striatal and olfactory tubercle dopamine. DOPAC and norepinephrine concentrations were determined from the animals within each of the five treatment conditions. Orchidectomy alone failed to alter striatal dopamine and DOPAC concentrations, with levels obtained being similar to that of Intact animals. MPTP treatment significantly reduced striatal reduced striatal dopamine and DOPAC concentrations, regardless of hormonal condition of the animal. Similar results were obtained for olfactory tubercle determinations, with the exception that DOPAC levels from Orchidectomized mice were significantly greater than Intact males. No significant differences were obtained for norepinephrine within either brain area sampled. These results show that unlike estrogen, testosterone is devoid of any capacity to modulate nigrostriatal dopaminergic neurotoxicity resulting from MPTP. These findings may be related to the gender differences which exist in the prevalence of Parkinson's disease.     

Expression of matrix proteins in uterine cervical neoplasia using immunohistochemistry

We investigated whether oral administration of coenzyme Q10 (CoQ10) could attenuate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in one-year-old mice. Four groups of one-year-old, male C57BL/6 mice received a either standard diet or a diet supplemented with CoQ10 (200 mg/kg/day) for five weeks. After four weeks, one group that had received the standard diet and one group that had received the CoQ10 supplemented diet were treated with MPTP. The four groups continued on their assigned diets for an additional week prior to sacrifice. Striatal dopamine concentrations were reduced in both groups treated with MPTP, but they were significantly higher (37%) in the group treated with CoQ10 and MPTP than in the group treated with MPTP alone. The density of tyrosine hydroxylase immunoreactive (TH-IR) fibers in the caudal striatum was reduced in both MPTP-treated groups, but the density of TH-IR fibers was significantly (62%) greater in the group treated with CoQ10 and MPTP than in the group treated with MPTP alone. Our results indicate that CoQ10 can attenuate the MPTP-induced loss of striatal dopamine and dopaminergic axons in aged mice and suggest that CoQ10 may be useful in the treatment of Parkinson's disease.     

Electroconvulsive shock does not modify striatal contents of dopamine in MPTP-treated mice

It has been suggested that the therapeutic response to electroconvulsive therapy in depressed patients could be mediated by functional changes in the dopaminergic pathways; a favorable response to electroconvulsive therapy was also observed recently in patients with Parkinson's disease. To study a possible interference of electroconvulsive shock in the course of MPTP-induced parkinsonism in rodents, we measured the striatal content of dopamine in MPTP-treated mice that received electroconvulsive shock at various intervals in the course of MPTP neurotoxicity. Our results showed no immediate or delayed differences in striatal dopamine content of animals that received MPTP and electroconvulsive shock when compared with animals that received only MPTP, thus suggesting that the strong biological effects of MPTP and electroconvulsive shock on the brain may follow different biochemical mechanisms.     

A robust increase in expression of arc gene, an effector immediate early gene, in the rat brain after acute and chronic methamphetamine administration

The effect of acute and chronic administration of methamphetamine (METH) on the levels of activity-regulated cytoskeleton-associated protein (arc), an effector-immediate early gene, mRNA has been investigated in rat brain using in situ hybridization. Levels of arc mRNAs in the brain regions examined increased significantly from 0.5-1 h after an acute METH (4 mg/kg) administration compared with basal levels. The increase in arc mRNA continued by 3 h, and then subsided to basal levels by 6 h. The degree of increase in arc mRNA and the peak time after METH administration varied according to brain area. Arc mRNA in cerebral cortices showed robust increase 1 h after METH administration. In the striatum and hippocampus, it showed earlier and later increase, respectively, and its degree of both was less than in the cortices. Microscopic examination revealed that the METH-induced arc mRNAs in the parietal cortex were enriched in layers IV and VI, and those in the striatum existed mainly in the medium-sized neuron. Pretreatment with either 0.5 mg/kg SCH23390 or 0.25 mg/kg MK-801 almost completely blocked the enhanced striatal arc mRNA levels induced by acute METH administration, whereas such pretreatments only partially reduced the effect of METH in the cerebral cortical regions. In the chronic treatment experiment, the arc mRNA levels of the group that received chronic treatment with METH followed by a METH challenge showed an increase like seen after acute METH administration. Since previous studies proposed that arc is one of cytoskeleton-associated proteins and is selectively localized in neural dendrites, the results of the present study suggested that arc may play an important role in the synaptic plasticity underlying METH-induced adaptational changes including behavioral sensitization.     

The effects of deprenyl on methamphetamine-induced dopamine depletions

The effects of deprenyl on methamphetamine-induced dopamine depletions were studied in mice. Four SC injections of 12.5 mg/kg of methamphetamine at two-hour intervals caused substantial (72-82%) and long-lasting depletions of striatal dopamine. Pretreatment with either 25 or 40 mg/kg of deprenyl did not significantly alter the magnitude of this depletion. These results indicate that, unlike what is observed following MPTP, there is no protection afforded dopaminergic cells by deprenyl pretreatment in the methamphetamine model of parkinsonism.     

Mammalian artificial chromosomes as tools for gene therapy

Parkinson's disease (PD) is one of the most frequent disorders of the basal ganglia. From epidemiological studies there is a controversial discussion on the question whether tobacco smoking is correlated with a decreased incidence of PD. The present study aimed to elucidate the role of nicotine and its potential neuroprotective effects in a rodent model of PD. These effects may be related to an altered hydroxyl radical formation; this possibility was studied in vitro. Nicotine and alpha-phenyl-N-tert-butyl nitrone (PBN) were examined in a cell-free in vitro Fenton system (Fe3+/EDTA + H2O2) for their radical scavenging properties using the salicylate trapping method. Salicylic acid (0.5 mM) was incubated in the presence and absence of nicotine or PBN and the main products of the reaction of hydroxyl radicals with salicylic acid, namely 2,3- and 2,5-dihydroxybenzoic acid, were immediately determined using HPLC in combination with electrochemical detection. Nicotine and PBN were both able to significantly reduce hydroxyl radical levels at concentrations of 1, 2.5 and 5 mM. Interestingly, at 5 mM nicotine was able to reduce hydroxyl radical levels significantly more than the radical scavenger PBN (5 mM). To investigate the in vivo effects of nicotine, male C57BL/6 mice were used in the MPTP mouse model of PD. Nicotine (0.1 or 0.4 mg/kg s.c.) was administered twice daily for a period of 14 days. On day 8 a single injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 30 mg/kg s.c.) was given as well as an enhanced protocol of nicotine treatment (0.1 or 0.4 mg/kg s.c., 30 min before MPTP and 30, 90, 210, 330, 450, 570 min after MPTP) for a total of seven injections of nicotine. High dosage nicotine treatment significantly increased the MPTP-induced loss of body weight and resulted in a significantly decreased striatal dopamine content and an increased dopamine turnover in comparison with the MPTP-treated controls at day 15. However, the lower dosage of nicotine did not significantly alleviate the MPTP-induced effects, although some parameters showed a slight tendency in this direction. These results demonstrate that in vitro nicotine has radical scavenging properties which might suggest neuroprotective effects. In vivo experiments with nicotine, however, showed that a low dosage of nicotine did not alleviate the MPTP-induced dopamine depletion, but a large dosage even enhanced it.     

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) decreases glutamate uptake in cultured astrocytes

The deleterious effect of the parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on dopaminergic neurons of the substantia nigra is well established. In addition, increased glutamatergic drive to basal ganglia output nuclei is considered a likely contributor to the pathogenesis of Parkinson's disease. One possibility for the increased excitatory tone may be related to an impairment in glutamate uptake. As astrocytes possess efficient transport mechanisms for both MPTP and glutamate, we have examined the effect of this agent on D-aspartate uptake into these cells. Treatment of cultures with 50 microM MPTP for 24 h decreased uptake by 39%. Kinetic analysis revealed that this effect was due to a 35% decrease in Vmax with no change in the Km. Treatment with deprenyl, a monoamine oxidase B inhibitor, produced a complete reversal of MPTP-induced uptake inhibition, but was ineffective following exposure of cells to the MPTP metabolite, 1-methyl-4-phenylpyridinium (MPP+). Removal of MPTP from cultures resulted in a complete restoration of glutamate uptake after 24 h. These results show that MPTP reversibly compromises glutamate uptake in cultured astrocytes, which is dependent on the conversion of MPTP to MPP+. Such findings suggest that the glutamate transporter in astrocytes plays an important role in MPTP-induced neurotoxicity and possibly in parkinsonism.     

A heroin-, but not a cocaine-expecting, self-administration state preferentially alters endogenous brain peptides

The effects of L-type voltage-dependent Ca2+ channel blockers on apomorphine, bromocriptine and morphine-induced changes in locomotor activity were examined in mice. Apomorphine (4 mg/kg) and morphine (20 mg/kg) produced locomotor stimulation. Bromocriptine (8 mg/kg) produced a biphasic effect on motor behaviour, an early depressant phase, followed by locomotor stimulation. Amlodipine (2.5 mg/kg), nicardipine (10 mg/kg), diltiazem (10 mg/kg) and verapamil (10 mg/kg), which by itself did not affect locomotor activity, inhibited the stimulant phase of bromocriptine without altering the depressant phase, while they did not affect apomorphine- and morphine-induced locomotor stimulation. Apomorphine, bromocriptine and morphine-induced locomotor stimulation was decreased by SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7- ol) (0.05 mg/kg) or haloperidol (0.1 mg/kg). These results indicate that L-type voltage-dependent Ca2+ channels are involved in the motor stimulant effect of bromocriptine, but not in apomorphine- and morphine-induced locomotor stimulation. The effects of Ca2+ channel blockers on the dopaminergic system appears not to be directly related to dopamine receptor blockade.     

Genetic evidence for mother-to-infant transmission of hepatitis G virus

Administration of a single high dose of methamphetamine (METH) causes a rapid and reversible decrease in the activity of the tryptophan hydroxylase (TPH), the rate-limiting enzyme in the synthesis of 5-hydroxytryptamine. This effect can be reversed completely by exposing the METH-impaired enzyme to a reducing environment, which suggests that the decrease in TPH activity is a reversible oxidative consequence of free radical formation. Consistent with this hypothesis, a single METH administration to male rats increased oxygen radical formation, as demonstrated by increased striatal dihydroxybenzoic acid formation after coadministration of salicylate with METH. Prevention of METH-induced hyperthermia attenuated both the increase in dihydroxybenzoic acid formation and the decrease in TPH activity observed 1 h after METH administration. These data suggest that both reactive oxygen species and hyperthermia contribute to the acute decrease in TPH activity which results from a single METH administration.     

A chemiluminescent microtiter plate assay for sensitive detection of protein kinase activity

The toxic effects of methamphetamine (METH) (2.5, 5.0 and 10.0 mg/kg) and methylenedioxymethamphetamine (MDMA) (5.0, 10.0 and 20.0 mg/kg) on dopaminergic systems were assessed in the striatum and of the nucleus accumbens in mdr1a wild-type and knockout mice. METH caused significant dose-dependent decreases of dopamine (DA) and DA transporters (DAT) in the striatum and the nucleus accumbens (NAc) of both wild-type and knockout mice. The lowest doses of METH (2.5 mg/kg) caused only small changes in the wild-type, but marked. decreases in the mdr1a knockout mice. The two higher doses (5 mg/kg and 10 mg/kg) caused similar changes in both strains of mice. In contrast to METH, MDMA caused greater percentage decreases in DAT in the wild-type mice. For example, the lowest dose (5 mg/kg) caused significant decreases in DAT in the NAc of wild-type but not of mdr1a knockout mice. The highest dose (20 mg/kg) caused similar changes in both the strains. These results suggest that METH and MDMA interact differentially with P-glycoproteins. These observations document, for the first time, a role for these proteins in the entry of METH and MDMA into the brain via the blood-brain barrier, with P-glycoprotein possibly facilitating the entry of MDMA but interfering with that of METH into the brain.