Estimating hydroxyl radical content in rat brain using systemic and intraventricular salicylate: impact of methamphetamine

Parkin-deficient mice are not more sensitive to 6-hydroxydopamine or methamphetamine neurotoxicity

Background

Autosomal recessive juvenile parkinsonism (AR-JP) is caused by mutations in the parkin gene which encodes an E3 ubiquitin-protein ligase. Parkin is thought to be critical for protecting dopaminergic neurons from toxic insults by targeting misfolded or oxidatively damaged proteins for proteasomal degradation. Surprisingly, mice with targeted deletions of parkin do not recapitulate robust behavioral or pathological signs of parkinsonism. Since Parkin is thought to protect against neurotoxic insults, we hypothesized that the reason Parkin-deficient mice do not develop parkinsonism is because they are not exposed to appropriate environmental triggers. To test this possibility, we challenged Parkin-deficient mice with neurotoxic regimens of either methamphetamine (METH) or 6-hydroxydopamine (6-OHDA). Because Parkin function has been linked to many of the pathways involved in METH and 6-OHDA toxicity, we predicted that Parkin-deficient mice would be more sensitive to the neurotoxic effects of these agents.

Results

We found no signs consistent with oxidative stress, ubiquitin dysfunction, or degeneration of striatal dopamine neuron terminals in aged Parkin-deficient mice. Moreover, results from behavioral, neurochemical, and immunoblot analyses indicate that Parkin-deficient mice are not more sensitive to dopaminergic neurotoxicity following treatment with METH or 6-OHDA.

Conclusion

Our results suggest that the absence of a robust parkinsonian phenotype in Parkin-deficient mice is not due to the lack of exposure to environmental triggers with mechanisms of action similar to METH or 6-OHDA. Nevertheless, Parkin-deficient mice could be more sensitive to other neurotoxins, such as rotenone or MPTP, which have different mechanisms of action; therefore, identifying conditions that precipitate parkinsonism specifically in Parkin-deficient mice would increase the utility of this model and could provide insight into the mechanism of AR-JP. Alternatively, it remains possible that the absence of parkinsonism in Parkin-deficient mice could reflect fundamental differences between the function of human and mouse Parkin, or the existence of a redundant E3 ubiquitin-protein ligase in mouse that is not found in humans. Therefore, additional studies are necessary to understand why Parkin-deficient mice do not display robust signs of parkinsonism.

Methamphetamine-induced neuronal apoptosis involves the activation of multiple death pathways. Review

The abuse of the illicit drug methamphetamine (METH) is a major concern because it can cause terminal degeneration and neuronal cell death in the brain. METH-induced cell death occurs via processes that resemble apoptosis. In the present review, we discuss the role of various apoptotic events in the causation of METH-induced neuronal apoptosis in vitro and in vivo. Studies using comprehensive approaches to gene expression profiling have allowed for the identification of several genes that are up-regulated or down-regulated after an apoptosis-inducing dose of the drug. Further experiments have also documented the fact that the drug can cause demise of striatal enkephalinergic neurons by cross-talks between mitochondria-, endoplasmic reticulum- and receptor-mediated apoptotic events. These neuropathological observations have also been reported in models of drug-induced neuroplastic alterations used to mimic drug addiction (Nestler, 2001).

Methamphetamine and lipid peroxidation in the rat retina

BACKGROUND

The use of psychoactive drugs during adolescence and early adult life has increased in the last few decades. It is known that developmental exposure to psychostimulants affects the sensory systems, and the retina has been shown to be a target tissue. This work was conducted to evaluate the pattern of lipid peroxidation in the rat retina following prenatal exposure to methamphetamine (MA).

METHODS

Pregnant female Wistar rats were given MA (5 mg/kg of body weight/day; SC, in 0.9% saline) from GD 8 to 22. Offspring were sacrificed at postnatal days (PNDs) 7, 14, and 21. The retinas were homogenized, and both the total antioxidant and superoxide dismutase (SOD) activities were measured by enzymatic-colorimetric methods. The lipid peroxidation byproducts (malondialdehyde [MDA] and MDA-like metabolites) were measured by the thiobarbituric acid test.

RESULTS

Total antioxidant levels were lower in the MA group at PND 21 in both males and females. The activity of SOD was higher in PND 7 females from the MA group. MDA levels were higher in the MA group at PND 21 in both genders.

CONCLUSIONS

These findings suggest that prenatal-induced MA toxicity in the retina may be related to lipid peroxidation processes and oxidative stress.

Ascorbate attenuates trimethyltin-induced oxidative burden and neuronal degeneration in the rat hippocampus by maintaining glutathione homeostasis

The specific role of endogenous glutathione in response to neuronal degeneration induced by trimethyltin (TMT) in the hippocampus was examined in rats. A single injection of TMT (8 mg/kg, i.p.) produced a rapid increase in the formation of hydroxyl radical and in the levels of malondialdehyde (MDA) and protein carbonyl. TMT-induced seizure activity significantly increased after this initial oxidative stress, and remained elevated for up to 2 weeks post-TMT. Although a significant loss of hippocampal Cornus Ammonis CA1, CA3 and CA4 neurons was observed at 3 weeks post-TMT, the elevation in the level of hydroxyl radicals, MDA, and protein carbonyl had returned to near-control levels at that time. In contrast, the ratio of reduced to oxidized glutathione remained significantly decreased at 3 weeks post-TMT, and the glutathione-like immunoreactivity of the pyramidal neurons was decreased. However glutathione-positive glia-like cells proliferated mainly in the CA1, CA3, and CA4 sectors and were intensely immunoreactive. Double labeling demonstrated the co-localization of glutathione-immunoreactive glia-like cells and reactive astrocytes, as indicated by immunostaining for glial fibrillary acidic protein. This suggests that astroglial cells were mobilized to synthesize glutathione in response to the TMT insult. The TMT-induced changes in glutathione-like immunoreactivity appear to be concurrent with changes in the expression levels of glutathione peroxidase and glutathione reductase. Ascorbate treatment significantly attenuated TMT-induced seizures, as well as the initial oxidative stress, impaired glutathione homeostasis, and neuronal degeneration in a dose-dependent manner. These results suggest that ascorbate is an effective neuroprotectant against TMT. The initial oxidative burden induced by TMT may be a causal factor in the generation of seizures, prolonged disturbance of endogenous glutathione homeostasis, and consequent neuronal degeneration.

Metallothionein provides zinc-mediated protective effects against methamphetamine toxicity in SK-N-SH cells

Methamphetamine (METH) is a drug of abuse and neurotoxin that induces Parkinson's-like pathology after chronic usage by targeting dopaminergic neurons. Elucidation of the intracellular mechanisms that underlie METH-induced dopaminergic neuron toxicity may help in understanding the mechanism by which neurons die in Parkinson's disease. In the present study, we examined the role of reactive oxygen species (ROS) in the METH-induced death of human dopaminergic SK-N-SH cells and further assessed the neuroprotective effects of zinc and metallothionein (MT) against METH-induced toxicity in culture. METH significantly increased the production of reactive oxygen species, decreased intracellular ATP levels and reduced the cell viability. Pre-treatment with zinc markedly prevented the loss of cell viability caused by METH treatment. Zinc pre-treatment mainly increased the expression of metallothionein and prevented the generation of reactive oxygen species and ATP depletion caused by METH. Chelation of zinc by CaEDTA caused a significant decrease in MT expression and loss of protective effects of MT against METH toxicity. These results suggest that zinc-induced MT expression protects dopaminergic neurons via preventing the accumulation of toxic reactive oxygen species and halting the decrease in ATP levels. Furthermore, MT may prevent the loss of mitochondrial functions caused by neurotoxins. In conclusion, our study suggests that MT, a potent scavenger of free radicals is neuroprotective against dopaminergic toxicity in conditions such as drug of abuse and in Parkinson's disease.

Neurodegeneration and neuroprotection in Parkinson disease

Many of the motoric features that define Parkinson disease (PD) result primarily from the loss of the neuromelanin (NM)-containing dopamine (DA) neurons of the substantia nigra (SN), and to a lesser extent, other mostly catecholaminergic neurons, and are associated with cytoplasmic "Lewy body" inclusions in some of the surviving neurons. While there are uncommon instances of familial PD, and rare instances of known genetic causes, the etiology of the vast majority of PD cases remains unknown (i.e., idiopathic). Here we outline genetic and environmental findings related to PD epidemiology, suggestions that aberrant protein degradation may play a role in disease pathogenesis, and pathogenetic mechanisms including oxidative stress due to DA oxidation that could underlie the selectivity of neurodegeneration. We then outline potential approaches to neuroprotection for PD that are derived from current notions on disease pathogenesis.

Reactive oxidative and nitrogen species in the nigrostriatal system following striatal 6-hydroxydopamine lesion in rats

Oxidative stress is a major contributing factor in the pathogenesis of Parkinson's disease. We therefore investigated the effect of the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) on hydroxyl-free radical and peroxynitrite formation in the intrastriatal 6-OHDA rat model of Parkinson's disease. The hydroxylation product of salicylate (2,3-dihydroxy-benzoic acid) as well as the hydroxylation and nitration products of d-phenylalanine (2- and 3-hydroxyl-phenylalanine, nitrotyrosine and nitrophenylalanine) were assessed in tissue samples of the striatum and, for the first time, the substantia nigra of adult rats at four different time points (25 min, 2 h, 4 h and 7 days) after unilateral stereotaxic intrastriatal injection of 6-OHDA. In the striatum, maxima of hydroxylating and nitrating markers were found at early time points after 6-OHDA lesion. These results suggest a direct interrelation between 6-OHDA-autoxidation and/or the increased dopamine turnover and hydroxyl-free radical and peroxynitrite formation. In the substantia nigra, i.e., at a distance from the injection site of the neurotoxin, an increase in hydroxyl-free radical formation was observed at 7 days after 6-OHDA lesion, with this modification possibly being independent of 6-OHDA autoxidation and rather representing a long-term effect of the toxin. Furthermore, we conclude that apart from the formation of reactive oxygen species, the production of reactive nitrogen species occurs in this experimental Parkinson's disease model. Finally, the similarity between the 6-OHDA model and Parkinson's disease supports the notion that reactive oxygen species as well as reactive nitrogen species may play an important role in the pathogenesis of this neurodegenerative disorder.

Periadolescent rats (P41-50) exhibit increased susceptibility to D-methamphetamine-induced long-term spatial and sequential learning deficits compared to juvenile (P21-30 or P31-40) or adult rats (P51-60)

We have previously shown that P11-20 treatment with d-methamphetamine (MA) induces impaired spatial navigation in the Morris water maze (MWM), whereas P1-10 treatment does not. Little is known about the long-term behavioral consequences of MA during juvenile, adolescent, and early adult brain development. In dose-response experiments, we tested successive 10-day intervals of exposure to MA in rats (P21-30, P31-40, P41-50, and P51-60; four doses per day). MA dosing prior to P21 produces little or no toxicity; however, we observed an increased toxicity with advancing age. Across-age comparisons revealed no MWM acquisition or Cincinnati water maze (CWM) effects after MA treatment on P21-30 (2.5-10 mg/kg/dose), P31-40 (1.25-7.5 mg/kg/dose), or P51-60 (1.25-5.0 mg/kg/dose); however, significantly impaired MWM acquisition was observed after P41-50 MA treatment at the highest dose (6.25 mg/kg/dose). Learning in the CWM was also impaired in this group. No effects were seen at 1.25, 2.5, or 5 mg/kg/dose following P41-50 MA treatment. MWM reversal learning trials after P41-50 treatment showed a trend towards longer latency in all MA dose groups, but no effect on double-reversal trials. Reversal and double-reversal also showed no effects at the other exposure ages. No differences in straight channel swimming or cued learning in the MWM were seen after MA treatment at any exposure age. P41-50 is the periadolescent stage of brain development in rodents. The effects observed at this age may suggest a previously unrecognized period of susceptibility for MA-induced cognitive deficits.

Neuronal inclusions in degenerative disorders

This brief paper analyzes a few degenerative diseases expressing as movement disorders and featuring at sub-cellular level the presence of neuronal inclusions in selective brain regions. We will first draw a short draft of representative neurological diseases featuring inclusion bodies by describing the type of inclusions occurring in various disorders and analyzing both common features and distinctive aspects. As a further step, we move from the bed to the bench side discussing recent developments obtained from experimental models of these disorders which shed new light into the cause and progression of neuronal inclusions, thus helping to understand the pathophysiology of neuronal degeneration underlying movement disorders. In line with this, we will focus on recent studies which led to reproduce neuronal inclusions in vivo and in vitro by manipulating selective cellular structures/enzymatic pathways. In this way, we will try to encompass the dynamics of inclusion formation based on their fine ultrastructure and the analysis of the molecular components as well as their subcellular compartmentalization trying to relate the dynamics of inclusion formation and the pathophysiology of the disease process. An emphasis will be made on the ubiquitin proteasome system and Parkinson's disease where the analysis of neuronal inclusions enlightened potential therapeutic strategies to occlude the progression of this neuronal degeneration featured by movement disorders.

Specific Gene Expression and Possible Involvement of Inflammation in Methamphetamine-Induced Neurotoxicity

To reveal specific gene expression in methamphetamine (METH) -induced dopamine neurotoxicity, temporal characteristics of METH-induced changes in gene expression in dopaminergic neuronal cells were examined using the cDNA array and the differential display method. A number of genes in the class of "trafficking & protein turnover," "metabolic pathways," "transmitters & receptors," and "growth factors, cytokines" were upregulated after the METH treatment in the cDNA array assay. Whereas, some genes related to trafficking & protein turnover and "modulators, effectors & intracellular transducers" were decreased by METH. Some proteins associated with synaptic vesicle transportation indeed up- or downregulated after the METH treatment. These data suggest that the protein trafficking and degradation system is involved in the dopaminergic cell death induced by METH. Furthermore, focusing on inflammatory reactions after METH injection, possible neuroprotective property of nonsteroidal anti-inflammatory drugs were examined against METH-induced neurotoxicity. Coadministration of NSAID with METH significantly attenuated striatal dopamine terminal degeneration and microgliosis induced by METH, suggesting that the protective effects are based on their inhibitory activity on production of cytokines and nitric oxides or their suppressive action against microglia activation.

Lack of increased oxidative stress in catechol-O-methyltransferase (COMT)-deficient mice

The effect of catechol-O-methyltransferase (COMT) deficiency on methamphetamine-induced hydroxyl radical production in the brain was assessed by the salicylate trapping method. Methamphetamine-induced hyperthermia was also studied. Furthermore, the effect of COMT deficiency on the activities of glutathione S-transferase, quinone reductase and liver mono-oxygenases was assessed with and without l-dopa challenge. Finally, two alternative pathways of l-dopa metabolism were evaluated. Methamphetamine increased 2,3-dihydroxybenzoic acid levels only slightly (n.s.) at the lowest dose level (2.5 mg/kg x 4 i.p.). This was accompanied by a simultaneous increase in salicylate levels so that the 2,3-dihydroxybenzoic acid/salicylate ratio decreased correspondingly. Most importantly, no COMT genotype-dependent changes were observed. However, hyperthermia was induced even at the lowest methamphetamine dose, the COMT-deficient mice being most sensitive. COMT deficiency did not significantly change the activities of liver glutathione S-transferase, quinone reductase or 7-ethoxyresorufin and 7-pentoxyresorufin O-dealkylation. In COMT-deficient female mice, l-dopa (30-80 mg/kg b.i.d. for 2 days) did not induce any significant changes in liver or brain glutathione S-transferase and quinone reductase activity or liver 7-ethoxyresorufin O-deethylation activity. The levels of l-dopa conjugates in urine were also negligible in COMT-deficient mice. Skin tyrosinase activity was increased in 7- to 8-day-old hairless COMT-deficient pups. The present results suggest that despite the increased hyperthermic response, COMT deficiency does not increase methamphetamine-induced hydroxyl radical production or change significantly the activity of certain enzymes involved in defense against reactive oxygen species. In conclusion, we found no evidence of increased oxidative stress in the liver or brain of adult mice lacking COMT activity.

Microglial activation precedes dopamine terminal pathology in methamphetamine-induced neurotoxicity

Previous studies have demonstrated methamphetamine (METH)-induced toxicity to dopaminergic and serotonergic axons in rat striatum. Although several studies have identified the nature of reactive astrogliosis in this lesion model, the response of microglia has not been examined in detail. In this investigation, we characterized the temporal relationship of reactive microgliosis to neuropathological alterations of dopaminergic axons in striatum following exposure to methamphetamine. Adult male Sprague-Dawley rats were administered a neurotoxic regimen of methamphetamine and survived 12 h, or 1, 2, 4, and 6 days after treatment. Immunohistochemical methods were used to evaluate reactive changes in microglia throughout the brain of methamphetamine-treated rats, with a particular focus upon striatum. Pronounced morphological changes, indicative of reactive microgliosis, were evident in the brains of all methamphetamine-treated animals and were absent in saline-treated control animals. These included hyperplastic changes in cell morphology that substantially increased the size and staining intensity of reactive microglia. Quantitative analysis of reactive microglial changes in striatum demonstrated that these changes were most robust within the ventrolateral region and were maximal 2 days after methamphetamine administration. Analysis of tissue also revealed that microglial activation preceded the appearance of pathological changes in striatal dopamine fibers. Reactive microgliosis was also observed in extra-striatal regions (somatosensory and piriform cortices, and periaqueductal gray). These data demonstrate a consistent, robust, and selective activation of microglia in response to methamphetamine administration that, at least in striatum, precedes the appearance of morphological indicators of axon pathology. These observations raise the possibility that activated microglia may contribute to methamphetamine-induced neurotoxicity.

Methamphetamine increases dopamine transporter higher molecular weight complex formation via a dopamine- and hyperthermia-associated mechanism

Multiple high-dose administrations of methamphetamine (METH) both rapidly (within hours) decrease plasmalemmal dopamine (DA) uptake and cause long-term deficits in DA transporter (DAT) levels and other dopaminergic parameters persisting weeks to months in rat striatum. In contrast, either a single administration of METH or multiple administrations of methylenedioxymethamphetamine (MDMA) cause less of an acute reduction in DA uptake and little or no persistent dopaminergic deficits. The long-term dopaminergic deficits caused by METH have been suggested, in part, to involve the DAT. Hence, this study assessed the impact of METH and MDMA administration on the DAT protein per se. Results revealed that multiple administrations of METH promoted formation of higher molecular weight (>170 kDa) DAT-associated protein complexes 24-48 hr after treatment. This increase was attenuated by either preventing hyperthermia or pretreatment with the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine; notably, each of these manipulations has also been demonstrated previously to prevent the persistent deficits in dopaminergic function caused by METH treatment. In contrast, either a single injection of METH or multiple injections of MDMA caused little or no formation of these DAT complexes. The addition of the reducing agent beta-mercaptoethanol to samples prepared from METH-treated rats diminished the intensity of these complexes. Taken together, these data are the first to demonstrate higher molecular weight DAT complex formation in vivo and that such formation can be altered by both pharmacological and physiological manipulations. The implications of this phenomenon with regard to the neurotoxic potential of these stimulants are discussed.

Methamphetamine produces neuronal inclusions in the nigrostriatal system and in PC12 cells

Mice treated with the psychostimulant methamphetamine (MA) showed the appearance of intracellular inclusions in the nucleus of medium sized striatal neurones and cytoplasm of neurones of the substantia nigra pars compacta but not in the frontal cortex. All inclusions contained ubiquitin, the ubiquitin activating enzyme (E1), the ubiquitin protein ligase (E3-like, parkin), low and high molecular weight heat shock proteins (HSP 40 and HSP 70). Inclusions found in nigral neurones stained for alpha-synuclein, a proteic hallmark of Lewy bodies that are frequently observed in Parkinson's disease and other degenerative disorders. However, differing from classic Lewy bodies, MA-induced neuronal inclusions appeared as multilamellar bodies resembling autophagic granules. Methamphetamine reproduced this effect in cultured PC12 cells, which offered the advantage of a simple cellular model for the study of the molecular determinants of neuronal inclusions. PC12 inclusions, similar to those observed in nigral neurones, were exclusively localized in the cytoplasm and stained for alpha-synuclein. Time-dependent experiments showed that inclusions underwent a progressive fusion of the external membranes and developed an electrodense core. Inhibition of dopamine synthesis by alpha-methyl-p-tyrosine (alphaMpT), or administering the antioxidant S-apomorphine largely attenuated the formation of inclusions in PC12 cells exposed to MA. Inclusions were again observed when alphaMpT-treated cells were loaded with l-DOPA, which restored intracellular dopamine levels.

Lack of hydroxyl radical generation upon central administration of methamphetamine in rat caudate nucleus: a microdialysis study

The most widely accepted concept of oxidative damage centers on the formation of hydroxyl radical (*OH) which has an extremely short-life and is the major damaging free radical. It was suggested that methamphetamine (METH) toxicity is mediated via production of *OH, as measured by 2,3-dihydroxybenzoic acid (2,3-DHBA). In this study we compared the effects of local caudate nucleus perfusion of METH with systemic administration of METH on *OH generation in relation to DA release. Local perfusion of METH (5 mM, 140 min) induced a higher level of dopamine (DA) release compared to the first METH injection (10 mg/kg, 3 times, i.p.). No significant correlation was found between changes in extracellular DA levels and *OH generation when perfusing METH locally; however, both increased after systemic METH administration.

The methamphetamine experience: a NIDA partnership

The neurotoxic properties of the amphetamines such as methamphetamine (METH) were originally described about the time of the National Institute on Drug Abuse's organization, in the early 1970s. It required more than 20 years to confirm these neurotoxic properties in humans. Much like Parkinson's disease, multiple high-dose administration of METH somewhat selectively damages the nigrostriatal dopamine (DA) projection of the brain. This effect appears to be related to the intracellular accumulation of cytosolic DA and its ability to oxidize into reactive oxygen species. Both the dopamine plasmalemmal transporter and the vesicular monoamine transporter-2 seem to play critical roles in this neurotoxicity. METH and related analogs such as methylenedioxymethamphetamine (MDMA) can also damage selective CNS serotonin neurons. The mechanism of the serotonergic neurotoxicity is not as well characterized, but also appears to be related to the formation of reactive oxygen species and monoamine transporters. Studies examining the pharmacological and neurotoxicological properties of the amphetamines have helped to elucidate some critical features of monoamine regulations as well as helped to improve our understanding of the processes associated with degenerative disorders such as Parkinson's disease.

Speed kills: cellular and molecular bases of methamphetamine‐induced nerve terminal degeneration and neuronal apoptosis

Methamphetamine (METH) is a drug of abuse that has long been known to damage monoaminergic systems in the mammalian brain. Recent reports have provided conclusive evidence that METH can cause neuropathological changes in the rodent brain via apoptotic mechanisms akin to those reported in various models of neuronal death. The purpose of this review is to provide an interim account for a role of oxygen-based radicals and the participation of transcription factors and the involvement of cell death genes in METH-induced neurodegeneration. We discuss data suggesting the participation of endoplasmic reticulum and mitochondria-mediated activation of caspase-dependent and -independent cascades in the manifestation of METH-induced apoptosis. Studies that use more comprehensive approaches to gene expression profiling should allow us to draw more instructive molecular portraits of the complex plastic and degenerative effects of this drug.

HIV-1 protein Tat potentiation of methamphetamine-induced decreases in evoked overflow of dopamine in the striatum of the rat

HIV-1 infection of the brain can lead to the development of clinical syndromes reminiscent of Parkinson's disease, suggesting that HIV infection may damage nigrostriatal dopamine (DA) neurons. Although the responsible mechanisms have not been well defined, neurotoxic viral proteins, such as Tat, released from infected cells may be involved. Drug abuse is a major risk factor for contracting HIV infection. Methamphetamine (METH), a psychostimulant with high abuse potential, may also be toxic to brain DA neurons. Thus, the combination of METH abuse and HIV infection may lead to substantial alterations in DA neuron functioning. The present experiments examined how Tat, alone and with METH, affects DA release in the striatum. Male rats were given an intrastriatal injection of Tat (25 micro g) or vehicle 24 h before treatment with saline or neurotoxic doses of METH. Seven days later microdialysis studies were carried out to measure potassium- and amphetamine-evoked overflow of DA from the striatum. The Tat treatment alone led to no change in potassium-evoked overflow of DA, a 20% decrease in amphetamine-evoked overflow of DA, and a 16% decrease in striatal DA content. The METH alone led to a 37-42% decrease in striatal DA overflow and content. The combined treatment with Tat and METH led to significantly greater 70-78% decreases in striatal DA overflow and content. These results indicate that Tat enhances METH-induced reductions in striatal DA release and content, possibly in a synergistic manner, and suggest that METH abusers infected with HIV may be at increased risk for basal ganglia dysfunction.

Current research on methamphetamine-induced neurotoxicity: animal models of monoamine disruption

Methamphetamine (METH)-induced neurotoxicity is characterized by a long-lasting depletion of striatal dopamine (DA) and serotonin as well as damage to striatal dopaminergic and serotonergic nerve terminals. Several hypotheses regarding the mechanism underlying METH-induced neurotoxicity have been proposed. In particular, it is thought that endogenous DA in the striatum may play an important role in mediating METH-induced neuronal damage. This hypothesis is based on the observation of free radical formation and oxidative stress produced by auto-oxidation of DA consequent to its displacement from synaptic vesicles to cytoplasm. In addition, METH-induced neurotoxicity may be linked to the glutamate and nitric oxide systems within the striatum. Moreover, using knockout mice lacking the DA transporter, the vesicular monoamine transporter 2, c-fos, or nitric oxide synthetase, it was determined that these factors may be connected in some way to METH-induced neurotoxicity. Finally a role for apoptosis in METH-induced neurotoxicity has also been established including evidence of protection of bcl-2, expression of p53 protein, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL), activity of caspase-3. The neuronal damage induced by METH may reflect neurological disorders such as autism and Parkinson's disease.

Methamphetamine-induced TNF-alpha gene expression and activation of AP-1 in discrete regions of mouse brain: potential role of reactive oxygen intermediates and lipid peroxidation

Cellular and molecular mechanisms of methamphetamine (METH)-induced neurotoxicity may involve alterations of cellular redox status and induction of inflammatory genes. To study this hypothesis, molecular signaling pathways of METH-induced inflammatory responses via activation of redox-sensitive transcription factors were investigated in discrete regions (corpus striatum, frontal cortex, and hippocampus) of mouse brain. Intraperitoneal injection of METH at a dose of 10 mg/kg body weight resulted in a significant increase in oxidative stress, as measured by 2,7-dichlorofluorescein (DCF) fluorescence assay, thiobarbituric acid-reactive substances (TBARS), and total glutathione levels. Glutathione peroxidase activity was also significantly increased after METH exposure. In addition, DNA binding activity of activator protein-1 (AP-1), a redox-responsive transcription factor, was increased in all studied brain regions in response to METH treatment. Because AP-1 is known to regulate expression of inflammatory genes, levels of TNF-alpha mRNA were also studied. Expression of the tumor necrosis factor-alpha (TNF-alpha) gene was induced 3 h after METH injection and remained elevated for up to 6 h of METH exposure. In addition, stimulation of the TNF-alpha gene was associated with increased TNF-a protein production in the frontal cortex. These results suggest that METH-induced disturbances in cellular redox status and that activation of AP-1 can play a critical role in signaling pathways leading to upregulation of inflammatory genes in vivo. Furthermore, these data provide evidence for the role of oxidative stress in the neurotoxic effects of METH.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine pretreatment attenuates methamphetamine-induced dopamine toxicity

The effects of pretreatment with MPTP (1-methyl4-phenyl-1,2,3,6-tetrahydropyridine) on the acute and long-term effects of methamphetamine on striatal dopamine were evaluated in BALB/c mice. Four subcutaneous injections of a non-toxic dose of MPTP (8 mg/kg, at 2 hr intervals) were followed three days later by a toxic regimen of methamphetamine (four injections of 4 mg/kg, at 2 hr intervals) and mice were sacrificed immediately or three days later. Control mice received saline in place of the MPTP or methamphetamine and mice were observed for acute changes in body temperature, self-injurious behaviour, and striatal dopamine metabolites, or long-term changes in striatal dopamine levels, tyrosine hydroxylase immunoreactivity and glial fibrillary acidic protein. It was observed that pretreatment with MPTP protected mice against the acute increase in body temperature caused by the methamphetamine but, at the same time, delayed the occurrence of self-injurious behaviour following the repeated injections of methamphetamine. Likewise, pretreatment with MPTP attenuated the long-term depletion of striatal dopamine induced by the methamphetamine as well as the large increase in glial fibrillary acidic protein and the reduction in tyrosine hydroxylase immunoreactivity. The MPTP-treatment itself did not alter any of these neurotoxic markers. Finally, the acute decrease in 3,4-dihydroxyphenyacetic acid levels and increased ratio of 3-methoxytyramine/dopamine observed 60 min. after a single injection of methamphetamine (4 mg/kg) were also attenuated in MPTP-treated mice. These results are discussed in the context of the hypothesis that the low-dose treatment with MPTP may modify exchange diffusion across the striatal cell membrane thereby altering the acute and long-lasting effects of methamphetamine.

Methamphetamine potentiates HIV-1 Tat protein-mediated activation of redox-sensitive pathways in discrete regions of the brain

Tat is a major regulatory protein encoded by human immunodeficiency viral genome, which has been implicated in the pathogenesis of HIV infection, including neurologic complications associated with this disease. In addition, drug abuse has been identified as a major risk factor of HIV infection. We hypothesize that abusive drugs, such as methamphetamine (METH), can directly influence specific molecular processes that can further contribute to toxic effects of Tat. To elucidate the molecular signaling pathways of Tat- and/or METH-induced toxicity, we investigated the effects of a single injection of Tat (25 microg/microl into the right hippocampus) and/or METH (10 mg/kg, intraperitoneally) on the generation of cellular oxidative stress, DNA-binding activity of specific redox-responsive transcription factors, and expression of inflammatory genes. Administration of Tat or METH resulted in stimulation of cellular oxidative stress and activation of redox-regulated transcription factors in the cortical, striatal, and hippocampal regions of the mouse brain. In addition, DNA-binding activities of NF-kappaB, AP-1, and CREB in the frontal cortex and hippocampus were more pronounced in mice injected with Tat plus METH compared to the effects of Tat or METH alone. Intercellular adhesion molecule-1 gene expression also was upregulated in a synergistic manner in cortical, striatal, and hippocampal regions in mice which received injections of Tat combined with METH compared to the effects of these agents alone. Moreover, synergistic effects of Tat plus METH on the tumor necrosis factor-alpha and interleukin-1beta mRNA levels were observed in the striatal region. These results indicate that Tat and METH can cross-amplify their cellular effects, leading to alterations of redox-regulated inflammatory pathways in the brain. Such synergistic proinflammatory stimulation may have significant implications in HIV-infected patients who abuse drugs.

Further insights into the reaction of melatonin with hydroxyl radical

Recent interest has focused on the use of exogenous melatonin as an antioxidant, particularly to scavenge the highly cytotoxic hydroxyl radical (HO(z.rad;)) which may be generated in many pathological conditions. However, in vitro and in vivo studies aimed at assessing the antioxidant properties of melatonin have produced conflicting results. While it is known that HO(z.rad;) reacts with melatonin at a diffusion limited rate, very little is known about the products of this reaction. In this investigation it is shown that incubation of melatonin with a Fenton-type HO(z.rad;)-generating system at pH 7.4 forms a complex mixture of primary products. These include 2-hydroxymelatonin, which was isolated as its more stable oxindole tautomer, 4- and 6-hydroxymelatonin, N-acetyl-N(2)-formyl-5-methoxykynurenine and 7,7(')-bi-(5-methoxy-N-acetyltryptamine-4-one). Reaction pathways that might lead to these products are described. The differing biological effects of these products, while currently incompletely understood, might account for the controversy concerning the antioxidant properties of melatonin.

Morphological and biochemical evidence that apomorphine rescues striatal dopamine terminals and prevents methamphetamine toxicity

Apomorphine, given by a single injection, repeated injections, or by continuous infusion, was tested for neuroprotective effects in mice administered methamphetamine or N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in order to induce striatal dopamine (DA) depletion. In the first part of the study, the DA agonist (R)-apomorphine was administered at various doses (1, 5, and 10 mg/kg), 15 min before methamphetamine (5 mg/kg x 3, 2 h apart). Mice were sacrificed 5 days later. In the second part, apomorphine was administered either continuously by subcutaneous minipump (cumulative daily dose of 0.5, 1, and 3.15 mg/kg), or as single, repeated daily injections (up to 5 mg/kg) starting 40 h after an acute administration of MPTP (30 mg/kg). Mice were sacrificed at different time intervals (up to 1 month) following MPTP injection. In all the animals, the integrity of striatal DA terminals was evaluated by measuring striatal DA levels and TH immunohistochemistry. Apomorphine dose-dependently prevented methamphetamine toxicity. These effects were neither due to a decrease in the amount of striatal methamphetamine nor to the hypothermia, and they were not reversed by the DA antagonist haloperidol. Moreover, chronic, continuous (but not pulsatile) administration of apomorphine rescued damaged striatal dopaminergic terminals. These findings confirm a protective effect of apomorphine that also consists of a neurorescue of damaged striatal DA terminals. This suggests a new hypothesis about the long-term benefits observed during continuous apomorphine administration in Parkinson's disease patients.

Studies, using in vivo microdialysis, on the effect of the dopamine uptake inhibitor GBR 12909 on 3,4-methylenedioxymethamphetamine ('ecstasy')-induced dopamine release and free radical formation in the mouse striatum

The present study examined the mechanisms by which 3,4-methylenedioxymethamphetamine (MDMA) produces long-term neurotoxicity of striatal dopamine neurones in mice and the protective action of the dopamine uptake inhibitor GBR 12909. MDMA (30 mg/kg, i.p.), given three times at 3-h intervals, produced a rapid increase in striatal dopamine release measured by in vivo microdialysis (maximum increase to 380 +/- 64% of baseline). This increase was enhanced to 576 +/- 109% of baseline by GBR 12909 (10 mg/kg, i.p.) administered 30 min before each dose of MDMA, supporting the contention that MDMA enters the terminal by diffusion and not via the dopamine uptake site. This, in addition to the fact that perfusion of the probe with a low Ca(2+) medium inhibited the MDMA-induced increase in extracellular dopamine, indicates that the neurotransmitter may be released by a Ca(2+) -dependent mechanism not related to the dopamine transporter. MDMA (30 mg/kg x 3) increased the formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) from salicylic acid perfused through a probe implanted in the striatum, indicating that MDMA increased free radical formation. GBR 12909 pre-treatment attenuated the MDMA-induced increase in 2,3-DHBA formation by approximately 50%, but had no significant intrinsic radical trapping activity. MDMA administration increased lipid peroxidation in striatal synaptosomes, an effect reduced by approximately 60% by GBR 12909 pre-treatment. GBR 12909 did not modify the MDMA-induced changes in body temperature. These data suggest that MDMA-induced toxicity of dopamine neurones in mice results from free radical formation which in turn induces an oxidative stress process. The data also indicate that the free radical formation is probably not associated with the MDMA-induced dopamine release and that MDMA does not induce dopamine release via an action at the dopamine transporter.

A study of the mechanisms involved in the neurotoxic action of 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') on dopamine neurones in mouse brain

1. Administration of 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') to mice produces acute hyperthermia and long-term degeneration of striatal dopamine nerve terminals. Attenuation of the hyperthermia decreases the neurodegeneration. We have investigated the mechanisms involved in producing the neurotoxic loss of striatal dopamine. 2. MDMA produced a dose-dependent loss in striatal dopamine concentration 7 days later with 3 doses of 25 mg kg(-1) (3 h apart) producing a 70% loss. 3. Pretreatment 30 min before each MDMA dose with either of the N-methyl-D-aspartate antagonists AR-R15896AR (20, 5, 5 mg kg(-1)) or MK-801 (0.5 mg kg(-1)x3) failed to provide neuroprotection. 4. Pretreatment with clomethiazole (50 mg kg(-1)x3) was similarly ineffective in protecting against MDMA-induced dopamine loss. 5. The free radical trapping compound PBN (150 mg kg(-1)x3) was neuroprotective, but it proved impossible to separate neuroprotection from a hypothermic effect on body temperature. 6. Pretreatment with the nitric oxide synthase (NOS) inhibitor 7-NI (50 mg kg(-1)x3) produced neuroprotection, but also significant hypothermia. Two other NOS inhibitors, S-methyl-L-thiocitrulline (10 mg kg(-1)x3) and AR-R17477AR (5 mg kg(-1)x3), provided significant neuroprotection and had little effect on MDMA-induced hyperthermia. 7. MDMA (20 mg kg(-1)) increased 2,3-dihydroxybenzoic acid formation from salicylic acid perfused through a microdialysis tube implanted in the striatum, indicating increased free radical formation. This increase was prevented by AR-R17477AR administration. Since AR-R17477AR was also found to have no radical trapping activity this result suggests that MDMA-induced neurotoxicity results from MDMA or dopamine metabolites producing radicals that combine with NO to form tissue-damaging peroxynitrites.

Molecular neurotoxicological models of Parkinsonism: focus on genetic manipulation of mice

Parkinson's disease is a neurodegenerative disorder that affects mainly the nigrostriatal dopaminergic system in humans. Several propositions have been put forward to explain the cellular and molecular pathobiology of this syndrome. Initial attempts were made through the use of various agents to manipulate the deleterious effects of toxins that destroy dopaminergic cells both in vitro and in vivo. These studies led to the idea that oxidative stress is an important factor in killing these cells. More recent attempts have made use of genetically modified mice to eliminate or over-express genes of interest. These experiments have suggested that the destruction of dopaminergic cells might be the result of the convergence of dependent and independent molecular pathways and that trigger cellular events might lead to the demise of these dopaminergic cells.

Parallel increases in lipid and protein oxidative markers in several mouse brain regions after methamphetamine treatment

The neurotoxic actions of methamphetamine (METH) may be mediated in part by reactive oxygen species (ROS). Methamphetamine administration leads to increases in ROS formation and lipid peroxidation in rodent brain; however, the extent to which proteins may be modified or whether affected brain regions exhibit similar elevations of lipid and protein oxidative markers have not been investigated. In this study we measured concentrations of TBARs, protein carbonyls and monoamines in various mouse brain regions at 4 h and 24 h after the last of four injections of METH (10 mg/kg/injection q 2 h). Substantial increases in TBARs and protein carbonyls were observed in the striatum and hippocampus but not the frontal cortex nor the cerebellum of METH-treated mice. Furthermore, lipid and protein oxidative markers were highly correlated within each brain region. In the hippocampus and striatum elevations in oxidative markers were significantly greater at 24 h than at 4 h. Monoamine levels were maximally reduced within 4 h (striatal dopamine [DA] by 95% and serotonin [5-HT] in striatum, cortex and hippocampus by 60-90%). These decrements persisted for 7 days after METH, indicating effects reflective of nerve terminal damage. Interestingly, NE was only transiently depleted in the brain regions investigated (hippocampus and cortex), suggesting a pharmacological and non-toxic action of METH on the noradrenergic nerve terminals. This study provides the first evidence for concurrent formation of lipid and protein markers of oxidative stress in several brain regions of mice that are severely affected by large neurotoxic doses of METH. Moreover, the differential time course for monoamine depletion and the elevations in oxidative markers indicate that the source of oxidative stress is not derived directly from DA or 5HT oxidation.

Inhibitors of Na(+)/H(+) and Na(+)/Ca(2+) exchange potentiate methamphetamine-induced dopamine neurotoxicity: possible role of ionic dysregulation in methamphetamine neurotoxicity

Although the neurotoxic potential of methamphetamine (METH) is well established, underlying mechanisms have yet to be identified. In the present study, we sought to determine whether ionic dysregulation was a feature of METH neurotoxicity. In particular, we reasoned that if METH impairs the function of Na(+)/H(+) and/or Na(+)/Ca(2+) antiporters by compromising the inward Na(+) gradient [via prolonged DA transporter (DAT) activation and Na(+)/K(+) ATPase inhibition], then amiloride (AMIL) and other inhibitors of Na(+)/H(+) and/or Na(+)/Ca(2+) exchange would potentiate METH neurotoxicity. To test this hypothesis, mice were treated with METH alone or in combination with AMIL or one of its analogs; 1 week later, the animals were killed for studies of dopamine (DA) neuronal integrity. AMIL markedly potentiated the toxic effect of METH on DA neurons. Potentiation was not caused by increased core temperature, enhanced DAT activity or higher METH brain levels. The DAT inhibitor, WIN-35,428, protected completely against METH-induced DA neurotoxicity in AMIL pretreated animals, suggesting that the potentiating effects of AMIL require a METH/DAT interaction. Findings with METH and AMIL were extended to six other AMIL analogs (MIA, EIPA, DIMA, BENZ, BEP, DiCBNZ), another species (rats), and neuronal type (5-HT neurons). These results support the notion that ionic dysregulation may play a role in METH neurotoxicity.

Methamphetamine-induced dopaminergic neurotoxicity: role of peroxynitrite and neuroprotective role of antioxidants and peroxynitrite decomposition catalysts

Oxidative stress, reactive oxygen (ROS), and nitrogen (RNS) species have been known to be involved in a multitude of neurodegenerative disorders such as Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). Both ROS and RNS have very short half-lives, thereby making their identification very difficult as a specific cause of neurodegeneration. Recently, we have developed a high performance liquid chromatography/electrochemical detection (HPLC/EC) method to identify 3-nitrotyrosine (3-NT), an in vitro and in vivo biomarker of peroxynitrite production, in cell cultures and brain to evaluate if an agent-driven neurotoxicity is produced by the generation of peroxynitrite. We show that a single or multiple injections of methamphetamine (METH) produced a significant increase in the formation of 3-NT in the striatum. This formation of 3-NT correlated with the striatal dopamine depletion caused by METH administration. We also show that PC12 cells treated with METH has significantly increased formation of 3-NT and dopamine depletion. Furthermore, we report that pretreatment with antioxidants such as selenium and melatonin can completely protect against the formation of 3-NT and depletion of striatal dopamine. We also report that pretreatment with peroxynitrite decomposition catalysts such as 5, 10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and 5, 10, 15, 20-tetrakis (2,4,6-trimethyl-3,5-sulfonatophenyl) porphinato iron III (FETPPS) significantly protect against METH-induced 3-NT formation and striatal dopamine depletion. We used two different approaches, pharmacological manipulation and transgenic animal models, in order to further investigate the role of peroxynitrite. We show that a selective neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole (7-NI), significantly protect against the formation of 3-NT as well as striatal dopamine depletion. Similar results were observed with nNOS knockout and copper zinc superoxide dismutase (CuZnSOD)-overexpressed transgenic mice models. Finally, using the protein data bank crystal structure of tyrosine hydroxylase, we postulate the possible nitration of specific tyrosine moiety in the enzyme that can be responsible for dopaminergic neurotoxicity. Together, these data clearly support the hypothesis that the reactive nitrogen species, peroxynitrite, plays a major role in METH-induced dopaminergic neurotoxicity and that selective antioxidants and peroxynitrite decomposition catalysts can protect against METH-induced neurotoxicity. These antioxidants and decomposition catalysts may have therapeutic potential in the treatment of psychostimulant addictions.

Dose-dependent protective effects of apomorphine against methamphetamine-induced nigrostriatal damage

(R)-apomorphine is a non-selective dopamine (DA) agonist which is used in the treatment of Parkinson's disease. In addition to symptomatic effects, apomorphine exerts a neuroprotective activity in specific experimental models. For instance, apomorphine prevents experimental parkinsonism induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Neuroprotection obtained with apomorphine does not seem to be related to its dopamine (DA) agonist properties, instead it appears to be grounded on the antioxidant and the free radical scavenging effects of the compound. In this study, we sought to determine whether apomorphine protects against methamphetamine toxicity. We found that apomorphine (1; 5 and 10 mg/kg) dose-dependently protects against methamphetamine- (5 mg/kg X3, 2 h apart) induced striatal DA loss and reduction of tyrosine hydroxylase (TH) activity in the rat striatum. These protective effects are neither due to a decrease in the amount of striatal methamphetamine nor to hypothermia as indicated by measurement of striatal methamphetamine and body temperature at different time intervals after drug administration. The effects of apomorphine were neither opposite to, nor reversed by the DA antagonist haloperidol despite no decrease in body temperature was observed when apomorphine was given in combination with haloperidol. The present data are in line with recent studies suggesting a DA receptor-independent neuroprotective effect of apomorphine on DA neurons and call for further studies aimed at evaluating potential neuroprotective effects of apomorphine in Parkinson's disease.

Salicylate and cocaine: interactive toxicity during chicken mid-embryogenesis

Increased free radical production, due to ischemia and reperfusion, has been postulated as a cause of cocaine's (COC) developmental toxicity. Salicylate reacts with hydroxyl free radicals (*OH) to form stable, quantifiable reaction products, which can be measured with high-pressure liquid chromatography (HPLC). To determine if chicken embryos' brains and hearts were exposed to increased *OH concentrations after injection of COC, an injection of a nontoxic dose of sodium salicylate (NaSAL, 100 mg/kg egg, or 5 mg/egg), followed by 5 injections of COC (13.5 mg/kg or 0.675 mg/egg, every 1.5 h), was administered to eggs containing embryos on the 12th day of embryogenesis (E12). In addition to finding increased *OH concentrations in E12 embryonic hearts and brains, we observed that the developmental toxicity of COC, manifest as vascular disruption (hemorrhage) and lethality, was enhanced by NaSAL injection. These results confirm and extend results of similar experiments performed upon older embryos (E18), and indicate that increased &z.rad;OH concentration in embryonic tissues after COC exposure and toxic interactions of COC and NaSAL can also occur at an earlier stage of development. The results are discussed in light of possible exposure of human fetuses to both COC and salicylates, since COC-abusing pregnant women can be misdiagnosed with pre-eclampsia and aspirin is used to treat this syndrome.

Role of mitochondrial dysfunction and dopamine-dependent oxidative stress in amphetamine-induced toxicity

To define the molecular mechanisms underlying amphetamine (AMPH) neurotoxicity, primary cultures of dopaminergic neurons were examined for drug-induced changes in dopamine (DA) distribution, oxidative stress, protein damage, and cell death. As in earlier studies, AMPH rapidly redistributed vesicular DA to the cytoplasm, where it underwent outward transport through the DA transporter. DA was concurrently oxidized to produce a threefold increase in free radicals, as measured by the redox-sensitive dye dihydroethidium. Intracellular DA depletion using the DA synthesis inhibitor alpha-methyl-p-tyrosine or the vesicular monoamine transport blocker reserpine prevented drug-induced free radical formation. Despite these AMPH-induced changes, neither protein oxidation nor cell death was observed until 1 and 4 days, respectively. AMPH also induced an early burst of free radicals in a CNS-derived dopaminergic cell line. However, AMPH-mediated attenuation of ATP production and mitochondrial function was not observed in these cells until 48 to 72 hours. Thus, neither metabolic dysfunction nor loss of viability was a direct consequence of AMPH neurotoxicity. In contrast, when primary cultures of dopaminergic neurons were exposed to AMPH in the presence of subtoxic doses of the mitochondrial complex I inhibitor rotenone, cell death was dramatically increased, mimicking the effects of a known parkinsonism-inducing toxin. Thus, metabolic stress may predispose dopaminergic neurons to injury by free radical-promoting insults such as AMPH.

Effects of methamphetamine-induced neurotoxicity on the development of neural circuitry: a hypothesis

Exposure of the developing brain to methamphetamine has well-studied biochemical and behavioral consequences. We review: (1) the effects of methamphetamine on mature serotonergic and dopaminergic pathways; (2) the mechanisms of methamphetamine neurotoxicity and (3) the role of serotonergic and dopaminergic signaling in sculpting developing neural circuitry. Consideration of these data suggest the types of neural circuit alterations that may result from exposure of the developing brain to methamphetamine and that may underlie functional defects.

Methamphetamine-induced striatal dopamine release, behavior changes and neurotoxicity in BALB/c mice

The behaviors associated with the neurotoxic effects of methamphetamine were evaluated in BALB/c mice. Hyperthermia and behavioral observations were measured 60 min after each subcutaneous injection of methamphetamine (4x4 or 8 mg/kg) or saline, each given 2 h apart. The behavioral observations included stereotyped behaviors, incidence of hemorrhage in breast, salivation and self-injurious behavior (SIB). Repeated administration of methamphetamine produced these behavioral changes and hyperthermia, but resulted in hypothermia by the final injection (8 mg/kg). In addition, the methamphetamine treatment induced a long-lasting dopamine depletion of similar magnitude in the 4 and 8 mg/kg-treated animals. In a time course study striatal monoamine levels were measured 60 min after each injection of these doses. The first and second injections of methamphetamine (8 mg/kg) produced a drastic increase in striatal 3-methoxytyramine; this failed to occur after the third or fourth injection of the same dose. In contrast, 4 mg/kg of methamphetamine also produced an increase in 3-methoxytyramine after the second and third injections of the drug and, in this case, these were maintained for the duration of the treatment. Striatal 3, 4-dihydroxyphenylacetic acid levels also drastically decreased following both doses of methamphetamine, suggesting inhibition of monoamine oxidase in striatum. Moreover, a single injection of methamphetamine increased striatal 2,3-dihydroxybenzoic acid formation. These results suggest that the incidence of hyperthermia, SIB and striatal dopamine neurotoxicity are closely linked to striatal dopamine release and inhibition of monoamine oxidase produced by methamphetamine in BALB/c mice.

The effects of methamphetamine on serotonin transporter activity: role of dopamine and hyperthermia

Multiple administrations of methamphetamine (METH) rapidly decreased serotonin (5HT) transporter (SERT) function in rat striatum and hippocampus. The purpose of this study was to identify the mechanisms/ factors contributing to this METH-induced decrease in SERT function. Multiple high-dose METH injections rapidly decreased 5HT uptake without altering binding of the 5HT transporter ligand paroxetine. Hyperthermia contributed to this deficit in transporter function in striatum and hippocampus, as prevention of METH-induced hyperthermia attenuated this decrease. A role for dopamine (DA) was suggested by findings that pretreatment with the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine, the D1 antagonist SCH-23390, or the D2 antagonist eticlopride attenuated the METH-induced decrease in striatal, but not hippocampal, SERT activity. These effects were independent of the ability of these DA-antagonizing drugs to prevent METH-induced hyperthermia. These results suggest that DA contributes to the decrease in SERT function caused by multiple METH injections in the striatum, but not hippocampus, and that hyperthermia facilitates these deficits in SERT function in both brain regions. In contrast, the response of SERT to a single administration of METH was DA and hyperthermia independent. These findings suggest that the mechanisms/ factors involved in decreasing SERT activity after a single administration of METH are distinct from that caused by multiple administrations.

Methamphetamine toxicity is attenuated in mice that overexpress human manganese superoxide dismutase

We have investigated methamphetamine (MA) toxicity in transgenic mice that overexpress the human form of mitochondrial manganese superoxide dismutase (MnSOD). Our results reveal a significant reduction in the long-term depletion of striatal dopamine and protein oxidation following repeated administration of MA in transgenic vs. non-transgenic littermates. These findings support the notion that ROS contribute to MA-induced brain damage and suggest that mitochondria may play an important role in this form of neurodegeneration.

Direct interactions of methamphetamine with the nucleus

Possible direct effects of methamphetamine (METH) on transcription factors AP-1 and cAMP response element-binding protein (CREB) in the nucleus were assessed by electrophoretic mobility-shift assay. In vitro addition of METH to nuclear extract from brain tissue increased DNA-binding activities of both transcription factors. In addition, injections of METH to mice induced increases in the binding of AP-1 and CREB, which were depleted by preincubating the nuclear extract with anti-METH antibody. We also examined the cellular distribution of METH in mesencephalic neuronal cells using an immunofluorescence experiment with anti-METH antibody. METH-like immunoreactivity was seen to accumulate in the cytosol 4-6 h after the METH treatment. Furthermore, METH-positive signals were also observed in the nuclei of the METH-treated cells. The present study is the first demonstration that METH can have direct effects on DNA-binding protein complex by redistributing not only in the cytosol but also into the nucleus.

Comparison between the role of the neuronal and inducible nitric oxide synthase in methamphetamine-induced neurotoxicity and sensitization

The involvement of the neuronal and inducible nitric oxide synthase (nNOS and iNOS, respectively) in methamphetamine (METH)-induced dopaminergic neurotoxicity and behavioral sensitization was investigated. To determine METH-induced neurotoxicity, mice deficient in the nNOS and iNOS genes, nNOS(-/-) and iNOS(-/-) mice, and wild-type controls received either saline or METH (5 mg/kg x 3). After 72 h the level of striatal dopaminergic markers were measured. Administration of METH to nNOS(-/-) mice had no significant effect on the level of striatal dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), or dopamine transporter (DAT) binding sites. However, METH caused 25-40% depletion of dopaminergic markers in iNOS(-/-) mice and 63-69% depletion in the wild-type mice. METH-induced locomotor activity was measured following the administration of a low dose (1 mg/kg) on day 1. Subsequently animals received the high dose of METH (5 mg/kg x 3). On day 4, after a 68-72 h drug free period, animals were challenged with 1 mg/kg METH, and locomotor activity was recorded. The intensity of METH-induced locomotion in nNOS(-/-) mice on day 1 and 4 was similar, suggesting that locomotor sensitization did not develop. However, the intensity of METH-induced locomotion in the iNOS(-/-) and wild-type mice on day 4 was doubled compared to day 1, suggesting the development of sensitization. The present findings indicate that nNOS(-/-) mice are more resistant to METH-induced neurotoxicity and behavioral sensitization than iNOS(-/-) mice. These results suggest a major role for nNOS rather than iNOS in the effects of METH.

The effects of single dose of methamphetamine on lipid peroxidation levels in the rat striatum and prefrontal cortex

The administration of methamphetamine to experimental animals results in damage to dopaminergic neurons. In the present study, we demonstrated that a single dose (15 mg/kg) of methamphetamine results in production of oxidative stress as demonstrated by increased thiobarbituric acid reactive substances levels in the rat striatum and prefrontal cortex. In conclusion, the results of present study provide further evidence in support of the notion that oxidative stress may play an important role in the methamphetamine-induced neurotoxicity.

Methamphetamine-induced oxidative stress in cultured mouse astrocytes

Methamphetamine (METH) is a monoaminergic toxin that destroys dopamine terminals and causes astrogliosis in vivo. Oxidative stress has been shown to play an important role in the toxic effects of METH. In the present study, we sought to determine whether astrocytes are involved in METH-induced oxidative stress. Reactive oxygen species (ROS), ATP, and change in mitochondria membrane potential (delta psi(m)) were examined in cultured striatal, mesencephalic, and cortical astrocytes after 4 to 48 h of 4 mM METH treatment. Results showed that only striatal and mesencephalic astrocytes showed a significant increase in ROS formation from 8 and 12 h, respectively. At 48 h treatment, there was a 55 and 53% increase in ROS content in striatal and mesencephalic astrocytes, respectively, whereas cortical astrocytes showed only a 25% (not significant) increase. JC-1, a delta psi(m)-sensitive dye, showed a decrease in delta psi(m) at 8 h treatment for striatal and mesencephalic astrocytes and at 12 h for cortical astrocytes. Astrocytes from all three regions showed a similar pattern of initial increase followed by a decrease in ATP content, with striatal astrocytes resulting in a maximum depletion (39% of control value) at 48 h treatment. These findings showed that METH treatment resulted in the formation of ROS in the order of striatal > mesencephalic > cortical astrocytes. Although the formation of ROS did not severely interfere with ATP production, a depolarization of mitochondria was observed. The present study suggested that astrocytes may be an important element governing the selective vulnerability to the striatum to METH-induced oxidative stress.

Molecular footprints of neurotoxic amphetamine action

Methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA or Ecstasy) are amphetamine analogs with high abuse potential. These drugs also cause damage to dopamine and serotonin nerve terminals in vivo. The mechanisms by which these drugs cause neurotoxicity are not known, but a great deal of attention has been focused on reactive oxygen species (ROS) and reactive nitrogen species (RNS) as mediators of this toxicity. ROS and RNS have very short biological half-lives in vivo, and it is virtually impossible to measure them in brain directly. However, ROS and RNS are also characterized by their extreme reactivity with proteins and nucleotides. Tryptophan hydroxylase (TPH) and tyrosine hydroxylase (TH), the initial and rate limiting enzymes in the synthesis of serotonin and dopamine, respectively, are identified targets for the actions of METH and MDMA. Using recombinant forms of these proteins, we have found that nitric oxide, catechol-quinones, and peroxynitrite, all of which are potentially produced by the neurotoxic amphetamines, covalently modify both TPH and TH. The ROS and RNS cause reductions in catalytic function of these enzymes in a manner that is consistent with the effects of METH and MDMNA in vivo. Protein-bound ROS or RNS may serve as molecular footprints of neurotoxic amphetamine action.

Preferential resistance of dopaminergic neurons to glutathione depletion in a reconstituted nigrostriatal system

Depletion of glutathione in the substantia nigra is one of the earliest changes observed in Parkinson's disease (PD), and could initiate dopaminergic neuronal degeneration. Nevertheless, we have previously demonstrated that mesencephalic dopaminergic neurons in primary monolayer cultures are more resistant to the toxicity of glutathione depletion than nondopaminergic neurons. To extend this finding to a system that more closely resembles the in vivo situation, we characterized the effects of glutathione depletion on reaggregate cultures derived from ventral mesencephalic and their striatal target neurons, as well as supporting elements including glia. Dopaminergic neurons were found to be more resistant to the toxicity of buthionine-(S,R)-sulfoximine, an inhibitor of glutathione synthesis, than other nigrostriatal neurons, while striatal target cells exhibited an intermediate susceptibility when examined after 48 h. Glutathione depletion, however, decreased the intracellular content of catecholamines after 48 h and eventually led to the loss of dopaminergic neurons after 7 days. Our data indicate that the intrinsic resistance of dopaminergic neurons to the toxicity of glutathione depletion occurs in a variety of experimental paradigms, and suggest that global glutathione depletion alone is unlikely to account for the selective loss of dopaminergic neurons in PD. Rather, it is more likely that either the selective loss of glutathione from dopaminergic neurons, or the combination of glutathione loss with other insults contributes to the preferential death of dopaminergic neurons in PD.

Role of peroxynitrite in methamphetamine-induced dopaminergic neurotoxicity and sensitization in mice

Abstract Methamphetamine (METH)-induced dopaminergic neurotoxicity is thought to be associated with the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Recently, we have reported that copper/zinc(CuZn)-superoxide dismutase transgenic mice are resistant to METH-induced neurotoxicity. In the present study, we examined the role of the neuronal nitric oxide synthase (nNOS), susceptibility of nNOS knockout (KO) mice and sensitization to psychostimulants after neurotoxic doses of METH. Male SwissWebster mice were treated with or without 7-nitroindazole (7-NI) along with METH (5 mg/kg,ip,q 3h x 3) and were sacrificed 72 h after the last METH injection. Dopamine (DA) and dopamine transporter (DAT) binding sites were determined in striatum from saline and METH-treated animals. 7-NI completely protected against the depletion of DA, and DAT in striatum. In follow-up experiments nNOS KO mice along with appropriate control (C57BL/6N, SV129 and B6JSV129) mice were treated with METH (5 mg/kg,ip, q 3h x 3) and were sacrificed 72 h after dosing. This schedule of METH administrations resulted in only 10-20% decrease in tissue content of DA and no apparent change in the number of DAT binding sites in nNOS KO mice. However, this regime of METH resulted in a significant decrease in the content of DA as well as DAT binding sites in the wild-type animals. Pre-exposure to single or multiple doses of METH resulted in a marked locomotion sensitization in response to METH. However, the nNOS KO mice show no sensitization in response to METH after single or multiple injections of METH. Therefore, these studies strongly suggest the role of peroxynitrite, nNOS and DA system in METH-induced neurotoxicity and behavioral sensitization.

Methamphetamine rapidly decreases vesicular dopamine uptake

Vesicular sequestration is important in the regulation of cytoplasmic concentrations of monoamines such as dopamine. Moreover, recent evidence suggests that increases in cytoplasmic dopamine levels, perhaps attributable to changes in vesicular monoamine transporter function, contribute to methamphetamine-induced dopaminergic deficits. Hence, we examined whether striatal vesicular uptake is altered following methamphetamine treatment. Multiple administrations of methamphetamine rapidly (within 1 h) decreased vesicular dopamine uptake and dihydrotetrabenazine binding, an effect that (a) persisted at least 24 h, (b) was associated with dopamine and not serotonin neurons, and (c) was unrelated to residual drug introduced by the original methamphetamine treatment. These data suggest that methamphetamine rapidly decreases vesicular monoamine transporter function in dopaminergic neurons, a phenomenon that may be associated with the long-term damage caused by this stimulant.

Differential effects of methamphetamine on Na(+)/Cl(-)-dependent transporters

It has been demonstrated that methamphetamine (METH) administration affects Na(+)/Cl(-)-dependent transporters; for example, METH treatment rapidly and reversibly decreases dopamine (DA) and serotonin (5HT) transporter function in rat striatum in vivo, as assessed in synaptosomes prepared from METH-treated rats. Because acute effects of METH on other transporters within this family have been less studied, the responses of norepinephrine (NE) and gamma-aminobutyric acid (GABA) transporters to METH administration(s) were determined. Both single and multiple METH administrations inhibited hippocampal NE uptake 1 h after METH treatment(s). In contrast, striatal GABA uptake was not affected by either treatment paradigm. The effects observed after both single and multiple METH administrations on NE transporters were attributable to increases in K(m,) with no changes in V(max); effects that were eliminated by repeated washing of the synaptosomes. These 'washout' data suggest that residual METH introduced by the in vivo subcutaneous injection(s) directly reduced NE transporter activity in the in vitro assay and that, unlike DA and 5HT transporters, METH did not indirectly alter NE transporter function. Taken together, these data demonstrate differences in the responses of NE, GABA, DA, and 5HT transporters to METH treatment.

Methamphetamine-induced striatal dopamine neurotoxicity and cyclooxygenase-2 protein expression in BALB/c mice

The expression of cyclooxygenase-2 (COX-2) and striatal dopamine (DA) depletion in BALB/cAnNcrj (BALB/c) mice following a neurotoxic dose of methamphetamine (METH) was investigated. METH-treatment (4 mg/kg x 4, 2 h intervals, s.c.) induced a significant hyperthermia and a persistent depletion of striatal DA levels 72 h after the treatment. COX-2, a marker of the cytotoxic effect of inflammation and oxidative stress and thiobarbituric acid (TBA) were significantly induced in the striatum 72 h after the METH-treatment, but not in the hippocampus. These results suggest that COX-2 may participate in METH-induced neurotoxicity in striatum.