Protective effects of MK-801 on methamphetamine-induced depletion of dopaminergic and serotonergic terminals and striatal astrocytic response: an immunohistochemical study

Differential vulnerability of locus coeruleus and dorsal raphe neurons to chronic methamphetamine-induced degeneration

Methamphetamine (meth) increases monoamine oxidase (MAO)-dependent mitochondrial stress in axons of substantia nigra pars compacta (SNc), and ventral tegmental area (VTA) dopamine neurons. Chronic administration of meth results in SNc degeneration and MAO inhibition is neuroprotective, whereas, the VTA is resistant to degeneration. This differential vulnerability is attributed, at least in part, to the presence of L-type Ca²⁺ channel-dependent mitochondrial stress in SNc but not VTA dopamine neurons. MAO is also expressed in other monoaminergic neurons such as noradrenergic locus coeruleus (LC) and serotonergic dorsal raphe (DR) neurons. The impact of meth on mitochondrial stress in LC and DR neurons is unknown. In the current study we used a genetically encoded redox biosensor to investigate meth-induced MAO-dependent mitochondrial stress in LC and DR neurons. Similar to SNc and VTA neurons, meth increased MAO-dependent mitochondrial stress in axonal but not somatic compartments of LC norepinephrine and DR serotonin neurons. Chronic meth administration (5 mg/kg; 28-day) resulted in degeneration of LC neurons and MAO inhibition was neuroprotective whereas DR neurons were resistant to degeneration. Activating L-type Ca²⁺ channels increased mitochondrial stress in LC but not DR axons and inhibiting L-type Ca²⁺ channels in vivo with isradipine prevented meth-induced LC degeneration. These data suggest that similar to recent findings in SNc and VTA dopamine neurons, the differential vulnerability between LC and DR neurons can be attributed to the presence of L-type Ca²⁺ channel-dependent mitochondrial stress. Taken together, the present study demonstrates that both meth-induced MAO- and L-type Ca²⁺ channel-dependent mitochondrial stress are necessary for chronic meth-induced neurodegeneration.

The Role of α-Synuclein in Methamphetamine-Induced Neurotoxicity

Methamphetamine (METH), a highly addictive psychostimulant, is the second most widely used illicit drug. METH produces damage dopamine neurons and apoptosis via multiple inter-regulating mechanisms, including dopamine overload, hyperthermia, oxidative stress, mitochondria dysfunction, endoplasmic reticulum stress, protein degradation system dysfunction, and neuroinflammation. Increasing evidence suggests that chronic METH abuse is associated with neurodegenerative changes in the human brain and an increased risk of Parkinson's disease (PD). METH use and PD may share some common steps in causing neurotoxicity. Accumulation of α-synuclein, a presynaptic protein, is the pathological hallmark of PD. Intriguingly, α-synuclein upregulation and aggregation are also found in dopaminergic neurons in the substantia nigra in chronic METH users. This suggests α-synuclein may play a role in METH-induced neurotoxicity. The mechanism of α-synuclein cytotoxicity in PD has attracted considerable attention; however, how α-synuclein affects METH-induced neurotoxicity has not been reviewed. In this review, we summarize the relationship between METH use and PD, interdependent mechanisms that are involved in METH-induced neurotoxicity and the significance of α-synuclein upregulation in response to METH use. The identification of α-synuclein overexpression and aggregation as a contributor to METH-induced neurotoxicity may provide a novel therapeutic target for the treatment of the deleterious effect of this drug and drug addiction.

Postmortem Study of Molecular and Histological Changes in the CA1 Hippocampal Region of Chronic Methamphetamine User

Methamphetamine (Meth) is recognized as one of the most important new distributed abused drug that causes severe damage to the different parts of the brain, especially hippocampus. Previous studies have demonstrated that Meth can induce apoptosis and cell death in the brain. In this study, we evaluated the long-term effects of Meth abuse in the CA1 region of postmortem hippocampus. Postmortem molecular and histological analysis was performed for five non-addicted subjects and five Meth addicted ones. Iba-1 (microglia) and glial fibrillary acidic protein, GFAP (astrocytes) expression were assayed by western blotting and immunohistochemistry (IHC) methods. Histopathological assessment was done with stereological counts of hippocampal cells stained with hematoxylin and eosin (H and E). Tunel staining was used to detect DNA damage in human brains. In addition, protein-protein interaction analysis network was investigated. Western blotting and immunohistochemistry assay showed overexpression of GFAP and Iba-1 protein in the CA1 hippocampal region of Meth users’ brain. Stereological analysis in the CA1 region revealed increased neuron degeneration. Furthermore, significant apoptosis and cell death were confirmed by Tunel assay in the hippocampus. The prominent role of TLR4, IL1B, CASP1, and NLRP3 in the molecular mechanism of Meth was highlighted via PPI network analysis. Chronic Meth use can induce GFAP and Iba-1 upregulation and neuronal apoptosis in the CA1 region of the postmortem hippocampus.

Effects of ketamine use on psychotic disorders and symptoms in male, methamphetamine-dependent subjects

BACKGROUND

Repeated and extensive methamphetamine or ketamine use may cause psychotic symptoms. Whether the chronic and combined use of these substances has a greater psychotic effect is still unknown.

OBJECTIVES

To examine the effect of different levels of ketamine use on psychotic disorders and symptoms in male methamphetamine-dependent subjects.

METHODS

A cross-sectional, structured, and clinical interview method was used to examine the differences in DSM-IV-TR Axis I psychotic disorders and symptoms among methamphetamine-dependent subjects in three categories: 205 with no ketamine use, 38 with occasional ketamine use, and 72 with ketamine abuse or dependence from compulsory rehabilitation centers.

RESULTS

Both methamphetamine-dependent subjects with occasional ketamine use and those with ketamine abuse or dependence had a higher prevalence of psychotic disorders than those who had not used ketamine (p = 0.021; p < 0.001). Subjects who used ketamine occasionally had a higher prevalence of referential and persecutory delusions (p < 0.001; p = 0.013) and auditory hallucinations (p = 0.030), and those with ketamine abuse or dependence had a higher prevalence of referential and persecutory delusions (p = 0.005; p = 0.021), compared with those who had not used ketamine. There was no significant difference in any psychotic disorders or symptoms between subjects with occasional ketamine use and those with ketamine abuse or dependence.

CONCLUSIONS

The combination of methamphetamine and ketamine was associated with greater psychotic effects than methamphetamine alone. Both occasional ketamine use and ketamine abuse or dependence were associated with increased psychotic symptoms and disorders in methamphetamine-dependent males.

Astrocytic clasmatodendrosis in the cerebral cortex of methamphetamine abusers

Postmortem investigation of methamphetamine (MA) abuse is an important task in forensic pathology. The present study investigated morphological changes in the astrocytes in the parietal cerebral cortex of MA abusers. Glial fibrillary acidic protein immunoreactivity in the cerebral cortex was examined in forensic autopsy cases for MA-detected group and control group. Clasmatodendrotic astrocytes (including those with swollen cell bodies and disintegrating distal processes) were frequently observed in the cerebral cortex of MA abusers. Quantitative analysis using a colour image processor showed a concomitant increase in the astrocyte area and astrocyte-to-vessel area ratio (size and number of astrocytes) in the grey matter in acute MA fatality and other MA-involved cases, although the astrocyte area (size) was also increased in cases of asphyxiation. The total astrocyte area (size) in the white matter was significantly higher in MA fatalities and asphyxia than in the other groups involving MA abusers. Those indices were independent of blood MA level, age, sex, survival or postmortem time. These observations suggest the increasing number and hypertrophic changes of astrocytes in the grey matter in MA abusers can be the outcome of long-term abuse, while disintegrating distal processes may exist only in acute fatal MA intoxication.

Nucleus accumbens invulnerability to methamphetamine neurotoxicity

Methamphetamine (Meth) is a neurotoxic drug of abuse that damages neurons and nerve endings throughout the central nervous system. Emerging studies of human Meth addicts using both postmortem analyses of brain tissue and noninvasive imaging studies of intact brains have confirmed that Meth causes persistent structural abnormalities. Animal and human studies have also defined a number of significant functional problems and comorbid psychiatric disorders associated with long-term Meth abuse. This review summarizes the salient features of Meth-induced neurotoxicity with a focus on the dopamine (DA) neuronal system. DA nerve endings in the caudate-putamen (CPu) are damaged by Meth in a highly delimited manner. Even within the CPu, damage is remarkably heterogeneous, with ventral and lateral aspects showing the greatest deficits. The nucleus accumbens (NAc) is largely spared the damage that accompanies binge Meth intoxication, but relatively subtle changes in the disposition of DA in its nerve endings can lead to dramatic increases in Meth-induced toxicity in the CPu and overcome the normal resistance of the NAc to damage. In contrast to the CPu, where DA neuronal deficiencies are persistent, alterations in the NAc show a partial recovery. Animal models have been indispensable in studies of the causes and consequences of Meth neurotoxicity and in the development of new therapies. This research has shown that increases in cytoplasmic DA dramatically broaden the neurotoxic profile of Meth to include brain structures not normally targeted for damage. The resistance of the NAc to Meth-induced neurotoxicity and its ability to recover reveal a fundamentally different neuroplasticity by comparison to the CPu. Recruitment of the NAc as a target of Meth neurotoxicity by alterations in DA homeostasis is significant in light of the numerous important roles played by this brain structure.

Differential phosphoproteome of the striatum from pleiotrophin knockout and midkine knockout mice treated with amphetamine: correlations with amphetamine-induced neurotoxicity

The neurotrophic factors pleiotrophin (PTN) and midkine (MK) have been shown to modulate amphetamine-induced neurotoxicity. Accordingly, PTN-/- and MK-/- mice show an increased vulnerability to amphetamine-induced neurotoxic effects. In an effort to uncover new pharmacological targets to prevent amphetamine neurotoxic effects, we have now used a proteomic approach to study protein phosphorylation, in which we combined phosphoprotein enrichment, by immobilized metal affinity chromatography (IMAC), with two-dimensional gel electrophoresis and mass spectrometry, in order to identify the phosphoproteins regulated in the striatum of PTN-/-, MK-/- and wild type (WT) mice treated with amphetamine. We identified 13 differentially expressed phosphoproteins that are judged to be relevant in the neuroprotective roles of PTN and MK against amphetamine-induced neurotoxicity. It is very interesting to note that 4 of these phosphoproteins, annexin A7 (ANXA7), COP9 signalosome subunit 5 (COPS5), aldehyde dehydrogenase family 1 member A1 (ALDH1A1) and creatine kinase U-type (CKMT1), are known to be involved in Parkinson's disease, a result of significant importance since PTN and MK have been also demonstrated to limit Parkinson's disease (PD) progress and have been suggested to be among the important genetic factors possibly preventing the development of PD in methamphetamine abusers. The data identify phosphoproteins differentially regulated by amphetamine treatment and/or the presence of endogenous PTN/MK which may be relevant mediators of PTN/MK neuroprotective effects against amphetamine-induced neurotoxicity. The data support further studies to validate the phosphoproteins here identified as possible new pharmacological targets to prevent amphetamine neurotoxic effects.

Methamphetamine influences on brain and behavior: unsafe at any speed?

Methamphetamine damages monoamine-containing nerve terminals in the brains of both animals and human drug abusers, and the cellular mechanisms underlying this injury have been extensively studied. More recently, the growing evidence for methamphetamine influences on memory and executive function of human users has prompted studies of cognitive impairments in methamphetamine-exposed animals. After summarizing current knowledge about the cellular mechanisms of methamphetamine-induced brain injury, this review emphasizes research into the brain changes that underlie the cognitive deficits that accompany repeated methamphetamine exposure. Novel approaches to mitigating or reversing methamphetamine-induced brain and behavioral changes are described, and it is argued that the slow spontaneous reversibility of the injury produced by this drug may offer opportunities for novel treatment development.

Involvement of metabotropic glutamate receptor 5, AKT/PI3K signaling and NF-κB pathway in methamphetamine-mediated increase in IL-6 and IL-8 expression in astrocytes

Methamphetamine (MA) is one of the commonly used illicit drugs and the central nervous system toxicity of MA is well documented. The mechanisms contributing to this toxicity have not been fully elucidated. In this study, we investigated the effect of MA on the expression levels of the proinflammatory cytokines/chemokines, IL-6 and IL-8 in an astrocytic cell line. The IL-6 and IL-8 RNA levels were found to increase by 4.6 ± 0.2 fold and 3.5 ± 0.2 fold, respectively, after exposure to MA for three days. Exposure of astrocytes to MA for 24 hours also caused increased expression of IL-6 and IL-8 at the level of both RNA and protein. The potential involvement of the nuclear factor-Kappa B (NF-κB) pathway was explored as one of the possible mechanism(s) responsible for the increased induction of IL-6 and IL-8 by MA. The MA-mediated increases in IL-6 and IL-8 were significantly abrogated by SC514. We also found that exposure of astrocytes to MA results in activation of NF-κB through the phosphorylation of IκB-α, followed by translocation of active NF-κB from the cytoplasm to the nucleus. In addition, treatment of cells with a specific inhibitor of metabotropic glutamate receptor-5 (mGluR5) revealed that MA-mediated expression levels of IL-6 and IL-8 were abrogated by this treatment by 42.6 ± 5.8% and 65.5 ± 3.5%, respectively. Also, LY294002, an inhibitor of the Akt/PI3K pathway, abrogated the MA-mediated induction of IL-6 and IL-8 by 77.9 ± 6.6% and 81.4 ± 2.6%, respectively. Thus, our study demonstrates the involvement of an NF-κB-mediated signaling mechanism in the induction of IL-6 and IL-8 by MA. Furthermore, we showed that blockade of mGluR5 can protect astrocytes from MA-mediated increases of proinflammatory cytokines/chemokines suggesting mGluR5 as a potential therapeutic target in treating MA-mediated neurotoxicity.

Electroencephalographic and convulsive effects of binge doses of (+)-methamphetamine, 5-methoxydiisopropyltryptamine, and (±)-3,4-methylenedioxymethamphetamine in rats

The abuse of drugs such as methamphetamine (MA), 3,4-methylenedioxymethamphetamine (Ecstasy, MDMA), and 5-methoxydiisopropyltryptamine (5-MeO-DIPT; Foxy) is global. Symptoms from taking these drugs include tachycardia, agitation, hyperpyrexia, and sometimes seizures. We compared the EEG effects of these drugs in male Sprague-Dawley rats (~300 g) implanted with cortical electroencephalographic (EEG) electrodes prior to testing. Animals received four subcutaneous injections of MA, MDMA, or Foxy (10 mg/kg each as freebase, administered every 2 h), or saline as these doses produce lasting effects on learning, memory, and monoamines. EEG tracings were recorded before, during, and after treatment. Animals receiving MDMA showed no significant EEG abnormalities or myoclonus. MA treatment resulted in myoclonic activity and in brief (<10 s) EEG epileptiform activity in ~50% of the rats. Longer seizure activity (10 s to 5 min) was recorded in some MA-treated rats following the third and fourth doses. The onset of myoclonic activity following Foxy treatment occurred shortly after the first dose. All rats receiving Foxy showed seizures by the second dose and this continued throughout the treatment regimen. The results show that binge doses of MA and MDMA, which mimic the neurochemical changes seen in chronic users, increase EEG abnormalities after MA but not after MDMA. While the neurochemical effects of Foxy are not known in humans, this drug causes severe EEG abnormalities and overt seizures in 100% of tested animals.

Comparison of (+)-methamphetamine, ±-methylenedioxymethamphetamine, (+)-amphetamine and ±-fenfluramine in rats on egocentric learning in the Cincinnati water maze

(+)-Methamphetamine (MA), (±)-3,4-methylenedioxymethamphetamine (MDMA), (+)-amphetamine (AMPH), and (±)-fenfluramine (FEN) are phenylethylamines with CNS effects. At higher doses, each induces protracted reductions in brain dopamine (DA) and/or serotonin. Chronic MA and MDMA users show persistent monoamine reductions and cognitive impairments. In rats, similar neurochemical effects can be induced, yet cognitive impairments have been difficult to demonstrate. We recently showed that rats treated on a single day with MA (10 mg/kg x 4 at 2 h intervals) exhibit impaired egocentric learning (Cincinnati water maze [CWM]) without affecting spatial learning (Morris water maze [MWM]) (Herring et al., [2008] Psychopharmacology (Berl) 199:637–650). Whether this effect is unique to MA or is a general characteristic of these drugs is unknown. Accordingly, this experiment compared these drugs on CWM performance. Drugs were given s.c. in four doses at 2 h intervals. MA doses were 10 or 12.5 mg/kg/dose, AMPH 25 mg/kg/dose (to match MA12.5-induced hyperthermia), MDMA 15 mg/kg/dose (previously established hyperthermia-inducing dose), and FEN 16.5 mg/kg/dose (equimolar to MA12.5). Two weeks later, rats were tested in the CWM (2 trials/day, 21 days). AMPH and MA (both doses) induced significant increases in CWM errors and latency to reach the goal with no differences in swim speed. MDMA and FEN did not significantly alter learning. Given that FEN selectively and MDMA preferentially affect serotonin whereas AMPH selectively and MA preferentially affect DA, the data suggest that egocentric learning may be predominantly dopaminergically mediated.

The neurotrophic factor pleiotrophin modulates amphetamine-seeking behaviour and amphetamine-induced neurotoxic effects: evidence from pleiotrophin knockout mice

Pleiotrophin (PTN), a neurotrophic factor with important roles in survival and differentiation of dopaminergic neurons, is up-regulated in the nucleus accumbens after amphetamine administration suggesting that PTN could modulate amphetamine-induced pharmacological or neuroadaptative effects. To test this hypothesis, we have studied the effects of amphetamine administration in PTN genetically deficient (PTN -/-) and wild type (WT, +/+) mice. In conditioning studies, we found that amphetamine induces conditioned place preference in both PTN -/- and WT (+/+) mice. When these mice were re-evaluated after a 5-day period without amphetamine administration, we found that WT (+/+) mice did not exhibit amphetamine-seeking behaviour, whereas, PTN -/- mice still showed a robust drug-seeking behaviour. In immunohystochemistry studies, we found that amphetamine (10 mg/kg, four times, every 2 hours) causes a significant increase of glial fibrillary acidic protein positive cells in the striatum of amphetamine-treated PTN -/- mice compared with WT mice 4 days after last administration of the drug, suggesting an enhanced amphetamine-induced astrocytosis in the absence of endogenous PTN. Interestingly, we found in concomitant in vitro studies that PTN (3 µM) limits amphetamine (1 mM)-induced loss of viability of PC12 cell cultures, effect that could be related to the ability of PTN to induce the phosphorylation of Akt and ERK1/2. To test this possibility, we used specific Akt and ERK1/2 inhibitors uncovering for the first time that PTN-induced protective effects against amphetamine-induced toxicity in PC12 cells are mediated by the ERK1/2 signalling pathway. The data suggest an important role of PTN to limit amphetamine-induced neurotoxic and rewarding effects.

Genetic inactivation of pleiotrophin triggers amphetamine-induced cell loss in the substantia nigra and enhances amphetamine neurotoxicity in the striatum

Pleiotrophin (PTN) is a neurotrophic factor with important effects in survival and differentiation of dopaminergic neurons that has been suggested to play important roles in drug of abuse-induced neurotoxicity. To test this hypothesis, we have studied the effects of amphetamine (10 mg/kg, four times, every 2 h) on the nigrostriatal pathway of PTN genetically deficient (PTN-/-) mice. We found that amphetamine causes a significantly enhanced loss of dopaminergic terminals in the striatum of PTN-/- mice compared to wild type (WT+/+) mice. In addition, we found a significant decrease ( approximately 20%) of tyrosine hydroxylase (TH)-positive neurons only in the substantia nigra of amphetamine-treated PTN-/- mice, whereas this area of WT+/+ animals remained unaffected after amphetamine treatment. This effect was accompanied by enhanced amphetamine-induced astrocytosis in the substantia nigra of PTN-/- mice. Interestingly, we found a significant decrease in the phosphorylation levels of p42 extracellular-signal regulated kinase (ERK2) in both saline- and amphetamine-treated PTN-/- mice, whereas phosphorylation of p44 ERK (ERK1) was almost abolished in the striatum of PTN-/- mice compared to WT+/+ mice, suggesting that basal deficiencies in the phosphorylation levels of ERK1/2 could underlie the higher vulnerability of PTN-/- mice to amphetamine-induced neurotoxic effects. The data suggest an important role of PTN in the protection of nigrostriatal pathways against amphetamine insult.

Implication of activated astrocytes in the development of drug dependence: differences between methamphetamine and morphine

Astrocytes are a subpopulation of glial cells that directly affect neuronal function. This review focuses on the potential functional roles of astrocytes in the development of behavioral sensitization and rewarding effects induced by chronic treatment with drugs of abuse. In vitro treatment of cortical neuron/glia cocultures with either methamphetamine or morphine caused activation of astrocytes via protein kinase C (PKC). Purified cortical astrocytes were markedly activated by methamphetamine, whereas morphine had no such effect. Methamphetamine, but not morphine, caused a long-lasting astrocytic activation in cortical neuron/glia cocultures. Morphine-induced behavioral sensitization, assessed as hyperlocomotion, was reversed by 2 months of withdrawal from intermittent morphine administration, whereas behavioral sensitization to methamphetamine-induced hyperlocomotion was maintained even after 2 months of withdrawal. In vivo treatment with methamphetamine, which was associated with behavioral sensitization, caused PKC-dependent astrocytic activation in the mouse cingulate cortex and nucleus accumbens. Furthermore, the glial modulator propentofylline dramatically diminished the activation of astrocytes and the rewarding effect induced by methamphetamine and morphine. On the other hand, intra-nucleus accumbens and intra-cingulate cortex administration of astrocyte-conditioned medium aggravated the development of rewarding effects induced by methamphetamine and morphine. Furthermore, astrocyte-conditioned medium, but not methamphetamine itself, clearly induced differentiation of neural stem cells into astrocytes. These findings provide direct evidence that astrocytes may, at least in part, contribute to the development of the rewarding effects induced by drugs of abuse in the nucleus accumbens and cingulate cortex.

Distinct mechanisms mediating methamphetamine-induced neuronal apoptosis and dopamine terminal damage share the neuropeptide substance p in the striatum of mice

Methamphetamine (METH) is an addictive psychostimulant that induces damage to the dopamine terminals and the apoptosis of some neurons of the striatum. Our laboratory demonstrated using either a single bolus dose (30 mg/kg) or a binge (10 mg/kg 4x at 2-h intervals) of METH that pharmacological blockade of the substance P receptor (neurokinin-1) attenuates METH-induced damage to both the presynaptic dopamine terminals and the apoptosis of some neurons of the striatum. To determine the phenotype of striatal neuron ablated by METH, we combined TUNEL (Terminal Deoxyncleotidyl Transferase-Mediated dUTP Nick End Labeling) with immunofluorescence for selective markers of projection and interneurons. METH induces the loss of approximately 20% of the projection neurons. The cholinergic and gamma-aminobutyric acid (GABA)-parvalbumin interneurons sustain losses of 30% and 50%, respectively. The somatostatin/neuropeptide Y (NPY)/nitric oxide synthase (NOS) interneurons are not impacted by METH. To investigate the mechanism by which substance P mediates METH-induced damage in this part of the brain, we ablated the striatal interneurons that express the neurokinin-1 receptor (NK-1R) with the selective neurotoxin substance P-SAP. Ablation of the NK-1R-expressing interneurons prevented METH-induced apoptosis in the striatum but was without effect on depletion of dopamine terminal markers. We propose that substance P mediates the apoptosis of some striatal neurons via the intrastriatal activation of nitric oxide synthesis. In contrast, substance P may mediate damage of the dopamine terminals via an extrastriatal mechanism involving the substantia nigra and cortical glutamate release.

The role of the plasmalemmal dopamine and vesicular monoamine transporters in methamphetamine‐induced dopaminergic deficits

Amphetamine (AMPH) and methamphetamine (METH) are members of a collection of phenethylamine psychostimulants that are commonly referred to collectively as "amphetamines." Amphetamines exert their effects, in part, by affecting neuronal dopamine transport. This review thus focuses on the effects of AMPH and METH on the plasmalemmal dopamine transporter and the vesicular monoamine transporter-2 in animal models with a particular emphasis on how these effects, which may vary for the different stereoisomers, contribute to persistent dopaminergic deficits.

Mechanisms of methamphetamine-induced dopaminergic neurotoxicity

Methamphetamine (METH) is a powerful stimulant of abuse with potent addictive and neurotoxic properties. More than 2.5 decades ago, METH-induced damage to dopaminergic neurons was described. Since then, numerous advancements have been made in the search for the underlying mechanisms whereby METH causes these persistent dopaminergic deficits. Although our understanding of these mechanisms remains incomplete, combinations of various complex processes have been described around a central theme involving reactive species, such as reactive oxygen and/or nitrogen species (ROS and RNS, respectively). For example, METH-induced hyperthermia, aberrant dopamine(DA), or glutamate transmission; or mitochondrial disruption leads to the generation of reactive species with neurotoxic consequences. This review will describe the current understanding of how high-dose METH administration leads to the production of these toxic reactive species and consequent permanent dopaminergic deficits.

Induction of striatal pre- and postsynaptic damage by methamphetamine requires the dopamine receptors

Methamphetamine (METH) is a psychostimulant that induces excessive release of dopamine (DA) in the striatum. In this study we have assessed the role of DA D1 and D2 receptors (D1R and D2R) on striatal METH-induced apoptosis and depletion of DA-terminal markers. Male mice were given one i.p. injection of METH (30 mg/kg). Apoptosis was assessed at 24 h, and DA-terminal marker depletion 3 days, after METH. A single toxic dose of METH induced apoptosis in approximately 10-13% of striatal neurons. This was completely prevented by pretreatment (30 min before METH) with either the D1R antagonist SCH-23390 (0.1 mg/kg) or the D2R antagonist raclopride (1 mg/kg). The same dose of METH induced depletion of DA transporter sites up to 61, 56, 71, and 69% in dorsal-medial, ventral-medial, dorsal-lateral, and ventral-lateral striatum, respectively, relative to vehicle-injected controls. Similarly, METH induced depletion of TH protein levels up to 80, 72, 87, and 90% in those respective quadrants. METH induced the expression of glial fibrillary acidic protein throughout the striatum. All these neurochemical changes were significantly attenuated by pretreatment with SCH-23390 (0.1 mg/kg) or raclopride (1 mg/kg). However, pretreatment with either raclopride or SCH-23390 did not prevent METH-induced hyperthermia in mice. These data demonstrate that the induction by METH of both striatal apoptosis and DA-terminal damage requires the activity of the postsynaptic DA receptors in the mouse brain. Moreover, since blockade of either receptor subtype protected from METH, the activity of both DA receptor subtypes is required for the induction of toxicity by METH in the striatum.

Long-lasting change in brain dynamics induced by methamphetamine: enhancement of protein kinase C-dependent astrocytic response and behavioral sensitization

It is well known that long-term exposure to psychostimulants induces neuronal plasticity. Recently, accumulating evidence suggests that astrocytes may actively participate in synaptic plasticity. In this study, we found that in vitro treatment of cortical neuron/glia co-cultures with either methamphetamine (METH) or morphine (MRP) caused the activation of astrocytes via protein kinase C (PKC). Purified astrocytes were markedly activated by METH, whereas MRP had no such effect. METH, but not MRP, caused a long-lasting astrocytic activation in cortical neuron/glia co-cultures. Furthermore, MRP-induced behavioral sensitization to hyper-locomotion was reversed by 2 months of withdrawal following intermitted MRP administration, whereas behavioral sensitization to METH-induced hyper-locomotion was maintained even after 2 months of withdrawal. Consistent with this cell culture study, in vivo treatment with METH, which was associated with behavioral sensitization, caused a PKC-dependent astrocytic activation in the cingulate cortex and nucleus accumbens of mice. These findings provide direct evidence that METH induces a long-lasting astrocytic activation and behavioral sensitization through the stimulation of PKC in the rodent brain. In contrast, MRP produced a reversible activation of astrocytes via neuronal PKC and a reversibility of behavioral sensitization. This information can break through the definition of drugs of abuse and the misleading of concept that morphine produces a long-lasting neurotoxicity.

Antagonists of the neurokinin-1 or dopamine D1 receptors confer protection from methamphetamine on dopamine terminals of the mouse striatum

Methamphetamine (METH) is a highly addictive compound that induces toxicity of the dopamine (DA) terminals of the neostriatum. Exposure to METH induces long-term deficits in dopamine transporter (DAT) and tyrosine hydroxylase (TH) levels as well as induction of glial fibrillary acidic protein (GFAP) in the caudate putamen (CPu) and the nucleus accumbens (NAc). The primary effect of exposure to METH is elevation of the level of extracellular DA; therefore, we assessed the role of the DA D1 receptor (D1R) and neurokinin-1 receptor (NK-1R) on the expression of toxicity. METH was injected intraperitoneally (10 mg/kg) four times at 2-h intervals (an acute toxic dose), and the mice were sacrificed three days after the treatment. Exposure to METH resulted in marked reduction of DAT sites (reduced to 30 and 21% relative to control in medial and lateral aspects of the CPu) assessed by binding of [125I]RTI-121 by autoradiography or Western blot analysis. Pretreatment with the nonpeptide NK-1R antagonist WIN-51,708 (10 mg/kg) 30 min prior to the first and fourth injections of METH prevented the loss of DAT sites of the CPu. Moreover, pretreatment with WIN-51,708 also prevented the reduction of TH levels induced by METH as well as the induction of GFAP in astrocytes. Pretreatment with the D1R antagonist SCH-23390 (0.25 mg/kg) 30 min before the first and fourth injections of METH conferred partial protection on DAT sites of the CPu. These results demonstrate that receptors postsynaptic to the DA terminals of the CPu are needed in order to express the neurotoxic effects of METH on integral components of the DA terminals of the nigrostriatal projection.

Interactions of dopamine D1 and D2 receptor antagonists with D-methamphetamine-induced hyperthermia and striatal dopamine and serotonin reductions

The effects of the dopamine D1 receptor antagonist R(+)-SCH-23390 and D2 receptor antagonist S(-)-eticlopride on d-methamphetamine-induced striatal monoamine reductions 72 h after treatment were investigated in relation to changes in body temperature. Rats were administered four 10-mg/kg doses of d-methamphetamine or saline with a 2-h interval between treatments; 0.5 mg/kg eticlopride or SCH-23390 was administered 15 min before each methamphetamine or saline injection. Two ambient temperature conditions were investigated: 24 and 33 degrees C. Methamphetamine administered at 24 degrees C induced hyperthermia and reduced striatal dopamine content by 73%; 0.5 mg/kg eticlopride or SCH-23390 administered in combination with methamphetamine at 24 degrees C attenuated methamphetamine-induced hyperthermia and prevented significant reductions in dopamine content. At 33 degrees C, eticlopride and SCH-23390 were ineffective in blocking methamphetamine-induced hyperthermia and dopamine content was reduced by 65% in the SCH-23390-methamphetamine group. By contrast, dopamine content was reduced by only 31% in the 33 degrees C eticlopride-methamphetamine group. Thus, although the eticlopride-methamphetamine treatment combination at 33 degrees C exhibited a hyperthermic response comparable to that seen with methamphetamine alone at 24 degrees C, reductions in dopamine content were attenuated in the combination group compared with methamphetamine alone at 24 degrees C. Serotonin changes showed similar attenuated reductions after SCH-23390 or eticlopride pretreatment at 24 degrees C in combination with methamphetamine, but this attenuation was absent at 33 degrees C. The dissociation of methamphetamine-induced striatal dopamine reduction and hyperthermia seen after eticlopride pretreatment suggests a dopamine D2 receptor mechanism in mediating methamphetamine-induced dopamine depletion. However this D2 mechanism does not apply to methamphetamine-induced striatal serotonin reductions.

Histological evidence supporting a role for the striatal neurokinin-1 receptor in methamphetamine-induced neurotoxicity in the mouse brain

Several studies have documented the effect of methamphetamine (METH) on the toxicity of the dopamine (DA) terminals of the striatum but only a few studies have assessed the damaging effects of METH on striatal neurons postsynaptic to the nigrostriatal DA terminals. In the present study, we employed histological methods to study the effect of METH on DA terminals and striatal neurons. We also assessed the role of the striatal neurokinin-1 (NK-1) receptor on pre- and post-synaptic METH-induced damage. Male mice were treated with METH (10 mg/kg) four times at 2-h intervals and were sacrificed 3 days after the treatment. A number of animals received the non-peptide NK-1 receptor antagonist WIN-51,708 (10 mg/kg) 30 min before the first and fourth injections of METH. Immunocytochemical staining for tyrosine hydroxylase (TH) showed significant deficits throughout all aspects of the caudate-putamen in animals exposed to METH. Pretreatment with WIN-51,708 prevented the METH-induced loss of TH immunostaining. Sections from a separate set of mice were stained with Fluoro-Jade B (FJB), a fluorochrome that binds specifically to degenerating fibers and cell bodies of neurons. Treatment with METH shows Fluoro-Jade B positive cell bodies in the striatum and pretreatment with WIN-51,708 abolished Fluoro-Jade B staining. Moreover, double labeling with Fluoro-Jade B and glial fibrillary acidic protein (GFAP) shows reactive astrocytosis in the area adjacent to the Fluoro-Jade B-positive cells but no Fluoro-Jade B staining of the astrocytes. This observation suggests that the degenerating cells must be striatal neurons and not astrocytes. The data demonstrate that METH induces pre- and post-synaptic damage in the striatum and the damage can be prevented with pharmacological blockade of the NK-1 receptor. These findings represent a new direction in the study of the mechanism of toxicity to METH and could be useful in the treatment of some neurological disorders.

Identification of differentially regulated transcripts in mouse striatum following methamphetamine treatment - an oligonucleotide microarray approach

Methamphetamine is an addictive drug of abuse that can produce neurotoxic effects in dopamine nerve endings of the striatum. The purpose of this study was to identify new genes that may play a role in the highly complex cascade of events associated with methamphetamine intoxication. Using Affymetrix oligonucleotide arrays, 12 488 genes were simultaneously interrogated and there were 152 whose expression levels were changed following methamphetamine treatment. The genes are grouped into broad functional categories with inflammatory/immune response elements, receptor/signal transduction components and ion channel/transport proteins among the most populated. Many genes within these categories can be linked to ion regulation and apoptosis, both of which have been implicated in methamphetamine toxicity, and numerous factors associated with microglial activation emerged with significant changes in expression. For example, brain-derived neurotrophic factor (BDNF), chemokine (C-C) receptor 6 (CCr6) and numerous chemokine transcripts were increased or decreased in expression more than 2.8-fold. These results point to activated microglia as a potential source of the reactive oxygen/nitrogen species and cytokines that have been previously associated with methamphetamine toxicity and other neurotoxic conditions.

Escalating dose methamphetamine pretreatment alters the behavioral and neurochemical profiles associated with exposure to a high-dose methamphetamine binge

The neurotoxic effects of methamphetamine (METH) have been characterized primarily from the study of high-dose binge regimens in rodents. However, this drug administration paradigm does not include a potentially important feature of stimulant abuse in humans, that is, the gradual escalation of stimulant doses that frequently occurs prior to high-dose exposure. We have argued that pretreatment with escalating doses (EDs) might significantly alter the neurotoxic profile produced by a single high-dose binge. In the present study, we tested this hypothesis by pretreating rats with saline or gradually increasing doses of METH (0.1-4.0 mg/kg over 14 days), prior to an acute METH binge (4 x 6 mg/kg at 2 h intervals). These animals, whose behavior was continuously monitored throughout drug treatment, were then killed 3 days later for determination of caudate-putamen dopamine (DA) content, levels of [(3)H]WIN 35,428 binding to the DA transporter, and levels of [(3)H]dihydrotetrabenazine ([(3)H]DTBZ) binding to the vesicular monoamine transporter. ED pretreatment markedly attenuated the stereotypy response, as well as the hyperthermia and indices of sympathetic activation associated with the acute binge. In addition, ED pretreatment prevented the decline in [(3)H]WIN 35,428 binding, and significantly diminished the decrease in DA levels, but did not affect the decrease in [(3)H]DTBZ binding associated with the acute binge. We suggest that further study of the effects produced by a regimen which includes a gradual escalation of doses prior to high-dose METH binge exposure could more accurately identify the neurochemical and behavioral changes relevant to those that occur as a consequence of high-dose METH abuse in humans.

Substance P and cholecystokinin regulate neurochemical responses to cocaine and methamphetamine in the striatum

The mechanism of action of drugs of abuse like cocaine and amphetamines has been studied extensively in the dopamine terminal field areas of the caudate-putamen (CPu) and the nucleus accumbens (NAc) of the rodent brain. These brain regions contain several neuropeptides that must play important roles in the normal physiological functions of these brain regions. The study of neuropeptide physiology in the context of the neurobiological responses to drugs of abuse may shed some light on the intrinsic mechanism of action of neuropeptides of the CPu and the NAc. The neuropeptides substance P (SP) and cholecystokinin (CCK) are present in the striatum where they could play an important role regulating the effects of psychostimulants like cocaine and amphetamines (methamphetamine [METH] is a long acting derivative of d-amphetamine). These highly addictive agents induce the release of dopamine (DA) (and other catecholamines) from dopaminergic terminals of the striatum. The excessive release of DA in the striatum and the NAc has been implicated in the habit-forming properties of these drugs. In order to study the contribution of SP and CCK in the striatum during psychostimulant treatment, we employed selective non-peptide neurokinin-1 (NK-1) and cholecystokinin-2 (CCK-2) receptor antagonists that readily cross the blood brain barrier. We infused the neurokinin-1 receptor (NK-1R) antagonist, L-733,060, into the striatum of freely moving rats via a microdialysis probe in order to assess the effects of SP on cocaine-induced DA overflow in the striatum. Infusion of the NK-1R antagonist prior to a systemic injection of cocaine (10 mg/kg i.p.) significantly attenuated DA overflow in the striatum. Conversely, infusion of a CCK-2 receptor (CCK-2R) antagonist, L-369,293, through the microdialysis probe evoked DA overflow in the striatum in the absence of cocaine and potentiated DA overflow after a single injection of cocaine (10 mg/kg i.p.). Exposure to METH (10 mg/kg 4x at two-hour intervals) produced deficits of dopamine transporters (DAT) in mice striatum that are detectable three days after the treatment and are long lasting. Pre-treatment (i.p. injections) with the NK-1R antagonist, WIN-51,708 30 minutes before the 1st and 4th injections of METH prevented the loss of DAT in the striatum. Moreover, pre-treatment with the NK-1R antagonist prevents METH-induced cell death. Taken together, these results demonstrate that the NK-1R and the CCK-2R are important modulators of the actions of the psychostimulants cocaine and METH. Neuropeptide receptors represent an important control point mediating the effects of the neurotransmitter DA in the striatum of the rodent brain.

Enhanced P2Y1 receptor expression in the brain after sensitisation with d-amphetamine

RATIONALE AND OBJECTIVES

Many pathological and physiological processes are associated with the transcriptional induction of specific receptors. The aim of the present study was to examine whether the development of d-amphetamine (AMPH)-induced sensitisation is related to an altered P2Y(1) receptor expression.

METHODS

Rats, treated for 5 successive days with AMPH (1.5 mg/kg, i.p.), alone or after pre-treatment with the non-specific P2 receptor antagonist pyridoxal-phosphate-6-azophenyl-2,4-disulphonic acid (PPADS, 0.6 nmol, i.c.v.) and tested in an open field system with respect to locomotor response, were studied immunocytochemically 5 days after the last AMPH injection.

RESULTS

In the behaviourally sensitised animals, astrogliosis, characterised by hypertrophy, increase in glial fibrillary acidic protein (GFAP) immunoreactivity (IR) and astrocytic proliferation in striatal areas and the nucleus accumbens were observed. Quantification of the P2Y(1) receptor stained cells revealed an increase in the receptor expression after AMPH-induced sensitisation in the studied regions. Pre-treatment with PPADS prior to each AMPH administration prevented the development of sensitisation, astrogliosis and P2Y(1) receptor up-regulation. PPADS failed to alter the number of P2Y(1) receptor-labelled cells when given alone. Confocal laser scanning microscopy indicated the localisation of P2Y(1) receptors on GFAP-labelled astrocytes as well as on tubulin (betaIII)-labelled neurones, under control conditions and after AMPH administration.

CONCLUSION

The present results confirm the existence of P2Y(1) receptors on astrocytes and neurones as possible targets of endogenous ATP and in addition show their up-regulation as a consequence of P2Y(1) receptor-involvement in AMPH-induced sensitisation in vivo.

Neurokinin-1 (NK-1) receptor antagonists abrogate methamphetamine-induced striatal dopaminergic neurotoxicity in the murine brain

Methamphetamine (METH) is an addictive substance that also causes extensive neural degeneration in the central nervous system. Because METH augments striatal substance P (SP) levels, we hypothesized that this neuropeptide plays a role in methamphetamine-induced toxicity and neural damage in the striatum. In this study we present evidence demonstrating that signaling through the neurokinin-1 (NK-1) receptor by SP plays an important role in methamphetamine-induced toxicity in the striatum. We tested the effects of the selective NK-1 receptor antagonists WIN-51,708 and L-733,060 on several markers of dopaminergic terminal toxicity in the mouse striatum. Administration of NK-1 receptor antagonist prevented the loss of dopamine transporters assessed by autoradiography and western blotting, the loss of tissue dopamine assessed by high-pressure liquid chromatography, and the loss of tyrosine hydroxylase, as well as the induction of glial fibrillary acidic protein determined by western blotting. Pre-treatment with NK-1 receptor antagonist had no effect on METH-induced hyperthermia. Pre-exposure of mice to either of the NK-1 receptor antagonists alone was without effect on all of these neurochemical markers. These results provide the first evidence that tachykinins, particularly SP, acting through NK-1 receptors, play a crucial role in the pathogenesis of nigrostriatal dopaminergic terminal degeneration induced by METH. This finding could lead to novel therapeutic strategies to offset drug addictions as well as in the treatment of a number of disorders including Parkinson's and Huntington's diseases.

Biphasic effects of selegiline on striatal dopamine: lack of effect on methamphetamine-induced dopamine depletion

We tested the hypothesis that selegiline can attenuate dopamine depletion if administered following high doses of methamphetamine that cause neurotoxicity in the striatum. Methamphetamine produced decreases of 50% or greater in both striatal concentrations of dopamine and combined concentrations of homovanillic acid and DOPAC in mice. For animals not exposed to methamphetamine, chronic treatment with selegiline over 18 days caused biphasic effects on striatal dopamine content, with decreases, no effect, or increases observed for mice receiving treatment with 0.02, 0.2, and 2.0 mg/kg, respectively. Selegiline failed to modify methamphetamine-induced reductions in striatal dopamine content or combined concentrations of homovanillic acid and DOPAC. Significant increases in mortality following the onset of selegiline treatment (24 hours after the initial dose of methamphetamine) occurred in methamphetamine-treated mice that received saline or 2.0 mg/kg of selegiline, but not for mice treated with 0.02 or 0.2 mg/kg of selegiline. These results indicate that selegiline fails to attenuate dopamine depletion when administered chronically following exposure to methamphetamine, but may attenuate methamphetamine-induced mortality. In control animals that did not receive methamphetamine, low doses of selegiline produced decreases the concentration of striatal dopamine, while high dose treatment caused increases in striatal dopamine content.

Methamphetamine neurotoxicity: necrotic and apoptotic mechanisms and relevance to human abuse and treatment

Research into methamphetamine-induced neurotoxicity has experienced a resurgence in recent years. This is due to (1) greater understanding of the mechanisms underlying methamphetamine neurotoxicity, (2) its usefulness as a model for Parkinson's disease and (3) an increased abuse of the substance, especially in the American Mid-West and Japan. It is suggested that the commonly used experimental one-day methamphetamine dosing regimen better models the acute overdose pathologies seen in humans, whereas chronic models are needed to accurately model human long-term abuse. Further, we suggest that these two dosing regimens will result in quite different neurochemical, neuropathological and behavioral outcomes. The relative importance of the dopamine transporter and vesicular monoamine transporter knockout is discussed and insights into oxidative mechanisms are described from observations of nNOS knockout and SOD overexpression. This review not only describes the neuropathologies associated with methamphetamine in rodents, non-human primates and human abusers, but also focuses on the more recent literature associated with reactive oxygen and nitrogen species and their contribution to neuronal death via necrosis and/or apoptosis. The effect of methamphetamine on the mitochondrial membrane potential and electron transport chain and subsequent apoptotic cascades are also emphasized. Finally, we describe potential treatments for methamphetamine abusers with reference to the time after withdrawal. We suggest that potential treatments can be divided into three categories; (1) the prevention of neurotoxicity if recidivism occurs, (2) amelioration of apoptotic cascades that may occur even in the withdrawal period and (3) treatment of the atypical depression associated with withdrawal.

Preweaning treatment with methamphetamine induces increases in both corticosterone and ACTH in rats

Treatment with methamphetamine (MA) on postnatal days P11-20 induces adult spatial learning and memory deficits without affecting monoamine levels in various brain regions. In this study, we examined the pituitary and adrenal response of animals administered MA four times daily on P11, P11-15, or from P11 to P20. Corticosterone (CORT) and adrenocorticotropin hormone (ACTH) levels were assessed over a 1-hour period following MA exposure. On P11, MA produced marked elevations of both CORT and ACTH; this is during the stress hyporesponsive period (SHRP). On P15 and P20, the maximal effect of MA on CORT titers was observed at 30 min, with lower, but still significantly increased, levels at 60 min compared to controls. Males receiving MA on P15 had higher levels of ACTH than did control males, while no differences were noted among females. On P20, MA treatment resulted in higher levels of ACTH relative to vehicle-injected controls, but levels were not different from controls that were only weighed at each drug administration. MA treatment inhibited body, but not brain weight gain, resulting in hippocampal weights that were heavier in the MA-treated animals when expressed as a percent of body weight. The elevations of adrenal steroids by MA, during late phases of hippocampal neurogenesis, may contribute to neuronal alterations that are later manifested in deficits of learning and memory.

Restorative effects of GDNF on striatal dopamine release in rats treated with neurotoxic doses of methamphetamine

Repeated methamphetamine (METH) administration to animals can result in long-lasting decreases in striatal dopamine (DA) release and content. Glial cell line-derived neurotrophic factor (GDNF) has pronounced effects on dopaminergic systems in vivo, including neuroprotective effects against METH. The present experiments were designed to examine the ability of GDNF to reverse, or accelerate recovery from, METH-induced alterations in striatal DA release. Male Fischer-344 rats were administered METH (5 mg/kg, s.c.) or saline 4 times in one day at 2-hour intervals. Seven days later the animals were anesthetized and given a single injection of 10 microg GDNF, or vehicle, into the right striatum. Three weeks later microdialysis experiments were carried out in both the right and left striata to examine basal and evoked levels of DA and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). In animals treated with METH followed by vehicle 7 days later, there were significant reductions in potassium- and amphetamine-evoked overflow of DA, and in basal levels of DOPAC and HVA, compared to control animals. In rats treated with METH followed 7 days later with GDNF, there were significant increases in potassium- and amphetamine-evoked overflow of DA on the right, GDNF-treated, side of the brain compared to the left side. Basal levels of DOPAC and HVA were also elevated on the GDNF-treated side of the brain. These results suggest that GDNF can accelerate recovery of dopaminergic release processes in the striatum of rats treated with neurotoxic doses of METH.

Protein phosphorylation cascades associated with methamphetamine-induced glial activation

Reactive gliosis is the most prominent response to diverse forms of central nervous system (CNS) injury. The signaling events that mediate this characteristic response to neural injury are under intense investigation. Several studies have demonstrated the activation of phosphoproteins within the mitogen-activated protein kinase (MAPK) and Janus kinase (JAK) pathways following neural insult. These signaling pathways may be involved or responsible for the glial response following injury, by virtue of their ability to phosphorylate and dynamically regulate the activity of various transcription factors. This study sought to delineate, in vivo, the relative contribution of MAPK- and JAK-signaling components to reactive gliosis as measured by induction of glial-fibrillary acidic protein (GFAP), following chemical-induced neural damage. At time points (6, 24, and 48 h) following methamphetamine (METH, 10 mg/kg x 4, s.c.) administration, female C57BL/6J mice were sacrificed by focused microwave irradiation, a technique that preserves steady-state phosphorylation. Striatal (target) and nontarget (hippocampus) homogenates were assayed for METH-induced changes in markers of dopamine (DA) neuron integrity as well as differences in the levels of activated phosphoproteins. GFAP upregulation occurred as early as 6 h, reaching a threefold induction 48 h following METH exposure. Neurotoxicant-induced reductions in striatal levels of DA and tyrosine hydroxylase (TH) paralleled the temporal profile of GFAP induction. Blots of striatal homogenates, probed with phosphorylation-state specific antibodies, demonstrated significant changes in activated forms of extracellular-regulated kinase 1/2 (ERK 1/2), c-jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK), MAPK/ERK kinase (MEK1/2), 70-kDa ribosomal S6 kinase (p70 S6), cAMP responsive element binding protein (CREB), and signal transducer and activator of transcription 3 (STAT3). MAPK-related phosphoproteins exhibited an activation profile that peaked at 6 h, remained significantly increased at 24, and fell to baseline levels 48 h following neurotoxicant treatment. The ribosomal S6 kinase was enhanced over 60% for all time points examined. Immunoreactivity profiles for the transcription factors CREB and STAT3 indicated maximal increases in phosphorylation occurring at 24 h, and measuring greater than 2- or 17-fold, respectively. Specific signaling events were found to occur with a time course suggestive of their involvement in the gliotic response. The toxicant-induced activation of these growth-associated signaling cascades suggests that these pathways could be obligatory for the triggering and/or persistence of reactive gliosis and may therefore serve as potential targets for modulation of glial response to neural damage.

Time-course of methamphetamine-induced neurotoxicity in rat caudate-putamen after single-dose treatment

The time-course of monoamine and tyrosine hydroxylase depletion after single-dose administration of D-methamphetamine (40 mg/kg s.c.) was investigated in caudate-putamen of male Sprague-Dawley rats. Times evaluated were 6, 12, 48, 72 and 240 h following treatment. Tyrosine hydroxylase was significantly reduced by 29, 60, 66, 76 and 76% of control at each of the respective post-treatment time intervals. Dopamine was not reduced 6 h following treatment. Dopamine was significantly reduced by 53, 57, 68 and 74% 12, 48, 72 and 240 h post-treatment, respectively. Reductions in caudate-putamen serotonin began earlier and were ultimately larger than for dopamine, with significant reductions of 28, 33 55, 74 and 81% at each of the respective post-treatment intervals. Confirmation of neurotoxicity was provided by measurement of glial fibrillary acidic protein (GFAP) 240 h post-treatment. GFAP was increased at this time interval by 150% above control. Methamphetamine-induced hyperthermia during the 6 h immediately after treatment was comparable among the groups of animals used for analyses at each time interval. The results demonstrate that methamphetamine-induced monoamine reductions in the caudate-putamen occur rapidly, peak at 75-80% below controls, and last for at least 10 days after a single dose. These effects are as large or larger than those reported after the commonly used 10 mg/kgx4 dose treatment regimen administered at 2-h intervals and provides an alternate model for the investigation of methamphetamine-induced neurotoxicity.

Attenuation and recovery of evoked overflow of striatal serotonin in rats treated with neurotoxic doses of methamphetamine

Repeated administration of methamphetamine to animals can lead to long-lasting decreases in striatal monoamine content. In the present study, the effects of neurotoxic doses of methamphetamine on basal and evoked overflow of striatal serotonin and of its primary metabolite 5-hydroxyindoleacetic acid were examined in awake rats using in vivo microdialysis. Male Fischer-344 rats were administered methamphetamine (5 mg/kg, s.c.) or saline four times in 1 day at 2-h intervals. Microdialysis studies were carried out 1 week, 1 month, and 6 months later. At 1 week posttreatment there were significant decreases in potassium- and amphetamine-evoked overflow of serotonin in the striatum of the methamphetamine-treated animals. Basal extracellular levels of 5-hydroxyindoleacetic acid but not of serotonin were also decreased. Evoked overflow of serotonin recovered by 1 month, and extracellular levels of 5-hydroxyindoleacetic acid had recovered by 6 months. Tissue levels of serotonin and 5-hydroxyindoleacetic acid were decreased at 1 week posttreatment but back to control levels by 1 month after treatment. These results indicate that presynaptic serotonergic functioning is attenuated in the striatum of rats treated 1 week earlier with neurotoxic doses of methamphetamine. However, in the model used, the changes are transient, and recovery can occur within 1-6 months posttreatment.

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.

Null mutation of c-fos causes exacerbation of methamphetamine-induced neurotoxicity

Methamphetamine neurotoxicity has been demonstrated in rodents and nonhuman primates. These neurotoxic effects may be associated with mechanisms involved in oxidative stress and the activation of immediate early genes (IEG). It is not clear, however, whether these IEG responses are involved in a methamphetamine-induced toxic cascade or in protective mechanisms against the deleterious effects of the drug. As a first step toward clarifying this issue further, the present study was thus undertaken to assess the toxic effects of methamphetamine in heterozygous and homozygous c-fos knock-out as well as wild-type mice. Administration of methamphetamine caused significant reduction in [(125)I]RTI-121-labeled dopamine uptake sites, dopamine transporter protein, and tyrosine hydroxylase-like immunohistochemistry in the striata of wild-type mice. These decreases were significantly exacerbated in heterozygous and homozygous c-fos knock-out mice, with the homozygous showing greater loss of striatal dopaminergic markers. Moreover, in comparison with wild-type animals, both genotypes of c-fos knock-out mice showed more DNA fragmentation, measured by the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeled nondopaminergic cells in their cortices and striata. In contrast, wild-type mice treated with methamphetamine demonstrated a greater number of glial fibrillary acidic protein-positive cells than did c-fos knock-out mice. These data suggest that c-fos induction in response to toxic doses of methamphetamine might be involved in protective mechanisms against this drug-induced neurotoxicity.

Recovery of presynaptic dopaminergic functioning in rats treated with neurotoxic doses of methamphetamine

Repeated administration of methamphetamine (METH) to animals can result in long-lasting decreases in striatal dopamine (DA) content. In addition, the evoked overflow of striatal DA is reduced in rats 1 week after neurotoxic doses of METH. However, whether these functional changes in DA release are permanent or tend to recover over time has not been established. In the present study we used in vivo electrochemistry and microdialysis to examine evoked overflow of DA in the striatum of METH-treated rats at several time points after treatment to determine if DA overflow would spontaneously recover. Male Fischer-344 rats were administered METH (5 mg/kg, s.c. ) or saline four times in one day at 2 hr intervals. In vivo electrochemistry experiments in anesthetized rats, and in vivo microdialysis studies in awake rats, were carried out 1 week, 1 month, 6 months, and 12 months after treatment. At 1 week after treatment there were significant decreases in potassium- and amphetamine-evoked overflow of DA, and in clearance of DA, in the striatum of the METH-treated animals. Basal extracellular levels of DA and its metabolites were also decreased. Evoked overflow had partially recovered by 1 month. By 6 months evoked overflow of DA appeared to be normal in the METH-treated rats. However, whole tissue levels of striatal DA were still significantly decreased. All parameters were back to control values by 12 months. These results suggest that presynaptic dopaminergic functioning can recover to normal levels in the striatum of METH-treated rats by 12 months after treatment.

Methamphetamine neurotoxicity: dissociation of striatal dopamine terminal damage from parietal cortical cell body injury

Methamphetamine (m-AMPH) administration injures both striatal dopaminergic terminals and certain nonmonoaminergic cortical neurons. Fluoro-Jade histochemistry was used to label cortical cells injured by m-AMPH in order to identify factors that contribute to the cortical cell body damage. Rats given four injections of m-AMPH (4 mg/kg) at 2-h intervals showed hyperthermia (mean = 40.0 +/- 0.10 degrees C) and increased behavioral activation relative to animals given saline (SAL). Three days later, m-AMPH-treated animals showed indices of injury to striatal DA terminals (depletion of tyrosine hydroxylase immunoreactivity) and parietal cortical cell bodies (appearance of Fluoro-Jade stained cells). Pretreatment with a dopamine (DA) D1, D2, or N-methyl-D-aspartate (NMDA) receptor antagonist, or administration of m-AMPH in a 4 degrees C environment, prevented or attenuated m-AMPH-induced hyperthermia, behavioral activation, and injury to striatal DA terminals and parietal cortical cell bodies. Animals pretreated with a DA transport inhibitor prior to m-AMPH showed hyperthermia, behavioral activation, and parietal cortical cell body injury, but they did not show striatal DA terminal injury. Pretreatment with a 5HT transport inhibitor failed to prevent m-AMPH-induced damage to striatal DA terminals or parietal cortical cell bodies. Animals given four injections of SAL in a 37 degrees C environment became hyperthermic, but showed no injury to striatal DA terminals or cortical cell bodies. The ability of the DA transport inhibitor to block m-AMPH-induced striatal DA damage, but not cortical injury, and the inability of hyperthermia alone to cause the cortical cell body injury suggests that m-AMPH-induced behavioral activation and hyperthermia may both be necessary for the subsequent parietal cortical cell body damage.

Enhancement of cocaine-induced hyperthermia fails to elicit neurotoxicity

The neurotoxic potential of cocaine when administered under conditions conducive to the initiation of hyperthermia was investigated. Rats were administered cocaine at ambient temperatures of 22 degrees C or 30 degrees C. To determine the thermal response, body temperatures were measured every 30 min and the total thermal response (TTR), representing the area under the temperature vs. time curve, was calculated. Saline administered at 22 degrees C or 30 degrees C resulted in a normal thermal response (TTR = 9.8+/-0.9 and 11.2+/-0.9, respectively). Cocaine administration resulted in ambient temperature-dependent hyperthermia. Cocaine (4 x 25 mg/kg) administered at 22 degrees C resulted in a TTR of 15.1+/-0.9 whereas cocaine (4 x 15 or 25 mg/kg) administered at 30 degrees C resulted in TTRs of 22.2+/-0.9 and 21.9+/-0.8, respectively. Regardless of the dose or thermal response, cocaine administration did not result in depletion of dopamine (DA) or serotonin (5-HT) in the caudate-putamen. Cocaine administration also failed to induce an increase in the concentration of glial fibrillary acidic protein (GFAP), a marker for neurotoxicity. These results demonstrate that hyperthermia does not promote cocaine-induced neurotoxicity in the rat caudate-putamen.

Glutamatergic involvement in psychomotor stimulant action

The sympathomimetic psychomotor stimulants, including cocaine, amphetamines, and the phenylethylamine amphetamine-like derivatives, exert actions in mammalian systems that implicate involvement of the excitatory neurotransmitter, glutamate and its receptors. Despite evidence that psychomotor stimulants do not directly stimulate glutamate receptors, blockade of acute lethal, convulsive, circulatory, thermoregulatory, locomotor and stereotypical responses, as well as interference with slowly developing behavioral sensitization and brain monoaminergic neurotoxicities, can be achieved by receptor antagonists at both N-methyl-D-aspartate and AMPA/kainate glutamate receptor subtypes. Alterations in glutamatergic neurobiology, including elevations in extracellular glutamate levels, changes in glutamate receptor properties and glutamatergic neuronal degeneration, have also been attributed to psychomotor stimulant administration. Blockade of glutamate receptors offers therapeutic options in management of psychomotor stimulant toxicity.

Ontogeny of methamphetamine-induced neurotoxicity and associated hyperthermic response

Methamphetamine (MA) administration to adult rats results in neurotoxicity characterized by depletion of caudate-putamen (CP) dopamine (DA) and serotonin (5-HT) and an accompanying increase in glial fibrillary acidic protein (GFAP) content. The severity of MA-induced neurotoxicity correlates with the accompanying thermoregulatory response, i.e., a hyperthermic response facilitates neurotoxicity while a hypothermic response is neuroprotective. In the following study, the thermoregulatory and neurotoxic effects of MA administration (4 x 10 mg/kg) were investigated in developing rats at postnatal days (PND) 20, 40 and 60. Rats at PND 20 and PND 40 were administered MA at ambient temperatures of 22 degrees C and 30 degrees C; and PND 60 rats were administered MA at 22 degrees C only. Temperatures were measured and thermal responses were compared by calculating the total thermal response (TTR) induced by MA treatment. MA administration to PND 60 rats at 22 degrees C induced a hyperthermic response, resulted in a 47% reduction of neostriatal DA and a 49% increase of GFAP content. Administration of MA to PND 40 rats at 22 degrees C failed to induce a hyperthermic response and did not result in reduced DA or increased GFAP. However, administration of MA to PND 40 rats at 30 degrees C induced hyperthermia, reduced neostriatal DA by 54% and increased GFAP by 70%. MA administration to PND 20 rats at either 22 degrees C or 30 degrees C did not result in DA depletion or increased GFAP, even though MA administration to PND 20 rats at 30 degrees C induced hyperthermia. These results demonstrate that the induction of hyperthermia is necessary to exhibit MA-induced neurotoxicity at PND 40; however, PND 20 rats are resistant to the DA depleting effects of MA despite the induction of hyperthermia.

GDNF selectively protects dopamine neurons over serotonin neurons against the neurotoxic effects of methamphetamine

Repeated methamphetamine (METH) administration to animals can result in long-lasting decreases in striatal dopamine (DA) and serotonin (5-HT) levels. Glial cell line-derived neurotrophic factor (GDNF) has pronounced effects on dopaminergic systems in vivo, including partial neuroprotective effects against 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine -induced lesions. The present study examined the ability of GDNF to prevent METH-induced reductions in potassium-evoked overflow of DA, and DA and 5-HT content, in striatum. GDNF (10 microg) or vehicle was injected into the right striatum of anesthetized rats. Twenty-four hours later, the rats were injected four times at 2 hr intervals with METH (5 mg/kg, s.c.) or saline. One week later, in vivo electrochemistry was used to monitor the overflow of DA evoked by local potassium application. Evoked overflow of DA was dramatically decreased in the striatum of METH-treated animals. GDNF prevented the reduction in evoked overflow of DA in the right striatum of the METH-treated animals. After each experiment, the animals were killed, and striatal DA and 5-HT levels determined by HPLC. The METH treatment produced significant decreases in both neurotransmitters. GDNF administration prevented the reduction in striatal DA levels on the treated side of the brain, whereas levels on the contralateral side were still decreased. In dose-response studies, 1 microg of GDNF was as protective as 10 microg, whereas 0.1 microg was only partially protective. In contrast, 5-HT levels were only minimally protected by previous administration of GDNF. These results suggest that GDNF can selectively protect DA neurons, compared with 5-HT neurons, against the neurotoxic effects of METH.

Ultrastructural immunocytochemical localization of the N-methyl-D-aspartate receptor and tyrosine hydroxylase in the shell of the rat nucleus accumbens

The N-methyl-D-aspartate (NMDA)-type glutamate receptors in the shell region of the nucleus accumbens (ACB) have been implicated in the modulation of dopamine release and in amphetamine-induced neurotoxicity. We used electron microscopic immunocyto-chemistry to determine the anatomical sites for NMDA-mediated effects of glutamate and for their potential interactions with dopaminergic afferents identified by the presence of tyrosine hydroxylase (TH) in this region of the rat brain. Immunogold and immunoperoxidase methods were used to localize antisera against the R1 subunit of the NMDA receptor (NMDAR1) alone or combined with TH. In single labeling experiments, approximately half of the NMDAR1-like immunoreactivity (NMDAR1-LI) was localized to extrasynaptic plasma membranes of neuronal processes, many (92 out of 215) of which were dendrites, and only 33 out of 215 were unmyelinated axons or terminals. Surprisingly, the neuronal labeling of NMDAR1 was almost equaled by that seen in astrocytic processes (88 out of 215). Dual labeling for TH and NMDAR1 was rarely observed and was only seen in axons. However, in favorable planes of section, NMDAR1 was noted along intervaricose segments of axons in which TH was more readily seen in the varicosity. This differential intra-axonal distribution suggests an underestimation of dual labeling in single coronal sections through unmyelinated axons and terminals. The TH-immunoreactive terminals were more often seen apposed to NMDA-immunoreactive astrocytic processes and dendrites. These results provide the first ultrastructural evidence for presynaptic modulation of dopamine release by NMDA receptors in the shell of the nucleus accumbens. They also indicate that NMDA receptors modulate postsynaptic neurons receiving input from the dopaminergic afferents and suggest a previously unsuspected functional association involving glial NMDA receptors and dopaminergic afferents in this brain region.

Striatal and cortical NMDA receptors are altered by a neurotoxic regimen of methamphetamine

Methamphetamine (m-AMPH) treatment produces long-lasting damage to striatal and cortical monoaminergic terminals and may also injure nonmonoaminergic cortical neurons. Evidence suggests that both dopamine (DA) and glutamate (GLU) play crucial roles in producing this damage. We used quantitative autoradiography to examine [3H]mazindol ([3H]MAZ) binding to striatal DA transporters and [3H]GLU binding to N-methyl-D-aspartate (NMDA) receptors in the striatum and cortex 1 week and 1 month after a neurotoxic regimen of m-AMPH. Rats received m-AMPH (4 mg/kg) or saline (SAL) (1 ml/kg) in four s.c. injections separated by 2 h intervals. One week after m-AMPH, the ventral and lateral sectors of the striatum showed the greatest decreases in both [3H]MAZ and [3H]GLU binding, while the nucleus accumbens (NA) showed no significant decreases. One month after m-AMPH, striatal [3H]MAZ binding was still significantly decreased, while NMDA receptor binding had recovered. Surprisingly, the parietal cortex showed a m-AMPH-induced increase in NMDA receptor binding in layers II/III and IV 1 week after m-AMPH and only in layers II/III 1 month after m-AMPH. The prefrontal cortex showed no m-AMPH-induced changes in NMDA receptor binding at either time point. This is the first demonstration that a regimen of m-AMPH that results in long-lasting damage to DA terminals can alter forebrain NMDA receptor binding. Thus, repeated m-AMPH treatments may produce changes in glutamatergic transmission in selected striatal and cortical regions.