Single Injection Of Methamphetamine Research Articles

Clavulanic acid inhibits methamphetamine locomotor sensitization in mice and normalizes methamphetamine-induced changes in glutaminase mRNA levels in the nucleus accumbens

Clavulanic acid (CLAV) is a component of Augmentin® that preserves antibiotic efficacy by inhibiting β-lactamase activity. It also enhances cellular glutamate uptake and is a potential CNS therapeutic. Because increased glutamate transmission in brain reward circuits facilitates methamphetamine (METH) locomotor activation and sensitization, we tested the hypothesis that CLAV inhibits acute and sensitized locomotor responses to METH in mice and investigated effects of CLAV on METH-induced changes in glutaminase, the major glutamate-producing enzyme in the brain. Acute METH (3 mg/kg) produced hyperlocomotion that was reduced by CLAV (20 mg/kg but not 10 mg/kg). Mice injected with METH (3 mg/kg) every other day for 9 d and then challenged with METH 27 d later displayed locomotor sensitization. CLAV (10 mg/kg), when injected 15 min before each METH injection during the 9-d exposure interval, blocked locomotor sensitization induced by METH challenge. In METH-sensitized mice, mRNA levels of both isoforms of glutaminase (GLS and GLS2) were altered in the nucleus accumbens compared to mice exposed to a single injection of METH (i.e., GLS decreased and GLS2 increased). CLAV normalized the METH-induced GLS deficit but not the increase in GLS2. In summary, CLAV reduced acute and sensitized locomotor responses to METH and normalized the METH-induced reduction of GLS gene expression in the NAC. Given that glutaminases belong to the β-lactamase superfamily and CLAV is a β-lactamase inhibitor, our data point toward studying glutaminase as a therapeutic target of CLAV.

A Single Prior Injection of Methamphetamine Enhances Methamphetamine Self-Administration (SA) and Blocks SA-Induced Changes in DNA Methylation and mRNA Expression of Potassium Channels in the Rat Nucleus Accumbens

The transition from occasional to escalated psychostimulant use is accelerated by prior drug exposure. These behavioral observations may be related to long-lasting transcriptional and/or epigenetic changes induced by the drug pre-exposure. Herein, we investigated if a single methamphetamine (METH) injection would enhance METH self-administration (SA) and impact any METH SA-induced epigenetic or transcriptional alterations. We thus injected a single METH dose (10 mg/kg) or saline to rats before training them to self-administer METH or saline. There were three experimental groups in SA experiments: (1) a single saline injection followed by saline SA (SS); (2) a single saline injection followed by METH SA (SM); and (3) a single METH injection followed by METH SA (MM). METH-pretreated rats escalated METH SA earlier and took more METH than saline-pretreated animals. Both groups showed similar incubation of cue-induced METH craving. Because compulsive METH takers and METH-abstinent rats show differences in potassium (K+) channel mRNA levels in their nucleus accumbens (NAc), we wondered if K+ channel expression might also help to distinguish between SM and MM groups. We found increases in mRNA and protein expression of shaker-related voltage-gated K+ channels (Kv1: Kcna1, Kcna3, and Kcna6) and calcium-activated K+ channels (Kcnn1) in the SM compared to MM rats. SM rats also showed decreased DNA methylation at the CpG-rich sites near the promoter region of Kcna1, Kcna3 and Kcnn1 genes in comparison to MM rats. Together, these results provide additional evidence for potentially using K+ channels as therapeutic targets against METH use disorder.

Effects of methamphetamine in the hippocampus of cynomolgus monkeys according to age

The aim of this study was to investigate differentially expressed genes (DEGs) and their functions in the hippocampi after methamphetamine (MA) administration in cynomolgus macaques according to age. Cynomolgus monkeys were divided by age as follows: control, 6–12 months (age 1, A1), 3–4 (A2) years, 7–9 (A3) years, and more than 11 years (A4). After MA was injected into the monkeys (2 mg/kg, intramuscular injection in each of A1, A2, A3 and A4), we performed large-scale transcriptome profiling in the hippocampus. Some genes associated with neuron differentiation, development, and transmission were validated with real-time RT-PCR. The expression patterns of validated genes were also investigated in the hippocampi of monkeys one year after a single injection of MA. The correlation of DEGs between A2 and A3 animals, who are similar to humans in early teens to early twenties, was higher than that of other groups, showing the possibility that biological mechanisms in the hippocampus of A2 and A3 are similarly affected by MA. Genes associated with neuron differentiation (FEZF1, GPR1N1, DLX1, and KCNIP2), neuron (projection) development (NGFR, CDKN1C, and VAX2), and synaptic transmission (SYT4, SYT1, GAD2, CORT, and NPTX2) were differentially expressed among control and MA-treated animals. In particular, the expression patterns of GPR1N1 among control and MA-treated animals following a single injection of MA were not altered even one year after single MA administration. Our results suggest that genes associated with neuron differentiation and synaptic transmission in the hippocampus of different maturation stages are differentially regulated by MA.

Pharmacological activation of the neurotensin receptor 1 abrogates the methamphetamine-induced striatal apoptosis in the mouse brain

Methamphetamine (METH) is a widely abused psychostimulant displaying potent addictive and neurotoxic properties. METH induces neurotoxicity of dopaminergic terminals and striatal neurons in the striatum. Despite much information on neurotransmitters, the role of neuropeptides is poorly understood. In this study, we investigated the role of the neuropeptide neurotensin on the METH-induced apoptosis of some striatal neurons in mice. We observed that a single injection of METH (30mg/kg, ip) induced the loss of approximately 15% of striatal neurons. An agonist of the neurotensin receptor 1 (PD149163, ip at various doses) attenuated the METH-induced striatal neuron apoptosis. Utilizing quantitative real time PCR, we showed that METH also up-regulated neurotensin gene expression with 96% increase in preproneurotensin mRNA levels in the striatum as compared to the control. Additionally, NTR1 agonist (ip injection) attenuated hyperthermia at 2h post-METH injection; hyperthermia is a putative and significant component of METH-induced neurotoxicity. To investigate the role of neurotensin without affecting core body temperature, we performed stereotactic injection of PD149163 into the striatum and observed that this compound maintained attenuated the METH-induced apoptosis in the striatum, while leaving core body temperature unaffected. There was no effect of NTR1 agonist on METH-induced dopamine terminal degeneration, as evidenced by tyrosine hydroxylase levels determined by Western blot. These data indicate that the neuropeptide neurotensin modulates the striatal neuronal apoptosis induced by METH through diverse mechanisms that need to be investigated. Furthermore, due to its neuroprotective properties, neurotensin receptor agonists show potential as drug candidates for the treatment of METH abuse and some neurological disorders.

Additive Effects of Coadministration of A2A Receptor Agonist CGS-21680and mGluR5 Antagonist MPEP on the Development and Expression of Methamphetamine-Induced Locomotor Sensitization in Rats

Background. Accumulating evidence suggests that A2A adenosine receptors and metabotropic glutamate receptors 5 (mGluR5) may modulate the nucleus accumbens (nAcc) dopamine neurotransmission. This study examined the effects of coadministration of the A2A receptor agonist CGS-21680 and the mGluR5 antagonist MPEP on the development and expression of methamphetamine (METH)-induced locomotor sensitization. Methods. Rats were treated with different doses of CGS (0.1 mg/kg, 0.2 mg/kg or 0.4 mg/kg) or MPEP (1.0 mg/kg, 3.0 mg/kg or 10.0 mg/kg) or coadministration of CGS (0.1 mg/kg, 0.2 mg/kg or 0.4 mg/kg) with MPEP (3.0 mg/kg) plus METH (1.0 mg/kg). For the challenge test, rats received a single injection of METH (1.0mg/kg). In experiments to assess the expression of METH-induced locomotor sensitization, rats were treated with a daily dose of METH (1.0mg/kg), and the challenge test was preceded by injection of CGS (0.1 mg/kg, 0.2 mg/kg or 0.4 mg/kg), MPEP (1.0 mg/kg, 3.0 mg/kg or 10.0 mg/kg) or coadministration of CGS (0.1 mg/kg, 0.2 mg/kg or 0.4 mg/kg) with MPEP (3.0 mg/kg) plus METH (1.0 mg/kg). Results. The data showed that CGS and MPEP treatment prevented both the development and expression of METH-induced locomotor sensitization. Furthermore, CGS increased the effects of a low MPEP dose on METH-induced locomotor sensitization under both conditions. Conclusion. These findings suggest the potential utility of adenosine A2A receptors and mGluR5 ligands to treat psychostimulant addiction.

Methamphetamine Induces Anhedonic-Like Behavior and Impairs Frontal Cortical Energetics in Mice.

We recently showed that a single high dose of methamphetamine (METH) induces a persistent frontal cortical monoamine depletion that is accompanied by helpless-like behavior in mice. However, brain metabolic alterations underlying both neurochemical and mood alterations remain unknown. Herein, we aimed at characterizing frontal cortical metabolic alterations associated with early negative mood behavior triggered by METH. Adult C57BL/6 mice were injected with METH (30 mg/kg, i.p.), and their frontal cortical metabolic status was characterized after probing their mood and anxiety-related phenotypes 3 days postinjection. Methamphetamine induced depressive-like behavior, as indicated by the decreased grooming time in the splash test and by a transient decrease in sucrose preference. At this time, METH did not alter anxiety-like behavior or motor functions. Depolarization-induced glucose uptake was reduced in frontocortical slices from METH-treated mice compared to controls. Consistently, astrocytic glucose transporter (GluT1) density was lower in the METH group. A proton high rotation magic angle spinning (HRMAS) spectroscopic approach revealed that METH induced a significant decrease in N-acetyl aspartate (NAA) and glutamate levels, suggesting that METH decreased neuronal glutamatergic function in frontal cortex. We report, for the first time, that a single METH injection triggers early self-care and hedonic deficits and impairs frontal cortical energetics in mice.

Reward related neurotransmitter changes in a model of depression: An in vivo microdialysis study

Objectives: The self-medication hypothesis assumes that symptoms related to potential monoaminergic deficits in depression may be relieved by drug abuse. The aim of this study was to elucidate the neurotransmitter changes in a rat model of depression by measuring their levels in the nucleus accumbens shell, which is typically involved in the drug of abuse acquisition mechanism. Methods: Depression was modelled by the olfactory bulbectomy (OBX) in Wistar male rats. In vivo microdialysis was performed, starting from the baseline and following after a single methamphetamine injection and behaviour was monitored. The determination of neurotransmitters and their metabolites was performed by high-performance liquid chromatography combined with mass spectrometry. Results: OBX animals had lower basal levels of dopamine and serotonin and their metabolites. However, γ-aminobutyric acid (GABA) and glutamate levels were increased. The methamphetamine injection induced stronger dopamine and serotonin release in the OBX rats and lower release of glutamate in comparison with sham-operated rats; GABA levels did not differ significantly. Conclusions: This study provides an evidence of mesolimbic neurotransmitter changes in the rat model of depression which may elucidate mechanisms underlying intravenous self-administration studies in which OBX rats were demonstrated to have higher drug intake in comparison to intact controls.

Enhanced Upregulation of CRH mRNA Expression in the Nucleus Accumbens of Male Rats after a Second Injection of Methamphetamine Given Thirty Days Later

Methamphetamine (METH) is a widely abused amphetamine analog. Few studies have investigated the molecular effects of METH exposure in adult animals. Herein, we determined the consequences of an injection of METH (10 mg/kg) on transcriptional effects of a second METH (2.5 mg/kg) injection given one month later. We thus measured gene expression by microarray analyses in the nucleus accumbens (NAc) of 4 groups of rats euthanized 2 hours after the second injection: saline-pretreated followed by saline-challenged (SS) or METH-challenged (SM); and METH-pretreated followed by saline-challenged (MS) or METH-challenged (MM). Microarray analyses revealed that METH (2.5 mg/kg) produced acute changes (1.8-fold; P<0.01) in the expression of 412 (352 upregulated, 60 down-regulated) transcripts including cocaine and amphetamine regulated transcript, corticotropin-releasing hormone (Crh), oxytocin (Oxt), and vasopressin (Avp) that were upregulated. Injection of METH (10 mg/kg) altered the expression of 503 (338 upregulated, 165 down-regulated) transcripts measured one month later (MS group). These genes also included Cart and Crh. The MM group showed altered expression of 766 (565 upregulated, 201 down-regulated) transcripts including Avp, Cart, and Crh. The METH-induced increased Crh expression was enhanced in the MM group in comparison to SM and MS groups. Quantitative PCR confirmed the METH-induced changes in mRNA levels. Therefore, a single injection of METH produced long-lasting changes in gene expression in the rodent NAc. The long-term increases in Crh, Cart, and Avp mRNA expression suggest that METH exposure produced prolonged activation of the endogenous stress system. The METH-induced changes in oxytocin expression also suggest the possibility that this neuropeptide might play a significant role in the neuroplastic and affiliative effects of this drug.

In vivo evidence of methamphetamine induced attenuation of brain tissue oxygenation as measured by EPR oximetry

Abuse of methamphetamine (METH) is a major and significant societal problem in the US, as a number of studies have suggested that METH is associated with increased cerebrovascular events, hemorrhage or vasospasm. Although cellular and molecular mechanisms involved in METH-induced toxicity are not completely understood, changes in brain O2 may play an important role and contribute to METH-induced neurotoxicity including dopaminergic receptor degradation. Given that O2 is the terminal electron acceptor for many enzymes that are important in brain function, the impact of METH on brain tissue pO2in vivo remains largely uncharacterized. This study investigated striatal tissue pO2 changes in male C57BL/6 mice (16–20g) following METH administration using EPR oximetry, a highly sensitive modality to measure pO2in vivo, in situ and in real time. We demonstrate that 20min after a single injection of METH (8mg/kg i.v.), the striatal pO2 was reduced to 81% of the pretreatment level and exposure to METH for 3 consecutive days further attenuated striatal pO2 to 64%. More importantly, pO2 did not recover fully to control levels even 24h after administration of a single dose of METH and continual exposure to METH exacerbates the condition. We also show a reduction in cerebral blood flow associated with a decreased brain pO2 indicating an ischemic condition. Our findings suggests that administration of METH can attenuate brain tissue pO2, which may lead to hypoxic insult, thus a risk factor for METH-induced brain injury and the development of stroke in young adults.

Comparison of single versus repeated methamphetamine injection induced behavioral sensitization in mice

Repeated exposure to drugs of abuse produces a persistent behavioral sensitization to stimulants, which is often used to study drug-associated behavioral plasticity. Interestingly, even a single exposure to some drugs of abuse is sufficient to elicit long-lasting behavioral sensitization. However, few studies have directly compared the magnitude of sensitization between single versus repeated drug treatments. This study examined the magnitude and duration of single methamphetamine (METH) injection-induced behavioral sensitization and compared it to the more typical repeated drug injection-induced sensitization in mice. Different groups of mice were injected with METH (0.5, 1.0, 2.0mg/kg, i.p.) only once or daily for 7 consecutive days. A challenge dose of METH (1.0mg/kg, i.p.) was tested 7 days later. The time-course of a single METH injection-induced behavioral sensitization was assessed where METH (2.0mg/kg, i.p.) was injected and a challenge dose of METH (1.0mg/kg, i.p.) was tested after different drug-free periods. Single METH injection produced similar magnitude of behavioral sensitization as compared to repeated injection. Such a sensitized locomotor response peaked 8 days after METH injection and lasted for at least 21 days. This long lasting behavioral alteration induced by single METH injection suggests the value of future studies to explore the underlying neural mechanisms, particularly in comparison to those underlying repeated METH-induced sensitization.

Extended‐access, but not limited‐access, methamphetamine self‐administration induces behavioral and nucleus accumbens dopamine response changes in rats

To better understand the neurobiology of methamphetamine (METH) dependence and the cognitive impairments induced by METH use, we compared the effects of extended (12h) and limited (1h) access to METH self-administration on locomotor activity and object place recognition, and on extracellular dopamine levels in the nucleus accumbens and caudate-putamen. Rats were trained to self-administer intravenous METH (0.05mg/kg). One group had progressively extended access up to 12-h sessions. The other group had limited-access 1-h sessions. Microdialysis experiments were conducted during a 12-h and 1-h session, in which the effects of a single METH injection (self-administered, 0.05mg/kg, i.v.) on extracellular dopamine levels were assessed in the nucleus accumbens and caudate-putamen compared with a drug-naive group. The day after the last 12-h session and the following day experimental groups were assessed for their locomotor activities and in a place recognition procedure, respectively. The microdialysis results revealed tolerance to the METH-induced increases in extracellular dopamine only in the nucleus accumbens, but not in the caudate-putamen in the extended-access group compared with the control and limited-access groups. These effects may be associated with the increased lever-pressing and drug-seeking observed during the first hour of drug exposure in the extended-access group. This increase in drug-seeking leads to higher METH intake and may result in more severe consequences in other structures responsible for the behavioral deficits (memory and locomotor activity) observed in the extended-access group, but not in the limited-access group.

Chicago sky blue 6B, a vesicular glutamate transporters inhibitor, attenuates methamphetamine-induced hyperactivity and behavioral sensitization in mice

Several lines of evidence demonstrate that glutamatergic system plays an important role in drug addiction. The present study was designed to investigate the effects of Chicago sky blue 6B (CSB6B), a vesicular glutamate transporters (VGLUTs) inhibitor, on methamphetamine (METH)-induced behaviors in mice. Mice were induced behavioral sensitization to METH by subcutaneous injection of 1mg/kg METH once daily for 7 days and then challenged with 1mg/kg METH in 14th day. Intracerebroventricular administration of CSB6B (7.5μg) 2.5h prior to METH was to observe its effects on METH -induced behavioral sensitization. Our results showed that the expressions of behavioral sensitization were significantly attenuated by intracerebroventricular administration of CSB6B 2.5h prior to METH either during the development period or before methamphetamine challenge in mice, while CSB6B itself had no effect on locomotor activity. Meanwhile, pretreatment of CSB6B also attenuated hyperactivity caused by a single injection of METH in mice. These results demonstrated that CSB6B, a VGLUTs inhibitor, attenuated acute METH-induced hyperactivity and chronic METH-induced behavioral sensitization, which indicated that VGLUTs were involved in the effect of chronic METH-induced behavioral sensitization and may be a new target against the addiction of METH.

Methamphetamine-Evoked Depression of GABAB Receptor Signaling in GABA Neurons of the VTA

Psychostimulants induce neuroadaptations in excitatory and fast inhibitory transmission in the ventral tegmental area (VTA). Mechanisms underlying drug-evoked synaptic plasticity of slow inhibitory transmission mediated by GABA(B) receptors and G protein-gated inwardly rectifying potassium (GIRK/Kir(3)) channels, however, are poorly understood. Here, we show that 1 day after methamphetamine (METH) or cocaine exposure both synaptically evoked and baclofen-activated GABA(B)R-GIRK currents were significantly depressed in VTA GABA neurons and remained depressed for 7 days. Presynaptic inhibition mediated by GABA(B)Rs on GABA terminals was also weakened. Quantitative immunoelectron microscopy revealed internalization of GABA(B1) and GIRK2, which occurred coincident with dephosphorylation of serine 783 (S783) in GABA(B2), a site implicated in regulating GABA(B)R surface expression. Inhibition of protein phosphatases recovered GABA(B)R-GIRK currents in VTA GABA neurons of METH-injected mice. This psychostimulant-evoked impairment in GABA(B)R signaling removes an intrinsic brake on GABA neuron spiking, which may augment GABA transmission in the mesocorticolimbic system.

Ephedrine decreases vesicular monoamine transporter‐2 function

Ephedrine decreases vesicular monoamine transporter‐2 function

Methamphetamine-Induced Dopamine-Independent Alterations in Striatal Gene Expression in the 6-Hydroxydopamine Hemiparkinsonian Rats

Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle are used extensively as a model of Parkinson's disease. The present experiments sought to identify genes that were affected in the dopamine (DA)–denervated striatum after 6-hydroxydopamine-induced destruction of the nigrostriatal dopaminergic pathway in the rat. We also examined whether a single injection of methamphetamine (METH) (2.5 mg/kg) known to cause changes in gene expression in the normally DA-innervated striatum could still influence striatal gene expression in the absence of DA. Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle resulted in METH-induced rotational behaviors ipsilateral to the lesioned side and total striatal DA depletion on the lesioned side. This injection also caused decrease in striatal serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels. DA depletion was associated with increases in 5-HIAA/5-HT ratios that were potentiated by the METH injection. Microarray analyses revealed changes (± 1.7-fold, p<0.025) in the expression of 67 genes on the lesioned side in comparison to the intact side of the saline-treated hemiparkinsonian animals. These include follistatin, neuromedin U, and tachykinin 2 which were up-regulated. METH administration caused increases in the expression of c-fos, Egr1, and Nor-1 on the intact side. On the DA-depleted side, METH administration also increased the expression of 61 genes including Pdgf-d and Cox-2. There were METH-induced changes in 16 genes that were common in the DA-innervated and DA-depleted sides. These include c-fos and Nor-1 which show greater changes on the normal DA side. Thus, the present study documents, for the first time, that METH mediated DA-independent changes in the levels of transcripts of several genes in the DA-denervated striatum. Our results also implicate 5-HT as a potential player in these METH-induced alterations in gene expression because the METH injection also caused significant increases in 5-HIAA/5-HT ratios on the DA-depleted side.

Challenge dose of methamphetamine affects kainic acid-induced seizures differently depending on prenatal methamphetamine exposure, sex, and estrous cycle

Even though it is obvious that glutamate plays an important role in the effect of psychostimulants on seizures, the role of non-NMDA receptors remains uncertain. The aim of the present study was to determine whether acute methamphetamine (MA) administration changes sensitivity to seizures induced with kainic acid in prenatally MA-exposed adult rats. Adult male and female rats (prenatally MA exposed, prenatally saline exposed, and controls) were divided into groups that received a challenge dose (1 mg/kg) of MA and groups that did not receive the MA challenge (saline injected). Systemic administration of 15 mg/kg kainic acid was used as a seizure model. Our results demonstrated that a single injection of MA (1 mg/kg) affects kainic acid-induced seizures differently depending on prenatal exposure, sex, and female estrous cycle. Even though daily injections of MA (5 mg/kg) in maternal rats did not have a long-term effect on susceptibility to seizures induced with kainic acid in adult progeny, sensitivity to the challenge dose of MA differed between the prenatal exposure groups.

Repeated administration of methamphetamine blocked cholecystokinin-octapeptide injection-induced c-fos mRNA expression without change in capsaicin-induced junD mRNA expression in rat cerebellum

In the cerebellum, there are numerous cholecystokinin (CCK-8)-containing fibers. Since systemic CCK-8 injection-induced anxiety (psychological stress) activates the locus coeruleus cells that send mossy fiber inputs to the cerebellum, we examined whether systemic CCK-8 injections activate the rat and mouse cerebellum. First, injections of CCK-8 were found to induce c-fos mRNA expression in a vague patchy pattern that is different from single methamphetamine-induced Zebrin band-like c-fos mRNA expression, suggesting that the CCK-8 activating mossy fibers induce gene expression differently from the dopamine-containing mossy fibers in the ventral tegmental area. Second, since CCK-8 facilitates neural activity of dopamine in the midbrain, we examined whether repeated methamphetamine administration that induced behavioral sensitization had similar effects on the cerebellar CCK system. Repeated administration of methamphetamine suppressed the CCK-8-induced c-fos mRNA expression in the rat cerebellum. Third, capsaicin injections (physical stress) into a hind limb of the rat increased junD mRNA expression with no effect on c-fos mRNA expression, and repeated methamphetamine injections had no effect on the capsaicin-induced expression of junD mRNA. Fourth, either single injection of methamphetamine or CCK-8 to mice increased c-fos mRNA expression in the locus coeruleus, and so noradrenalin, but not dopamine, might interact with CCK-8-activating system. However, we considered the possibility unlikely. Thus, we conclude that repeated methamphetamine administration though dopamine selectively inhibits the c-fos mRNA expression after CCK-8 injection in the cerebellum.

Methamphetamine alters vesicular monoamine transporter‐2 function and potassium‐stimulated dopamine release

This report demonstrates that a repeated 'challenge' high-dose methamphetamine (METH) injection regimen rapidly decreases striatal K(+)-stimulated dopamine (DA) release concurrent with decreases in both synaptosomal membrane-associated (referred to herein as membrane-associated) and previously reported decreases in non-synaptosomal membrane-associated (presumably cytoplasmic) vesicular DA uptake and content. Resembling previously reported effects involving cytoplasmic vesicles wherein uptake was decreased 48 h after treatment, the decrease in membrane-associated uptake persisted 72 h. Cytoplasmic and membrane-associated vesicular DA uptakes were decreased 7 days after the challenge regimen. A single METH injection also rapidly decreased K(+)-stimulated DA release, membrane-associated DA content, and membrane-associated DA uptake; however, unlike after the challenge regimen, the decrease in uptake recovered by 24 h. Pre-treatment with the D(2) receptor antagonist, eticlopride, did not attenuate the decrease in membrane-associated uptake as assessed 1 h after either a single or challenge treatment. However, eticlopride attenuated the decrease in membrane-associated uptake caused by the challenge regimen as assessed 24 h later. These data reveal complex effects of METH on vesicular function that vary according to the vesicle population under study, dosing regimen, and time after treatment. These may contribute to both the decrease in K(+)-stimulated DA release and the persistent dopaminergic deficits caused by METH.

The neurokinin‐1 receptor modulates the methamphetamine‐induced striatal apoptosis and nitric oxide formation in mice

In a previous study we showed that pharmacological blockade of the neurokinin-1 receptors attenuated the methamphetamine (METH)-induced toxicity of the striatal dopamine terminals. In the present study we examined the role of the neurokinin-1 receptors on the METH-induced apoptosis of some striatal neurons. To that end, we administered a single injection of METH (30 mg/kg, i.p.) to male mice. METH induced the apoptosis (terminal deoxyncleotidyl transferase-mediated dUTP nick end labeling) of approximately 20% of striatal neurons. This percentage of METH-induced apoptosis was significantly attenuated by either a single injection of the neurokinin-1 receptor antagonist, 17-beta-hydroxy-17-a-ethynyl-5-a-androstano[3,2-beta]pyrimido[1,2-a]benzimidazole (WIN-51,708) (5 mg/kg, i.p.), or the ablation of the striatal interneurons expressing the neurokinin-1 receptors (cholinergic and somatostatin) with the selective neurotoxin [Sar(9),Met(O(2))(11)] substance P-saporin. Next we assessed the levels of striatal 3-nitrotyrosine (3-NT) by HPLC and immunohistochemistry. METH increased the levels of striatal 3-NT and this increase was attenuated by pre-treatment with WIN-51,708. Our data support the hypothesis that METH-induced striatal apoptosis occurs via a mechanism involving the neurokinin-1 receptors and the activation of nitric oxide synthesis. Our findings are relevant for the treatment of METH abuse and may be relevant to certain neurological disorders involving the dopaminergic circuitry of the basal ganglia.

Methamphetamine Induces Dopamine D1 Receptor-Dependent Endoplasmic Reticulum Stress-Related Molecular Events in the Rat Striatum

Methamphetamine (METH) is an illicit toxic psychostimulant which is widely abused. Its toxic effects depend on the release of excessive levels of dopamine (DA) that activates striatal DA receptors. Inhibition of DA-mediated neurotransmission by the DA D1 receptor antagonist, SCH23390, protects against METH-induced neuronal apoptosis. The initial purpose of the present study was to investigate, using microarray analyses, the influence of SCH23390 on transcriptional responses in the rat striatum caused by a single METH injection at 2 and 4 hours after drug administration. We identified 545 out of a total of 22,227 genes as METH-responsive. These include genes which are involved in apoptotic pathways, endoplasmic reticulum (ER) stress, and in transcription regulation, among others. Of these, a total of 172 genes showed SCH23390-induced inhibition of METH-mediated changes. Among these SCH23390-responsive genes were several genes that are regulated during ER stress, namely ATF3, HSP27, Hmox1, HSP40, and CHOP/Gadd153. The secondary goal of the study was to investigate the role of DA D1 receptor stimulation on the expression of genes that participate in ER stress-mediated molecular events. We thus used quantitative PCR to confirm changes in the METH-responsive ER genes identified by the microarray analyses. We also measured the expression of these genes and of ATF4, ATF6, BiP/GRP78, and of GADD34 over a more extended time course. SCH23390 attenuated or blocked METH-induced increases in the expression of the majority of these genes. Western blot analysis revealed METH-induced increases in the expression of the antioxidant protein, Hmox1, which lasted for about 24 hours after the METH injection. Additionally, METH caused DA D1 receptor-dependent transit of the Hmox1 regulator protein, Nrf2, from cytosolic into nuclear fractions where the protein exerts its regulatory functions. When taken together, these findings indicate that SCH23390 can provide protection against neuronal apoptosis by inhibiting METH-mediated DA D1 receptor-mediated ER stress in the rat striatum. Our data also suggest that METH-induced toxicity might be a useful model to dissect molecular mechanisms involved in ER stress-dependent events in the rodent brain.