Persistence of tolerance to methamphetamine-induced monoamine deficits

Tryptophan and Substance Abuse: Mechanisms and Impact

Addiction, the continuous misuse of addictive material, causes long-term dysfunction in the neurological system. It substantially affects the control strength of reward, memory, and motivation. Addictive substances (alcohol, marijuana, caffeine, heroin, methamphetamine (METH), and nicotine) are highly active central nervous stimulants. Addiction leads to severe health issues, including cardiovascular diseases, serious infections, and pulmonary/dental diseases. Drug dependence may result in unfavorable cognitive impairments that can continue during abstinence and negatively influence recovery performance. Although addiction is a critical global health challenge with numerous consequences and complications, currently, there are no efficient options for treating drug addiction, particularly METH. Currently, novel treatment approaches such as psychological contingency management, cognitive behavioral therapy, and motivational enhancement strategies are of great interest. Herein, we evaluate the devastating impacts of different addictive substances/drugs on users' mental health and the role of tryptophan in alleviating unfavorable side effects. The tryptophan metabolites in the mammalian brain and their potential to treat compulsive abuse of addictive substances are investigated by assessing the functional effects of addictive substances on tryptophan. Future perspectives on developing promising modalities to treat addiction and the role of tryptophan and its metabolites to alleviate drug dependency are discussed.

Inflammasome Inhibition Prevents Motor Deficit and Cerebellar Degeneration Induced by Chronic Methamphetamine Administration

Methamphetamine (METH), a psychostimulant, has the potential to cause neurodegeneration by targeting the cerebrum and cerebellum. It has been suggested that the NLRP3 inflammasome may be responsible for the neurotoxicity caused by METH. However, the role of NLRP3 in METH-induced cerebellar Purkinje cell (PC) degeneration and the underlying mechanism remain elusive. This study aims to determine the consequences of NLRP3 modulation and the underlying mechanism of chronic METH-induced cerebellar PC degeneration. In METH mice models, increased NLRP3 expression, PC degeneration, myelin sheath destruction, axon degeneration, glial cell activation, and motor coordination impairment were observed. Using the NLRP3 inhibitor MCC950, we found that inhibiting NLRP3 alleviated the above-mentioned motor deficits and cerebellar pathologies. Furthermore, decreased mature IL-1β expression mediated by Caspase 1 in the cerebellum may be associated with the neuroprotective effects of NLRP3 inflammasome inhibition. Collectively, these findings suggest that mature IL-1β secretion mediated by NLRP3-ASC-Caspase 1 may be a critical step in METH-induced cerebellar degeneration and highlight the neuroprotective properties of inflammasome inhibition in cerebellar degeneration.

Luteolin Ameliorates Methamphetamine-Induced Podocyte Pathology by Inhibiting Tau Phosphorylation in Mice

Methamphetamine (METH) can cause kidney dysfunction. Luteolin is a flavonoid compound that can alleviate kidney dysfunction. We aimed to observe the renal-protective effect of luteolin on METH-induced nephropathies and to clarify the potential mechanism of action. The mice were treated with METH (1.0-20.0 mg/kg/d bodyweight) for 14 consecutive days. Morphological studies, renal function, and podocyte specific proteins were analyzed in the chronic METH model in vivo. Cultured podocytes were used to support the protective effects of luteolin on METH-induced podocyte injury. We observed increased levels of p-Tau and p-GSK3β and elevated glomerular pathology, renal dysfunction, renal fibrosis, foot process effacement, macrophage infiltration, and podocyte specific protein loss. Inhibition of GSK3β activation protected METH-induced kidney injury. Furthermore, luteolin could obliterate glomerular pathologies, inhibit podocyte protein loss, and stop p-Tau level increase. Luteolin could also abolish the METH-induced podocyte injury by inactivating GSK3β-p-Tau in cultured podocytes. These results indicate that luteolin might ameliorate methamphetamine-induced podocyte pathology through GSK3β-p-Tau axis.

A Zebrafish Model of Neurotoxicity by Binge-Like Methamphetamine Exposure

Hyperthermia is a common confounding factor for assessing the neurotoxic effects of methamphetamine (METH) in mammalian models. The development of new models of methamphetamine neurotoxicity using vertebrate poikilothermic animals should allow to overcome this problem. The aim of the present study was to develop a zebrafish model of neurotoxicity by binge-like methamphetamine exposure. After an initial testing at 20 and 40 mg/L for 48 h, the later METH concentration was selected for developing the model and the effects on the brain monoaminergic profile, locomotor, anxiety-like and social behaviors as well as on the expression of key genes of the catecholaminergic system were determined. A concentration- and time-dependent decrease in the brain levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) was found in METH-exposed fish. A significant hyperactivity was found during the first hour of exposure, followed 3 h after by a positive geotaxis and negative scototaxis in the novel tank and in the light/dark paradigm, respectively. Moreover, the behavioral phenotype in the treated fish was consistent with social isolation. At transcriptional level, th1 and slc18a2 (vmat2) exhibited a significant increase after 3 h of exposure, whereas the expression of gfap, a marker of astroglial response to neuronal injury, was strongly increased after 48 h exposure. However, no evidences of oxidative stress were found in the brain of the treated fish. Altogether, this study demonstrates the suitability of the adult zebrafish as a model of METH-induced neurotoxicity and provides more information about the biochemical and behavioral consequences of METH abuse.

Transfer of α-synuclein from neurons to oligodendrocytes triggers myelin sheath destruction in methamphetamine administration mice

Methamphetamine (METH), a widely abused nervous system stimulant, could induce neurotoxicity through α-synuclein (α-syn). Not much is known about the neuronal derived α-syn transmission that underlies oligodendrocyte pathology in METH mice model. In this study, we tested α-syn level, oligodendroglial pathology and autophagy lysosome pathway (ALP) function in corpus callosum in a chronic METH mice model. METH increased α-syn level in neurons and then accumulated in oligodendrocytes. METH increased phosphor-mTOR level, decreased transcription factor EB (TFEB) level and triggered autophagy lysosomal pathway (ALP) impairment, leading to myelin sheath destruction, oligodendroglial proteins loss, mature dendritic spine loss, neuron loss, and astrocyte activation. Deleting endogenous α-syn increased TFEB level, alleviated ALP deficit, and diminished neuropathology induced by METH. TFEB overexpression in oligodendrocytes exerted beneficial effects in METH mice model. These neuroprotective effects were associated with the rescued ALP machinery after oligodendroglial TFEB overexpression. Our study demonstrated, for the first time, that α-syn-TFEB axis might be involve in the METH induced myelin loss, oligodendroglial pathology, and neuropathology. In summary, targeting at the α-syn-TFEB axis might be a promising therapeutic strategy for treating METH induced oligodendroglial pathology, and to a broader view, neurodegenerative diseases.

Effect of Chaihu-jia-Longgu-Muli decoction on withdrawal symptoms in rats with methamphetamine-induced conditioned place preference

Traditional Chinese medicine detoxification prescription Chaihu-jia-Longgu-Muli decoction (CLMD) relieves depressive symptoms in patients withdrawing from methamphetamine. In the present study, we assessed the effects of CLMD on methamphetamine withdrawal in rats. A methamphetamine-intoxicated rat model was established. Rats were randomly divided into the control, model, high-dosage, medium-dosage, and low-dosage groups, receiving high, medium, and low doses of CLMD, respectively. Weekly body weight measurements revealed that rats treated with methamphetamine had the lowest body weight. The conditioned place preference (CPP) experiment revealed that methamphetamine-intoxicated rats stayed significantly longer in the drug-paired chamber than the control rats. However, after administering high-dosage CLMD, the amount of time the rats spent in the drug-paired chamber was significantly less than that of the model rats. Our open-field test revealed that the model group had lower crossing and rearing scores than the control group. Additionally, rats that received CLMD treatment exhibited higher crossing and rearing scores than the model rats. Striatal dopamine (DA), 5-hydroxytryptamine (5-HT), and endorphins (β-EP) and serum interleukin (IL)-1α and IL-2 concentrations were estimated. Rats in the model group had lower striatal DA, 5-HT, and β-EP and higher serum IL-1α and IL-2 concentrations than those in the control group. High-dosage CLMD administration significantly changed the concentrations of these molecules, such that they approached normal concentrations. In general, CLMD could prevent the development of methamphetamine-induced withdrawal symptoms in rats by increasing the DA, 5-HT, and β-EP and lowering the IL-1α and IL-2 concentrations.

Alpha-Synuclein deficiency ameliorates chronic methamphetamine induced neurodegeneration in mice

The α-Synuclein (α-syn) and tau have synergistic effects on neurodegenerative diseases induced by environmental factors or genetic mutation. Thus, we investigated the role of α-syn and tau in neurodegeneration induced by chronic methamphetamine (METH) exposure (1.0∼20.0 mg/kg/d body weight, for 14 consecutive days). Here, we present a mice model with evidences of α-syn and tau participating in toxicology in chronic METH. METH increased α-syn level in the stratum oriens, pyramidal layer, stratum radiatum and stratum moleculare of hippocampal CA1, CA2 and CA3, polymorph layer of hippocampal dentate gyrus (DG), and substantia nigra (SN). The subcellular locations of the upregulated α-syn were mainly found in mitochondria and axons. The METH upregulated α-syn may directly induce mitochondrial damage, myelin sheath destruction, and synaptic failure. Also, the excess α-syn might indirectly promote tau phosphorylation through tau kinase GSK3β and CDK5, leading to microtubule depolymerization and eventually fusion deficit of autophagosome and lysosome. In the in vitro experiment, the autophagic vacuoles failed to fuse with the lysosome. The neuropathology induced by both the direct and indirect effects of α-syn could be alleviated by α-syn knockout. Taking together, these results indicate that the α-syn mediates the neurodegenerative process induced by chronic METH and that reducing α-syn might be a potential approach to protect the toxic effects of METH and also be, to a broader view, of therapeutic value in neurodegenerative diseases.

Chronic Methamphetamine Exposure Attenuates Neural Activation in Hypothalamic-Pituitary-Adrenal Axis-Associated Brain Regions in a Sex-specific Manner

Sex differences in methamphetamine (MA) abuse and consequences of MA have been reported with females showing an increased addiction phenotype and withdrawal symptoms. One mechanism through which these effects might occur is via sex-specific alterations in the hypothalamic-pituitary-adrenal (HPA) axis and its associated brain regions. In this study, mice were administered MA (5 mg/kg) or saline for 10 consecutive days. During early withdrawal, anxiety-like behaviors were assessed in the open field, light/dark box, and elevated plus maze. At ten days of withdrawal, mice were injected with a final dose of MA (5 mg/kg) or saline. Chronic MA did not alter anxiety-like behaviors or corticosterone responses to a final dose of MA, although females showed elevated corticosterone responses compared to males. Chronic MA attenuated final MA-induced c-Fos in both sexes in the paraventricular hypothalamus (PVH), bed nucleus of the stria terminalis (BNST), cingulate cortex, central and basolateral amygdala. In CA1 and CA3 hippocampal areas, c-Fos attenuation by chronic MA occurred only in females. Within the PVH, final MA injection increased c-Fos to a greater extent in females compared to males regardless of prior MA exposure. Dual-labeling of c-Fos with glucocorticoid receptor revealed a specific attenuation of neural activation within this cell type in the PVH, central and basolateral amygdala, and BNST. Together these findings demonstrate that chronic MA can suppress subsequent activation of HPA axis-associated brain regions and cell phenotypes. Further, in select regions this reduction is sex-specific. These changes may contribute to reported sex differences in MA abuse patterns.

Effects of Housing on Methamphetamine-Induced Neurotoxicity and Spatial Learning and Memory

Severe stress potentiates methamphetamine (MA) neurotoxicity. However, whether moderate stress increases or decreases the neurotoxic effects of MA is unknown. We assessed the effects of MA (4 × 10 mg/kg at 2 h intervals) in combination with prior barren-cage housing in adult male Sprague-Dawley rats on monoamines and glial fibrillary acid protein (GFAP) in one cohort and spatial learning and memory in the Morris water maze in another cohort. MA reduced dopamine (DA) and serotonin (5-HT) in the neostriatum and nucleus accumbens, 5-HT in the hippocampus, and increased GFAP in neostriatum and nucleus accumbens compared with saline controls. In neostriatum, barren-cage housing protected against MA-induced increases in GFAP, but it did not prevent DA and 5-HT reductions, although it did increase hippocampal norepinephrine. MA impaired spatial learning during acquisition, reversal, and shift phases and impaired reference memory on reversal and shift probe trials. Barren-cage housing enhanced performance during acquisition but not during reversal or shift or on probe trials. The data indicate that prior barren-cage housing moderates MA-induced neostriatal astrogliosis and initial spatial learning, but has no protective effect when the platform is smaller and relocated and therefore requires cognitive flexibility in relearning.

Nupr1 Modulates Methamphetamine-Induced Dopaminergic Neuronal Apoptosis and Autophagy through CHOP-Trib3-Mediated Endoplasmic Reticulum Stress Signaling Pathway

Methamphetamine (METH) is an illegal and widely abused psychoactive stimulant. METH exposure causes detrimental effects on multiple organ systems, primarily the nervous system, especially dopaminergic pathways, in both laboratory animals and humans. In this study, we hypothesized that Nuclear protein 1 (Nupr1/com1/p8) is involved in METH-induced neuronal apoptosis and autophagy through endoplasmic reticulum (ER) stress signaling pathway. To test this hypothesis, we measured the expression levels of Nupr1, ER stress protein markers CHOP and Trib3, apoptosis-related protein markers cleaved-caspase3 and PARP, as well as autophagy-related protein markers LC3 and Beclin-1 in brain tissues of adult male Sprague-Dawley (SD) rats, rat primary cultured neurons and the rat adrenal pheochromocytoma cells (PC12 cells) after METH exposure. We also determined the effects of METH exposure on the expression of these proteins after silencing Nupr1, CHOP, or Trib3 expression with synthetic small hairpin RNA (shRNA) or siRNA in vitro, and after silencing Nupr1 in the striatum of rats by injecting lentivirus containing shRNA sequence targeting Nupr1 gene to rat striatum. The results showed that METH exposure increased Nupr1 expression that was accompanied with increased expression of ER stress protein markers CHOP and Trib3, and also led to apoptosis and autophagy in rat primary neurons and in PC12 cells after 24 h exposure (3.0 mM), and in the prefrontal cortex and striatum of rats after repeated intraperitoneal injections (15 mg/kg × 8 injections at 12 h intervals). Silencing of Nupr1 expression partly reduced METH-induced apoptosis and autophagy in vitro and in vivo. These results suggest that Nupr1 plays an essential role in METH-caused neuronal apoptosis and autophagy at relatively higher doses and may be a potential therapeutic target in high-dose METH-induced neurotoxicity.

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.

Effects of repeated high-dose methamphetamine and ceftriaxone post-treatments on tissue content of dopamine and serotonin as well as glutamate and glutamine

Repeated exposure to high doses of methamphetamine (METH) is known to alter several neurotransmitters in certain brain regions. Little is known about the effects of ceftriaxone (CEF), a β-lactam antibiotic, known to upregulate glutamate transporter subtype 1, post-treatment on METH-induced depletion of dopamine and serotonin (5-HT) tissue content in brain reward regions. Moreover, the effects of METH and CEF post-treatment on glutamate and glutamine tissue content are not well understood. In this study, Wistar rats were used to investigate the effects of METH and CEF post-treatment on tissue content of dopamine/5-HT and glutamate/glutamine in the nucleus accumbens (NAc) and prefrontal cortex (PFC). Rats received either saline or METH (10mg/kg, i.p. every 2h×4) followed by either saline or CEF (200mg/kg, i.p, every day×3) post-treatment. METH induced a significant depletion of dopamine and 5-HT in the NAc and PFC. Importantly, dopamine tissue content was completely restored in the NAc following CEF post-treatment. Additionally, METH caused a significant decrease in glutamate and glutamine tissue content in PFC, and this effect was attenuated by CEF post-treatment. These findings demonstrate for the first time the attenuating effects of CEF post-treatment on METH induced alterations in the tissue contents of dopamine, glutamate, and glutamine.

Pharmacological Targeting the REV-ERBs in Sleep/Wake Regulation

The circadian clock maintains appropriate timing for a wide range of behaviors and physiological processes. Circadian behaviors such as sleep and wakefulness are intrinsically dependent on the precise oscillation of the endogenous molecular machinery that regulates the circadian clock. The identical core clock machinery regulates myriad endocrine and metabolic functions providing a link between sleep and metabolic health. The REV-ERBs (REV-ERBα and REV-ERBβ) are nuclear receptors that are key regulators of the molecular clock and have been successfully targeted using small molecule ligands. Recent studies in mice suggest that REV-ERB-specific synthetic agonists modulate metabolic activity as well as alter sleep architecture, inducing wakefulness during the light period. Therefore, these small molecules represent unique tools to extensively study REV-ERB regulation of sleep and wakefulness. In these studies, our aim was to further investigate the therapeutic potential of targeting the REV-ERBs for regulation of sleep by characterizing efficacy, and optimal dosing time of the REV-ERB agonist SR9009 using electroencephalographic (EEG) recordings. Applying different experimental paradigms in mice, our studies establish that SR9009 does not lose efficacy when administered more than once a day, nor does tolerance develop when administered once a day over a three-day dosing regimen. Moreover, through use of a time response paradigm, we determined that although there is an optimal time for administration of SR9009 in terms of maximal efficacy, there is a 12-hour window in which SR9009 elicited a response. Our studies indicate that the REV-ERBs are potential therapeutic targets for treating sleep problems as those encountered as a consequence of shift work or jet lag.

Methamphetamine addiction: involvement of CREB and neuroinflammatory signaling pathways

RATIONALE AND OBJECTIVES

Addiction to psychostimulant methamphetamine (METH) remains a major public health problem in the world. Animal models that use METH self-administration incorporate many features of human drug-taking behavior and are very helpful in elucidating mechanisms underlying METH addiction. These models are also helping to decipher the neurobiological substrates of associated neuropsychiatric complications. This review summarizes our work on the influence of METH self-administration on dopamine systems, transcription and immune responses in the brain.

METHODS

We used the rat model of METH self-administration with extended access (15 h/day for eight consecutive days) to investigate the effects of voluntary METH intake on the markers of dopamine system integrity and changes in gene expression observed in the brain at 2 h-1 month after cessation of drug exposure.

RESULTS

Extended access to METH self-administration caused changes in the rat brain that are consistent with clinical findings reported in neuroimaging and postmortem studies of human METH addicts. In addition, gene expression studies using striatal tissues from METH self-administering rats revealed increased expression of genes involved in cAMP response element binding protein (CREB) signaling pathway and in the activation of neuroinflammatory response in the brain.

CONCLUSION

These data show an association of METH exposure with activation of neuroplastic and neuroinflammatory cascades in the brain. The neuroplastic changes may be involved in promoting METH addiction. Neuroinflammatory processes in the striatum may underlie cognitive deficits, depression, and parkinsonism reported in METH addicts. Therapeutic approaches that include suppression of neuroinflammation may be beneficial to addicted patients.

The Body Mass Index, Blood Pressure, and Fasting Blood Glucose in Patients With Methamphetamine Dependence

Methamphetamine (MA) is a prevalently abused psychostimulant in the world. Previously published studies and case reports indicated potential associations between MA and body mass index (BMI) and cardiovascular factors (eg, blood pressure and fasting blood glucose). However, these associations have not been studied clearly. This study aimed to investigate BMI and cardiovascular factors in the MA-dependent patients.A total of 1019 MA-dependent patients were recruited between February 2, 2008 and March 11, 2013. A case report was used to gather information on sociocharacteristics and drug-dependent history. Meanwhile, a number of 1019 age- and sex-matched controls' information were collected from the physical examination center. We measured BMI, blood pressure, and fasting blood glucose among the participants.MA-dependent patients had significantly lower BMI (20.4 ± 0.1 vs 23.9 ± 0.1 kg/m, P < 0.001), lower fasting blood glucose (5.0 ± 0.01 vs 5.2 ± 0.01 mmol/L, P < 0.001) and higher systolic blood pressure (122.1 ± 0.4 vs 114.8 ± 0.4 mmHg, P < 0.001) compared with the control group after adjustment of possible confounders. Additional, we only found the duration of MA use was independently associated with BMI (B = -0.08, P = 0.04).This study demonstrated that MA dependence was associated with BMI and cardiovascular factors. In addition, we found a negative association between duration of MA use and BMI.

Effects of DDIT4 in Methamphetamine-Induced Autophagy and Apoptosis in Dopaminergic Neurons

Methamphetamine (METH) is an illicit psychoactive drug that can cause a variety of detrimental effects to the nervous system, especially dopaminergic pathways. We hypothesized that DNA damage-inducible transcript 4 (DDIT4) is involved in METH-induced dopaminergic neuronal autophagy and apoptosis. To test the hypothesis, we determined changes of DDIT4 protein expression and the level of autophagy in rat catecholaminergic PC12 cells and human dopaminergic SH-SY5Y cells, and in the hippocampus, prefrontal cortex, and striatum of Sprague Dawley rats exposed to METH. We also examined the effects of silencing DDIT4 expression on METH-induced dopaminergic neuronal autophagy using fluorescence microscopy and electron microscopy. Flow cytometry and Western blot were used to determine apoptosis and the expression of apoptotic markers (cleaved caspase-3 and cleaved PARP) after blocking DDIT4 expression in PC12 cells and SH-SY5Y cells with synthetic siRNA, as well as in the striatum of rats by injecting LV-shDDIT4 lentivirus using a stereotaxic positioning system. Our results showed that METH exposure increased DDIT4 expression that was accompanied with increased autophagy and apoptosis in PC12 cells (3 mM) and SH-SY5Y cells (2 mM), and in the hippocampus, prefrontal cortex, and striatum of rats. Inhibition of DDIT4 expression reduced METH-induced autophagy and apoptosis in vitro and in vivo. However, DDIT4-related effects were not observed at a low concentration of METH (1 μM). These results suggest that DDIT4 plays an essential role in METH-induced dopaminergic neuronal autophagy and apoptosis at higher doses and may be a potential gene target for therapeutics in high-dose METH-induced neurotoxicity.

Immediate and lasting effects of chronic daily methamphetamine exposure on activation of cells in hypothalamic-pituitary-adrenal axis-associated brain regions

RATIONALE

Chronic methamphetamine (MA) abuse leads to dependence and symptoms of withdrawal after use has ceased. Negative mood states associated with withdrawal, as well as drug reinstatement, have been linked to drug-induced disruption of the hypothalamic-pituitary-adrenal (HPA) axis. However, effects of chronic MA exposure or acute MA exposure following withdrawal on neural activation patterns within brain regions that regulate the HPA axis are unknown.

OBJECTIVES

In this study, neural activation patterns were assessed by quantification of c-Fos protein in mice exposed to different regimens of MA administration.

METHODS

(Experiment 1) Adult male mice were treated with MA (5 mg/kg) or saline once or once daily for 10 days. (Experiment 2) Mice were treated with MA or saline once daily for 10 days and following a 10-day withdrawal period were re-administered a final dose of MA or saline. c-Fos was quantified in brains after the final injection.

RESULTS

(Experiment 1) Compared to exposure to a single dose of MA (5 mg/kg), chronic MA exposure decreased the number of c-Fos expressing cells in the paraventricular hypothalamus, dorsomedial hypothalamus, central amygdala, basolateral amygdala, bed nucleus of the stria terminalis (BNST), and CA3 hippocampal region. (Experiment 2) Compared to mice receiving their first dose of MA, mice chronically treated with MA, withdrawn, and re-administered MA, showed decreased c-Fos expressing cells within the central and basolateral amygdala, BNST, and CA3.

CONCLUSIONS

HPA axis-associated amygdala, extended amygdala, and hippocampal regions endure lasting effects following chronic MA exposure and therefore may be linked to stress-related withdrawal symptoms.

DNA damage-inducible transcript 4 (DDIT4) mediates methamphetamine-induced autophagy and apoptosis through mTOR signaling pathway in cardiomyocytes

Methamphetamine (METH) is an amphetamine-like psychostimulant that is commonly abused. Previous studies have shown that METH can induce damages to the nervous system and recent studies suggest that METH can also cause adverse and potentially lethal effects on the cardiovascular system. Recently, we demonstrated that DNA damage-inducible transcript 4 (DDIT4) regulates METH-induced neurotoxicity. However, the role of DDIT4 in METH-induced cardiotoxicity remains unknown. We hypothesized that DDIT4 may mediate METH-induced autophagy and apoptosis in cardiomyocytes. To test the hypothesis, we examined DDIT4 protein expression in cardiomyocytes and in heart tissues of rats exposed to METH with Western blotting. We also determined the effects on METH-induced autophagy and apoptosis after silencing DDIT4 expression with synthetic siRNA with or without pretreatment of a mTOR inhibitor rapamycin in cardiomyocytes using Western blot analysis, fluorescence microscopy and TUNEL staining. Our results showed that METH exposure increased DDIT4 expression and decreased phosphorylation of mTOR that was accompanied with increased autophagy and apoptosis both in vitro and in vivo. These effects were normalized after silencing DDIT4. On the other hand, rapamycin promoted METH-induced autophagy and apoptosis in DDIT4 knockdown cardiomyocytes. These results suggest that DDIT4 mediates METH-induced autophagy and apoptosis through mTOR signaling pathway in cardiomyocytes.

Prior methamphetamine self-administration attenuates the dopaminergic deficits caused by a subsequent methamphetamine exposure

Others and we have reported that prior methamphetamine (METH) exposure attenuates the persistent striatal dopaminergic deficits caused by a subsequent high-dose "binge" METH exposure. The current study investigated intermediate neurochemical changes that may contribute to, or serve to predict, this resistance. Rats self-administered METH or saline for 7 d. On the following day (specifically, 16 h after the conclusion of the final METH self-administration session), rats received a binge exposure of METH or saline (so as to assess the impact of prior METH self-administration), or were sacrificed without a subsequent METH exposure (i.e., to assess the status of the rats at what would have been the initiation of the binge METH treatment). Results revealed that METH self-administration per se decreased striatal dopamine (DA) transporter (DAT) function and DA content, as assessed 16 h after the last self-administration session. Exposure to a binge METH treatment beginning at this 16-h time point decreased DAT function and DA content as assessed 1 h after the binge METH exposure: this effect on DA content (but not DAT function) was attenuated if rats previously self-administered METH. In contrast, 24 h after the binge METH treatment prior METH self-administration: 1) attenuated deficits in DA content, DAT function and vesicular monoamine transporter-2 function; and 2) prevented increases in glial fibrillary acidic protein and DAT complex immunoreactivity. These data suggest that changes 24 h, but not 1 h, after binge METH exposure are predictive of tolerance against the persistence of neurotoxic changes following binge METH exposures.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

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.

The effects of methamphetamine self-administration on cortical monoaminergic deficits induced by subsequent high-dose methamphetamine administrations

Preclinical models suggest that repeated high-dose methamphetamine (METH) exposures, administered in a "binge-like" pattern, acutely decrease norepinephrine (NE), and acutely and persistently decrease serotonin (5-hydroxytryptamine; 5HT) content in the frontal cortex. However, the impact of METH self-administration on this region is unknown. Because of the importance of the monoaminergic neurons in the frontal cortex to a variety of cognitive and addictive processes, effects of METH self-administration on cortical NE and 5HT content were assessed. Results revealed several novel findings. First, METH self-administration decreased cortical NE content as assessed 24 h after last exposure. Consistent with previous preclinical reports after a binge METH regimen, this decrease was reversed 8 days after the final METH exposure. Second, and in contrast to our previous reports involving the hippocampus or striatum, METH self-administration caused persistent decreases in 5HT content as assessed 8 days after the final METH exposure. Of note, the magnitude of this decrease (≈ 20%) was less than that observed typically after a binge METH treatment. Third, prior METH self-administration attenuated METH-induced serotonergic deficits as assessed 7 days, but not 1 h, following a neurotoxic METH regimen. No protection was observed when the binge exposure occurred 15 days after the last self-administration session. Taken together, these data demonstrate important and selective alterations in cortical serotonergic neuronal function subsequent to METH self-administration. These data provide a foundation to investigate complex questions involving "resistance" to the persistent deficits caused by neurotoxic METH exposure and frontal cortical function.

Alterations in the striatal dopamine system during intravenous methamphetamine exposure: effects of contingent and noncontingent administration

The continuing spread of methamphetamine (METH) abuse has stimulated research aimed at understanding consequences of its prolonged exposure. Alterations in nigrostriatal dopamine (DA) system parameters have been characterized in experimental studies after discontinuation of long-term METH but fewer studies have included similar assessments during METH exposure. Here, we report METH plasma pharmacokinetics and striatal DA system alterations in rat after noncontingent and contingent METH administration for 7.5 weeks. Escalating METH exposure was delivered by dynamic infusion (DI) that incorporated a "humanized" plasma METH half life or by intravenous self-administration (IVSA) that included binge intakes. Kinetic modeling of DI and IVSA for 24 h periods during the final week of METH exposure showed that plasma METH levels remained between 0.7 and 1.5 µM. Animals were sacrificed during their last METH administration for autoradiography assessment using [³H]ligands and D2 agonist-induced [³⁵S]GTPγS binding. DA transporter binding was decreased (DI, 34%; IVSA, 15%) while vesicular monoamine transporter binding and substantia nigra DA cell numbers were unchanged. Decreases were measured for D2 receptor (DI and IVSA, 15-20%) and [³⁵S]GTPγS binding (DI, 35%; IVSA, 18%). These similar patterns of DI and IVSA associated decreases in striatal DA markers reflect consequences of cumulative METH exposure and not the drug delivery method. For METH IVSA, individual differences were observed, yet each animal's total intake was similar within and across three 24-h binges. IVSA rodent models may be useful for identifying molecular mechanisms that are associated with METH binges in humans.

Prior methamphetamine self-administration attenuates serotonergic deficits induced by subsequent high-dose methamphetamine administrations

BACKGROUND

Pre-clinical studies indicate that high-dose, non-contingent methamphetamine (METH) administration both rapidly and persistently decreases serotonergic neuronal function. Despite research indicating the hippocampus plays an important role in METH abuse and is affected by METH use, effects of METH self-administration on hippocampal serotonergic neurons are not well understood, and were thus an important focus of the current study. Because humans often administer METH in a binge-like pattern, effects of prior METH self-administration on a subsequent "binge-like" METH treatment were also examined.

METHODS

Rats were treated as described above, and sacrificed 1 or 8d after self-administration or 1h or 7d after the final binge METH or saline exposure. Hippocampal serotonin (5-hydroxytryptamine; 5HT) content and transporter (SERT) function were assessed.

RESULTS

METH self-administration per se had no persistent effect on hippocampal 5HT content or SERT function. However, this treatment attenuated the persistent, but not acute, hippocampal serotonergic deficits caused by a subsequent repeated, high-dose, non-continent METH treatment administered 1 d the last self-administration session. No attenuation in persistent deficits were seen when the high-dose administration of METH occurred 15d after the last self-administration session.

CONCLUSIONS

The present findings demonstrate that METH self-administration alters serotonergic neurons so as to engender "tolerance" to the persistent serotonergic deficits caused by a subsequent METH exposure. However, this "tolerance" does not persist. These data provide a foundation to investigate complex questions including how the response of serotonergic neurons to METH may contribute to contingent-related disorders such as dependence and relapse.

Juvenile exposure to methamphetamine attenuates behavioral and neurochemical responses to methamphetamine in adult rats

Previous research has shown that children living in clandestine methamphetamine (MA) labs are passively exposed to the drug [1]. The long-term effects of this early exposure on the dopaminergic systems are unknown, but may be important for adult behaviors mediated by dopamine, such as drug addiction. The current study sought to determine if juvenile exposure to low doses of MA would lead to altered responsiveness to the stimulant in adulthood. Young male and female rats (PD20-34) were injected daily with 0 or 2 mg/kg MA or left undisturbed and then tested at PD90. In the open field, adult rats exposed to MA during preadolescence had reduced locomotor activity compared to control non-exposed rats following an acute injection of MA (2 mg/kg). Likewise, methamphetamine-induced dopamine increases in the dorsal striatum were attenuated in male and female rats that had been exposed to MA as juveniles, although there were no changes in basal in vivo or ex vivo dopamine levels. These findings suggest that exposure of juveniles to MA leads to persistent changes in the behavioral and neurochemical responses to stimulants in adulthood.

Methods in drug abuse models: comparison of different models of methamphetamine paradigms

Methamphetamine (METH) is a widely abused psychomotor stimulant. Investigating the effects of METH use on the brain has been applied in different animal models, including rats, mice, and nonhuman primates. Human abuse of METH occurs in different paradigms ranging from episodes of binge abuse to chronic abuse over years; different animal models have been established to replicate these various patterns of human behavior. In this chapter, we discuss the different models of METH abuse, including the acute model which assesses the immediate effects of METH on the brain and chronic exposure model which simulates the more common long-term use observed in humans; additionally, two other relevant models, escalating dose paradigm and METH self-administration, are examined. In comparing the models, this chapter briefly considers the METH-induced neurotoxic effects associated with each METH administration paradigm and the behavioral changes observed.

Long-term protective effects of methamphetamine preconditioning against single-day methamphetamine toxic challenges

Methamphetamine (METH) use is associated with neurotoxic effects which include decreased levels of dopamine (DA), serotonin (5-HT) and their metabolites in the brain. We have shown that escalating METH dosing can protect against METH induced neurotoxicity in rats sacrificed within 24 hours after a toxic METH challenge. The purpose of the current study was to investigate if the protective effects of METH persisted for a long period of time. We also tested if a second challenge with a toxic dose of METH would cause further damage to monoaminergic terminals. Saline-pretreated rats showed significant METH-induced decreases in striatal DA and 5-HT levels in rats sacrificed 2 weeks after the challenge. Rats that received two METH challenges showed no further decreases in striatal DA or 5-HT levels in comparison to the single METH challenge. In contrast, METH-pretreated rats showed significant protection against METH-induced striatal DA and 5-HT depletion. In addition, the METH challenge causes substantial decreases in cortical 5-HT levels which were not further potentiated by a second drug challenge. METH preconditioning provided almost complete protection against METH -induced 5-HT depletion. These results are consistent with the idea that METH pretreatment renders the brain refractory to METH-induced degeneration of brain monoaminergic systems.

Low concentrations of methamphetamine can protect dopaminergic cells against a larger oxidative stress injury: mechanistic study

Mild stress can protect against a larger insult, a phenomenon termed preconditioning or tolerance. To determine if a low intensity stressor could also protect cells against intense oxidative stress in a model of dopamine deficiency associated with Parkinson disease, we used methamphetamine to provide a mild, preconditioning stress, 6-hydroxydopamine (6-OHDA) as a source of potentially toxic oxidative stress, and MN9D cells as a model of dopamine neurons. We observed that prior exposure to subtoxic concentrations of methamphetamine protected these cells against 6-OHDA toxicity, whereas higher concentrations of methamphetamine exacerbated it. The protection by methamphetamine was accompanied by decreased uptake of both [(3)H] dopamine and 6-OHDA into the cells, which may have accounted for some of the apparent protection. However, a number of other effects of methamphetamine exposure suggest that the drug also affected basic cellular survival mechanisms. First, although methamphetamine preconditioning decreased basal pERK1/2 and pAkt levels, it enhanced the 6-OHDA-induced increase in these phosphokinases. Second, the apparent increase in pERK1/2 activity was accompanied by increased pMEK1/2 levels and decreased activity of protein phosphatase 2. Third, methamphetamine upregulated the pro-survival protein Bcl-2. Our results suggest that exposure to low concentrations of methamphetamine cause a number of changes in dopamine cells, some of which result in a decrease in their vulnerability to subsequent oxidative stress. These observations may provide insights into the development of new therapies for prevention or treatment of PD.

Biphasic dopamine regulation in mesoaccumbens pathway in response to non-contingent binge and escalating methamphetamine regimens in the Wistar rat

RATIONALE

Methamphetamine (MA) increases extracellular dopamine (DA) and at chronic high doses induces toxicity as indicated by decreased expression of tyrosine hydroxylase (TH) and dopamine transporter (DAT). Notably, rats will self-administer MA in escalating quantities producing such toxicity. However, the impact of MA at sub-toxic doses on DA regulation is not well established.

OBJECTIVE

The temporal dynamics of DA regulation following cessation of sub-toxic escalating and binge doses of non-contingent MA were investigated as changes therein may be associated with escalation of MA intake.

MATERIALS AND METHODS

MA was administered 3×/day using an established 14-day escalating-dose regimen (0.1-4.0 mg/kg) or a single-day binge-style administration (3 × 4 mg/kg). DA tissue content, DA turnover, TH protein, TH phosphorylation, DAT, and vesicular monoamine transporter 2 were measured in nigrostriatal and mesoaccumbens pathways 48 h and 2 weeks after MA cessation.

RESULTS

Changes in striatal DA regulation were limited to increased DA turnover. However, in the mesoaccumbens pathway, escalating MA had biphasic effects. DA was increased in ventral tegmental area (VTA) and decreased in nucleus accumbens at 48 h post-MA while the reverse was seen at 2 weeks. These changes were matched by similar changes in TH protein and, in the VTA, by changes in DAT.

CONCLUSION

Escalation of MA intake produces both transient and long-lasting effects upon DA, TH, and DAT in the mesoaccumbens pathway. The eventual decrease of DA in the VTA is speculated to contribute to craving for MA and, thus, may be associated with MA escalation and resulting dopaminergic toxicity.

Chronic methamphetamine administration causes differential regulation of transcription factors in the rat midbrain

Methamphetamine (METH) is an addictive and neurotoxic psychostimulant widely abused in the USA and throughout the world. When administered in large doses, METH can cause depletion of striatal dopamine terminals, with preservation of midbrain dopaminergic neurons. Because alterations in the expression of transcription factors that regulate the development of dopaminergic neurons might be involved in protecting these neurons after toxic insults, we tested the possibility that their expression might be affected by toxic doses of METH in the adult brain. Male Sprague-Dawley rats pretreated with saline or increasing doses of METH were challenged with toxic doses of the drug and euthanized two weeks later. Animals that received toxic METH challenges showed decreases in dopamine levels and reductions in tyrosine hydroxylase protein concentration in the striatum. METH pretreatment protected against loss of striatal dopamine and tyrosine hydroxylase. In contrast, METH challenges caused decreases in dopamine transporters in both saline- and METH-pretreated animals. Interestingly, METH challenges elicited increases in dopamine transporter mRNA levels in the midbrain in the presence but not in the absence of METH pretreatment. Moreover, toxic METH doses caused decreases in the expression of the dopamine developmental factors, Shh, Lmx1b, and Nurr1, but not in the levels of Otx2 and Pitx3, in saline-pretreated rats. METH pretreatment followed by METH challenges also decreased Nurr1 but increased Otx2 and Pitx3 expression in the midbrain. These findings suggest that, in adult animals, toxic doses of METH can differentially influence the expression of transcription factors involved in the developmental regulation of dopamine neurons. The combined increases in Otx2 and Pitx3 expression after METH preconditioning might represent, in part, some of the mechanisms that served to protect against METH-induced striatal dopamine depletion observed after METH preconditioning.

Mutant DISC1 affects methamphetamine-induced sensitization and conditioned place preference: a comorbidity model

Genetic factors involved in neuroplasticity have been implicated in major psychiatric illnesses such as schizophrenia, depression, and substance abuse. Given its extended interactome, variants in the Disrupted-In-Schizophrenia-1 (DISC1) gene could contribute to drug addiction and psychiatric diseases. Thus, we evaluated how dominant-negative mutant DISC1 influenced the neurobehavioral and molecular effects of methamphetamine (METH). Control and mutant DISC1 mice were studied before or after treatment with non-toxic escalating dose (ED) of METH. In naïve mice, we assessed METH-induced conditioned place preference (CPP), dopamine (DA) D2 receptor density and the basal and METH-induced activity of DISC1 partners, AKT and GSK-3β in the ventral striatum. In ED-treated mice, 4 weeks after METH treatment, we evaluated fear conditioning, depression-like responses in forced swim test, and the basal and METH-induced activity of AKT and GSK-3β in the ventral striatum. We found impairment in METH-induced CPP, decreased DA D2 receptor density and altered METH-induced phosphorylation of AKT and GSK-3β in naïve DISC1 female mice. The ED regimen was not neurotoxic as evidenced by unaltered brain regional monoamine tissue content. Mutant DISC1 significantly delayed METH ED-produced sensitization and affected drug-induced phosphorylation of AKT and GSK-3β in female mice. Our results suggest that perturbations in DISC1 functions in the ventral striatum may impact the molecular mechanisms of reward and sensitization, contributing to comorbidity between drug abuse and major mental diseases.

A neurotoxic regimen of methamphetamine exacerbates the febrile and neuroinflammatory response to a subsequent peripheral immune stimulus

Methamphetamine (MA) use is associated with activation of microglia and, at high doses, can induce neurotoxicity. Given the changes in the neuroinflammatory environment associated with MA, we investigated whether MA administration would interfere with the thermoregulatory and neuroinflammatory response to a subsequent peripheral immune stimulus. C57BL6/J mice were given four i.p. injections of either 5 mg/kg MA or saline at two hour intervals. Twenty-four hours following the first MA injection, mice were given 100 μg/kg LPS or saline i.p. and blood and brains were collected. Here we report that mice exposed to MA developed higher fevers in response to LPS than did those given LPS alone. MA also exacerbated the LPS-induced increase in central cytokine mRNA. MA alone increased microglial Iba1 expression and expression was further increased when mice were exposed to both MA and LPS, suggesting that MA not only activated microglia but also influenced their response to a peripheral immune stimulus. Taken together, these data show that MA administration exacerbates the normal central immune response, most likely by altering microglia.

Methamphetamine preconditioning causes differential changes in striatal transcriptional responses to large doses of the drug

Methamphetamine (METH) is a toxic drug of abuse, which can cause significant decreases in the levels of monoamines in various brain regions. However, animals treated with progressively increasing doses of METH over several weeks are protected against the toxic effects of the drug. In the present study, we tested the possibility that this pattern of METH injections might be associated with transcriptional changes in the rat striatum, an area of the brain which is known to be very sensitive to METH toxicity and which is protected by METH preconditioning. We found that the presence and absence of preconditioning followed by injection of large doses of METH caused differential expression in different sets of striatal genes. Quantitative PCR confirmed METH-induced changes in some genes of interest. These include small heat shock 27 kD proteins 1 and 2 (HspB1 and HspB2), brain derived neurotrophic factor (BDNF), and heme oxygenase-1 (Hmox-1). Our observations are consistent with previous studies which have reported that ischemic or pharmacological preconditioning can cause reprogramming of gene expression after lethal ischemic insults. These studies add to the growing literature on the effects of preconditioning on the brain transcriptome.

Methamphetamine sensitization attenuates the febrile and neuroinflammatory response to a subsequent peripheral immune stimulus

Methamphetamine (MA) use is associated with activation of microglia and, at high doses, can induce neurotoxicity. Given the changes in the neuroinflammatory environment associated with MA, we investigated whether MA sensitization, a model of stimulant psychosis and an indicator of drug addiction, would interfere with the thermoregulatory and neuroinflammatory response to a subsequent peripheral immune stimulus. C57BL6/J mice were given either 1 mg/kg MA or saline i.p. once a day for 5 days to produce behavioral sensitization. Seventy-two hours following the last MA injection, 100 microg/kg LPS or saline was co-administered with 1 mg/kg MA or saline and blood and brains were collected. Here we report that while co-administration of LPS and MA did not affect the LPS-induced increase in central cytokine mRNA, mice sensitized to MA showed an attenuated central response to LPS. Interestingly, the peripheral response to LPS was not affected by MA sensitization. Plasma cytokines increased similarly in all groups after LPS. Further, c-Fos expression in the nucleus of the solitary tract did not differ between groups, suggesting that the periphery-to-brain immune signal is intact in MA-sensitized mice and that the deficit lies in the central cytokine compartment. We also show that MA sensitization decreased LPS- or acute MA-induced microglial Iba1 expression compared to non-sensitized mice. Taken together, these data show that MA sensitization interferes with the normal central immune response, preventing the CNS from efficiently responding to signals from the peripheral immune system.

Methamphetamine self-administration and the effect of contingency on monoamine and metabolite tissue levels in the rat

A number of studies have shown that exposure to high doses of methamphetamine (MA) is toxic to central dopamine (DA) and serotonin (5-HT) neurons. In most of those studies, however, high doses of MA were experimenter-administered during a short exposure time. Because contingency is a determinant for many effects of drug exposure, the present objective was to investigate the effects of self-administered MA on tissue monoamine levels following a short (24 hours) or longer (7 days) withdrawal period. As previously reported, a noncontingent "binge" high-dose treatment regimen (4 injections of 10 mg/kg MA administered every 2 hours) produced persistent depletion of cortical 5-HT and striatal DA. Effects of self-administered MA (0.1 mg/kg/infusion) were then determined following a 20-day duration where a yoked design was employed such that some rats received MA contingent on an operant lever press and others received either MA or saline dependent on the responses of the contingent rat. Self-administered MA produced a transient striatal DA depletion with a more persistent increase in DA turnover, indicating the presence of some lasting adaptations. Furthermore, the yoked design revealed that there was no effect of contingency on these parameters.

Methamphetamine preconditioning alters midbrain transcriptional responses to methamphetamine-induced injury in the rat striatum

Methamphetamine (METH) is an illicit drug which is neurotoxic to the mammalian brain. Numerous studies have revealed significant decreases in dopamine and serotonin levels in the brains of animals exposed to moderate-to-large METH doses given within short intervals of time. In contrast, repeated injections of small nontoxic doses of the drug followed by a challenge with toxic METH doses afford significant protection against monoamine depletion. The present study was undertaken to test the possibility that repeated injections of the drug might be accompanied by transcriptional changes involved in rendering the nigrostriatal dopaminergic system refractory to METH toxicity. Our results confirm that METH preconditioning can provide significant protection against METH-induced striatal dopamine depletion. In addition, the presence and absence of METH preconditioning were associated with substantial differences in the identity of the genes whose expression was affected by a toxic METH challenge. Quantitative PCR confirmed METH-induced changes in genes of interest and identified additional genes that were differentially impacted by the toxic METH challenge in the presence of METH preconditioning. These genes include small heat shock 27 kD 27 protein 2 (HspB2), thyrotropin-releasing hormone (TRH), brain derived neurotrophic factor (BDNF), c-fos, and some encoding antioxidant proteins including CuZn superoxide dismutase (CuZnSOD), glutathione peroxidase (GPx)-1, and heme oxygenase-1 (Hmox-1). These observations are consistent, in part, with the transcriptional alterations reported in models of lethal ischemic injuries which are preceded by ischemic or pharmacological preconditioning. Our findings suggest that multiple molecular pathways might work in tandem to protect the nigrostriatal dopaminergic pathway against the deleterious effects of the toxic psychostimulant. Further analysis of the molecular and cellular pathways regulated by these genes should help to provide some insight into the neuroadaptive potentials of the brain when repeatedly exposed to drugs of abuse.

Methamphetamine treatment causes delayed decrease in novelty-induced locomotor activity in mice

Methamphetamine (METH) is a psychostimulant that causes damage to dopamine (DA) axons and to non-monoaminergic neurons in the brain. The aim of the present study was to investigate short- and long-term effects of neurotoxic METH treatment on novelty-induced locomotor activity in mice. Male BALB/c mice, 12-14 weeks old, were injected with saline or METH (i.p., 7.5 mg/kg x 4 times, every 2 h). Behavior and neurotoxic effects were assessed at 10 days, 3 and 5 months following drug treatment. METH administration caused marked decreases in DA levels in the mouse striatum and cortex at 10 days post-drug. However, METH did not induce any changes in novelty-induced locomotor activity. At 3 and 5 months after treatment METH-exposed mice showed significant recovery of DA levels in the striatum and cortex. In contrast, these animals demonstrated significant decreases in locomotor activity at 5 months in comparison to aged-matched control mice. Further assessment of METH toxicity using TUNEL staining showed that the drug induced increased cell death in the striatum and cortex at 3 days after administration. Taken together, these data suggest that delayed deficits in novelty-induced locomotor activity observed in METH-exposed animals are not due to neurodegeneration of DA terminals but to combined effects of METH and age-dependent dysfunction of non-DA intrinsic striatal and/or corticostriatal neurons.

Repeated exposure to MDMA provides neuroprotection against subsequent MDMA-induced serotonin depletion in brain

Repeated exposure to sub-lethal insults has been reported to result in neuroprotection against a subsequent deleterious insult. The purpose of this study was to evaluate whether repeated exposure (preconditioning) to a non-5-HT depleting dose of MDMA in adult rats provides neuroprotection against subsequent MDMA-induced 5-HT depletion. Treatment of rats with MDMA (10 mg/kg, ip every 2 h for 4 injections) resulted in a 50-65% depletion of 5-HT in the striatum, hippocampus and cortex, and these depletions were significantly attenuated in rats that received a preconditioning regimen of MDMA (10 mg/kg, ip daily for 4 days). The 5-HT depleting regimen of MDMA also resulted in a 40-80% reduction in 5-HT transporter immunoreactivity (SERT(ir)), and the reduction in SERT(ir) also was completely attenuated in MDMA-preconditioned animals. Preconditioning with MDMA (10 mg/kg, ip) daily for 4 days provided neuroprotection against methamphetamine-induced 5-HT depletion, but not dopamine depletion, in the striatum. Additional studies were conducted to exclude the possibility that alterations in MDMA pharmacokinetics or MDMA-induced hyperthermia in rats previously exposed to MDMA contribute towards neuroprotection. During the administration of the 5-HT depleting regimen of MDMA, there was no difference in the extracellular concentration of the drug in the striatum of rats that had received 4 prior, daily injections of vehicle or MDMA. Moreover, there was no difference in the hyperthermic response to the 5-HT depleting regimen of MDMA in rats that had earlier received 4 daily injections of vehicle or MDMA. Furthermore, hyperthermia induced by MDMA during preconditioning appears not to contribute towards neuroprotection, inasmuch as preconditioning with MDMA at a low ambient temperature at which hyperthermia was absent did not alter the neuroprotection provided by the preconditioning regimen. Thus, prior exposure to MDMA affords protection against the long-term depletion of brain 5-HT produced by subsequent MDMA administration. The mechanisms underlying preconditioning-induced neuroprotection for MDMA remain to be determined.

Methamphetamine toxicity and messengers of death

Methamphetamine (METH) is an illicit psychostimulant that is widely abused in the world. Several lines of evidence suggest that chronic METH abuse leads to neurodegenerative changes in the human brain. These include damage to dopamine and serotonin axons, loss of gray matter accompanied by hypertrophy of the white matter and microgliosis in different brain areas. In the present review, we summarize data on the animal models of METH neurotoxicity which include degeneration of monoaminergic terminals and neuronal apoptosis. In addition, we discuss molecular and cellular bases of METH-induced neuropathologies. The accumulated evidence indicates that multiple events, including oxidative stress, excitotoxicity, hyperthermia, neuroinflammatory responses, mitochondrial dysfunction, and endoplasmic reticulum stress converge to mediate METH-induced terminal degeneration and neuronal apoptosis. When taken together, these findings suggest that pharmacological strategies geared towards the prevention and treatment of the deleterious effects of this drug will need to attack the various pathways that form the substrates of METH toxicity.

Methamphetamine preconditioning: differential protective effects on monoaminergic systems in the rat brain

Pretreatment with methamphetamine (METH) can attenuate toxicity due to acute METH challenges. The majority of previous reports have focused mainly on the effects of the drug on the striatal dopaminergic system. In the present study, we used a regimen that involves gradual increases in METH administration to rats in order to mimic progressively larger doses of the drug used by some human METH addicts. We found that this METH preconditioning was associated with complete protection against dopamine depletion caused by a METH challenge (5 mg/kg x 6 injections given 1 h apart) in the striatum and cortex. In contrast, there was no preconditioning-mediated protection against METH-induced serotonin depletion in the striatum and hippocampus, with some protection being observed in the cortex. There was also no protection against METH-induced norepinephrine (NE) depletion in the hippocampus. These results indicate that, in contrast to the present dogmas, there might be differences in the mechanisms involved in METH toxicity on monoaminergic systems in the rodent brain. Thus, chronic injections of METH might activate programs that protect against dopamine toxicity without influencing drug-induced pathological changes in serotoninergic systems. Further studies will need to evaluate the cellular and molecular bases for these differential responses.

The effects of methamphetamine on core body temperature in the rat--part 2: an escalating regimen

RATIONALE

Methamphetamine (METH) induces hyperthermia, which is diminished with chronic treatment in a dose-dependent manner. Our objective was to determine whether the temperature responses produced by a chronic, escalating-dose METH regimen and a chronic, 5.0 mg/kg dose regimen.

METHODS

Rats received pretreatment injections of saline, 5.0 mg/kg METH, 10.0 mg/kg METH (second comparison group), or an escalating-METH regimen (2-9 mg/kg) for 12 days. On day 13, all four groups were challenged with 10.0 mg/kg METH. Temperature measurements were made telemetrically at 24 degrees C ambient temperature.

RESULTS

Escalating pretreatment produced hyperthermia; with successive exposures, the hyperthermic peak shifted to the right. The 5.0-mg/kg-pretreatment group initially showed no change in temperature at 60 min post-treatment but developed hypothermia at 60 min with chronic treatment; at 3 h post-treatment, significant hyperthermia was present and did not diminish with chronic treatment. After the 10.0-mg/kg-METH challenge, the saline-pretreatment group was hyperthermic, and the 10.0-mg/kg-pretreatment group was hypothermic; the 5.0 mg/kg and escalating pretreatment groups were intermediate and were not different from each other. At 3 h post-challenge, no group differences were apparent. Dopamine (DA) and serotonin (5-HT) were not depleted when measured 2 weeks after treatment ended.

CONCLUSIONS

(1) Escalating and 5.0-mg/kg regimens produced different temperature profiles during the 12-day pretreatment period but a similar diminished response to the 10.0-mg/kg-METH challenge on day 13. (2) The diminished temperature responses with chronic treatment occurred in the absence of long-term DA and 5-HT depletions.

The effects of methamphetamine on core body temperature in the rat--part 1: chronic treatment and ambient temperature

RATIONALE

Stimulants such as methamphetamine (METH) alter core temperature in a manner that is dependent on ambient temperature and that shows tolerance after chronic use. Our objectives were to (1) determine whether tolerance to METH-induced hyperthermia was a consequence of neurotoxicity to dopamine or serotonin and (2) determine the relationship between ambient temperature and chronic treatment on the METH-induced temperature response.

MATERIALS AND METHODS

Rats were treated with 1.0, 5.0, or 10.0 mg/kg METH at 24 degrees C (experiment 1) or treated with 5.0 mg/kg METH at 20 degrees C, 24 degrees C, or 28 degrees C (experiment 2). Treatment occurred for 12 days, and temperature measurements were made once per minute telemetrically during 7-h sessions in computer-regulated environments.

RESULTS

Peak increases in core temperature occurred at 60 min post-treatment for the 1.0 and 10.0 mg/kg doses, and at 180 min for the 5.0 mg/kg dose. Tolerance-like effects were seen with chronic 5.0 (mixed results) and 10.0 mg/kg METH in the absence of dopamine or serotonin depletions measured 2 weeks after the completion of treatment. After 5.0 mg/kg METH, variations in ambient temperature resulted in an early flexible change in core temperature (phase 1) (hyperthermia at 28 degrees and hypothermia at 20 degrees ) and a later inflexible hyperthermia (phase 2).

CONCLUSIONS

The results suggest that (1) the peak effect of different doses of METH occurs at different times (24 degrees ), (2) the diminished temperature response with chronic METH treatment was not associated with long-term dopamine and serotonin depletions, and (3) a two-phase temperature response to METH may reflect two independent mechanisms.

Differential neurochemical consequences of an escalating dose-binge regimen followed by single-day multiple-dose methamphetamine challenges

Chronic intake of methamphetamine (METH) causes tolerance to its behavioral and subjective effects. To better mimic human patterns of drug abuse, the present study used a rodent model that took into account various facets of human drug administration and measured METH-induced effects on brain monoamine levels. Adult male Sprague-Dawley rats were injected with METH or saline according to an escalating dose schedule for 2 weeks. This was followed by a challenge regimen of either saline or one of two doses of METH (3 x 10 mg/kg every 2 h or 6 x 5 mg/kg given every hour, both given within a single day). Both challenge doses of METH caused significant degrees of depletion of dopamine in the striatum and norepinephrine and serotonin in the striatum, cortex, and hippocampus. Animals pre-treated with METH showed significant attenuation of METH-induced striatal dopamine depletion but not consistent attenuation of norepinephrine and serotonin depletion. Unexpectedly, METH pre-treated animals that received the 3 x 10 mg/kg challenge showed less increases in tympanic temperatures than saline pre-treated rats whereas METH pre-treated animals that received the 6 x 5 mg/kg METH challenge showed comparable increases in temperatures to saline pre-treated rats. Therefore, pre-treatment-induced partial protection against monoamine depletion is probably not because of attenuated METH-induced hyperthermia in those rats.