Protein phosphorylation cascades associated with methamphetamine-induced glial activation

Elevated C-reactive protein/albumin ratio in patients with methamphetamine use disorder

BACKGROUND

Methamphetamine use disorder causes significant crises, which have individual, familial, and social consequences. Identifying inflammatory biomarkers for methamphetamine use disorder may be useful for following the inflammatory status of patients in clinical assessment. In this study, we aimed to investigate whether neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR), monocyte/lymphocyte ratio (MLR), C-reactive protein/albumin ratio (CAR) and neutrophil/albumin ratio (NAR) levels can be used as inflammatory biomarkers in methamphetamine use disorder.

METHODS

The sample comprised 139 treatment-seeking participants who met the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria for methamphetamine use disorder and 139 sociodemographically matched controls. Only hospitalised patients were included. An independent sample t-test, Pearson's correlation test, and binominal logistic regression analysis were performed.

RESULTS

CAR (p = 0.016) and NAR (p = 0.048) levels were significantly higher in individuals with methamphetamine use disorder when compared with healthy controls. The CAR level was found to be a significant predictor of group membership in regression analysis for methamphetamine use disorder.

CONCLUSION

CAR may be a potential inflammatory biomarker for patients with methamphetamine use disorder. CAR as a relatively easier-to-measure biomarker could be beneficial to follow the inflammatory status and treatment response of patients.

Nanowired Delivery of Mesenchymal Stem Cells with Antioxidant Compound H-290/51 Reduces Exacerbation of Methamphetamine Neurotoxicity in Hot Environment

Military personnel are often exposed to hot environments either for combat operations or peacekeeping missions. Hot environment is a severe stressful situation leading to profound hyperthermia, fatigue and neurological impairments. To avoid stressful environment, some people frequently use methamphetamine (METH) or other psychostimulants to feel comfortable under adverse situations. Our studies show that heat stress alone induces breakdown of the blood-brain barrier (BBB) and edema formation associated with reduced cerebral blood flow (CBF). On the other hand, METH alone induces hyperthermia and neurotoxicity. These effects of METH are exacerbated at high ambient temperatures as seen with greater breakdown of the BBB and brain pathology. Thus, a combination of METH use at hot environment may further enhance the brain damage-associated behavioral dysfunctions. METH is well known to induce severe oxidative stress leading to brain pathology. In this investigation, METH intoxication at hot environment was examined on brain pathology and to explore suitable strategies to induce neuroprotection. Accordingly, TiO₂-nanowired delivery of H-290/51 (150 mg/kg, i.p.), a potent chain-breaking antioxidant in combination with mesenchymal stem cells (MSCs), is investigated in attenuating METH-induced brain damage at hot environment in model experiments. Our results show that nanodelivery of H-290/51 with MSCs significantly enhanced CBF and reduced BBB breakdown, edema formation and brain pathology following METH exposure at hot environment. These observations are the first to point out that METH exacerbated brain pathology at hot environment probably due to enhanced oxidative stress, and MSCs attenuate these adverse effects, not reported earlier.

Stress- and drug-induced neuroimmune signaling as a therapeutic target for comorbid anxiety and substance use disorders

Stress and substance use disorders remain two of the most highly prevalent psychiatric conditions and are often comorbid. While individually these conditions have a debilitating impact on the patient and a high cost to society, the symptomology and treatment outcomes are further exacerbated when they occur together. As such, there are few effective treatment options for these patients, and recent investigation has sought to determine the neural processes underlying the co-occurrence of these disorders to identify novel treatment targets. One such mechanism that has been linked to stress- and addiction-related conditions is neuroimmune signaling. Increases in inflammatory factors across the brain have been heavily implicated in the etiology of these disorders, and this review seeks to determine the nature of this relationship. According to the "dual-hit" hypothesis, also referred to as neuroimmune priming, prior exposure to either stress or drugs of abuse can sensitize the neuroimmune system to be hyperresponsive when exposed to these insults in the future. This review completes an examination of the literature surrounding stress-induced increases in inflammation across clinical and preclinical studies along with a summarization of the evidence regarding drug-induced alterations in inflammatory factors. These changes in neuroimmune profiles are also discussed within the context of their impact on the neural circuitry responsible for stress responsiveness and addictive behaviors. Further, this review explores the connection between neuroimmune signaling and susceptibility to these conditions and highlights the anti-inflammatory pharmacotherapies that may be used for the treatment of stress and substance use disorders.

Sex, Drugs, and the Medial Amygdala: A Model of Enhanced Sexual Motivation in the Female Rat

Methamphetamine (METH) is a psychomotor stimulant that is reported to enhance sexual desire and behavior in both men and women, leading to increases in unplanned pregnancies, sexually-transmitted infections, and even comorbid psychiatric conditions. Here, we discuss our rodent model of increased sexually-motivated behaviors in which the co-administration of METH and the ovarian hormones, estradiol and progesterone, intensify the incentive properties of a sexual stimulus and increases measures of sexually-motivated behavior in the presence of an androgen-specific cue. We then present the neurobiological mechanisms by which this heightened motivational salience is mediated by the actions of METH and ovarian hormones, particularly progestins, in the posterodorsal medial nucleus of the amygdala (MePD), a key integration site for sexually-relevant sensory information with generalized arousal. We finally demonstrate the cellular and molecular mechanisms underlying this facilitation of sexual motivation by METH, including the upregulation, increased phosphorylation, and activation of progestin receptors (PRs) in the MePD by METH in the presence of ovarian hormones. Taken together, this work extends our understanding of the neurobiology of female sexual motivation.

Identification of cytotoxic markers in methamphetamine treated rat C6 astroglia-like cells

Methamphetamine (METH) is a powerfully addictive psychostimulant that has a pronounced effect on the central nervous system (CNS). The present study aimed to assess METH toxicity in differentiated C6 astroglia-like cells through biochemical and toxicity markers with acute (1 h) and chronic (48 h) treatments. In the absence of external stimulants, cellular differentiation of neuronal morphology was achieved through reduced serum (2.5%) in the medium. The cells displayed branched neurite-like processes with extensive intercellular connections. Results indicated that acute METH treatment neither altered the cell morphology nor killed the cells, which echoed with lack of consequence on reactive oxygen species (ROS), nitric oxide (NO) or inhibition of any cell cycle phases except induction of cytoplasmic vacuoles. On the other hand, chronic treatment at 1 mM or above destroyed the neurite-like processors and decreased the cell viability that paralleled with increased levels of ROS, lipid peroxidation and lactate, depletion in glutathione (GSH) level and inhibition at G0/G1 phase of cell cycle, leading to apoptosis. Pre-treatment of cells with N-acetyl cysteine (NAC, 2.5 mM for 1 h) followed by METH co-treatment for 48 h rescued the cells completely from toxicity by decreasing ROS through increased GSH. Our results provide evidence that increased ROS and GSH depletion underlie the cytotoxic effects of METH in the cells. Since loss in neurite connections and intracellular changes can lead to psychiatric illnesses in drug users, the evidence that we show in our study suggests that these are also contributing factors for psychiatric-illnesses in METH addicts.

Effects of lithium and valproate on ERK/JNK signaling pathway in an animal model of mania induced by amphetamine

Bipolar disorder (BD) is a severe and chronic psychiatric disorder, characterized by recurrent mood episodes of depression and mania. Some studies have indicated that there are ERK and JNK pathways alterations in the brain from bipolar patients. The animal model of mania induced by dextroamphetamine (d-AMPH) has been considered an excellent model to study intracellular alterations related to BD. The present study aimed to evaluate the effects of lithium (Li) and valproate (VPA) on the behavioral and ERK1/2/JNK1/2 signaling pathway in an animal model of mania induced by d-AMPH. Wistar rats were first given d-AMPH or saline (Sal) for 14 days, and then, between the 8th and 14th days, the rats were treated with Li, VPA, or Sal. The open-field test was used to evaluate the locomotion and exploration behaviors of rats. The levels of phosphorylated ERK1/2 and JNK1/2 were assessed in the hippocampus and frontal cortex of the rats. Li and VPA reversed the increased of locomotion and exploration induced by d-AMPH. The treatment with VPA or AMPH per se decreased the levels of pERK1 in the hippocampus. The treatment with VPA in the animals submitted to the administration of d-AMPH decreased the levels of ERK1, JNK-1, and JNK-2 phosphorylated in the hippocampus of the animals. The treatment with Li decreased the JNK-1 phosphorylated in the hippocampus of the animals submitted to the animal model of mania induced by d-AMPH. Although the association of VPA plus amphetamine alters some proteins involved in the JNK pathway in the hippocampus, these alterations were very random and seemed that were not related to the d-AMPH-induced manic-like behavior. These results suggest that the manic-like effects induced by d-AMPH and the antimanic effects of mood stabilizers, Li and VPA, are not related to the alteration on ERK1/2 and JNK1/2 pathways.

Critical Roles of the PI3K-Akt-mTOR Signaling Pathway in Apoptosis and Autophagy of Astrocytes Induced by Methamphetamine

This study aimed to reveal potential roles of the phosphatidylinositol 3 kinase (PI3K)-protein kinase B (Akt)-mammalian target of rapamycin (mTOR) signaling pathway in apoptosis and autophagy of astrocytes induced by methamphetamine (METH). A Cell Counting Kit-8 (CCK-8) was used to determine the reduction in proliferation of U-118 MG cells induced by METH. Hoechst 33258 and flow cytometry were used to observe the astrocytes. Western blot analysis was performed to evaluate protein expression and phosphorylation levels. METH inhibited the proliferation of U-118 MG cells and induced apoptosis and autophagy. Western blot analysis showed that the ratio of LC3-II/I was increased, whereas the expression of Bcl-2 was decreased. The phosphorylation cascade of kinases in the PI3K-Akt-mTOR signaling pathway was significantly inhibited by METH exposure, as were proteins downstream of mTORC1, such as p70s6k, rps6, 4EBP1 and eIF4E. METH inhibited proliferation of U-118 MG cells and induced apoptosis and autophagy. The PI3K-Akt-mTOR signaling pathway likely plays a critical role in these effects.

Metabolites Alterations in the Medial Prefrontal Cortex of Methamphetamine Users in Abstinence: A 1H MRS Study

Background: The medial prefrontal cortex (mPFC) contains various neurotransmitter systems and plays an important role in drug use. Broad body of literature on how methamphetamine (MA) affects the structure and metabolism in the animal's mPFC is emerging, while the effects on metabolites of mPFC among human is still unclear. In this study, proton magnetic resonance spectroscopy (1H MRS) was used to measure metabolites of mPFC in methamphetamine dependent subjects. Methods: Sixty-one subjects with a history of MA dependence (fulfiled the Diagnostic and Statistical Manual of Mental Disorders, fourth edition criteria) and 65 drug-naïve control subjects (age19-45) completed 1H MRS scans using 3.0T Siemens MRI scanner. Single voxel spectra were acquired from the mPFC bilaterally using a point resolved spectroscopy sequence (PRESS). The 1H MRS data were automatically fit with linear combination model for quantification of metabolite levels of n-acetyl-aspartate (NAA), myo-inositol (mI), glycerophosphocholine plus phosphocholine(GPC+PC), phosphocreatine plus creatine (PCr+Cr), and glutamate (Glu). Metabolite levels were reported as ratios to PCr+Cr. Results: The MA group showed a significant reduction in NAA/PCr+Cr ratio and elevation in Glu/PCr+Cr ratio and mI/PCr+Cr ratio, compared with healthy control. No significant correlation was found between metabolite ratios and MA use variables. Conclusions: MA use is associated with a significant increased Glu/PCr+Cr ratio, mI/PCr+Cr ratio and reduced NAA/PCr+Cr ratio in the mPFC of MA dependence subjects. These findings suggest that Glu may play a key role in MA induced neurotoxicity.

Epigenetic Effects Induced by Methamphetamine and Methamphetamine-Dependent Oxidative Stress

Methamphetamine is a widely abused drug, which possesses neurotoxic activity and powerful addictive effects. Understanding methamphetamine toxicity is key beyond the field of drug abuse since it allows getting an insight into the molecular mechanisms which operate in a variety of neuropsychiatric disorders. In fact, key alterations produced by methamphetamine involve dopamine neurotransmission in a way, which is reminiscent of spontaneous neurodegeneration and psychiatric schizophrenia. Thus, understanding the molecular mechanisms operated by methamphetamine represents a wide window to understand both the addicted brain and a variety of neuropsychiatric disorders. This overlapping, which is already present when looking at the molecular and cellular events promoted immediately after methamphetamine intake, becomes impressive when plastic changes induced in the brain of methamphetamine-addicted patients are considered. Thus, the present manuscript is an attempt to encompass all the molecular events starting at the presynaptic dopamine terminals to reach the nucleus of postsynaptic neurons to explain how specific neurotransmitters and signaling cascades produce persistent genetic modifications, which shift neuronal phenotype and induce behavioral alterations. A special emphasis is posed on disclosing those early and delayed molecular events, which translate an altered neurotransmitter function into epigenetic events, which are derived from the translation of postsynaptic noncanonical signaling into altered gene regulation. All epigenetic effects are considered in light of their persistent changes induced in the postsynaptic neurons including sensitization and desensitization, priming, and shift of neuronal phenotype.

Region-specific changes in markers of neuroplasticity revealed in HIV-1 transgenic rats by low-dose methamphetamine

Methamphetamine abuse co-occurring with HIV infection presents neuropathology in brain regions that mediate reward and motivation. A neuronal signaling cascade altered acutely by meth and some HIV-1 proteins is the mitogen-activated protein kinase (MAPK) pathway. It remains unknown if chronic co-exposure to meth and HIV-1 proteins converge on MAPK in vivo. To make this determination, we studied young adult Fischer 344 HIV-1 transgenic (Tg) and non-Tg rats that self-administered meth (0.02-0.04 mg/kg/0.05 ml iv infusion, 2 h/day for 21 days) and their saline-yoked controls. One day following the operant task, rats were killed. Brain regions involved in reward-motivation [i.e., nucleus accumbens (NA) and ventral pallidum (VP)], were assayed for a MAPK cascade protein, extracellular signal-regulated kinase (ERK), and a downstream transcription factor, ΔFosB. In the NA, activated (phosphorylated; p) ERK-to-ERK ratio (pERK/ERK) was increased in meth-exposed Tg rats versus saline Tg controls, and versus meth non-Tg rats. ΔFosB was increased in meth Tg rats versus saline and meth non-Tg rats. Assessment of two targets of ΔFosB-regulated transcription revealed (1) increased dopamine D1 receptor (D1R) immunoreactivity in the NA shell of Tg-meth rats versus saline Tg controls, but (2) no changes in the AMPA receptor subunit, GluA2. No changes related to genotype or meth occurred for ERK, ΔFosB or D1R protein in the VP. Results reveal a region-specific activation of ERK, and increases in ΔFosB and D1R expression induced by HIV-1 proteins and meth. Such effects may contribute to the neuronal and behavioral pathology associated with meth/HIV comorbidity.

Toll-Like Receptor 4 Mediates Methamphetamine-Induced Neuroinflammation through Caspase-11 Signaling Pathway in Astrocytes

Methamphetamine (METH) is an amphetamine-typed stimulant drug that is increasingly being abused worldwide. Previous studies have shown that METH toxicity is systemic, especially targeting dopaminergic neurons in the central nervous system (CNS). However, the role of neuroinflammation in METH neurotoxicity remains unclear. We hypothesized that Toll-like receptor 4 (TLR4) and Caspase-11 are involved in METH-induced astrocyte-related neuroinflammation. We tested our hypothesis by examining the changes of TLR4 and Caspase-11 protein expression in primary cultured C57BL/6 mouse astrocytes and in the midbrain and striatum of mice exposed to METH with western blot and double immunofluorescence labeling. We also determined the effects of blocking Caspase-11 expression with wedelolactone (a specific inhibitor of Caspase-11) or siRNA on METH-induced neuroinflammation in astrocytes. Furthermore, we determined the effects of blocking TLR4 expression with TAK-242 (a specific inhibitor of TLR4) or siRNA on METH-induced neuroinflammation in astrocytes. METH exposure increased Caspase-11 and TLR4 expression both in vitro and in vivo, with the effects in vitro being dose-dependent. Inhibition of Caspase-11 expression with either wedelolactone or siRNAs reduced the expression of inflammasome NLRP3 and pro-inflammatory cytokines. In addition, blocking TLR4 expression inhibited METH-induced activation of NF-κB and Caspase-11 in vitro and in vivo, suggesting that TLR4-Caspase-11 pathway is involved in METH-induced neuroinflammation. These results indicate that Caspase-11 and TLR4 play an important role in METH-induced neuroinflammation and may be potential gene targets for therapeutics in METH-caused neurotoxicity.

HIV-1, methamphetamine and astrocytes at neuroinflammatory Crossroads

As a popular psychostimulant, methamphetamine (METH) use leads to long-lasting, strong euphoric effects. While METH abuse is common in the general population, between 10 and 15% of human immunodeficiency virus-1 (HIV-1) patients report having abused METH. METH exacerbates the severity and onset of HIV-1-associated neurocognitive disorders (HAND) through direct and indirect mechanisms. Repetitive METH use impedes adherence to antiretroviral drug regimens, increasing the likelihood of HIV-1 disease progression toward AIDS. METH exposure also directly affects both innate and adaptive immunity, altering lymphocyte numbers and activity, cytokine signaling, phagocytic function and infiltration through the blood brain barrier. Further, METH triggers the dopamine reward pathway and leads to impaired neuronal activity and direct toxicity. Concurrently, METH and HIV-1 alter the neuroimmune balance and induce neuroinflammation, which modulates a wide range of brain functions including neuronal signaling and activity, glial activation, viral infection, oxidative stress, and excitotoxicity. Pathologically, reactive gliosis is a hallmark of both HIV-1- and METH-associated neuroinflammation. Significant commonality exists in the neurotoxic mechanisms for both METH and HAND; however, the pathways dysregulated in astroglia during METH exposure are less clear. Thus, this review highlights alterations in astrocyte intracellular signaling pathways, gene expression and function during METH and HIV-1 comorbidity, with special emphasis on HAND-associated neuroinflammation. Importantly, this review carefully evaluates interventions targeting astrocytes in HAND and METH as potential novel therapeutic approaches. This comprehensive overview indicates, without a doubt, that during HIV-1 infection and METH abuse, a complex dialog between all neural cells is orchestrated through astrocyte regulated neuroinflammation.

The cross-talk of HIV-1 Tat and methamphetamine in HIV-associated neurocognitive disorders

Antiretroviral therapy has dramatically improved the lives of human immunodeficiency virus 1 (HIV-1) infected individuals. Nonetheless, HIV-associated neurocognitive disorders (HAND), which range from undetectable neurocognitive impairments to severe dementia, still affect approximately 50% of the infected population, hampering their quality of life. The persistence of HAND is promoted by several factors, including longer life expectancies, the residual levels of virus in the central nervous system (CNS) and the continued presence of HIV-1 regulatory proteins such as the transactivator of transcription (Tat) in the brain. Tat is a secreted viral protein that crosses the blood–brain barrier into the CNS, where it has the ability to directly act on neurons and non-neuronal cells alike. These actions result in the release of soluble factors involved in inflammation, oxidative stress and excitotoxicity, ultimately resulting in neuronal damage. The percentage of methamphetamine (MA) abusers is high among the HIV-1-positive population compared to the general population. On the other hand, MA abuse is correlated with increased viral replication, enhanced Tat-mediated neurotoxicity and neurocognitive impairments. Although several strategies have been investigated to reduce HAND and MA use, no clinically approved treatment is currently available. Here, we review the latest findings of the effects of Tat and MA in HAND and discuss a few promising potential therapeutic developments.

Functional alterations of astrocytes in mental disorders: pharmacological significance as a drug target

Astrocytes play an essential role in supporting brain functions in physiological and pathological states. Modulation of their pathophysiological responses have beneficial actions on nerve tissue injured by brain insults and neurodegenerative diseases, therefore astrocytes are recognized as promising targets for neuroprotective drugs. Recent investigations have identified several astrocytic mechanisms for modulating synaptic transmission and neural plasticity. These include altered expression of transporters for neurotransmitters, release of gliotransmitters and neurotrophic factors, and intercellular communication through gap junctions. Investigation of patients with mental disorders shows morphological and functional alterations in astrocytes. According to these observations, manipulation of astrocytic function by gene mutation and pharmacological tools reproduce mental disorder-like behavior in experimental animals. Some drugs clinically used for mental disorders affect astrocyte function. As experimental evidence shows their role in the pathogenesis of mental disorders, astrocytes have gained much attention as drug targets for mental disorders. In this paper, I review functional alterations of astrocytes in several mental disorders including schizophrenia, mood disorder, drug dependence, and neurodevelopmental disorders. The pharmacological significance of astrocytes in mental disorders is also discussed.

Neuroimmune basis of methamphetamine toxicity

Although it is not known which antigen-specific immune responses (or if antigen-specific immune responses) are relevant or required for methamphetamine's neurotoxic effects, it is apparent that methamphetamine exposure is associated with significant effects on adaptive and innate immunity. Alterations in lymphocyte activity and number, changes in cytokine signaling, impairments in phagocytic functions, and glial activation and gliosis have all been reported. These drug-induced changes in immune response, particularly within the CNS, are now thought to play a critical role in the addiction process for methamphetamine dependence as well as for other substance use disorders. In Section 2, methamphetamine's effects on glial cell (e.g., microglia and astrocytes) activity and inflammatory signaling cascades are summarized, including how alterations in immune cell function can induce the neurotoxic and addictive effects of methamphetamine. Section 2 also describes neurotransmitter involvement in the modulation of methamphetamine's inflammatory effects. Section 3 discusses the very recent use of pharmacological and genetic animal models which have helped elucidate the behavioral effects of methamphetamine's neurotoxic effects and the role of the immune system. Section 4 is focused on the effects of methamphetamine on blood-brain barrier integrity and associated immune consequences. Clinical considerations such as the combined effects of methamphetamine and HIV and/or HCV on brain structure and function are included in Section 4. Finally, in Section 5, immune-based treatment strategies are reviewed, with a focus on vaccine development, neuroimmune therapies, and other anti-inflammatory approaches.

p-CREB expression in human gliomas: potential use in the differential diagnosis between astrocytoma and oligodendroglioma

Phosphorylated cyclic-AMP responsive element binding protein (p-CREB) is a transcription factor that is involved in gliomagenesis. For this reason, it was recently proposed as a potential therapeutic target in gliomas; however, gliomas comprise tumors with different biomolecular profile, clinical behavior, and response to chemotherapy. In the present study, we aimed to investigate whether p-CREB expression varies in the 2 main types of gliomas, astrocytomas and oligodendrogliomas. Thus, we analyzed the expression of p-CREB in a series of astrocytomas and oligodendrogliomas of different histologic grades by immunohistochemistry and Western blot analysis. p53 overexpression and the Ki-67 labeling index were also assessed in all the tumors. p-CREB immunohistochemical expression was present in 100% of the astrocytic tumors, but in only 46% of oligodendrogliomas (P = .0033 for grade II; P = .0041 for grade III tumors). Absence of p-CREB immunohistochemical expression was significantly associated with 1p/19q codeletion (P < .0001) and identified 1p/19q codeleted tumors, with 70% sensitivity and 100% specificity (area under the curve = 0.85; P < .0001). In addition, p-CREB expression correlated with higher Ki-67 labeling index (P = .049) and p53 overexpression (P < .0001) as well as with the histologic grade of astrocytomas (P = .044). Immunohistochemical results were further confirmed by Western blot analysis. Our findings demonstrate that astrocytomas and oligodendrogliomas are characterized by distinctive patterns of p-CREB expression. These distinct expression patterns might provide insight into the mechanism of tumorigenesis of glial tumors and represent a useful tool for the differential diagnosis of astrocytoma and oligodendroglioma.

Sigma receptors as potential therapeutic targets for neuroprotection

Sigma receptors comprise a unique family of proteins that have been implicated in the pathophysiology and treatment of many central nervous system disorders, consistent with their high level of expression in the brain and spinal cord. Mounting evidence indicate that targeting sigma receptors may be particularly beneficial in a number of neurodegenerative conditions including Alzheimer׳s disease, Parkinson׳s disease, stroke, methamphetamine neurotoxicity, Huntington׳s disease, amyotrophic lateral sclerosis, and retinal degeneration. In this perspective, a brief overview is given on sigma receptors, followed by a focus on common mechanisms of neurodegeneration that appear amenable to modulation by sigma receptor ligands to convey neuroprotective effects and/or restorative functions. Within each of the major mechanisms discussed herein, the neuroprotective effects of sigma ligands are summarized, and when known, the specific sigma receptor subtype(s) involved are identified. Together, the literature suggests sigma receptors may provide a novel target for combatting neurodegenerative diseases through both neuronal and glial mechanisms.

SN79, a sigma receptor antagonist, attenuates methamphetamine-induced astrogliosis through a blockade of OSMR/gp130 signaling and STAT3 phosphorylation

Methamphetamine (METH) exposure results in dopaminergic neurotoxicity in striatal regions of the brain, an effect that has been linked to an increased risk of Parkinson's disease. Various aspects of neuroinflammation, including astrogliosis, are believed to be contributory factors in METH neurotoxicity. METH interacts with sigma receptors at physiologically relevant concentrations and treatment with sigma receptor antagonists has been shown to mitigate METH-induced neurotoxicity in rodent models. Whether these compounds alter the responses of glial cells within the central nervous system to METH however has yet to be determined. Therefore, the purpose of the current study was to determine whether the sigma receptor antagonist, SN79, mitigates METH-induced striatal reactive astrogliosis. Male, Swiss Webster mice treated with a neurotoxic regimen of METH exhibited time-dependent increases in striatal gfap mRNA and concomitant increases in GFAP protein, indicative of astrogliosis. This is the first report that similar to other neurotoxicants that induce astrogliosis through the activation of JAK2/STAT3 signaling by stimulating gp-130-linked cytokine signaling resulting from neuroinflammation, METH treatment also increases astrocytic oncostatin m receptor (OSMR) expression and the phosphorylation of STAT3 (Tyr-705) in vivo. Pretreatment with SN79 blocked METH-induced increases in OSMR, STAT3 phosphorylation and astrocyte activation within the striatum. Additionally, METH treatment resulted in striatal cellular degeneration as measured by Fluoro-Jade B, an effect that was mitigated by SN79. The current study provides evidence that sigma receptor antagonists attenuate METH-induced astrocyte activation through a pathway believed to be shared by various neurotoxicants.

Sigma (σ) receptors as potential therapeutic targets to mitigate psychostimulant effects

Many psychostimulants, including cocaine and methamphetamine, interact with sigma (σ) receptors at physiologically relevant concentrations. The potential therapeutic relevance of this interaction is underscored by the ability to selectively target σ receptors to mitigate many behavioral and physiological effects of psychostimulants in animal and cell-based model systems. This chapter begins with an overview of these enigmatic proteins. Provocative preclinical data showing that σ ligands modulate an array of cocaine and methamphetamine effects are summarized, along with emerging areas of research. Together, the literature suggests targeting of σ receptors as an innovative option for combating undesired actions of psychostimulants through both neuronal and glial mechanisms.

Traumatic scratch injury in astrocytes triggers calcium influx to activate the JNK/c-Jun/AP-1 pathway and switch on GFAP expression

Astrocyte activation is a hallmark of central nervous system injuries resulting in glial scar formation (astrogliosis). The activation of astrocytes involves metabolic and morphological changes with complex underlying mechanisms, which should be defined to provide targets for astrogliosis intervention. Astrogliosis is usually accompanied by an upregulation of glial fibrillary acidic protein (GFAP). Using an in vitro scratch injury model, we scratched primary cultures of cerebral cortical astrocytes and observed an influx of calcium in the form of waves spreading away from the wound through gap junctions. Using the calcium blocker BAPTA-AM and the JNK inhibitor SP600125, we demonstrated that the calcium wave triggered the activation of JNK, which then phosphorylated the transcription factor c-Jun to facilitate the binding of AP-1 to the GFAP gene promoter to switch on GFAP upregulation. Blocking calcium mobilization with BAPTA-AM in an in vivo stab wound model reduced GFAP expression and glial scar formation, showing that the calcium signal, and the subsequent regulation of downstream signaling molecules, plays an essential role in brain injury response. Our findings demonstrated that traumatic scratch injury to astrocytes triggered a calcium influx from the extracellular compartment and activated the JNK/c-Jun/AP-1 pathway to switch on GFAP expression, identifying a previously unreported signaling cascade that is important in astrogliosis and the physiological response following brain injury.

Substance use disorders: psychoneuroimmunological mechanisms and new targets for therapy

An estimated 76.4 million people worldwide meet criteria for alcohol use disorders, and 15.3 million meet criteria for drug use disorders. Given the high rates of addiction and the associated health, economic, and social costs, it is essential to develop a thorough understanding of the impact of substance abuse on mental and physical health outcomes and to identify new treatment approaches for substance use disorders (SUDs). Psychoneuroimmunology is a rapidly expanding, multidisciplinary area of research that may be of particular importance to addiction medicine, as its focus is on the dynamic and complex interactions among behavioral factors, the central nervous system, and the endocrine and immune systems (Ader, 2001). This review, therefore, focuses on: 1) the psychoneuroimmunologic effects of SUDs by substance type and use pattern, and 2) the current and future treatment strategies, including barriers that can impede successful recovery outcomes. Evidence-based psychosocial and pharmacotherapeutic treatments are reviewed. Psychological factors and central nervous system correlates that impact treatment adherence and response are discussed. Several novel therapeutic approaches that are currently under investigation are introduced; translational data from animal and human studies is presented, highlighting immunotherapy as a promising new direction for addiction medicine.

SN79, a sigma receptor ligand, blocks methamphetamine-induced microglial activation and cytokine upregulation

Methamphetamine (METH) abuse is associated with several negative side effects including neurotoxicity in specific brain regions such as the striatum. The precise molecular mechanisms by which METH usage results in neurotoxicity remain to be fully elucidated, with recent evidence implicating the importance of microglial activation and neuroinflammation in damaged brain regions. METH interacts with sigma receptors which are found in glial cells in addition to neurons. Moreover, sigma receptor antagonists have been shown to block METH-induced neurotoxicity in rodents although the cellular mechanisms underlying their neuroprotection remain unknown. The purpose of the current study was to determine if the prototypic sigma receptor antagonist, SN79, mitigates METH-induced microglial activation and associated increases in cytokine expression in a rodent model of METH-induced neurotoxicity. METH increased striatal mRNA and protein levels of cluster of differentiation 68 (CD68), indicative of microglial activation. METH also increased ionized calcium binding adapter molecule 1 (IBA-1) protein expression, further confirming the activation of microglia. Along with microglial activation, METH increased striatal mRNA expression levels of IL-6 family pro-inflammatory cytokines, leukemia inhibitory factor (lif), oncostatin m (osm), and interleukin-6 (il-6). Pretreatment with SN79 reduced METH-induced increases in CD68 and IBA-1 expression, demonstrating its ability to prevent microglial activation. SN79 also attenuated METH-induced mRNA increases in IL-6 pro-inflammatory cytokine family members. The ability of a sigma receptor antagonist to block METH-induced microglial activation and cytokine production provides a novel mechanism through which the neurotoxic effects of METH may be mitigated.

S-nitrosoglutathione induces ciliary neurotrophic factor expression in astrocytes, which has implications to protect the central nervous system under pathological conditions

Accumulating evidence suggests that reactive astrogliosis has beneficial and detrimental outcomes in various CNS disorders, but the mechanism behind this dichotomy is unclear. Recent advances in this direction suggested that NO signaling is critical to regulate the outcomes of reactive astrogliosis in vivo. Using biochemical and genetic approaches, we here investigated the effect of S-nitrosoglutathione (GSNO; a physiological NO donor) in astrocytes in vitro settings. GSNO enhanced the expressions of glial fibrillary acidic protein and neurotrophic factors including ciliary neurotrophic factor (CNTF) in astrocytes in a dose-dependent manner. The enhanced CNTF expression in GSNO-treated astrocytes was ascribed to NO-mediated sGC/cGMP/PKG signaling. It was associated with p38 MAPK-dependent increased peroxisome proliferator-activated receptor-γ transactivation. In addition, the chromatin accessibility of peroxisome proliferator-activated receptor-γ accompanied with ATF2 and CREB (cAMP-response element-binding protein) was enhanced across the CNTF gene promoter in GSNO treated astrocytes. Interestingly, secreted CNTF was responsible for increased expression of glial fibrillary acidic protein in GSNO-treated astrocytes in an autocrine manner via a JAK2- and STAT3-dependent mechanism. In addition, CNTF secreted by GSNO-treated astrocytes enhanced the differentiation of immature oligodendrocytes in vitro. These effects of GSNO were consistent with an endogenously produced NO in astrocytes stimulated with proinflammatory cytokines in vitro. We conclude that NO signaling induces CNTF expression in astrocytes that favors the beneficial outcomes of reactive astrogliosis in vivo. Our data suggest that the endogenously produced NO or its exogenous source has potential to modulate the outcomes of reactive astrogliosis to protect CNS under pathological conditions.

Maintenance of amphetamine-induced place preference does not correlate with astrocytosis

Astrocytosis, a process in which astrocytes undergo proliferation and enhancement of glial fibrillary acidic protein (GFAP) expression, has been suggested to play important roles in the maintenance of dependence to amphetamine and its derivatives. It was previously shown that mice with genetic deletion of pleiotrophin (PTN), a neurotrophic factor upregulated in different brain areas after administration of amphetamine, show a longer lasting amphetamine-induced conditioned place preference (CPP) when compared to wild type mice. In this work, we aimed to pursue the possibility of a different astrocytic response induced by amphetamine in PTN-/- and PTN+/+ mice, which could underlie the higher vulnerability of PTN-/- mice to maintain amphetamine CPP. In confirmation of previous studies, we found that PTN-/- mice significantly maintained amphetamine (3mg/kg)-induced CPP 5 days after the last drug administration compared to PTN+/+ mice. Interestingly, the number of astrocytes in nucleus accumbens (NAcc), cingulate cortex (CG) and caudate putamen (CPu) did not differ between mice that maintained and did not maintain amphetamine-induced CPP independently of the genotype considered. However, we found that PTN-/- mice showed significantly decreased numbers of astrocytes in CG and CPu compared to PTN+/+ mice independently of whether they maintained amphetamine-induced CPP 5 days after the last drug administration or not. The data demonstrate that maintenance of amphetamine-induced CPP depends on the endogenous expression of PTN. The data tend to discard a correlation between activated astrocytes and maintenance of amphetamine conditioning effects and suggest PTN as a potential modulator of activation of astrocytes after amphetamine treatment.

Taok2 controls behavioral response to ethanol in mice

Despite recent advances in the understanding of ethanol's biological action, many of the molecular targets of ethanol and mechanisms behind ethanol's effect on behavior remain poorly understood. In an effort to identify novel genes, the products of which regulate behavioral responses to ethanol, we recently identified a mutation in the dtao gene that confers resistance to the locomotor stimulating effect of ethanol in Drosophila. dtao encodes a member of the Ste20 family of serine/threonine kinases implicated in MAP kinase signaling pathways. In this study, we report that conditional ablation of the mouse dtao homolog, Taok2, constitutively and specifically in the nervous system, results in strain-specific and overlapping alterations in ethanol-dependent behaviors. These data suggest a functional conservation of dtao and Taok2 in mediating ethanol's biological action and identify Taok2 as a putative candidate gene for ethanol use disorders in humans.

HIV-1, methamphetamine and astrocyte glutamate regulation: combined excitotoxic implications for neuro-AIDS

Glutamate, the most abundant excitatory transmitter in the brain can lead to neurotoxicity when not properly regulated. Excitotoxicity is a direct result of abnormal regulation of glutamate concentrations in the synapse, and is a common neurotoxic mediator associated with neurodegenerative disorders. It is well accepted that methamphetamine (METH), a potent central nervous stimulant with high abuse potential, and human immunodeficiency virus (HIV)-1 are implicated in the progression of neurocognitive malfunction. Both have been shown to induce common neurodegenerative effects such as astrogliosis, compromised blood brain barrier integrity, and excitotoxicity in the brain. Reduced glutamate uptake from neuronal synapses likely leads to the accumulation of glutamate in the extracellular spaces. Astrocytes express the glutamate transporters responsible for majority of the glutamate uptake from the synapse, as well as for vesicular glutamate release. However, the cellular and molecular mechanisms of astrocyte-mediated excitotoxicity in the context of METH and HIV-1 are undefined. Topics reviewed include dysregulation of the glutamate transporters, specifically excitatory amino acid transporter-2, metabotropic glutamate receptor(s) expression and the release of glutamate by vesicular exocytosis. We also discuss glutamate concentration dysregulation through astrocytic expression of enzymes for glutamate synthesis and metabolism. Lastly, we discuss recent evidence of various astrocyte and neuron crosstalk mechanisms implicated in glutamate regulation. Astrocytes play an essential role in the neuropathologies associated with METH/HIV-1-induced excitotoxicity. We hope to shed light on common cellular and molecular pathways astrocytes share in glutamate regulation during drug abuse and HIV-1 infection.

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

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

Sex and temporally-dependent effects of methamphetamine toxicity on dopamine markers and signaling pathways

Methamphetamine induces a greater neurodegenerative effect in male versus female mice. In order to investigate this sex difference we studied the involvement of Akt and extracellular signal-regulated kinase (ERK1/2) in methamphetamine toxicity as a function of time post-treatment (30 min, 1 and 3 days). Methamphetamine-induced decreases in dopamine concentrations and dopamine transporter (DAT) specific binding in the medial striatum were similar in female and male mice when evaluated 1 day post-methamphetamine (40 mg/kg). At 3 days post-methamphetamine, striatal dopamine concentration and DAT specific binding continued to decline in males, whereas females showed a recovery with increases in dopamine content and DAT specific binding in medial striatum at day 3 versus day 1 post-methamphetamine. The reduction in striatal vesicular monoamine transporter 2 specific binding observed at 1 and 3 days post-methamphetamine showed neither a sex- nor temporal-dependent effect. Under the present experimental conditions, methamphetamine treatments had modest effects on dopamine markers measured in the substantia nigra. Proteins assessed by Western blots showed similar reductions in both female and male mice for DAT proteins at 1 and 3 days post-methamphetamine. An increase in the phosphorylation of striatal Akt (after 1 day), glycogen synthase kinase 3β (at 1 and 3 days) and ERK1/2 (30 min post-methamphetamine) was only observed in females. Striatal glial fibrillary acidic protein levels were augmented in both females and males at 3 days post-methamphetamine. These results reveal some of the sex- and temporally-dependent effects of methamphetamine toxicity on dopaminergic markers and suggest some of the signaling pathways associated with these responses.

Implications of central immune signaling caused by drugs of abuse: mechanisms, mediators and new therapeutic approaches for prediction and treatment of drug dependence

In the past two decades a trickle of manuscripts examining the non-neuronal central nervous system immune consequences of the drugs of abuse has now swollen to a significant body of work. Initially, these studies reported associative evidence of central nervous system proinflammation resulting from exposure to the drugs of abuse demonstrating key implications for neurotoxicity and disease progression associated with, for example, HIV infection. However, more recently this drug-induced activation of central immune signaling is now understood to contribute substantially to the pharmacodynamic actions of the drugs of abuse, by enhancing the engagement of classical mesolimbic dopamine reward pathways and withdrawal centers. This review will highlight the key in vivo animal, human, biological and molecular evidence of these central immune signaling actions of opioids, alcohol, cocaine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA). Excitingly, this new appreciation of central immune signaling activity of drugs of abuse provides novel therapeutic interventions and opportunities to identify 'at risk' individuals through the use of immunogenetics. Discussion will also cover the evidence of modulation of this signaling by existing clinical and pre-clinical drug candidates, and novel pharmacological targets. Finally, following examination of the breadth of central immune signaling actions of the drugs of abuse highlighted here, the current known common immune signaling components will be outlined and their impact on established addiction neurocircuitry discussed, thereby synthesizing a common neuroimmune hypothesis of addiction.

The glial cell modulators, ibudilast and its amino analog, AV1013, attenuate methamphetamine locomotor activity and its sensitization in mice

Over 800,000 Americans abuse the psychomotor stimulant, methamphetamine, yet its abuse is without an approved medication. Methamphetamine induces hypermotor activity, and sensitization to this effect is suggested to represent aspects of the addiction process. Methamphetamine's regulation of 3'-5'-cyclic adenosine monophosphate (cAMP) levels may be partially responsible for its behavioral effects, and compounds that inhibit phosphodiesterase (PDE), the enzyme that degrades cAMP, can alter methamphetamine-induced behaviors. Methamphetamine also activates glial cells and causes a subsequent increase in pro-inflammatory cytokine levels. Modulation of glial cell activation is associated with changes in behavioral responses, and substances that oppose inflammatory activity can attenuate drug-induced behaviors. Ibudilast (aka AV411; 3-isobutyryl-2-isopropylpyrazolo-[1,5-a]pyridine), inhibits both PDE and glial pro-inflammatory activity. Ibudilast's amino analog, AV1013, modulates similar glial targets but negligibly inhibits PDE. The present study determined whether ibudilast and AV1013 would attenuate methamphetamine-induced locomotor activity and its sensitization in C57BL/6J mice. Mice were treated b.i.d. with ibudilast (1.8-13 mg/kg), AV1013 (10-56 mg/kg) or their vehicles intraperitoneally for 7 days, beginning 48 h before 5 days of daily 1-h locomotor activity tests. Each test was initiated by either a methamphetamine (3 mg/kg) or a saline injection. Ibudilast significantly (P<0.05) reduced the acute, chronic, and sensitization effects of methamphetamine's locomotor activity without significantly affecting activity by itself. AV1013 had similar anti-methamphetamine effects, suggesting that glial cell activity, by itself, can modulate methamphetamine's effects and perhaps serve as a medication target for its abuse.

Chronic Methamphetamine Causes Differential Expression of Immediate Early Genes in the Nucleus Accumbens and Midbrain of Rats

The present study investigated whether chronic methamphetamine (METH) would suppress METH-induced mRNA expression of immediate early genes (IEGs) in the rat brain. Rats were given METH or saline over two weeks. After an overnight withdrawal, saline- and METH-pretreated rats received an acute saline or METH challenge. The acute METH challenge increased expression of members of activator protein 1 (AP-1) and Nr4a IEG families in the nucleus accumbens (NAc) and midbrain of saline-pretreated rats. Chronic METH exposure attenuated the effects of acute METH challenge on AP-1 IEG expression in the NAc. However, chronic METH failed to attenuate acute METH-induced increases of Nr4a1 and Nr4a3 expression in the NAc. In contrast to observations in the NAc, chronic METH did not prevent acute METH-induced changes in IEG expression in the midbrain. These results suggest that these two brain regions that are implicated in neuroplastic effects of illicit substances might be differentially affected by psychostimulants.

Sex differences in methamphetamine toxicity in mice: effect on brain dopamine signaling pathways

Male mice were reported to display greater methamphetamine-induced neurotoxicity than females. The present study evaluated the involvement of phosphatidylinositol-3 kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK1/2) pathways in this sex-dependent methamphetamine toxicity. Intact female and male mice were administered methamphetamine (20 or 40mg/kg) and euthanized a week later. Dopamine transporter (DAT) and vesicular monoamine transporter 2 (VMAT2) autoradiography in the lateral striatum showed a greater sensitivity in male mice treated with 20mg/kg methamphetamine compared to female mice. Striatal dopamine concentration and DAT autoradiography showed a more extensive depletion in male mice given 40mg/kg methamphetamine compared to female mice. Mice administered 40mg/kg methamphetamine showed no sex difference in striatal VMAT2 autoradiography. In the substantia nigra, DAT specific binding was decreased only in male mice treated with 40mg/kg methamphetamine and DAT mRNA levels decreased in methamphetamine-treated female and male mice. Methamphetamine-treated male mice presented a dose-dependent decrease of VMAT2 mRNA levels. Methamphetamine reduced insulin-like growth factor 1 receptor levels in females at both methamphetamine doses tested whereas it elevated G protein-coupled estrogen receptor 1 (GPER1) only in male mice. Phosphorylated Akt levels decreased only in male mice treated with 40mg/kg methamphetamine. Glycogen synthase kinase 3β levels were reduced in male mice at both methamphetamine doses tested and in females receiving 40mg/kg. Bcl-2 levels were increased in male mice treated with methamphetamine, whereas ERK1/2 and BAD levels were unchanged. These results implicate some of the signaling pathways associated with the sex differences in methamphetamine-induced toxicity.

STAT3 signalling pathway is involved in the activation of microglia induced by 2.45 GHz electromagnetic fields

PURPOSE

Microglia activation plays a pivotal role in the initiation and progression of central nervous system (CNS) insult. The aim of the present work was to investigate the activation of microglia and involvement of signal transducer and activator of transcription 3 (STAT3) in microglia activation after 2.45 GHz electromagnetic fields (EMF) exposure.

MATERIALS AND METHODS

In this study, murine N9 microglial cells were exposed to 2.45 GHz EMF, the protein expressions of STAT3, Janus Tyrosine kinase 1 and 2(JAK1 and JAK2), phosphor-(Try705)STAT3 and DNA binding activity of STAT3 were examined by Western blot analysis and electrophoresis mobility shift assay (EMSA). Levels of the nitric oxide (NO) derivative nitrite were determined in the culture medium by the Griess reaction. The mRNA expression of tumour necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) were detected by reverse transcription and polymerase chain reaction (RT-PCR).

RESULTS

A significant increase of STAT3 DNA-binding ability was noted after exposure. Consistent with this, EMF rapidly induced phosphorylation of STAT3 and activated JAK1 and JAK2. In addition, EMF exposure increased transcription levels of the inflammation-associated genes, iNOS and TNF-alpha, which are reported to contain STAT-binding elements in their promoter region. P6, a JAK inhibitor, reduced induction of iNOS and TNF-alpha, nuclear factor binding activity, and activation of STAT3 in EMF-stimulated microglia.

CONCLUSION

These results provide evidence that EMF exposure can initiate the activation of microglia cells and STAT3 signalling involves in EMF-induced microglial activation.

MAPK induces AQP1 expression in astrocytes following injury

Aquaporin-4 (AQP4) is the principle water channel and the primary route for water transport across astrocytic membranes. AQP4 co-localizes with Kir4.1 channels at astrocytic endfeet, and it has been suggested that these channels cooperate in K(+) and water homeostasis. In response to injury, two additional aquaporins, AQP1 and AQP9, can be detected in astrocytes, yet neither is found in cultured astrocytes, and therefore their contribution to astrocyte water uptake and biology is poorly investigated. In this study, we used a cortical stab wound assay to demonstrate an upregulation of AQP1 following injury in reactive glia. We were able to mimic such injury in astrocytic cultures and show that AQP1 expression is induced within 16 h following injury in vitro. This induction could be blocked by inhibition of MEK1/2 using U0126, and suggests that AQP1 is specifically induced in reactive astrocytes via the mitogen-activated protein kinases signaling pathway.

Differential effects of methamphetamine and SCH23390 on the expression of members of IEG families of transcription factors in the rat striatum

Methamphetamine (METH) is a psychostimulant that can cause long-lasting neurodegenerative effects in humans and animals. These toxic effects appear to occur, in part, via activation of dopamine (DA) D1 receptors. This paper assessed the possibility that the DA D1 receptor antagonist, SCH23390, might inhibit METH-induced changes in the expression of several members of immediate early genes (IEGs) which are known to control more delayed expression of other genes. We found that injections of METH (4x10 mg/kg, given at 2 h intervals) caused significant increases in c-fos and fra-2 expression which lasted from 30 min to 4 h. Pre-treatment with SCH23390, given 30 min before each METH injection, completely blocked METH-induced expression of c-fos, but only partially inhibited fra-2 mRNA expression. These results were confirmed by Western blot analysis which showed METH-induced changes in c-Fos protein expression that were blocked by pretreatment with SCH23390. There were also delayed METH-induced DA D1 receptor-dependent effects on fosB mRNA expression. Even though fra-1 expression was not affected by pretreatment with METH alone, the repeated injections of SCH23390 caused substantial decreases in fra-1 mRNA expression in both the presence and absence of METH. The repeated injections of METH caused no changes in the mRNAs for c-jun, junB or junD. However, there were significant increases in the phosphorylation of c-Jun protein (ser63). Phosphorylation of c-Jun occurred in a delayed fashion (16 and 24 h after the last METH injections) and was attenuated by SCH23390 pretreatment. Interestingly, SCH23390 given alone caused significant decreases in phospho-c-Jun at all time-points. The METH injections also caused delayed induction in the expression of members of the Egr family of transcription factors in a DA D1 receptor-dependent fashion. Repeated injections of SCH23390 caused substantial suppression of basal striatal egr-1 and egr-2 mRNA expression but not of that of egr-3. Both crem and arc mRNA levels were induced by METH in a SCH23390-sensitive fashion. Moreover, multiple injections of SCH23390 given alone caused marked inhibition of basal arc expression. These results show that multiple injections of METH can differentially affect the expression of several IEGs, some of which occurred in a DA D1 receptor dependent fashion. The SCH23390-mediated suppression of basal fra-1, egr-1, and egr-2 mRNA levels suggests that their basal expression in the striatum might be dependent on tonic stimulation of the DA D1 receptor.

Methamphetamine induces heme oxygenase-1 expression in cortical neurons and glia to prevent its toxicity

The impairment of cognitive and motor functions in humans and animals caused by methamphetamine (METH) administration underscores the importance of METH toxicity in cortical neurons. The heme oxygenase-1 (HO-1) exerts a cytoprotective effect against various neuronal injures; however, it remains unclear whether HO-1 is involved in METH-induced toxicity. We used primary cortical neuron/glia cocultures to explore the role of HO-1 in METH-induced toxicity. Exposure of cultured cells to various concentrations of METH (0.1, 0.5, 1, 3, 5, and 10 mM) led to cytotoxicity in a concentration-dependent manner. A METH concentration of 5 mM, which caused 50% of neuronal death and glial activation, was chosen for subsequent experiments. RT-PCR and Western blot analysis revealed that METH significantly induced HO-1 mRNA and protein expression, both preceded cell death. Double and triple immunofluorescence staining further identified HO-1-positive cells as activated astrocytes, microglia, and viable neurons, but not dying neurons. Inhibition of the p38 mitogen-activated protein kinase pathway significantly blocked HO-1 induction by METH and aggravated METH neurotoxicity. Inhibition of HO activity using tin protoporphyrine IX significantly reduced HO activity and exacerbated METH neurotoxicity. However, prior induction of HO-1 using cobalt protoporphyrine IX partially protected neurons from METH toxicity. Taken together, our results suggest that induction of HO-1 by METH via the p38 signaling pathway may be protective, albeit insufficient to completely protect cortical neurons from METH toxicity.

Neuroprotective actions of sex steroids in Parkinson's disease

The sex difference in Parkinson's disease, with a higher susceptibility in men, suggests a modulatory effect of sex steroids in the brain. Numerous studies highlight that sex steroids have neuroprotective properties against various brain injuries. This paper reviews the protective effects of sex hormones, particularly estradiol, progesterone and androgens, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson's disease as compared to methamphetamine toxicity. The molecular mechanisms underlying beneficial actions of sex steroids on the brain have been investigated showing steroid, dose, timing and duration specificities and presently focus is on the dopamine signaling pathways, the next frontier. Both genomic and non-genomic actions of estrogen converge to promote survival factors and show sex differences. Neuroprotection by estrogen involves activation of signaling molecules such as the phosphatidylinositol-3 kinase/Akt and the mitogen-activated protein kinase pathways. Interaction with growth factors, such as insulin-like growth factor 1, also contributes to protective actions of estrogen.

The Role of Glial Cells in Drug Abuse

Neuronal dysfunction in the prefrontal cortex, limbic structures, nucleus accumbens and ventral tegmental area is considered to underlie the general physiopathological mechanisms for substance use disorders. Glutamatergic, dopaminergic and opioidoergic neuronal mechanisms in those brain areas have been targeted in the development of pharmacotherapies for drug abuse and dependence. However, despite the pivotal role of neurons in the mechanisms of addiction, these cells are not the only cell type in charge of sustaining and regulating neurotransmission. Glial cells, particularly astrocytes, play essential roles in the regulation of glutamatergic neurotransmission, neurotransmitter metabolism, and supply of energy substrates for synaptic transmission. In addition, astrocytes are markedly affected by exposure to ethanol and other substances of abuse. These features of astrocytes suggest that alterations in the function of astrocytes and other glial cells in reward circuits may contribute to drug addiction. Recent research has shown that the control of glutamate uptake and the release of neurotrophic factors by astrocytes influences behaviors of addiction and may play modulatory roles in psychostimulant, opiate, and alcohol abuse. Less is known about the contributions of microglia and oligodendrocytes to drug abuse, although, given the ability of these cells to produce growth factors and cytokines in response to alterations in synaptic transmission, further research should better define their role in drug addiction. The available knowledge on the involvement of glial cells in addictive behaviors suggests that regulation of glutamate transport and neurotrophins may constitute new avenues for the treatment of drug addiction.

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

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

Defining "neuroinflammation"

Neuroinflammation is a hot topic in contemporary neuroscience. A relatively new open-access journal, the Journal of Neuroinflammation, focuses on this field. As another example, abstracts to the 2007 Annual Meeting of the Society for Neuroscience could be submitted in several subcategories of neuroinflammation, a strong signal of growth in this research area. While it is becoming clear that activation of microglia and astroglia and the attendant expression of proinflammatory cytokines and chemokines often are associated with disease-, trauma-, and toxicant-induced damage to the CNS, it is by no means clear that a cause-and-effect relationship exists between the presence of a neuroinflammatory process and neural damage. We have explored this issue with two models of dopaminergic neurotoxicity. We used a single low-dose regimen of MPTP or METH, a paradigm that causes selective degeneration of striatal dopaminergic nerve terminals without affecting the cell body in the substantia nigra. Both compounds increased the expression of the microglia-associated factors, Il-1alpha, Il6, Ccl2, and Tnf-alpha, and also elicited morphologic evidence of microglial activation prior to induction of astrogliosis. Pharmacologic antagonism of MPTP and METH neurotoxicity prevented these proinflammatory responses, findings suggestive of a link between neuroinflammation and the observed neurotoxic outcomes. Nevertheless, when we used minocycline to suppress the expression of all these mediators, with the exception of Tnf-alpha, we failed to see neuroprotection. Likewise, when we examined the effects of MPTP or METH in transgenic mice lacking Il6, Ccl2, or Tnfr1/2 genes, deficiency of either Il6 or Ccl2 did not alter neurotoxicity, whereas deficiency in Tnfr1/2 was neuroprotective. Although these observations pointed to a role of the proinflammatory cytokine, TNF-alpha, in the neurotoxic effects of MPTP and METH, other observations did not support this supposition. For example, activation of NF-kappaB or induction of iNOS, known components of inflammatory responses and free radical formation, were not observed. Moreover, immunosuppressive regimens of glucocorticoids failed to suppress TNF-alpha or attenuate neurotoxicity. Taken together, our observations suggest that MPTP and METH neurotoxicity are associated with the elaboration of a "neuroinflammatory" response, yet this response lacks key features of inflammation and, with the exception of TNF-alpha, neurotoxicity appears to be the cause rather than the consequence of proinflammatory signals.

Minocycline restores striatal tyrosine hydroxylase in GDNF heterozygous mice but not in methamphetamine-treated mice

Inflammation, phospho-p38 MAPK activation, and a reduction in glial cell line-derived neurotrophic factor (GDNF) occur in Parkinson's disease. Microglial activation in the substantia nigra and a tyrosine hydroxylase deficit in the striatum of 3-month-old GDNF heterozygous (GDNF(+/-)) mice were previously reported and both were exacerbated by a toxic methamphetamine binge. The current study assessed the effects of minocycline on these methamphetamine-induced effects. Minocycline (45 mg/kg, i.p.x 14 days post-methamphetamine or saline injections) reduced microglial activation and phospho-p38 MAPK in the substantia nigra of saline-treated GDNF(+/-) mice and in methamphetamine-treated wildtype and GDNF(+/-) mice. Although minocycline increased tyrosine hydroxylase-immunoreactivity in GDNF(+/-) mice, it did not attenuate the methamphetamine-induced reduction of tyrosine hydroxylase. The results suggest that neuroinflammation is deleterious to the dopamine system of GDNF(+/-) mice but is not the primary cause of methamphetamine-induced damage to the dopamine system in either GDNF(+/-) or wildtype mice.

Induction of activating transcription factors (ATFs) ATF2, ATF3, and ATF4 in the nucleus accumbens and their regulation of emotional behavior

Previous research has shown that cAMP response element (CRE) binding protein (CREB) in the nucleus accumbens gates behavioral responses to emotional stimuli. For example, overexpression of CREB decreases anxiety, sucrose preference, and sensitivity to drugs of abuse and increases depression-like behavior, whereas blocking CREB via overexpression of inducible cAMP early repressor (ICER) or other dominant-negative inhibitors of CRE-mediated transcription has the opposite effects. However, CREB and ICER are but two members of a larger family of leucine zipper-containing transcription factors composed of multiple products of the creb, crem (cAMP response element modulator), and atf (activating transcription factor) genes. We demonstrate here that ATF2, ATF3, and ATF4 are each robustly induced in the nucleus accumbens and dorsal striatum by restraint stress or by amphetamine administration. In contrast, little induction is seen for ATF1 or CREM. Using viral-mediated gene transfer, we show that ATF2 overexpression in nucleus accumbens produces increases in emotional reactivity and antidepressant-like responses, a behavioral phenotype similar to that caused by dominant-negative antagonists of CREB. In contrast, ATF3 or ATF4 overexpression in nucleus accumbens decreases emotional reactivity and increases depression-like behavior, consistent with the behavioral phenotype induced by CREB. Because amphetamine and stress induce ATF2, ATF3, and ATF4 in nucleus accumbens, and overexpression of these transcription factors in this brain region in turn alters behavioral responsiveness to amphetamine and stress, our findings support novel roles for these ATF family members in regulating emotional behavior.

Inducible IL-23p19 expression in human microglia via p38 MAPK and NF-kappaB signal pathways

Activated microglia can release a variety of proinflammatory cytokines that play a crucial role in the pathogenesis of multiple sclerosis (MS). IL-23, a novel proinflammatory cytokine, is required for the induction of experimental autoimmune encephalomyelitis. Previously we demonstrated that IL-23 is expressed in MS lesions and that microglia are one cellular source of IL-23 in MS patients. In the present study we investigated the inducible expression and regulation of p19, a key subunit of IL-23, in human microglia. We demonstrated the inducible expression of IL-23p19 by lipopolysaccharide-stimulated microglial cells. Using signaling pathway-specific inhibitors, we showed that blocking p38 MAP kinase or NF-kappaB signaling pathway significantly reduced p19 expression in microglia. The regulatory role of p38 MAP kinase in p19 expression was further confirmed by decreased expression in microglia transduced with dominant-negative p38. We concluded that the p38 MAP kinase and NF-kappaB signaling pathways play an important role in regulation of IL-23p19 expression on human microglia, and are thus potential therapeutic targets in the treatment of MS.

Structural and metabolic brain changes in the striatum associated with methamphetamine abuse

AIMS

To review structural, chemical and metabolic brain changes, particularly those in the basal ganglia, in individuals who used methamphetamine, as well as in children with prenatal methamphetamine exposure.

METHODS

Magnetic resonance imaging (MRI) and positron emission tomography (PET) studies that evaluated brain structural, chemical and metabolite changes in methamphetamine subjects, or children with prenatal methamphetamine exposure, were reviewed and summarized. Relevant pre-clinical studies that provided insights to the interpretations of these imaging studies were also reviewed.

RESULTS

In adults who used methamphetamine, MRI demonstrates enlarged striatal volumes, while MR spectroscopy shows reduced concentrations of the neuronal marker N-acetylasparate and total creatine in the basal ganglia. In contrast, children with prenatal methamphetamine exposure show smaller striatal structures and elevated total creatine. Furthermore, PET studies consistently showed reduced dopamine transporter (DAT) density and reduced dopamine D(2) receptors in the striatum of methamphetamine subjects. PET studies also found lower levels of serotonergic transporter density and vesicular monoamine transporter (VMAT2) across striatal subregions, as well as altered brain glucose metabolism that correlated with severity of psychiatric symptoms in the limbic and orbitofrontal regions.

CONCLUSION

Neuroimaging studies demonstrate abnormalities in brain structure and chemistry convincingly in individuals who used methamphetamine and in children with prenatal methamphetamine exposure, especially in the striatum. However, many important questions remain and larger sample sizes are needed to validate these preliminary observations. Furthermore, longitudinal studies are needed to evaluate the effects of treatment and abstinence on these brain changes and to determine whether imaging, and possibly genetic, markers can be used to predict treatment outcome or relapse.

Statins induce differentiation and cell death in neurons and astroglia

Statins are potent inhibitors of the hydroxy-methyl-glutaryl-coenzyme A reductase, the rate limiting enzyme for cholesterol biosynthesis. Experimental and clinical studies with statins suggest that they have beneficial effects on neurodegenerative disorders. Thus, it was of interest to characterize the direct effects of statins on CNS neurons and glial cells. We have treated defined cultures of neurons and astrocytes of newborn rats with two lipophilic statins, atorvastatin and simvastatin, and analyzed their effects on morphology and survival. Treatment of astrocytes with statins induced a time- and dose-dependent stellation, followed by apoptosis. Similarly, statins elicited programmed cell death of cerebellar granule neurons but with a higher sensitivity. Analysis of different signaling cascades revealed that statins fail to influence classical pathways such as Akt or MAP kinases, known to be activated in CNS cells. In addition, astrocyte stellation triggered by statins resembled dibutryl-cyclic AMP (db-cAMP) induced morphological differentiation. However, in contrast to db-cAMP, statins induced upregulation of low-density lipoprotein receptors, without affecting GFAP expression, indicating separate underlying mechanisms. Analysis of the cholesterol biosynthetic pathway revealed that lack of mevalonate and of its downstream metabolites, mainly geranylgeranyl-pyrophosphate (GGPP), is responsible for the statin-induced apoptosis of neurons and astrocytes. Moreover, astrocytic stellation triggered by statins was inhibited by mevalonate and GGPP. Interestingly, neuronal cell death was significantly reduced in astrocyte/neuron co-cultures treated with statins. We postulate that under these conditions signals provided by astrocytes, e.g., isoprenoids play a key role in neuronal survival.