Improvement by minocycline of methamphetamine-induced impairment of recognition memory in mice

A Review on the Disruption of Novel Object Recognition Induced by Methamphetamine

Background

Methamphetamine (MA), is a widely abused synthetic psychostimulant that leads to irreversible brain damage manifested as cognitive impairments in humans and animals. The novel object recognition (NOR) task is a commonly used behavioral assay for the investigation of non-spatial memory in rodents. This test is based on the natural tendency of rodents to spend more time exploring a novel object than a familiar one. NOR test has been used in many studies investigating cognitive deficits caused by MA in rodents. The objective of the present study was to review neurobiological mechanisms that might be responsible for MA-induced NOR alterations.

Methods

A PubMed search showed 83 publications using novel object recognition and methamphetamine as keywords in the past 10 years.

Findings

The present study revealed different MA regimens cause recognition memory impairment in rodents. In addition, it was found that the main neurobiological mechanism involved in MA-induced recognition deficits is the dysfunction of monoaminergic systems.

Conclusion

NOR is a useful test to assess the cognitive functions following MA administration and evaluate the efficacy of new therapeutic agents in MA-addicted individuals.

Ginsenoside Re blocks Bay k-8644-induced neurotoxicity via attenuating mitochondrial dysfunction and PKCδ activation in the hippocampus of mice: Involvement of antioxidant potential

Although the anticonvulsant effects of ginsenosides are recognized, little is known about their effects on the convulsive behaviors induced by the activation of L-type Ca²⁺ channels. Here, we investigated whether ginsenoside Re (GRe) modulates excitotoxicity induced by the L-type Ca²⁺ channel activator Bay k-8644. GRe significantly attenuated Bay k-8644-induced convulsive behaviors and hippocampal oxidative stress in mice. GRe-mediated antioxidant potential was more pronounced in the mitochondrial fraction than cytosolic fraction. As L-type Ca²⁺ channels are thought to be targets of protein kinase C (PKC), we investigated the role of PKC under excitotoxic conditions. GRe attenuated Bay k-8644-induced mitochondrial dysfunction, PKCδ activation, and neuronal loss. The PKCδ inhibition and neuroprotection mediated by GRe were comparable to those by the ROS inhibitor N-acetylcysteine, the mitochondrial protectant cyclosporin A, the microglial inhibitor minocycline, or the PKCδ inhibitor rottlerin. Consistently, the GRe-mediated PKCδ inhibition and neuroprotection were counteracted by the mitochondrial toxin 3-nitropropionic acid or the PKC activator bryostatin-1. GRe treatment did not have additional effects on PKCδ gene knockout-mediated neuroprotection, suggesting that PKCδ is a molecular target of GRe. Collectively, our results suggest that GRe-mediated anticonvulsive/neuroprotective effects require the attenuation of mitochondrial dysfunction and altered redox status and inactivation of PKCδ.

Inhibition of glycolysis prevents behavioural changes in mice with MK801-induced SCZ model by alleviating lactate accumulation and lactylation

Schizophrenia (SCZ) is a debilitating neuropsychiatric disorder with a complex aetiology. Cognitive symptoms and hippocampal changes have been implicated in the pathophysiology of SCZ. Changes in metabolites level and up-regulated glycolysis have been reported in previous studies, which may be related to the hippocampal dysfunction in SCZ. However, the pathological mechanism of glycolysis involved in the pathogenesis of SCZ remains unclear. Therefore, the change of glycolysis level and the involvement in SCZ need to be further studied. In our study, MK801 was used to induce an SCZ mouse model and cell model in vivo and in vitro. Western blotting was performed to evaluate the levels of glycolysis, metabolites, and lactylation in hippocampal tissue of mice with SCZ or cell models. The level of high mobility group protein 1 (HMGB1) in the medium of MK801-treated primary hippocampal neurons was examined. Apoptosis was evaluated in HMGB1-treated hippocampal neurons by flow cytometry. The glycolysis inhibitor 2-DG prevented behavioural changes in the MK801-induced SCZ mouse model. The lactate accumulation and level of lactylation were alleviated in the hippocampal tissue of MK801-treated mice. Glycolysis was enhanced, and lactate accumulated in MK-801-treated primary hippocampal neurons. In addition, the level of HMGB1 increased in the medium and induced apoptosis in primary hippocampal neurons. Together, the data showed that glycolysis and lactylation increased in the MK801-induced SCZ model in vivo and in vitro, and this effect could be prevented by 2-DG (a glycolysis inhibitor). Glycolytic related HMGB1 upregulation may induce apoptosis in hippocampal neurons downstream.

Adolescent microglia stimulation produces long-lasting protection against chronic stress-induced behavioral abnormalities in adult male mice

Our previous studies had reported that microglia activation one day before stress exposure prevented the behavioral abnormalities induced by chronic stress in adult mice, and a 10-day interval between microglia stimulation and stress exposure can abolish the prophylactic effect of LPS preinjection on the behavioral abnormalities induced by chronic stress, which, however, could be rescued by repeated LPS injection. This suggests that increased stimulation of microglia results in animals developing a strong ability to prevent deleterious stress stimuli. Because microglia in the adolescent brain exhibit flexible immunological plasticity, we hypothesize that a single low-dose LPS injection during adolescence may provide long-lasting protection against behavioral abnormalities induced by chronic stress in adult mice. As expected, our results showed that a single injection of LPS (100 μg/kg) at post-natal day 28 (PND 28) prevented the development of abnormal behaviors and shifted neuroinflammatory responses toward an anti-inflammatory phenotype in adult mice treated with CSDS at their different stages of the age (PND 56, 140, and 252). Moreover, pretreatment with minocycline or PLX3397 to inhibit microglial activation abolished the prophylactic effect of LPS preinjection after PND 28 on behavioral abnormalities and neuroinflammatory responses induced by CSDS in adult mice at their different stages of the age, PND 56, 140, and 252. These results indicate that stimulation of microglia in adolescence may confer long-lasting protection against neuroinflammatory responses and behavioral abnormalities induced by chronic stress in adult mice. This may offer the potential for the development of a "vaccine-like strategy" to prevent mental disorders.

Linking Inflammation, Aberrant Glutamate-Dopamine Interaction, and Post-synaptic Changes: Translational Relevance for Schizophrenia and Antipsychotic Treatment: a Systematic Review

Evidence from clinical, preclinical, and post-mortem studies supports the inflammatory/immune hypothesis of schizophrenia pathogenesis. Less evident is the link between the inflammatory background and two well-recognized functional and structural findings of schizophrenia pathophysiology: the dopamine-glutamate aberrant interaction and the alteration of dendritic spines architecture, both believed to be the “quantal” elements of cortical-subcortical dysfunctional network. In this systematic review, we tried to capture the major findings linking inflammation, aberrant glutamate-dopamine interaction, and post-synaptic changes under a direct and inverse translational perspective, a paramount picture that at present is lacking. The inflammatory effects on dopaminergic function appear to be bidirectional: the inflammation influences dopamine release, and dopamine acts as a regulator of discrete inflammatory processes involved in schizophrenia such as dysregulated interleukin and kynurenine pathways. Furthermore, the link between inflammation and glutamate is strongly supported by clinical studies aimed at exploring overactive microglia in schizophrenia patients and maternal immune activation models, indicating impaired glutamate regulation and reduced N-methyl-D-aspartate receptor (NMDAR) function. In addition, an inflammatory/immune-induced alteration of post-synaptic density scaffold proteins, crucial for downstream NMDAR signaling and synaptic efficacy, has been demonstrated. According to these findings, a significant increase in plasma inflammatory markers has been found in schizophrenia patients compared to healthy controls, associated with reduced cortical integrity and functional connectivity, relevant to the cognitive deficit of schizophrenia. Finally, the link between altered inflammatory/immune responses raises relevant questions regarding potential new therapeutic strategies specifically for those forms of schizophrenia that are resistant to canonical antipsychotics or unresponsive to clozapine.

Exploring the role and mechanism of gut microbiota in methamphetamine addiction using antibiotic treatment followed by fecal microbiota transplantation

Recently, the role of the gut microbiota in the context of drug addiction has attracted the attention of researchers; however, the specific effects and underlying mechanisms require further exploration. To accomplish this, C57BL/6 mice were firstly treated with methamphetamine (MA). Conditioned place preference (CPP) behavior changes, gut permeability and function, microglial activation, and inflammatory cytokine expression were systematically analyzed in antibiotics-treated mice with microbiota depletion and in fecal microbiota transplantation mice with microbiota reconstitution. MA treatment altered microbiota composition and caused gut dysbiosis. Depletion of gut microbiota with antibiotics inhibited MA-induced CPP formation, and fecal microbiota transplantation reversed this inhibition. Mechanistic analyses indicated that antibiotic treatment decreased gut permeability and neuroinflammation, while fecal microbiota transplantation offset the impact of antibiotic treatment. Additionally, MA-induced microglial activation was suppressed by antibiotics but restored by microbiota transplantation, and this correlated well with the CPP score. Compared to antibiotic treatment, microbiota transplantation significantly increased 5-HT4 receptor expression in both the nucleus accumbens and the hippocampus. Furthermore, when fecal microbiota from healthy mice was transplanted into MA-treated mice, the CPP scores decreased. Our results provide a novel avenue for understanding MA addiction and suggest a potential future intervention strategy.

Innate immune stimulation prevents the development of anxiety-like behaviors in chronically stressed mice

Anxiety is a common psychological disease which can induce severe social burdens. Searching methods that prevent the onset of anxiety is of great significance for ameliorating the social and individual problems induced by this type of disease. In this study, we investigated how innate immune pre-stimulation influences the anxiety-like behaviors in chronically stressed mice. Our results showed that a single injection of an innate immune stimulant lipopolysaccharide (LPS) at the dose of 50, 100, and 500 μg/kg 1 day before stress exposure prevented chronic social defeat stress (CSDS)-induced anxiety-like behaviors in mice. A single injection of LPS (100 μg/kg) 5 days before stress exposure produced similar preventive effects on CSDS-induced anxiety-like behaviors, while similar effects were not observed at the condition of 10-days interval between LPS injection and stress exposure. A second LPS injection 10 days after the first LPS injection or a 4 × LPS injection 10 days before stress exposure also prevented CSDS-induced anxiety-like behaviors. Moreover, a single injection of LPS (100 μg/kg) 1 day before stress exposure prevented the production of pro-inflammatory cytokines in the hippocampus and prefrontal cortex of CSDS mice. Suppression of innate immune stimulation by minocycline pretreatment simultaneously abrogated the preventive effect of LPS pre-injection (100 μg/kg) on CSDS-induced anxiety-like behaviors and pro-inflammatory cytokine production in the brain. Our results demonstrated that the pre-stimulation of the innate immune system can prevent the development of anxiety-like behaviors and the progression of the neuroinflammatory responses in the brain in chronically stressed mice.

Melatonin ameliorates methamphetamine-induced cognitive impairments by inhibiting neuroinflammation via suppression of the TLR4/MyD88/NFκB signaling pathway in the mouse hippocampus

Methamphetamine (METH) is a highly addictive psychostimulant that causes significant health issues due to high prevalence of its illegal use. Chronic use of METH is associated with cognitive impairments in both human and animal studies, but the underlying mechanism remains unclear. METH-induced neuroinflammation is, potentially, one of the factors that causes cognitive impairments. Therefore, the present study aimed to assess whether melatonin could provide protection against inflammation, in a manner comparable to the anti-inflammatory agent, minocycline, with consequent improvements of METH-induced cognitive impairments and associated abnormalities in the mouse hippocampus. Results from the Morris water maze (MWM) test and the novel object recognition test (NORT) showed that melatonin given after METH injections could ameliorate both METH-induced spatial and recognition memory impairments. These memory impairments are associated with changes in the neuroinflammatory profiles, including IL-6, IL-1β, and TNF-α, both in the blood serum and hippocampus of adult mice. METH-treated mice also exhibited reactive astrocytes and activated microglia in the hippocampus. METH-induced activation of glial cells is associated with the activation of the TLR4/MyD88/NFκB signaling pathway. Moreover, melatonin administration led to recovery of these METH-induced markers to control levels. Thus, we conclude that melatonin could potentially be used as a cognitive enhancer and anti-inflammatory agent in the treatment of METH use disorder in humans.

New Insights Regarding Diagnosis and Medication for Schizophrenia Based on Neuronal Synapse-Microglia Interaction

Schizophrenia is a common psychiatric disorder that usually develops during adolescence and young adulthood. Since genetic and environmental factors are involved in the disease, the molecular status of the pathology of schizophrenia differs across patients. Recent genetic studies have focused on the association between schizophrenia and the immune system, especially microglia–synapse interactions. Microglia physiologically eliminate unnecessary synapses during the developmental period. The overactivation of synaptic pruning by microglia is involved in the pathology of brain disease. This paper focuses on the synaptic pruning function and its molecular machinery and introduces the hypothesis that excessive synaptic pruning plays a role in the development of schizophrenia. Finally, we suggest a strategy for diagnosis and medication based on modulation of the interaction between microglia and synapses. This review provides updated information on the involvement of the immune system in schizophrenia and proposes novel insights regarding diagnostic and therapeutic strategies for this disease.

Novel object recognition memory in REM sleep-deprived rats: Role of the cannabinoid CB1 receptor

A survey of the literature indicates that both rapid eye movement sleep deprivation (RSD) and activation of cannabinoid CB₁ receptor (CB₁R) may impair novel object recognition (NOR) memory in rodents. To our knowledge, so far, no previous study has investigated the probable effects of RSD on the different phases of NOR memory. Moreover, far too little attention has been paid to the potential role of the CB₁R in the effects of RSD on object memory. Therefore, the major objective of this study was to investigate the probable role of the CB₁R in the acquisition, consolidation, retrieval, and reconsolidation of NOR memory in the RSD rats. A 12-h paradigm of RSD using the multiple platform method did not affect acquisition, but it impaired the consolidation, retrieval, and reconsolidation of NOR memory. Administration of the CB₁R antagonist rimonabant (1 or 3 mg/kg, i.p.) did not have significant effects on the acquisition and reconsolidation, but it improved RSD-induced impairment of the consolidation and retrieval of object memory, especially at the dose of 3 mg/kg. In addition, the RSD paradigm did not affect the levels of plasma corticosterone as an important marker of stress in rat. The results revealed that RSD may have different effects on the different phases of NOR memory which may not be attributable to the effects of stress. Our findings would seem to suggest that the CB₁R can be targeted to, at least partially, modulate the adverse effects of RSD on the process of NOR memory.

The effect of minocycline on amelioration of cognitive deficits and pro-inflammatory cytokines levels in patients with schizophrenia

BACKGROUND

Cognitive deficits of schizophrenia are predictors of poor function, but antipsychotic medication has limited efficacy for cognitive deficits. These deficits in learning and memory may result from activity of pro-inflammatory cytokines, which microglia produce. The microglia inhibitor minocycline might arrest this cytokine damage to the hippocampus and reverse the cognitive deficits of schizophrenia.

METHODS

A double-blind, placebo-controlled study involved 75 patients with schizophrenia who randomly received low dose (100 mg/day) or high dose minocycline (200 mg/day) or placebo added to risperidone. MATRICS Consensus Cognitive Battery (MCCB) was used to assess the cognitive functioning, and serum levels of Interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) were assessed.

RESULTS

Minocycline_{high dose} group was significantly superior to minocycline_{low dose} or placebo group not only for the improvements in cognitive tests' scores as well (P < 0.05), but for IL-1β and IL-6 serum levels reduction (P < 0.01). The amelioration of cognitive deficits with minocycline correlated not only with the remission of negative symptoms, but also with the reduction in serum levels of IL-1β and IL-6.

CONCLUSIONS

Minocycline adjunctive treatment was effective in improving cognitive deficits of patients with schizophrenia. The beneficial effect of minocycline may be related to reducing pro-inflammatory cytokines through microglia inhibition.

COX-2 Inhibitors, Aspirin, and Other Potential Anti-Inflammatory Treatments for Psychiatric Disorders

Inflammatory processes associated with persistent (chronic) infection have long been discussed as etiological factors in psychiatric disorders. Studies have found that people with major depression have higher levels of pro-inflammatory cytokines, for example, IL-1, IL-6, and tumor necrosis factor-alpha, and C-reactive protein. In schizophrenia, many reports have described raised levels of cytokines, for example, IL-6; and meta-analyses have confirmed these findings. Microglia cells are important in inflammatory processes, and positron emission tomography studies have shown microglia activation in both depression and schizophrenia.As a consequence of the above findings, immunomodulation is widely discussed as a potential treatment approach in both major depression and schizophrenia. The COX-2 inhibitor celecoxib was found to have a significant positive effect on major depression, not only in single studies but also in meta-analyses. Celecoxib has also been studied in schizophrenia and has shown efficacy, in particular, in early disease stages. The mixed COX inhibitor aspirin (acetylsalicylic acid) seems to have both protective and therapeutic effects on schizophrenia.This paper discusses the hypothesized role of inflammation in major depression and schizophrenia, including markers of inflammation; pertinent studies on celecoxib and aspirin; and additional immunomodulatory therapeutic strategies.

Downregulation of HCN1 channels in hippocampus and prefrontal cortex in methamphetamine re-exposed mice with enhanced working memory

The hyperpolarization-activated cyclic-nucleotide-gated non-selective cation (HCN) channels play a potential role in the neurological basis underlying drug addiction. However, little is known about the role of HCN channels in methamphetamine (METH) abuse. In the present study, we examined the changes in working memory functions of METH re-exposed mice through Morris water maze test, and investigated the protein expression of HCN1 channels and potential mechanisms underlying the modulation of HCN channels by Western blotting analysis. Mice were injected with METH (1 mg/kg, i.p.) once per day for 6 consecutive days. After 5 days without METH, mice were re-exposed to METH at the same concentration. We found that METH re-exposure caused an enhancement of working memory, and a decrease in the HCN1 channels protein expression in both hippocampus and prefrontal cortex. The phosphorylated extracellular regulated protein kinase 1/2 (p-ERK1/2), an important regulator of HCN channels, was also obviously reduced in hippocampus and prefrontal cortex of mice with METH re-exposure. Meanwhile, acute METH exposure did not affect the working memory function and the protein expressions of HCN1 channels and p-ERK1/2. Overall, our data firstly showed the aberrant protein expression of HCN1 channels in METH re-exposed mice with enhanced working memory, which was probably related to the down-regulation of p-ERK1/2 protein expression.

Glial mechanisms underlying substance use disorders

Addiction is a devastating disorder that produces persistent maladaptive changes to the central nervous system, including glial cells. Although there is an extensive body of literature examining the neuronal mechanisms of substance use disorders, effective therapies remain elusive. Glia, particularly microglia and astrocytes, have an emerging and meaningful role in a variety of processes beyond inflammation and immune surveillance, and may represent a promising therapeutic target. Indeed, glia actively modulate neurotransmission, synaptic connectivity and neural circuit function, and are critically poised to contribute to addictive-like brain states and behaviors. In this review, we argue that glia influence the cellular, molecular, and synaptic changes that occur in neurons following drug exposure, and that this cellular relationship is critically modified following drug exposure. We discuss direct actions of abused drugs on glial function through immune receptors, such as Toll-like receptor 4, as well as other mechanisms. We highlight how drugs of abuse affect glia-neural communication, and the profound effects that glial-derived factors have on neuronal excitability, structure, and function. Recent research demonstrates that glia have brain region-specific functions, and glia in different brain regions have distinct contributions to drug-associated behaviors. We will also evaluate the evidence demonstrating that glial activation is essential for drug reward and drug-induced dopamine release, and highlight clinical evidence showing that glial mechanisms contribute to drug abuse liability. In this review, we synthesize the extensive evidence that glia have a unique, pivotal, and underappreciated role in the development and maintenance of addiction.

Inflammation in Schizophrenia: Pathogenetic Aspects and Therapeutic Considerations

This paper discusses the current evidence from animal and human studies for a central role of inflammation in schizophrenia. In animal models, pre- or perinatal elicitation of the immune response may increase immune reactivity throughout life, and similar findings have been described in humans. Levels of pro-inflammatory markers, such as cytokines, have been found to be increased in the blood and cerebrospinal fluid of patients with schizophrenia. Numerous epidemiological and clinical studies have provided evidence that various infectious agents are risk factors for schizophrenia and other psychoses. For example, a large-scale epidemiological study performed in Denmark clearly showed that severe infections and autoimmune disorders are such risk factors. The vulnerability-stress-inflammation model may help to explain the role of inflammation in schizophrenia because stress can increase pro-inflammatory cytokines and may even contribute to a chronic pro-inflammatory state. Schizophrenia is characterized by risk genes that promote inflammation and by environmental stress factors and alterations of the immune system. Typical alterations of dopaminergic, serotonergic, noradrenergic, and glutamatergic neurotransmission described in schizophrenia have also been found in low-level neuroinflammation and consequently may be key factors in the generation of schizophrenia symptoms. Further support for the relevance of a low-level neuroinflammatory process in schizophrenia is provided by the loss of central nervous system volume and microglial activation demonstrated in neuroimaging studies. Last but not least, the benefit of anti-inflammatory medications found in some studies and the intrinsic anti-inflammatory and immunomodulatory effects of antipsychotics provide further support for the role of inflammation in this debilitating disease.

Immunological aspects of the treatment of depression and schizophrenia

Schizophrenia and major depression (MD) have been associated with immune system dysfunction. One example of this is the altered level of cytokines—important inflammatory mediators—in blood, and a proinflammatory immune state has been described in some subgroups of patients. A knock to the immune system in early life might trigger a life-long increased immune reactivity, and infections and autoimmune disorders are now known to be risk factors for development of schizophrenia and MD. Pro- and anti-inflammatory cytokines mediate indoleamine 2,3-dioxygenase activity; this enzyme drives metabolism of tryptophan and kynurenin in the central nervous system and degrades serotonin. Alterations of serotonergic, noradrenergic, and glutamatergic neurotransmission have been associated with low-level neuroinflammation, and anti-inflammatory compounds have a therapeutic benefit in MD and schizophrenia, as shown in meta-analyses. Moreover, antidepressants and antipsychotics have intrinsic immunomodulatory effects. With evidence pointing to the role inflammatory processes play in the pathogenesis of major psychiatric disorders, this review will look at various immunological aspects of treatment of such disorders.

Cannabinoids and Vanilloids in Schizophrenia: Neurophysiological Evidence and Directions for Basic Research

Much of our knowledge of the endocannabinoid system in schizophrenia comes from behavioral measures in rodents, like prepulse inhibition of the acoustic startle and open-field locomotion, which are commonly used along with neurochemical approaches or drug challenge designs. Such methods continue to map fundamental mechanisms of sensorimotor gating, hyperlocomotion, social interaction, and underlying monoaminergic, glutamatergic, and GABAergic disturbances. These strategies will require, however, a greater use of neurophysiological tools to better inform clinical research. In this sense, electrophysiology and viral vector-based circuit dissection, like optogenetics, can further elucidate how exogenous cannabinoids worsen (e.g., tetrahydrocannabinol, THC) or ameliorate (e.g., cannabidiol, CBD) schizophrenia symptoms, like hallucinations, delusions, and cognitive deficits. Also, recent studies point to a complex endocannabinoid-endovanilloid interplay, including the influence of anandamide (endogenous CB₁ and TRPV₁ agonist) on cognitive variables, such as aversive memory extinction. In fact, growing interest has been devoted to TRPV₁ receptors as promising therapeutic targets. Here, these issues are reviewed with an emphasis on the neurophysiological evidence. First, we contextualize imaging and electrographic findings in humans. Then, we present a comprehensive review on rodent electrophysiology. Finally, we discuss how basic research will benefit from further combining psychopharmacological and neurophysiological tools.

Postsynaptic density protein transcripts are differentially modulated by minocycline alone or in add-on to haloperidol: Implications for treatment resistant schizophrenia

In this study, we investigated whether minocycline, a second-generation tetracycline proposed as an add-on to antipsychotics in treatment-resistant schizophrenia (TRS), may affect the expression of Homer and Arc postsynaptic density (PSD) transcripts, implicated in synaptic regulation. Minocycline was administered alone or with haloperidol in rats exposed or not to ketamine, mimicking acute glutamatergic psychosis or naturalistic conditions, respectively. Arc expression was significantly reduced by minocycline compared with controls. Minocycline in combination with haloperidol also significantly reduced Arc expression compared with both controls and haloperidol alone. Moreover, haloperidol/minocycline combination significantly affected Arc expression in cortical regions, while haloperidol alone was ineffective on cortical gene expression. These results suggest that minocycline may strongly affect the expression of Arc as mediated by haloperidol, both in terms of quantitative levels and of topography of haloperidol-related expression. It is noteworthy that no significant pre-treatment effect was found, suggesting that pre-exposure to ketamine did not grossly affect gene expression. Minocycline was not found to significantly affect haloperidol-related Homer1a expression. No significant changes in Homer1b/c expression were observed. These results are consistent with previous observations that minocycline may modulate postsynaptic glutamatergic transmission, affecting distinct downstream pathways initiated by N-methyl-D-aspartate (NMDA) receptor modulation, i.e. Arc-mediated but not Homer1a-mediated pathways.

Effects of chronic methamphetamine on psychomotor and cognitive functions and dopamine signaling in the brain

Methamphetamine (MA) studies in animals usually involve acute, binge, or short-term exposure to the drug. However, addicts take substantial amounts of MA for extended periods of time. Here we wished to study the effects of MA exposure on brain and behavior, using an animal model analogous to this pattern of MA intake. MA doses, 4 and 8mg/kg/day, were based on previously reported average daily freely available MA self-administration levels. We examined the effects of 16 week MA treatment on psychomotor and cognitive function in the rat using open field and novel object recognition tests and we studied the adaptations of the dopaminergic system, using in vitro and in vivo receptor imaging. We show that chronic MA treatment, at doses that correspond to the average daily freely available self-administration levels in the rat, disorganizes open field activity, impairs alert exploratory behavior and anxiety-like state, and downregulates dopamine transporter in the striatum. Under these treatment conditions, dopamine terminal functional integrity in the nucleus accumbens is also affected. In addition, lower dopamine D1 receptor binding density, and, to a smaller degree, lower dopamine D2 receptor binding density were observed. Potential mechanisms related to these alterations are discussed.

Disrupted axon-glia interactions at the paranode in myelinated nerves cause axonal degeneration and neuronal cell death in the aged Caspr mutant mouse shambling

Emerging evidence suggests that axonal degeneration is a disease mechanism in various neurodegenerative diseases and that the paranodes at the nodes of Ranvier may be the initial site of pathogenesis. We investigated the pathophysiology of the disease process in the central and peripheral nervous systems of a Caspr mutant mouse, shambling (shm), which is affected by disrupted paranodal structures and impaired nerve conduction of myelinated nerves. The shm mice manifest a progressive neurological phenotype as mice age. We found extensive axonal degeneration and a loss of neurons in the central nervous system and peripheral nervous system in aged shm mice. Axonal alteration of myelinated nerves was defined by abnormal distribution and expression of neurofilaments and derangements in the status of phosphorylated and non/de-phosphorylated neurofilaments. Autophagy-related structures were also accumulated in degenerated axons and neurons. In conclusion, our results suggest that disrupted axon-glia interactions at the paranode cause the cytoskeletal alteration in myelinated axons leading to neuronal cell death, and the process involves detrimental autophagy and aging as factors that promote the pathogenesis.

Minocycline protects against lipopolysaccharide-induced cognitive impairment in mice

RATIONALE

The role of glial cells, especially microglia and astrocytes, in neuroinflammation and cognition has been studied intensively. Lipopolysaccharide (LPS), a commonly used inducer of neuroinflammation, can cause cognitive impairment. Minocycline is known to possess potent neuroprotective activity, but its effect on LPS-induced cognitive impairment is unknown.

OBJECTIVES

This study aims to investigate the effects of minocycline on LPS-induced cognitive impairment and glial cell activation in mice.

METHODS

Behavioral tests were conducted for cognitive function, immunohistochemistry for microglial and astrocyte response, and quantitative PCR for mRNA expression of proinflammatory cytokines.

RESULTS

Minocycline significantly reversed the decreased spontaneous alternation induced by intrahippocampal administration of LPS in the Y-maze task. In the Morris water maze place navigation test, minocycline decreased the escape latency and distance traveled compared to LPS-treated mice. In the probe test, minocycline-treated mice spent more time in the target quadrant and crossed the platform area more frequently than animals in the LPS-treated group. Minocycline produced a significant decrease in the number of Iba-1- and GFAP-positive hippocampal cells compared to the LPS-treated group. Minocycline-treated mice had significantly reduced hippocampal TNF-α and IL-1β mRNA levels compared with LPS-treated animals. Minocycline caused a significant increase in hippocampal BDNF expression compared to the LPS-treated group.

CONCLUSIONS

Minocycline can attenuate LPS-induced cognitive impairments in mice. This effect may be associated with its action to suppress the activation of microglia and astrocytes and to normalize BDNF expression. Since neuroinflammatory processes and cognitive impairments are implicated in neurodegenerative disorders, minocycline may be a promising candidate for treating such diseases.

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.

The role of inflammation in schizophrenia

High levels of pro-inflammatory substances such as cytokines have been described in the blood and cerebrospinal fluid of schizophrenia patients. Animal models of schizophrenia show that under certain conditions an immune disturbance during early life, such as an infection-triggered immune activation, might trigger lifelong increased immune reactivity. A large epidemiological study clearly demonstrated that severe infections and autoimmune disorders are risk factors for schizophrenia. Genetic studies have shown a strong signal for schizophrenia on chromosome 6p22.1, in a region related to the human leucocyte antigen (HLA) system and other immune functions. Another line of evidence demonstrates that chronic (dis)stress is associated with immune activation. The vulnerability-stress-inflammation model of schizophrenia includes the contribution of stress on the basis of increased genetic vulnerability for the pathogenesis of schizophrenia, because stress may increase pro-inflammatory cytokines and even contribute to a lasting pro-inflammatory state. Immune alterations influence the dopaminergic, serotonergic, noradrenergic, and glutamatergic neurotransmission. The activated immune system in turn activates the enzyme indoleamine 2,3-dioxygenase (IDO) of the tryptophan/kynurenine metabolism which influences the serotonergic and glutamatergic neurotransmission via neuroactive metabolites such as kynurenic acid. The described loss of central nervous system volume and the activation of microglia, both of which have been clearly demonstrated in neuroimaging studies of schizophrenia patients, match the assumption of a (low level) inflammatory neurotoxic process. Further support for the inflammatory hypothesis comes from the therapeutic benefit of anti-inflammatory medication. Metaanalyses have shown an advantageous effect of cyclo-oxygenase-2 inhibitors in early stages of schizophrenia. Moreover, intrinsic anti-inflammatory, and immunomodulatory effects of antipsychotic drugs are known since a long time. Anti-inflammatory effects of antipsychotics, therapeutic effects of anti-inflammtory compounds, genetic, biochemical, and immunological findings point to a major role of inflammation in schizophrenia.

Adjunctive Minocycline in Clozapine-Treated Schizophrenia Patients With Persistent Symptoms

OBJECTIVE

Clozapine is the most effective antipsychotic for treatment refractory people with schizophrenia, yet many patients only partially respond. Accumulating preclinical and clinical data suggest benefits with minocycline. We tested adjunct minocycline to clozapine in a 10-week, double-blind, placebo-controlled trial. Primary outcomes tested were positive, and cognitive symptoms, while avolition, anxiety/depression, and negative symptoms were secondary outcomes.

METHODS

Schizophrenia and schizoaffective participants (n = 52) with persistent positive symptoms were randomized to receive adjunct minocycline (100 mg oral capsule twice daily; n = 29) or placebo (n = 23).

RESULTS

Brief Psychiatric Rating Scale (BPRS) psychosis factor (P = 0.098; effect size [ES], 0.39) and BPRS total score (P = 0.075; ES, 0.55) were not significant. A change in total BPRS symptoms of more than or equal to 30% was observed in 7 (25%) of 28 among minocycline and 1 (4%) of 23 among placebo participants, respectively (P = 0.044). Global cognitive function (MATRICS Consensus Cognitive Battery) did not differ, although there was a significant variation in size of treatment effects among cognitive domains (P = 0.03), with significant improvement in working memory favoring minocycline (P = 0.023; ES, 0.41). The Scale for the Assessment of Negative Symptoms total score did not differ, but significant improvement in avolition with minocycline was noted (P = 0.012; ES, 0.34). Significant improvement in the BPRS anxiety/depression factor was observed with minocycline (P = 0.028; ES, 0.49). Minocycline was well tolerated with significantly fewer headaches and constipation compared with placebo.

CONCLUSIONS

Minocycline's effect on the MATRICS Consensus Cognitive Battery composite score and positive symptoms were not statistically significant. Significant improvements with minocycline were seen in working memory, avolition, and anxiety/depressive symptoms in a chronic population with persistent symptoms. Larger studies are needed to validate these findings.

Neurodevelopmental Animal Models Reveal the Convergent Role of Neurotransmitter Systems, Inflammation, and Oxidative Stress as Biomarkers of Schizophrenia: Implications for Novel Drug Development

Schizophrenia is a life altering disease with a complex etiology and pathophysiology, and although antipsychotics are valuable in treating the disorder, certain symptoms and/or sufferers remain resistant to treatment. Our poor understanding of the underlying neuropathological mechanisms of schizophrenia hinders the discovery and development of improved pharmacological treatment, so that filling these gaps is of utmost importance for an improved outcome. A vast amount of clinical data has strongly implicated the role of inflammation and oxidative insults in the pathophysiology of schizophrenia. Preclinical studies using animal models are fundamental in our understanding of disease development and pathology as well as the discovery and development of novel treatment options. In particular, social isolation rearing (SIR) and pre- or postnatal inflammation (PPNI) have shown great promise in mimicking the biobehavioral manifestations of schizophrenia. Furthermore, the "dual-hit" hypothesis of schizophrenia states that a first adverse event such as genetic predisposition or a prenatal insult renders an individual susceptible to develop the disease, while a second insult (e.g., postnatal inflammation, environmental adversity, or drug abuse) may be necessary to precipitate the full-blown syndrome. Animal models that emphasize the "dual-hit" hypothesis therefore provide valuable insight into understanding disease progression. In this Review, we will discuss SIR, PPNI, as well as possible "dual-hit" animal models within the context of the redox-immune-inflammatory hypothesis of schizophrenia, correlating such changes with the recognized monoamine and behavioral alterations of schizophrenia. Finally, based on these models, we will review new therapeutic options, especially those targeting immune-inflammatory and redox pathways.

Memory impairment and alterations in prefrontal cortex gamma band activity following methamphetamine sensitization

RATIONALE

Repeated methamphetamine (MA) use leads to increases in the incentive motivational properties of the drug as well as cognitive impairments. These behavioral alterations persist for some time following abstinence, and neuroadaptations in the structure and function of the prefrontal cortex (PFC) are particularly important for their expression. However, there is a weak understanding of the changes in neural firing and oscillatory activity in the PFC evoked by repeated drug use, thus complicating the development of novel treatment strategies for addiction.

OBJECTIVES

The purpose of the current study was to assess changes in cognitive and brain function following MA sensitization.

METHODS

Sensitization was induced in rats, then temporal and recognition memory were assessed after 1 or 30 days of abstinence. Electrophysiological recordings from the medial PFC were also acquired from rats whereupon simultaneous measures of oscillatory and spiking activity were examined.

RESULTS

Impaired temporal memory was observed after 1 and 30 days of abstinence. However, recognition memory was only impaired after 1 day of abstinence. An injection of MA profoundly decreased neuronal firing rate and the anesthesia-induced slow oscillation (SO) in both sensitized (SENS) and control (CTRL) rats. Strong correlations were observed between the SO and gamma band power, which was altered in SENS animals. A decrease in the number of neurons phase-locked to the gamma oscillation was also observed in SENS animals.

CONCLUSIONS

The changes observed in PFC function may play an integral role in the expression of the altered behavioral phenotype evoked by MA sensitization.

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.

Future pharmacological treatments for substance use disorders

Substance use disorders represent a serious public health and social issue worldwide. Recent advances in our understanding of the neurobiological basis of the addictive processes have led to the development of a growing number of pharmacological agents to treat addictions. Despite this progress, there are no approved pharmacological treatments for cocaine, methamphetamine and cannabis addiction. Moving treatment development to the next stage will require novel ways of approaching substance use disorders. One such novel approach is to target individual vulnerabilities, such as cognitive function, sex differences and psychiatric comorbidities. This review provides a summary of promising pharmacotherapies for alcohol, opiate, stimulant and nicotine addictions. Many medications that target positive and negative reinforcement of drugs, as well as individual vulnerabilities to addiction, are in different phases of development. Clinical trials testing the efficacy of these medications for substance use disorder are warranted.

Tetrahydropalmatine protects against methamphetamine-induced spatial learning and memory impairment in mice

OBJECTIVE

The purpose of this study was to investigate the effect of methamphetamine (MA) on spatial learning and memory and the role of tetrahydropalmatine (THP) in MA-induced changes in these phenomena in mice.

METHODS

Male C57BL/6 mice were randomly divided into eight groups, according to different doses of MA, different doses of THP, treatment with both MA and THP, and saline controls. Spatial learning and memory were assessed using the Morris water maze. Western blot was used to detect the expression of extracellular signal-regulated protein kinase (ERK) in the mouse prefrontal cortex (PFC) and hippocampus.

RESULTS

Repeated MA treatment significantly increased the escape latency in the learning phase and decreased the number of platform site crossings in the memory-test phase. ERK1/2 expression was decreased in the PFC but not in the hippocampus of the MA-treated mice. Repeated THP treatment alone did not affect the escape latency, the number of platform site crossings or the total ERK1/2 expression in the brain. Statistically significantly shorter escape latencies and more platform site crossings occurred in MA+THP-treated mice than in MA-treated mice.

CONCLUSION

Repeated MA administration impairs spatial learning and memory in mice, and its co-administration with THP prevents this impairment, which is probably attributable to changed ERK1/2 expression in the PFC. This study contributes to uncovering the mechanism underlying MA abuse, and to exploring potential therapies.

Fingolimod increases brain-derived neurotrophic factor levels and ameliorates amyloid β-induced memory impairment

Alzheimer's disease is a progressive neurodegenerative disorder. Amyloid β, a neurotoxic protein, causes disruption of hippocampal synaptic plasticity, and induces cognitive impairment in Alzheimer's disease. We previously revealed that fingolimod, a new oral immunosuppressant used to treat multiple sclerosis, ameliorates oligomeric amyloid β-induced neuronal damage via up-regulation of neuronal brain-derived neurotrophic factor (BDNF). Here, we showed that oral administration of fingolimod ameliorated the impairment in object recognition memory and associative learning in mice injected with amyloid β. This effect was associated with restoration of normal BDNF expression levels in the cerebral cortices and hippocampi, suggesting that neuroprotection was mediated by up-regulation of neuronal BDNF levels. Therefore, fingolimod may provide therapeutic effects in patients with Alzheimer's disease.

Minocycline and risperidone prevent microglia activation and rescue behavioral deficits induced by neonatal intrahippocampal injection of lipopolysaccharide in rats

BACKGROUND

Various signs of activation of microglia have been reported in schizophrenia, and it is hypothesized that microglia activation is closely associated with the neuropathology of schizophrenia.

METHODS

Neonatal intrahippocampal injection of lipopolysaccharide (LPS), an activator of microglia, was performed in rats at postnatal day 7 (P7), and they were separately given saline, risperidone (0.5 mg/kg), minocycline (40 mg/kg) or a combination of both of them at P42 for consecutive 14 days. Behavioral changes (locomotion activity, social interaction, novel object recognition and prepulse inhibition) were examined and the number of microglia was assessed by using immunohistochemistry in adulthood.

RESULTS

The adult rats in LPS-injected group showed obvious behavioral alteration (e. g. deficits in social interaction, novel object recognition and prepulse inhibition) and a dramatic increase of number of activated microglial cells in the hippocampus and other brain regions such as cerebral cortex and thalamus compared to those in saline-injected group. Interestingly, application of either minocycline, risperidone or both of them significantly rescued behavioral deficits and attenuated microglia activation.

CONCLUSION

Our results suggest that inhibition of microglia activation may be one of mechanisms underlying the antipsychotic effect of minocycline and risperidone.

Minocycline improves recognition memory and attenuates microglial activation in Gunn rat: a possible hyperbilirubinemia-induced animal model of schizophrenia

BACKGROUND

Accumulating evidence indicates that neuroinflammation plays a significant role in the pathophysiology of schizophrenia. We previously reported evidence of schizophrenia-like behaviors and microglial activation in Gunn rats. We concluded that the Gunn rat, which exhibits a high concentration of unconjugated bilirubin, may be useful as an animal model of schizophrenia. On the other hand, there have been numerous reports that minocycline is effective in treating schizophrenia.

METHODS

In the present study, we investigated the effects of minocycline on performance of behavioral tests (prepulse inhibition (PPI) and novel object recognition test (NORT)) after animals received either 40mg/kg/d of minocycline or vehicle by intraperitoneal (i.p.) injection for 14 consecutive days. Furthermore, we examined the effects of minocycline on microglial activation in the hippocampal dentate gyrus of Gunn rats and Wistar rats.

RESULTS

We found that administration of minocycline for 14days significantly increased the exploratory preference in retention sessions and tended to improve the PPI deficits in Gunn rats. Immunohistochemistry analysis revealed that microglial cells in the minocycline-treated Gunn rat group showed less expression of CD11b compared to vehicle-treated Gunn and Wistar groups.

CONCLUSIONS

Our findings suggest that minocycline improves recognition memory and attenuates microglial activation in the hippocampal dentate gyrus of Gunn rats. Therefore, minocycline may be a potential therapeutic drug for schizophrenia.

Immunology of schizophrenia

Increased proinflammatory markers like cytokines have been described in the blood and cerebrospinal fluid of patients suffering from schizophrenia. Animal models have shown that a hit in early life to the immune system might trigger a lifelong increased immune reactivity. Many epidemiological and clinical studies show the role of various infectious agents as risk factors for schizophrenia with overlap to other psychoses. The first large-scale epidemiological study in psychiatry from Denmark clearly demonstrates severe infections and autoimmune disorders during lifetime to be risk factors for schizophrenia. Genetic studies have shown the strongest signal for schizophrenia on chromosome 6p22.1, in a region related to the major histocompatibility complex and other immune functions. The vulnerability-stress-inflammation model is important as stress may increase proinflammatory cytokines and even contribute to a lasting proinflammatory state. The immune system itself is considered an important further piece in the puzzle, as in autoimmune disorders in general, which are always linked to three factors: genes, the environment and the immune system. Alterations of dopaminergic, serotonergic, noradrenergic and glutamatergic neurotransmission have been shown with low-level neuroinflammation and may directly be involved in the generation of schizophrenic symptoms. Loss of central nervous system volume and microglial activation has been demonstrated in schizophrenia in neuroimaging studies, which supports the assumption of a low-level neuroinflammatory process. Further support comes from the therapeutic benefit of anti-inflammatory medications in specific studies and the anti-inflammatory and immunomodulatory intrinsic effects of antipsychotics.

Profile of minocycline and its potential in the treatment of schizophrenia

Accumulating evidence suggests that neuroinflammation affecting microglia plays an important role in the etiology of schizophrenia, and appropriate control of microglial activation may be a promising therapeutic strategy for schizophrenia. Minocycline, a second-generation tetracycline that inhibits microglial activation, has been shown to have a neuroprotective effect in various models of neurodegenerative disease, including anti-inflammatory, antioxidant, and antiapoptotic properties, and an ability to modulate glutamate-induced excitotoxicity. Given that these mechanisms overlap with neuropathologic pathways, minocycline may have a potential role in the adjuvant treatment of schizophrenia, and improve its negative symptoms. Here, we review the relevant studies of minocycline, ranging from preclinical research to human clinical trials.

Pretreatment of aripiprazole and minocycline, but not haloperidol, suppresses oligodendrocyte damage from interferon-γ-stimulated microglia in co-culture model

Recent imaging studies have indicated that the pathophysiology of schizophrenia is closely related to white matter abnormalities and microglial activation. Additionally, recent clinical trials have suggested that atypical antipsychotics may have brain protective properties and that minocycline, an antibiotic with inhibitory effects on microglial activation, improves symptoms of schizophrenia. We have reported that not only atypical antipsychotics with dopamine D2 receptor (D2R) antagonism but also aripiprazole, a unique antipsychotic drug with D2R partial agonism, inhibit microglial activation in vitro. Thus, atypical antipsychotics may exert a beneficial influence on both microglia and oligodendrocytes, while the underlying mechanisms have not been clarified. Here, we investigated whether antipsychotics suppress oligodendrocyte damage by inhibiting microglial activation utilizing a co-culture model with microglia and oligodendrocytes. Pretreatment of aripiprazole and minocycline suppressed apoptosis of oligodendrocytes in the co-culture model with interferon-γ (IFN-γ)-activated microglia, while haloperidol, a traditional antipsychotic drug, did not. Aripiprazole and minocycline inhibited the production of tumor necrosis factor-alpha (TNF-α) from IFN-γ-activated microglia. Moreover, aripiprazole and minocycline attenuated the phosphorylation of signal transducer and activator of transcription 1 (STAT1) in microglia. Overall, our results suggest that aripiprazole and minocycline may have antipsychotic effects through reducing oligodendrocyte damage caused by microglial activation. These results put forward a novel therapeutic hypothesis in schizophrenia research. Future in vivo studies to confirm the present results should be performed.

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.

Anti-inflammatory treatment in schizophrenia

Antipsychotics, which act predominantly as dopamine D2 receptor antagonists, have several shortcomings. The exact pathophysiological mechanism leading to dopaminergic dysfunction in schizophrenia is still unclear, but inflammation has been postulated to be a key player in the pathophysiology of the disorder. A dysfunction in activation of the type 1 immune response seems to be associated with an imbalance in tryptophan/kynurenine metabolism; the degrading enzymes involved in this metabolism are regulated by cytokines. Kynurenic acid (KYNA), an N-methyl-d-aspartate antagonist, was found to be increased in critical regions of the central nervous system (CNS) in schizophrenia, resulting in reduced glutamatergic neurotransmission. The differential activation of microglial cells and astrocytes as functional carriers of the immune system in the CNS may also contribute to this imbalance. The immunological effects of many existing antipsychotics, however, rebalance in part the immune imbalance and overproduction of KYNA. The immunological imbalance results in an inflammatory state combined with increased prostaglandin E(2) production and increased cyclo-oxygenase-2 (COX-2) expression. Growing evidence from clinical studies with COX-2 inhibitors points to favorable effects of anti-inflammatory therapy in schizophrenia, in particular in an early stage of the disorder. Further options for immunomodulating therapies in schizophrenia will be discussed.

Cognitive enhancement as a treatment for drug addictions

Drug addiction continues to be an important public health problem, with an estimated 22.6 million current illicit drug users in the United States alone. For many addictions, including cocaine, methamphetamine, and marijuana addiction, there are no approved pharmacological treatments. Behavioral treatments are effective but effects vary widely across individuals. Treatments that are effective across multiple addictions are greatly needed, and accumulating evidence suggests that one such approach may be pharmacological or behavioral interventions that enhance executive inhibitory control in addicts. Current evidence indicates that most forms of chronic drug use may be associated with significant cognitive impairments, especially in attention, working memory, and response inhibition functions. In some studies, these impairments predict poor treatment retention and outcome. A number of cognitive enhancing agents, including galantamine, modafinil, atomoxetine, methylphenidate, and guanfacine, have shown promising findings in human studies. Specific behavioral interventions, including cognitive remediation, also show promise. However, whether improvement of selective cognitive functions reduces drug use behavior remains to be determined. Cognitive enhancement to improve treatment outcomes is a novel strategy worthy of future research, as are related questions such as whether these approaches may be broadly beneficial to most addicts or best reserved for substance users with specific demonstrated cognitive impairments. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Drugs of abuse and increased risk of psychosis development

OBJECTIVE

There is considerable evidence to suggest that the abuse of illicit drugs, particularly cannabis and methamphetamine, has aetiological roles in the pathogenesis of psychosis and schizophrenia. Factors that may increase susceptibility to the propsychotic effects of these drugs include the age at which the abuse starts as well as family history of genetic polymorphisms relevant to the pathophysiology of this disorder. However, the neurobiological mechanisms involved in drug abuse-associated psychosis remain largely unclear.

METHODS AND RESULTS

This paper presents an overview of the available evidence, including clinical, animal model, and molecular studies, with a focus on brain regions and neurotransmitters systems, such as dopamine and glutamate, previously implicated in psychosis.

CONCLUSION

It is clear that further studies are urgently needed to provide a greater insight into the mechanisms that mediate the long-term and neurodevelopmental effects of cannabis and methamphetamine. A dialogue between basic science and clinical research may help to identify at-risk individuals and novel pathways for treatment and prevention.

Prevention of hypoglycemia-induced neuronal death by minocycline

Diabetic patients who attempt strict management of blood glucose levels frequently experience hypoglycemia. Severe and prolonged hypoglycemia causes neuronal death and cognitive impairment. There is no effective tool for prevention of these unwanted clinical sequelae. Minocycline, a second-generation tetracycline derivative, has been recognized as an anti-inflammatory and neuroprotective agent in several animal models such as stroke and traumatic brain injury. In the present study, we tested whether minocycline also has protective effects on hypoglycemia-induced neuronal death and cognitive impairment. To test our hypothesis we used an animal model of insulin-induced acute hypoglycemia. Minocycline was injected intraperitoneally at 6 hours after hypoglycemia/glucose reperfusion and injected once per day for the following 1 week. Histological evaluation for neuronal death and microglial activation was performed from 1 day to 1 week after hypoglycemia. Cognitive evaluation was conducted 6 weeks after hypoglycemia. Microglial activation began to be evident in the hippocampal area at 1 day after hypoglycemia and persisted for 1 week. Minocycline injection significantly reduced hypoglycemia-induced microglial activation and myeloperoxidase (MPO) immunoreactivity. Neuronal death was significantly reduced by minocycline treatment when evaluated at 1 week after hypoglycemia. Hypoglycemia-induced cognitive impairment is also significantly prevented by the same minocycline regimen when subjects were evaluated at 6 weeks after hypoglycemia. Therefore, these results suggest that delayed treatment (6 hours post-insult) with minocycline protects against microglial activation, neuronal death and cognitive impairment caused by severe hypoglycemia. The present study suggests that minocycline has therapeutic potential to prevent hypoglycemia-induced brain injury in diabetic patients.

Minocycline inhibits D-amphetamine-elicited action potential bursts in a central snail neuron

Minocycline is a second-generation tetracycline that has been reported to have powerful neuroprotective properties. In our previous studies, we found that d-amphetamine (AMPH) elicited action potential bursts in an identifiable RP4 neuron of the African snail, Achatina fulica Ferussac. This study sought to determine the effects of minocycline on the AMPH-elicited action potential pattern changes in the central snail neuron, using the two-electrode voltage clamping method. Extracellular application of AMPH at 300 μM elicited action potential bursts in the RP4 neuron. Minocycline dose-dependently (300-900 μM) inhibited the action potential bursts elicited by AMPH. The inhibitory effects of minocycline on AMPH-elicited action potential bursts were restored by forskolin (50 μM), an adenylate cyclase activator, and by dibutyryl cAMP (N(6),2'-O-Dibutyryladenosine 3',5'-cyclic monophosphate; 1mM), a membrane-permeable cAMP analog. Co-administration of forskolin (50 μM) plus tetraethylammonium chloride (TEA; 5mM) or co-administration of TEA (5mM) plus dibutyryl cAMP (1mM) also elicited action potential bursts, which were prevented and inhibited by minocycline. In addition, minocycline prevented and inhibited forskolin (100 μM)-elicited action potential bursts. Notably, TEA (50mM)-elicited action potential bursts in the RP4 neuron were not affected by minocycline. Minocycline did not affect steady-state outward currents of the RP4 neuron. However, minocycline did decrease the AMPH-elicited steady-state current changes. Similarly, minocycline decreased the effects of forskolin-elicited steady-state current changes. Pretreatment with H89 (N-[2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride; 10 μM), a protein kinase A inhibitor, inhibited AMPH-elicited action potential bursts and decreased AMPH-elicited steady-state current changes. These results suggest that the cAMP-protein kinase A signaling pathway and the steady-state current are involved in the inhibitory effects of minocycline upon AMPH-elicited action potential bursts.

Does minocycline, an antibiotic with inhibitory effects on microglial activation, sharpen a sense of trust in social interaction?

RATIONALE

Minocycline has long been applied to various infectious diseases as a tetracycline antibiotic and recently has found new application in the treatment of brain diseases such as stroke and multiple sclerosis. In addition, minocycline has also been suggested as an effective drug for psychiatric diseases. These suggestions imply that minocycline may modulate our mental activities, while the underlying mechanism remains to be clarified.

OBJECTIVE

To investigate how minocycline influences human mental activity, we experimentally examined how minocycline works on human social decision making in a double-blind randomized trial.

METHODS

Forty-nine healthy volunteers were administered minocycline or placebo over four days, after which they played (1) a trust game, in which they decided how much to trust an anonymous partner, and (2) a dictator game, in which they decided how to divide resources between themselves and an anonymous partner.

RESULTS

The minocycline group did not display increased trusting behavior or more altruistic resource allocation. In fact, the minocycline group displayed a slight reduction in trusting behavior. However, the minocycline group did show a strong positive correlation between the degree of risk taking in the trust game and in a separate evaluation of others' trustworthiness, whereas the placebo group showed no such correlation.

CONCLUSIONS

These results suggest that minocycline led to more rational decision-making strategies, possibly by increasing emotion regulation. Since minocycline is a well-known inhibitor of microglial activation, our findings may open a new optional pathway for treating mental states in which a component of rational decision making is impaired.

Inflammation in schizophrenia

Although there is no doubt that the dopaminergic neurotransmission is strongly involved in the pathophysiology of schizophrenia, the exact mechanism leading to dopaminergic dysfunction is still unclear. A disbalance in the immune response associated with a slight inflammatory process of the central nervous system (CNS) has been postulated. Such a mechanism is the basis for the "mild encephalitis" concept. A dysfunction in the activation of the type-1 immune response seems to be associated with decreased activity of the key enzyme of the tryptophan/kynurenine metabolism, indoleamine 2,3-dioxygenase (IDO). Theoretically, a decreased activity of IDO results in the increased production of kynurenic acid, an N-methyl-D-aspartate antagonist in the CNS, and a reduced glutamatergic neurotransmission in schizophrenia. Accordingly, in animal models of schizophrenia, increased levels of kynurenic acid in critical regions of the CNS were described, although studies of peripheral blood levels of kynurenic acid in schizophrenic patients showed controversial results. The immunological effects of a lot of existing antipsychotics, however, rebalance in part the immune imbalance and the overweight of the production of kynurenic acid. The inflammatory state in schizophrenia is associated with increased prostaglandin E(2) production and increased cyclooxygenase-2 (COX-2) expression. Growing evidence from clinical studies with COX-2 inhibitors points to favorable effects of anti-inflammatory therapy in schizophrenia, in particular in an early stage of the disorder. Further options for immunomodulating therapies in schizophrenia will be discussed.

Matrix metalloproteinases contribute to neuronal dysfunction in animal models of drug dependence, Alzheimer's disease, and epilepsy

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) remodel the pericellular environment by regulating the cleavage of extracellular matrix proteins, cell surface components, neurotransmitter receptors, and growth factors that mediate cell adhesion, synaptogenesis, synaptic plasticity, and long-term potentiation. Interestingly, increased MMP activity and dysregulation of the balance between MMPs and TIMPs have also been implicated in various pathologic conditions. In this paper, we discuss various animal models that suggest that the activation of the gelatinases MMP-2 and MMP-9 is involved in pathogenesis of drug dependence, Alzheimer's disease, and epilepsy.