Toluene induces rapid and reversible rise of hippocampal glutamate and taurine neurotransmitter levels in mice

Effect of Noise and Music on Neurotransmitters in the Amygdala: The Role Auditory Stimuli Play in Emotion Regulation

Stress caused by noise is becoming widespread globally. Noise may lead to deafness, endocrine disorders, neurological diseases, and a decline in mental health. The mechanism behind noise-induced neurodevelopmental abnormalities is unclear, but apoptosis and pro-inflammatory signals may play an important role. In this study, weaned piglets were used as a model to explore noise-induced neurodevelopmental abnormalities. We hypothesized that long-term noise exposure would induce anxiety and cause acute stress, exhibited by alterations in neurotransmission in the amygdala. A total of 72 hybrid piglets (Large White × Duroc × Min Pig) were randomly divided into three groups, including noise (exposed to mechanical noise, 80-85 dB), control (blank, exposed to natural background sound, <40 dB), and music (positive control, exposed to Mozart K.448, 60-70 dB) groups. The piglets were exposed to 6 h of auditory noise daily (10:00-16:00) for 28 days. Compared with the control group, piglets exposed to noise showed more aggressive behavior. The expression of Caspase3, Caspase9, Bax, NF-κB (p56), TLR4, MYD88, I κ B α, IL-1 β, TNF-α, and IL-12RB2 was significantly upregulated in the amygdala, while the expression of Nrf2, HO-1, CAT, and SOD was downregulated in piglets in the noise group. Cell death occurred, and numerous inflammatory cells accumulated in the amygdala of piglets in the noise group. Targeted metabolomics showed that the content of inhibitory neurotransmitter GABA was higher in the amygdala of piglets in the noise group. Compared with the noise group, piglets in the music group displayed more positive emotion-related behaviors. Compared with the noise group, the expression of genes related to apoptosis, inflammation, and oxidative damage was lower in the music group. Cells of the amygdala in the music group were also of normal morphology. Our results show that noise-induced stress causes apoptosis and neuroinflammation in the amygdala and induces anxiety during the early neonatal neural development of piglets. In contrast, to some extent, music alleviates noise-induced anxiety.

Solid-phase microextraction: An appealing alternative for the determination of endogenous substances - A review

The determination of endogenous substances is of great significance for obtaining important biotic information such as biological components, metabolic pathways and disease biomarkers in different living organisms (e.g. plants, insects, animals and humans). However, due to the complex matrix and the trace concentrations of target analytes, the sample preparation procedure is an essential step before the analytes of interest are introduced into a detection instrument. Solid-phase microextraction (SPME), an emerging sample preparation technique that integrates sampling, extraction, concentration, and sample introduction into one step, has gained wide acceptance in various research fields, including in the determination of endogenous compounds. In this review, recent developments and applications of SPME for the determination of endogenous substances over the past five years are summarized. Several aspects, including the design of SPME devices (sampling configuration and coating), applications (in vitro and in vivo sampling), and coupling with emerging instruments (comprehensive two-dimensional gas chromatography (GC × GC), ambient mass spectrometry (AMS) and surface enhanced Raman scattering (SERS)) are involved. Finally, the challenges and opportunities of SPME methods in endogenous substances analysis are also discussed.

Acute and Chronic Exposure of Toluene Induces Genotoxicity in Different Regions of the Brain in Normal and Allergic Mouse Models

Toluene is a widely used industrial organic solvent and is ubiquitous in our environment. The neurobehavioral and neurotoxic effects of toluene are well recognized; however, its genotoxicity is still under discussion. Toluene biotransformation leads to the generation of reactive oxygen species that cause oxidative stress and DNA damages. Individuals with different immunogenetic backgrounds have different sensitivities to toxic chemical exposure. Previous studies have suggested that allergic stimulation may influence the threshold for toluene sensitivity due to the modulation of neurotrophin-related genes. Therefore, we aimed to investigate toluene-induced genotoxicity in different brain regions following acute and chronic exposure in vivo and to further examine whether allergic stimulation may influence the sensitivity to toluene-induced genotoxicity. In this present study, we found that exposure of toluene induced oxidative DNA damages resulting in genotoxicity in different brain regions including cortex, cerebellum, and hippocampus using comet assay. Higher genotoxicity induced by toluene was observed in the hippocampus of control mice compared to OVA-immunized mice. These results provide evidence that toluene-induced genotoxicity may contribute to its neurotoxicity in different immunogenetic individuals.

Amyotrophic lateral sclerosis-A case report and mechanistic review of the association with toluene and other volatile organic compounds

Unmasking of latent neurodegenerative disease has been reported following exposure to chemicals that share one or more mechanisms of action in common with those implicated in the specific disease. For example, unmasking of latent Parkinson's disease (PD) has been associated with exposure to anti-dopaminergic agents, while the progression of pre-existing mild cognitive impairment and unmasking of latent Alzheimer's disease has been associated with exposure to general anesthetic agents which promote Aβ protein aggregation. This literature review and clinical case report about a 45-year-old man with no family history of motor neuron disease who developed overt symptoms of a neuromuscular disorder in close temporal association with his unwitting occupational exposure to volatile organic compounds (VOCs) puts forth the hypothesis that exposure to VOCs such as toluene, which disrupt motor function and increase oxidative stress, can unmask latent ALS type neuromuscular disorder in susceptible individuals.

A novel approach of substitution therapy with inhalation of essential oil for the reduction of inhalant craving: A double-blinded randomized controlled trial

Inhalants, which are neurotoxic central nervous system (CNS) suppressants, are frequently abused by young adults. Unlike other CNS depressants, including alcohol and opiates, no treatment is currently approved for inhalant dependence. In this report, a novel approach of substitution treatment for inhalant addiction was explored in a double-blinded, randomized, controlled crossover design to examine the effects of inhalation of essential oil and perfume on the reduction of cue-induced craving for inhalant in thirty-four Thai males with inhalant dependence. The craving response was measured by the modified version of Penn Alcohol Craving Score for Inhalants (PACS-inhalants). The participants (mean age ± SE = 27.9 ± 1.4) in this trial had used inhalant for 5.8 ± 1.1 years. Cravings could be induced in all participants by visual cues as assessed by ^50% increases in inhalant craving levels. Generalized estimating equations showed a significant suppressant effect of essential oil, but not perfume, on the craving response as compared with baseline cue-induced craving. Moreover, essential oil, but not perfume, had significant effects on physiological responses including decreasing pulse rate. It is concluded that inhaling essential oil as a substitution treatment for inhalant may be used as part of treatment programs for reducing inhalant craving.

Intense olfactory stimulation blocks seizures in an experimental model of epilepsy

There are reports of patients whose epileptic seizures are prevented by means of olfactory stimulation. Similar findings were described in animal models of epilepsy, such as the electrical kindling of amygdala, where olfactory stimulation with toluene (TOL) suppressed seizures in most rats, even when the stimuli were 20% above the threshold to evoke seizures in already kindled animals. The Wistar Audiogenic Rat (WAR) strain is a model of tonic-clonic seizures induced by acute acoustic stimulation, although it also expresses limbic seizures when repeated acoustic stimulation occurs - a process known as audiogenic kindling (AK). The aim of this study was to evaluate whether or not the olfactory stimulation with TOL would interfere on the behavioral expression of brainstem (acute) and limbic (chronic) seizures in the WAR strain. For this, animals were exposed to TOL or saline (SAL) and subsequently exposed to acoustic stimulation in two conditions that generated: I) acute audiogenic seizures (only one acoustic stimulus, without previous seizure experience before of the odor test) and II) after AK (20 acoustic stimuli [2 daily] before of the protocol test). We observed a decrease in the seizure severity index of animals exposed only to TOL in both conditions, with TOL presented 20s before the acoustic stimulation in both protocols. These findings were confirmed by behavioral sequential analysis (neuroethology), which clearly indicated an exacerbation of clusters of specific behaviors such as exploration and grooming (self-cleaning), as well as significant decrease in the expression of brainstem and limbic seizures in response to TOL. Thus, these data demonstrate that TOL, a strong olfactory stimulus, has anticonvulsant properties, detected by the decrease of acute and AK seizures in WARs.

Preclinical characterization of toluene as a non-classical hallucinogen drug in rats: participation of 5-HT, dopamine and glutamate systems

RATIONALE

Toluene is a misused inhalant with hallucinogenic properties and complex effects. Toluene blocks N-methyl-D-aspartate (NMDA) receptors, releases dopamine (DA), and modifies several neurotransmitter levels; nonetheless, the mechanism by which it produces hallucinations is not well characterized.

OBJECTIVES

This study aims (a) to study toluene's effects on the 5-HT2A-mediated head-twitch response (HTR), dopamine (DA), and serotonin (5-HT) tissue levels in discrete brain regions; (b) to compare the actions of toluene, ketamine, and 1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane (DOI) on HTR; and (c) to study the pharmacological blockade of toluene's and ketamine's effects by selective drugs.

METHODS

Independent groups of rats inhaled toluene (500-12,000 ppm) for 30 min during which the occurrence of serotonergic signs was analyzed. Brains were obtained after exposure to determine DA and 5-HT levels by HPLC.

RESULTS

Toluene concentration-dependently induced HTR. Other serotonin syndrome signs were evident at high concentrations. Toluene (4000 and 8000 ppm), and ketamine (3 and 10 mg/kg), significantly increased 5-HT levels in the frontal cortex (FC) striatum, hippocampus, and brain stem, as well as DA levels in the striatum and FC. Pretreatment with ketanserin (5HT2A/2C receptor antagonist), M100907 (selective 5-HT2A receptor antagonist), D-serine (co-agonist of the NMDA receptor glycine site), and haloperidol (D2 receptor antagonist) significantly decreased toluene's and ketamine's actions. The 5HT1A receptor antagonist WAY100635 had no effect.

CONCLUSION

Toluene stimulates 5HT2A and 5HT2C receptors, and increases 5-HT and DA levels. These actions are similar to those produced by ketamine and involve activation of a complex neurotransmitter network that includes NMDA receptor antagonism.

In vivo and ex vivo SPME: a low invasive sampling and sample preparation tool in clinical bioanalysis

Solid phase microextraction (SPME) is well-established technology in bioanalysis. Current review discusses the features of SPME, which determine the non- or low-invasiveness of the method in biomedical analysis. In the first section we analyze the factors, which have significant influence on the SPME sampling device performance in the view of sampling safety and efficiency. In the later sections applicability of various SPME approaches for analysis of easily accessible samples routinely used for analysis (e.g., urine, blood) as well as limited availability samples (tissues) is discussed. Moreover, the examples of sampling alternative matrices such as hair, saliva, sweat or breath are presented. The advantages and limitation of the technology in the view of future development of SPME are also reviewed.

Discovery of potential biomarkers in exhaled breath for diagnosis of type 2 diabetes mellitus based on GC-MS with metabolomics

Eight breath biomarkers of T2DM were discovered by a new SPME-GC-MS based metabolic profiling tool.

Review of toluene action: clinical evidence, animal studies and molecular targets

It has long been known that individuals will engage in voluntary inhalation of volatile solvents for their rewarding effects. However, research into the neurobiology of these agents has lagged behind that of more commonly used drugs of abuse such as psychostimulants, alcohol and nicotine. This imbalance has begun to shift in recent years as the serious effects of abused inhalants, especially among children and adolescents, on brain function and behavior have become appreciated and scientifically documented. In this review, we discuss the physicochemical and pharmacological properties of toluene, a representative member of a large class of organic solvents commonly used as inhalants. This is followed by a brief summary of the clinical and pre-clinical evidence showing that toluene and related solvents produce significant effects on brain structures and processes involved in the rewarding aspects of drugs. This is highlighted by tables highlighting toluene's effect on behaviors (reward, motor effects, learning, etc.) and cellular proteins (e.g. voltage and ligand-gated ion channels) closely associated the actions of abused substances. These sections demonstrate not only the significant progress that has been made in understanding the neurobiological basis for solvent abuse but also reveal the challenges that remain in developing a coherent understanding of this often overlooked class of drugs of abuse.

In vivo solid-phase microextraction for tissue bioanalysis

Conventional in vitro or ex vivo bioanalytical quantitative sample preparation methods for the determination of compounds in biological tissues are often coupled with challenges in obtaining an assay representative of the system of interest. The rising interest in in vivo microsampling bioanalytical methods is due to the unique advantages they offer over their in vitro counterparts. In vivo solid-phase microextraction (SPME), a diffusion-based microsampling tool, has been successfully applied in recent studies to various biological systems. This review presents recent trends in tissue bioanalysis using in vivo SPME as a sample preparation tool. Efforts were made to discuss the various bioapplications of the method while highlighting possible strategies for improved sensitivity where needed. In vivo SPME devices currently employed for the various applications have also been described. In addition, we highlight selectivity of a new class of biocompatible coatings that can potentially improve the coverage of metabolites for untargeted metabolomics.

Sarcosine attenuates toluene-induced motor incoordination, memory impairment, and hypothermia but not brain stimulation reward enhancement in mice

Toluene, a widely used and commonly abused organic solvent, produces various behavioral disturbances, including motor incoordination and cognitive impairment. Toluene alters the function of a large number of receptors and ion channels. Blockade of N-methyl-d-aspartate (NMDA) receptors has been suggested to play a critical role in toluene-induced behavioral manifestations. The present study determined the effects of various toluene doses on motor coordination, recognition memory, body temperature, and intracranial self-stimulation (ICSS) thresholds in mice. Additionally, the effects of sarcosine on the behavioral and physiological effects induced by toluene were evaluated. Sarcosine may reverse toluene-induced behavioral manifestations by acting as an NMDA receptor co-agonist and by inhibiting the effects of the type I glycine transporter (GlyT1). Mice were treated with toluene alone or combined with sarcosine pretreatment and assessed for rotarod performance, object recognition memory, rectal temperature, and ICSS thresholds. Toluene dose-dependently induced motor incoordination, recognition memory impairment, and hypothermia and lowered ICSS thresholds. Sarcosine pretreatment reversed toluene-induced changes in rotarod performance, novel object recognition, and rectal temperature but not ICSS thresholds. These findings suggest that the sarcosine-induced potentiation of NMDA receptors may reverse motor incoordination, memory impairment, and hypothermia but not the enhancement of brain stimulation reward function associated with toluene exposure. Sarcosine may be a promising compound to prevent acute toluene intoxications by occupational or intentional exposure.

Toluene effects on gene expression in the hippocampus of young adult, middle-age, and senescent Brown Norway Rats

Differential susceptibility to environmental exposures across life stages is an area of toxicology about which little is known. We examined the effects of toluene on transcriptomic changes and oxidative stress (OS) parameters (e.g., NQO1 and GPX) in the rat brain at different life stages to elucidate key molecular pathways responsible for toluene-induced neurotoxicity, as well as possible age-related interactions. Changes in assessed end points following acute oral toluene (0, 0.65, and 1.0 g/kg) were examined 4 h after exposure in hippocampi of Brown Norway Rats at 4, 12, and 24 months of age. Genomic data were analyzed by two-way ANOVA to identify the effects of age, toluene, and interactions between the two factors. Analysis by one-way ANOVA identified 183 genes whose expression changed ≥ 1.25-fold with age. The majority of the genes were upregulated between life stages (> 79%). Similar analysis for toluene-related genes found only two sequences to vary significantly with dose. Fifty-six genes were identified to have expression changes due to an age-toluene interaction. Expression of genes with roles in immune response, cytoskeleton, protein, and energy metabolism was changed with advancing life stage, indicating changes in basic cellular homeostasis. Toluene affected similar cell functions, enhancing the effects of aging. OS parameters also indicated age-related changes in response mechanisms, evidence of toluene damage, and supported an age-toluene interaction. The data indicate that life stage can alter the toxicity of acute toluene exposure in various and complex ways, highlighting the need for further investigation into the role of aging in susceptibility.

Translating neurobehavioural endpoints of developmental neurotoxicity tests into in vitro assays and readouts

The developing nervous system is particularly vulnerable to chemical insults. Exposure to chemicals can result in neurobehavioural alterations, and these have been used as sensitive readouts to assess neurotoxicity in animals and man. Deconstructing neurobehaviour into relevant cellular and molecular components may allow for detection of specific neurotoxic effects in cell-based systems, which in turn may allow an easier examination of neurotoxic pathways and modes of actions and eventually inform the regulatory assessment of chemicals with potential developmental neurotoxicity. Here, current developments towards these goals are reviewed. Imaging genetics (CB) provides new insights into the neurobiological correlates of cognitive function that are being used to delineate neurotoxic mechanisms. The gaps between in vivo neurobehaviour and real-time in vitro measurements of neuronal function are being bridged by ex vivo measurements of synaptic plasticity (RW). An example of solvent neurotoxicity demonstrates how an in vivo neurological defect can be linked via the N-methyl-d-aspartate (NMDA)-glutamate receptor as a common target to in vitro readouts (AB). Axonal and dendritic morphology in vitro proved to be good correlates of neuronal connectivity and neurobehaviour in animals exposed to polychlorinated biphenyls and organophosphorus pesticides (PJL). Similarly, chemically induced changes in neuronal morphology affected the formation of neuronal networks on structured surfaces. Such network formation may become an important readout for developmental neurotoxicity in vitro (CvT), especially when combined with human neurons derived from embryonic stem cells (ML). We envision that future in vitro test systems for developmental neurotoxicity will combine the above approaches with exposure information, and we suggest a strategy for test system development and cell-based risk assessment.

Binge toluene exposure alters glutamate, glutamine and GABA in the adolescent rat brain as measured by proton magnetic resonance spectroscopy

Despite the high incidence of toluene abuse in adolescents, little is known regarding the effect of binge exposure on neurochemical profiles during this developmental stage. In the current study, the effects of binge toluene exposure during adolescence on neurotransmitter levels were determined using high-resolution proton magnetic resonance spectroscopy ex vivo at 11.7T. Adolescent male Sprague-Dawley rats were exposed to toluene (0, 8000, or 12,000 ppm) for 15 min twice daily from postnatal day 28 (P28) through P34 and then euthanized either 1 or 7 days later (on P35 or P42) to assess glutamate (GLU), glutamine, and GABA levels in intact tissue punches from the medial prefrontal cortex (mPFC), anterior striatum and hippocampus. In the mPFC, toluene reduced GLU 1 day after exposure, with no effect on GABA, while after 7 days, GLU was no longer affected but there was an increase in GABA levels. In the hippocampus, neither GABA nor GLU was altered 1 day after exposure, whereas 7 days after exposure, increases were observed in GABA and GLU. Striatal GLU and GABA levels measured after either 1 or 7 days were not altered after toluene exposure. These findings show that 1 week of binge toluene inhalation selectively alters these neurotransmitters in the mPFC and hippocampus in adolescent rats, and that some of these effects endure at least 1 week after the exposure. The results suggest that age-dependent, differential neurochemical responses to toluene may contribute to the unique behavioral patterns associated with drug abuse among older children and young teens.

Neurotoxicity of toluene

Chemical susceptibility is triggered by a large range of chemicals present both indoors and outdoors including pesticides, cleaning products, perfumes, scented products and cigarette smoke. Health risk after chemical exposure depends on age, sex, genetic factors, socioeconomic status, nutritional status, and environmental factors. Toluene is one of volatile organic chemicals that causes different sensitivity in individuals. Although neurotoxic and immunotoxic effects of toluene have been studied extensively, the underlying mechanism remains obscure. This review highlights the possible neuroimmune factors influencing toluene sensitivity and neurotoxicity in a mouse model.

Neurochemistry of drug action: insights from proton magnetic resonance spectroscopic imaging and their relevance to addiction

Proton magnetic resonance spectroscopy ((1)H MRS) is a noninvasive imaging technique that permits measurement of particular compounds or metabolites within the tissue of interest. In the brain, (1)H MRS provides a snapshot of the neurochemical environment within a defined volume of interest. A search of the literature demonstrates the widespread utility of this technique for characterizing tumors, tracking the progress of neurodegenerative disease, and for understanding the neurobiological basis of psychiatric disorders. As of relatively recently, (1)H MRS has found its way into substance abuse research, and it is beginning to become recognized as a valuable complement in the brain imaging toolbox that also contains positron emission tomography, single-photon-emission computed tomography, and functional magnetic resonance imaging. Drug abuse studies using (1)H MRS have identified several biochemical changes in the brain. The most consistent alterations across drug class were reductions in N-acetylaspartate and elevations in myo-inositol, whereas changes in choline, creatine, and amino acid transmitters also were abundant. Together, the studies discussed herein provide evidence that drugs of abuse may have a profound effect on neuronal health, energy metabolism and maintenance, inflammatory processes, cell membrane turnover, and neurotransmission, and these biochemical changes may underlie the neuropathology within brain tissue that subsequently gives rise to the cognitive and behavioral impairments associated with drug addiction.

Up-regulation of neurotrophin-related gene expression in mouse hippocampus following low-level toluene exposure

To investigate the role of strain differences in sensitivity to low-level toluene exposure on neurotrophins and their receptor levels in the mouse hippocampus, 8-week-old male C3H/HeN, BALB/c and C57BL/10 mice were exposed to 0, 5, 50, or 500 ppm toluene for 6h per day, 5 days per week for 6 weeks in an inhalation chamber. We examined the expressions of neurotrophin-related genes and receptors in the mouse hippocampus using real-time reverse transcription polymerase chain reaction (RT-PCR). The expression of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), tyrosine kinase (Trk) A, and TrkB mRNAs in the C3H/HeN mice hippocampus was significantly higher in the mice exposed to 500 ppm toluene. Among the three strains of mice, the C3H/HeN mice seemed to be sensitive to toluene exposure. To examine the combined effect of toluene exposure and allergic challenge, the C3H/HeN mice stimulated with ovalbumin were exposed to toluene. The allergy group of C3H/HeN mice showed significantly elevated level of NGF mRNA in the hippocampus following exposure to 50 ppm toluene. Then, we also examined the expression of transcription factor, dopamine markers and oxidative stress marker in the hippocampus of sensitive strain C3H/HeN mice and found that the expression of CREB1 mRNA was significantly increased at 50 ppm toluene. In immunohistochemical analysis, the density of the NGF-immunoreactive signal was significantly stronger in the hippocampal CA3 region of the C3H/HeN mice exposed to 500 ppm toluene in non-allergy group and 50 ppm in allergy group. Our results indicate that low-level toluene exposure may induce up-regulation of neurotrophin-related gene expression in the mouse hippocampus depending on the mouse strain and an allergic stimulation in sensitive strain may decrease the threshold for sensitivity at lower exposure level.

Analytical methods used in conjunction with solid-phase microextraction: a review of recent bioanalytical applications

Integration of sampling and sample preparation with various analytical instruments is a highly desirable feature for any analytical method. This is most conveniently achieved by using microextraction techniques or various microdevices. Among these techniques, solid-phase microextraction (SPME) is particularly remarkable due to its simplicity and effectiveness. This review discusses the most recent applications of SPME in bioanalysis, grouped according to the analytical instrument that SPME is coupled to. It is shown that one of the most important aspects of such analytical methods is the ability of SPME to perform direct and selective extraction of analytes from complex biological samples. By far, the most popular method continues to be SPME coupled to GC. Nevertheless, the last 2 years have witnessed significant advances in other areas, such as successful automation of SPME coupled to liquid chromatography and the development of new coatings suitable for direct extraction from biological samples. Furthermore, a few bioanalytical applications based on direct coupling of SPME to MS, ion mobility spectrometry, CE and analytical chemiluminescence have been reported.

Neurochemical changes after acute binge toluene inhalation in adolescent and adult rats: a high-resolution magnetic resonance spectroscopy study

Inhalant abuse in young people is a growing public health concern. We reported previously that acute toluene intoxication in young rats, using a pattern of exposures that approximate abuse patterns of inhalant use in humans, significantly altered neurochemical measures in select brain regions. In this study, adolescent and young adult rats were exposed similarly to an acute (2 x 15 min), high dose (8000-12,000 ppm) of toluene and high-resolution magic angle spinning proton magnetic resonance spectroscopy (HR-MAS 1H-MRS) was used to assess neurochemical profiles of tissue samples from a number of brain regions collected immediately following solvent exposure. The current investigation focused on N-acetyl-aspartate (NAA), choline-containing compounds, creatine, glutamate, GABA, and glutamine. Contrary to our predictions, no significant alterations were found in the levels of NAA, choline, creatine, glutamate, or glutamine in adolescent animals. In contrast to these minimal effects in adolescents, binge toluene exposure altered several neurochemical parameters in young adult rats, including decreased levels of choline and GABA in the frontal cortex and striatum and lowered glutamine and NAA levels in the frontal cortex. One of the more robust findings was a wide-ranging increase in lactate after toluene exposure in adult animals, an effect not observed in adolescents. These age-dependent effects of toluene are distinct from those reported previously in juvenile rats and suggest a developmental difference in vulnerability to the effects of inhalants. Specifically, the results suggest that the neurochemical response to toluene in adolescents is attenuated compared to adults, and imply an association between these neurochemical differences and age-influenced differences in solvent abuse in humans.

Second-by-second measures of L-glutamate in the prefrontal cortex and striatum of freely moving mice

l-Glutamate (Glu) is the main excitatory neurotransmitter in the mammalian central nervous system, and it is involved in most aspects of normal brain function, including cognition, memory and learning, plasticity, and motor movement. Although microdialysis techniques have been used to study Glu, the slow temporal resolution of the technique may be inadequate to properly examine tonic and phasic Glu. Thus, our laboratory has developed an enzyme-based microelectrode array (MEA) with fast response time and low detection limits for Glu. We have modified the MEA design to allow for reliable measures in the brain of awake, freely moving mice. In this study, we chronically implanted the MEA in prefrontal cortex (PFC) or striatum (Str) of awake, freely moving C57BL/6 mice. We successfully measured Glu levels 7 days postimplantation without loss of MEA sensitivity. In addition, we determined resting (tonic) Glu levels to be 3.3 microM in the PFC and 5.0 microM in the Str. Resting Glu levels were subjected to pharmacological manipulation with tetrodotoxin (TTX) and dl-threo-beta-hydroxyaspartate (THA). TTX significantly (p < 0.05) decreased resting Glu by 20%, whereas THA significantly (p < 0.05) increased resting Glu by 60%. Taken together, our data show that chronic recordings of tonic and phasic clearance of exogenously applied Glu can be carried out in awake mice for at least 7 days in vivo, allowing for longer term studies of Glu regulation.

Glutamatergic substrates of drug addiction and alcoholism

The past two decades have witnessed a dramatic accumulation of evidence indicating that the excitatory amino acid glutamate plays an important role in drug addiction and alcoholism. The purpose of this review is to summarize findings on glutamatergic substrates of addiction, surveying data from both human and animal studies. The effects of various drugs of abuse on glutamatergic neurotransmission are discussed, as are the effects of pharmacological or genetic manipulation of various components of glutamate transmission on drug reinforcement, conditioned reward, extinction, and relapse-like behavior. In addition, glutamatergic agents that are currently in use or are undergoing testing in clinical trials for the treatment of addiction are discussed, including acamprosate, N-acetylcysteine, modafinil, topiramate, lamotrigine, gabapentin and memantine. All drugs of abuse appear to modulate glutamatergic transmission, albeit by different mechanisms, and this modulation of glutamate transmission is believed to result in long-lasting neuroplastic changes in the brain that may contribute to the perseveration of drug-seeking behavior and drug-associated memories. In general, attenuation of glutamatergic transmission reduces drug reward, reinforcement, and relapse-like behavior. On the other hand, potentiation of glutamatergic transmission appears to facilitate the extinction of drug-seeking behavior. However, attempts at identifying genetic polymorphisms in components of glutamate transmission in humans have yielded only a limited number of candidate genes that may serve as risk factors for the development of addiction. Nonetheless, manipulation of glutamatergic neurotransmission appears to be a promising avenue of research in developing improved therapeutic agents for the treatment of drug addiction and alcoholism.

Changes in neurotransmitter levels and proinflammatory cytokine mRNA expressions in the mice olfactory bulb following nanoparticle exposure

Recently, there have been increasing reports that nano-sized component of particulate matter can reach the brain and may be associated with neurodegenerative diseases. Previously, our laboratory has studied the effect of intranasal instillation of nano-sized carbon black (CB) (14 nm and 95 nm) on brain cytokine and chemokine mRNA expressions and found that 14-nm CB increased IL-1 beta, TNF-alpha, CCL2 and CCL3 mRNA expressions in the olfactory bulb, not in the hippocampus of mice. To investigate the effect of a single administration of nanoparticles on neurotransmitters and proinflammatory cytokines in a mouse olfactory bulb, we performed in vivo microdialysis and real-time PCR methods. Ten-week-old male BALB/c mice were implanted with guide cannula in the right olfactory bulb and, 1 week later, were instilled vehicle or CB (14 nm, 250 microg) intranasally. Six hours after the nanoparticle instillation, the mice were intraperitoneally injected with normal saline or 50 mug of bacteria cell wall component lipoteichoic acid (LTA), which may potentiate CB-induced neurologic effect. Extracellular glutamate and glycine levels were significantly increased in the olfactory bulb of CB-instilled mice when compared with vehicle-instilled control mice. Moreover, we found that LTA further increased glutamate and glycine levels. However, no alteration of taurine and GABA levels was observed in the olfactory bulb of the same mice. We also detected immunological changes in the olfactory bulb 11 h after vehicle or CB instillation and found that IL-1 beta mRNA expression was significantly increased in CB- and LTA-treated mice when compared with control group. However, TNF-alpha mRNA expression was increased significantly in CB- and saline-treated mice when compared with control group. These findings suggest that nanoparticle CB may modulate the extracellular amino acid neurotransmitter levels and proinflammatory cytokine IL-1 beta mRNA expressions synergistically with LTA in the mice olfactory bulb.

Athymic nude mice are insensitive to low-level toluene-induced up-regulation of memory-related gene expressions in the hippocampus

The function of the N-methyl-d-aspartate (NMDA) subtype of glutamatergic receptors is known to be antagonized by toluene, a well-characterized neurotoxic chemical known to impair memory functions. Recently, peripheral T cells have been clearly shown to play an important role in cognitive and behavioral functions. In the present study, we investigated the role of peripheral T cells in the hippocampal mRNA expression of memory-related genes induced by low levels of toluene exposure in mice. BALB/c wild-type (WT) and nude mice were exposed to 9ppm of toluene or filtered air (0ppm toluene; control groups) in a nose-only exposure chamber for 30min on 3 consecutive days followed by weekly sessions for 4 weeks. Twenty-four hours after the last exposure, the hippocampi were collected and the inducibility of memory-related genes was examined using a real-time quantitative PCR method. NMDA NR2A, calcium/calmodulin-dependent protein kinase IV (CaMKIV), cyclic AMP-responsive element binding protein 1 (CREB1), and BDNF were significantly up-regulated in the hippocampi of WT mice exposed to 9ppm of toluene, compared to the expressions observed in WT mice exposed to filtered air, but similar results were not observed in nude mice. To investigate the possible involvement of peripheral T cells in the toluene-induced up-regulation of memory-related genes in WT mice, we examined the mRNA expression of Thy-1 (a pan T cell-specific marker) and quantified the number of cells that were immunoreactive to a T cell antigen receptor, CD3 (CD3-ir). Both the expression of Thy-1 mRNA and the number of CD3-ir cells were significantly higher in the hippocampi of the WT mice exposed to 9ppm of toluene, compared with that in WT mice exposed to filtered air; similar results were not observed in nude mice. We also examined the expression of chemokine genes like CCL2 and CCL3. The expression of CCL3 mRNA was significantly up-regulated only in the toluene-exposed WT mice. Although other differences unrelated to immune function may exist between WT and nude mice from the same background, the findings of the present study strongly suggest that the recruitment of peripheral T cells in the hippocampi of BALB/c WT mice exposed to low levels of toluene may be involved in the toluene-induced up-regulation of memory-related genes at the mRNA level.

Physical activity in relation to cancer of the colon and rectum in a cohort of male smokers

We examined the association between occupational and leisure physical activity and colorectal cancer in a cohort of male smokers. Among the 29,133 men aged 50-69 years in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention study,152 colon and 104 rectal cancers were documented during up to 12 years of follow-up. For colon cancer, compared with sedentary workers, men in light occupational activity had a relative risk (RR) of 0.60 [95% confidence interval (CI), 0.34-1.04], whereas those in moderate/heavy activity had an RR of 0.45 (CI, 0.26-0.78; P for trend, 0.003). Subsite analysis revealed a significant association for moderate/heavy occupational activity in the distal colon (RR, 0.21; CI, 0.09-0.51) but not in the proximal colon (RR, 0.87; CI, 0.40-1.92). There was no significant association between leisure activity and colon cancer (active versus sedentary; RR, 0.82; CI, 0.59-1.13); however, the strongest inverse association was found among those most active in both work and leisure (RR, 0.33; CI, 0.16-0.71). For rectal cancer, there were risk reductions for those in light (RR, 0.71; CI, 0.36-1.37) and moderate/heavy occupational activity (RR, 0.50; CI, 0.26-0.97; P for trend, 0.04), and no association for leisure activity. These data provide evidence for a protective role of physical activity in colon and rectal cancer.