Toluene inhalation in adolescent rats reduces flexible behaviour in adulthood and alters glutamatergic and GABAergic signalling

AMP-activated protein kinase activators have compound and concentration-specific effects on brain metabolism

AMP-activated protein kinase (AMPK) is a key sensor of energy balance playing important roles in the balancing of anabolic and catabolic activities. The high energy demands of the brain and its limited capacity to store energy indicate that AMPK may play a significant role in brain metabolism. Here, we activated AMPK in guinea pig cortical tissue slices, both directly with A769662 and PF 06409577 and indirectly with AICAR and metformin. We studied the resultant metabolism of [1-13C]glucose and [1,2-13C]acetate using NMR spectroscopy. We found distinct activator concentration-dependent effects on metabolism, which ranged from decreased metabolic pool sizes at EC50 activator concentrations with no expected stimulation in glycolytic flux to increased aerobic glycolysis and decreased pyruvate metabolism with certain activators. Further, activation with direct versus indirect activators produced distinct metabolic outcomes at both low (EC50) and higher (EC50 × 10) concentrations. Specific direct activation of β1-containing AMPK isoforms with PF 06409577 resulted in increased Krebs cycle activity, restoring pyruvate metabolism while A769662 increased lactate and alanine production, as well as labelling of citrate and glutamine. These results reveal a complex metabolic response to AMPK activators in brain beyond increased aerobic glycolysis and indicate that further research is warranted into their concentration- and mechanism-dependent impact.

Immp2l knockdown in male mice increases stimulus-driven instrumental behaviour but does not alter goal-directed learning or neuron density in cortico-striatal circuits in a model of Tourette syndrome and autism spectrum disorder

Cortico-striatal neurocircuits mediate goal-directed and habitual actions which are necessary for adaptive behaviour. It has recently been proposed that some of the core symptoms of autism spectrum disorder (ASD) and Gilles de la Tourette syndrome (GTS), such as tics and other repetitive behaviours, may emerge because of imbalances in these neurocircuits. We have recently developed a model of ASD and GTS by knocking down Immp2l, a mitochondrial gene frequently associated with these disorders. The current study sought to determine whether Immp2l knockdown (KD) in male mice alters flexible, goal- or cue- driven behaviour using procedures specifically designed to examine response-outcome and stimulus-response associations, which underlie goal-directed and habitual behaviour, respectively. Whether Immp2l KD alters neuron density in cortico-striatal neurocircuits known to regulate these behaviours was also examined. Immp2l KD mice and wild type-like mice (WT) were trained on Pavlovian and instrumental learning procedures where auditory cues predicted food delivery and lever-press responses earned a food outcome. It was demonstrated that goal-directed learning was not changed for Immp2l KD mice compared to WT mice, as lever-press responses were sensitive to changes in the value of the food outcome, and to contingency reversal and degradation. There was also no difference in the capacity of KD mice to form habitual behaviours compared to WT mice following extending training of the instrumental action. However, Immp2l KD mice were more responsive to auditory stimuli paired with food as indicated by a non-specific increase in lever response rates during Pavlovian-to-instrumental transfer. Finally, there were no alterations to neuron density in striatum or any prefrontal cortex or limbic brain structures examined. Thus, the current study suggests that Immp2l is not necessary for learned maladaptive goal or stimulus driven behaviours in ASD or GTS, but that it may contribute to increased capacity for external stimuli to drive behaviour. Alterations to stimulus-driven behaviour could potentially influence the expression of tics and repetitive behaviours, suggesting that genetic alterations to Immp2l may contribute to these core symptoms in ASD and GTS. Given that this is the first application of this battery of instrumental learning procedures to a mouse model of ASD or GTS, it is an important initial step in determining the contribution of known risk-genes to goal-directed versus habitual behaviours, which should be more broadly applied to other rodent models of ASD and GTS in the future.

The Effects of the Inhalant Toluene on Cognitive Function and Behavioral Flexibility: A Review of Recent Findings

Substance use disorder (SUD) is characterized, in part, by lack of control over drug seeking and taking. The prefrontal cortex (PFC) is highly involved in control of behavior and deficits in PFC structure and function have been demonstrated in clinical and preclinical studies of SUD. Of the various classes of drugs associated with the development of SUD, inhalants are among the least studied despite their widespread use among adolescents and children. In this work, we review what is currently known regarding the sites and mechanisms of action of inhalants with a focus on the volatile solvent toluene that is contained in a wide variety of legal and easily obtained products. We then describe how inhalants including toluene affect various behaviors with an emphasis on those associated with PFC function and how chronic use of inhalants alters brain structure and neuronal signaling. Findings from these studies highlight advances made in recent years that have expanded our understanding of the effects of inhalants on brain structure and reinforce the need for continued work in this field.

Beneficial effects of atypical antipsychotics on object recognition deficits after adolescent toluene exposure in mice: involvement of 5-HT1A receptors

Background: Inhalant (e.g. toluene) misuse by adolescents has been linked to psychosis and persistent cognitive deficits. Identifying effective strategies to improve cognitive deficits following chronic toluene misuse is critical. 5-HT_1A receptor has been proposed as a target for the treatment of cognitive deficits.Objectives: We compared the effects of antipsychotics on recognition deficits after adolescent toluene exposure in mice and elucidated the role of 5-HT_1A receptors in the cognition-improving effects of antipsychotics.Methods: Male NMRI mice (n = 279) received one injection per day of either toluene (750 mg/kg) or corn oil at postnatal days 35-39 and 42-46. Thereafter, the acute and subchronic effects of haloperidol, aripiprazole, or clozapine on toluene-induced recognition deficits were evaluated by novel object recognition test.Results: Acute administration of aripiprazole (p < .05) and clozapine (p < .01), but not haloperidol, significantly attenuated the toluene-induced recognition deficits. Pretreatment with 5-HT_1A receptor antagonist WAY -100,635 (p < .05) blocked their beneficial effects. Moreover, 5-HT_1A receptor agonist buspirone (p < .01) ameliorated the toluene-induced recognition deficits, which was reversed by WAY -100,635 (p < .001). Finally, after repeated treatment with clozapine, aripiprazole, and buspirone daily for 14 days, the impaired object recognition in toluene-exposed mice was significantly improved (p < .05) and the beneficial effects lasted for at least 2 weeks (p < .05).Conclusions: The results indicate that clozapine and aripiprazole, which display 5-HT_1A agonist properties, restored cognitive deficits in mice induced by adolescent toluene exposure. These findings suggest that these antipsychotics should be further explored as a potential treatment option for cognitive deficits in patients with psychosis associated with toluene exposure.

Impact of Inhibition of Glutamine and Alanine Transport on Cerebellar Glial and Neuronal Metabolism

The cerebellum, or “little brain”, is often overlooked in studies of brain metabolism in favour of the cortex. Despite this, anomalies in cerebellar amino acid homeostasis in a range of disorders have been reported. Amino acid homeostasis is central to metabolism, providing recycling of carbon backbones and ammonia between cell types. Here, we examined the role of cerebellar amino acid transporters in the cycling of glutamine and alanine in guinea pig cerebellar slices by inhibiting amino acid transporters and examining the resultant metabolism of [1-¹³C]d-glucose and [1,2-¹³C]acetate by NMR spectroscopy and LCMS. While the lack of specific inhibitors of each transporter makes interpretation difficult, by viewing results from experiments with multiple inhibitors we can draw inferences about the major cell types and transporters involved. In cerebellum, glutamine and alanine transfer is dominated by system A, blockade of which has maximum effect on metabolism, with contributions from System N. Inhibition of neural system A isoform SNAT1 by MeAIB resulted in greatly decreased metabolite pools and reduced net fluxes but showed little effect on fluxes from [1,2-¹³C]acetate unlike inhibition of SNAT3 and other glutamine transporters by histidine where net fluxes from [1,2-¹³C]acetate are reduced by ~50%. We interpret the data as further evidence of not one but several glutamate/glutamine exchange pools. The impact of amino acid transport inhibition demonstrates that the cerebellum has tightly coupled cells and that glutamate/glutamine, as well as alanine cycling, play a major role in that part of the brain.

The last two decades on preclinical and clinical research on inhalant effects

This paper reviews the scientific evidence generated in the last two decades on the effects and mechanisms of action of most commonly misused inhalants. In the first section, we define what inhalants are, how they are used, and their prevalence worldwide. The second section presents specific characteristics that define the main groups of inhalants: (a) organic solvents; (b) aerosols, gases, and volatile anesthetics; and (c) alkyl nitrites. We include a table with the molecular formula, structure, synonyms, uses, physicochemical properties and exposure limits of representative compounds within each group. The third and fourth sections review the direct acute and chronic effects of common inhalants on health and behavior with a summary of mechanisms of action, respectively. In the fifth section, we address inhalant intoxication signs and available treatment. The sixth section examines the health effects, intoxication, and treatment of nitrites. The seventh section reviews current intervention strategies. Finally, we propose a research agenda to promote the study of (a) solvents other than toluene; (b) inhalant mixtures; (c) effects in combination with other drugs of abuse; (d) age and (e) sex differences in inhalant effects; (f) the long-lasting behavioral effects of animals exposed in utero to inhalants; (g) abstinence signs and neurochemical changes after interrupting inhalant exposure; (h) brain networks involved in inhalant effects; and finally (i) strategies to promote recovery of inhalant users.

Adolescent chronic intermittent toluene inhalation dynamically regulates the transcriptome and neuronal methylome within the rat medial prefrontal cortex

Inhalants containing the volatile solvent toluene are misused to induce euphoria or intoxication. Inhalant abuse is most common during adolescence and can result in cognitive impairments during an important maturational period. Despite evidence suggesting that epigenetic modifications may underpin the cognitive effects of inhalants, no studies to date have thoroughly investigated toluene-induced regulation of the transcriptome or discrete epigenetic modifications within the brain. To address this, we investigated effects of adolescent chronic intermittent toluene (CIT) inhalation on gene expression and DNA methylation profiles within the rat medial prefrontal cortex (mPFC), which undergoes maturation throughout adolescence and has been implicated in toluene-induced cognitive deficits. Employing both RNA-seq and genome-wide Methyl CpG Binding Domain (MBD) Ultra-seq analysis, we demonstrate that adolescent CIT inhalation (10 000 ppm for 1 h/day, 3 days/week for 4 weeks) induces both transient and persistent changes to the transcriptome and DNA methylome within the rat mPFC for at least 2 weeks following toluene exposure. We demonstrate for the first time that adolescent CIT exposure results in dynamic regulation of the mPFC transcriptome likely relating to acute inflammatory responses and persistent deficits in synaptic plasticity. These adaptations may contribute to the cognitive deficits associated with chronic toluene exposure and provide novel molecular targets for preventing long-term neurophysiological abnormalities following chronic toluene inhalation.

K369I Tau Mice Demonstrate a Shift Towards Striatal Neuron Burst Firing and Goal-directed Behaviour

Pathological forms of the microtubule-associated protein tau are involved in a large group of neurodegenerative diseases named tauopathies, including frontotemporal lobar degeneration (FTLD-tau). K369I mutant tau transgenic mice (K3 mice) recapitulate neural and behavioural symptoms of FTLD, including tau aggregates in the cortex, alterations to nigrostriatum, memory deficits and parkinsonism. The aim of this study was to further characterise the K3 mouse model by examining functional alterations to the striatum. Whole-cell patch-clamp electrophysiology was used to investigate the properties of striatal neurons in K3 mice and wildtype controls. Additionally, striatal-based instrumental learning tasks were conducted to assess goal-directed versus habitual behaviours (i.e., by examining sensitivity to outcome devaluation and progressive ratios). The K3 model demonstrated significant alterations in the discharge properties of striatal neurons relative to wildtype mice, which manifested as a shift in neuronal output towards a burst firing state. K3 mice acquired goal-directed responding faster than control mice and were goal-directed at test unlike wildtype mice, which is likely to indicate reduced capacity to develop habitual behaviour. The observed pattern of behaviour in K3 mice is suggestive of deficits in dorsal lateral striatal function and this was supported by our electrophysiological findings. Thus, both the electrophysiological and behavioural alterations indicate that K3 mice have early deficits in striatal function. This finding adds to the growing literature which indicate that the striatum is impacted in tau-related neuropathies such as FTLD, and further suggests that the K3 model is a unique mouse model for investigating FTLD especially with striatal involvement.

Accelerated habitual learning resulting from L-dopa exposure in rats is prevented by N-acetylcysteine

Instrumental actions are initially goal-directed and driven by their associated outcome. However, with repeated experience habitual actions develop which are automated and efficient, as they are instead driven by antecedent stimuli. Dopamine is thought to facilitate the transition from goal-directed to habitual actions. This idea has been largely derived from evidence that psychostimulants accelerate the development of habitual actions. In the current study, we examined the impact of L-dopa (levodopa or L-dihydroxyphenylalanine), which also potentiates dopamine activity, on habitual learning. L-dopa was systemically administered prior to training rats to press a lever for a food outcome. When tested, L-dopa exposed animals were insensitive to changes in the value of the food outcome, and hence demonstrated accelerated habitual behavioral control compared to control animals that remained goal directed. We also showed that when N-acetylcysteine (NAC), an antioxidant and regulator of glutamate activity, was co-administered with L-dopa, it prevented the transition to habitual behavior; an effect demonstrated previously for cocaine. Therefore, this study establishes similarities between L-dopa and psychostimulants in both the development and prevention of habitual actions, and supports the notion that excess dopamine potentiates habitual learning. This finding extends the limited existing knowledge of the impact of L-dopa on learning and behavior, and has implications for neurological disorders where L-dopa is the primary treatment.

L-Aspartate, L-Ornithine and L-Ornithine-L-Aspartate (LOLA) and Their Impact on Brain Energy Metabolism

L-Ornithine-L-aspartate (LOLA), a crystalline salt, is used primarily in the management of hepatic encephalopathy. The degree to which it might penetrate the brain, and the effects it might have on metabolism in brain are poorly understood. Here, to investigate the effects of LOLA on brain energy metabolism we incubated brain cortical tissue slices from guinea pig (Cavea porcellus) with the constituent amino acids of LOLA, L-ornithine or L-aspartate, as well as LOLA, in the presence of [1-¹³C]D-glucose and [1,2-¹³C]acetate; these labelled substrates are useful indicators of brain metabolic activity. L-Ornithine produced significant "sedative" effects on brain slice metabolism, most likely via conversion of ornithine to GABA via the ornithine aminotransferase pathway, while L-aspartate showed concentration-dependent excitatory effects. The metabolic effects of LOLA reflected a mix of these two different processes and were concentration-dependent. We also investigated the effect of an intraperitoneal bolus injection of L-ornithine, L-aspartate or LOLA on levels of metabolites in kidney, liver and brain cortex and brain stem in mice (C57Bl6J) 1 h later. No significant changes in metabolite levels were seen following the bolus injection of L-aspartate, most likely due to rapid metabolism of aspartate before reaching the target tissue. Brain cortex glutamate was decreased by L-ornithine but no other brain effects were observed with any other compound. Kidney levels of aspartate were increased after injection of L-ornithine and LOLA which may be due to interference by ornithine with the kidney urea cycle. It is likely that without optimising chronic intravenous infusion, LOLA has minimal impact on healthy brain energy metabolism due to systemic clearance and the blood - brain barrier.

Minocycline prevents neuronal hyperexcitability and neuroinflammation in medial prefrontal cortex, as well as memory impairment caused by repeated toluene inhalation in adolescent rats

Toluene can be intentionally misused by adolescents to experience psychoactive effects. Toluene has a complex mechanism of action and broad behavioral effects, among which memory impairment is reported consistently. We have previously reported that repeated toluene inhalation (8000 ppm) increases layer 5 prelimbic pyramidal cells' excitability in the medial prefrontal cortex (mPFC) of adolescent rats. Toluene also produces reactive oxygen species (ROS), which activate glial cells. Here, we tested the hypothesis that the anti-inflammatory agent minocycline would decrease toluene's effects because it inhibits NF-κB (nuclear factor enhancer of the kappa light chains of activated B cells) and reduces pro-inflammatory cytokine and ROS production. Our results show that minocycline (50 mg/kg, ip, for 10 days) prevents the hyperexcitability of mPFC neurons observed after repeated 8000 ppm toluene exposure (30 min/day, 2×/day for 10 days). Minocycline prevents toluene-induced hyperexcitability by a mechanism that averts the loss of the slow calcium-dependent potassium current, and normalizes mPFC neurons' firing frequency. These effects are accompanied by significant decreased expression of astrocytes and activated microglia in the mPFC, reduced NLRP3 inflammasome activation and mRNA expression levels of the pro-inflammatory cytokine interleukin 1β (IL-1β), as well as increased mRNA expression of the anti-inflammatory cytokine transforming growth factor β (TGF-β). Minocycline also prevents toluene-induced memory impairment in adolescent rats in the passive avoidance task and the temporal order memory test in which the mPFC plays a central role. These results show that neuroinflammation produces several effects of repeated toluene administration at high concentrations, and minocycline can significantly prevent them.

Airborne toluene exposure causes germline apoptosis and neuronal damage that promotes neurobehavioural changes in Caenorhabditis elegans

Toluene is a highly volatile organic solvent present in gasoline. Exposure mainly occurs by absorption via the pulmonary tract and easily reaches the central nervous system, which causes toxic effects. Toluene toxicity has been described but not well established. The present work aimed to evaluate the effects of airborne exposure to toluene, the in vivo model Caenorhabditis elegans was assessed to determine whether nematode could be used to evaluate the effects of exposure to toluene and the possible mechanisms of toxicity of the solvent. Worms at the first or fourth larval stages were exposed to toluene for 48 or 24 h, respectively, in a laboratory-developed vapor chamber at concentrations of 450, 850, 1250 and 1800 ppm. We observed increases in worm mortality and significant developmental delays that occurred in a concentration-dependent manner. An increased incidence of apoptotic events in treated germline cells was shown, which was consistent with observed reductions in reproductive capacity. In addition, toluene promoted significant behavioural changes affecting swimming movements and radial locomotion, which were associated with changes in the fluorescence intensity and morphology of GABAergic and cholinergic neurons. We conclude that toluene exposure was toxic to C. elegans, with effects produced by the induction of apoptosis and neuronal damage.

The Abused Inhalant Toluene Impairs Medial Prefrontal Cortex Activity and Risk/Reward Decision-Making during a Probabilistic Discounting Task

Inhalant (e.g., toluene) misuse is linked to behavioral and cognitive deficits in humans, yet preclinical studies of the effect of inhalants on higher-order cognition are limited. We addressed this gap in the literature by examining the effect of toluene vapor exposure on risk/reward decision-making in male and female Sprague-Dawley rats using a probabilistic discounting task. In this task, rodents chose a risky/large reward or a safe/small reward, with the odds of risky reinforcement descending or ascending throughout the test session. We observed a dose-dependent, sex-independent deficit in behavioral flexibility during probabilistic discounting caused by acute toluene exposure. Rats exposed to toluene vapor during adolescence and tested as adults performed comparably to air-treated controls and were susceptible to the effects of an acute toluene challenge. These behavioral flexibility deficits observed suggests dysfunctional medial prefrontal cortex (mPFC) activity. To address this hypothesis, we virally expressed the genetically encoded calcium sensor GCaMP6f in glutamatergic mPFC neurons and monitored calcium transients in real-time using in vivo fiber photometry. mPFC activity peaked before either lever press during free-choice trials in toluene- and air-treated animals. During forced-choice trials, GCaMP6f transients shifted from pre-risky to pre-safe choice, an effect mitigated by acute toluene exposure. mPFC activity decreased during rewarded trials, with larger decreases following risky/large wins compared with safe/small wins. Toluene-treated animals also had decreased mPFC activity during rewarded trials, but there was no distinction between risky/large wins and safe/small wins. These results provide physiological evidence for mPFC-dependent behavioral deficits caused by toluene.SIGNIFICANCE STATEMENT Inhalants (e.g., toluene) are an understudied class of drugs of abuse that cause devastating behavioral and cognitive deficits in humans. Understanding the neurobiological interactions of toluene vapor using animal models is important for developing effective treatment strategies for inhalant addicts. Here we find that toluene vapor reduces behavioral flexibility in rodents making risk/reward-based decisions. The medial prefrontal cortex (mPFC) drives behavioral flexibility during this type of decision-making and we show that toluene reduces the ability of mPFC neurons to track optimal choices as reward probabilities change. Toluene also reduces these neurons' ability to distinguish between small and large rewards. A combination of these factors likely leads to the impaired performance in probabilistic discounting following acute toluene exposure.

The effect of adolescent inhalant abuse on energy balance and growth

The abuse of volatile solvents such as toluene is a significant public health concern, predominantly affecting adolescents. To date, inhalant abuse research has primarily focused on the central nervous system; however, inhalants also exert effects on other organ systems and processes, including metabolic function and energy balance. Adolescent inhalant abuse is characterized by a negative energy balance phenotype, with the peak period of abuse overlapping with the adolescent growth spurt. There are multiple components within the central and peripheral regulation of energy balance that may be affected by adolescent inhalant abuse, such as impaired metabolic signaling, decreased food intake, altered dietary preferences, disrupted glucose tolerance and insulin release, reduced adiposity and skeletal density, and adrenal hypertrophy. These effects may persist into abstinence and adulthood, and the long-term consequences of inhalant-induced metabolic dysfunction are currently unknown. The signs and symptoms resulting from chronic adolescent inhalant abuse may result in a propensity for the development of adult-onset metabolic disorders such as type 2 diabetes, however, further research investigating the long-term effects of inhalant abuse upon energy balance and metabolism are needed. This review addresses several aspects of the short- and long-term effects of inhalant abuse relating to energy and metabolic processes, including energy balance, intake and expenditure; dietary preferences and glycemic control; and the dysfunction of metabolic homeostasis through altered adipose tissue, bone, and hypothalamic-pituitary-adrenal axis function.

Adolescent inhalant use and psychosis risk - a prospective longitudinal study

BACKGROUND

Cross-sectional studies have suggested inhalant use is associated with psychosis. This association was examined in a longitudinal study accounting for other substance use and potential confounders.

METHODS

We used a prospective sample (N = 6542) from the Northern Finland Birth Cohort 1986. Self-report questionnaires on substance use and psychotic experiences were completed when the cohort members were 15-16 years old. Inhalant use was categorized into four groups (never, once, 2-4 times, 5 times or more). Subsequent psychosis diagnoses (ICD-10) until age 30 years were obtained from national registers. Cox regression analysis was used to examine the association between adolescent inhalant use and risk of psychosis.

RESULTS

During the observation period 124 individuals were diagnosed with incident psychosis. Overall, there were 225 (3.4%) subjects with any inhalant use, 18 (8.0%) of whom were diagnosed with psychosis during the follow up. Of non-inhalant users (n = 6317) 106 (1.7%) were diagnosed with psychosis. Compared to non-users, those using inhalants had increased risk of incident psychosis with most frequent inhalant use associated with the greatest risk (unadjusted HR = 9.46; 3.86-23.20). After adjusting for baseline psychotic experiences, other substance use, comorbid mental disorder and parental substance abuse, the increased risk of psychosis persisted (HR = 3.06; 1.05-8.95). Furthermore, a dose-response effect between inhalant use and risk of psychosis was identified (OR = 2.34; 1.83-2.99).

CONCLUSIONS

Inhalant use in adolescence was independently associated with incident psychosis. The adverse health outcomes associated with adolescent inhalant use provide compelling reasons for implementation of policies to reduce the use of volatile substances in adolescents.

Growth changes after inhalant abuse and toluene exposure: A systematic review and meta-analysis of human and animal studies

Inhalant abuse is a significant public health issue, particularly for adolescents, the predominant group of inhalant users. Adolescence is a critical growth period, and inhalant abuse has been associated with growth impairments, including reduced body weight and height. However, the extent to which inhalant abuse affects growth remains unquantified, and potential moderators remain unknown. To address this knowledge gap, a systematic review and meta-analysis of clinical human and preclinical animal studies utilizing toluene exposure (the primary solvent in abused products) was conducted. Five-hundred and sixty-nine studies were screened; 31 met inclusion criteria, yielding 64 toluene-control comparisons for body weight and 6 comparisons for height. Toluene exposure was negatively associated with body weight ( d = -0.73) and height ( d = -0.69). Concentration of inhaled toluene, but not duration, moderated the effect of toluene exposure on body weight, with more severe impairments at higher concentrations. Differences in effect size for body weight were observed for study characteristic subgroups including sex, age at first exposure, administration route and species. However, these findings should be interpreted cautiously due to low study numbers. Growth impairments, particularly during adolescence, can cause long-term health consequences. These effects on growth are therefore an important clinical outcome for individuals with a history of inhalant abuse.

Methamphetamine promotes habitual action and alters the density of striatal glutamate receptor and vesicular proteins in dorsal striatum

Goal-directed actions are controlled by the value of the consequences they produce and so increase when what they produce is valuable and decrease when it is not. With continued invariant practice, however, goal-directed actions can become habits, controlled not by their consequences but by antecedent, reward-related states and stimuli. Here, we show that pre-exposure to methamphetamine (METH) caused abnormally rapid development of habitual control. Furthermore, these drug-induced habits differed strikingly from conventional habits; we found that they were insensitive both to changes in reward value and to the effects of negative feedback. In addition to these behavioral changes, METH exposure produced bidirectional changes to synaptic proteins in the dorsal striatum. In the dorsomedial striatum, a structure critical for goal-directed action, METH exposure was associated with a reduction in glutamate receptor and glutamate vesicular proteins, whereas in the dorsolateral striatum, a region that has previously been implicated in habit learning, there was an increase in these proteins. Together, these results indicate that METH exposure promotes habitual control of action that appears to be the result of bidirectional changes in glutamatergic transmission in the circuits underlying goal-directed and habit-based learning.

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.

Persistent cognitive and morphological alterations induced by repeated exposure of adolescent rats to the abused inhalant toluene

While thepsychoactive inhalant toluene causes behavioral effects similarto those produced by other drugs of abuse, the persistent behavioral and anatomical abnormalities induced by toluene exposure are not well known. To mimic human "binge-like" inhalant intoxication, adolescent, male Sprague-Dawley rats were exposed to toluene vapor (5700ppm) twice daily for five consecutive days. These rats remained in their home cages until adulthood (P60), when they were trained in operant boxes to respond to a palatable food reward and then challenged with several different cognitive tasks. Rats that experienced chronic exposure to toluene plus abstinence ("CTA") showed enhanced performance in a strategy set-shifting task using a between-session, but not a within-session test design. CTA also blunted operant and classical conditioning without affecting responding during a progressive ratio task. While CTA rats displayed normal latent inhibition, previous exposure to a non-reinforced cue enhanced extinction of classically conditioned approach behavior of these animals compared to air controls. To determine whether CTA alters the structural plasticity of brain areas involved in set-shifting and appetitive behaviors, we quantified basal dendritic spine morphology in DiI-labeled pyramidal neurons in layer 5 of the medial prefrontal cortex (mPFC) and medium spiny neurons in the nucleus accumbens (NAc). There were no changes in dendritic spine density or subtype in the mPFC of CTA rats while NAc spine density was significantly increased due to an enhanced prevalence of long-thin spines. Together, these findings suggest that the persistent effects of CTA on cognition are related to learning and memory consolidation/recall, but not mPFC-dependent behavioral flexibility.

Influence of oil-related environmental pollutants on female reproduction

The petroleum low-weight aromatic hydrocarbons benzene, toluene, ethylbenzene, m/p-xylene, and o-xylene, also known as BTEX, are among the most common hazardous sources of environmental contamination. This paper reviews the available data concerning the effects of BTEX on different aspects of female reproduction, including the fecundity, ovaries, central nervous system (CNS), oocytes, embryos, oviducts, cytogenetics of somatic and generative cells, intracellular signaling systems, and hypothalamic, pituitary and peripheral reproductive hormones. Analysis of the available literature demonstrates that BTEX can exert negative effects on various female reproductive sites, including the CNS-pituitary-ovarian axis, their signaling molecules and receptors, ovarian follicles, corpora lutea, oocytes, embryos, oviducts, ovarian cycles, fertility, and the viability of offspring. These effects could be due to the ability of BTEX to destroy chromosomes, to affect cell metabolism, including the accumulation of free radicals, and to affect the release of hormonal regulators of reproductive processes and intracellular protein kinases.