Multifocal central nervous system damage caused by toluene abuse

Drug- and Toxin-Induced Opsoclonus - a Systematized Review, including a Case Report on Amantadine-Induced Opsoclonus in Multiple System Atrophy

Background

Opsoclonus is a rare disorder characterized by conjugate multidirectional, horizontal, vertical, and torsional saccadic oscillations, without intersaccadic interval, resulting from dysfunction within complex neuronal pathways in the brainstem and cerebellum. While most cases of opsoclonus are associated with autoimmune or paraneoplastic disorders, infectious agents, trauma, or remain idiopathic, opsoclonus can also be caused by medications affecting neurotransmission. This review was prompted by a case of opsoclonus occurring in a patient with Multiple System Atrophy, where amantadine, an NMDA-receptor antagonist, appeared to induce opsoclonus.

Methods

Case report of a single patient and systematized review of toxic/drug-induced opsoclonus, selecting articles based on predefined criteria and assessing the quality of included studies.

Results

The review included 30 articles encompassing 158 cases of toxic/drug-induced opsoclonus. 74% of cases were attributed to bark scorpion poisoning, followed by 9% of cases associated with chlordecone intoxication. The remaining cases were due to various toxics/drugs, highlighting the involvement of various neurotransmitters, including acetylcholine, glutamate, GABA, dopamine, glycine, and sodium channels, in the development of opsoclonus.

Conclusion

Toxic/drug-induced opsoclonus is very rare. The diversity of toxics/drugs impacting different neurotransmitter systems makes it challenging to define a unifying mechanism, given the intricate neuronal pathways underlying eye movement physiology and opsoclonus pathophysiology.

Evaluating the Economic Benefits of Tightening Regulations on the Use of Toluene, a Hazardous Chemical, in South Korea

The South Korean government currently designates toluene as a hazardous chemical, only limiting its use in products that are feared to be harmful. Since no measures to prohibit the use of toluene have been implemented, toluene is frequently detected in amounts that exceed the limit. Accordingly, the Government is considering implementing a plan to tighten the current regulations related to the use of toluene to prevent the occurrence of diseases caused by exposure and addiction to it. Therefore, the most important objective of this research is to evaluate quantitatively the economic benefits arising from the implementation of the plan in South Korea. To achieve the purpose of this paper, contingent valuation, an economic technique for analyzing data collected from a survey of people based on economic theory, is applied. For this purpose, a survey of 1000 people nationwide is conducted, and an analysis model that is well received in the literature is adopted. In other words, the annual willingness to pay (WTP) per household to strengthen the regulations to reduce the human health risks of toluene is evaluated to calculate its economic benefits. All the estimated WTP models secure statistical significance. The average WTP per household per annum is derived as KRW 3394 (USD 3.02). Considering that the country contained 20,573,060 households in 2021, the national economic benefits are calculated as KRW 69.82 billion (USD 62.23 million) every year. It is difficult to estimate accurately the costs incurred by tightening the regulations on toluene use, but they do not seem to exceed the benefits. Because tightening the regulations would be socially desirable, the Government would be justified in making this decision.

Prenatal Exposure to Paint Thinner Alters Postnatal Development and Behavior in Mice

Occupational exposure and sniffing of volatile organic solvents continue to be a worldwide health problem, raising the risk for teratogenic sequelae of maternal inhalant abuse. Real life exposures usually involve simultaneous exposures to multiple solvents, and almost all the abused solvents contain a mixture of two or more different volatile compounds. However, several studies examined the teratogenicity due to industrial exposure to a single volatile solvent but investigating the teratogenic potential of complex chemical mixture such as thinner remains unexplored. This study was undertaken to evaluate developmental neurotoxicity of paint thinner using a mouse model. Mated female mice (N = 21) were, therefore, exposed to repeated and brief inhalation episodes of 0, 300 or 600 ppm of thinner during the entire period of pregnancy. Females weigh was recorded and their standard fertility and reproductive parameters were assessed. After birth postnatal day 1 (PND1), offspring (N = 88) length and body weight were measured in a daily basis. At PND5, the pups were assessed for their postnatal growth, physical maturation, reflex development, neuromotor abilities, sensory function, activity level, anxiety, depression, learning and memory functions. At adulthood, structural changes of the hippocampus were examined by estimating the total volume of the dentate gyrus. Except one case of thinner induced abortion at the higher dose, our results showed that the prenatal exposure to the solvent did not cause any maternal toxicity or decrease in the viability of the offspring. Therefore, a lower birth weight, decrease in the litter size and delayed reflexes ontogeny were registered in prenatally exposed offspring to both 300 ppm and 600 ppm of thinner. In addition, prenatally exposure to thinner resulted in increased anxiolytic- and depression-like behaviors. In contrast, impaired learning and memory functions and decreased hippocampal dentate gyrus volume were revealed only in the prenatally treated offspring by 600 ppm of thinner. Based on these results, we can conclude that prenatally exposure to paint thinner causes a long-lasting developmental neurotoxicity and alters a wide range of behavioral functions in mice. This shows the risk that mothers who abuse thinner paint expose their offspring.

Heterogeneous Reactions between Toluene and NO2 on Mineral Particles under Simulated Atmospheric Conditions

Heterogeneous reactions between organic and inorganic gases with aerosols are important for the study of smog occurrence and development. In this study, heterogeneous reactions between toluene and NO₂ with three atmospheric mineral particles in the presence or absence of UV light were investigated. The three mineral particles were SiO₂, α-Fe₂O₃, and BS (butlerite and szmolnokite). In a dark environment, benzaldehyde was produced on α-Fe₂O₃. For BS, nitrotoluene and benzaldehyde were obtained. No aromatic products were produced in the absence of NO₂ in the system. In the presence of UV irradiation, benzaldehyde was detected on the SiO₂ surface. Identical products were produced in the presence and absence of UV light over α-Fe₂O₃ and BS. UV light promoted nitrite to nitrate on mineral particles surface. On the basisi of the X-ray photoelectron spectroscopy (XPS) results, a portion of BS was reduced from Fe³⁺ to Fe²⁺ with the adsorption of toluene or the reaction with toluene and NO₂. Sulfate may play a key role in the generation of nitrotoluene on BS particles. From this research, the heterogeneous reactions between organic and inorganic gases with aerosols that occur during smog events will be better understood.

Toluene and methylethylketone: effect of combined exposure on their metabolism in rat

1. Multiple exposures are ubiquitous in industrial environments. In this article, we highlight the risks faced by workers and complete the data available on the metabolic impact of a common mixture: toluene (TOL) and methylethylketone (MEK). 2. Rats were exposed by inhalation under controlled conditions either to each solvent individually, or to mixtures of the two. How the interaction between the two solvents affected their fate in the blood and brain, their main relevant urinary metabolites (o-cresol, benzylmercapturic acid for TOL and 2,3-butanediols for MEK) and their hepatic metabolism were investigated. 3. Although the cytochrome P450 concentration was unchanged, and the activities of CYP1A2 and CYP2E1 isoforms were not additively or synergistically induced by co-exposure, TOL metabolism was inhibited by the presence of MEK (and vice versa). Depending on the relative proportions of each compound in the mixture, this sometimes resulted in a large increase in blood and brain concentrations. Apart from extreme cases (unbalanced mixtures), the amount of o-cresol and benzylmercapturic acid (and to a lesser extent 2,3-butanediols) excreted were proportional to the blood solvent concentrations. 4. In a co-exposure context, ortho-cresol and benzylmercapturic acid can be used as urinary biomarkers in biomonitoring for employees to relatively accurately assess TOL exposure.

Membrane fluidity does not explain how solvents act on the middle-ear reflex

Some volatile aromatic solvents have similar or opposite effects to anesthetics in the central nervous system. Like for anesthetics, the mechanisms of action involved are currently the subject of debate. This paper presents an in vivo study to determine whether direct binding or effects on membrane fluidity best explain how solvents counterbalance anesthesia's depression of the middle-ear reflex (MER). Rats were anesthetized with a mixture of ketamine and xylazine while also exposed to solvent vapors (toluene, ethylbenzene, or one of the three xylene isomers) and the amplitude of their MER was monitored. The depth of anesthesia was standardized based on the magnitude of the contraction of the muscles involved in the MER, determined by measuring cubic distortion product oto-acoustic emissions (DPOAEs) while triggering the bilateral reflex with contralateral acoustic stimulation. The effects of the aromatic solvents were quantified based on variations in the amplitude of the DPOAEs. The amplitude of the alteration to the MER measured in anesthetized rats did not correlate with solvent lipophilocity (as indicated by logKow values). Results obtained with the three xylene isomers indicated that the positions of two methyl groups around the benzene ring played a determinant role in solvent/neuronal cell interaction. Additionally, Solid-state Nuclear Magnetic Resonance (NMR) spectra for brain microsomes confirmed that brain lipid fluidity was unaffected by solvent exposure, even after three days (6h/day) at an extremely high concentration (3000ppm). Therefore, aromatic solvents appear to act directly on the neuroreceptors involved in the acoustic reflex circuit, rather than on membrane fluidity. The affinity of this interaction is determined by stereospecific parameters rather than lipophilocity.

Effects of acute and chronic inhalation of paint thinner in mice: behavioral and immunohistochemical study

Abuse of volatile inhalants has become a worldwide issue mainly among adolescents of low income social class. Acute and chronic exposure to these substances results in serious neurological and behavioral impairments. Although real exposure consists largely of simultaneous inhalation of multiple solvents, the vast majority of basic research studies have evaluated the actions of a single volatile component leaving the behavioral and neuronal effects of chemical mixture not fully understood. In this study, we investigated the acute behavioral effects of 300, 450 and 600 ppm of paint thinner inhalation on anxiety, locomotor activity and spatial memory. Additionally, the cognitive impairments related to chronic exposure of the same concentrations of thinner for 45 days were assessed. To understand the neuronal correlates of acute exposure to thinner, we used c-Fos immunohistochemistry as an endogenous marker of neuronal activation following 600 ppm of thinner. The results reveal that (i) chronically thinner exposed mice showed cognitive deficits in Morris water maze and object recognition tasks; (ii) acute inhalation of thinner induces a wide range of behavioral changes. These changes include an anxiolytic effect toward the aversive environmental bright light and a dose dependent effect on explorative locomotion. The wide range of behavioral alterations induced by acute thinner inhalation is consistent with the widespread distribution of thinner-induced c-Fos expression in multiple brain structures.

Subsurface cistern (SSC) proliferation in Purkinje cells of the rat cerebellum in response to acute and chronic exposure to paint thinner: A light and electron microscopy study

Intentional inhalation and occupational exposure are two ways humans are exposed to thinner, a widely employed solvent in industry. Inhalation of thinner induces toxic effects in various organs, with the cerebellum being one of the most affected structures of the CNS. The aim of this work was to describe specific structural alterations of cerebellum Purkinje cells in rats following exposure to thinner for 16 weeks. A histological analysis of the cerebellum of solvent-exposed rats revealed swollen Purkinje cell dendrites surrounded by empty space, and electronic microscopy showed an increase in the number of subsurface cisterns (SSCs) within their dendritic processes. After a period of non-exposure, the number of SSCs decreased without reaching normal levels, suggesting a degree of plasticity. Purkinje cell SSCs, which are derived from smooth endoplasmic reticulum, contain inositol trisphosphate receptors (IP3Rs), ryanodine receptors (RR), and a recently identified characteristic cluster of large conductance calcium-activated potassium (BKCa) channels. We found that SSCs in Purkinje cell dendrites were closely associated with mitochondria, and immunofluorescence microscopy showed higher levels of RR and calbindin receptors (CB), in Purkinje cells of exposed than normal rats. These changes are probably related to behavioral manifestations of cerebellar alterations, such as imbalance and ataxia, consistent with the suggested involvement of increases in SSCs in ataxia in rats and humans. This increase in SSCs, taken together with the localization of RR, IP3R and BKCa proteins in this structure, suggests altered intracellular calcium-buffering processes in the Purkinje cells of thinner-exposed rats.

Binge toluene exposure in pregnancy and pre-weaning developmental consequences in rats

Binge Toluene Exposure in Pregnancy and Pre-weaning Developmental Consequences in Rats. Bowen, S.E. and Hannigan, J.H. The persistent rate of abuse of inhaled organic solvents, especially among women of child-bearing age, raises the risk for teratogenic effects of maternal toluene abuse. In this study, timed-pregnant Sprague Dawley rats were exposed from Gestation Day (GD) 8 to GD20 to 12,000 or 8000 parts per million (ppm) toluene, or 0ppm (controls) for 30min twice daily, 60min total daily exposure. Pups were assessed from postnatal day (PN) 4 to PN21 using a developmental battery measuring growth (i.e., body weight), maturational milestones (e.g., eye opening & incisor eruption), and biobehavioral development (e.g., negative geotaxis & surface righting). Pups exposed in utero to 12,000ppm or 8000ppm toluene weighed significantly less than the non-exposed control pups beginning at PN4 and PN12 (respectively) until PN21. Toluene resulted in significant increases in an index of poor perinatal outcome, specifically a composite of malformations, defined "runting" and neonatal death. No significant delays were observed in reaching maturational milestones. The results reveal that brief, repeated, prenatal exposure to high concentrations of toluene can cause growth retardation and malformations in rats. A comparison of the present, conservative results with findings in previous studies implies that binge patterns of toluene exposure in pregnant rats modeling human solvent abuse can result in developmental and morphological deficits in offspring. These results do not exclude the possibility that maternal toxicity as well as teratogenic effects of toluene may contribute to outcomes. The results suggest that abuse of inhaled organic solvents like toluene may result in similar early developmental outcomes in humans.

Solvents and Parkinson disease: a systematic review of toxicological and epidemiological evidence

Parkinson disease (PD) is a debilitating neurodegenerative motor disorder, with its motor symptoms largely attributable to loss of dopaminergic neurons in the substantia nigra. The causes of PD remain poorly understood, although environmental toxicants may play etiologic roles. Solvents are widespread neurotoxicants present in the workplace and ambient environment. Case reports of parkinsonism, including PD, have been associated with exposures to various solvents, most notably trichloroethylene (TCE). Animal toxicology studies have been conducted on various organic solvents, with some, including TCE, demonstrating potential for inducing nigral system damage. However, a confirmed animal model of solvent-induced PD has not been developed. Numerous epidemiologic studies have investigated potential links between solvents and PD, yielding mostly null or weak associations. An exception is a recent study of twins indicating possible etiologic relations with TCE and other chlorinated solvents, although findings were based on small numbers, and dose-response gradients were not observed. At present, there is no consistent evidence from either the toxicological or epidemiologic perspective that any specific solvent or class of solvents is a cause of PD. Future toxicological research that addresses mechanisms of nigral damage from TCE and its metabolites, with exposure routes and doses relevant to human exposures, is recommended. Improvements in epidemiologic research, especially with regard to quantitative characterization of long-term exposures to specific solvents, are needed to advance scientific knowledge on this topic.

Inhaled toluene can modulate the effects of anesthetics on the middle-ear acoustic reflex

Toluene (Tol) is an organic solvent widely used in the industry. It is also abused as an inhaled solvent, and can have deleterious effects on hearing. Recently, it was demonstrated that Tol has both anticholinergic and antiglutamatergic effects, and that it also inhibits voltage-dependent Ca(2+) channels. This paper describes a study of the effects of inhaled Tol on rats anesthetized with isoflurane, pentobarbital, or a mixture of ketamine/xylazine. Hearing was tested using distortion product oto-acoustic emissions (DPOAEs) associated with a contralateral noise to evaluate contraction of the middle-ear muscles. This allowed us to assess the interactions between the effects of Tol and anesthesia on the central nervous system (CNS). Although both anesthetics and Tol are known to inhibit the middle-ear acoustic reflex, our data indicated that inhaled Tol counterbalances the effects of anesthetic in a dose-dependent manner. In other terms, Tol can increase the amplitude of the middle-ear reflex in anesthetized rats, whatever the nature of the anesthetic used. This indicates that inhaling Tol (a Ca(2+)-channel-blocking drug) modifies the potency of anesthesia, and thereby the amplitude of the middle-ear reflex.

Neurotoxins: free radical mechanisms and melatonin protection

Toxins that pass through the blood-brain barrier put neurons and glia in peril. The damage inflicted is usually a consequence of the ability of these toxic agents to induce free radical generation within cells but especially at the level of the mitochondria. The elevated production of oxygen and nitrogen-based radicals and related non-radical products leads to the oxidation of essential macromolecules including lipids, proteins and DNA. The resultant damage is referred to as oxidative and nitrosative stress and, when the molecular destruction is sufficiently severe, it causes apoptosis or necrosis of neurons and glia. Loss of brain cells compromises the functions of the central nervous system expressed as motor, sensory and cognitive deficits and psychological alterations. In this survey we summarize the publications related to the following neurotoxins and the protective actions of melatonin: aminolevulinic acid, cyanide, domoic acid, kainic acid, metals, methamphetamine, polychlorinated biphenyls, rotenone, toluene and 6-hydroxydopamine. Given the potent direct free radical scavenging activities of melatonin and its metabolites, their ability to indirectly stimulate antioxidative enzymes and their efficacy in reducing electron leakage from mitochondria, it would be expected that these molecules would protect the brain from oxidative and nitrosative molecular mutilation. The studies summarized in this review indicate that this is indeed the case, an action that is obviously assisted by the fact that melatonin readily crosses the blood brain barrier.

Addictive illegal drugs: structural neuroimaging

Illegal addictive drugs can lead to functional or structural impairment of the central nervous system. This review provides an overview of the structural imaging findings on CT, MR imaging, and conventional angiography related to chronic and acute abuse of the most commonly abused illegal drugs, including cannabis, organic solvents, and amphetamines and opioids and their respective derivatives. Pathomechanisms include excitotoxicity, which may lead to an acute or subacute leukoencephalopathy, and vascular complications, including vasoconstriction, vasculitis, or hypertension, which may lead to intracranial hemorrhage or ischemia. Because clinical findings alone are often nonspecific, and afflicted patients are unlikely to admit to the substance abuse, the neuroradiologist may play an important role in establishing the diagnosis and, thereby, initiating treatment.

Abuse pattern of toluene exposure alters mouse behavior in a waiting-for-reward operant task

Inhaling solvents for recreational purposes continues to be a world-wide public health concern. Toluene, a volatile solvent in many abused products, adversely affects the central nervous system. However, the long-term neurobehavioral effects of exposure to high-concentration, binge patterns typical of toluene abuse remain understudied. We studied the behavioral effects of repeated toluene exposure on cognitive function following binge toluene exposure on behavioral impulse control in Swiss Webster mice using a "wait-for-reward" operant task. Mice were trained on a fixed-ratio (FR) schedule using sweetened milk as a reward. Upon achieving FR15, a wait component was added which delivered free rewards in the absence of responses at increasing time intervals (2s, 4s, 6s, etc...). Mice continued to receive free rewards until they pressed a lever that reinstated the FR component (FR Reset). Once proficient in the FR-Wait task, mice were exposed to either 1000 ppm, 3600 ppm or 6000 ppm toluene, or 0ppm (air controls) for 30 min per day for 40 days. To avoid acute effects of toluene exposure, behavior was assessed approximately 22-23 h later. Repeated toluene exposure decreased response rates, the number of FR resets, and increased mean wait time, resulting in a higher response-to-reinforcer ratio than exhibited by controls. Mice receiving the higher exposure level (6000 ppm) showed a dramatic decrease in the number of rewards received, which was reversed when toluene exposure ceased. Mice receiving the lower exposure level (1000 ppm) showed little change in the number of rewards. These results indicate that repeated binge exposures to high concentrations of toluene can significantly interfere with performance as measured by a waiting-for-reward task, suggesting a significant impact on cognitive and/or psychomotor function.

Toluene misuse and long-term harms: a systematic review of the neuropsychological and neuroimaging literature

Organic solvent abuse is associated with increased risk for serious medical, neurological, and neuropsychological impairments. While animal research suggests that exposure to organic solvents (especially toluene) may be neurotoxic, much less is known about the consequences of long-term exposure in humans. We reviewed neuroimaging and neuropsychological studies examining chronic toluene misuse in humans. Thirty empirical studies fulfilled the inclusion and exclusion criteria, including case studies (n=9) as well as group studies with (n=11) and without a control group (n=10). Our review indicates that toluene preferentially affects white matter (relative to gray matter) structures and periventricular/subcortical (relative to cortical) regions. The lipid-dependent distribution and pharmacokinetic properties of toluene appears to explain the pattern of MRI abnormalities, as well as the common symptoms and signs of toluene encephalopathy. The commonly observed neuropsychological deficits such as impairments in processing speed, sustained attention, memory retrieval, executive function and language, are also consistent with white matter pathology. We discuss the implications of these findings in the context of a neurodevelopmental framework, as well as the neuropathology and pathophysiology of toluene abuse. We also propose a set of recommendations to guide future research in this area.

Maternal and fetal blood and organ toluene levels in rats following acute and repeated binge inhalation exposure

Inhalation of organic solvents is a persistent form of drug abuse with particular concern being the abuse of inhalants by women of child-bearing age. While studies have begun assessing postnatal outcomes of offspring exposed prenatally to inhalants, relatively little is known about the distribution of toluene in blood and body tissues of pregnant, inhalant-abusing women, or in the fetuses. The present study assessed the tissue toluene levels attained following brief toluene exposures using a pre-clinical rat model of maternal inhalant abuse. Timed-pregnant Sprague-Dawley rats were exposed to toluene at 8000 or 12,000 parts per million (ppm) for 15, 30 or 45 min/exposure. Exposures occurred twice each day from gestational day 8 (GD8) through GD20. Immediately following the second exposure on GD8, GD14 and GD20 blood was taken from the saphenous vein of the dams. Following saphenous vein blood collection on GD20, dams were sacrificed and trunk blood was collected along with maternal tissue specimens from cerebellum, heart, lung, kidney and liver. The placenta, amniotic fluid and fetal brain were also collected. Results demonstrated that maternal saphenous blood toluene levels increased as the inhaled concentration of toluene and duration of exposure increased. The maternal cerebellum, heart, kidney and liver appeared to be saturated after 30 min on GD20 such that toluene levels in those organs were equivalent across all ambient concentrations of inhaled toluene. Toluene levels also increased in fetal brain as the inhaled concentration of toluene increased and in placenta and amniotic fluid as the duration of exposure increased. Toluene levels in all tissues at GD20, except maternal lung and amniotic fluid, were higher than in maternal saphenous blood suggesting that toluene concentrated in those organs. Measurement of toluene levels in blood and other tissues following repeated toluene exposure demonstrated that toluene readily reaches a variety of potential sites of action throughout the maternal-placental-fetal unit.

An update on opsoclonus

PURPOSE OF REVIEW

The aim of this article is to review opsoclonus, with particular emphasis on its immunopathogenesis and pathophysiology.

RECENT FINDINGS

Infections (West Nile virus, Lyme disease), neoplasms (non-Hodgkin's lymphoma, renal adenocarcinoma), celiac disease, and allogeneic hematopoietic stem cell transplantation can cause opsoclonus. Newly identified autoantibodies include antineuroleukin, antigliadin, antiendomysial, and anti-CV2. Evidence suggests that the autoantigens of opsoclonus reside in postsynaptic density, or on the cell surface of neurons or neuroblastoma cells (where they exert antiproliferative and proapoptotic effects). Most patients, however, are seronegative for autoantibodies. Cell-mediated immunity may also play a role, with B and T-cell recruitment in the cerebrospinal fluid linked to neurological signs. Rituximab, an anti-CD20 monoclonal antibody, seems efficacious as an adjunctive therapy. Although changes in synaptic weighting of saccadic burst neuron circuits in the brainstem have been implicated, disinhibition of the fastigial nucleus in the cerebellum, or damage to afferent projections to the fastigial nucleus, is a more plausible pathophysiologic mechanism which is supported by functional magnetic resonance imaging findings in patients.

SUMMARY

There is increasing recognition that both humoral and cell mediated immune mechanisms are involved in the pathogenesis of opsoclonus. Further studies are needed to further elucidate its immunopathogenesis and pathophysiology in order to develop novel and efficacious therapy.

Gestational toluene exposure effects on spontaneous and amphetamine-induced locomotor behavior in rats

Gestational Toluene Exposure Effects on Spontaneous and Amphetamine-Induced Locomotor Behavior in Rats. Bowen, S.E., Mohammadi, M.H., Batis, J.C., and Hannigan, J.H. Neurotoxicology and Teratology, XX, 2006. The abuse of volatile organic solvents (inhalants) continues to be a major health concern throughout the world. Toluene, which is found in many products such as glues and household cleaners, is among the most commonly abused organic solvents. The neurobehavioral teratogenic sequelae of solvent abuse (i.e., repeated, brief inhalation exposures to very high concentrations of solvents) have not been examined thoroughly. In a preclinical model of inhalant abuse, timed-pregnant Sprague-Dawley rats were exposed to 0, 8000, or 12,000 parts per million (ppm) for 15 min twice daily from gestation day 8 (GD8) through GD20. In the first experiment, separate groups of offspring were observed individually in an open-field on postnatal day 22 (PN22), PN42 or PN63. In the second experiment, other offspring given identical prenatal toluene exposures were observed in an "open-field" following an acute i.p. injection of amphetamine (0, 0.56, 1.78 mg/kg) on PN28. Automated measurements of distance traveled and ambulatory time were recorded. Prenatal toluene exposure resulted in small alterations in spontaneous activity compared to non-exposed rats. Prenatal exposure to 12,000 ppm toluene resulted in significant hyposensitivity to the locomotor stimulatory effects of the amphetamine challenge in male but not female rats on PN28. The results demonstrate that prenatal exposure to abuse patterns of high concentrations of toluene through inhalation can alter spontaneous and amphetamine-induced locomotor behavior in rats. The expression of these effects also appears to depend upon the postnatal age of testing. These results imply that abuse of organic solvents during pregnancy in humans may also produce long-lasting effects on biobehavioral development.

Clinical, socio-demographic, neurophysiological and neuropsychiatric evaluation of children with volatile substance addiction

BACKGROUND

Abuse of organic volatile substances in children has become a social health problem that is increasing in the recent years. Among these substances, toluene is highly preferred by abusers because of its euphoric effect, cheapness and easy availability. There is no published research on the clinical and neurophysiological evaluation of children with short-term volatile substance addiction.

METHODS

In this study, socio-demographic characteristics were questioned in 12 children with a mean age of 15 years and a duration of toluene abuse for a mean of 2.3 years, and the clinical characteristics of central and peripheral nervous system damage caused by volatile substances, particularly by toluene were analysed, and probable neurological disorders were investigated by means of neurophysiological and neuropsychological tests. All tests were compared with a control group.

RESULTS

Fifty-eight percent of the children included in the study had pathological findings in the neurological examination. There was pyramidal involvement in 25% and peripheral nerve involvement in 33.3% of the cases. Evaluation of the cognitive functions revealed 33.3% pathology in the 'Short Test of Mental Status' which assesses functions of orientation, attention, learning, arithmetic calculation, abstraction, information, construction and recall. Sensorial polyneuropathy was found in 33.3% of the cases in nerve conduction studies. Somatosensory-evoked potentials revealed pathology in 16.7% of the cases and brainstem-evoked potentials in 50% of the cases. No pathology was observed in electroencephalography and visual-evoked potentials.

CONCLUSION

In our study, neurophysiological and neuropsychiatric tests revealed that toluene causes slow progressive, clinical and subclinical central and peripheral nerve damage. In Turkey, because of cheapness, easy availability and legal use of volatile substances, the clinical extent of systemic and neurological toxicity of volatile substance abuse is increasing. Abuse of volatile substances, a currently increasing social issue, may create important physical problems which can be permanent.

Toxic Encephalopathies

Effective brain function is dependent on precise and complex interactions among neurotransmitters, hormones, enzymes, and electrolytes. Many of the chemically complex substances with which we come into contact can disrupt this intricately balanced system. Toxic substances, whether ingested, inhaled, or absorbed through the skin, may cause an encephalopathic state directly by affecting the brain itself or indirectly by compromising the brain's supportive systems. The article focuses on neurotoxins (heavy metals, solvents and vapors, pesticides, and natural neurotoxins) that directly induce an encephalopathic state.

Abuse pattern of gestational toluene exposure and early postnatal development in rats

Inhalant abuse in the United States trails only alcohol, marijuana and nicotine abuse. Toluene, found in glues and cleaners, is among the most commonly abused inhalants. While teratogenicity due to occupational exposure to organic solvents (i.e., relatively long-term exposure to lower concentrations) has been studied, the teratogenic potential of organic solvent abuse (i.e., brief inhalation exposures to very high concentrations) has not been thoroughly examined. In a preclinical model of abuse patterns of fetal solvent exposure, timed-pregnant rats were exposed to 8000 parts per million (ppm) or 12,000 ppm of toluene, or to air (0 ppm), for 15 min twice daily from gestation day 8 (GD8) through GD20. After parturition, pups were tested from postnatal day 4 (PN4) to PN21 in a developmental test battery including measures of growth (i.e., body weight), maturational milestones (i.e., pinnae unfolding, incisor eruption and eye opening) and biobehavioral development (e.g., negative geotaxis, surface righting and grip strength). Pups exposed in utero to 12,000 ppm toluene weighed significantly less than the control pups at all ages before PN16. There were significant toluene-induced increases in an index of poor perinatal outcome (i.e., a combination of malformations, "runting" and neonatal death) and deficits in negative geotaxis. There were no significant delays in reaching maturational milestones. The results demonstrate that brief, repeated, prenatal exposure to high concentrations of toluene can cause growth restriction, malformation and impairments of biobehavioral development in rats. A comparison of the present outcomes to previous studies of occupational exposure patterns suggests that for a given daily "dose" of toluene, a binge pattern of exposure may pose a greater risk for fetal development. Since the pattern of exposure in this experiment models binge exposure in human solvent abuse, the results imply that abuse of inhaled organic solvents, such as toluene, can cause similar teratogenic outcomes in humans.

The effects of toluene on the central nervous system

In recent decades the organic solvent toluene (methylbenzene) has emerged as one of the best-studied neurotoxins. Long-term and intense exposure to toluene vapors in humans who abuse spray paint and related substances has led to the recognition that toluene has a severe impact on central nervous system myelin. Chronic toluene abuse produces a devastating neurological disorder, of which dementia is the most disabling component. The clinical syndrome, toluene leukoencephalopathy, can be detected by a combination of characteristic symptoms and signs, detailed neurobehavioral evaluation, and brain magnetic resonance imaging. In this paper, we consider the impact of toluene abuse on our society, describe the specific neurobehavioral deficits in toluene leukoencephalopathy, review the spectrum of neuroimaging findings in patients with this disorder, summarize the teratogenic effects of toluene in both humans and animal models, and offer possible explanations for the range of neuropathological damage seen in brains of individuals who chronically abuse toluene.

Single-voxel proton MR spectroscopy in toluene abuse

Inhalation of toluene, which is an organic solvent, causes toxic encephalopathy characterized by cognitive impairment, cerebellar and extra-pyramidal symptoms. We studied cranial MR images and single-voxel MR spectroscopy of 22 toluene abusers and age-matched control subjects. The mean age of the abusers and mean duration of abuse were 18,1 years and 47 months, respectively. We got three MR spectra from the centrum semiovale, cerebellum and thalamus by using STEAM sequence with a TE value of 30 ms. N-acetyl aspartate (NAA)/Creatine (Cr), Choline (Cho)/Cr, myo-inositol (mI)/Cr peak integral ratios were calculated. NAA/Cr in the cerebellum and centrum semiovale of the abusers were significantly lower than those of the control subjects. mI/Cr in centrum semiovale and cerebellum were higher in toluene abusers. No significant difference was found in the metabolite ratios of the thalami. The association of NAA/Cr and mI/Cr ratios in cerebellum and centrum semiovale with the duration of abuse was significant. Normal level of NAA in thalamus, which was a neuron rich gray matter structure, might imply that toluene inhalation did not cause direct neuronal injury. Selective reduction of NAA and increased level of mI in white matter supported the theory of that axonopathy and gliosis were the main mechanisms of pathophysiology in chronic toluene encepholopathy. Insignificance of elevation of Cho/Cr ratios demonstrated that toluene inhalation did not cause active demyelination.

Biological and health effects of exposure to kerosene-based jet fuels and performance additives

Over 2 million military and civilian personnel per year (over 1 million in the United States) are occupationally exposed, respectively, to jet propulsion fuel-8 (JP-8), JP-8 +100 or JP-5, or to the civil aviation equivalents Jet A or Jet A-1. Approximately 60 billion gallon of these kerosene-based jet fuels are annually consumed worldwide (26 billion gallon in the United States), including over 5 billion gallon of JP-8 by the militaries of the United States and other NATO countries. JP-8, for example, represents the largest single chemical exposure in the U.S. military (2.53 billion gallon in 2000), while Jet A and A-1 are among the most common sources of nonmilitary occupational chemical exposure. Although more recent figures were not available, approximately 4.06 billion gallon of kerosene per se were consumed in the United States in 1990 (IARC, 1992). These exposures may occur repeatedly to raw fuel, vapor phase, aerosol phase, or fuel combustion exhaust by dermal absorption, pulmonary inhalation, or oral ingestion routes. Additionally, the public may be repeatedly exposed to lower levels of jet fuel vapor/aerosol or to fuel combustion products through atmospheric contamination, or to raw fuel constituents by contact with contaminated groundwater or soil. Kerosene-based hydrocarbon fuels are complex mixtures of up to 260+ aliphatic and aromatic hydrocarbon compounds (C(6) -C(17+); possibly 2000+ isomeric forms), including varying concentrations of potential toxicants such as benzene, n-hexane, toluene, xylenes, trimethylpentane, methoxyethanol, naphthalenes (including polycyclic aromatic hydrocarbons [PAHs], and certain other C(9)-C(12) fractions (i.e., n-propylbenzene, trimethylbenzene isomers). While hydrocarbon fuel exposures occur typically at concentrations below current permissible exposure limits (PELs) for the parent fuel or its constituent chemicals, it is unknown whether additive or synergistic interactions among hydrocarbon constituents, up to six performance additives, and other environmental exposure factors may result in unpredicted toxicity. While there is little epidemiological evidence for fuel-induced death, cancer, or other serious organic disease in fuel-exposed workers, large numbers of self-reported health complaints in this cohort appear to justify study of more subtle health consequences. A number of recently published studies reported acute or persisting biological or health effects from acute, subchronic, or chronic exposure of humans or animals to kerosene-based hydrocarbon fuels, to constituent chemicals of these fuels, or to fuel combustion products. This review provides an in-depth summary of human, animal, and in vitro studies of biological or health effects from exposure to JP-8, JP-8 +100, JP-5, Jet A, Jet A-1, or kerosene.

Occupational exposure to organic solvents and long-term nervous system damage detectable by brain imaging, neurophysiology or histopathology

The purpose of the present review is to assess the evidence published in scientific literature that industrial organic solvents as a generic group have the ability to induce long-term nervous system damage in workers that can be detected by techniques other than neuropsychological testing. The main body of evidence considered in this review was 40 studies involving the use of brain imaging, neurophysiological testing, gross autopsy or histopathology in groups of workers with long-term solvent exposure. Case reports involving both solvent abuse and occupational exposure, and experimental animal data have also been reviewed as supporting data. A number of the studies in groups of workers provide evidence of the presence of marginal atrophic abnormalities in the brain or deficits in nerve conduction velocity in solvent-exposed workers. However, there are limitations in the design of many of these studies, the strength of association between exposure and effect is not consistently strong, no dose-response relationship can be detected, the reported changes lack specificity and there is no coherence between the human and experimental animal data. Overall, it is not possible to draw reliable conclusions with respect to the presence or absence of nervous system damage related to the common properties of organic solvents.

Differential susceptibility of rats and guinea pigs to the ototoxic effects of ethyl benzene

The present study was designed to compare the ototoxic effects of volatile ethyl benzene in guinea pigs and rats. Rats showed deteriorated auditory thresholds in the mid-frequency range, based on electrocochleography, after 550-ppm ethyl benzene (8 h/day, 5 days). Outer hair cell (OHC) loss was found in the corresponding cochlear regions. In contrast, guinea pigs showed no threshold shifts and no OHC loss after exposure to much higher ethyl benzene levels (2500 ppm, 6 h/day, 5 days). Subsequently, a limited study (four rats and four guinea pigs) was performed in an attempt to understand these differences in susceptibility. Ethyl benzene concentration in blood was determined in both species after exposure to 500-ppm ethyl benzene (8 h/day, 3 days). At the end of the first day, blood of the rats contained 23.2+/-0.8-microg/ml ethyl benzene, whereas the concentration in guinea pig blood was 2.8+/-0.1 microg/ml. After 3 days, the concentration in both species decreased with respect to the first day, but the ethyl benzene concentration in rat blood was still 4.3 times higher than that in guinea pig blood. Thus, the difference in susceptibility between the species may be related to the ethyl benzene concentration in blood.

Neuropsychologic impairment and MRI abnormalities associated with chronic solvent abuse

OBJECTIVE

Individuals chronically abusing organic solvents have been reported in the medical literature for almost four decades to have a variety of neurological abnormalities. Most have been single case reports or studies in small numbers of individuals. The purpose of this study was to evaluate the neurologic and neuropsychologic effects of chronic solvent abuse in a larger group of individuals and compare the results to a control group of other drug abusers. Attempts to estimate a dose-response relationship between solvent abuse and either neuropsychological tests or magnetic resonance imaging (MRI) abnormalities were also undertaken.

METHODS

A sample of 55 solvent abusers was compared to a sample of 61 users of other drugs, especially cocaine and alcohol, on a battery of cognitive and neuropsychological tests. Fifty of the solvent abusers and 51 members of the comparison sample also underwent MRI of the brain. Comparisons were made by means of multivariate analysis of variance and covariance.

RESULTS

Compared to the general population, both groups performed poorly, scoring below the mean on most neuropsychological measures. Solvent abusers performed more poorly than the comparison sample on measures of working memory and executive cognitive functions. Both groups showed evidence of abnormal MRI findings, but a greater percentage of the solvent abuse group showed such abnormalities. No clear dose-response relationship was seen between solvent abuse and abnormalities on neuropsychological tests, but a strong dose-response relationship was seen in the presence of MRI abnormalities.

CONCLUSION

The findings in this study document widespread cognitive impairment, which could not be attributed to the effects of solvents entirely. These findings expand upon previous data regarding neurological abnormalities in solvent abusers, by demonstrating a dose-response relationship with MRI abnormalities. An unexpected finding was the high prevalence of neuropsychological impairment and MRI abnormalities among the comparison group. The results of this study has implications regarding low-level solvent exposure, as in the occupational setting, suggesting that MRI may be a more useful tool to sort out the presence of neurological abnormalities rather than neuropsychological tests. Since no dose-response relationship was seen between solvent abuse and neuropsychological testing, reliance upon these tests in assessing neurological injury from solvents is a highly dubious practice.

Developmental neurotoxicity: do similar phenotypes indicate a common mode of action? A comparison of fetal alcohol syndrome, toluene embryopathy and maternal phenylketonuria

Developmental neurotoxicity can be ascribed to in utero exposure to exogenous substances or to exposure of the fetus to endogenous compounds that accumulate because of genetic mutations. One of the best recognized human neuroteratogens is ethanol. The Fetal Alcohol Syndrome (FAS) is characterized by growth deficiency, particular facial features, and central nervous system (CNS) dysfunctions (mental retardation, microencephaly and brain malformations). Abuse of toluene by pregnant women can lead to an embryopathy (fetal solvent syndrome, (FSS)) whose characteristics are similar to FAS. Phenylketonuria (PKU) is a genetic defect in phenylalanine (Phe) metabolism. Offspring of phenylketonuric mothers not under strict dietary control are born with maternal PKU (mPKU), a syndrome with similar characteristics as FAS and FSS. While ethanol has been shown to cause neuronal death, no such evidence is available for toluene or Phe and/or its metabolites. On the other hand, alterations in astrocyte proliferation and maturation have been found, mostly in in vitro studies, which may represent a potential common mode of action for at least some of the CNS effects found in FAS, mPKU, and FSS. Further in vivo and in vitro studies should validate this hypothesis and elucidate possible molecular targets.

The expression of excitatory amino acid transporter 2 (EAAT2) in forensic autopsy cases

Glutamate is the major excitatory neurotransmitter and the greater part of this amino acid is removed from the synaptic cleft by excitatory amino acid transporter 2 (EAAT2) located on perisynaptic astrocytes. Recently, it was reported that the EAAT2 protein content changed in rats following forebrain ischemia and administration of methamphetamine. We planned to demonstrate the immunohistochemical distribution of EAAT2 in the human brain and discuss the significance of its pathophysiological roles. Thirty-two cases were used from forensic autopsies. The tissues were sampled from the cerebral cortex, striatum and hippocampus. The distribution of EAAT2 was difficult to identify in cases of electrical fatalities. However, continuous and extensive staining of EAAT2 was observed in cases of death from hypothermia. In almost all asphyxia death, we were able to observe a weak stain of EAAT2. In case of solvent abuse, EAAT2 staining was continuous and extensive as in the cases of hypothermia, and patchy negative zones were mixed. This study clearly showed the differences in EAAT2 localization according to the cause of death. These findings suggested that the differences in EAAT2 staining depended on the cause and course (pathophysiological conditions) of death.

Inhalant abuse by adolescents

The deliberate misuse of volatile substances poses a poorly recognized risk for considerable morbidity and mortality in adolescent populations worldwide. The abuse of inhalants continues to be a significant problem among our country's youth. While many household and industrial chemicals can be inhaled, glues, paints, and aerosol propellants are among the most commonly abused. Adolescents are often unaware of the health threats posed by inhalation of solvents. Inhalation can result in serious organ system dysfunction or even sudden death. This review discusses the prevalence of inhalant abuse in the United States, summarizes the various types of substances used, highlights the major physiologic effects of inhalants, and briefly discusses associated risk behaviors, prevention and medical management.

The role of quantitative neurological examination in clinical neurotoxicology

The use of the clinical neurological examination to document abnormal signs in suspected neurotoxic disorders is described, recognizing that identifying an abnormal examination does not establish the cause of the problem. Several forms of quantitative tests of neurological function are discussed, and their application to the evaluation of neurotoxic disorders is reviewed. Although results of such testing are rarely specific for toxic exposure, these measures have important application in sequential evaluations to document small changes in neurologic function over time.

Brain SPECT findings in long-term inhalant abuse

This study evaluates brain perfusion in long-term inhalant abusers of toluene, acetone, benzene and derivatives. Ten patients in the age range 16-18 years (mean, 17.3+/-0.67 years), who had been inhalant dependent for a mean period of 48.3+/-6.2 months, but who had stopped using inhalants for 1-11 months (mean, 5.4+/-2.1 months), and ten controls (mean age, 17.3+/-0.67 years) were included in the study. Psychiatric tests, biochemical tests and Tc-99m-hexamethylpropyleneamine oxime (Tc-99m-HMPAO) brain single photon emission computed tomography (SPECT) were performed on all patients. Brain SPECT images were evaluated qualitatively and quantitatively. The mean IQ level was found to be 84 (by psychological tests). Brain SPECT showed non-homogeneous Tc-99m-HMPAO uptake and hypoperfusion areas in all patients (five left temporal, one right temporal, two left temporal plus bilateral parietooccipital, one biparietal and one left temporoparietal). Seven patients had hyperperfused foci (unifocal in five patients and multifocal in two patients). Six hyperperfused foci were in a parietal and one in a temporoparietal location. This study suggests that inhalant dependents exhibit serious abnormalities in brain SPECT images, including hypo-hyperperfusion foci and non-homogeneous uptake of the radiopharmaceutical. A further study with a larger number of patients and long-term follow-up may help to reach a more specific conclusion.

Inhalation of low concentrations of toluene induces persistent effects on a learning retention task, beam-walk performance, and cerebrocortical size in the rat

The organic solvent toluene is widely used in industry. The threshold limit value for extended occupational exposure to toluene is presently set to 200 ppm in the United States. We have investigated the effect of an inhalation exposure of 80 ppm for 4 weeks (6 h/day, 5 days/week), followed by a postexposure period of at least 4 weeks, on behavior and brain features in the rat. Toluene exposure appeared to affect spatial memory, since toluene-exposed rats showed a longer time in the correct quadrant in a Morris swim maze. This effect may indicate that the exposed rats used their praxis strategy longer before they started to look for the platform elsewhere. Toluene-exposed rats showed trends for increases in both locomotion and rearing behaviors and a significantly reduced beam-walk performance. The area of the cerebral cortex, especially the parietal cortex, was decreased by 6-10% in toluene-exposed rats, as shown by magnetic resonance imaging of living rats and autoradiograms of frozen brain sections. The K(D) and B(max) values of the dopamine D(3) agonist [(3)H]PD 128907 were not affected by toluene, as measured in caudate-putamen and subcortical limbic area using biochemical receptor binding assays and in caudate-putamen and islands of Calleja using quantitative receptor autoradiography. Hence, previously demonstrated persistent effects by toluene on the binding characteristics of radioligands binding to both D(2) and D(3) receptors seem to indicate a persistent effect of toluene selectively on dopamine D(2) receptors. Taken together, the present results indicate that exposure to low concentrations of toluene leads to persistent effects on cognitive, neurological, and brain-structural properties in the rat.

Cerebellar dysfunction in chronic toluene abuse: beneficial response to amantadine hydrochloride

CASE REPORT

A 21-year-old man who had sniffed toluene since the age of 13 presented with a 4-year history of progressive cerebellar dysfunction and visual deterioration. The patient's condition did not improve despite 5 months of abstinence. Magnetic resonance imaging revealed cerebral atrophy and hypointensity signals in the white matter and bilaterally in the globus pallidus, thalamus, red nucleus, and substantia nigra. Amantadine hydrochloride therapy (100 mg/d, then 200 mg/d) resulted in dramatic improvement of his cerebellar and visual symptoms.

The ototoxic effects of ethyl benzene in rats

Exposure to organic solvents has been shown to be ototoxic in animals and there is evidence that these solvents can induce hearing loss in humans. In this study, the effects of inhalation of the possibly ototoxic solvent ethyl benzene on the cochlear function and morphology were evaluated using three complementary techniques: (1) reflex modification audiometry (RMA), (2) electrocochleography and (3) histological examination of the cochleas. Rats were exposed to either ethyl benzene (800 ppm, 8 h/day for 5 days) or to control conditions. The RMA threshold increased significantly by about 25 dB, 1 and 4 weeks after the exposure, irrespective of the stimulus frequency tested (4-24 kHz). Electrocochleography was performed between 8 and 11 weeks after exposure to the organic solvent. The threshold for the compound action potential increased significantly by 10-30 dB at all frequencies tested (1-24 kHz). Histological examination of the cochlea showed outer hair cell (OHC) loss, especially in the upper basal and lower middle turns (corresponding to the mid-frequency region) to an extent of 65%. We conclude that exposure to 800 ppm ethyl benzene for 8 h/day during 5 days induces hearing loss in rats due to OHC loss.

Cortical atrophy detected by computed tomography in gasoline station attendants

BACKGROUND

To evaluate the contribution of leaded gasoline in the presence of abnormal calcifications or cortical atrophy seen in computed tomographies (CT) of the head of occupationally exposed professionals working in the centre of Athens.

METHODS

One hundred and twenty-two head CTs from gas station employees and traffic-exposed professionals (taxi and bus drivers) were analyzed for evidence of cortical atrophy or abnormal calcifications. Blood lead level (BLL) of these lead occupationally exposed groups was compared with 37 non-exposed subjects.

RESULTS

All three occupationally exposed-to-lead groups had similar blood lead levels compared to the non-exposed group and within the currently accepted norms for lead. No abnormal calcifications were found. Cortical atrophy was more frequently seen in the gas station employees group using univariate and multivariate analysis. In the logistic regression model gas station employment had a stronger impact in developing cortical atrophy [odds ratio of 6.43 (1.46-28.3, 95% CI)] than BLL [odds ratio of 1.4 (1.01-2.05, 95% CI)].

CONCLUSIONS

These results show that employment in gasoline stations may be associated with detectable cortical atrophy in imaging studies and suggest the contribution of a leaded gasoline to its development.

Acute neurologic complications of drug and alcohol abuse

Recreationally abused substances include both legal and illegal agents, broadly classified as opioids, psychostimulants, sedatives, cannabis (marijuana), hallucinogens, inhalants, dissociative anesthetics (phencyclidine), anticholinergics, ethanol, and tobacco. These substances are associated with an array of neurological emergencies resulting from overdose, withdrawal, and other medical and neurological complications.