Prenatal exposure to toluene results in abnormal neurogenesis and migration in rat somatosensory cortex

Chronic thinner inhalation alters olfactory behaviors in adult mice

Volatile solvents exposure can result in various behavioral impairments that have been partly associated to altered adult hippocampal neurogenesis. Despite recent evidence supporting this association, few studies have been devoted to examine the impact on olfactory functioning and olfactory bulb (OB) neurogenesis, although olfactory system is directly in contact with volatile molecules. Thus, this study was designed to evaluate in adult mice the potential modifications of the olfactory functioning after acute (1 day), subchronic (6 weeks) and chronic (12 weeks) exposure to thinner vapor at both behavioral and cellular levels. Firstly, behavioral evaluations showed that chronic thinner exposure impacts on odor detection ability of treated mice but does not affect mice ability to efficiently discriminate between two different odors. Moreover, chronic thinner exposure produces impairment in the olfactory-mediated associative memory. Secondly, analysis of the effects of thinner exposure in the subventricular zone (SVZ) of the lateral ventricle and in the OB revealed that thinner treatments do not induce apoptosis nor glial activation. Thirdly, immunohistochemical quantification of different markers of adult olfactory neurogenesis showed that inhalant treatments do not change the number of proliferating progenitors in the SVZ and the rostral migratory stream (RMS), as well as the number of newborn cells reaching and integrating in the OB circuitry. Altogether, our data highlight that the impaired olfactory performances in chronically-exposed mice are not associated to an alteration of adult neurogenesis in the SVZ-OB system.

Toluene Inhalation Causes Early Anxiety and Delayed Depression with Regulation of Dopamine Turnover, 5-HT1A Receptor, and Adult Neurogenesis in Mice

Inhaled solvents such as toluene are of particular concern due to their abuse potential that is easily exposed to the environment. The inhalation of toluene causes various behavioral problems, but, the effect of short-term exposure of toluene on changes in emotional behaviors over time after exposure and the accompanying pathological characteristics have not been fully identified. Here, we evaluated the behavioral and neurochemical changes observed over time in mice that inhaled toluene. The mice were exposed to toluene for 30 min at a concentration of either 500 or 2,000 ppm. Toluene did not cause social or motor dysfunction in mice. However, increased anxiety-like behavior was detected in the short-term after exposure, and depression-like behavior appeared as delayed effects. The amount of striatal dopamine metabolites was significantly decreased by toluene, which continued to be seen for up to almost two weeks after inhalation. Additionally, an upregulation of serotonin 1A (5-HT_1A) receptor in the hippocampus and the substantia nigra, as well as reduced immunoreactivity of neurogenesis markers in the dentate gyrus, was observed in the mice after two weeks. These results suggest that toluene inhalation, even single exposure, mimics early anxiety- and delayed depression-like emotional disturbances, underpinned by pathological changes in the brain.

In Utero Bisphenol A Exposure Induces Abnormal Neuronal Migration in the Cerebral Cortex of Mice

Bisphenol A (BPA) has been known to have endocrine-disrupting activity to induce reproductive and behavioral abnormalities in offspring of laboratory animal species. However, morphological basis of this abnormality during brain development is largely unknown. Cerebral cortex plays a crucial role in higher brain function, and its precisely laminated structure is formed by neuronal migration. In the present study, transfecting a plasmid (pCAG-mCherry) by in utero electroporation (IUE), we visualized developing neurons and investigated the possible effects of in utero BPA exposure on neuronal migration. Pregnant mice were exposed to BPA by osmotic pump at estimated daily doses of 0, 40 (BPA-40), or 400 (BPA-400) μg/kg from embryonic day 14.5 (E14.5) to E18.5. IUE was performed at E14.5 and neuronal migration was analyzed at E18.5. Compared with the control group, neuronal migration in the cortical plate was significantly decreased in the BPA-40 group; however, there was no significant difference in the BPA-400 group. Among several neuronal migration-related genes and cortical layer-specific genes, TrkB in the BPA-400 group was found significantly upregulated. In conclusion, in utero exposure to low BPA dose was found to disrupt neuronal migration in the cerebral cortex in a dose-specific manner.

Changes in developmental body weight as a function of toluene exposure: A meta-analysis of animal studies

Inhalant abuse is a globally prevalent health issue with particular concerns about substance-abusing pregnant women. In both animal models and clinical case reports of toluene exposure, the primary physiological outcome measure of prenatal inhalant exposure is low birth weight (BW). However, the effect of prenatal toluene exposure on animal BW varies widely in the literature. To clarify this effect and investigate possible design moderators of pup BW, a systematic review and meta-analytic techniques were applied to the existing peer-reviewed animal literature of prenatal and postnatal exposure models to the inhaled solvent toluene. Of 288 studies screened, 24 studies satisfied the inclusion criteria. Evaluation of these studies indicated that toluene exposure was negatively associated with pup BW (d = -0.39), with external inhaled concentration, route of administration, day of weighing, and toluene exposure magnitude moderating this association. Investigators doing animal studies should be cognizant of these factors before investigating the reproductive and developmental outcomes associated with prenatal and postnatal toluene exposure.

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.

Final Report of the Safety Assessment of Cosmetic Ingredients Derived From Zea Mays (Corn)

Many cosmetic ingredients are derived from Zea mays (corn). While safety test data were not available for most ingredients, similarities in preparation and the resulting similar composition allowed extrapolation of safety data to all listed ingredients. Animal studies included acute toxicity, ocular and dermal irritation studies, and dermal sensitization studies. Clinical studies included dermal irritation and sensitization. Case reports were available for the starch as used as a donning agent in medical gloves. Studies of many other endpoints, including reproductive and developmental toxicity, use corn oil as a vehicle control with no reported adverse effects at levels used in cosmetics. While industry should continue limiting ingredient impurities such as pesticide residues before blending into a cosmetic formulation, the CIR Expert Panel determined that corn-derived ingredients are safe for use in cosmetics in the practices of use and concentration described in the assessment.

Neurotoxicity of toluene

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

Reproductive toxicology and teratology of abused toluene

Toluene is an organic solvent that is widely used by industry and is ubiquitous in our environment. As a result, exposure to solvents like toluene in work-related settings (i.e., relatively constant, low-level exposures) or through inhalant abuse (i.e., relatively intermittent, high-level exposures) is increasing for many women of reproductive age. Evidence suggests that the risk for pregnancy problems, as well as developmental delays and neurobehavioral difficulties, is higher for the children of women who have been exposed to high concentrations of organic solvents during pregnancy than for those who have not. These risks appear to be higher in cases of abuse exposure to solvents such as toluene, particularly in comparison to the risk for teratogenic outcomes with occupational solvent exposure. Despite this, the reproductive toxicology and teratology following abuse of toluene and other inhalants remains under-investigated. This brief review describes the current state of our understanding of the reproductive and teratogenic risk of gestational toluene abuse. The data to date suggest that the high levels of toluene exposure typical with inhalant abuse are more detrimental to fetal development than typical occupational exposure, and preclinical paradigms can be beneficial for investigating the processes and risks of prenatal solvent exposure. While substantial research has been done on the reproductive effects of occupational exposures to organic solvents, more research is needed on the outcomes and mechanisms of exposures typical of inhalant abuse.

Solvent inhalation (toluene and n-hexane) during the brain growth spurt impairs the maturation of frontal, parietal and occipital cerebrocortical neurons in rats

Solvent abuse during pregnancy may cause "fetal solvent syndrome", which is characterized by mild brain atrophy and associated with behavioral, cognitive, and emotional abnormalities. The present study investigated whether solvent inhalation during the preweaning period (P2-P21) alters the morphological maturation of frontal, parietal, and occipital cortical neurons. Twelve hours after delivery (postnatal day 0, P0), litters were cross-fostered, culled to 8 pups/dam and housed together with a dam in standard laboratory cages. Litters were randomly assigned to the "air-only" group (n=64, 8 litters) and to the "solvent-sniffer" group (n=72, 9 litters). During P2-P21, each animal was exposed daily to either organic solvent vapors (75% toluene and 18% n-hexane, a solvent mixture commonly found in glues and adhesives) or clean air. To determine the impact of early solvent inhalation on cortical neuronal differentiation, brains were stained using the Golgi-Cox-Sholl procedure to quantitatively assess neocortical pyramidal cell dendrogenesis. Preweaning, solvent-exposed animals displayed dramatic impairments in dendritic growth as well as significant reductions in brain weight and size.

Toluene inhibits hippocampal neurogenesis in adult mice

Toluene, a representative industrial solvent and abused inhalant, decreases neuronal activity in vitro and causes mental depression and cognitive impairment in humans. However, the effects of toluene on brain function and the sites of its action are poorly understood. This study investigated the temporal changes of neurogenesis in the hippocampus of adult C57BL/6 mice after acute administration of toluene using two immunohistochemical markers for neurogenesis, Ki-67 and doublecortin (DCX). In addition, after toluene treatment, depression-like behaviors and learning and memory tasks were examined to assess hippocampal neurogenesis-related behavioral dysfunction. The number of Ki-67- and DCX-positive cells in the dentate gyrus of adult hippocampi declined acutely between 0 h and 24 h after toluene treatment (500 mg/kg, i.p.) and increased gradually from 2 to 8 days post-administration. The level of Ki-67 and DCX immunoreactivity decreased in a dose-dependent manner within the range of toluene administered (0-1000 mg/kg). In tail suspension and forced-swim tests performed at 1 and 4 days after toluene treatment (500 mg/kg), mice showed significant depression-like behaviors compared to the vehicle-treated controls. In the contextual fear conditioning and object recognition memory test, the mice trained at 1 and 4 days after toluene treatment showed significant memory defects compared to the vehicle-treated controls. This study suggests that acute exposure to toluene reduces the rate of adult hippocampal neurogenesis and can cause hippocampal dysfunction such as depression and cognitive impairment.

cGMP modulates stem cells differentiation to neurons in brain in vivo

During brain development neural stem cells may differentiate to neurons or to other cell types. The aim of this work was to assess the role of cGMP (cyclic GMP) in the modulation of differentiation of neural stem cells to neurons or non-neuronal cells. cGMP in brain of fetuses was reduced to 46% of controls by treating pregnant rats with nitroarginine-methylester (L-NAME) and was restored by co-treatment with sildenafil.Reducing cGMP during brain development leads to reduced differentiation of stem cells to neurons and increased differentiation to non-neuronal cells. The number of neurons in the prefrontal cortex originated from stem cells proliferating on gestational day 14 was 715+/-14/mm(2) in control rats and was reduced to 440+/-29/mm(2) (61% of control) in rats treated with L-NAME. In rats exposed to L-NAME plus sildenafil, differentiation to neurons was completely normalized, reaching 683+/-11 neurons/mm(2). In rats exposed to sildenafil alone the number of cells labelled with bromodeoxyuridine (BrdU) and NeuN was 841+/-16/mm(2). In prefrontal cortex of control rats 48% of the neural stem cells proliferating in gestational day 14 differentiate to neurons, but only 24% in rats exposed to L-NAME. This was corrected by sildenafil, 40% of cells differentiate to neurons. Similar results were obtained for neurons proliferating during all developmental period. Treatment with L-NAME did not reduce the total number of cells labelled with BrdU, further supporting that L-NAME reduces selectively the differentiation of stem cells to neurons. Similar results were obtained in hippocampus. Treatment with L-NAME reduced the differentiation of neural stem cells to neurons, although the effect was milder than in prefrontal cortex. These results support that cGMP modulates the fate of neural stem cells in brain in vivo and suggest that high cGMP levels promote its differentiation to neurons while reduced cGMP levels promote differentiation to non-neuronal cells.

Drugs, biogenic amine targets and the developing brain

Defects in the development of the brain have a profound impact on mature brain functions and underlying psychopathology. Classical neurotransmitters and neuromodulators, such as dopamine, serotonin, norepinephrine, acetylcholine, glutamate and GABA, have pleiotropic effects during brain development. In other words, these molecules produce multiple diverse effects to serve as regulators of distinct cellular functions at different times in neurodevelopment. These systems are impacted upon by abuse of a variety of illicit drugs, neurotherapeutics and environmental contaminants. In this review, we describe the impact of drugs and chemicals on brain formation and function in animal models and in human populations, highlighting sensitive periods and effects that may not emerge until later in life.

Effects of abuse pattern of gestational toluene exposure on metabolism, feeding and body composition

AIMS

Inhalant abuse during pregnancy lowers birth weight and impedes early development. These studies explored the effects of brief, repeated, prenatal toluene exposures in pregnant female rats on body weight, metabolic rate, body composition, and food intake in their offspring.

METHOD

Rats were exposed to 0, 8000, 12,000, or 16,000 ppm of toluene twice daily for 15 min from gestational days 8 to 20. The effects of such exposures on post-weaning litter weights, oxygen consumption, carbon dioxide output, and body fat content were determined in 2 cohorts (n=23, n=24) of offspring. Food intakes and weight changes in response to 3 different diets (regular chow, purified diet, purified high fat diet) were examined in another cohort (n=24) from postnatal days 72 to 116.

RESULTS

Litter weights showed a significant linear decrease as a function of toluene dose. Offspring exposed to the 16,000 ppm toluene dose displayed statistically lower energy expenditures than control rats. Male rats exposed to 8000 or 16,000 ppm toluene had significantly greater percentage of body fat as well as total body fat than the other groups. Toluene also significantly suppressed weight gain over the time chow was consumed compared to the 0 ppm control group. Finally there were trends for a main effect of toluene dose on food intake during chow and during high fat diet consumption, with rats in the 12,000 ppm group consuming more than the 0 ppm group on both diets.

DISCUSSION

These data suggest that, in addition to other previously documented abnormalities in neurological development and behavior, the physiological regulation of metabolism and body composition in males as well as food intake and weight gain in both sexes may be altered by prenatal exposure to toluene.

Defects in embryonic neurogenesis and initial synapse formation in the forebrain of the Ts65Dn mouse model of Down syndrome

Trisomy 21, one of the most prevalent congenital birth defects, results in a constellation of phenotypes collectively termed Down syndrome (DS). Mental retardation and motor and sensory deficits are among the many debilitating symptoms of DS. Alterations in brain growth and synaptic development are thought to underlie the cognitive impairments in DS, but the role of early brain development has not been studied because of the lack of embryonic human tissue and because of breeding difficulties in mouse models of DS. We generated a breeding colony of the Ts65Dn mouse model of DS to test the hypothesis that early defects in embryonic brain development are a component of brain dysfunction in DS. We found substantial delays in prenatal growth of the Ts65Dn cerebral cortex and hippocampus because of longer cell cycle duration and reduced neurogenesis from the ventricular zone neural precursor population. In addition, the Ts65Dn neocortex remains hypocellular after birth and there is a lasting decrease in synaptic development beginning in the first postnatal week. These results demonstrate that specific abnormalities in embryonic forebrain precursor cells precede early deficits in synaptogenesis and may underlie the postnatal disabilities in Ts65Dn and DS. The early prenatal period is therefore an important new window for possible therapeutic amelioration of the cognitive symptoms in DS.

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.

Prenatal exposure to bisphenol A affects adult murine neocortical structure

Prenatal exposure to low-doses of bisphenol A (BPA) has been shown to affect murine neocortical development by accelerating neuronal differentiation/migration through disrupting thyroid hormone function. We therefore studied whether prenatal exposure to low-doses of BPA affected organization of adult neocortical structures. Pregnant mice were injected with 20 microg/kg of BPA daily from embryonic day 0.5 (E0.5) and bromodeoxyuridine (BrdU) was injected at E12.5, E14.5 and at E16.5, and the fetal brains were analyzed after birth. The BrdU-positive cells labeled at E14.5 were significantly increased in the Vth and VIth cortical layers of BPA-treated mice at postnatal 3 weeks (P3W), whereas they were confined to the IVth layer of control mice, though such differences disappeared at P12W. The thalamocortical projections demonstrated by DiI-labeling were abnormal at P3W and P12W in BPA-treated mice. These results indicate that BPA might affect not only neocortical development but also thalamocortical connections.

The last decade of solvent research in animal models of abuse: mechanistic and behavioral studies

The abuse of volatile organic solvents (inhalants) leads to diverse sequelae at levels ranging from the cell to the whole organism. This paper reviews findings from the last 10 years of animal models investigating the behavioral and mechanistic effects of solvent abuse. In research with animal models of inhalant abuse, NMDA, GABA(A), glycine, nicotine, and 5HT(3) receptors appear to be important targets of action for several abused solvents with emerging evidence suggesting that other receptor subtypes and nerve membrane ion channels may be involved as well. The behavioral effects vary in magnitude and duration among the solvents investigated. The behavioral effects of acute and chronic inhalant abuse include motor impairment, alterations in spontaneous motor activity, anticonvulsant effects, anxiolytic effects, sensory effects, and effects on learning, memory and operant behavior (e.g., response rates and discriminative stimulus effects). In addition, repeated exposure to these solvents may produce tolerance, dependence and/or sensitization to these effects.

The GABAergic system of the developing neocortex has a reduced capacity to recover from in utero injury in experimental cortical dysplasia

Cortical dysplasia is frequently associated with epilepsy but mechanisms underlying this association are poorly understood. Rats irradiated in utero serve as an injury-based model of cortical dysplasia. Prior studies in mature rats have shown a selective reduction in the number of neocortical interneurons after in utero irradiation. This study attempted to clarify the nature of the radiation injury to the developing neocortical GABAergic system after exposure to gamma-irradiation on the 17th day of gestation (E17). Stereological methods were used to quantify absolute numbers of total neurons (TN) and GABAergic neurons in the neocortex on E21 and postnatal day 6 (P6). In irradiated rats, TN was decreased to about 50% of controls at both time points. However, TN doubled between the 2 time points, even in irradiated animals. In controls, GABAergic neurons increased 10-fold between E21 and P6, but there was no difference in GABAergic counts between the 2 time points in irradiated animals. This led to a dramatic reduction in the percentage of neocortical neurons that were GABAergic in irradiated animals at P6 (9% vs 18%). This study shows that, in contrast to non-GABAergic neurons, the neocortical GABAergic system has a limited capacity to recover from radiation-induced in utero injury.

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.

Increased synthesis of GFAP by TCDD in differentiation-disrupted SFME cells

The effects of 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) on gene expression and synthesis of glial fibrillary acidic protein (GFAP) in differentiation-disrupted serum-free mouse embryo (SFME) cells were examined. SFME cells were exposed to fetal calf serum (FCS) and dimethyl sulfoxide (DMSO) to induce differentiation and increase GFAP synthesis. Disruption of differentiation was caused by low-level toluene, significantly inhibiting GFAP synthesis. TCDD at 0.01, 0.1 and 1 pg/ml in the presence of low-level toluene increased GFAP synthesis in the SFME cells, while expression of GFAP mRNA showed no significant change. The TCDD-treated SFME cells detached from the culture substratum, indicating an apparent change in cell adhesion. These results suggest that low-level TCDD further disrupts differentiation of SFME cells in the presence of low-level toluene by upregulating GFAP synthesis and by altering the ability in cell adhesion and that GFAP synthesis is not disrupted at transcription but at translation.

Toluene inhibits muscarinic receptor-mediated cytosolic Ca2+ responses in neural precursor cells

Toluene is widely used as a component in industrial solvents and many toluene-containing products are abused via inhalation. While many studies have demonstrated its inhibitory effects on neuronal activity, the effects of toluene on receptor signaling in proliferating and differentiating neural precursor cells are presently unclear. Here, using digital video microscopy and Ca2+ imaging, we investigated the effects of acute exposure to toluene on the function of muscarinic acetylcholine receptors (mAChRs) expressed in neural precursor cells. The neural precursor cells were isolatedfrom embryonic day 13 (E13) rat cortex and expanded in serum-free medium containing basic fibroblast growth factor (bFGF). We found that the acetylcholine (ACh) analog carbachol (CCh) induced a dose-dependent increase in cytosolic Ca2+, which was blocked by the muscarinic receptor antagonist atropine in a reversible manner. Toluene was added to the perfusion medium and concentrations of toluene in the medium were determined by gas chromatographic analysis. Following imaging, the cells were fixed and processed for 5-bromo-2'-deoxyuridine (BrdU, cell proliferation marker) and beta-tubulin (TuJ1, neuronal marker) immunostaining. In the 5 day culture, most cells continued to divide (BrdU+), while afew cells differentiated into young neurons (TuJ1-). The CCh-induced Ca2+ elevations in proliferating (BrdU+TuJ1-) neural precursor cells were significantly reduced by acute exposure to 0.15 mM toluene and completely blocked by 10 mM toluene. Toluene's inhibition of muscarinic receptor-mediated Ca2+ signaling was rapid, reversible and dose-dependent with an IC50 value 0.5 mM. Since muscarinic receptors mediate cell proliferation and differentiation during neural precursor cell development, these results suggest that depression of muscarinic signaling may play a role in toluene's teratogenic effect on the developing nervous system.

Toluene at environmentally relevant low levels disrupts differentiation of astrocyte precursor cells

Recent findings that describe endocrine disruption caused by exposure to low levels of certain chemicals in the environment have led to a paradigm shift in the way toxicology studies are designed. Toluene at high levels damages the human central nervous system; however, the effects of toluene at low levels have not been studied. The authors used serum-free mouse embryo cells-a precursor of astrocytes-to predict the effect of chemicals on developing brain cells. When serum-free mouse embryo cells were exposed to low levels of toluene, induction of glial fibrillary acidic protein was inhibited. This study demonstrated that environmentally relevant low levels of toluene could disrupt normal prenatal brain development.

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.