Some aspects of the mechanisms by which industrial solvents produce neurotoxic effects

Effects of acute and prolonged naphthalene exposure on brain monoaminergic neurotransmitters in rainbow trout (Oncorhynchus mykiss)

We have shown previously that acute (1 to 6 h) and prolonged (1 to 5 days) exposure of rainbow trout to naphthalene resulted in decreased plasmatic cortisol and 17-beta-estradiol levels. In order to elucidate the mechanisms through which naphthalene might disrupt endocrine regulation, the present study investigated whether brain monoaminergic neurotransmitters are altered by the action of this polycyclic aromatic hydrocarbon. In a first experiment, immature rainbow trout were injected with vegetable oil alone or containing naphthalene (10 and 50 mg/kg, i.p.), and sacrificed 1, 3 and 6 h after treatment. In a second experiment, slow-coconut oil implants alone or containing naphthalene (doses of 10 and 50 mg/kg) were i.p. located and fish sacrificed 1, 3 and 5 days after treatment. Levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and noradrenaline (NA) were measured in several brain regions by HPLC. The results show that short-term naphthalene increases DA and 5-HT contents in hypothalamus and telencephalon, but differentially alter contents of the acid metabolites. Implants with naphthalene reduced DA content in hypothalamus and preoptic region but increased in telencephalon. 5-HT metabolism was decreased in hypothalamus, preoptic region, pituitary and brain stem after 3 to 6 days of treatment. In addition, the levels of NA were increased in hypothalamus and telencephalon after acute treatment and in hypothalamus and preoptic area after several days of exposure to naphthalene. These data suggest that brain neurotransmitter systems are sensitive to polycyclic aromatic hydrocarbons and could represent a target of the naphthalene-induced neuroendocrine disruption.

Effects of a single inhalative exposure to formaldehyde on the open field behavior of mice

The effects of formaldehyde on the explorative behavior and locomotor activity of mice after a single inhalative exposure were examined in an open field. Adult male mice were exposed to approximately 1.1 ppm, 2.3 ppm, or 5.2 ppm formaldehyde vapour for 2 hours and the open field test was carried out two hours after the end of exposure (trial 1) and repeated 24 hours thereafter (trial 2). The following behavioral parameters were quantitatively examined: numbers of crossed floor squares (inner, peripheral, total), sniffing, grooming, rearing, climbing, and incidence of fecal boli. The results of the first trial revealed that the motion activity was significantly reduced in all exposed groups. In the 1.1 ppm group, the frequency of rearing was reduced and that of floor sniffing increased. The exposure to the two higher formaldehyde concentrations caused a significant decrease in total numbers of floor squares crossed by the subjects, air sniffing, and rearing. The open field test on the next day (trial 2) showed that the frequencies of floor sniffing, grooming, and rearing in all formaldehyde groups were significantly altered. In the 2.5 ppm group, an increased incidence of fecal boli was observed. From the results obtained, we conclude that the exposure of male mice to formaldehyde vapour affects their locomotor and explorative activity in the open field, and that some open field parameters are still altered in the exposed animals even after 24 hours.

A study on the effect of inhalative formaldehyde exposure on water labyrinth test performance in rats

We investigated the effects of repeated inhalative exposure to several formaldehyde concentrations (2 hours/day, 10 consecutive days) on the behavior of adult male and female LEW.1K rats during a period in which they learned to perform a water labyrinth task. We also examined the effects on the histology of some organ tissues. While the controls needed increasingly shorter swimming periods to complete the water labyrinth test and made fewer errors with advancing trial duration, such progress could not be observed in the learning behavior of the exposed animals. They took significantly longer swimming periods to reach the finish and made significantly more errors in comparison to the controls. The statistical comparison between the collected data in the formaldehyde exposed male and female rats reveals that females in general reached the end point of the swimming labyrinth in significantly less time. On some trial days, however, they made more mistakes than males. In the highest concentration group, no gender differences were evident in the frequency of errors. The histological examination revealed no pathological changes attributable to formaldehyde exposure. Since the water labyrinth test is used to investigate changes in memory and learning behavior in animals, we conclude that under investigational conditions, formaldehyde affects the learning behavior and the memory of male and female rats.

Encephalomyeloradiculoneuropathy following exposure to an industrial solvent

A 19-year-old male developed complaints including weakness of the lower extremities and right hand, numbness, dysphagia and urinary difficulties following a 2 month exposure to an industrial solvent constituted mainly of 1-bromopropane, but also containing butylene oxide, 1,3 dioxolane, nitromethane, and other components. Nerve conduction studies revealed evidence of a primary, symmetric demyelinating polyneuropathy. Evidence of CNS involvement came from gadolinium enhanced MRI scans of the brain, showing patchy areas of increased T2 signal in the periventricular white matter, similar scans of the spinal cord revealing root enhancement at several lumbar levels, and SSEP studies. The patient's symptoms had started to resolve following the discontinuation of the exposure, before he was lost to follow-up. Similar findings have been reported following 1-bromopropane exposure in rats. I hypothesize that this patient's symptoms may have been due to 1-bromopropane-induced neurotoxicity.

Positron emission tomography studies of healthy volunteers--no effects on the dopamine terminals and synthesis after short-term exposure to toluene

Despite extensive research, the mechanisms for the effects of organic solvents on the central nervous system are still unknown. One mechanism proposed is that solvents interfere with the synthesis of neurotransmitters. In the present study 11 male healthy volunteers were exposed during 15 min to 100 p.p.m. toluene at light physical exercise, and the dopamine decarboxylase activity and number of terminals in putamen were measured before and after exposure by positron emission tomography. Two different tracers were used [beta-11C]L-DOPA for decarboxylase activity during the in vivo synthesis of dopamine, and [11C]nomifensine to estimate the number of terminals. Although there was a slight increase in the rate of dopamine synthesis in the putamen after the exposure, this difference was not statistically significant (P = 0.4). No effect was observed with regard to the uptake of nomifensine. There was no significant relationship between the dose of toluene and rate of dopamine synthesis, and no significant correlation between the time from end of exposure to start of the PET-camera and DOPA. Our findings indicate that short term exposure to 100 p.p.m. of toluene does not affect the rate of dopamine synthesis or the number of presynaptic terminals.

Trichloroethylene--a review of the literature from a health effects perspective

This report reviews the literature on the impact of exposure to trichloroethylene (TCE) on human health. Special emphasis is given to the health effects reported in excess of national norms by participants in the TCE Subregistry of the Volatile Organic Compounds Registry of the National Exposure Registries--persons with documented exposure to TCE through drinking and use of contaminated water. The health effects reported in excess by some or all of the sex and age groups studied were speech and hearing impairments, effects of stroke, liver problems, anemia and other blood disorders, diabetes, kidney disease, urinary tract disorders, and skin rashes.

Three weeks' exposure of rats to dearomatized white spirit modifies indices of oxidative stress in brain, kidney, and liver

The present study was undertaken in order to investigate whether dearomatized white spirit induces indices of oxidative stress in subcellular fractions of hemisphere, hippocampus, kidney and liver tissue of rats exposed to 0, 400 and 800 ppm 6 hr/day, 7 days a week for 3 weeks. The results show that white spirit is a strong in vivo inducer of oxidative stress in subcellular fractions of brain, kidney and liver. In the liver there was a statistically significant increase in the rate of reactive oxygen species (ROS) generation and a decrease in glutamine synthetase activity. In the kidney there was a statistically significant decrease in the rate of ROS generation. In the hemisphere there was a statistically significant increase in the level of reduced glutathione. In the hippocampus there was a statistically significant increase in the rate of ROS generation. However, in vitro addition of dearomatized white spirit had no effect on the rate of cerebrocortical P2 fraction ROS generation. The results suggest that cumulative oxidative damage may be an underlying mechanism of dearomatized white spirit-induced neurotoxicity and that various regions of the brain may respond differently.

Neurobehavioral impairment and seizures from formaldehyde

Three patients were evaluated for effects of formaldehyde on central nervous system function. Three patients had used formalin, formaldehyde with or without phenol, to fix whole animals for 14-30 y, and a fourth patient was covered several times by formaldehyde and phenol rainout from manufacturing spills. All were disabled, and two had developed seizures. They had elevated mood state scores (82 to 162) and elevated symptom frequency scores (111 to 138), compared with referent subjects. There was excessive fatigue, somnolence, headache, difficulty remembering, irritability, and instability of mood. Compared with referents, choice reaction time was prolonged in four of four (4/4) subjects, blink latency was delayed in 2/2, balance was abnormal in 3/4, and visual fields were constricted in 2/3. Cognitive functions, measured by Culture Fair, block design, and digit symbol tests, were impaired in all. Delayed verbal recall and visual reproduction were impaired in 3/4. Perceptual motor speed on slotted pegboard and trail making A and B tests was reduced in 4/4. Errors on fingertip number writing were abnormal in all. Long-term memory was decreased in only one. Extensive use of formaldehyde at work or repeated airborne exposure to formaldehyde and phenol appears to have impaired central nervous system function.

Effects on neurobehavioral performance of chronic exposure to chemically contaminated well water

Occupational exposure to trichloroethylene (TCE) and other solvents impairs neurobehavioral performance. Use of well water contaminated with TCE and solvents has been associated with excessive symptoms, cancers, birth defects and impaired blink reflex. We extended these observations by measuring the neurophysiological (NPH) and neuropsychological (NPS) status of subjects who used water contaminated with 6 to 500 ppb of TCE for 1 to 25 years. The 170 well-water exposed subjects who resided in southwest Tucson, Arizona overlying the Santa Cruz River aquifer, were compared to 68 referent subjects for NPH and NPS tests. Also, 113 histology technicians (HT) were referents for blink reflex latency only. Affective status was assayed by a Profile of Mood States (POMS). Exposed subjects were statistically significantly impaired when compared to referents for NPH tests. These impairments included sway speed with eyes open and closed, blink reflex latency (R-1), eye closure speed, and two choice visual reaction time. NPS status was statistically significant impaired for Culture Fair (intelligence) scores, recall of stories, visual recall, digit span, block design, recognition of fingertip numbers, grooved pegboard and Trail making A and B. POMS scores were elevated. Prolonged residential exposure to well-water containing TCE at lower levels than occupational exposures, but without time away from exposure for metabolism and excretion of toxins, was associated with neurobehavioral impairment.

Toluene-induced oxidative stress in several brain regions and other organs

The in vivo dose-response relationship between toluene and reactive oxygen species (ROS) formation in rat brain, liver, kidney, and lung, and the time-course of these effects has been characterized. The rate of oxygen radical formation was measured using the probe 2',7'-dichlorofluorescin diacetate. In vivo exposure to various doses of toluene (0.5, 1.0, and 1.5 g/kg ip) elicited a dose-dependent elevation of ROS generation within crude mitochondrial fractions obtained from rat lung and kidney, and within crude synaptosomal fractions from cerebellum. ROS formation in crude mitochondrial fractions from liver, and crude synaptosomal fractions from striatum and hippocampus, reached a maximum value at relatively low doses of toluene. Of the brain regions, the hippocampus had the highest induced levels of ROS. In vivo exposure to a single dose of toluene (1.5 g/kg ip), revealed that toluene-induced ROS reached a peak within 2 h, which correlated directly with measured toluene blood levels. This elevated oxidative activity was maintained throughout the next 24 h, even though blood values of toluene decreased to negligible amounts. These results demonstrate that exposure to toluene results in broad systemic elevation in the normal rate of oxygen radical generation, with such effects persisting in the tissues despite a rapid decline in toluene blood levels. Acute exposure to toluene may lead to extended ROS-related changes, and this may account for some of the clinical observations made in chronic toluene abusers.

Blink reflex measurement of effects of trichloroethylene exposure on the trigeminal nerve

Trichloroethylene (TCE) exposure is known to have specific toxic effects on cranial nerves, the trigeminal nerve (V) in particular. The electrophysiological measurement of the blink reflex (BR) can quantify latency changes in the Vth and VIIth cranial nerve reflex arc. Prior study looked at the blink reflex measurement in a community group exposed to TCE in their drinking water. This study evaluated the use of the electrophysiologic blink reflex as an indicator of neurotoxic effects of TCE in occupationally exposed workers. The BR was tested in individual cases with documented histories of exposure to known chemical neurotoxins including TCE (n = 18). When compared with the nonexposed laboratory control values (n = 30), the subjects with a significant history of TCE exposure demonstrated the most prolonged latencies (greater than or equal to 3.0 SD above the nonexposed group mean) in the R1 component of the blink reflex measurement. The electrophysiological study of the blink reflex has application in assessing TCE exposure and in documenting the neurotoxic effects of that exposure on trigeminal nerve functions in humans.

Subclinical effects of groundwater contaminants. IV. Effects of repeated oral exposure to combinations of benzene and toluene on regional brain monoamine metabolism in mice

Benzene and toluene are known neurotoxicants that may interact in vivo. The effect of combined treatment with benzene and toluene on the endogenous concentrations of the catecholamines norepinephrine (NE) and dopamine (DA), the catecholamine metabolites vanillylmandelic acid (VMA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the indoleamine serotonin (5-HT) and its metabolite 5-hydroxy-indoleacetic acid (5-HIAA), were investigated in six discrete brain regions of CD-1 mice. Groups of male, adult mice were continuously exposed to benzene (166 mg/l), toluene (80 and 325 mg/l), and combinations of benzene + toluene (80 or 325 mg/l) in drinking water for 4 weeks. Benzene produced increases of NE in the hypothalamus, cortex, midbrain and medulla oblongata, DA in the hypothalamus and corpus striatum, and 5-HT in all dissected brain regions except cerebellum. Elevated levels of various monoamine metabolites were also observed in these brain areas. Toluene ingestion alone also significantly increased the concentrations of NE, DA, 5-HT, and their metabolites in several brain regions. Mice given the combined treatments exhibited raised regional neurochemical levels when compared to the untreated controls. Increased concentrations of biogenic amine metabolites in several brain regions were greater in the combined exposures of benzene and toluene than when either chemical was used alone. The findings were different from those observed on immune parameters using similar treatment protocols, where simultaneous exposure to toluene prevented the immunotoxic effects of benzene.

Uptake of trihalomethanes by patients during hemodialysis

Trihalomethanes (THM) present in tap water were also found in dialysis fluid because they were not eliminated by water treatment. THM, absorbed through the dialyser membranes, increased considerably in blood and in expired air of patients on hemodialysis during the dialysis sessions. The uptake of THM during each dialysis session was about 1 mg.

An examination of factors that could affect choice reaction time in histology technicians

Histology technicians exposed to formaldehyde and solvents have symptoms and objective evidence of neurobehavioral impairment of memory, judgment, and equilibrium. Because reaction time has been prolonged in many groups of workers exposed to toxicants, choice reaction time was measured in 385 female formaldehyde and solvent-exposed histology technicians, and 79 unexposed female laboratory workers. Choice reaction time to a visual stimulus (CRT) is defined, for the purpose of this study, as the time required for discriminated cancellation of two different letters on a microcomputer screen by pressing the matching keys. Initial analysis showed that increases in age, years of cigarette smoking, and hours per day of formaldehyde exposure significantly lengthened CRT, but xylene-toluene exposure had no effect. Since duration of smoking and length of daily formaldehyde exposure were age related, multiple linear regression analysis of CRT was performed using them as independent variables. Increasing age was the only significant factor in lengthening CRT. However, in these female histology technicians, the second measurement one year later was 44 msec faster (p less than .04). The reason for improved performance is unclear, but it may be an effect of training encompassing familiarity, improved attention, or learning.

Blink reflex latency after exposure to trichloroethylene in well water

The electrophysiological measurement of the blink reflex (BR) can quantify the conduction latency in the reflex arc involving the Vth (trigeminal) and VIIth (facial) cranial nerves. We measured the electrophysiological BR in a population (N = 21), which had alleged chronic exposure to trichloroethylene (TCE) through the public drinking water at levels 30-80 times higher than the Environmental Protection Agency (EPA) Maximum Contamination Level (MCL). A highly significant difference was observed in the conduction latency means of the BR components (p less than .0001), when the study population was compared with laboratory controls (N = 27). This difference suggests a subclinical alteration of the Vth cranial nerve function due to chronic, environmental exposure to TCE.

The pathogenesis of equine laryngeal hemiplegia — a review

Recent research on the muscular and nervous changes which occur in idiopathic equine laryngeal hemiplegia has indicated that many of the traditional concepts of the aetiology of this disease are erroneous. In light of the new knowledge gained, the various predispositions and possible causes of laryngeal hemiplegia are discussed, and it is suggested that the underlying mechanism of axonal damage in this neuropathy of horses may be related to abnormal energy metabolism in the axon.

Formaldehyde impairs memory, equilibrium, and dexterity in histology technicians: effects which persist for days after exposure

Results of neurobehavioral testing in 305 histology technicians were studied by regression analysis with age, years of cigarette smoking, and hours per day of exposure to formaldehyde and to solvents as major independent variables. Increasing age was associated with poorer performance on visual memory, block design, trails, dexterity by pegboard, sharpened-Romberg, finger writing, as well as with longer choice reaction time. Increased daily hours of exposure to formaldehyde were correlated with reduced performance on story memory, visual memory, digit span, pegboard and sharpened-Romberg, as well as with errors on trails. Exposure to solvents was associated only with diminished recall of story.

Pacinian corpuscles in rats with carbon disulphide neuropathy

Adult Wistar rats were exposed to carbon disulphide vapours at a concentration of 2.4 mg/l of air for 5 days a week (6 h a day), and the ultrastructure of Pacinian corpuscles and their nerve supply was investigated after 6 months of exposure. Both degenerative and regenerative changes were observed in sensory axons and the corpuscles. In a sample of corpuscles examined, 30% were denervated and about 60% showed clear signs of reinnervation. Some of the reinnervated corpuscles were supplied by unmyelinated axons. In others, one to three myelinated axons were already found at the nerve entry. The axons branched and formed three to eight terminals in the inner core. Due to continuous intoxication, most regenerated terminals were again undergoing degeneration. In peripheral nerves, the evidence of axonal regeneration has been reported in various toxic distal axonopathies. However, the reinnervation of Pacinian corpuscles has not been described before. It can be expected that reinnervation of Pacinian corpuscles and other end-organs also occurs in other axonopathies, if not during continuous poisoning, then at least after its cessation.

Choice reaction time in workers exposed to styrene vapour

Behavioural effects of occupational exposure to vapour from styrene-based resin were investigated in 10 female workers with a portable test of choice reaction time. Testing was carried out both at the beginning and end of the day's shift. Uptake and metabolism of styrene were assessed by monitoring post-shift urinary mandelic acid excretion rates. By using these data workers were allocated to three groups reflecting zero, low or high exposure. After exposure slowing of reaction times was found in those with the highest mandelic acid excretion rates, whereas a slight improvement or no change was found in those with low or zero exposure. Subsequent improvements in extraction and ventilation in the workroom were shown to be associated with both decreased mandelic acid excretion and absence of long reaction times in those previously most heavily exposed.

Neonatal exposure to toluene: effects on the development of liver microsomal cytochrome P-450 and serum hormone levels in the rat

Lactating Sprague-Dawley rats and their pups were exposed on postnatal days 1-7, 6 h/day, to 80, 500 and 1000 ppm toluene, respectively, by inhalation. Exposure to 80 ppm toluene decreased the liver microsomal AHH activity and the rate of 7 alpha- and 6 beta-hydroxylation of androstenedione in 8-day-old-pups. On the other hand, neonatal exposure to 500 or 1000 ppm toluene resulted in a significant increase in AHH and 7-ethoxyresorufin O-deethylase activities and in the formation of 16-oxygenated metabolites of androstenedione in 8-day-old animals. Exposure to toluene increased the cytochrome P-450 content at all 3 dose levels in male but not in female pups. Twenty-one days after neonatal exposure no such effects were seen in young animals of either sex. In 56-day-old male rats, however, neonatal exposure to 80 ppm toluene resulted in a decreased rate of 6 beta-hydroxylation of androstenedione and a reduced AHH activity. No such effects were seen in female rats of the same age. Neonatal exposure to toluene affected the body and liver weights in 8-day-old pups of both sexes but had no effect on these parameters in 21-day-old animals of either sex. Exposure to 80 ppm toluene during the neonatal period gave a significantly increased body weight of 56-day-old male but not of female rats of the same age although this treatment increased liver weight in both sexes at this age. Serum testosterone levels were decreased in 21-day-old male rats following neonatal exposure to 80 or 500 ppm toluene and in 56-day-old male rats exposed neonatally to 1000 ppm toluene. In conclusion, exposure to toluene during the first week of life caused significant changes in various liver microsomal cytochrome P-450 dependent enzyme activities in 8-day-old pups, whereas the long-term effects on liver metabolism of the adult animal were small.

Pathogenesis of experimental giant neurofilamentous axonopathies: a unified hypothesis based on chemical modification of neurofilaments

This review summarizes current evidence suggesting that the pathogenetic basis of giant axonal neuropathies induced by neurotoxic chemicals involves a direct chemical modification of neurofilaments (NF) and/or related cytoskeletal proteins. Chemical modification of NF is believed to disrupt the normal cytoskeletal organization, which results in an alteration in NF transport rate and accumulation of NF at prenodal sites along the axon. The exact location at which axonal enlargements occur appears to be a continuous function, dependent on both the structure and dosage schedule of the chemical toxin. A unified hypothesis for the neuropathologic effect of the diverse spectrum of toxic chemicals known to induce giant axonopathies is presented, based on recently published data on the structure of NF protein. Neurotoxic chemicals are believed to alter the charge balance of highly ionic domains of NF proteins which are thought to enter into intermolecular coulombic interactions in forming the supramolecular cytoskeletal framework.

Effects of toluene inhalation on brain biogenic amines in the rat

The effects of toluene exposure on the biogenic amine concentrations in the central nervous system were investigated in the rat. Toluene was administered via inhalation to groups of rats at concentrations of 0, l00, 300, or 1000 ppm. After an 8-h continuous exposure, animals were sacrificed and whole brain concentrations of dopamine (DA), norepinephrine (NE), and 5-hydroxytryptamine (5-HT) were determined. The data indicated a significant increase in whole brain concentrations of DA following the 100-ppm exposure. A regional analysis of DA, NE, and 5-HT concentrations in rats exposed to 1000 ppm of toluene for 8-h indicated a significant increase in DA concentration in the striatum. A significant increase in NE concentrations was detected in the medulla and midbrain while 5-HT concentrations were significantly increase in the cerebellum, medulla, and striatum. The results indicate that toluene action results in elevated concentrations of behaviorally significant neuro-transmitters.

Toluene-induced decrease in rat plasma concentrations of tyrosine and tryptophan

The organic solvent toluene is demonstrated to cause a decrease in rat plasma concentrations of tyrosine and tryptophan both after intraperitoneal injections and after inhalation. Tyrosine and tryptophan are precursors to neurotransmitters and are transported from plasma into the brain. As the concentrations of these amino acids in plasma could influence the monoamine synthesis in the brain, this phenomenon might be of importance for the pathophysiology behind solvent-induced effects on brain function.

Side effects of phenobarbital and phenytoin during long-term treatment of epilepsy

Phenobarbital and phenytoin have good antiepileptic effect, but clinically significant untoward effects occur during their long-term use. Phenobarbital may cause hyperactivity, behavioral problems, sedation, and even dementia; these effects are dose related to some extent. Side effects of phenytoin include sedation, a cerebellar syndrome, phenytoin encephalopathy, psychosis, locomotor dysfunction, hyperkinesia, megaloblastic anemia, decreased serum folate level, decreased bone mineral content, liver disease, IgA deficiency, gingival hyperplasia, and a lupus-like hypersensitivity syndrome. Especially susceptible to the neurotoxic effects of phenytoin are epileptic children with severe brain damage who are on multiple drugs. In those children, balance disturbance may develop and be followed by gradual loss of locomotion. Among 131 mentally retarded epileptic patients, phenytoin intoxication occurred in 73 (56%), of whom 18 experienced persistent loss of locomotion. There is experimental evidence that the toxic action of phenytoin lies at the cellular level, predominantly in the cerebellum. Many experts avoid the long-term use of phenytoin because of its insidious and potentially dangerous side effects.

Concentration-dependent behavioral changes in mice following short-term inhalation exposure to various industrial solvents

Mice were exposed during a 4-hr period to various concentrations of 13 aliphatic or aromatic solvents which affect primarily the central nervous system (CNS). The test compounds were benzyl chloride, butyl alcohol, chlorobenzene, cyclohexanone, 1,2-dichloroethylene, diisobutyl ketone, isopropyl acetate, methyl ethyl ketone, styrene, tetrachloroethylene, 1,1,1-trichloroethane, toluene, and ortho-xylene. After exposure, measurements were made to see whether these neurotoxicants would decrease the immobility developed in a "behavioral despair" swimming test. Each chemical was shown to reduce the total duration of immobility measured over a 3-min period in a concentration-related manner. The systematic determination of the atmospheric concentrations responsible for a 50% decrease in immobility (ID50) permitted classification of the solvents in terms of their relative potencies. The possibility of using such experimental data as tentative guidelines for setting safe levels of work exposure to the neurotoxicants was suggested, considering the existence of quantitative relationships between the ID50 values and the current occupational standards.

Neuropsychiatric symptoms in workers occupationally exposed to jet fuel--a combined epidemiological and casuistic study

Some aircraft personel and airline industry workers are exposed to jet fuel, a mixture of aliphatic hydrocarbons (petroleum 80%) and some organic solvents (petroleum 80%) and some organic solvents (aromatic hydrocarbons 20%). In order to evaluate the possible neuropsychiatric sequeale of such long-term occupational exposure, we examined 30 workers exposed at about 250 mg/m3 for 4-32 years at a jet motor factory. They were compared with two control groups (2 x 30) of matched non-exposed workers. The medical history was first assessed by standardized interviews and examination of medical records kept by the factory physician. The exposed subjects had, after their employment, much more often sought medical advice because of emotional dysfunctions, such as depression and anxiety, than had the control groups (P less than 0.005). When the prevalent mental symptoms, indicative of brain lesion, later were rated by psychiatrists, the exposed workers scored higher than did the controls (P less than 0.001). 14 subjects showing most symptoms were then selected for a thorough neuropsychiatric clinical investigation comprising psychosocial inquiries, psychological testing, personality assessment and neurological/neurophysiological examination. Seven were judged to suffer from mild organic brain syndrome (i.e. "organic neurasthenia") of which one subject was a severe case. The subjects had all undergone a slow but steady personality change over the years--starting from an ordinary strength without neurotic traits and moving towards an asthenic state with fatigue, anxiety and vegetative hyperreactivity. No other cause for this change could be identified as an alternative to the occupational exposure to jet fuel. It is concluded that personality changes and emotional dysfunctions are the foremost effects of such long-term exposure to petroleum products.

Application and results of whole-body autoradiography in distribution studies of organic solvents

With the growing concern for the health hazards of occupational exposure to toxic substances attention has been focused on the organic solvents, which are associated with both deleterious nervous system effects and specific tissue injuries. Relatively little is known about the distribution of organic solvents and their metabolites in the living organism. Knowledge of the specific tissue localizations and retention of solvents and solvent metabolites is of great value in revealing and understanding the sites and mechanisms of organic solvent toxicity. Whole-body autoradiography has been modified and applied to distribution studies of benzene, toluene, m-xylene, styrene, methylene chloride, chloroform, carbon tetrachloride, trichloroethylene and carbon disulfide. The high volatility of these substances has led to the development of cryo-techniques. Whole-body autoradiographic techniques applicable to the study of volatile substances are reviewed. The localizations of nonvolatile solvent metabolites and firmly bound metabolites have also been examined. The obtained results are discussed in relation to toxic effects and evaluated by comparison with other techniques used in distribution studies of organic solvents and their metabolites.

Neurotoxicity of industrial chemicals and contaminants: aspects of biochemical mechanisms and effects

Nervous system toxicity by industrial chemicals and contaminants cannot be explained by a single mechanism because of the complex functional capacity of the brain and spinal cord. The nervous system is dependent on the adequate supply of oxygen, and therefore, its lack in the ambient air causes rapid dysfunction. Similar effects to hypoxia are caused by agents which reduce oxygen availability at the cellular level by histotoxic mechanisms, e.g., through the inhibition of mitochondrial respiration. Hypoxic effects are rapidly produced, and in cases where a significant number of cells are fatally damaged permanent disability may remain. Acutely harmful effects are also brought about by organic solvents. The typical mode of exposure is that of vapour inhalation. The lipid-soluble molecules pass the blood-brain barrier rapidly and depress the nerve cell membrane functions. This hinders the formation of action potentials. Neuronal cells acquire tolerance towards the membrane-depressant effects in repeated or prolonged exposure so that similar doses do not produce equivalent effects. The development of the tolerance can be regarded as one of the long-term effects of lipophilic chemicals. They may also produce metabolic adaptation so that their biotransformation is enhanced. This may increase the risk of producing more toxic intermediates. The toxic effects thus created can be cumulative since neurons do not multiply by cell division in the postnatal life. The neurotoxicity of metals is more clearly associated with the accumulation of the dose. Adult brain possesses a blood-brain barrier to many water-soluble compounds such that a threshold concentration must be overcome before appreciable toxic effects are seen. Children are in this respect more vulnerable because of their immature barrier function.

Electronystagmographic findings in rats exposed to styrene or toluene

A previously described experimental model for studying the effect of industrial solvents in the vestibular system of rabbits has been applied to rats. To achieve a constant concentration, the solvent was infused intravenously, dissolved in a lipid emulsion. Arterial blood levels were estimated by gas chromatography. The vestibulo-oculomotor behaviour of rats during repeated rotatory acceleration was investigated by electronystagmography. The effect of two solvents-toluene and styrene-on the rotatory induced nystagmus was examined. Both solvents caused an exaggerated reaction at arterial blood levels above 75 ppm. The investigation indicated that the rat will be suitable species for further electronystagmographic investigation of the influence of organic solvents on the vestibular system, for example in screening studies of the toxicity of these solvents.

Neurotransmitter metabolizing enzymes and plasma butyrylcholinesterase in mice exposed to trichloroethylene

Acetylcholinesterase, glutamine synthetase, acid phosphatase and glutamate dehydrogenase activity in brain and cholinesterase activity in blood were investigated in mice exposed to 170 p.p.m. trichloroethylene (TCE) during 30 days. The neuronal enzymes remained unaffected which suggests that no general damage occurred to either the glia or the nerve cell populations. In accordance with this no effect was seen on acid phosphatase. In contrast, plasma butyrylcholinesterase increased twofold in exposed male mice while it was unaffected in females. Liver weight in males and females increased with a factor of 1.5 and 1.9, respectively.

Vestibular dysfunction in occupational chronic solvent intoxication

Neurotoxic volatile organic solvents used by house and car painters may lead to professional toxic encephalopathy after several years of exposure. The symptoms are memory impairment, fatigue, personality changes, headache and dizziness. Vestibular dysfunction was found in 55% of 113 painters examined, mainly in the form of reduced caloric vestibular reactions. No correlation between vestibular dysfunction and the duration of exposure, cerebral atrophy or intellectual impairment could be demonstrated. Vestibular examination may be helpful in detecting early changes in exposed persons and in determining more accurate safety limits for harmful chemicals.

Neurochemical effects of short-term inhalation exposure to vinyltoluene vapor

Male rats were exposed to vinyltoluene vapor after pretreatment with polychlorinated biphenyl (PCB). Brain and body solvent burdens were in a linear relationship to the exposure level although it changed between the two weeks while the solvent accumulated in the perirenal fat. The pretreatment caused a significantly smaller burden in the fat samples. Lysosomal acid proteinase was above the control range in the brain homogenate in the highest exposure, while glutathione peroxidase and 2',3'-cyclic nucleotide 3'-phosphohydrolase showed a dose-dependent decrease in the homogenate during the first week. Acid proteinase activity in the glial cells increased above the control range only in the PCB-pretreated rats in the first week. Azoreductase increased in the glial cells above the control range only in the first week, and the pretreatment augmented the increase very significantly. All biochemical effects were largely abolished within two weeks of solvent-free period with the exception of an increase in the cerebral RNA at the highest dose level. Vinyltoluene can cause more pronounced neurochemical effects compared to styrene, xylene, or toluene at similar exposure levels.

Neurological picture of organic solvent poisoning in industry. A retrospective clinical study of 37 patients

A retrospective evaluation of neurological, neuroradiological, neurophysiological, psychological, and laboratory findings on 37 patients, remitted to the Institute of Occupational Health, Helsinki because of suspected poisoning due to organic solvents, was performed. Patient selection was made on the basis of performed pneumoencephalography (PEG). Most of the patients had been exposed to a mixture of solvents (19 cases). Carbon disulphide exposure had occurred in six cases, trichloroethylene in five cases, and the rest of the patients had been exposed to styrene (one case), thinner (two cases), toluene (1 case), methanol (1 case), and carbon tetrachloride (two cases). Clinical neurological findings comprised slight psycho-organic alteration, cerebellar dysfunction, and peripheral neuropathy. The PEG showed changes suggesting brain atrophy in 63% of the patients. Slight asymmetric central atrophy and localized cortical atrophy were the most frequent findings. The main electroencephalographic finding was slight diffuse slow-wave. Electroneuromyography showed slight changes suggesting peripheral neuropathy in 23 of the 28 patients examined. Psychological alterations were seen in all patients: personality changes and psychomotor disturbances were the most common findings. Because individual constitutional differences existed, no clear-cut exposure-effect relationship could be established. Thus, neurological evaluation of all those exposed to neurotoxic agents who present symptoms, regardless of the degree of current exposure, is important.

Dose-dependent neurochemical changes during short-term inhalation exposure to m-xylene

Male Wistar were exposed to m-xylene vapor at concentrations of 2.0, 16.1, and 30.3 mumol/1 for 2 weeks (5 days a week, 6 h daily). Xylene concentrations in brain and perirenal fat increased between weeks 1 and 2 of exposure, in proportion to the exposure concentrations. Increase in brain NADPH-diaphorase and azoreductase activities was seen after week 2 at the two higher exposure levels, while superoxide dismutase activity decreased in a dose-related manner at the same time. Biochemical analyses on rats withdrawn from exposure for 2 weeks indicated that the biochemical effects were largely abolished within that time, although cerebral RNA was above the control value at the two higher exposure levels.

Behavioural and glial cell effects of inhalation exposure to styrene vapour with special reference to interactions of simultaneous peroral ethanol intake

Male Wistar rats were exposed to 300 p.p.m. of styrene vapour with simultaneous ethanol ingestion for 4 to 17 weeks. The effects on behaviour were analyzed after 4, 9 and 13 weeks of the experiment. The most manifest behavioural effects were found in rats exposed to the combination, and the changes included increased preening time at the 4th week and increased ambulation and rearing at the end of the exposure. The ethanol ingestion affected also the accumulation of the solvent burden by delaying the peak solvent concentration in the perirenal fat to the 8th week of exposure. The fat solvent concentration did not differ from each other in the two groups at the end of the experiment, and they were similar as compared the concentration found in phenobarbital-pretreated rats exposed for reference. The styrene exposure had almost no effects on cerebral glial cells whereas ethanol induced unexpectedly increased protein destruction in them throughout the experiment. Co-exposure to ethanol and styrene decreased the magnitude of protein destruction in the glial cells. Withdrawal of the rats after an 8-week exposure showed that the styrene effects were largely abolished in two weeks of exposure-free period as analyzed by the determination of brain RNA and acid proteinase activity. Brain RNA was lower than control after two weeks of ethanol deprivation. The present data indicate that marked metabolic interactions between ethanol and styrene take place in agreement with experience on other similar solvent combinations.

Neurochemical effects on rats of n-heptane inhalation exposure

Inhalation exposure of male rats at three dose levels (4.2, 21, 62 mol/L) to n-heptane vapor caused a dose-dependent brain and body solvent burden, which increased during two weeks of exposure. Initial neurochemical effects included reduced RNA concentration and increased NADPH-diaphorase in brain at the lowest dose. Increased proteolysis was detected in the cerebral samples in the second week at all doses, and the NADPH-diaphorase returned to the control range. Brain RNA content tended to be larger than in the controls. All biochemical effects were abolished after two weeks of withdrawal from the two-week exposure, with the exception of reduced glutathione at the lowest dose. None of the rats presented clinical signs of neuropathy, which indicates that heptane and its metabolites do not share the specific neurotoxicity of hexane and its metabolites.

Neurasthenic symptoms in workers occupationally exposed to jet fuel

Long-term exposure to petroleum distillation products (e.g. jet fuel) has been suggested to cause chronic mental and neurological symptoms. In the present "cross-sectional epidemiological study" the extent of neuropsychiatric ill-health in 30 workers exposed to jet fuel was compared with that in 60 non-exposed matched controls. Standardized medical interviews showed a higher occurrence of neurasthenic symptoms in exposed subjects (P less than 0.001). The result was confirmed by examination of the medical records kept by the factory physician (P less than 0.01). The prevalence of psychiatric symptoms was assessed with a rating scale of 37 items (a modified CPRS). Again, the exposed workers scored higher than the controls (P less than 0.001), particularly regarding the neurasthenic symptoms, i.e. fatigue, anxiety, mood changes, memory difficulties, and various psychosomatic symptoms (P less than 0.01). The results could neither be explained by observer's bias, nor by a greater susceptibility for mental disorders in the exposed subjects. We therefore conclude that occupational exposure to jet fuel vapours around the present threshold limit values may induce a neurasthenic syndrome.

Effects of long-term turpentine inhalation on rat brain protein metabolism

Chronic exposure of adult male rats to commercial turpentine resulted in an accumulation of the solvent in perinephric fat and brain. The body solvent content remained virtually stable during 8 weeks. Brain RNA content was below the control range initially and it increased to the control level at the 4th week of exposure. Serum non-specific cholinesterase activity was somewhat below the control range at the first and second week of exposure and it returned to the control level thereafter. The present data are in agreement with the small effects of turpentine exposure on human central nervous system in clinical follow-up studies.