Regional alterations of brain catecholamines by styrene exposure in rabbits

A critical review finds styrene lacks direct endocrine disruptor activity

The European Commission lists styrene (S) as an endocrine disruptor based primarily on reports of increased prolactin (PRL) levels in S-exposed workers. The US Environmental Protection Agency included S in its list of chemicals to be tested for endocrine activity. Therefore, the database of S for potential endocrine activity is assessed. In vitro and in vivo screening studies, as well as non-guideline and guideline investigations in experimental animals indicate that S is not associated with (anti)estrogenic, (anti)androgenic, or thyroid-modulating activity or with an endocrine activity that may be relevant for the environment. Studies in exposed workers have suggested elevated PRL levels that have been further examined in a series of human and animal investigations. While there is only one definitively known physiological function of PRL, namely stimulation of milk production, many normal stress situations may lead to elevations without any chemical exposure. Animal studies on various aspects of dopamine (DA), the PRL-regulating neurotransmitter, in the central nervous system did not give mechanistic explanations on how S may affect PRL levels. Overall, a neuroendocrine disruption of PRL regulation cannot be deduced from a large experimental database. The effects in workers could not consistently be reproduced in experimental animals and the findings in humans represented acute reversible effects clearly below clinical and pathological levels. Therefore, unspecific acute workplace-related stress is proposed as an alternative mode of action for elevated PRL levels in workers.

Effects of subchronic exposure to styrene on the extracellular and tissue levels of dopamine, serotonin and their metabolites in rat brain

At present, there is controversy over the neurotoxic potential of styrene. Several epidemiological and clinical studies have shown that styrene exposure causes alterations of central nervous system functions in humans. Neurotransmitters have been implicated in the pathogenesis of styrene neurotoxicity in rodents. Several studies carried out on postmortem brain tissue suggest that styrene may alter dopaminergic neurotransmission in rabbit or rat brain. Moreover, in vitro studies suggest that both styrene and styrene oxide inhibit the uptake of dopamine (DA) in purified synaptic vesicles prepared from rat brain striata. To date, biochemical studies on animals have explored global tissue levels of neurotransmitters with sub-acute exposures to styrene. However, extracellular levels of neurotransmitters are more closely related to behaviour than are global tissue levels. The present study determined changes in the extracellular concentrations of DA, serotonin (5-HT) and their acid metabolites, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindolacetic acid (5-HIAA), in striatal dialysates from freely moving adult male rats after exposure to 750 and 1,000 ppm styrene, 6 h per day, 5 days per week for 4 weeks. We also determined the concentrations of DA, 5-HT and their acid metabolites in striatum, nucleus accumbens and prefrontal cortex obtained postmortem from similarly exposed rats. Exposure to 1,000 ppm of styrene caused a significant decrease in extracellular acid metabolite concentrations. Tissue levels of acid metabolites were also decreased to a lesser extent. The effects were observed 72 h after discontinuing exposure but had vanished 17 days later. There was no change in DA or 5-HT concentrations either in the dialysates or tissues. Exposure to 750 ppm styrene caused no changes in the concentrations of DA, 5-HT and their acid metabolites either in the dialysates or tissues. The possibility that the effect of styrene is mediated by monoamine oxidase (MAO) inhibition is discussed.

Acute effects of styrene inhalation on the neuroendocrinological system of rats and the different effects in male and female rats

There have been several epidemiological and experimental studies about styrene from the neuroendocrinological viewpoint. Some reported that styrene exposure affected the neuroendocrinological system and enhanced prolactin (PRL) secretion, but others have denied those effects. It was assumed that styrene exposure caused depletion of dopamine (DA), which is a PRL inhibitor, and that, in consequence, the PRL level increased. However, not only DA but also many other factors control PRL secretion. Therefore, the mechanism of hypersecretion of PRL has not yet been clearly elucidated. In addition, effects of styrene on the female reproductive system have been reported, but the susceptibility needs to be further studied. Therefore, to investigate what causes hypersecretion of PRL and how different the susceptibility is in males and females, we studied acute effects of styrene exposure on the neuroendocrinological system in male and female rats. Immediately after exposure to 150 ppm styrene vapor for 10 days (8 h/day), male and female rats were killed, and blood and brain samples were collected. The styrene concentration in blood, hormones such as PRL, growth hormone (GH) and thyroid-stimulating hormone (TSH) in plasma and neurotransmitters in various brain regions were measured. The styrene concentration in the blood of female rats was higher than that in male rats, and the PRL level was significantly increased in female exposed rats compared with controls. No significant change was observed in male rats. We did not observe any significant changes in DA, 5-hydroxytryptamine (5-HT) or their metabolites. Because neurotransmitters were not affected in either male or female rats, the mechanism enhancing PRL secretion remains unclear. These results suggest that styrene exposure may cause hypersecretion of PRL and that the sensitivity to styrene exposure of the female may be higher than that of the male.

Analysis of oxidative stress in SK-N-MC neurons exposed to styrene-7,8-oxide

Styrene-7,8-oxide (SO) is the main metabolite of styrene, a neurotoxic volatile organic compound used industrially. Here we report the novel observation that several markers of oxidative stress were affected in SK-N-MC cells exposed for 16 h to concentrations of SO that induce apoptotic cell death. The production of Thiobarbituric Acid Reactive Substances (TBARS), rose from 69.1 +/- 15.7 nmol/g protein (control) to 119.3 +/- 39.2 and 102.0 +/- 17.3 nmol/g protein after exposure to 0.3 and 1 mM SO, respectively. Carbonyl group levels were significantly enhanced by SO at both concentrations. The lower dose also decreased sulphydryl groups. SO caused a marked oxidative DNA damage, as shown by a fivefold increase in 8-hydroxy-2(')-deoxyguanosine (8-OHdG). In addition, SO exposure resulted in alterations of scavenging abilities, given the reduction of both glutathione (GSH) and glutathione-S-transferase (GST) activity. Induction of expression of the oxidative stress response gene heme-oxygenase-1 (HO-1) and an increased HO-1 activity were also observed. These data provide compelling evidence that oxidative stress significantly contributes to SO toxicity in neuronal cells.

Temporal association between serum prolactin concentration and exposure to styrene

BACKGROUND

Previous studies have suggested that occupational exposure to styrene is associated with increased serum levels of the anterior pituitary hormone prolactin (PRL).

AIMS

To test the hypotheses that: (1) the effect of styrene exposure on PRL secretion is an acute effect, not a subchronic or chronic effect; (2) blood styrene, as a measure of absorbed dose, is a stronger predictor of serum PRL level than personal breathing zone air styrene concentration.

METHODS

Subjects were recruited from 17 workplaces in the reinforced plastics industry. Personal breathing zone air styrene, whole blood styrene, and serum PRL were measured during one to three sessions, approximately one year apart. Linear multiple regression was used to model the relations between acute (air styrene or blood styrene obtained at same time as PRL), subchronic (average air or blood styrene over two or three sessions), and chronic (years of work in industry or facility times average air styrene over all sessions) indices of styrene exposure and serum PRL.

RESULTS

Acute blood styrene concentration was the strongest predictor of serum PRL concentration, with the model predicting a 2.06-fold increase in PRL (95% CI 1.11 to 3.84) for every 10-fold increase in blood styrene. Serum PRL tended to increase with increasing styrene exposure in both men and women; however, women tended to have higher PRL levels. For women, the change in blood styrene between sessions 1 and 2 was a significant predictor of the change in serum PRL between sessions.

CONCLUSIONS

Results confirm that styrene exposure enhances serum PRL concentrations and support an acute effect of styrene on PRL secretion.

Styrene 7,8-oxide induces caspase activation and regular DNA fragmentation in neuronal cells

Neurobehavioral changes have been described in workers occupationally exposed to styrene vapors. Alterations of neurotransmitters and loss of neurons have been observed in brains of styrene-exposed rats. However, the mechanisms of neuronal damage are not yet clearly understood. We have characterized the cellular alterations induced by the main reactive intermediate of styrene metabolism, styrene 7,8-oxide (SO) in the human neuroblastoma SK-N-MC cell line and primary culture of rat cerebellar granule cells (CGC). SK-N-MC cells exposed to SO (0.3-1 mM) displayed apoptotic morphology, together with chromatin condensation and DNA cleavage into high molecular weight fragments of regular size. These features were accompanied by the activation of class II caspases, as detected with the DEVD assay, by following the cleavage of the caspase-substrate poly (ADP-ribose) polymerase (PARP) and by detection of the active fragment of caspase-3. Pre-incubation of the cells with the caspase inhibitor z-VAD-fmk reduced the cellular damage induced by SO, suggesting that caspases play an important role in SO toxicity. Increased proteolysis by class II caspases was detected also in primary culture of CGC exposed to SO. In addition, the presence of the 150-kDa cleavage product of alpha-fodrin suggests a possible activation of calpains in SK-N-MC cells. Moreover, SO did not affect the level of expression of the p53 protein, even though it is known to cause DNA damage. The identified intracellular pathways affected by SO exposure provides end-points that can be used in future studies for the evaluation of the neurotoxic effect of styrene in vivo.

p-Fluorophenylglycine in the urine of baboons treated with HPTP, the tetrahydropyridine analog of haloperidol

We report the presence of p-fluorophenylglycine (p-FPG) in the urine of six baboons treated with HPTP, the tetrahydropyridine dehydration product of haloperidol (HP). Oxidative N-dealkylation, the major metabolic pathway of HP, gives rise to 3-(4-fluorobenzoyl)propionic acid (p-FBPA). Subsequent beta-oxidation of p-FBPA produces p-fluorophenylacetic acid (p-FPA). The presence of p-FPA argues for the formation also of p-fluorophenylglyoxylic acid (p-FPGA) derived from beta-oxidation of p-FBPA. Plasma aminotransferases should convert p-FPGA to p-FPG. The presence of p-FPG in these animals suggest the presence of phenylglycine aminotransferases in the baboon and possibly also in other primates, including the human. Reports by other authors found that treatment with alpha-phenylglycine (alpha-PG), an "unnatural" amino acid, leads to striatal dopamine (DA) depletion in rabbits--an effect explained on the basis of alpha-PG competing with DA for the neuronal vesicular storage sites. We performed in vitro DA release assays in mouse striatal synaptosomal preparations but found that neither alpha-PG nor p-FPG released any DA. It therefore remains unclear whether p-FPG may be a contributing factor to neurologic side-effects such as tardive dyskinesia (TD) found in patients after long-term HP treatment.

Neurobehavioural changes and persistence of complaints in workers exposed to styrene in a polyester boat building plant: influence of exposure characteristics and microsomal epoxide hydrolase phenotype

OBJECTIVES

To investigate neurobehavioural effects and the persistence of complaints in workers exposed to styrene relative to exposure characteristics and the enzyme microsomal epoxide hydrolase (mEH) activity.

METHODS

A cross sectional study was performed in a retrospective cohort of workers of a polyester boat building plant 3 years after the main activity shut down in 1989. Workers still currently exposed to a much lower concentration of styrene in air than before (n=27) and formerly exposed workers (n=90) were compared with matched control workers (n=64). Currently and formerly exposed workers laminated 4700 and 3610 hours on average at mean exposure to styrene concentrations of 148 and 157 mg/m(3) respectively. A structured neurological anamnesis into former and present complaints, the NSC-60 questionnaire, and computer assisted neurobehavioural tests (NES) were administered. The mEH phenotype activity was measured in lymphocytes with a novel gas chromatography-mass spectroscopy (GC-MS) method.

RESULTS

For the period before 1989, currently and formerly exposed workers reported more complaints than control workers which related well with the mean exposure to airborn styrene concentration (p=0.03). Most complaints disappeared after the end of exposure, although the chest, equilibrium, and somatic category scores of NSC-60 and the number of workers reporting diminished sense of smell remained increased in formerly exposed workers (p<or=0.05). Symbol-digit substitution and digit span forwards test results were worse in currently and formerly exposed workers (p<or=0.01). In the combined group of currently and formerly exposed workers, the symbol-digit substitution and colour-word vigilance results related well to duration of exposure (p<0.01 and p=0.03) and mEH phenotype activity (p=0.01 and p=0.05), whereas the digit span forwards results only showed associations of borderline significance (duration of exposure (p=0.08) and mEH phenotype activity (p=0.08)).

CONCLUSION

Most subjective symptoms were reversible but some persisted after the end of exposure to styrene, whereas dysfunction of visuomotor performance and perceptual speed seemed to persist. Duration of exposure at lamination tasks and the interaction, duration of exposurexconcentration of exposure, were found to be the best predictors of worsening visuomotor and perceptual speed performances. Activity of the mEH phenotype may play a modulating part in styrene neurotoxicity. The results suggested that less than 10 years of exposure to atmospheric styrene at an average concentration of 155 mg/m(3) may result in persistent neurotoxic effects.

A review of the developmental and reproductive toxicity of styrene

The reproductive and developmental toxicity of styrene has been studied in animals and humans. The animal studies on styrene have diverse study designs and conclusions. Developmental or reproductive toxicity studies have been conducted in rats, mice, rabbits, and hamsters. In most cases, high doses are required to elicit effects, and the effects are not unique to reproduction or development. In a number of the reports, either the experimental designs are limited or the descriptions of the designs and the endpoints measured are insufficient to draw conclusions about the toxicity of styrene. The more complete and better-reported studies show that styrene does not cause developmental toxicity at dose levels that are not maternally toxic. Some neurochemical or neurobehavioral effects have been reported at high exposures. Styrene does not affect fertility or reproductive function. Considerable animal toxicity data on styrene support the conclusion that styrene is neither an endocrine-active substance nor an endocrine disrupter. Human studies often suffer from either inadequate exposure data or exposure to a wide variety of materials, so that attribution of effects to styrene exposure is impossible. Furthermore, investigators often have failed to account for other exposures in the workplace or for other potentially confounding factors in their studies. Menstrual cycle irregularities and congenital abnormalities were initially reported; however, the better and more recent reports do not show that styrene causes developmental or reproductive effects in humans. Human studies also support the conclusion that styrene is not an endocrine disrupter. Although some study authors have concluded that styrene is either a human or an animal reproductive or developmental toxicant, careful review demonstrates that such conclusions are not justified.

Altered regulation of dopaminergic activity and impairment in motor function in rats after subchronic exposure to styrene

Animal and human studies suggest a dopamine-mediated effect of styrene neurotoxicity. However, the results reported to date are incomplete and not consistent. As such, the mechanism of its neurotoxicity is still unclear. The present study has, therefore, reexamined the central dopaminergic system in relation to some neurobehavioral effects in rats following subchronic exposure to styrene. Groups of adult male Sprague-Dawley rats received 0, 0.25, or 0.5 g styrene per kg b.wt. by gavage for 13 consecutive weeks. Twenty-four hours after cessation of such treatment with the higher dose (0.5 g/kg), the contents of dopamine (DA) and its metabolites were significantly reduced in the corpus striatum, hypothalamus, and lateral olfactory tract regions. In vitro styrene showed a significant increase in DA release from rat striatal synaptosomes similar to that of tyramine. Significant loss of motor function was observed on days 56, 70, and 84 during the styrene treatment with the higher dose, and lasted over a month after such treatment. However, the treated animals recovered their motor function within 45-60 days after cessation of such treatment, along with the recovery of normal levels of dopamine and its metabolites. Furthermore, styrene-induced initial impairments in measures of dopaminergic activity cannot be attributed to altered regulation of tyrosine hydroxylase activity. Specific [3H]-spiroperidol binding was also unaltered 7 or 15 days after subchronic treatment with styrene. These data imply that despite the dopaminergic neuronal loss due to styrene, dopaminergic transmission was not reduced to a level that would result in an overall development of dopamine receptor supersensitivity in the striatum. Collectively, these studies indicate that the subchronic neurotoxic action of styrene may be primarily presynaptic in nature and may involve impaired regulation of DA content and stimulation of DA release.

Styrene and styrene oxide affect the transport of dopamine in purified rat striatal synaptic vesicles

Animal and human studies suggest a dopamine-mediated effect of styrene neurotoxicity. To date, mechanisms of cerebral membrane transport of neurotransmitter amines in the presence of styrene in relation to its neurotoxicity have not been addressed properly. So, the present study has examined to test the hypothesis that dopaminergic malfunction in vesicular transport is a critical component in styrene-induced neurotoxicity in rats. Both styrene and its intermediate reactive metabolite, styrene oxide antagonized the in vitro striatal binding of [3H] tyramine, a putative marker of the vesicular transporter for dopamine. Both styrene and styrene oxide potently inhibited the uptake of [3H] dopamine in purified synaptic vesicles prepared from rat brain striata, in a dose-related manner, with inhibitory constants (Ki) 2.5 and 2.2 microM respectively. However, neither styrene nor styrene oxide significantly increased the basal efflux of [3H] dopamine that has been preloaded into striatal vesicles in vitro. On the other hand, both styrene and styrene oxide have failed to significantly inhibit the uptake of either [3H] norepinephrine, or [3H] serotonin into striatal synaptic vesicles. It is concluded that both styrene and styrene oxide are capable of producing impairments in dopaminergic transport in purified striatal synaptic vesicles, an effect which may be a critical component in styrene-induced neurotoxicity.

Selective vulnerability of dopaminergic systems to industrial chemicals: risk assessment of related neuroendocrine changes

Increased serum prolactin (PRL) is a common finding among subjects exposed to styrene, perchloroethylene, lead (Pb), and manganese (Mn) at levels below the current threshold limit values. On a group basis, abnormally high basal PRL shows a dose-related distribution among workers exposed to styrene, Pb, and Mn. On the basis of dose-response relationships, the benchmark doses (BMD) for styrene metabolites in urine, lead in blood (Pb-B), and Mn in urine (Mn-U), are 4 mg/g creatinine, 112 micrograms/L, and 0.3 microgram/L, respectively. Noteworthy, the BMD for Mn-U and Pb-B is well below the upper reference limit. A shift in the distribution but not in the prevalence of abnormally high values of serum PRL was observed among perchloroethylene-exposed dry cleaners, which makes interpretation in terms of risk difficult. The measurement of PRL thus provides opportunities for early identification of excess exposure to neurotoxic chemicals affecting dopaminergic control of pituitary secretion. For styrene, Pb, and Mn the BMD provides an objective and statistically determined threshold, which seems to be in good agreement with the estimated no-observed-adverse-effect-level (NOAEL). The NOAEL, however, is based on traditional approaches that require the application of uncertainty factors, e.g., a default factor of 10 when extrapolating the NOAEL from the lowest-observed-adverse-effect-level (LOAEL). Due to its sensitivity to a number of potential confounders, caution must be exercised when using PRL as a screening test at the individual level. Also, age and sex dependent variations in susceptibility may hamper extrapolations from the occupational settings to the general population.

Effects of ethanol administration on cerebral non-protein sulfhydryl content in rats exposed to styrene vapour

Glutathione (GSH) and other non-protein sulfhydryls (NPS) are known to protect cells from oxidative stress and from potentially toxic electrophiles formed by biotransformation of xenobiotics. This study examined the effect of a simultaneous administration of styrene and ethanol on NPS content and lipid peroxidation in rat liver and brain. Hepatic cytochrome P450 and cytochrome b5 content, aniline hydroxylase and aminopyrine N-demethylase activities as well as the two major urinary metabolites of styrene, mandelic and phenylglyoxylic acids were also measured. Groups of rats given ethanol for 3 weeks in a liquid diet were exposed, starting from the second week, to 326 ppm of styrene (6 h daily, 5 days a week, for 2 weeks). In control pair-fed animals, styrene produced about 30% depletion of brain NPS and 50% depletion of hepatic NPS. Subchronic ethanol treatment did not affect hepatic NPS levels, but caused 23% depletion of brain NPS. Concomitant administration of ethanol and styrene caused a NPS depletion in brain tissue in the order of 60%. These results suggest that in the rat, simultaneous exposure to ethanol and styrene may lead to considerable depletion of brain NPS. This effect is seen when both compounds are given on a subchronic basis, a situation which better resembles possible human exposure.

Assessment of the neurotoxicity of styrene, styrene oxide, and styrene glycol in primary cultures of motor and sensory neurons

The neurotoxicity of styrene and its major metabolites, styrene oxide and styrene glycol, was investigated in dissociated primary cultures of murine spinal cord-dorsal root ganglia (DRG)-skeletal muscle using morphological and electrophysiological endpoints. Styrene and styrene oxide (but not styrene glycol) were acutely cytotoxic to both neuronal and non-neuronal cells in the cultures; concentrations in excess of 2 and 0.2 mM, respectively, induced blebbing, vacuolation, detachment from the substratum and cell death in neuronal and non-neuronal cells within 4 days. No effects on neuronal morphology were observed in cultures treated with sublethal concentrations of styrene or styrene oxide for up to 3 weeks. The results suggest that oxidation of multiple cellular macromolecules that underlies the toxicity of styrene in other organ systems may also be responsible for damage to cells in the nervous system. No changes in action potential production indicative of a 'solvent effect' on membrane electrical properties was apparent in cultures treated with up to 8 mM styrene or 10 mM styrene glycol.

Neuropsychological effects of styrene exposure: a review of current literature

Research on the neuropsychological effects of exposure to styrene are reviewed, including subjective complaints, laboratory exposure, short- and long-term occupational exposure, possible long-term occupational illness, neuropsychiatric implications, and animals' behavior. The findings are discussed in relation to optimal levels of exposure, drivers' safety, a sensitive neuropsychological screening battery, current controversies, and future directions for research.

Neurochemical effects in rats following gestational exposure to styrene

Styrene was evaluated for the reproductive effects of pregnant rats and the neurochemical effects in the offspring of rats exposed during gestation. Pregnant Wistar rats were exposed to 0, 50, or 300 ppm styrene for 6 h/day during days 7 to 21 of gestation. No significant differences in the number of offspring delivered were observed between the exposed and control groups. Body weights at 1 day of age of the offspring whose mothers were exposed to styrene were significantly lower than those of the control group. Although, there were neither statistically significant differences of protein contents nor brain weights among styrene-exposed and their control offsprings of rats, analyses of neurotransmitter studies showed dose-dependent decreases of neuroamines, especially 5-HT (serotonin) and its metabolite 5HIAA (5-hydroxyindoleacetic acid) in the newborn offspring of styrene-exposed rats. The results suggest that gestational exposure to styrene at these concentrations does not produce apparent reproductive toxicity but affects the body weight of pups and causes lowering of the neurotransmitter levels in the brain.

Hormone status in occupational toluene exposure

Twenty toluene-exposed rotogravure printers, without signs of solvent-induced toxic encephalopathy, had lower median plasma levels of follicle stimulating hormone (FSH) (3.2 vs. 4.9 IU/L; p = .02) and luteinizing hormone (LH) (6.4 vs. 7.2 IU/L; p = .05) and also lower serum levels of free testosterone (7.8 vs. 86.8 pmol/L; p = .05), respectively, than 44 unexposed referents. The individual time-weighted toluene levels in air were 36 (median; range 8-111) ppm. The printers' median toluene levels in blood were 1.7 (1.0-6.6) mumol/l, and in subcutaneous adipose tissue 5.7 (2.5-21) mg/kg fat. There was a negative association between blood toluene and plasma levels of prolactin. In eight printers, the levels of FSH and LH increased during a 4 week vacation, while the levels of thyroid stimulating hormone, free triiodothyronine, and free thyroxine decreased during the same period. The results indicate a slight, reversible effect of toluene on the cortical level or on the hypothalamic-pituitary axis at exposures well below the permissible levels, possibly mediated through an effect on catecholamine neurotransmission.

Psychosis following styrene exposure: a case report of neuropsychological sequelae

A patient with a significant history of substance abuse was exposed to styrene and other solvents in the workplace. He became acutely psychotic, experiencing visual hallucinations. The psychosis was controlled with neuroleptic medications and avoidance of solvent exposure, but he continued to show significant deficits in visual-spatial and memory abilities. These deficits cleared with time away from the workplace. The case is of interest in terms of neuropsychological sequelae of solvent exposure and potential interaction of solvents with alcohol and recreational drugs.

Endogenous homovanillic acid levels differ between rat and rabbit caudate, hippocampus, and cortical regions

Endogenous dopamine (DA) levels and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3MT) and homovanillic acid (HVA) were measured by high-performance liquid chromatography in the entorhinal-piriform (EnPi), cingulate (CIN), sensorimotor (SSM) and visual (VIS) cortices as well as is the caudate (CAU) and hippocampus (HIP) of Sprague-Dawley (SD) rats and New Zealand (NZ) rabbits. The DA, DOPAC and 3MT contents were similar in both species. The HVA levels however, although they followed DA distribution, were several-fold higher in NZ rabbits than in SD rats for all cortices, HIP and CAU. In addition, total metabolite contents and DA turnover (estimated from 'DA metabolite/DA' ratios) were significantly higher in NZ rabbits than in SD rats, suggesting an increased release and/or metabolism in the former species. The HVA/DA ratios were much higher for NZ rabbit regions than for SD rats, indicating an increased DA release in the former species since the DOPAC/DA ratios (index of intraneuronal degradation) were similar.

Distribution of monoamines and metabolites in rabbit neostriatum, hippocampus and cortex

The monoamines noradrenaline (NA), dopamine (DA), adrenaline (AD) and 5-hydroxytryptamine (5-HT) were assayed in the putamen (PUT), the lateral (lCAU) and medial (mCAU) portions of the caudate, the dorsal (dHIP) and ventral (vHIP) hippocampus, as well as in four cortical areas, i.e., anterior cingulate (CIN), entorhinal-piriform (EnPi), sensorimotor (SSC; somatosensory) and primary visual (VIS). The use of an HPLC procedure enabled us to perform these measurements in microdissected samples and to assay as well monoamine metabolites. The DA levels were highest in the neostriatum, moderate in the EnPi and CIN and very low in the SSC, VIS and hippocampus. The distribution of NA was more uniform, although higher concentrations were measured in the neostriatum, hippocampus and EnPi. The largest amounts of 5-HT were in the EnPi, while moderate concentrations were found in the other regions. The ratios between the neurotransmitters and their metabolites were used as an index of turnover and indicate that the terminal fields of the monoamine systems are heterogenous within the neostriatal, hippocampal and cortical subdivisions.

The neurobehavioral effects of chronic styrene exposure in the rat

Groups of rats were exposed by inhalation to either clear air (controls) or styrene monomer (STY) at 350, 700 or 1400 ppm for 16 hr/day, 5 days/week for 18 weeks. At preselected intervals, animals were evaluated for changes in: 1) spontaneous activity, 2) grip-strength, 3) coordinated hindlimb movement, 4) performance on a discrete-trial two-choice visual discrimination task, and 5) peripheral nerve conduction velocity. Compared to controls, STY-treated rats showed a mild but somewhat inconsistent reduction in activity and gripstrength during the course of exposure. Coordinated movement and peripheral nerve conduction time were unaffected. With respect to discrimination performance, exposure on Day 1 produced marked deficits in response speed and accuracy. By Day 2, deficits in discrimination performance were reduced by greater than 50% and the performance of STY-treated rats continued to improve as exposure continued. Finally, during the last weeks of exposure, the performance of STY-treated rats was equivalent to that of controls and no styrene-related deficits could be measured in the postexposure period.

Brain dopamine as a target for solvent toxicity: effects of some monocyclic aromatic hydrocarbons

Adult male rabbits were exposed to toluene, xylene, styrene, ethylbenzene, vinyltoluene or were dosed with hippuric, methylhippuric, mandelic, phenylglyoxylic, and 7-methyl-mandelic acids. Styrene, vinyltoluene and ethylbenzene caused a marked depletion of striatal and tubero-infundibular dopamine. Such an effect was also caused by treatment with mandelic and phenylglyoxylic acids. These results indicate that dopamine is a target for some solvents of their metabolites, the presence of a lateral vinyl- or ethyl-chain which may be biotransformed into alpha-keto acids being crucial for the effect. Experiments in vitro suggest that dopamine condenses non-enzymatically with reactive carbonylic groups of such and other alpha-keto acids, thus becoming ineffective as neurotransmitter. This mechanism might account for the neurobehavioral and neuroendocrine changes which have been reported in workers occupationally exposed to styrene and to some solvent mixtures.

Neurobehavioral investigation as a tool for revealing preclinical disorders

This paper calls attention to the methodologies designed to investigate the higher cortical functions in order to elicit signis of encephalopathy in apparently normal conditions. This can be done by testing the blobal hemispheric funcionts or the interhemispheric functional balance. This shows up the clinical sequels that may precede or be the outcome both of transient pathological disorders, such as transient global anemia, migraine, TIAs and subarachnoid hemorrhage without apparent clinical consequences and of nontransient pathological conditions, such as epilepsy, occupational diseases, arterial hypertension and cerebral revascularization.

Effects of some monocyclic aromatic solvents and their metabolites on brain dopamine in rabbits

Adult male rabbits were exposed to high concentrations (750 ppm, 12 hours daily for 7 days) of toluene, xylenes, styrene, ethylbenzene, vinyltoluene (3-methylstyrene), and 7-methyl-styrene vapours or were dosed with 4 mM/kg/day i.p. of hippuric, methylhippuric, mandelic, phenylglyoxylic, and 7-methyl-mandelic acids. Styrene, vinyltoluene and ethylbenzene caused a marked depletion of striatal and tuberoinfundibular dopamine. Such an effect was also caused by treatment with phenylglyoxylic and mandelic acids. Dopamine depletion was associated with an increase in homovanillic acid concentration in the same regions. These results indicate that dopamine metabolism is a target for the neurotoxic effects of some monocyclic aromatic hydrocarbons and their metabolites, a lateral vinyl- or ethyl-chain being crucial for the structure/activity relationship of such compounds.

High-performance liquid chromatography of biogenic amines and metabolites in brain, cerebrospinal fluid, urine and plasma

A method for high-performance liquid chromatographic separation and electrochemical detection of biogenic amines and metabolites in a variety of biological matrices is described. The method employs either homogenization, precipitation or dilution followed by direct injection of the samples and permits the chromatographic resolution of dopamine, norepinephrine, epinephrine, serotonin (5-HT), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) in brain; 3-methoxy-4-hydroxyphenylglycol, DOPAC, 5-HIAA and HVA in cerebrospinal fluid; 5-HIAA, HVA and 5-HT in plasma; and 5-HIAA and HVA in urine. Alterations in chromatographic conditions, voltammetry and in vivo pharmacological manipulations are employed to verify the identity of the putative neurotransmitter and metabolite peaks in the biological samples.

Styrene metabolism and striatal dopamine depletion in rabbits

The striatal concentration of dopamine (DA), norepinephrine (NE), and homovanillic acid (HVA) was assessed in adult male rabbits exposed to styrene vapours or dosed with mandelic acid (MA), phenylglyoxylic acid (PGA) and phenylglycine (PG). Styrene exposure produced a marked and dose-dependent decrease in striatal DA, concomitant with a consistent increase in HVA. The same effects were caused by i.p. administration of PGA and PG, but not of MA. The increased catabolism of DA was concomitant with a normal turnover time after inhibition of tyrosine hydroxylase by the administration of methyl-p-tyrosine. The amination of PGA to PG with a subsequent competition of the latter with DA for the vesicular storage capacity is suggested as the possible mechanism for styrene-induced brain dysfunction.