Effects of manganese oxide on monkeys as revealed by a combined neurochemical, histological and neurophysiological evaluation

Manganese neurotoxicity: lessons learned from longitudinal studies in nonhuman primates

BACKGROUND

Exposure to excess levels of the essential trace element manganese produces cognitive, psychiatric, and motor abnormalities. The understanding of Mn neurotoxicology is heavily governed by pathologic and neurochemical observations derived from rodent studies that often employ acute Mn exposures. The comparatively sparse studies incorporating in vivo neuroimaging in nonhuman primates provide invaluable insights on the effects of Mn on brain chemistry.

OBJECTIVES

The purpose of this review is to discuss important aspects of Mn neurotoxicology and to synthesize recent findings from one of the largest cohorts of nonhuman primates used to study the neurologic effects of chronic Mn exposure.

DISCUSSION

We reviewed our recent in vivo and ex vivo studies that have significantly advanced the understanding of Mn-induced neurotoxicity. In those studies, we administered weekly doses of 3.3-5.0 (n=4), 5.0-6.7 (n=5), or 8.3-10.0 mg Mn/kg (n=3) for 7-59 weeks to cynomolgus macaque monkeys. Animals expressed subtle deficits in cognition and motor function and decreases in the N-acetylaspartate-to-creatine ratio in the parietal cortex measured by magnetic resonance spectroscopy reflective of neuronal dysfunction. Impaired striatal dopamine release measured by positron emission tomography was observed in the absence of changes in markers of dopamine neuron degeneration. Neuropathology indicated decreased glutamine synthetase expression in the globus pallidus with otherwise normal markers of glutamatergic and GABAergic neurotransmission. Increased amyloid beta (A4) precursor-like protein 1 gene expression with multiple markers of neurodegeneration and glial cell activation was observed in the frontal cortex.

CONCLUSIONS

These findings provide new information on mechanisms by which Mn affects behavior, neurotransmitter function, and neuropathology in nonhuman primates.

Mapping prefrontal circuits in vivo with manganese-enhanced magnetic resonance imaging in monkeys

Manganese-enhanced magnetic resonance imaging (MEMRI) provides a powerful tool to study multisynaptic circuits in vivo and thereby to link information about neural structure and function within individual subjects. Making the best use of MEMRI in monkeys requires minimizing manganese-associated neurotoxicity, maintaining sensitivity to manganese-dependent signal changes and mapping transport throughout the brain without a priori anatomical hypotheses. Here, we performed intracortical injections of isotonic MnCl(2), comparisons of preinjection and postinjection scans, and voxelwise statistical mapping. Isotonic MnCl(2) did not cause cell death at the injection site, damage to downstream targets of manganese transport, behavioral deficits, or changes in neuronal responsiveness. We detected and mapped manganese transport throughout cortical-subcortical circuits by using voxelwise statistical comparisons of at least 10 preinjection and two postinjection scans. We were able to differentiate between focal and diffuse projection fields and to distinguish between the topography of striatal projections from orbitofrontal and anterior cingulate cortex in a single animal. This MEMRI approach provides a basis for combining circuit-based anatomical analyses with simultaneous single-unit recordings and/or functional magnetic resonance imaging in individual monkeys. Such studies will enhance our interpretations of functional data and our understanding of how neuronal activity is transformed as it propagates through a circuit.

The neurotoxic effects of manganese on the dopaminergic innervation of the gill of the bivalve mollusc, Crassostrea virginica

We examined effects of manganese on the nervous system and innervation of lateral cilia of Crassostrea virginica. While essential in trace amounts, tissue manganese accumulation is neurotoxic, inducing Manganism, a Parkinson's-like disease in humans. Lateral cilia of the gill of C. virginica are controlled by a reciprocal serotonergic-dopaminergic innervation from their ganglia. Oysters were incubated 3 days in the presence of up to 1 mM manganese, followed by superfusion of the cerebral ganglia, visceral ganglia or gill with dopamine or serotonin. Beating rates of cilia were measured by stroboscopic microscopy of isolated gill preparations or gill preparations with the ipsilateral cerebral and/or visceral ganglia attached. Acute manganese treatments impaired the dopaminergic, cilio-inhibitory system, while having no effect on the serotonergic, cilio-excitatory system, which is in agreement with the proposed mechanism of manganese toxicity in humans. Manganese treatments also decreased endogenous dopamine levels in the cerebral and visceral ganglia, and gills, but not serotonin levels. We demonstrated that manganese disrupts the animal's dopaminergic system, and also that this preparation can be used to investigate mechanisms that underlie manganese neurotoxicity. It also may serve as a model in pharmacological studies of drugs to treat or prevent Manganism and other dopaminergic cell disorders.

Inhalation of divalent and trivalent manganese mixture induces a Parkinson's disease model: immunocytochemical and behavioral evidences

The present study investigates the effects of divalent and trivalent manganese (Mn(2+)/Mn(3+)) mixture inhalation on mice to obtain a novel animal model of Parkinson disease (PD) inducing bilateral and progressive cell death in the substantia nigra compacta (SNc) and correlating these alterations with motor disturbances. CD-1 male mice inhaled a mixture of 0.04 M manganese chloride (MnCl(2)) and manganese acetate (Mn(OAc)(3)), 1 h twice a week for 5 months. Before Mn exposure, animals were trained to perform motor function tests and were evaluated each week after the exposure. By doing this, overall behavior was assessed by ratings and by videotaped analyses; by the end of Mn exposure period, animals were killed. The mesencephalon was processed for tyrosine hydroxylase (TH) immunocytochemistry. After 5 months of Mn mixture inhalation, mice developed evident deficits in their motor performance manifested as akinesia, postural instability and action tremor. SNc of the Mn-exposed animals showed an important decrease (67.58%) in the number of TH-immunopositive neurons. Our data provide evidence that MnCl(2) and Mn(OAc)(3) mixture inhalation produces similar morphological and behavioral alterations to those observed in PD providing a useful experimental model for the study of this neurodegenerative disease.

Nmr spectroscopic analysis of regional brain energy metabolism in manganese neurotoxicity

A central question in manganese neurotoxicity concerns the focal neuronal damage in the globus pallidus. In the present study, we investigated specific pathways of [1-(13)C]glucose as well as of [2-(13)C]acetate in this brain region and the frontal cortex following 4-day manganese treatment by high-resolution NMR spectroscopy. Following administration of 50 mg/kg/day manganese, glutamine concentration in the globus pallidus was decreased to 67% of control values but increased in frontal cortex by 56%. Manganese treatment also caused pronounced changes in glutamine-glutamate-GABA interconversion in which region-selective differences were observed in the isotopomer pattern of GABA compared with that of glutamine when including the astrocyte-specific substrate [2-(13)C]acetate. In particular, decreased (13)C-labeled glutamine, synthesized from [1-(13)C]glucose, paralleled accumulation of (13)C-labeled GABA in globus pallidus but not in frontal cortex. On the other hand, increased synthesis of glutamine from [2-(13)C]acetate showed that GABA accumulation was not due to increased synthesis from astrocytic glutamine. Furthermore, treatment with manganese resulted in a selective decrease in N-acetyl-aspartate in the globus pallidus. These data illustrate the potential importance of alterations in neuronal metabolic function. In particular, neuronal metabolic derangements and regional differences in the ability of astrocytes to fulfill their contribution to the glutamine-glutamate-GABA cycle during the early phase of manganese neurotoxicity may be crucial in determining the severity of cellular injury.

Neurobehavioral functioning after cessation of manganese exposure: a follow-up after 14 years

BACKGROUND

Little is known on the long-term course of early manganese (Mn) neurotoxic effects. Mn alloy workers were examined in a follow-up study 14 years after exposure ceased at a Canadian facility.

METHODS

The same battery of neurofunctional tests used in the initial examination in 1990 was administered to 77 Mn-workers and 81 referents in 2004.

RESULTS

Manganese-workers had poorer scores compared to referents both in the initial and follow-up examinations for several motor tasks of the Luria Motor Scale. At follow-up, older Mn-workers (>45 years at cessation of exposure) had poorer scores than referents for tests of cognitive flexibility. Cumulated exposure was associated with poorer test scores for certain neuromotor and cognitive tests and on a mood scale. Differences on certain tests observed at initial examination were not present at follow-up.

CONCLUSIONS

Manganese exposure was associated with persistent deficits for certain neuromotor functions, cognitive flexibility, and adVerse mood states, while recovery occurred for other functions.

State-of-the-science review: Does manganese exposure during welding pose a neurological risk?

Recent studies report that exposure to manganese (Mn), an essential component of welding electrodes and some steels, results in neurotoxicity and/or Parkinson's disease (PD) in welders. This "state-of-the-science" review presents a critical analysis of the published studies that were conducted on a variety of Mn-exposed occupational cohorts during the last 100 yr, as well as the regulatory history of Mn and welding fumes. Welders often perform a variety of different tasks with varying degrees of duration and ventilation, and hence, to accurately assess Mn exposures that occurred in occupational settings, some specific information on the historical work patterns of welders is desirable. This review includes a discussion of the types of exposures that occur during the welding process--for which limited information relating airborne Mn levels with specific welding activities exists--and the human health studies evaluating neurological effects in welders and other Mn-exposed cohorts, including miners, millers, and battery workers. Findings and implications of studies specifically conducted to evaluate neurobehavioral effects and the prevalence of PD in welders are also discussed. Existing exposure data indicate that, in general, Mn exposures in welders are less than those associated with the reports of clinical neurotoxicity (e.g., "manganism") in miners and smelter workers. It was also found that although manganism was observed in highly exposed workers, the scant exposure-response data available for welders do not support a conclusion that welding is associated with clinical neurotoxicity. The available data might support the development of reasonable "worst-case" exposure estimates for most welding activities, and suggest that exposure simulation studies would significantly refine such estimates. Our review ends with a discussion of the data gaps and areas for future research.

Basal ganglia neurotransmitter concentrations in rhesus monkeys following subchronic manganese sulfate inhalation

BACKGROUND

Manganese neurotoxicity in humans is recognized as a form of parkinsonism with lesions occurring predominantly within the globus pallidus, subthalamic nucleus, putamen, and caudate nucleus.

METHODS

This study evaluated dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, serotonin, norepinephrine, 5-hydroxyindoleacetic acid, gamma-aminobutyric acid (GABA), and glutamate concentrations in the globus pallidus, caudate, and putamen of male rhesus monkeys exposed subchronically to either air or manganese sulfate (MnSO4) at 0.06, 0.3, or 1.5 mg Mn/m3.

RESULTS

An approximate 1.5-6-fold increase (vs. air-exposed controls) in mean brain manganese concentration was observed following subchronic MnSO4 exposure. A marginally significant (P < 0.1) decrease in pallidal GABA and 5-hydroxyindoleacetic acid concentration and caudate norepinephrine concentration occurred in monkeys exposed to MnSO4 at 1.5 mg Mn/m3.

CONCLUSIONS

Despite the presence of increased tissue manganese concentrations, high-dose exposure to MnSO4 was associated with relatively few changes in basal ganglial neurotransmitter concentrations.

The Neuropathology of Manganese-Induced Parkinsonism

Manganese is an essential trace metal that is widely used in industry, particularly in the manufacture of steel. Exposure to high levels of manganese can cause neurotoxicity with the development of a form of parkinsonism known as manganism. It has recently been hypothesized that manganese exposure might also cause or accelerate the development of Parkinson disease (PD). This article is a review of the pathologic studies that have been reported in patients with manganism and in primates experimentally intoxicated with manganese. They demonstrate a consistent pattern characterized by damage to the globus pallidus (particularly the internal segment) with sparing of the substantia nigra pars compacta and the absence of Lewy bodies. This finding contrasts with what is seen in PD, in which there is preferential degeneration of dopamine neurons in the substantia nigra pars compacta coupled with Lewy bodies and preservation of the pallidum. These pathologic findings do not support the notion that manganese causes PD but rather argues that manganese-induced parkinsonism and PD are distinct and separate disease entities.

Manganese chloride stimulates rat microglia to release hydrogen peroxide

Elevated exposure to manganese is known to cause neurodegeneration in the basal ganglia and to induce movement abnormalities called manganism. However, the underlying mechanism of action is not fully understood. Activation of the resident immune cells in the brain, microglia that release a variety of neurotoxic factors, has been implicated to contribute to neurodegeneration. Of the various neurotoxic factors released by activated microglia, reactive oxygen species such as superoxide and hydrogen peroxide are particularly detrimental to the survival of the oxidative damage-prone neurons. In this study, we report that exposure of rat microglia to manganese chloride (MnCl(2)) resulted in a time- and concentration-dependent release of hydrogen peroxide (H(2)O(2)). The MnCl(2)-stimulated microglial H(2)O(2) release was sensitive to inhibitors of mitogen-activated protein kinases (MAPK) but not that of NADPH oxidase. MnCl(2)-induced a rapid activation of the extracellular signal-regulated kinase (ERK) and p38-MAPK in microglia that appeared to precede the MnCl(2)-induced H(2)O(2) release, suggesting that ERK and p38-MAPK influenced the MnCl(2)-induced H(2)O(2) release in microglia. In summary, these results demonstrate that manganese chloride is capable of activating microglia to release ROS and MAPK may, in part, be key regulators of the process. These findings may shed significant light on the potential role of microglia in the manganese-induced neurotoxicity.

Manganese: recent advances in understanding its transport and neurotoxicity

The present review is based on presentations from the meeting of the Society of Toxicology in San Diego, CA (March 2006). It addresses recent developments in the understanding of the transport of manganese (Mn) into the central nervous system (CNS), as well as brain imaging and neurocognitive studies in non-human primates aimed at improving our understanding of the mechanisms of Mn neurotoxicity. Finally, we discuss potential therapeutic modalities for treating Mn intoxication in humans.

Adequacy and consistency of animal studies to evaluate the neurotoxicity of chronic low-level manganese exposure in humans

The adequacy of existing animal studies to understand the effects of chronic low-level manganese exposures in humans is unclear. Here, a collection of subchronic to chronic rodent and nonhuman primate studies was evaluated to determine whether there is a consistent dose-response relationship among studies, whether there is a progression of effects with increasing dose, and whether these studies are adequate for evaluating the neurotoxicity of chronic low-level manganese exposures in humans. Neurochemical and behavioral effects were compared along the axis of estimated internal cumulative manganese dose, independent of the route of exposure. In rodents, motor effects emerged at cumulative doses below those where occupationally exposed humans start to show motor deficits. The main neurochemical effects in rodents were an increase in striatal gamma-aminobutyric acid (GABA) concentration throughout the internal cumulative dose range of 18 to 5300 mg Mn/kg but a variable effect on striatal dopamine concentration emerging at internal cumulative doses above approximately 200 mg Mn/kg. Monkey studies showed motor deficits and effects on the globus pallidus at relatively low doses and consistent harmful effects on both the globus pallidus and the caudate and putamen at higher doses (> 260 mg Mn/kg). Internal cumulative manganese doses of animal studies extend more than two orders of magnitude (< 1 to 5300 mg Mn/kg) above the doses at which occupationally exposed humans show neurological dysfunction (10-15 mg Mn/kg). Since the animal data indicate that manganese neurotoxicity may be different at low compared to elevated exposures, most existing animal model studies might be of limited relevance for the risk assessment of chronic low-level manganese exposure to humans.

Hair manganese and hyperactive behaviors: pilot study of school-age children exposed through tap water

BACKGROUND

Neurotoxic effects are known to occur with inhalation of manganese particulates, but very few data are available on exposure to Mn in water. We undertook a pilot study in a community in Quebec (Canada) where naturally occurring high Mn levels were present in the public water system. Our objective was to test the hypothesis that greater exposure to Mn via drinking water would be reflected in higher Mn content in hair which, in turn, would be associated with increased level of hyperactive behaviors.

METHODS

Forty-six children participated in the study, 24 boys and 22 girls, 6-15 years of age (median, 11 years). Their homes received water from one of two wells (W) with different Mn concentrations: WI: mean 610 microg/L; W2: mean 160 microg/L. The Revised Conners' Rating Scale for parents (CPRS-R) and for teachers (CTRS-R) were administered, providing T-scores on the following subscales: Oppositional, Hyperactivity, Cognitive Problems/Inattention, and ADHD Index.

RESULTS

Children whose houses were supplied by WI had higher hair Mn (MnH) than those supplied by W2 (mean 6.2+/-4.7 microg/g vs. 3.3+/-3.0 microg/g, p = 0.025). MnH was significantly associated with T-scores on the CTRS-R Oppositional (p = 0.020) and Hyperactivity (p = 0.002) subscales, after adjustment for age, sex, and income. All children with Oppositional and Hyperactivity T-scores > 65 had MnH > 3.0 microg/g.

CONCLUSIONS

The findings of this pilot study are sufficiently compelling to warrant more extensive investigations into the risks of Mn exposure in drinking water.

Effects of chronic manganese exposure on cognitive and motor functioning in non-human primates

Acute exposure to manganese is associated with complex behavioral/psychiatric signs that may include Parkinsonian motor features. However, little is known about the behavioral consequences of chronic manganese exposures. In this study, cynomolgus macaque monkeys were exposed to manganese sulfate (10-15 mg/kg/week) over an exposure period lasting 272+/-17 days. Prior to manganese exposure, animals were trained to perform tests of cognitive and motor functioning and overall behavior was assessed by ratings and by videotaped analyses. By the end of the manganese exposure period, animals developed subtle deficits in spatial working memory and had modest decreases in spontaneous activity and manual dexterity. In addition, stereotypic or compulsive-like behaviors such as compulsive grooming increased in frequency by the end of the manganese exposure period. Blood manganese levels measured at the end of the manganese exposure period ranged from 29.4 to 73.7 micro g/l (mean=55.7+/-10.8 (compared to levels of 5.1-14.2 micro g/l at baseline (mean=9.2+/-2.7)), placing them within the upper range of levels reported for human environmental, medical or occupational exposures. These results suggest that chronic exposure to levels of manganese achieved in this study may have detrimental effects on behavior, cognition and motor functioning.

Neuropsychiatric symptoms and past manganese exposure in a ferro-alloy plant

INTRODUCTION

Psychiatric manifestations have been reported in cases of manganism, and mood disorders are often observed in manganese (Mn) exposed workers. We examined neuropsychiatric symptoms among formerly Mn-exposed workers 14 years after cessation of exposure.

MATERIALS AND METHODS

A study was conducted in 1990 among workers from a ferro- and silico-Mn plant and unexposed working men referents from the same region in South-West Quebec. At follow-up in 2004, 77 former Mn-workers and 81 referents agreed to participate and responded to a neuropsychiatric symptom checklist, the Brief Symptom Inventory (BSI); scores were transformed into T-scores based on a normative population. Cumulated exposure indices (CEI) were computed for each former Mn-worker. Linear and logistic regression analyses were used.

RESULTS

Mean T-scores were significantly higher among former Mn-workers than referents on scales of Depression and Anxiety. Mean T-scores of psychological distress increased with the CEI tertiles, with significant associations for the scales Somatization, Depression, Anxiety and Hostility. Former Mn-workers in the two highest tertiles of CEI showed a higher risk for T-scores >or=63 for Hostility (OR, 7.5; 95% CI, 1.5-38.9), Depression (OR, 2.6; 95% CI, 1.1-8.4) and Anxiety (OR, 3.0; 95% CI, 1.1-8.4).

CONCLUSION

These results suggest that past exposure to Mn may have lasting consequences on neuropsychiatric symptoms.

Brain accumulation and toxicity of Mn(II) and Mn(III) exposures

Concern over the neurotoxic effects of chronic moderate exposures to manganese has arisen due to increased awareness of occupational exposures and to the use of methylcyclopentadienyl manganese tricarbonyl, a manganese-containing gasoline antiknock additive. Little data exist on how the oxidation state of manganese exposure affects toxicity. The objective of this study was to better understand how the oxidation state of manganese exposure affects accumulation and subsequent toxicity of manganese. This study utilized a rat model of manganese neurotoxicity to investigate how ip exposure to Mn(II)-chloride or Mn(III)-pyrophosphate at total cumulative doses of 0, 30, or 90 mg Mn/kg body weight affected the brain region distribution and neurotoxicity of manganese. Results indicate that Mn(III) exposures produced significantly higher blood manganese levels than equimolar exposures to Mn(II). Brain manganese concentrations increased in a dose-dependent manner, with Mn(III) exposures producing significantly higher (> 25%) levels than exposures to Mn(II) but with no measurable differences in the accumulation of manganese across different brain regions. Gamma amino butyric acid concentrations were increased in the globus pallidus (GP) with manganese exposure. Dopamine (DA) levels were altered in the GP, with the highest Mn(II) and Mn(III) exposures producing significantly different DA levels. In addition, transferrin receptor and H-ferritin protein expression increased in the GP with manganese exposure. These data substantiate the heightened susceptibility of the GP to manganese, and they indicate that the oxidation state of manganese exposure may be an important determinant of tissue toxicodynamics and subsequent neurotoxicity.

Manganese induces inducible nitric oxide synthase (iNOS) expression via activation of both MAP kinase and PI3K/Akt pathways in BV2 microglial cells

It is well documented that manganese neurotoxicity induces clinical symptoms similar to those of idiopathic Parkinson's disease. Although microglial cytotoxic mediator-induced neurotoxicity is suggested, the mechanism by which manganese up-regulates cytotoxic mediator, such as nitric oxide (NO), remains poorly understood. Therefore, in this study, we investigated the mechanism of manganese on induction of iNOS in microglial cells. iNOS promoter/luciferase assay revealed that manganese (500 (M) regulated the iNOS expression at the transcriptional level. Immunoblot analysis also revealed that phosphorylation levels of ERK, JNK MAPKs and Akt (PKB, PI 3-kinase downstream effector), were increased. Both protein and mRNA levels of iNOS expression were abrogated by specific inhibitors, SP600125 (JNK inhibitor, 20 microM), PD98059 (ERKs inhibitor, 50 microM), or LY294002 (PI 3-kinase inhibitor, 20 microM), but not by SB203580 (20 microM), a p38 specific inhibitor. These data lead to the conclusion that manganese regulates the iNOS expression at the transcriptional level in BV2 microglial cells and the increased iNOS protein expression is mediated via both JNK-ERK MAPK and PI3K/Akt signaling pathways, but not via p38 MAPK pathway. Increased iNOS protein level was also found in RAW264.7 murine macrophage cells.

The diagnosis of manganese-induced parkinsonism

Parkinsonism is a clinical syndrome consisting of tremor, bradykinesia, rigidity, gait, balance problems, in addition to various non-motor symptoms. There are many causes of parkinsonism such as neurodegenerative disease, drugs, vascular causes, structural lesions, infections, and toxicants. Parkinson's disease, or idiopathic parkinsonism, is the most common form of parkinsonism observed in the clinic. There is degeneration of the substantia nigra, pars compacta, which results in loss of striatal dopamine. Parkinson's disease is a slowly progressive condition in which there is a dramatic and sustained responsiveness to levodopa therapy. Manganese is an essential trace element that can be associated with neurotoxicity. Hypermanganism can occur in a variety of clinical settings. The clinical symptoms of manganese intoxication include non-specific complaints, neurobehavioral changes, parkinsonism, and dystonia. Although the globus pallidus is the main structure of damage, other basal ganglia areas can also be involved. MRI scans may show globus pallidus changes during (and for a short period after) exposure. Fluorodopa PET scans that assess the integrity of the substantia nigra dopaminergic system are abnormal in Parkinson's disease. However, these scans re-reported to be normal in a few cases studied with manganese-induced parkinsonism. The parkinsonism due to manganese may have some clinical features that occur less commonly in Parkinson's disease, such as kinetic tremor, dystonia, specific gait disturbances, and early mental, balance and speech changes. The clinical signs tend to be bilateral whereas Parkinson's disease begins on one side of the body. Patients with manganese-induced parkinsonism may be younger at the onset of the disease than with Parkinson's disease. Lastly, there appears to be a lack of response to levodopa therapy in manganese-induced parkinsonism. In summary it may be possible to differentiate manganese-induced parkinsonism from Parkinson's disease using clinical and imaging studies.

Neurobehavioral evaluation of rhesus monkey infants fed cow's milk formula, soy formula, or soy formula with added manganese

The possible neurobehavioral effects of excess manganese in soy formula were studied. Male rhesus monkeys (n=8/group) were fed a commercial cow's milk based formula (Control), a commercial soy protein based formula (Soy), or the soy formula with added manganese (Soy+Mn) from birth to 4 months of age. Soy formulas naturally have higher manganese (Mn) content than cow's milk formulas. Monkeys received behavioral evaluations, growth measurements, and cerebrospinal fluid (CSF) sampling from birth to 18 months of age. Soy and Soy+Mn groups engaged in less play behavior and more affiliative clinging in social dyadic interactions. These groups also had shorter wake cycles and shorter periods of daytime inactivity than controls. An impulsivity test was sensitive to the Soy group diet. The Soy+Mn group also had a blunted response to the dopamine agonist apomorphine. Groups did not differ significantly in CSF dopamine and serotonin metabolite concentrations, but these concentrations were correlated with several tasks affected by experimental formula. This experiment suggests that components of soy formula, including Mn, may influence brain development as reflected in behavioral measures.

Behavioral effects of adult rats concurrently exposed to high doses of oral manganese and restraint stress

The behavioral effects of concurrent exposure of high doses of manganese (Mn) and restraint stress were assessed in adult rats. Male Sprague-Dawley rats (250-300 g) received 0, 275 and 550 mg/kg/day of Mn in the drinking water for 19 weeks. Each group was divided into two subgroups. Animals in one subgroup were restrained for 2h/day. During the treatment period, food and water intake, and body weight were weekly recorded. At the end of the treatment period, activity levels were monitored in an open-field. Learning was evaluated by a water-maze task during five consecutive days. A trial probe was also conducted to assess the time spent in the platform quadrant. Body weight and food consumption were significantly reduced in the group receiving 550 mg/kg/day of Mn. A two-way analysis of variance (ANOVA) revealed an overall effect of Mn on the total distance traveled. Differences on spatial learning were observed in the acquisition period, in which rats given 550 mg/kg/day of Mn (alone or restrained) were impaired in comparison with the control and the restrained only groups. In the probe trial, there was an impaired retention in the group treated with Mn at 550 mg/kg/day. The results of this investigation in the open-field and water maze suggest that it would be plausible that restraint stress and a high exposure to Mn interact at common neurotransmitter levels but inducing opposite effects.

Toxin-Induced Movement Disorders

Toxins can be cited as a cause of several movement disorders, but this association is rare and the resultant syndromes usually include additional signs that are not typical for the idiopathic movement disorders. Most instances of confirmed toxin-induced movement disorders show lesions on CT and MRI scans of cortical or subcortical structures. A common underlying element in these toxin-induced syndromes is the development of lesions primarily in the pallidum and striatum. Because many toxins result in lesions affecting these structures, a selective vulnerability to hypoxic or metabolic insults has long been postulated. The susceptibility of these structures may relate to a number of factors, including the pattern of oxidative metabolism, heavy metal concentration, vascular perfusion, and neuronal innervation. Finally, in addition to causing disability, certain neurotoxins have led to a better understanding of human disease through the development of research models. As an example, the MPTP model has not only provided an animal model to study therapeutic strategies in PD but has also contributed important insights into the mechanism of neuronal degeneration.

Manganese toxicity upon overexposure

Manganese (Mn) is a required element and a metabolic byproduct of the contrast agent mangafodipir trisodium (MnDPDP). The Mn released from MnDPDP is initially sequestered by the liver for first-pass elimination, which allows an enhanced contrast for diagnostic imaging. The administration of intravenous Mn impacts its homeostatic balance in the human body and can lead to toxicity. Human Mn deficiency has been reported in patients on parenteral nutrition and in micronutrient studies. Mn toxicity has been reported through occupational (e.g. welder) and dietary overexposure and is evidenced primarily in the central nervous system, although lung, cardiac, liver, reproductive and fetal toxicity have been noted. Mn neurotoxicity results from an accumulation of the metal in brain tissue and results in a progressive disorder of the extrapyramidal system which is similar to Parkinson's disease. In order for Mn to distribute from blood into brain tissue, it must cross either the blood-brain barrier (BBB) or the blood-cerebrospinal fluid barrier (BCB). Brain import, with no evidence of export, would lead to brain Mn accumulation and neurotoxicity. The mechanism for the neurodegenerative damage specific to select brain regions is not clearly understood. Disturbances in iron homeostasis and the valence state of Mn have been implicated as key factors in contributing to Mn toxicity. Chelation therapy with EDTA and supplementation with levodopa are the current treatment options, which are mildly and transiently efficacious. In conclusion, repeated administration of Mn, or compounds that readily release Mn, may increase the risk of Mn-induced toxicity.

Brain energy metabolism in a sub-acute rat model of manganese neurotoxicity: an ex vivo nuclear magnetic resonance study using [1-13C]glucose

Ex vivo high-resolution NMR spectroscopy combined with in vivo injection of [1-13C]glucose was applied to gain insight into the mechanism(s) leading to energy failure in manganese neurotoxicity. In rats treated for 4 days with 50mg/kg MnCl(2) (intraperitoneally, i.p.), the concentration of 13C-labeled lactate increased to 154% compared to control rats. Changes in the absolute amounts of lactate were much less, resulting in increased fractional 13C-enrichments in lactate (indicating relative changes of de novo synthesis from glucose via the glycolytic pathway) to 143% of control values (P < 0.001). Analysis of samples obtained from blood plasma and peripheral organs demonstrate a selective increase of lactate synthesis from [1-13C]glucose in the brain, which is released into the circulation. In parallel, manganese treatment resulted in stimulation of flux through pyruvate dehydrogenase (PDH), leading to accumulation of [4-13C]glutamate, [4-13C]glutamine and [2-13C]GABA to 168, 247 and 144% of control, respectively. The relative flux of glucose through astrocytic pyruvate carboxylase (PC), on the other hand, was impaired by manganese, as evident from a decreased ratio of [2-13C]/[4-13C]glutamate or [2-13C]/[4-13C] glutamine. Consistent with stimulated glucose oxidative metabolism, the fractional 13C-enrichment in [2-13C]acetyl-CoA entering the tricarboxylic acid (TCA) cycle and contributing to glutamate and glutamine synthesis increased to 138 and 156% of control, respectively (P < 0.001). In parallel, the TCA cycling ratio increased to 134% compared to control rats, prior to the label ending up in glutamate. In contrast, glutamine is synthesized mainly during the first TCA cycle turn. The present data provide new evidence in support of changes in brain energy metabolism playing an important role in manganese neurotoxicity. In particular, increased glycolytic flux and lactate synthesis may contribute to the deleterious effects of manganese in the brain. Furthermore, stimulated astrocytic glucose oxidation and glutamine synthesis may be associated with astrocytic pathology and altered astrocytic-neuronal metabolic trafficking in manganese neurotoxicity.

Diffusion abnormalities of the globi pallidi in manganese neurotoxicity

Manganese is an essential trace metal required for normal central nervous system function, which is toxic when in excess amounts in serum. Manganese neurotoxicity has been demonstrated in patients with chronic liver/biliary failure where an inability to excrete manganese via the biliary system causes increased serum levels, and in patients on total parenteral nutrition (TPN), occupational/inhalational exposure, or other source of excess exogenous manganese. Manganese has been well described in the literature to deposit selectively in the globi pallidi and to induce focal neurotoxicity. We present a case of a 53-year-old woman who presented for a brain MR 3 weeks after liver transplant due to progressively decreasing level of consciousness. The patient had severe liver failure by liver function tests and bilirubin levels, and had also been receiving TPN since the transplant. The MR demonstrated symmetric hyperintensity on T1-weighted images in the globi pallidi. Apparent diffusion coefficient (ADC) map indicated restricted diffusion in the globi pallidi bilaterally. The patient eventually succumbed to systemic aspergillosis 3 days after the MR. The serum manganese level was 195 mcg/l (micrograms per liter) on postmortem exam (over 20 times the upper limits of normal). The patient was presumed to have suffered from manganese neurotoxicity since elevated serum manganese levels have been shown in the literature to correlate with hyperintensity on T1-weighted images, neurotoxicity symptoms, and focal concentration of manganese in the globi pallidi. Neuropathologic sectioning of the globi pallidi at autopsy was also consistent with manganese neurotoxicity.

Effect of high dietary manganese intake of neonatal rats on tissue mineral accumulation, striatal dopamine levels, and neurodevelopmental status

Mn is an essential element, but may become neurotoxic at high levels. Recent reports of high Mn levels in hair of children with neurodevelopmental deficits suggest that these deficits could be due to Mn-induced neurotoxic effects on brain dopamine (DA) systems, although the mechanism is not well understood. Infant formulas contain considerably higher concentrations of Mn than human milk. Thus, formula-fed infants are exposed to high levels of Mn at a time when Mn homeostasis is incompletely developed. We studied the effects of dietary Mn supplementation of rat pups on tissue Mn accumulation, brain dopamine levels, infant neurodevelopmental status, and behavior at maturity. Newborn rats were supplemented daily with 0, 50, 250, or 500 microg Mn given orally from day 1 to day 20. Mineral analysis of small intestine and brain at day 14 showed a significant increase of tissue Mn in supplemented rats. Neurodevelopmental tests conducted at various ages showed significant delays as a function of Mn supplementation. At day 32, there was a significant positive relationship between passive avoidance errors and Mn supplementation levels. Brains of animals killed on day 40 showed a significant inverse relationship between Mn supplementation level and striatal dopamine concentration. These observations suggest that dietary exposure to high levels of Mn during infancy can be neurotoxic to rat pups and result in developmental deficits.

Effects of neonatal dietary manganese exposure on brain dopamine levels and neurocognitive functions

Neonatal exposure to high levels of manganese (Mn) has been indirectly implicated as a causal agent in attention deficit hyperactivity disorder (ADHD), since Mn toxicity and ADHD both involve dysfunction in brain dopamine (DA) systems. This study was undertaken to examine this putative relationship in an animal model by determining if levels of neonatal dietary Mn exposure were related to brain DA levels and/or behavioral tests of executive function (EF) when the animals reached maturity. We used 32 newborn male Sprague-Dawley rats and randomly assigned them to one of the four dietary Mn supplementation conditions: 0, 50, 250 and 500 microg per day, administered daily in water from postnatal days 1-21. During days 50-64, the animals were given a burrowing detour test and a passive avoidance test. At day 65, the animals were killed and brains were assayed for DA. There was a statistically significant relationship (P = 0.003) between dietary Mn exposure and striatal DA. On the burrowing detour and passive avoidance, greater deficits were observed for animals subjected to higher Mn exposure, but these differences did not reach statistical significance. However, tests for heterogeneity of variance between groups were statistically significant for all measures, with positive relationship between Mn exposure and degree of within-group behavioral variability. Kendall's nonparametric test of the relationship between the three behavioral measures and striatal DA levels was also statistically significant (P = 0.02). These results lend support to the hypothesis that neonatal Mn exposure is related to brain DA levels and neurocognitive deficit in the rodent.

Manganese neurotoxicity: behavioral, pathological, and biochemical effects following various routes of exposure

The human central nervous system is an important target for manganese intoxication, which causes neurological symptoms similar to those of Parkinson's disease. With the increasing use of methylcyclopentadienyl manganese tricarbonyl (MMT) as an octane-improving additive to unleaded gasoline, the prospect of worldwide manganese exposure is once again attracting attention as increases in environmental manganese concentrations have been recorded relative to traffic density. One crucial question is whether a small increase of manganese contamination resulting from the widespread use of MMT could have neurotoxic effects. In this review we concentrate on central nervous system abnormalities and neurobehavioral disturbances. Most experimental animal studies on manganese neurotoxicity have been conducted in nonhuman primates and rodents. Most studies performed in rodents used oral manganese administration and did not assess bioaccumulation or central nervous system changes. The major effect found was transient modification of spontaneous motor activity. Very few inhalation toxicological studies were carried out. As manganese intoxication in humans usually occurs via inhalation, more studies are required using the respiratory route of administration. Given the proven neurotoxic effects of manganese and the prospect of worldwide MMT usage, this metal should be considered a new environmental pollutant having potentially widespread public health consequences.

Low cumulative manganese exposure affects striatal GABA but not dopamine

The introduction of the anti-knock methylcyclopentadienyl manganese (Mn) tricarbonyl (MMT) in gasoline has raised concerns about the potential for manganese neurotoxicity. Because subpopulations such as the elderly in the early stages of neurodegenerative disease may be at increased risk for manganese toxicity, a pre-Parkinsonism rat model was used to evaluate whether sub-chronic manganese exposure can aggravate the neurochemical and behavioral dysfunctions characteristic of Parkinsonism. Sub-threshold levels of dopamine depletion of 3.5, 53 and 68% were generated via intrastriatal unilateral 6-hydroxydopamine (6-OHDA) doses. A sub-chronic dosing regimen of low cumulative manganese exposure (4.8 mg Mn/kg body weight, 3 i.p. injections per week x 5 weeks) was started 4 weeks after 6-OHDA treatments. Neurochemical and neuromotor (functional observational battery (FOB)) measures were evaluated. Manganese produced significant (P < 0.05) reductions of 30-60% in motor function. This effect was exacerbated in the presence of a pre-Parkinsonism condition [Neurotox. Teratol. 22 (2000) 851]. Manganese did not affect striatal dopamine, but resulted in significant increases in striatal y-aminobutyric acid (GABA) of 16 and 22% (P < 0.01) in both striati and a borderline non-significant 4% increase in frontal cortex (P = 0.076). Manganese treatment produced increased aspartate (P < 0.01) in the manganese and 6-OHDA treated striatum. In light of previous studies predominantly showing dopamine depletion with elevated manganese exposures, the significant effects of manganese on striatal GABA but not on striatal dopamine at the low cumulative exposure administered here suggest a progression in manganese toxicity with increasing cumulative dose, whereby GABA levels are adversely affected before striatal dopamine levels. Because these neurochemical disruptions were accompanied by motor dysfunction that was exacerbated in the presence of a pre-Parkinsonism condition, an increased environmental burden of manganese may have deleterious effects on populations with sub-threshold neurodegeneration in the basal ganglia (e.g. pre-Parkinsonism).

The neurobehavioral effects of subchronic manganese exposure in the presence and absence of pre-parkinsonism

Recent studies have implicated chronic elevated exposures to environmental agents, such as metals (e.g., manganese, Mn) and pesticides, as contributors to neurological disease. In particular, there is a concern that sensitive subpopulations such as the aged may be at increased risk for the onset of neurologic disorders because elevated exposures to Mn is associated with increased incidence of parkinsonism. Here, we utilized a rat model of pre-parkinsonism to investigate the effects of Mn exposure on neurotoxicity and the exacerbation of parkinsonism. A pre-parkinsonism state was induced using a unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA), followed 4 weeks later by Mn exposure (4.8 mg Mn/kgx3 intraperitoneal injections/week) for 5 weeks. Female Sprague-Dawley rats (n=44) were divided among the following treatments: (A) control, saline/vehicle; (B) Mn only; (C) 6-OHDA only; and (D) 6-OHDA+Mn. Brain Mn levels were measured by ICP-MS. Neurobehavioral function was assessed following Mn exposure using a functional observational battery (FOB) consisting of 10 neurobehavioral tests. Unilateral 6-OHDA lesions produced significant ipsilateral vs. contralateral striatal dopamine depletions (60-70%), but no measurable impairment of neurobehavioral function, thereby substantiating this pre-parkinsonism (i.e., subthreshold) model. In contrast, Mn exposure resulted in significant impairment of neurobehavioral function for eight of the 10 FOB tests. No effects of Mn exposure on striatal dopamine depletion were detected, despite the 3.4-fold increase in brain Mn levels over controls. Notably, Mn exposure in the presence of a pre-parkinsonism state significantly exacerbated the neurobehavioral impairment in the reactivity to handling (P<.049) and hopping contralateral rear limb (P<.033) FOB tests. While the persistence and Mn dose-response relationship of these neurobehavioral effects were not evaluated here, these results nonetheless suggest that chronic Mn exposure may increase the risk of neurobehavioral impairment in subpopulations that are in a pre-parkinsonism state.

Manganese deposition in the globus pallidus in patients with biliary atresia

BACKGROUND

Chronic liver diseases may alter trace element contents in the brain. Among these trace elements, manganese is a ubiquitous transition metal excreted by the liver into the bile. Blood concentrations of manganese are elevated in patients with biliary atresia who have undergone hepatic portoenterostomy. The present study investigated the effects of liver transplantation on manganese deposition in the brain in such patients.

METHODS

The signal intensity of the globus pallidus was calculated as an index defined as the percentile ratio of signal intensity in the globus pallidus to the subcortical frontal white-matter in sagittal T1-weighted magnetic resonance imaging planes.

RESULTS

Brain magnetic resonance imaging revealed hyperintense signals in the globus pallidus due to manganese deposition in biliary atresia patients. Few neurologic symptoms related to manganese intoxication were observed. However, one 23-year-old female with biliary atresia had depressive symptoms and dyskinesia; she improved after oral administration of the dopamine precursor, L-DOPA. Manganese deposition disappeared in two patients after living-related reduced-size hepatic transplantation.

CONCLUSIONS

Manganese accumulates in the brain during cholestasis associated with biliary atresia and disappears after hepatic transplantation. Manganese deposition is likely to be subclinical and reversible but may be associated with some age-related neurologic symptoms.

Neurotoxicity of manganese chloride in neonatal and adult CD rats following subchronic (21-day) high-dose oral exposure

The purpose of this study was to evaluate the relative sensitivity of neonatal and adult CD rats to manganese-induced neurotoxicity. Identical oral manganese chloride (MnCl(2)) doses (0, 25, or 50 mg kg(-1) body wt. day(-1)) were given to neonatal rats throughout lactation (i.e. from postnatal day (PND) 1 through 21) and to adult male rats for 21 consecutive days. The MnCl(2) doses administered to neonates were ca. 100-fold higher than those resulting from the consumption of an equivalent volume of rat's milk. Rats were assessed using similar behavioral and neurochemical evaluations. Several statistically significant changes occurred in Mn-exposed rats relative to control animals. Neonates given the high dose of MnCl(2) had reduced body weight gain. An increased pulse-elicited acoustic startle response amplitude was observed in neonates from both MnCl(2) treatment groups on PND 21. Increased striatal, hippocampal, hindbrain and cortical Mn concentrations were observed in all Mn-exposed neonates on PND 21. Increased hypothalamic and cerebellar Mn concentrations were also observed on PND 21 in neonates from the high-dose group only. Increased striatal, cerebellar and brain residue Mn concentrations were observed in adult rats from the high-dose group. Increased striatal dopamine and 3,4-dihydroxyphenylacetic acid levels were observed only in PND 21 neonates from the high-dose group. No treatment-related changes were observed in clinical signs, motor activity (assessed in neonates on PND 13, 17, 21 +/- 1 and in adults), passive avoidance (assessed in neonates on PND 20 +/- 1 and in adults) or neuropathology (assessed in PND 21 neonates only). The results of our experiment suggest that neonates may be at greater risk for Mn-induced neurotoxicity when compared to adults receiving similar high oral levels of Mn.

Significance of magnetic resonance image and blood manganese measurement for the assessment of brain manganese during total parenteral nutrition in rats

In this study, we report on the influence of trace elements (TE) on signal intensities of nuclear magnetic resonance images (MRI), both in vivo and in vitro. Optimal parameters for the assessment of Mn concentration in the brain of rats on total parenteral nutrition were established. For the in vitro study, Mn and trace element solutions, one containing Zn, Cu, Fe, and I (TE-4) and another containing the above elements plus Mn (TE-5), were diluted with physiological saline or with rat brain homogenate and used to measure signal intensities in MRI. Concentration-dependent signal hyperintensity was observed in both cases in the Mn and the TE-5 solutions, but no effect was observed with the TE-4 solution. The signal increase was greater for brain tissue homogenates. In the in vivo study, the experimental animals were maintained under total parenteral nutrition (TPN) with a standard clinical dose of TE-5 and/or with 10-fold the clinical dose of TE-4 and TE-5 for 1 wk. Only rats that were receiving the increased TE-5 dose showed signal hyperintensity on MRI. Positive correlations were observed among the signal hyperintensity, the blood Mn concentrations, and that of the rat brain. Our results suggest that Mn in TE preparations may be the cause of signal hyperintensity on MRI in a concentration-dependent fashion, and that MRI and measurement of blood Mn may be used to estimate Mn accumulation in brain tissue.

Perinatal manganese exposure: behavioral, neurochemical, and histopathological effects in the rat

Manganese chloride (Mn) was dissolved in the drinking water (0, 2, or 10 mg/ml) of dams and their litters from conception until postnatal day (PND) 30. Parturition was uneventful in the Mn-exposed rats and no physical abnormalities were observed. The rats exposed to 10 mg/ml Mn showed a 2.5-fold increase in cortical Mn levels. Their weight gain was attenuated from PND 9-24 and they were hyperactive at PND 17. Neither the 2 nor the 10 mg/ml Mn-exposed groups differed from the controls on the elevated plus apparatus or on the Morris water maze and the radial arm maze. Brain monoamine levels and choline acetyltransferase activity were affected. Tyrosine hydroxylase immunohistochemistry showed that dopamine cells of the substantia nigra were intact. Glial fibrillary acidic protein immunoreactivity was not increased in cortex, caudate, and hippocampus. However, both the low- and high-dose Mn-exposed groups showing thinning of the cerebral cortex. This could have resulted from perinatal malnutrition or from a direct effect of Mn on cortical development.

Manganese toxicity in serumless dissociated mesencephalic and striatal primary culture

Exposure to elevated levels of Manganese (Mn) can result in an irreversible brain disease characterized by extrapyramidal signs and symptoms resembling Parkinson's disease. To identify the neuronal target of Mn neurotoxicity, MnCl2 was added to serumless dissociated mesencephalic-striatal cultures from rat embryo on day 4 in vitro. High affinity 3H-dopamine (DA) and 14C-GABA uptakes were assessed as specific functional markers of DAergic and GABAergic cell viability, respectively. After 60-min exposure, MnCl2 at 0-200 microM did not modify the morphologic appearance of the cultures, specific DA and GABA uptakes, or the number of DA neurons visualized by immuno-cytochemical staining with tyrosine hydroxylase. In contrast, culture exposure to 20 microM MnCl2 for 24 h selectively reduced specific GABA uptake without affecting specific DA uptake or the number of DA neurons. The exposure to a higher MnCl2 concentration was accompanied by signs of general toxicity. Striatal GABA neurons seemed to be more susceptible to Mn toxicity than mesencephalic GABA neurons. Overall, our data suggest that striatal neurons rather than mesencephalic DA neurons may be the main target of Mn neurotoxicity.

Axonal transport of manganese and its relevance to selective neurotoxicity in the rat basal ganglia

The present study provides evidence for anterograde axonal transport of manganese (Mn) in the basal ganglia. Microinjections of 54Mn into rat substantia nigra or striatum revealed region-specific accumulation and retention of the isotope in globus pallidus, striatum, thalamus and substantia nigra for up to at least 48 or 72 h respectively. Within 4 h after intrastriatal injection of 54Mn, radioactivity accumulated in the substantia nigra, suggesting axonal transport of the metal. Subsequent studies using bilateral 54Mn injections into striatum or substantia nigra and unilateral colchicine injections into or transection of the medial forebrain bundle confirmed axonal transport of Mn through these fibres. Selective destruction of the striatonigral or nigrostriatal pathways using quinolinic acid or 6-hydroxydopamine 2 weeks before injection of the isotope, revealed uptake of 54Mn by cell bodies of both gamma-aminobutyric acidergic striatal and dopaminergic nigral neurons and subsequent anterograde transport through striatonigral or nigrostriatal fibres. In addition, the quinolinic acid-lesioned striatum retained three times more radioactivity than the intact striatum. In conclusion, the present data suggest that both glial cells and striatonigral and nigrostriatal neurons are potential targets for Mn toxicity. These results and the selective neurotoxicity of Mn are discussed with respect to the iron transport protein transferrin, transferrin receptors, the iron storage protein ferritin, and mitochondrial dysfunction.

Dystonia, hyperintense basal ganglia, and high whole blood manganese levels in Alagille's syndrome

Hyperintensity of the globus pallidus on T1-weighted magnetic resonance imaging (MRI) has been reported in patients with chronic liver disease. This abnormality has been associated with the severity of liver disease and tremor, but its cause is unknown. Similar MRI signal abnormalities have been reported in experimental models of manganese neurotoxicity. This case report describes a child with Alagille's syndrome and end-stage liver disease who developed dystonia and tremor associated with an elevated whole blood manganese level and symmetric hyperintense globus pallidi and subthalamic nuclei on T1-weighted but not T2-weighted MRI. Liver transplantation was performed; 2 months later, neurological function was improved, manganese levels were normal, and the MRI signal abnormality had completely resolved. This child had neurological findings described in manganese neurotoxicity with compatible laboratory and radiological findings. Manganese is excreted by the liver in bile, and toxicity may have resulted from the inadequacy of this mechanism, subsequently corrected by liver transplantation.

Selective lesions by manganese and extensive damage by iron after injection into rat striatum or hippocampus

Regional 45Ca2+ accumulation and analysis of monoamines and metabolites in dissected tissues were used to localize, quantify, and characterize brain damage after intracerebral injections of Mn2+ into striatum and hippocampus. The specificity of Mn(2+)-induced lesions is described in relation to brain damage produced by local Fe2+ or 6-hydroxydopamine (6-OHDA) injections. In striatum, Fe2+ and Mn2+ produced dose-dependent (0.05-0.8 mumol) dopamine (DA) depletion, with Fe2+ being 3.4 times more potent than Mn2+. Studies examining the time course of changes in monoamine levels in striatum following local application of 0.4 mumol of Mn2+ revealed maximal depletion of all substances investigated (except 5-hydroxyindoleacetic acid) after 3 days. The effects on DA (87% depletion at day 3) and its major metabolites were most pronounced and lasted until at least 90 days (40% depletion), whereas serotonin and noradrenaline levels recovered within 21 and 42 days, respectively. In addition, levels of 3-methoxytyramine, which is used as an index of DA release, also recovered within 42 days, indicating a functional restoration of DA neurotransmission despite substantial loss of DA content. Intrastriatal Mn2+ (0.4 mumol) produced time-dependent 45Ca2+ accumulation in striatum, globus pallidus, entopeduncular nucleus, several thalamic nuclei, and substantia nigra pars reticulata ipsilateral to the injection site. In contrast, 6-OHDA injected at a dose equipotent in depleting DA produced significantly less 45Ca2+ accumulation in striatum and globus pallidus and no labeling of other brain areas, whereas Fe2+ (0.4 mumol) produced extensive 45Ca2+ accumulation throughout basal ganglia, accumbens, and cerebral cortex. In hippocampus, high Mn2+ (0.4 mumol) produced limited 45Ca2+ accumulation in subiculum and dentate gyrus, whereas low Fe2+ (0.1 mumol) produced widespread 45Ca2+ accumulation throughout hippocampus, thalamus, and cerebral cortex. It is concluded that (a) Mn2+ is selectively neurotoxic to pathways intrinsic to the basal ganglia, (b) intrastriatal injections can be used as a model for systemic Mn2+ intoxications, and (c) high endogenous Fe3+ and/or catecholamine levels potentiate the neurotoxicity of Mn2+.

Urinary excretion of homovanillic acid in workers exposed to manganese

Homovanillic acid, an end product of dopamine catabolism, and manganese (Mn) were measured in the urine of 68 male workers exposed to Mn-containing dust in a dry alkaline battery plant or an Mn oxide and salt producing plant, and in 35 control male subjects. The geometric mean of the airborne concentration of inhalable (total) dust amounted to 0.95 and 1.37 mg/m3 in the dry alkaline battery plant and the Mn oxide and salt producing plant, respectively. In the latter, a higher prevalence of increased values of urinary homovanillic acid concentration was found. In the total population, there was a low but statistically significant positive correlation between the concentration of homovanillic acid and Mn in urine (r = 0.20, P = 0.04) but there was no significant correlation between the level of homovanillic acid in urine and Mn in airborne dust or duration of exposure. This observation might be compatible with the stimulation of dopamine turnover in the brain, which has been observed in the early phase of Mn intoxication in animals. However, the large variability in urinary homovanillic acid excretion in control subjects precludes the use of this biological indicator to detect early interference of Mn with the dopaminergic system.

Receptor-mediated endocytosis of a manganese complex of transferrin into neuroblastoma (SHSY5Y) cells in culture

Exposure to manganese compounds often occurs as the result of industrial production or mining. Although manganese appears in traces in animal and human tissue and is essential to certain biological processes, it is also toxic. In humans and animals, toxicity is mainly associated with the nervous system. The mechanism underlying behavioral and biochemical alterations observed after manganese intoxication is not fully understood. We have shown that the manganese present in serum after exposure to manganese oxide is bound to transferrin as trivalent manganic ion. In this study of manganese uptake and storage we used a clone of human neuroblastoma cells (SHSY5Y). These cells differentiate and express catecholaminergic properties. Saturation binding analysis of the transferrin-manganese complex to the cells revealed a single class of binding sites, with an apparent KD of 13 +/- 1 nM and a density of 11,000 +/- 2,000 binding sites per cell. The complex was internalized in a temperature-dependent way and reached saturation after 2 h when approximately 2% of the added manganese had been internalized. About 80% of the internalized manganese was found in ferritin after 24 h of exposure. The results demonstrate that the transferrin receptor on SHSY5Y cells can bind and internalize a manganese-transferrin complex as efficiently as an iron-transferrin complex, although a saturation of the manganese uptake was achieved.

Manganese induced brain lesions in Macaca fascicularis as revealed by positron emission tomography and magnetic resonance imaging

A series of positron emission tomography scans was made on two monkeys during a 16-month period when they received manganese(IV)oxide by subcutaneous injection. The distribution of [11C]-nomifensine uptake, indicating dopamine terminals, was followed in both monkey brains. The brain distributions of [11C]-raclopride, demonstrating D2 dopamine receptors, and [11C]-L-dopa, as a marker of dopamine turnover, were followed in one monkey each. The monkeys developed signs of poisoning namely unsteady gait and hypoactivity. The [11C]-nomifensine uptake in the striatum was reduced with time and reached a 60% reduction after 16 months exposure. This supports the suggestion that dopaminergic nerve endings degenerate during manganese intoxication. The [11C]-L-dopa decarboxylation was not significantly altered indicating a sparing of [11C]-L-dopa decarboxylation during manganese poisoning. A transient decrease of [11C]-raclopride binding occurred but at the end of the study D2-receptor binding had returned to starting values. The magnetic resonance imaging (MRI) revealed that the manganese accumulated in the globus pallidus, putamen and caudate nucleus. There were also suggestions of gliosis/edema in the posterior limb of the internal capsule. MRI might be useful to follow manganese intoxication in humans as long as the scan is made within a few months of exposure to manganese, i.e. before a reversal of the manganese accumulation.

Receptor alterations in manganese intoxicated monkeys

The density of four different receptors and one marker of dopamine uptake sites were analyzed in monkey brains after manganese exposure (0.1 g manganese per month during 26 months, a dose comparable to that workers might inhale in dusty environments) by means of quantitative receptor autoradiography. The binding of 3H-mazindol to the dopamine uptake sites was reduced by 75% in both the head of the caudate nucleus and putamen, while it remained unchanged in the other regions analyzed. The binding of the D1 receptor ligand 3H-SCH 23,390 was reduced about 45% in the same areas as mazindol binding, while the density of D2 receptors was unaffected. The muscarinic acetylcholine receptors as well as GABAA receptors remained also unchanged in all brain areas analyzed after manganese exposure. Thus the dopaminergic neurons must be considered to be vulnerable to manganese concentrations attainable in the work environment. Our results also indicate that postsynaptic structures containing D1 receptors are sensitive while cells containing D2 receptors are either spared or compensated for by up-regulation of the number of receptors on remaining sites.

Persistent effects of manganese on effortful responding and their relationship to manganese accumulation in the primate globus pallidus

Manganese produces signs and symptoms that suggest involvement of the basal ganglia, especially the globus pallidus and substantia nigra. Overt neurological signs have been reported in primates exposed to high levels of manganese (over 100 mg/kg) but little is known about the effects of lower doses. To examine these issues, three cebus monkeys were trained to operate a response device with their arms and legs by executing a rowing-like movement against a 3.9- to 4.1-kg spring through an arc length of 10 cm under a multiple fixed-ratio fixed-interval schedule of reinforcement. Over the course of 450 days, these monkeys were administered acute doses of 5 or 10 mg/kg iv of manganese chloride using a multiple baseline experimental design. Doses as low as 5 mg/kg provoked a large increase in the number of incomplete responses. The onset of manganese's effect appeared within days of exposure and developed over the course of several weeks. Its magnitude declined over the course of months, but after a cumulative dose of 10 to 40 mg/kg it did not return to baseline. Action tremor appeared at cumulative doses greater than 40 mg/kg and dystonia was never observed at the cumulative doses examined. Behavioral microanalysis revealed that manganese's effects initially appeared as increased variability of interresponse times and response duration. Later, the response pattern during the fixed ratio component shifted to one of progressively increasing durations through the course of the ratio. Magnetic resonance imaging revealed that the behavioral effects of manganese corresponded to an apparent increase in the manganese content of the globus pallidus and substantia nigra.

Acute exposure to maneb alters some behavioral functions in the mouse

Maneb, an organomanganese fungicide, is largely used in agricultural regions for control of field crop pathologies. Despite its apparent low toxicity, there are reports showing that maneb has harmful effects on peripheral and central nervous systems. In this work the effects of acute administration of maneb were studied on some experimental animal models. Male adult mice were treated with several doses of maneb, IP, and submitted to gross behavioral observation (200-1000 mg/kg) and measurement of locomotor activity, barbiturate-induced sleeping time, isolation-induced aggressiveness, catatonia, climbing behavior and of rota-rod performance (30, 60 and 100 mg/kg). The results showed that maneb has an inhibitory effect on locomotor activity and aggressiveness and increases barbiturate-induced sleeping time and haloperidol-induced catatonia. However, maneb did not affect the apomorphine-induced climbing behavior of animals. These data indicate that maneb has a CNS depressant-like effect, and suggest, at least partially, the involvement of dopaminergic systems in the mediation of this effect.

Retention and distribution of manganese in the mouse brain following acute exposure on postnatal day 0, 7, 14 or 42: an autoradiographic and gamma counting study

The relationship between postnatal age at time of Mn exposure, and the retention and distribution of Mn in the brain of the mouse was studied using gamma counting and autoradiography. A single intraperitoneal dose of Mn2+ (11 micrograms/kg or 25 mg/kg) containing radioactive 54Mn was administered on postnatal day 0, 7, 14 or 42. Animals were then killed at various times post exposure (1-114 days) and retention and distribution determined. Maximum retention of Mn in the brain (calculated as a percentage of administered dose) occurred 43 days following exposure on day 0. For day 7, 14 or 42 the highest Mn retention was 24 h after exposure. Maximum retention was 2.9%, 3.5%, 2.5% or 0.3% respectively, Mn retention after 114 days was 0.4%, 0.3%, 0.3% or 0.04% respectively. For the carrier-added group maximum retention was lower with corresponding figures of 2.5%, 2.4%, 1.1% or 0.2% and retention after 114 days was also lower 0.1%, 0.06%, 0.05% or 0.01%. The autoradiography studies indicated that Mn was located in areas of the brain which had a high perikaryal density at the time of exposure and in the choroid plexus. High and low doses of Mn were similarly distributed and there was little change in distribution with time.

Morvan's fibrillary chorea. A case with possible manganese poisoning

The clinical picture of Morvan's fibrillary chorea includes a. spontaneous muscular activity resulting from repetitive motor unit action potentials of peripheral origin (multiplets), b. autonomic dysregulation with profuse hyperhidrosis, and c. central nervous system involvement as shown by severe insomnia and hallucinosis. A case featuring all these symptoms is presented. Whereas known causative factors range from gold or mercury poisoning to autoimmune disorders, the presented case is the first one in which chronic manganese intoxication (occupational exposure) seems to be implicated. Manganese has been found to inhibit acetylcholine esterase, and, as a consequence, may produce peripheral and central cholinergic hyperactivity.