Ultrastructural changes in the nervous system of rabbits poisoned with methyl mercury

Mechanisms Underlying Sensory Nerve-Predominant Damage by Methylmercury in the Peripheral Nervous System

Sensory disturbances and central nervous system symptoms are important in patients with Minamata disease. In the peripheral nervous system of these patients, motor nerves are not strongly injured, whereas sensory nerves are predominantly affected. In this study, we investigated the mechanisms underlying the sensory-predominant impairment of the peripheral nervous system caused by methylmercury. We found that the types of cell death in rat dorsal root ganglion (DRG) neurons caused by methylmercury included apoptosis, necrosis, and necroptosis. Methylmercury induced apoptosis in cultured rat DRG neurons but not in anterior horn neurons or Schwann cells. Additionally, methylmercury activated both caspase 8 and caspase 3 in DRG neurons. It increased the expression of tumor necrosis factor (TNF) receptor-1 and the phosphorylation of receptor-interacting protein kinase 3 (RIP3) and mixed-lineage kinase domain-like pseudokinase (MLKL). The expression of TNF-α was increased in macrophage-like RAW264.7 cells by methylmercury. The increase was suggested to be mediated by the NF-κB pathway. Moreover, methylmercury induced neurological symptoms, evaluated by a hindlimb extension response, were significantly less severe in TNF-α knockout mice. Based on these results and our previous studies, we propose the following hypothesis regarding the pathogenesis of sensory nerve-predominant damage by methylmercury: First, methylmercury accumulates within sensory nerve neurons and initiates cell death mechanisms, such as apoptosis, on a small scale. Second, cell death triggers the infiltration of macrophages into the sensory fibers. Third, the macrophages are stimulated by methylmercury and secrete TNF-α through the NF-κB pathway. Fourth, TNF-α induces cell death mechanisms, including necrosis, apoptosis through the caspase 8/3 pathway, and necroptosis through the TNFR1-RIP1-RIP3-MLKL pathway, activated by methylmercury in sensory neurons. Consequently, methylmercury exhibits potent cytotoxicity specific to the DRG/sensory nerve cells in the peripheral nervous system. This chain of events caused by methylmercury may contribute to sensory disturbances in patients with Minamata disease.

Pathology of human organic mercury poisoning: Lessons from an autopsy case

We had an opportunity to perform a general autopsy of a case with chronic organic mercury toxicosis in 2017. He had been engaged in synthesizing a variety of organic mercury compounds throughout the four years from 1966 and developed chronic organic mercury poisoning in 1969. Almost forty years on, he still remained to complain of persistent paresthesia at finger tips and tongue, and of narrowed visual field. Neurological examinations clarified a rise of two-point discrimination thresholds, a systemic increase of touch thresholds, constriction of the visual field caused by general visual depression, and sensorineural hearing loss while primary modalities of his somatic, visual, and auditory sensations were preserved. These symptoms and signs are characteristic of human organic mercury poisoning. Furthermore, he had difficulty in processing a lot of visual and auditory information at a time. His two-point discrimination thresholds and systemic elevation of touch thresholds were comparable to those of mild organic mercury poisoning cases. He had slight sensory ataxia, but not cerebellar ataxia. Brain [18F]-2-fluorodeoxyglucose positron emission tomography analysis exhibited marked hypometabolism at bilateral postcentral gyrus, striate cortex, and superior temporal gyrus, but not the cerebellum. Histopathological studies revealed considerable decrease of granular neurons and neuronal networks in bilateral primary somatosensory, visual, and auditory cortices. Those characteristic brain lesions fairly explain increase of thresholds of somatic, visual, and auditory sensations, and degradation of integrating sensory information. It is noted that damages to the peripheral nervous system and the cerebellum were not detected and that his intellectual faculties were preserved.

Evaluation of Mercury Transformation and Benthic Organisms Uptake in a Creek Sediment of Pearl River Estuary, China

A large fraction of mercury contaminant in the environment is from industrial production, and it potentially impairs human health once entering the food chain. Millions of people reside in the Pearl River Delta region, and water quality in the estuary directly affects their drinking water safety. Considering the highly intense anthropogenic activities and industrial productions, we attempted to measure the sediment mercury concentration in the Pearl River estuary. In this work, samples of a creek sediment within this region were collected and mercury concentrations were quantified. Total mercury, simultaneously extracted mercury, methylmercury, and bio-accumulated mercury were individually assayed. Results indicated that total mercury concentrations of investigated sites ranged from 1.073 to 4.450 µg/g dry sediment. The mercury in the sediment also transformed into more toxic methylmercury, which then adversely affected benthos biodiversity. Correlation analysis revealed that, mercury was accumulated into benthic microorganisms, mainly through the uptake of methylmercury. High concentrations of acid-volatile sulfide in the sediment indicated the presence of active sulfate-reducing bacteria, which could also catalytically transform inorganic mercury into methylmercury. Correlation analysis further showed that sulfate-reducing bacteria activity accounted for methylmercury formation.

First report on fish cysteine as a biomarker of contamination in the River Chenab, Pakistan

The eastern and southern parts of the Faisalabad city produce considerable quantities of industrial and municipal pollutants, much of which is drained into the River Chenab, reducing the productivity of fauna and flora in the river. This study was aimed to determine whether cysteine is useful as a biomarker of exposure to polluted fresh water. The amino acid profile of fish muscle was analyzed by paper chromatography in Cirrhinus mrigala and Labeo rohita from the River Chenab to determine habitat related variations due to the pollution from industrial and domestic sources. C. mrigala showed higher level of metal contamination in muscle tissues for Sn, Cr, Pb, Zn, Mn, Cu, and Cd when compared to L. rohita. Both fish species collected from polluted areas of the river Chenab showed significantly (P < 0.01) higher levels of metals in comparison to upstream and farmed fish. Farmed C. mrigala showed cysteine concentrations in the muscle tissue as 22 ± 1 mg/g dry weight, but concentrations increased to 45 ± 2 mg/g dry weight for fish from a mildly polluted section of the river, and further increased to 83 ± 2 mg/g dry weight in more heavily polluted sections. Cysteine concentration in farmed L. rohita was detected as 28 ± 2 and 25 ± 4 mg/g dry weight, respectively for farmed fish and fish from a mildly polluted section of the river, and then increased to 94 ± 3 mg/g dry weight for fish from highly polluted water. C. mrigala from a mildly polluted area of the river also had higher levels of cysteine in the muscle, along with increases in aspartic acid, glutamic acid, and alanine. Elevated concentrations of cysteine seem to be associated with a threat to these fish species in polluted sections of the river, and thus may be used as a biomarker.

Toxicity of copper and zinc to Puntius parrah (Day, 1865)

The toxicities of the trace metals copper and zinc on the fish Puntius parrah were assessed based on standard renewal bioassay methods, and the 96 h LC50 values for copper and zinc were 0.5 mg/L and 9 mg/L, respectively. The zinc and copper concentrations in water and sediment were high in a highly industrialized area compared with those in non-industrialized zones of the Periyar River. The fish exposed to a sublethal concentration of 0.05 mg/L of Cu and 0.9 mg/L of Zn showed a higher accumulation of both of the metals in the liver than in the kidneys, gills, and muscles. The histological changes induced by copper and zinc on the test organism under sublethal concentrations on the 3rd, 7th, 14th, and 28th -days of exposure were also studied. There was a significant decrease (p < 0.001) in the erythrocyte count after exposure to sublethal concentrations, whereas the hemoglobin, hematocrit, and mean corpuscular hemoglobin concentrations were significantly decreased after 28 days of exposure. Effective management strategies need to be developed and implemented to protect water bodies and aquatic organisms from trace metal pollution and its toxic effects.

The toxicology of mercury and its compounds

A concentrated review on the toxicology of inorganic mercury together with an extensive review on the neurotoxicology of methylmercury is presented. The challenges of using inorganic mercury in dental amalgam are reviewed both regarding the occupational exposure and the possible health problems for the dental patients. The two remaining "mysteries" of methylmercury neurotoxicology are also being reviewed; the cellular selectivity and the delayed onset of symptoms. The relevant literature on these aspects has been discussed and some suggestions towards explaining these observations have been presented.

Degeneration of peripheral nervous system in rats experimentally induced by methylmercury intoxication

The objective of this study is to elucidate the primary action of methylmercury chloride (MMC) intoxication on peripheral nervous system. We chronologically observed the pathological changes of sciatic nerve, dorsal root ganglion (DRG) neurons, ventral and dorsal roots in rats given 4 mg/kg/day of MMC on consecutive days and killed on days 11, 15, 18 and 21. On day 11, an initial axonal degeneration of type B neuron occurred, predominantly in the distal portions of sciatic nerve. The DRG type A neuron was infiltrated by MRF-1-positive macrophages on day 11. Electron microscopy also demonstrated degenerated mitochondria in type A neuron. On day 21, most of type A neurons seemed to have disappeared. However, type B neurons were well preserved. Immunoblotting with monoclonal antibodies, P0 and neurofilament, demonstrated that both of proteins significantly decreases from day 15. In conclusion, these results indicate that the primary action on type A neuron is the neuron body that consequently results in an anterograde degeneration of nerve fibers, while the type B neuron degeneration occurs in a dying-back process in this subacute model. These findings suggest that the mechanisms involved in the degeneration induced by MMC vary and may depend on certain intrinsic factors peculiar to these neurons.

Mercury exposure and public health

Mercury is a metal that is a liquid at room temperature. Mercury has a long and interesting history deriving from its use in medicine and industry, with the resultant toxicity produced. In high enough doses, all forms of mercury can produce toxicity. The most devastating tragedies related to mercury toxicity in recent history include Minamata Bay and Niagata, Japan in the 1950s, and Iraq in the 1970s. More recent mercury toxicity issues include the extreme toxicity of the dimethylmercury compound noted in 1998, the possible toxicity related to dental amalgams, and the disproved relationship between vaccines and autism related to the presence of the mercury-containing preservative, thimerosal.

Neuromotor deficits and mercury concentrations in rats exposed to methyl mercury and fish oil

It has been suggested that docosahexaenoic acid (DHA) or other n-3 polyunsaturated fatty acids (PUFAs) may prevent or ameliorate methyl mercury's neurotoxicity. To examine interactions between PUFAs and methyl mercury exposure, sixty-six female Long-Evans rats were exposed to methyl mercury continuously via drinking water from fifteen weeks of age. Water included methyl mercury concentrations of 0, 0.5, and 5.0 ppm, creating estimated intakes of about 0, 40, and 400 microg/kg/day across exposure groups. An additional fifty-eight female offspring were exposed to methyl mercury only during gestation. Rats consumed one of two diets, each based on AIN-93 formulation, providing a 2 (generation) X 2 (diet) X 3 (methyl mercury exposure) factorial experimental design. A "coconut oil" diet (1/3 of fats were provided by coconut oil) was marginally adequate in n-3 PUFAs and contained no DHA. A "fish oil" diet was rich in n-3 fatty acids, including DHA. The diets were approximately equal in n-6 fatty acids. Forelimb grip strength declined with age for all groups, but the decline was greatest for those exposed chronically to 400 microg/kg/day of methyl mercury. This high-dose group also displayed hind limb crossing, gait disorders, and diminished running wheel activity. Dietary n-3 fatty acids did not influence these effects. Chronic exposure to 400 microg/kg/day of methyl mercury resulted in blood and brain concentrations of about 70 and 10 ppm, respectively, approximately 50-fold higher than concentrations seen in rats exposed to 40 microg/kg/day. Rats that became ill and died before the experiment ended had higher concentrations of mercury than their cohorts who survived to the end. Organic mercury was highly correlated with total mercury in these rats but inorganic mercury remained approximately constant. Some deaths were due to urolithiasis (kidney or bladder stones) associated with a dietary contaminant and that was eventually fatal to 22% of the females in the colony. Neurobehavioral effects are reported on rats that did not become ill.

Organic mercury compounds: human exposure and its relevance to public health

Humans may be exposed to organic forms of mercury by either inhalation, oral, or dermal routes, and the effects of such exposure depend upon both the type of mercury to which exposed and the magnitude of the exposure. In general, the effects of exposure to organic mercury are primarily neurologic, while a host of other organ systems may also be involved, including gastrointestinal, respiratory, hepatic, immune, dermal, and renal. While the primary source of exposure to organic mercury for most populations is the consumption of methylmercury-contaminated fish and shellfish, there are a number of other organomercurials to which humans might be exposed. The antibacterial and antifungal properties of organomercurials have resulted in their long use as topical disinfectants (thimerosal and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Phenylmercury has been used in the past in paints, and dialkyl mercurials are still used in some industrial processes and in the calibration of certain analytical laboratory equipment. The effects of exposure to different organic mercurials by different routes of exposure are summarized in this article.

Changes in neuropeptide immunoreactivity in cultured adult mouse sensory neurons following methylmercury chloride treatments

Changes in the neuropeptide expression of sensory neurons, related to functional modulation, have been widely reported both following physical injury in vivo, and after toxic insult in vitro and in vivo. The current immunocytochemical study aimed to monitor the neuropeptide status of neuronal cultures prepared from adult mouse dorsal root ganglia (DRG), and to ascertain whether changes occurred following treatments with 0.1-1 microM methylmercury (MeHg). Proportions of both substance P (SP) and calcitonin gene related peptide (CGRP) containing neurons increased significantly, and were maintained throughout the 24 h exposure period. In contrast the numbers of somatostatin (SOM)-ir neurons decreased. Substance P- and CGRP-ir neuron increases may be related to nociceptive responses, whereas the decreases in SOM containing neurons could reflect a differential loss in this subset of sensory neurons.

The effect of selenium on the localization of autometallographic mercury in dorsal root ganglia of rats

The autometallographic technique was used to demonstrate the localization of mercury in dorsal root ganglia of adult Wistar rats. The animals were either exposed to mercury vapour, 100 micrograms Hg m-3, 6 h day-1, 5 days per week, or treated with organic mercury in the drinking water, 20 mg CH3HgCl per litre, for 4 weeks. The effect of orally administered sodium selenite on the pattern of intracellular distribution of mercury in these two situations was investigated. In rats exposed to mercury vapour alone, faint staining was present in ganglion cells. The selenite induced a conspicuous increase in the number of stained cells and in the intracellular staining intensity. In rats treated with organic mercury, mercury deposits were detected within ganglion cells and macrophages. The number of mercury-containing cells was increased by co-administration of selenite. In addition, satellite cells, the capsule and vessel walls were faintly stained. Twenty weeks after cessation of the organic mercury treatment, mercury staining was reduced. Again, selenite treatment enhanced staining intensity. When studied using the electron microscope, mercury was restricted to lysosomes, irrespective of treatments. The present study shows that the deposition of autometallographic mercury in the dorsal root ganglia depends on the chemical type of mercury, the co-administration of selenite and the length of the survival period.

The localization of mercury and metallothionein in the cerebellum of rats experimentally exposed to methylmercury

Rats were dosed with methylmercuric chloride, either by gastric gavage (5 x 10 mg kg-1 body weight over a 15-day period), or in their drinking water (20 mg methylmercuric chloride l-1 for 14 or 42 days). Localization of mercury within the cerebellum was performed with a silver physical development technique, and metallothionein with dinitrophenyl hapten-sandwich immunohistochemistry. Mercury was detected in structurally undamaged Purkinje neurones and adjacent Bergmann glial cells; no mercury was detected in granule cells even though these small cells nearest the Purkinje layer had a high incidence of pyknotic nuclei. In general, metallothionein was detected mainly in Bergmann glial cells, Purkinje cells, astrocytes and glial cells of white matter; no metallothionein was detected in granule cells. We hypothesized that the resistance of Purkinje cells to methylmercuric chloride reflects their ability to transform organic mercurials to inorganic mercury that, in turn, induces the synthesis of radical-scavenging metallothionein molecules.

In vivo and in vitro effects of methylmercury on the activities of aminoacyl-tRNA synthetases in rat brain

The activities of six aminoacyl-tRNA synthetase species were determined using enzyme preparations partially purified from the brains of control and methylmercury (MeHg)-treated rats. The activities of Asp-, Leu- and Tyr-tRNA synthetases were significantly reduced in the brains of MeHg-intoxicated rats, whereas those of Lys- and Met-tRNA synthetases remained unchanged. In contrast, the activity of His-tRNA synthetase was significantly increased in the symptomatic phase of MeHg intoxication. The activities of these six aminoacyl-tRNA synthetases in the control brains were affected to different extents on the direct addition of MeHg to the assay system in vitro. No positive correlation was observed between the in vivo and in vitro effects of MeHg on the enzyme activities. These results indicate that the aminoacylation of tRNA is one of the actions of MeHg, which leads to inhibition of protein synthesis, and it is suggested that the syntheses of cellular proteins may be modified in different ways by MeHg, depending on their amino acid compositions.

In vivo incorporation of [14C]leucine into brain protein of mice treated with methylmercury and thiol complexes of methylmercury

The effect of methylmercury and thiol complexes of methylmercury on inhibition of protein synthesis was evaluated. Mice were injected (i.p.) with the following treatments: methylmercuric chloride, methylmercury-glutathione, methylmercury-cysteinylglycine and control (vehicle) for 10 days. Ten animals from each group were injected with [14C]leucine 90 min prior to death. The brains were removed and the extracted protein was subjected to liquid scintillation analysis. Mice receiving the methylmercury and methylmercury-glutathione treatments exhibited significantly greater weight loss than the control while the methylmercury-cysteinylglycine treatment was not significantly different than the control. Incorporation of [14C]leucine into brain protein was significantly depressed in the methylmercury (81% of control) and the methylmercury-glutathione (79% of control) treatments. Protein synthesis in mice receiving the methylmercury-cysteinylglycine complex although not significantly different than the methylmercury treatments was only 92% of the control mice.

Effects of methylmercury on hypnotic action of hexobarbital, liver hydroxylase and cytochrome P-450 in mice

The effects of methylmercury hydroxide (MeHgOH) on the hypnotic action of hexobarbital was investigated in adult 129/SvSl mice of both sexes. It was found that there was no sex difference in the response to MeHgOH treatment. The action of MeHgOH was intimately related to the interval between MeHgOH administration and the test of hexobarbital hypnosis. A biphasic effect was observed. An initial dose-dependent prolongation of hexobarbital hypnosis was observed in animals pretreated with MeHgOH 24 h earlier. If the interval was extended from 24 h to 1 week, a shortening of sleeping time was observed in MeHgOH treated animals. The animals recovered from the effects of MeHgOH in 3 weeks. The initial effect of MeHgOH was found closely related to the decrease in the rate of hexobarbital metabolism in the liver through lowering of cytochrome P-450 concentration. On the other hand, the delayed shortening of hexobarbital hypnosis was not related to the rate of hexobarbital metabolism. It is assumed that the delayed effect of MeHgOH on the hexobarbital hypnosis is due to MeHgOH acting on the central nervous system to decrease its sensitivity to hexobarbital via interaction with the barbiturate receptors on the GABA-chloride ionophore complex. In animals exposed in utero to MeHgOH, it was found that the duration of hexobarbital-induced sleeping time was significantly longer in the offsprings tested for hexobarbital hypnosis 3.5 months after birth following prenatal exposure to MeHgOH. Repeated administration of hexobarbital to adult offsprings prenatally exposed to MeHgOH and to control mice shortened hexobarbital sleeping time, however, the maximum shortening capacity was smaller in the treated group. It is concluded that the hypnotic action of hexobarbital in mice can be altered by MeHgOH exposure both prenatally and postnatally. The effects of prenatal exposure to MeHg were observed in adult offsprings, indicating that MeHg may have a functional teratogenic effect on barbiturate-induced hypnosis in the absence of gross anomalies.

Chronic idiopathic ataxic neuropathy

Fifteen patients with chronic sensory ataxia caused by a large-fiber sensory neuropathy were studied and followed up for a period of 17.4 years (range, 4 to 41). When first seen, they had distal paresthesias and sensory ataxia of slow onset and progression, areflexia, normal strength, and a profound loss of proprioceptive and kinesthetic sensation extending up to the most proximal joints. Needle electromyogram and motor-nerve conduction velocity findings were normal in most of the patients and sensory potentials were absent in all. Nerve biopsy showed severe loss of the large myelinated fibers. Nine patients had a serum monoclonal or polyclonal gammopathy (3 with IgM kappa, 1 with IgA kappa, and 5 with a polyclonal increase of IgG, IgA, or IgM), and 8 had elevated cerebrospinal fluid gamma globulin levels in spite of low normal total cerebrospinal fluid protein levels. No circulating antibodies to ganglionic neurons were found. Therapy with immunosuppressants or plasmapheresis was unsuccessful. All patients are disabled and their conditions have continued to worsen without signs of malignancy or systemic illness during a mean follow-up period of 17.4 years. Chronic idiopathic ataxic neuropathy is a proprioceptive neuropathy, clinically indistinguishable from the one associated with carcinoma or pyridoxine abuse due to involvement of the dorsal root ganglia, and could represent a distinct form of an indolent, slowly progressive sensory neuronopathy (ganglionopathy). Although immunopathological mechanisms may play a role, especially in patients with an associated paraproteinemia, the resistance of such patients to therapy, the progressive course, and the resemblance of this disorder to other toxic neuronopathies associated with pyridoxine abuse or doxorubicin administration suggest a possible toxic etiopathogenesis.

Changes in the distribution of histochemically localized mercury in the CNS and in tissue levels of organic and inorganic mercury during the development of intoxication in methylmercury treated rats

The development of neurotoxicity in rats after exposure to methylmercuric chloride was monitored using behavioural indices. At selected time points the cellular localization of mercury and the relative amounts of organic and inorganic mercury were determined in several regions of the CNS, and in some non-neural tissues. The CNS showed an affinity for organic mercury, the levels of inorganic mercury remaining low throughout symptomatic intoxication. Histopathological changes were not closely related to the regional tissue content of the organic or inorganic forms, nor to mercury localized histochemically at the cellular level. The stained deposits, which had focal cytoplasmic distribution, appeared in glial cells initially then in larger neurones as the intoxication progressed. These observations may represent changes in the mercury content of different cell types or reflect differences in the way that they handle a similar burden of mercury. A transitory accumulation of mercury in glial cells may be a factor contributing to the occurrence of a latent period and sequestration of mercury in cytoplasmic organelles may serve to protect some cell types from injury.

Methyl mercury ototoxicity in mice determined by auditory brainstem responses

Mice of the C57 B1/6 strain were used to assess auditory deficits due to methyl mercury chloride intoxication. Auditory Brainstem Responses were obtained to pure-tone stimuli from 4 to 78 kHz. Physiologic thresholds were compared with behavioral methods for determining audibility in mice. Two dosage levels were studied; 4 and 8 mg/kg. Recordings were taken weekly, for each mouse, for 3 consecutive weeks after initial injection. Analysis of physiologic threshold and latency indicated that methyl mercury chloride causes auditory deficits at all frequencies tested with the greater effect in the higher frequencies. Additionally, latencies indicated nerve conduction hypersensitivity in the brainstem.

Effects of methyl mercury on protein synthesis in vitro

Methyl mercury has been shown to interact with protein synthesis in vivo and in vitro. In the present paper a brain postmitochondrial supernatant was used for studies in vitro. Inorganic mercury (Hg2+) was shown to be more potent inhibitor of protein synthesis than methyl mercury, puromycin or cycloheximide. The inhibitory effect of methyl mercury was potentiated by puromycin. It is thus possible that methyl mercury causes disintegration of polysomes in brain cells.

Effect of methylmercury and inorganic mercury on the nerve growth factor-induced neurite outgrowth in chick embryonic sensory ganglia

Methylmercury inhibited the fiber outgrowth in chick embryonic sensory ganglia in the presence of nerve growth factor (NGF) by 50% at 2 x 10(-6) M and completely depressed it at 5 x 10(-6) M. Whereas inorganic mercury completely inhibited the fiber outgrowth at 10(-4) M. The possible role of microtubules is discussed.

A Golgi and electron-microscopic study of cerebellum in methylmercury-poisoned neonatal mice

Neonatal C57BL/6J mice were injected with 5 mg/kg body weight of 203Hg-labeled methylmercuric chloride on postnatal days 3, 4, and 5, totaling 15 mg/kg body weight per animal. The experimental and control animals were sacrificed on postnatal by 15. Whole body radioactivity of 203Hg progressively increased during the 3-day injection period and reached the peak level and remained at peak levels until the time of sacrifice. This indicates a lack of clearance of 203Hg by neonatal mice during the period examined in this study. Golgi preparations of cerebella of MeHg-treated animals revealed significant reduction in dendritic arborization of Purkinje cells. Ultrastructurally, the vascular endothelium showed attenuation with increased electron density and frequent vacuolization of cytoplasm. Marked swelling of perivascular glia was noted in most of the capillaries throughout the cerebella of MeHg-treated animals.

The acute sensory neuronopathy syndrome: a distinct clinical entity

Four to twelve days following initial antibiotic treatment for a febrile illness, three adults suddenly experienced numbness and pain over the face and entire body. Each had received a penicillin or a semisynthetic derivative, and two patients also received other antibiotics. Signs appeared rapidly and included profound sensory ataxia, areflexia, and widespread sensory loss, primarily of large fiber modalities (proprioceptive sensibility). Slowed or absent sensory conduction was found. There was no weakness, and electrical study of muscle and motor nerve conduction was normal in all. The cerebrospinal fluid was acellular, and protein levels were elevated to 126 and 175 mg/dl in two cases and were normal in the other. Presently, all have a severe, static, residual sensory deficit. During follow-up of five years, no evidence of neoplastic disease or immunological disorder has appeared. Because of the rapid onset, widespread and pure sensory involvement, and poor recovery, the lesion is most likely confined to the dorsal root and gasserian ganglia (sensory neuronopathy). This pattern resembles that of the experimental lesions induced by doxorubicin and pyridoxine. It appears likely that either the previously administered antibiotics or the illness for which they were administered were of pathogenetic importance. We designate this previously unrecognized disorder the acute sensory neuronopathy syndrome and suggest that it represents a distinct, readily identifiable clinical entity.

Morphometric evaluation of primary sensory neurons in experimental p-bromophenylacetylurea intoxication

To evaluate the three-dimensional pathology of lumbar primary sensory neurons in p-bromophenylacetylurea intoxication, the number and size distribution of neurons and of myelinated fibers were evaluated at the L-6 spinal ganglion level and at proximal and distal levels of sural nerve and thoracic (proximal) and cervical (distal) levels of Goll's tract, respectively, 2 and 6 weeks after the intoxication in rats. The number and size distribution of ganglion neuron cell bodies were not significantly different between intoxicated and control rats. The distal level of sural nerve had significantly fewer large myelinated fibers than did control, and a significantly higher frequency of fibers undergoing degeneration. Proximal levels of sural nerve showed similar, but less severe changes. Similarly, the myelinated fibers of Goll's tract were significantly more affected at cervical than at thoracic level. Therefore, by morphometric criteria both centrally and peripherally directed myelinated fibers are most affected distally and less affected proximally while neuron cell bodies are not affected at all. These three-dimensional morphological changes must be taken into consideration in formulating possible mechanisms for the development of this neuropathy.

Histochemical demonstration of mercury induced changes in rat neurons

A histochemical method modified for ultrastructural studies of mercury induced changes is described. Rat neurons from areas known to be influenced by mercury are used as examples. The histochemical reaction, suggested to be caused by polymercury sulphide complexes, is localized to "dense bodies" where it is visible 14 days after initiation of peroral mercury treatment (20 mg HgCl2/l drinking water).

Accumulation and removal of Hg203 in different regions of the rat brain

We have studied the brain regional distribution of methyl mercury following intravenous administration of CH3 203HgCl in rat. Early peak levels were obtained in cerebellum, medulla oblongata and midbrain. The efficacy of removal of 203Hg by different chelators is also region dependent. The most efficient chelator for brain mercury proved to be mesodimercaptosuccinic acid.

Evoked potential alterations following prenatal methyl mercury exposure

Pregnant hooded rats were administered either 5 mg/kg CH3, Hg or 0 mg/kg CH3 Hg by gastric intubation on day seven of gestation. Female offspring were implanted with recording electrodes 60 days after birth and had their cortically recorded visual evoked potentials studied at four different flash intensities. Mercury exposed animals had higher P1-N1 and N1-P2 amplitudes and shorter P2 and N2 latencies than controls. The data provides evidence that a single ingestion of CH3 Hg by pregnant rats is sufficient to produce long term alterations in CNS activity.