Kenneth R. Reuhl

Neuropathology of trimethyltin intoxication: I. Light microscopy study

Abstract BALB c mice with average body weight of 25 g were injected intraperitoneally with trimethyltin chloride (TMT) at a dosage of 3.0 mg TMT/kg body wt. Control animals were injected with saline solution. Mice were found to be extremely sensitive to TMT toxicity. Within 24 hr postinjection, the TMT-treated animals displayed severe tremor, hyperexcitability, and aggression. All animals were sacrificed at 48 hr postinjection by intracardial perfusion with glutaraldehyde. Neuronal degradation could be observed in the neocortex, hippocampus, pyriform cortex, amygdaloid nucleus, and brain stem. In the hippocampus, severe neuronal necrosis was found among the granule cells of the fascia dentata with relatively sparing of the pyramidal cells of the Ammons horn. Degeneration of some large brain stem neurons was also a prominent finding, particularly those neurons in the mesencephalic trigeminal nuclei. Chromatolytic and hyalinization of these nerve cells occurred with eventual disintegration and vacuolation of the neurons. Electron microscopic findings will be presented in future papers of the series.

Degenerative changes in the developing nervous system as a result of in utero exposure to methylmercury

Abstract Tissue samples from the cerebral and cerebellar cortex of neonatal rats which had been prenatally exposed to low doses of methylmercury were examined by electron microscopy. Although all these neonates appeared to be physically normal, ultrastructural examination revealed various degenerative changes in their nervous systems. The most prominent pathological findings, including disruption and myelin-figure formation of the nuclear membranes and large areas of focal degradation and endothelial damage, were found in both the cerebellum and cerebral cortex of the animals. The present study provides evidence that minute amounts of methylmercury, which by itself may produce no significant injury to the maternal tissues nor any observable gross teratology of the neonate, may still be hazardous to the developing nervous system.

Prenatal and Neonatal Toxicology and Pathology of Heavy Metals

Publisher Summary This chapter presents only those metals that have the greatest health hazard. Because the established information on the toxic effects of each metal varies, different emphasis will be put on each of the toxic metals. It can be stated that mercury, cadmium, and lead all have deleterious impacts on the development of the fetus; however, the specific fetotoxicity and teratogenicity of each of these metals differ. It is difficult to make any definitive conclusion or to extrapolate the animal findings to human situations. Many of the problems are associated with the differences in animal species used in the studies, the dose levels used, the chronicity of the intoxications, the gestational stages explored, and the lack of interdisciplinary correlations. Thus, a direct comparison of the findings is almost impossible. The phenomena of metal-metal interaction and metal–element interaction within maternal and fetal systems make the overall understanding of metal toxicology that much more complex. There is no doubt that metal-induced teratology represents one of the most important areas in toxicology.

Neuropathology of trimethyltin intoxication: II. Electron microscopic study on the hippocampus

Abstract When mice ( BALB c ) were given a single injection of trimethyltin chloride (TMT) at a dosage of 3.0 mg TMT/kg body wt, extensive lesions were observed in the hippocampus at 48 hr after TMT administration. Electron microscopy revealed extensive neuronal necrosis among the granule cells and many of these necrotic neurons also displayed the phenomenon of karyorrhexis (fragmentation of the pyknotic nuclei). Although few necrotic cells were found among the pyramidal neurons, extensive accumulation of lysosomes was found within the neuronal bodies and processes of these nerve cells. Intracellular edema was a prominent finding in both cell types of the hippocampus. Such phenomenon was represented by severe distention of the cytoplasmic membrane systems (endoplasmic reticulum and Golgi complex) within the pyramidal cells and extensive swelling of the cytoplasm and neuronal processes of the granule neurons. Vacuolation of both cell types occurred as a result of these edematous conditions. It is postulated that TMT induced a severe disruption of oxidative phosphorylation and ATP production in these neurons leading to rapid cell death and/or cellular edema of these nerve cells.

Effects of methyl mercury on the microtubule system of mouse lymphocytes

The effects of in vivo and in vitro methyl mercury (MeHg) treatments on the microtubule system of murine splenic lymphocytes were examined by immunofluorescence microscopy. In vitro exposures to 1 to 10 microM MeHg resulted in time- and concentration-dependent microtubule disassembly. Lymphocytes isolated from mice receiving a single 10 mg/kg injection displayed microtubule damage when examined 2 and 5 days post-treatment. The capacity of in vivo and in vitro treated lymphocytes to respond to the mitogen concanavalin A (Con A) was generally inhibited by MeHg. There was a good correlation between the degree of microtubule disassembly and the inhibition of mitogen responsiveness. In vivo and in vitro treatments that resulted in extensive microtubule damage suppressed the ConA response and blocked lymphocytes early in the stimulation sequence. In vitro MeHg treatment late in mitogenesis caused a rapid, concentration-dependent inhibition of [3H]thymidine incorporation. These results suggest that damage to the microtubule system can serve as an indicator of MeHg toxicity and may underlie the toxicants effects on lymphocyte functions.

The effects of methylmercury on the cytoskeleton of murine embryonal carcinoma cells

Immunofuorescence staining with antibodies to tubulin and vimentin and staining with phalloidin have been used to examine the effects of methylmercury on the cytoskeleton of embryonal carcinoma cells in culture. Exposure of embryonal carcinoma cells to methylmercury (0.01 to 10 μm) resulted in concentration- and time-dependent disassembly of microtubules in interphase and mitotic cells. These effects were reversible when cultures were washed free of methylmercury. Spindle microtubules were more sensitive than those of interphase cells. Spindle damage resulted in an accumulation of cells in prometaphase/metaphase, which; correlated with a temporary delay in the resumption of normal proliferation rate upon removal of methylmercury. Of the interphase cytoskeletal components, microtubules were the first affected by methylmercury. Vimentin intermediate filaments appeared relatively insensitive to methylmercury, but showed a reorganization secondary to the microtubule disassembly. Actin microfilaments appeared unchanged in cells showing complete absence of microtubules. Our results 1) support previous reports suggesting that microtubules are a primary target of methylmercury, 2) document a differential sensitivity of mitotic and interphase microtubule systems and 3) demonstrate the relative insensitivities of other cytoskeletal components.

Pathological effects of in utero methylmercury exposure on the cerebellum of the golden hamster: I. Early effects upon the neonatal cerebellar cortex

Abstract Pregnant golden hamsters ( Mesocricetus auratus ) were given either a single dose of 10 mg methylmercury/kg on gestational day 10 or daily doses of 2 mg/kg on gestational days 10–15. Cerebella of experimental and control offspring were examined by light and electron microscopy during the first month of postnatal life. Degenerative changes, characterized by accumulations of lysosomes and areas of floccular cytoplasmic degradation, were frequently observed in neuroblasts of the external granular layer (EGL) as well as in more differentiated neural elements in the molecular and internal granular layers. Pyknotic nuclei were seen singly and in groups throughout the EGL of treated animals. Developing dendrites appeared particularly sensitive to methylmercury. Affected dendrites were swollen and packed with degenerating cytoplasmic material. Astrocytes and perivascular macrophages also contained large aggregates of irregular electron-opaque debris, lysosomes, and large lipid droplets. Pathological alterations in the cerebellum were most pronounced during the first 15 days of postpartum life.

Microtubular Aggregates in the Rough Endoplasmic Reticulum of a Myxoid Chondrosarcoma

A tumor with the light microscopic and histochemical characteristics of myxoid chondrosarcoma is examined ultrastructurally. Instead of the usual features of chondroblasts, the tumor cells exhibited prominent collections of long straight microtubules within the endoplasmic reticulum. This finding is compared with other previously reported tubular aggregates. The differential diagnosis and ultrastructure of myxoid chondrosarcoma are also discussed.

Effects of methylmercury on retinoic acid-induced neuroectodermal derivatives of embryonal carcinoma cells

Immunofluorescence staining with antibodies to tubulin, neurofilaments and glial filaments was used to study the effects of methylmercury on the differentiation of retinoic acid-induced embryonal carcinoma cells into neurons and astroglia and on the cytoskeleton of these neuroectodermal derivatives. Methylmercury did not prevent undifferentiated embryonal carcinoma cells from developing into neurons and glia. Treatment of committed embryonal carcinoma cells with methylmercury doses exceeding 1 μM resulted in the formation of neurons with abnormal morphologies. In differentiated cultures, microtubules were the first cytoskeletal element to be affected. Their disassembly was time- and concentration-dependent. Microtubules in glial cells and in neuronal perikarya were more sensitive than those in neuronal processes. Neurofilaments and glial filaments appeared relatively insensitive to methylmercury treatment but showed reorganization after complete disassembly of the microtubules. The data demonstrate 1) the sensitivity of microtubules of both neurons and glia to methylmercury-induced depolymerization, and 2) the heterogeneous response of neuronal

Acute trimethyltin intoxication in the monkey (Macaca fascicularis)

Adult cynomolgus monkeys were administered trimethyltin (TMT) iv in dosages ranging from 0.75 to 4.0 mg TMT/kg and observed for behavioral changes. Animals were subsequently killed for light and electron microscopic examination. TMT showed a dose-related toxicity, with high dose animals (4.0 and 3.0 mg/kg) dying within 24 hr, and low dose animals (0.75 mg/kg) surviving without morphological effects. Animals given 1.10 mg TMT/kg displayed a reproducible clinical course, characterized by tremor, hyperactivity, and ataxia which progressed to stupor and finally unconsciousness. By light microscopy, neuropathology was most pronounced in the CA-3 and CA-4 regions of Ammons horn. Degenerating pyramidal neurons, micro- and astrogliosis, and neuronophagia were commonly observed. Mild degenerative changes were identified in amygdala, medulla, spinal cord, and Purkinje cells. The fascia dentata remained intact. Ultrastructurally, injured neurons contained accumulations of lysosomes and lysosome-like structures within perikarya and neurites. Demyelination or vascular damage was not observed. Data indicate the monkey to be highly sensitive to TMT, with morphological injury most severe in limbic structures.