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Chronic effects of methylmercury in rats. II. Pathological aspects
K Eto1, A Yasutake, K Miyamoto
1National Institute for Minamata Disease, Japan.
Abstract:
Chronic effects of methylmercury (MeHg) were examined pathologically in male Wistar rats fed on diet containing 0, 1 or 5 ppm Hg (as MeHg) for two years. Organs including the central nervous tissues were examined histopathologically using hematoxylin and eosin (H & E), Klüver-Barrera (KB), PAS or phenol-congo red stains. The peripheral nerve system tissues were also examined, using H & E and trichrome stains. Furthermore, immunoglobulins of renal specimens were demonstrated by direct immunofluorescence microscopy. Localization of mercury in the paraffin-embedded sections of the nervous tissue, kidney, liver, pancreas, spleen and testis was demonstrable by the photoemulsion histochemical method. In the 5 ppm group, mercury was readily detectable in tissues of the rats exposed for one year, one and half years, two years and two and half years. Mercury was detected in the cells of the brain such as neurons, neuroglial cells, and phagocytes, and also in most organs, particularly in the epithelium of renal tubules, liver cells, myocardium, in the macrophages of pancreas, spleen and testis. In the 1 ppm group, mercury was detectable in the epithelium of renal tubules and liver cells. Fibrosis of the glomeruli was found in the rat group given a high dose of methylmercury with all experimental methods. Granular IgG, IgM and C3 deposits were demonstrated in the glomeruli by direct immunofluorescence microscopy. The etiology of the pathological changes of glomeruli was suspected to be autoimmune glomerulopathy due to inorganic mercury filtration for a long time. It was difficult to determine the clinical signs and symptoms and pathological changes in the nervous system in spite of the deposition of mercury in the brain.
Insights
Chronic methylmercury (MeHg) exposure in rats caused kidney damage, suspected autoimmune glomerulopathy, and mercury accumulation in various organs, including the brain. Pathological changes in the nervous system were difficult to ascertain despite mercury deposition.
Area of Science:
- Toxicology
- Pathology
- Neuroscience
Background:
- Methylmercury (MeHg) is a potent neurotoxin with known chronic health effects.
- Understanding the long-term pathological consequences of MeHg exposure is crucial for public health.
- Wistar rats are a common model for studying chronic toxicity.
Purpose of the Study:
- To investigate the chronic pathological effects of methylmercury (MeHg) exposure in male Wistar rats.
- To determine the distribution and accumulation of mercury in various organs and tissues.
- To explore potential autoimmune mechanisms in MeHg-induced kidney damage.
Main Methods:
- Rats were fed diets containing 0, 1, or 5 ppm MeHg for two years.
- Histopathological examination of central and peripheral nervous system tissues using various stains (H&E, KB, PAS, phenol-congo red, trichrome).
- Immunofluorescence microscopy for immunoglobulins (IgG, IgM, C3) in renal specimens and histochemical methods for mercury localization.
Main Results:
- Mercury was detected in brain cells (neurons, neuroglial cells, phagocytes) and organs (kidney tubules, liver, myocardium, pancreas, spleen, testis) in the 5 ppm group.
- The 1 ppm group showed mercury in renal tubules and liver cells.
- Glomerular fibrosis and immune deposits (IgG, IgM, C3) were observed in the high-dose group, suggesting autoimmune glomerulopathy.
- Nervous system pathology was difficult to correlate with mercury deposition.
Conclusions:
- Chronic methylmercury exposure leads to mercury accumulation in multiple organs and induces glomerular fibrosis.
- The observed renal pathology suggests an autoimmune mechanism triggered by mercury.
- Further research is needed to elucidate the precise neurotoxic mechanisms and clinical manifestations of chronic MeHg exposure.