Effects of food deprivation on open-field behavior of mice exposed to methyl mercury

The joint effects of methyl mercury and food deprivation on activity of 40 mice in an open field were examined. Analysis gave a significant main effect for mercury but not deprivation, and a significant interaction between mercury and deprivation. Simple tests indicated that food deprivation enhanced the depression of activity associated with exposure to mercury.

Degradation of methylmercury by bacteria isolated from environmental samples

A total of 207 bacterial cultures, isolated from environmental samples, was screened for ability to degrade methylmercury. Of these, 30 were found positive for aerobic demethylation. Twenty-two of these were shown to be facultative anaerobes and 21 of these degraded methylmercury anaerobically. All positive species volatilized methylmercury aerobically, and methane was produced as a degradation product. Although methylmercury degradation was complete in most cases, material balances indicated some of the inorganic mercury formed was not volatilized and is presumed bound to the cells. All positive isolates were tolerant to at least 0.5 mug of methylmercury per ml, and the extent of volatilization of mercury increased with concentration to the threshold value. The results indicate that demethylating species are prevalent in the environment and may be important in suppressing the methylmercury content of sediments.

Action of some centrally active drugs and heavy metals on in vitro oxidation of dopamine by rat brain tissue

The effect of chlorpromazine, amitryptyline, amphetamine, diphenhydramine, and iproniazid on the in vitro oxidation of dopamine to melanin by rat brain mitochondrial preparation was investigated. Chlorpromazine and amitryptyline very markedly inhibited the oxidation (ED50 60 and 180 μM, respectively) while iproniazid was ineffective. Other drugs were moderately active. The reaction was enzyme catalyzed and could not be ascribed to the anionic component. Chronic administration of chlorpromazine and amitryptyline (19 and 9.5 mg/kg, i.p.) produced a biphasic response characterized by stimulation of melanogenesis during the first 2–3 weeks followed by inhibition. On the other hand, physostigmine and choline markedly stimulated the oxidation process. The chronic ingestion of heavy metals; mercury, lead, and cadmium, up to toxic levels had no effect on the in vitro oxidation of dopamine.

The morphologic effects of dieldrin and methyl mercuric chloride on pars recta segments of rat kidney proximal tubules

This investigation was undertaken to evaluate the morphologic effects in rat kidney resulting from chronic exposure to low doses of the pesticide dieldrin, methyl mercuric chloride (CH(3)HgCl) and the combination of dieldrin plus CH(3)HgCl. Histologic and ultrastructural changes were confined to the proximal tubules. Alterations in these tubules were consistent and reproducible for each regimen and did not become more severe with duration of exposure. The straight segment of the proximal tubule (pars recta) was more severely affected by dieldrin and CH(3)HgCl than the convoluted portion. Female rats were more markedly affected than males. Pars recta tubule cells of male and female rats exposed to dieldrin showed an increase of smooth endoplasmic reticulum (SER). Male rats displayed a greater increase in SER than females. Pars recta tubule cells of animals given CH(3)HgCl also exhibited increased amounts of SER, degenerating mitochondria and cell death. Pars recta tubules of females were dilated and contained within the lumens many spherical, hematoxylin-positive staining, cytoplasmic masses, which were visible by light microscopy. These masses were characterized ultrastructurally by the presence of an SER aggregate in an area of material similar to cell matrix. In addition, cells of the pars recta of female animals contained electron-dense membranous cytosomes not present in control animals. Pars recta cells of males showed an increase in SER, but the dense membranous cytosomes observed in the pars recta cells of female rats were not seen. Rats exposed to dieldrin plus CH(3)CgCl showed less morphologic alteration of the pars recta tubules than animals given methyl mercuric chloride; however, increased amounts of SER and more degeneration in tubule cells were observed in these animals when compared to control animals. The findings are discussed in relation to the conversion of CH(3)HgCl to inorganic mercury in vivo and the known toxicity of inorganic mercury to the pars recta. Decreased tubular alteration in males and dieldrin-treated animals may be explained by sexual differences in renal enzyme levels or activities and the induction of microsomal enzyme systems by dieldrin.

Subtle consequences of methylmercury exposure: behavioral deviations in offspring of treated mothers

Overt neurological impairment is the endpoint currently used to document a case of methylmercury poisoning. No consideration is given to possible subtle consequences. Offspring from mice exposed to methylmercury on day 7 or 9 of pregnancy were apparently unaffected during postnatal development. However, subtle behavioral differences between treated and control offspring were found when the overtly normal animals were tested in an open field and evaluated in a swimming apparatus at 1 month of age. Brain weight, protein, choline acetyltransferase, and cholinesterase were not significantly altered.