Mercury distribution in the neonatal and adult cerebellum after mercury vapor exposure of pregnant squirrel monkeys

The objectives of the study were (1) to map the detailed localization of me rcury in the monkey cerebellum after mercury vapour exposure; (2) to invest igate whether there is any difference in mercury distribution between neona tal and adult cerebellum after mercury vapor exposure; (3) to investigate t he ability of mercury to accumulate in the cerebellum years after the end o f exposure. Pregnant squirrel monkeys were exposed 5 days/ week to mercury vapor at a concentration of 0.5 mg Hg/m(3) air 4 or 7h/day or 1 mg Hg/m(3) air for 4 or 7h/day, Mercury concentration in the offspring and maternal br ains was examined by cold vapor, flameless atomic absorption spectrophotome try, Mercury distribution was examined by processing cerebellar sections fo r autometallographic (AMG) silver enhancement. Mercury concentration in the offspring cerebral occipital pole ranged between 0.20 and 0.70 mu g Hg/g t issue, and in the maternal between 0.80 and 2.58 mu g/Hg tissue in animals killed immediately after the end of exposure. AMG revealed that the externa l granule cell layer of offspring cerebellar tissue contained small amounts of mercury. The molecular layer contained mercury in some of the mercury-e xposed monkeys. In the Purkinje cell layer, the Bergmann glial cells togeth er with the Purkinje cells contained mercury. The granule cells and the Gel s cells contained small amounts of mercury. The astrocytes of the medullary layer, identified by immunohistochemistry, contained considerable amounts of mercury, but the cerebellar nuclei accumulated the highest amounts of me rcury. No correlation was found between cellular accumulation and maturity of the brain; that is, the cellular localization of mercury did not differ between adult and neonatal brain, except for the amount of visualized mercu ry. This pattern corresponded well to the mercury concentrations found in t he cerebral occipital pole. The differences found in mercury accumulation w ere instead considered to be dose-related. The results demonstrate that the distribution of mercury in the cerebellum after mercury vapor exposure is similar to the distribution pattern obtained after methyl mercury exposure and that mercury is trapped in the cerebellum over a long period of time. ( C) 2000 Academic Press.