Mercury Distribution in the Neonatal and Adult Cerebellum after Mercury Vapor Exposure of Pregnant Squirrel Monkeys

Abstract

The objectives of the study were (1) to map the detailed localization of mercury in the monkey cerebellum after mercury vapour exposure; (2) to investigate whether there is any difference in mercury distribution between neonatal and adult cerebellum after mercury vapor exposure; (3) to investigate the ability of mercury to accumulate in the cerebellum years after the end of exposure. Pregnant squirrel monkeys were exposed 5 days/week to mercury vapor at a concentration of 0.5 mg Hg/m3 air 4 or 7 h/day or 1 mg Hg/m3 air for 4 or 7 h/day. Mercury concentration in the offspring and maternal brains was examined by cold vapor, flameless atomic absorption spectrophotometry. Mercury distribution was examined by processing cerebellar sections for autometallographic (AMG) silver enhancement. Mercury concentration in the offspring cerebral occipital pole ranged between 0.20 and 0.70 μg Hg/g tissue, and in the maternal between 0.80 and 2.58 μg/Hg tissue in animals killed immediately after the end of exposure. AMG revealed that the external granule cell layer of offspring cerebellar tissue contained small amounts of mercury. The molecular layer contained mercury in some of the mercury-exposed monkeys. In the Purkinje cell layer, the Bergmann glial cells together with the Purkinje cells contained mercury. The granule cells and the Golgi 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 mercury. 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 mercury. This pattern corresponded well to the mercury concentrations found in the cerebral occipital pole. The differences found in mercury accumulation were 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.