AUTOMETALLOGRAPHIC DETERMINATION OF INORGANIC MERCURY DISTRIBUTION INTHE CORTEX OF THE CALCARINE SULCUS OF THE MONKEY MACACA-FASCICULARIS FOLLOWING LONG-TERM SUBCLINICAL EXPOSURE TO METHYLMERCURY AND MERCURIC-CHLORIDE

The distribution of accumulated inorganic mercury deposits in the cort ex of the calcarine sulcus of adult female Macaca fascicularis followi ng long-term subclinical exposure to methylmercury (MeHg) and mercuric chloride (inorganic mercury-IHg) has been determined by autometallogr aphy. Four groups of monkeys were exposed to MeHg (50 mu g Hg/kg body wt/day) by mouth for 6, 12, and 18 months or 12 months followed by 6 m onths without exposure (clearance group). A fifth group of monkeys was administered inorganic mercury (as HgCl2; 200 mu g Hg/kg body wt/day) for 3 months by constant rate intravenous infusion via an indwelling catheter. Staining of IHg deposits in the MeHg-exposed groups increase d for all cell types with increased length of exposure. The astrocytes and microglia in the MeHg exposure groups contained the largest depos its of IHg. Neurons in the 6-month MeHg exposure group were either not labeled or contained very fine deposits of IHg. The frequency of labe led neurons increased somewhat in the 12-month and clearance exposure groups. Virtually all neurons in the 18-month exposure group contained labeled deposits of IHg; however, these total deposits were considera bly smaller than those present within the astrocytes and microglia. Th e majority of endothelial cells and pericytes did not contain notable mercury deposits, although scattered individual cells were heavily lab eled. Labeled oligodendrocytes were relatively rare in all MeHg-expose d groups. Gitter cells, primarily located in a perivascular position, were common in the 12-month, 18-month, and clearance groups and many o f these were found to be heavily labeled. The staining of mercury depo sits in the IHg-exposed animals was low compared to the MeHg-exposed g roups. The astrocytes and microglia were the primary cell types labele d. It is concluded that the astrocytes, and possibly microglia, are th e primary location of the demethylation of MeHg into IHg within the co rtex of the calcarine sulcus. (C) 1995 Academic Press, Inc.