AN ANALYSIS OF AUTOPSY BRAIN-TISSUE FROM INFANTS PRENATALLY EXPOSED TO METHYLMERCURY

Brains from 32 neonatal autopsies from the Seychelles were examined hi stologically and analyzed for mercury levels. Six brain regions were s ampled: frontal and occipital cortex, temporal cortex with hippocampus , basal ganglia with thalamus, cerebellum, and pens with medulla. Tiss ue blocks for histology and mercury analysis were taken from opposing faces to provide for correlation of findings. Similar studies were per formed on 12 reference neonatal brains from Rochester, New York. No cl ear-cut developmental abnormality was found, but some brains exhibited low-grade, non-specific destructive changes. Total mercury levels, mo st of it in the organic form, were elevated in many of the Seychelles specimens. No correlation was demonstrated between mercury levels and degree or type of histologic change. There was considerable variabilit y in total mercury for each anatomic region among the 32 Seychelles ca ses, as well as from one region to another in individual brains. All v alues of total mercury were under 300 ppb. Statistical analysis of mea n mercury levels for each region demonstrated higher values in deep su bcortical nuclei, brain stem, and cerebellum, phylogenetically older p arts of the brain. When total mercury concentration of each region was paired with all other areas in the same brain and the paired values p lotted for the entire group of brains, high correlations were obtained for all brain pairs, suggesting a strong concentration-dependent rela tionship between mercury intake and brain content Analysis of mercury levels in separately dissected blocks of grey and white matter from 12 specimens revealed no significant differences between grey and white. In comparison with other human developmental studies and with experim ental developmental studies in animals, where toxicity has been demons trated with total mercury brain levels above 1,000 ppb, this study fou nd no evidence of toxicity within a range of mercury levels below 300 ppb. Submicroscopic changes, subcellular alterations, subtle disturban ces in the unfolding of brain architectonics - none of these are exclu ded with methods used in this report Further studies of threshold effe cts of MeHg on fetal brain are essential. That approximately half of t he mercury resides in glial elements in white matter reinforces the ne ed to focus attention upon glia as well as neurons during development. (C) 1995 Inter Press, Inc.