Sensory and cognitive effects of developmental methylmercury exposure in monkeys, and a comparison to effects in rodents.

Developmental exposure to methylmercury in the macaque monkey produced impairment of function in the visual, auditory, and somatosensory systems. In addition, delayed neurotoxicity was observed in monkeys years after cessation of dosing, manifested as overall clumsiness and slowness in reaching for objects. The effects of developmental methylmercury exposure on cognitive function in monkeys are more equivocal; both positive and negative results have been obtained, with no obvious pattern with regard to possible domains of impairment. Prenatal methylmercury exposure in rodents produced retarded development and impairment of motor function, while the evidence for cognitive impairment is less consistent. Derivation of reference doses based on the available data from monkeys and rodents is remarkably congruent, and is virtually identical to values derived from evidence for developmental impairment in humans. Research needs include determination of neurotoxic effects at lower body burdens in the monkey, including dose-effect data, and a more systematic exploration of the pattern of behavioral deficits in both primates and rodents.