revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 277
2. HEALTH EFFECTS
1983; Ngim et al. 1992). Photophobia has been reported exclusively in children with acrodynia (Fagala and
Wigg 1992; Warkany and Hubbard 1953). The physiological basis for the photophobia is unknown.
The neurotoxicity of inorganic and organic mercury in experimental animals is manifested as functional,
behavioral, and morphological changes, as well as alterations in brain neurochemistry (Arito and Takahashi
1991; Ashe et al. 1953; Berthoud et al. 1976; Burbacher et al. 1988; Cavanaugh and Chen 1971; Chang and
Hartmann 1972a, 1972b; Chang et al. 1974; Charbonneau et al. 1976; Concas et al. 1983; Evans et al. 1977;
Fukuda 1971; Fuyuta et al. 1978; Ganser and Kirschner 1985; Inouye and Murakami 1975; Jacobs et al.
1977; Kishi et al. 1978; Lehotzky and Meszaros 1974; Leyshon and Morgan 1991; MacDonald and Harbison
1977; Magos and Butler 1972; Magos et al. 1980, 1985; Mitsumori et al. 1981; Miyama et al. 1983; Post et
al. 1973; Rice 1989c; Rice and Gilbert 1982, 1992; Salvaterra et al. 1973; Sharma et al. 1982; Tsuzuki 1981;
Yip and Chang 1981).
Animal studies have shown damage to the cerebellar cortex and dorsal root ganglion cells following both
mercuric chloride and methylmercuric chloride exposure (Chang and Hartmann 1972b). These structures
appear to be especially sensitive to the toxic effects of mercury (Chang and Hartmann 1972a, 1972b; Chang
et al. 1974; Charbonneau et al. 1976; Falk et al. 1974; Hirano et al. 1986; Jacobs et al. 1977; Leyshon and
Morgan 1991; MacDonald and Harbison 1977; Magos and Butler 1972; Magos et al. 1980, 1985; Mitsumori
et al. 1990; Yip and Chang 1981), although other areas (e.g., the cerebral cortex, corpus striatum, thalamus,
hypothalamus, organ of Corti, and peripheral nerves) have also shown degenerative changes after exposure
to methylmercury (Berthoud et al. 1976; Chang et al. 1974; Charbonneau et al. 1976; Falk et al. 1974;
Fehling et al. 1975; Jacobs et al. 1977; Miyakawa et al. 1974, 1976; Yip and Chang 1981). Cats and
monkeys appear to be more sensitive to the toxic effects than rodents and have shown signs of neurotoxicity
at approximately 10-fold lower doses (0.05 mg Hg/kg/day) following long-term exposure to methylmercuric
chloride (Charbonneau et al. 1976; Rice 1989c; Rice and Gilbert 1982, 1992).
Although it is unclear whether changes in neurochemical parameters are primary targets of mercury or
whether the changes are secondary to degenerative changes in neurons, several neurotransmitter systems
have been shown to be affected by mercury exposure. Cholinergic transmission at the neuromuscular
junction has been shown to be affected by mercury exposure (Eldefrawi et al. 1977; Sager et al. 1982).
Changes in GABA receptor activity and number have also been observed (Arakawa et al. 1991; Concas et al.
1983). Changes in the activities of enzymes involved in cholinergic, adrenergic, dopaminergic, and