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Thyroid hormones, T3 and T4, have been shown to play significant but poorly understood roles in development and differentiation of rodent and human brain(Lauder, 1989; Legrand, 1982–83; Stein et al, 1989a; 1991a,d; Eayrs, 1968; Morreale de Escobar et al, 1984; Garza et al, 1988; Ruiz-Marcos, 1989; Nunez et al, 1989). Hypothyroidism leads to molecular(Stein et al, 1989a,c; 1991a; Nunez et al, 1989; Hendrich et al, 1987), neuroendocrinological(Noguchi et al, 1986, Bakke et al, 1975, Stein et al, 1989b, Porterfield et al, 1981), neuroanatomical(Lauder et al, 1986; Lauder, 1989; Ruiz-Marcos, 1989; Eayrs, 1955; Garza et al, 1988; Morreale de Escobar et al, 1989; Marc et al, 1985; Legrand, 1982–83; Rami et al, 1986b; Narayanan et al, 1985; Marinesco, 1924; Lotmar, 1928; Rosman, 1975), behavioral and neuropsychological(Adams et al, 1989,1991; Anthony et al, 1991; Eayrs, 1968; Davenport et al, 1976; Klein, 1985; Rovet et al, 1987; Rovet, 1989; Man, 1971; Boyages et al, 1988; Pharoah,1984), and neurological abnormalities(Chaouki et al, 1989; Boyages et al, 1988; Delong et al, 1985; Nelson et al, 1986; Macfaul et al; 1978; Stein et al, 1991d, Rochiccioli et al, 1989) in the developing brain. Specifically, disorders of neuronal process growth and connectivity are noted neuroanatomically and motor syndromes involving motor cortex and pyramidal tracts are commonly observed in hypothyroid humans and rodents. These neurological and neuropathological abnormalities may be predicated on abnormalities in the cytoskeletal structures and in their molecular components. The cytoskeleton is a primary target for thyroid hormone in euthyroid and hypothyroid brain.

Thyroid hormones, T3 and T4, have been shown to play significant but poorly understood roles in development and differentiation of rodent and human brain (1–7). In the human, disorders of maternal and fetal thyroid function include maternal and secondary fetal iodine deficiency, maternal hypothyroidism or hyperthyroidism, as well as disorders related to deficient fetal autonomous thyroid hormone secretion, i.e., goiter or sporadic congenital hypothyroidism. These disorders are identifiable causes of mental retardation (4, 8, 9, 10), cerebral palsy (11, 12), and other significant neurological abnormalities (5, 6, 11).