Effects of methylmercury and inorganic mercury on the growth of nerve fibers in cultured chick dorsal root ganglia

Inhibition of the growth of nerve fibers by mercurials was quantitatively estimated by measuring the length of fibers in the cultured chick dorsal root ganglion, Morphological changes in nonneuronal cells were also evaluated. The growth rates of nerve fibers were constant for 2 to 6 days after the start of incubation. Methylmercury depressed nerve fiber growth dose- and time-dependently by 50% and completely at 3 x 10(-6) M and 7 x 10(-6) M, respectively. About 10-fold higher concentrations of inorganic mercury were required for the same extent of inhibition. The nerve fibers exposed to inorganic mercury shrank at an early stage of exposure and thereafter grew again within 24 hours. Electron microscopic examination revealed that methylmercury decreased microtubule mass extensively in nerve fibers, while inorganic mercury markedly altered surface membrane structure. These results suggested that microtubule disruption is involved in methylmercury induced depression of nerve fibers but not in that induced by inorganic mercury. Characteristic effects on the growth of nerve fibers and the proliferation of nonneuronal cells mere observed on the treatment with other metals such as cadmium, silver and chromium, Thus, dorsal root ganglion culture seems to be useful for the evaluation of toxic effects of metals in vitro.