Differential morphological changes in sympathetic nerve fibers elicited by lead,cadmium, and mercury

Effects of intraocular injection of lead acetate, cadmium chloride, or mercury chloride on the sympathetic adrenergic ground plexus of the iris were studied using monoamine fluorescence histochemistry. Injection of 5 μl of a 1.4 mm lead solution into the anterior eye chamber caused a significant hyperinnervation as compared to sodium acetate-injected control irides. This hyperinnervation persisted 2 weeks after injection. Increasing the dose to 42 mm did not increase the extent of the hyperinnervation. Cadmium chloride solutions (1.4 and 7 mm) did not affect the adrenergic nerve fiber density as compared to sodium chloride-injected controls. Injection of mercury chloride caused a marked and dose-dependent degeneration of adrenergic nerves. Two weeks after injection of a 3.5 mm mercury chloride solution, the nerves had regenerated almost completely. Our results demonstrate that intraocular injections of neurotoxic heavy metals, and subsequent analysis with Falck-Hillarp fluorescence microscopy, is a rapid and sensitive method to evaluate adrenergic neurotoxicity.