Effect of lead on the developing peripheral nervous system.

Abstract

The effect of lead on the developing nervous system was studied in the Long-Evans rat. Pups were intoxicated with lead from day 2 through the 20th day of life with a dosage of 1 gm Pb/kg body weight. Doses were administered via gastric gavage on the second and third days of life, and bidaily thereafter. Lead-treated and age-matched controls were then studied at selected intervals up to and including 20 days of age. Central and peripheral nervous systems were examined by light and electron microscopy. Morphometric analysis focused on defined segments of proximal and distal sciatic nerves and the 6th dorsal and ventral lumbar roots. For teased fiber studies, a segment of the contralateral proximal sciatic nerve was used. The investigation revealed that during the period studied, the myelin formed is stable. Multiple lead effects, however, were found: the Schwann cell is initially swollen but this effect gradually wanes during the 20 day period; myelin compaction is initially delayed, particularly in the ventral roots; axonal segregation proceeds, but appears to be accelerated in the ventral roots of the lead-treated pups where the larger bundles of naked axons disappear by five days of life. All of the changes noted, except axonal segregation, are reversed in the face of continued lead intoxication. While the hallmarks of "classical" lead neuropathy--segmental demyelination and the selective involvement of large fibers were not observed--the sensitivity of the somatic efferent fibers to lead was apparent in the accentuation of the lead effects in the ventral roots.