ULTRASTRUCTURAL CHANGES IN EMBRYONIC MOUSE NEURAL TUBE CELLS AFTER URETHANE EXPOSURE

The 10-day-old embryonic mouse neural tube was examined by electron microscopy at intervals after exposure to urethane. Early changes were hypertrophy of the Golgi elements, smooth-surfaced endoplasmic reticulum, and the formation of cytoplasmic inclusions. Thick-thin sectioning techniques were used to correlate staining affinities as seen by light microscopy with fine structure of cytoplasmic inclusions. Three types of inclusions were described: (1) small Feulgen-positive particles which may arise from nuclear extrusion or chromosomal breakage following urethane damage; (2) thionine-positive particles composed of ribosomal aggregates or, in later stages, aggregates of ribosomes, mitochondria, vacuoles, and disrupted membranes; and (3) complexes consisting of a dense core (Feulgen-positive) surrounded or capped by a less dense zone containing thionine-positive ribosomal aggregates or other ruptured cell organelles. The present study suggests that urethane-induced inclusions represent damaged cell components which may be either metabolized within the neural tube cells or extruded into the central canal. © 1968.