Ultrastructural observations on the vincristine-induced neuronal crystalloid inclusion in young rats

Vincristine-induced crystalloid inclusions were examined in the neurons and neuronal processes of young rats by the electron microscope (EM) equipped with a tilting stage. Using a computer system that reproduces three-dimensional organization, an optical transformation method was applied to the microtubules and neurofilaments in an attempt to clarify the morphological appearance and internal pattern of crystalloid inclusions. The dimensional models obtained were compared with actual EM photographs, and the characteristic ultrastructural component and morphology were drawn out. Basically, a crystalloid inclusion is composed of four strands of intermediate 10 nm neurofilaments connected to one another by four side-arms producing a circular profile on a transverse section. These four side-arms seemed to arise from nodules within the filaments at regular intervals simulating a bead-like appearance. These data did not significantly differ from those obtained from EM images. Characteristically, these crystalloid inclusions began to appear 6 h after the administration of 10(-3) M vincristine sulfate and persisted up to a period of 6 days. Beyond that, however, these inclusions were no longer demonstrable suggesting a transient state. This was in contrast to neurofibrillary tangles which appeared to be permanent changes.