Vinblastine and griseofulvin reversibly disrupt the living mitotic spindle.

Using polarized light we have studied the effects of various mitotic poisons on mitotic spindles of living Pectinaria oocytes; we have studied fixed specimens with phase and electron microscopy. Vinblastine caused attrition and eventual disappearance of spindle structure as rapidly as did colcemid, and subsequent recovery from this treatment was at least as fast as that from colcemid. Griseofulvin, however, was easily the best agent for rapid, reversible, and repeated dissolution of the spindle. Agents that arrest metaphase may act on nondividing cells by interfering with the organization of other gelated structures.