Effects of diazepam on mitosis and basal body duplication of synchronously dividing flagellate cells.

We report here that diazepam (Valium, Roche) has an inhibitory effect on proliferation of synchronously dividing cultures of Dunaliella, whenever the drug is added during the cell cycle. The drug induced an accumulation of abnormal mitotic figures after 17 to 24 hr of treatment with the chromosomes distributed around the nuclei and a monopolar spindle, although the pole-to-chromosome microtubules were well-formed. Diazepam seemed to affect mitosis by inhibiting the separation of the basal bodies, whose duplication was perturbed in a dose-related manner. After 48 hr of treatment, the nucleus returned to interphase without having undergone mitosis, but cytokinesis might have taken place. The mechanism of this action of diazepam on mitosis remains to be elucidated. However, it does not appear to act in the same way here as it does on the central nervous system.