1. It was found that picrotoxine has an effect to arrest the sexual cycle on mature female rats for the period of 8 to 15 days, with the picture of diestrus. During the arrest of the sexual cycle the uterus presented a picture of luteohormone action, and the ovaries showed that of vigorous activity of the lutein body and the growth of ovarian follicles was inhibited and on about the seventh day of the reststadium the ovarian follicles began to develop and the luteinbody under-went retrogressive metamorphosis.
2. When luminal, a brain-stem narcotics, was concurrently used, there could be seen no such effects of picrotoxine just mentioned nor any noteworthy findings of the uterus and ovaries while in the case of concurrent use of urethan the effect of picrotoxine was rather potentiated.
3. The combined use of atropine or yohimbine had practically no influence on the effect of picrotoxine.
4. It seems that picrotoxine attacks the sexual function regulating center in the diencephalon, especially its inhibitory center of the sympathetic nervous system. In this instance, since the duration of the arrest of the sexual cycle and the findings of both organs coincide with those of pseudopregnancy, as reported by Long et al., the excitation of the central nervous system induces the pseudopregnancy phenomenon and the cerebral cortex plays a role of inhibitor and the resultant paralysis enhances the excitation of this center