Factors limiting the histochemical reaction of choline dehydrogenase activity.

~ 113-The histochemical reaction of choline dehydrogenase was completely inhibited by the pretreatment of cryostat sections with either absolute acetone or lO<yo water-in-acetone at room temperature (25°C). The temperature of the organic solvents was critical in the inhibition of the staining for choline dehydrogenase. As the temperature was lowered, the inhibitory effects of the pretreatment decreased. The stammg lost by absolute acetone was restored by coenzyme QlO, phenazine methosulfate, menadione, section-extracts and mitochondrial fraction extracts. On the other hand, the staining lost by lO<yo water-in-acetone was not restored. Both absolute acetone and lO~~ water-in-acetone produced the same inhibitory effect upon the staimng. There was, however, a difference between the effect of absolute acetone and that of lO~/o water-in-acetone in the restoration of the staining lost by the pretreatment of the sections. Coenzyme Ql0 and phospholipids are suggested as limiting factors in the histochemical reaction of choline dehydrogenase.