Cytophotometric studies on the reaction kinetics of acid phosphatase in motoneurons marked by injection of Evans blue into the soleus muscle of the mouse.

Evans blue was injected into the soleus muscle of albino mice in order to mark retrogradely the corresponding motoneurons of the spinal cord. Subsequently, reaction kinetics of acid phosphatase were studied in the marked nerve cells. 41-51 motoneurons per animal were counted. They are located in the dorsolateral portion of the Rexed zone IX where they form motor cell columns approximately 1.5 mm in length. After identification of the motoneurons, the enzyme reaction for acid phosphatase was performed by covering the section with a gel film containing naphthol-AS-BI-phosphate-hexazonium-pararosanilin. The formation of the azo dye was measured cytophotometrically at 520 nm. During the first 10 min of registration, a linear decrease in transmission of 0.4 per cent/min was shown. Because of the unimodal distribution of changes in transmission, the motoneurons of the soleus muscle could not be characterized as fast or slow types on the basis of the reaction kinetics of acid phosphatase.