HISTOLOGICAL STUDIES ON EFFECT OF ACTINOMYCIN D ON RETROGRADE NERVE CELL REACTION IN FACIAL NUCLEUS OF MICE

The retrograde reaction in the facial nucleus of mice was studied after intracerebral injection of actinomycin D. Normally these neurons show increasing cytoplasmic basophilia and decreasing size of the Nissl granules during the first days after section of the facial nerve. The nerve cell diameter increases between the 2nd and 4th day after section of the nerve. After intracerebral injection of actinomycin D the nucleolus of all neurons disintegrates rapidly while the cytoplasm shows only slight changes. The Nissl substance of normal neurons appears well preserved after 2 days'' treatment. When actinomycin is given at the time of section of the facial nerve, all aspects of retrograde reaction is blocked during the next 48 hr. The dispersion of the Nissl substance during retrograde reaction is possibly mediated through induced enzyme synthesis. When the first injection of actinomycin is given 2 days after section of the nerve the neurons on the operated side show extreme chromatolysis 2 days later. This may indicate a more rapid turnover rate of the RNA of the finely dispersed cytoplasmic basophilic particles than of the large Nissl granules of normal neurons.