EFFECT OF ACTINOMYCIN D ON RETROGRADE NERVE CELL REACTION - FURTHER OBSERVATIONS

The retrograde nerve cell reaction was studied in the neurons of the reticular formation and in the facial nucleus of mice after intracerebral injections of actinomycin D. Normally the reticular neurons show a classical type of retrograde reaction with dispersion of the Nissl substance and central chromatolysis. The facial neurons also show a dispersion of the Nissl granules but there is an early increase in the cytoplasmic basophilia instead of chromatolysis. The two types of neurons thus show somewhat different patterns of retrograde reaction. It was shown previously that actinomycin prevented the appearance of retrograde reaction in the facial nucleus when the drug was injected at the time of operation (Torvik and Heding, 1967). The present study showed that actinomycin blocked the retrograde reaction also in the reticular formation when it was given 2 h before the reticulospinal fibers were cut. When the drug was given 12 h after section of the reticulospinal fibers, the retrograde reaction developed normally in the reticular formation, although the neurons were morphologically normal at the time of injection. In the facial nucleus the retrograde reaction was blocked when the drug was given 9 h after the operation but not by 15 h. The findings suggest that the morphological nerve cell changes after axon lesions are preceded by the synthesis of new enzymes in the injured cells, which in some way are necessary for the ensuing dispersion of the Nissl substance. © 1969 Springer-Verlag.