Axotomy increases glycogen phosphorylase activity in motoneurones

The relative distribution of glycogen phosphorylase a and b in the lumbar spinal cord of the adult rat following either transection or crush of the sciatic nerve has been studied. The activity of the glycogen phosphorylase was measured histochemically by its capacity to convert glucose-1-phosphate to glycogen which was then stained with iodine. Prior to any treatment, the enzyme was largely in its inactive b form. Sciatic section and crush produced a transient (24 h) decrease in the amount of the active glycogen phosphorylase a in the sciatic motoneurone pool. Fourteen days post-transection, but not crush, a marked increase in the level of the active glycogen phosphorylase a form of the enzyme could be detected in the axotomised motoneurones which persisted for up to 6 weeks. No equivalent changes occurred in the axotomized dorsal root ganglion cells. Glycogen phosphorylase although normally present in neurones in its inactive b form can be converted to the active a form by calcium or adenosine 3':5'-phosphate. The substantial increase in the level of glycogen phosphorylase a in axotomized motoneurones may be a reflection of an increased calcium influx into these cells due to the development of abnormally hyperexcitable membranes and the appearance of dendritic spikes that is known to occur in these motoneurones.