Summary

Abstract

Although the glycogen content of the CNS is relatively small its function as an energy reserve is significant, and its turnover is considerable. Both glycogen and its related enzymes of metabolism—phosphorylase, branching enzyme and glycogen synthetase—are composed of various subunits and forms, most of which are histochemically distinguishable in the normal mammalian CNS. They have an essentially similar distribution, a fact that may reflect certain metabolic needs and inherent susceptibilities. They also undergo similar alterations as part of normal physiologic activity, as a result of exposure to certain physical or chemical stimuli or as a consequence of direct or indirect damage by, e.g. ionizing radiation, various forms and combinations of hypoxia and direct or indirect mechanical injury; the glycogen content is also increased in several human pathological states. When the stimulus is mild, and the response reversible, the glycogen content is temporarily enhanced within and around the sites that normally contain most glycogen. Activity of phosphorylase and glycogen synthetase usually undergo parallel increases then; the status of the branching enzyme is difficult to determine. Under these circumstances enzymes of the Embden-Meyerhof pathway, and some oxidoreductive enzymes, show less pronounced alterations. More noxious stimuli cause loss of glycogen and all enzymatic activity within necrotic foci and enhanced glycogen and enzymatic activity around such foci.