Cytochemical identification of cerebral glycogen and glucose-6-phosphatase activity under normal and experimental conditions. II. Choroid plexus and ependymal epithelia, endothelia and pericytes

Abstract

Intracellular glycogen and glucose-6-phosphatase (G6Pase) activity were identified cytochemically within epithelia of the choroid plexus and ependyma of the cerebral ventricles including the median eminence and area postrema, the cerebral endothelium and pericytes from control, salt-stressed and fasted adult mice. Identification of glycogen was obtained by employing osmium tetroxide-potassium ferrocyanide and the periodic acid-thiocarbohydrazide-silver protein technique as ultrastructural contrast stains. A lead-capture method was used to localize G6Pase activity with glucose-6-phosphate or mannose-6-phosphate as substrate. Cerebral G6Pase functions predominantly as a phosphohydrolase to convert glucose-6-phosphate to glucose. Some glucose-6-phosphate in vivo may be derived from the breakdown of glycogen stores. Within the sampled cell types, presumptive glycogen appeared as electron-dense, isodiametric particles scattered throughout the cytoplasm. Reaction product for G6Pase activity was localized consistently within the lumen of the nuclear envelope and endoplasmic reticulum and frequently within an outer saccule of the Golgi complex under normal conditions. Choroid plexus epithelia from stressed mice exhibited a qualitative increase in cytoplasmic glycogen and a decrease in G6Pase activity; the other cell types did not express demonstrable alterations in glycogen concentration and G6Pase activity. The results indicate that glycogen and G6Pase activity are prevalent within non-neural cells of the adult mammalian CNS. Glucose utilization in the choroid plexus epithelium may be altered by stressful conditions that influence the functional activity of this cell.