Cytochemical localization of glucose-6-phosphatase activity in the central nervous system of the rat.

The histochemical detection of glucose-6-phosphatase (G-6-Pase) in neurons of the CNS has been confirmed at the level of electron microscope. Both glucose-6-phosphate (G-6-P) and alpha-glycerophosphate (alpha-gP) can be used as substrates to localize the reaction product of this enzyme, which we have found in all cell types of the cerebral cortex, cerebellum and brain stem. The reaction was most prominent in large neurons, such as the Purkinje cells of the cerebellum and the pyramidal cells of the cerebral cortex. This is due to their extensive content of rough and smooth endoplasmic reticulum, the ultrastructural sites of G-6-Pase activity. It was possible to measure quantitatively the hydrolysis of G-6-P and alpha-gP in brain homogenates and also in microsomal fractions, the biochemical correlate of the cytochemically demonstrable activity. These results call for a reappraisal of the previous biochemical evidence, which negates the existence of brain G-6-Pase, and consequently a reassessment of current concepts pertaining to the metabolic regulation of brain glucose.