Histochemical determinations of Km and Vmax. for hexokinase type I in three layers of rat cerebellum

NADPH-consuming enzymes correlate with glucose-6-phosphate dehydrogenase in Purkinje cells: an immunohistochemical and enzyme histochemical study of the rat cerebellar cortex

In cerebellum of the adult rat, glucose-6-phosphate dehydrogenase (G6PD) activity is particularly localized in Purkinje cells, showing lower activity in the molecular and granule cell layers. G6PD is the first and rate-limiting step of the hexose monophosphate shunt (HMS), which has the physiological role of providing NADPH for reductive biosynthesis and detoxifying reactions. In this study, we searched for a possible correlation between G6PD and other NADPH-consuming enzymes, such as NADPH-cytochrome P450 reductase (P450R), glutathione reductase (GR) and NADPH-diaphorase (NADPH-d). This study was performed by means of immunohistochemistry and enzyme histochemistry followed by quantitative densitometric and confocal laser scanning microscopic analyses. Our results demonstrated that G6PD, P450R and GR have a similar distribution pattern characterized by the highest concentration of these enzymes in the somata of Purkinje cells, and by lower concentrations in the molecular and the granule cell layers. Moreover, in Purkinje cells, G6PD colocalized with both P450R and GR. NADPH-d activity showed a different distribution pattern when compared to the other enzymes, revealing the highest activity in the molecular layer and the lowest in Purkinje cells. Our results suggest a coordinated regulative mechanism of G6PD, P450R and GR based on the request of NADPH or on specific transcription factors.

Glucose-6-phosphate dehydrogenase expression associated with NADPH-dependent reactions in cerebellar neurons

This review describes the variation of glucose-6-phosphate dehydrogenase (G6PD) activity in the main neurons of the molecular and granular layers as well as in the deep nuclei of the cerebellum as observed so far by optical and electron microscopy studies. Light microscopy and semiquantitative microphotometry of histochemical staining showed that the highest G6PD activity was expressed by Purkinje cells and neurons of the deep cerebellar nuclei; the elements of the molecular layer showed a diffuse G6PD staining, while the granular layer displayed only scattered G6PD activity. Electron microscopy analysis showed that the basket and stellate cells, as well as the Golgi cells, have a remarkable G6PD activity, while in the granule cells the enzyme was barely detectable. The results show that cerebellar G6PD activity changes with different neuron types as a function of its role in sustaining NADPH dependent pathways in these cells.