On the histochemistry of neuronal and glial TPPase.

Thiamine pyrophosphatase (TPPase) activity in the neuronal Golgi apparatus and in glia cells was investigated using different tissue preparation techniques such as fresh frozen and fixed frozen sections, the effect of ATP as an activator and the fine structural localization of the enzyme activity in glia cell processes and the glio-vascular contact point was observed under the electron microscope. TPPase was demonstrated in the glia cell using only a fixed frozen tissue preparation, activated by ATP with the concentration as low as 0.1 mM. On the contrary, enzyme activity was detected in the Golgi apparatus of the neuron regardless of tissue preparation, fresh or fixed frozen, or by the addition of ATP to the incubation medium. The identity of the glia cell type showing a positive reaction for TPPase is thought to be part astrocyte and part microglia. The fine structural observation of TPPase localization at the glia cell process ending, particularly at the glio-vascular and glio-fibral (medullated fiber) contact point suggests a functional role of this enzyme for transport of metabolites through glia cell processes to neurons and/or the blood capillary, and also may play a role in regulation of co-carboxylase.