A histochemical study of the regional distribution in the rat brain of enzymatic activity hydrolyzing glucose- and 2-deoxyglucose-6-phosphate.

A modified Wachstein-Meisel lead salt method using glucose-6-phosphate or 2-deoxyglucose-6-phosphate as substrates was employed at the light microscopic level to map the rat brain for glucose-6-phosphatase (G-6-Pase). As has been described, most of the activity of the enzyme resided in neuronal cell bodies and dendritic stems. No differences were found between the results obtained with the two substrates. Two categories of brain structures with heavy and with moderate staining could be distinguished while the majority of brain regions contained only barely discernible neurons. Structures displaying very high enzyme activity included nuclei of cranial nerves, nuclei of the reticular formation, Purkinje cells, and some parts of the limbic system, e.g., CA 3 and CA 4 pyramidal fields of the hippocampus. It is pointed out that accurate biochemical determinations of G-6-Pase activity will critically depend on painstaking microdissection of nuclei and cell layers. The histochemical results may be pertinent to the interpretation of the 2-deoxyglucose method for assessment of regional glucose utilization rates in brain. The present observations make it unlikely that regional variations in G-6-Pase activity account for differences in uptake and retention of radioactivity from (1-14C)glucose and (14C)2-deoxyglucose reported previously by our group.