A COMPARATIVE MAPPING OF ENZYMES INVOLVED IN HEXOSEMONOPHOSPHATE SHUNT AND CITRIC ACID CYCLE IN THE BRAIN *

REPORTS of preceding investigations (FRIEDE, 1959~2, 1961 c; FRIEDE and FLEMING, 1962) have contained detailed charts of the distribution of several enzymes in the brain. The purpose of this paper is to compare enzyme patterns with each other and to describe similarities and, particularly, differences of the patterns that were observed. The regional patterns in the brain of seven enzymes which are concerned with glucose metabolism were studied and compared. Most of the data were obtained from histochemical series from rhesus monkey and human brains. These were compared with tissue homogenate assays. The enzymes studied were cytochrome oxidasef succinic dehydrogenase, DPN-diaphorase, TPN-diaphorase, malic dehydrogenase glucose-6-phosphate dehydrogenase, 6-phosphogluconic dehydrogenase and lactic dehydrogenase. In order to render this article more complete, some previously published data have been included. MATERIALS AND METHODS Because of difficulty in obtaining adequate human material, the systematic work reported in this study was done on rhesus monkey brains. Most of the Observations were compared with observations on human material as it became available during the course of the study. The following material was used: Monkey: Microscopic histochemicai surveys w2ere made by series for LDH, G-6-P, GPD, DPN-diaphorase, TPN-diaphorase, CYO and SD. Extensive spectrophotometric measurements of LDH were made from histochemical sections. SD, DPN-diaphorase, and G-6-P were assayed in homogenates from various regions and the data were compared with the histochemical staining gradients. Plans to assay all the nuclei of the monkey brain had to be discarded because the small size of the brain did not permit accurate macroscopical sampling of smaller nuclei. Random histochemical material was available for SD, LDH, CYO and G-6-P. The distribution of DPN-diaphorase was available from previous mappings (FRIEDE and FLEMING, 1962). In addition, G-6-P, DPN-diaphorase and SD were assayed in homogenates of seventeen representative regions from five normal human brains obtained 3.5 to 10 hours after death. The assay measurements were used for comparison with the histochemical gradations, as well as for comparison with each other (Table 1, line 6). Man: Also included are some observations on the distribution of MDH in the cat brain stem. Methods : Complete details of methodology are given in a separate publication (FRIEDE, FLEMING and KNOLLER, 1963) in which histochemical methods were tested extensively by comparison with assays in tissue homogenates. At this time, it may suffice to indicate that the use of formalin-fixed material was an advantage for histochemical studies of DPN-diaphorase and LDH. When carried out under carefully controlled conditions, fixation prevented loss of these two enzymes from tissue blocks and sections; histochemical data obtained by spectrophotometric measurement of formazan were in excellent agreement with the data of assays of unfixed tissue homogenates. Attempts to elaborate and standardize fixation methods for the other enzymes studied have failed so far.