1. The oxidative enzyme activity of glial cells was studied histochemically in a local brain injury associated with edema in the white matter.2. In the area of edema an increase of glutamic dehydrogenase activity was observed in astrocytes within 12 hours after the lesion was produced. Increase of DPN diaphorase, DPN-linked isocitric dehydrogenase and alpha;-glycerophosphate dehydrogenase activity was manifest within 24 hours. TPN diaphorase and TPN-linked dehydrogenase activity was increased after 48 hours. This enzymatic change in astrocytes was preceded by enlargement of these cells and the formation of Holzer fibers which appeared within 6 hours in the edematous white matter.3. From 24 hours to 7 days the area of edema in the white matter showed the presence of isolated, roundish microglial elements with intense oxidation-reduction activity. These cells were identified as corresponding to those filled with serum protein inclusions demonstrated in FAN stain and under the fluorescence microscope in cats injected with FLA.4. Following edema of several days' duration the hypertrophic astrocytes in the white matter continued to exhibit an increased tetrazolium reductase activity and this was demonstrable in the last animal 95 days after cortical injury.5. The correlation of histochemical findings with other observations on glia provides further support for the view that the astrocytes are primarily implicated in the process of cerebral edema and emphasizes the dynamic character of this involvement.
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