Quantitative histochemical measurement of GABA-transaminase: method for evaluation of intracerebral lesions produced by excitotoxic agents.

GABA-transaminase (GABA-T) activity of fresh frozen coronal sections through rat striatum was evaluated 4-6 weeks after intrastriatal application of kainic or ibotenic acid. 16 micrograms sections were processed for GABA-T histochemistry and were evaluated quantitatively by computerized densitometry using image analysis. Alternate sections (200 micrograms) were assayed for GABA-T activity in vitro. Gross examination of sections stained for GABA-T revealed obvious lack of staining in the vicinity of lesions produced by either kainate (0.5-1.0 micrograms) or ibotenate (10-20 micrograms); the extent of each lesion was clearly delineated by the stain. Quantitative analysis of stained sections revealed that the lesioned tissue contained 80-90% less GABA-T activity than control tissue. This loss of GABA-T was in agreement with values obtained in adjacent sections assayed in vitro. Similar studies in substantia nigra clearly and quantitatively demonstrated damage induced by ibotenate or kainate in this nucleus as well as in tissue in the overlying reticular formation. Moreover, two compartments of GABA-T were discriminated in substantia nigra: one associated with neural perikarya, which was sensitive to kainic and ibotenic acids (80% of total GABA-T), and a second associated with afferent terminals arising from forebrain projections (20%). Thus, after destruction of neurons with kainic or ibotenic acid, GABA-T activity is largely eliminated. Under these conditions, it appears that glia contribute relatively little to the GABA-T activity measured either histochemically or by direct chemical assay in homogenates.

Skin necrosis following prolonged administration of coumarin in a patient with inherited protein S deficiency.

Depression of the vitamin K-dependent modulators of coagulation during the initial phase of oral anticoagulant therapy may lead to a transient hypercoagulable state and skin necrosis. We report a case of skin necrosis associated with inherited protein S deficiency following prolonged coumarin therapy. As a result of a stasis ulceration causing a rise in c4b binding protein and concurrent treatment with topical sulfonamide, we hypothesize that a precipitous decrease in free protein S led to skin necrosis. Progression of the necrosis was halted with unactivated prothrombin complex concentrate. This case confirms the rare association between coumarin induced skin necrosis and protein S deficiency and emphasizes potential drug interactions.