INDUCTION OF NADPH-DIAPHORASE ACTIVITY IN THE RAT FOREBRAIN AFTER MIDDLE CEREBRAL-ARTERY OCCLUSION

Induction of NADPH-diaphorase (NDP) following ischemic infarction was studied by means of histochemistry in the rat cerebral cortex 1, 2, 7, and 14 days after distal occlusion of the right middle cerebral arter y (MCA). The fine structure of cells in the penumbra region of the nec rotic center was also investigated. MCA distal occlusion resulted in i schemic lesion of the frontoparietal cortex of variable extent; NDP in duction was detected in neurons, astrocytes, macrophages, and endothel ial cells, with a regional specificity and a temporal gradient. One, t wo, and seven days after MCA occlusion, weak NDP positivity was consis tently induced in some pyramidal neurons in cortical areas neighboring the necrotic area; NDP induction was also seen in pyramidal neurons o f the ipsilateral anterior cingulate and infralimbic cortices and in t he tenia tecta. In addition, numerous NDP-positive pyramidal neurons w ere detected in the contralateral frontoparietal cortex after relative ly large ischemic lesions. Two weeks after MCA occlusion, NDP inductio n in neurons was only evident in the deep cortical layers near the les ion. NDP histochemistry combined with glial fibrillary acidic protein immunofluorescence, performed 7 days after MCA occlusion, indicated th at the astrocytes at the periphery of the necrotic area were hypertrop hic and some of them were also NDP-positive. One and two days after MC A occlusion, numerous macrophages displaying NDP positivity of variabl e intensity were seen at the periphery of the necrotic area and in the external capsule of the ischemic cerebral hemisphere. Many endothelia l cells in the cortex and subcortical white matter were consistently N DP-positive in all rats. Electron microscopic study indicated that the area adjacent to the necrotic center was composed of fibrous astrocyt es, with the morphological characteristics of proliferation, and numer ous lysosome-filled macrophages. Altogether the present results sugges t that focal cerebral ischemia may induce in different cell types nitr ic oxide synthase, which is equivalent to NDP in fixed tissue. The ind uction of nitric oxide synthase may be related to (1) blood-how regula tion at relatively early postischemic stages, which may decline when c ollateral circulation is established, and/or (2) cytotoxic or neuropro tective mechanisms. (C) 1996 Academic Press, Inc.