Marked Induction of Calcium-Independent Nitric Oxide Synthase Activity after Focal Cerebral Ischemia

Abstract

We studied the effect of focal cerebral ischemia on inducible (iNOS) and constitutive (cNOS) nitric oxide synthase enzymatic activities in the affected brain. The middle cerebral artery (MCA) was occluded in spontaneously hypertensive rats. Animals were killed 1, 2, 4, and 7 days later. cNOS and iNOS enzymatic activities were determined in the infarcted cortex using the assay of Bredt and Snyder. cNOS was assayed in the presence of calcium, whereas iNOS was assayed in the absence of calcium and in the presence of tetrahydrobiopterin. The validity of the iNOS assay was verified in rats treated with bacterial lipopolysaccharide. In these animals, the magnitude of the induction of iNOS enzymatic activity in lung, spleen, and brain paralleled the expression of iNOS mRNA, assessed by reverse-transcription polymerase chain reaction. After MCA occlusion, calcium-dependent (cNOS) activity was markedly reduced only in lesioned cerebral cortex at days 1-7 (p < 0.001; analysis of variance and Tukey's test). In contrast to cNOS, calcium-independent (iNOS) activity was induced substantially in the infarct (p < 0.005) but not in the contralateral intact cortex (p > 0.05). iNOS activity peaked at day 2 and was not different from baseline at day 7 (p > 0.05). No NADPH diaphorase-positive neurons were observed in the area of the lesion at days 1-7. Macrophages appeared at day 2 and invaded the infarcted tissue by day 7. At this time, numerous glial fibrillary acidic protein-positive astrocytes were observed within the lesion. The results suggest that the decline in calcium-dependent (cNOS) activity reflects loss of NOS neurons within the lesion.(ABSTRACT TRUNCATED AT 250 WORDS)

Ginsenoside Rb1 Reduces Neurodegeneration in the Peri-infarct Area of a Thromboembolic Stroke Model in Non-human Primates

“…It is known that the reaction of astrocytes to cerebral ischemia is similar in some respects to the inflammatory response of peripheral tissues, such as inducing the expression of iNOS. It is reported that astrocyte iNOS expression is detectable within several hours and is maximal by 2 to 3 days after cerebral ischemia (22,23). Our data also demonstrated that ginsenoside Rb 1 markedly suppressed an increase of GFAP-positive cells in the peripheral area around the area of ischemic infarction 7 days after embolization.…”

Characterization of the Cytoprotective Action of Peroxynitrite Decomposition Catalysts

“…Neurons of the central nervous system, especially those of the hippocampus, are very susceptible to cytokine-mediated damage especially in the context of the later stages of stroke (47)(48)(49)(50)(51)(52). Glial cells, on the other hand, seem to be more resistant to such injury (11).…”

Vicious Cycle Involving Na+Channels, Glutamate Release, and NMDA Receptors Mediates Delayed Neurodegeneration through Nitric Oxide Formation

“…Ischemic injury can lead to the expression of the inducible form of NOS (iNOS) (Iadecola et al, 1995), and the observed time course of NO generation, based on NO x measurement, and the kinetics of cell death are not dissimilar to those found in other tissues exposed to iNOS inducers such as LPS or cytokines (Gross and Wolin, 1995). The possibility arose, therefore, that the neurodegeneration triggered by brief NMDA treatment could be effected by iNOS expression which, conceivably (e.g., through activation of gene transcription), could depend on NMDA receptor activity (Gross and Wolin, 1995).…”