Nitric oxide synthase-I containing cortical interneurons co-express antioxidative enzymes and anti-apoptotic Bcl-2 following focal ischemia: evidence for direct and indirect mechanisms towards their resistance to neuropathology
ABSTRACT Neuronal nitric oxide-I is constitutively expressed in ≈2% of cortical interneurons and is co-localized with γ-amino butric acid, somatostatin or neuropeptide Y. These interneurons additionally express high amounts of glutamate receptors which mediate the glutamate-induced hyperexcitation following cerebral injury, under these conditions nitric oxide production increases contributing to a potentiation of oxidative stress. However, perilesional nitric oxide synthase-I containing neurons are known to be resistant to ischemic and excitotoxic injury. In vitro studies show that nitrosonium and nitroxyl ions inactivate N-methyl-d-aspartate receptors, resulting in neuroprotection. The question remains of how these cells are protected against their own high intracellular nitric oxide production after activation. In this study, we investigated immunocytochemically nitric oxide synthase-I containing cortical neurons in rats after unilateral, cortical photothrombosis. In this model of focal ischemia, perilesional, constitutively nitric oxide synthase-I containing neurons survived and co-expressed antioxidative enzymes, such as manganese- and copper-zinc-dependent superoxide dismutases, heme oxygenase-2 and cytosolic glutathione peroxidase. This enhanced antioxidant expression was accompanied by a strong perinuclear presence of the antiapoptotic Bcl-2 protein. No colocalization was detectable with upregulated heme oxygenase-1 in glia and the superoxide and prostaglandin G2-producing cyclooxygenase-2 in neurons. These results suggest that nitric oxide synthase-I containing interneurons are protected against intracellular oxidative damage and apoptosis by Bcl-2 and several potent antioxidative enzymes. Since nitric oxide synthase-I positive neurons do not express superoxide-producing enzymes such as cyclooxygenase-1, xanthine oxidase and cyclooxygenase-2 in response to injury, this may additionally contribute to their resistance by reducing their internal peroxynitrite, H2O2-formation and caspase activation.
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ABSTRACT: It is expected that clinical recovery after surgically induced brain trauma is followed by molecular and biochemical restitution. Seven days after surgery, we investigated whether the plastic cannula implanted in the left brain ventricle of adult Wistar rats (n = 6-7), performed in pentobarbital anesthesia, could influence oxidative stress elements (superoxide anion and lipid peroxidation), as well as the antioxidative system (superoxide dismuthase-SOD). Also, we investigated whether nitric oxide (NO) is involved in these processes. Biochemical analyses was performed in the forebrain cortex, striatum and hippocampus. Clinical recovery was complete seven days after surgery. Thereafter, thirty minutes before decapitation, through the cannula, one group of rats received saline intracerebroventricularly (control group), and the treated group received Nω-nitro-L-arginine methyl ester (L-NAME). The third group was left unoperated and untreated. Before and after the treatments, rectal body temperature was measured. Compared to the untreated group the index of lipid peroxidation was increased in all three brain structures in the group that received saline (p<0.05 to 0.01). Application of L-NAME deteriorated it in the striatum and hippocampus (p<0.01 compared to the both other groups), but the value in the forebrain cortex was similar to the untreated group. Supeoxide anion level was decreased in the L-NAME treated group only in the striatum (p<0.01 compared to control and untreated groups), but SOD was increased in the hippocampus compared to the saline treated group (p<0.05). Seven days after brain surgery in pentobarbital anesthesia, recovery of biochemical disturbances was not parallel to clinical recovery. Long lasting biochemical changes are rather the consequence of brain injury than to pentobarbital anesthesia. In this experimental model, NO had protective effects, acting against lipid per oxidation in the striatum and hippocampus, but not in the forebrain cortex i. e. NO involvement in the free radical processes strongly depends on the observed brain region.Acta Veterinaria. 01/2005;