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Background and Purpose PD5 inhibitors have recently been reported to exert beneficial effects against ischaemia-reperfusion injury in several organs. However, there are few studies regarding their neuroprotective effects in brain ischaemia. The present study was designed to assess the effects of sildenafil against chemical hypoxia induced by malonate. Intrastriatal injection of malonate produces energy depletion and striatal lesions similar to that seen in cerebral ischaemia through mechanisms that involve generation of reactive oxygen species ( ROS). Experimental Approach Volume lesion was analysed by cytochrome oxidase histochemistry. Generation of reactive species was determined by in situ visualization of superoxide production and nitrotyrosine measurement. Protein levels were determined by Western blot after subcellular fractionation. Key Results Sildenafil, given 30 min before malonate, significantly decreased the lesion volume in the rat. This protective effect cannot be attributed to any effect on ROS production but to the inhibition of downstream pathways. Thus, malonate induced the activation of apoptosis signal-regulating kinase-1 ( ASK1) and two MAPK kinases, MKK3/6 and MKK7, which lead to an increased phosphorylation of JNK and p38 MAPK, effects that were blocked by sildenafil. Selective inhibitors of p38 and JNK ( SB203580 or SP600125, respectively) were used in combination with malonate in order to evaluate the plausible implication of these pathways in the protection afforded by sildenafil. While inhibition of p38 provided a significant protection against malonate-induced neurotoxicity, inhibition of JNK did not. Conclusions and Implications Sildenafil protects against the chemical hypoxia induced by malonate through the regulation of the ASK1-MKK3/6-p38/ MAPK signalling pathway. [ABSTRACT FROM AUTHOR]

Background and Purpose: 3,4-methylenedioxymethamphetamine (MDMA) causes a persistent loss of dopaminergic cell bodies in the substantia nigra of mice. Current evidence indicates that such neurotoxicity is due to oxidative stress but the source of free radicals remains unknown. Inhibition of mitochondrial electron transport chain complexes by MDMA was assessed as a possible source., Experimental Approach: Activities of mitochondrial complexes after MDMA were evaluated spectrophotometrically. In situ visualization of superoxide production in the striatum was assessed by ethidium fluorescence and striatal dopamine levels were determined by HPLC as an index of dopaminergic toxicity., Key Results: 3,4-methylenedioxymethamphetamine decreased mitochondrial complex I activity in the striatum of mice, an effect accompanied by an increased production of superoxide radicals and the inhibition of endogenous aconitase. alpha-Lipoic acid prevented superoxide generation and long-term toxicity independent of any effect on complex I inhibition. These effects of alpha-lipoic acid were also associated with a significant increase of striatal glutathione levels. The relevance of glutathione was supported by reducing striatal glutathione content with L-buthionine-(S,R)-sulfoximine, which exacerbated MDMA-induced dopamine deficits, effects suppressed by alpha-lipoic acid. The nitric oxide synthase inhibitor, N(G)-nitro-L-arginine, partially prevented MDMA-induced dopamine depletions, an effect reversed by L-arginine but not D-arginine. Finally, a direct relationship between mitochondrial complex I inhibition and long-term dopamine depletions was found in animals treated with MDMA in combination with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine., Conclusions and Implications: Inhibition of mitochondrial complex I following MDMA could be the source of free radicals responsible for oxidative stress and the consequent neurotoxicity of this drug in mice.