Neuroprotective effect of sigma(1)-receptor ligand 4-phenyl-1-(4-phenylbutyl) piperidine (PPBP) is linked to reduced neuronal nitric oxide production

Background and Purpose-The potent sigma (1)-receptor ligand 4-phenyl-1-(4-p henylbutyl) piperidine (PPBP) provides neuroprotection in experimental stro ke. We tested the hypothesis that PPBP attenuates striatal tissue damage af ter middle cerebral artery occlusion (MCAO) by a mechanism involving reduct ion of ischemia-evoked nitric oxide (NO) production. Furthermore, we determ ined whether the agent fails to protect ischemic brain when neuronal nitric oxide synthase (nNOS) is genetically deleted or pharmacologically inhibite d (selective nNOS inhibitor, 7-nitroindazole [7-NI]). Methods-Halothane-anesthetized adult male Wistar rats were subjected to 2 h ours of MCAO by the intraluminal filament occlusion technique. All physiolo gical variables were controlled during the ischemic insult. In vivo striata l NO production was estimated via microdialysis by quantification of local, labeled citrulline recovery after labeled arginine infusion, In a second s eries of experiments, nNOS null mutants (nNOSKOs) and the genetically match ed wild-type (WT) strain were treated with 90 minutes of MCAO. Brains were harvested at 22 hours of reperfusion for measurement of infarction volume b y triphenyltetrazolium chloride histology. Results-PPBP attenuated infarction volume at 22 hours of reperfusion in cer ebral cortex and striatum and markedly attenuated NO production in ischemic and nonischemic striatum during occlusion and early reperfusion. Treatment with 7-NI mimicked the effects of PPBP. In WT mice, infarction volume was robustly decreased by both PPBP and 7-NI, but the efficacy of PPBP was not altered by pharmacological nNOS inhibition in combined therapy. In contrast , PPBP did not decrease infarction volume in nNOSKO mice. Conclusions-These data suggest that the mechanism of neuroprotection of PPB P in vivo is through attenuation of nNOS activity and ischemia-evoked NO pr oduction. Neuroprotective effects of PPBP are lost when nNOS is not present or is inhibited; therefore, PPBP likely acts upstream from NO generation a nd its subsequent neurotoxicity.