Intracerebroventricular injection of a neuropeptide Y-Y1 receptor agonist increases while BIBP3226, a Y1 antagonist, reduces the infarct volume following transient middle cerebral artery occlusion in rats

Abstract

Recent studies using middle cerebral artery occlusion in the rat have suggested a role of neuropeptide Y in ischemic pathophysiology. In this study, we investigated the effects of an i.c.v. injection of a neuropeptide Y–Y2 receptor agonist, neuropeptide Y 3-36, a Y1 receptor agonist, [Leu 31,Pro 34]–neuropeptide Y, or a Y1 receptor antagonist, BIBP3226, on infarct volume and hemodynamic parameters following middle cerebral artery occlusion. Adult male Sprague–Dawley rats were subjected to transient middle cerebral artery occlusion for 2 h. A single i.c.v. injection of neuropeptide Y 3-36 (15 μg/kg), [Leu 31,Pro 34]–neuropeptide Y (30 μg/kg), or BIBP3226 (5, 15, or 45 μg/kg) was given at 30 min of ischemia. Blood pressure, heart rate, and regional cerebral perfusion were monitored during ischemia and reperfusion. The rats were decapitated after 70 h of reperfusion, and their brains were cut into 2-mm-thick coronal slices before reaction with a 2% solution of 2,3,5-triphenyltetrazolium chloride to reveal the infarct. When compared with an infarct volume of 17.4±4.4% of the ipsilateral hemisphere following injection of neuropeptide Y 3-36, administration of the Y1 receptor analogs significantly modified the infarct volume (ordinary one-way analysis of variance (ANOVA), P<0.0001). [Leu 31,Pro 34]–neuropeptide Y increased the infarct volume to 32.0±4.1% (Student-Newman-Keuls post-test, P<0.01), whereas BIBP3226 at 15 μg/kg decreased the infarct volume to 6.5±1.0% (post-test P<0.05). Although there was no major difference in the hemodynamic parameters among the groups, injection of [Leu 31,Pro 34]–neuropeptide Y tended to further reduce cerebral perfusion during ischemia, while injection of BIBP3226 at 15 μg/kg appeared to have the opposite effect. In addition to glutamate, calcium ion and nitric oxide, activation of the neuropeptide Y–Y1 receptors may mediate cerebral damage during focal ischemia. Conversely, inhibiting the Y1 receptors may protect the brain against ischemic injury. Further studies are warranted to confirm the neuroprotective potential of neuropeptide Y–Y1 receptor inhibition.