Recent studies suggest that dietary supplementing with olive leaf extract (OLE) leads to ischemic tolerance and reduced ischemic brain injury. In this research, we have attempted to determine the effect of dietary supplementing with OLE on up-regulation of group I and group II metabotropic glutamate receptors (mGluR) in a rat stroke model. 75 male adult Wistar rats were divided into five groups, each consisting of 15 animals. First group (control) received distilled water, while three pretreatment groups received oral administration of OLE (50, 75, and 100 mg/kg/day, respectively). Each group was further subdivided into two groups: intact and middle cerebral artery occlusion (MCAO) groups. Sham-operated group (n = 6) underwent the same surgery but without nylon filament insertion. Sham-operated and intact groups were used to assess the mGluRs and glutathione levels. OLE induced ischemic tolerance by reducing the neurologic deficit scores and infarct volume. The dose 100 mg/kg/ day of OLE for 30 days increased expression of mGluR I and II in various rat brain tissues. mGluR5 levels were elevated in the penumbra, core, and subcortex when administered at the dose 75 mg/kg/day. The glutathione levels were increased significantly in the core and subcortex at doses 75 and 100 mg/kg/day. Although our data suggest that OLE-mediated neuroprotection is due to the increase of glutathione levels by group I and the reduction of glutamate release in synaptic spaces and ROS accumulation by group II mGluR, other mechanisms may be at work.
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