Focal brain ischemia caused by reduced supply of blood to cerebral tissue, results in cellular damage within the first few hours up to weeks after the insult. Extensive loss of neurons as well as glia in such ischemic brain areas is the characteristic pathological feature of cerebral infarcts causing mild to severe neurological symptoms that may even lead to the death of the subject. The cascade of events in the pathogenesis of stroke involves oxidative and nitrosative stress, i.e., the deleterious effects of reactive oxygen and nitrogen species (ROS / RNS). It is known that RNS / ROS cause mitochondrial damage and lead to an accumulation of pro-apoptotic high cytosolic Ca2+ ([Ca2+]c) in the cells. It is now realised that an activation of the mitochondrial permeability transition pore (mtPTP), a megachannel formed in the mitochondrial membranes contributes to such pro-apoptotic [Ca2+]c rise. Also, the mtPTP opening leads to the release of pro-apoptotic proteins like cytochrome c (cyt c), apoptosis inducing factor (AIF), Smac / DiaBLO and procaspases from the mitochondrial intermembrane space into the cytoplasm. The release of cyt c into the cytosol initiates the cascade of mitochondrial apoptotic cell death by activating caspase-3. Treatment with drugs that can either directly inhibit the mtPTP or can reduced the oxidative / nitrosative stress are therefore potential pharmacological interventions to reduce the ischemia- induced brain injury. 1. Melatonin, the secretory product of the pineal gland, is known to be neuroprotective in cerebral ischemia, which is so far mostly attributed to its antioxidant properties. Here we show that melatonin directly inhibits the mtPTP. Consistently, NMDA-induced [Ca2+]c rises were diminished by melatonin in cultured mouse striatal neurons, similar to the pattern seen with cyclosporine A (CsA), an inhibitor of mtPTP. When the mouse striatal neurons were subjected to oxygen-glucose deprivation (OGD), melatonin strongly prevented the OGD-induced loss of mitochondrial membrane potential. To assess the direct effect of melatonin on the mtPTP activity at the single channel level, recordings from the inner mitochondrial membrane were obtained by a patch-clamp approach using rat liver mitoplasts. Melatonin strongly inhibited mtPTP currents in a dose-dependent manner with an IC50 of 0.8 mM. If melatonin is an inhibitor of the mtPTP, it should prevent mitochondrial cyt c release as seen in stroke models. Rats underwent middle cerebral artery occlusion (MCAO) for 2 h followed by reperfusion. Melatonin (10 mg/kg intrapertoneal, i.p.) or vehicle was given at the time of occlusion and at the time of reperfusion. Indeed, infarct area in the brain sections of melatonin-treated animals displayed a considerably decreased cyt c release along with less activation of caspase-3 and apoptotic DNA fragmentation. Melatonin treatment diminished the loss of neurons and decreased the infarct volume as compared to vehicle-treated MCAO rats. Our findings suggest that the direct inhibition of the mtPTP by melatonin may essentially contribute to its anti-apoptotic effects in transient brain ischemia. 2. Since oxidative / nitrosative stress is one of the major pathological factors in the cascade of cell death in cerebral ischemia, we investigated the neuroprotective effect of a naturally occurring antioxidant, oxyresveratrol (OXY) to reduce brain injury after cerebral stroke. We used the MCAO model of transient brain ischemia to induce a defined brain infarction. OXY was given twice i.p.: immediately after occlusion and at the time of reperfusion. OXY (10 or 20 mg / kg) significantly reduced the brain infarct volume by approximately 54 „b 4 % and 63 „b 5 %, respectively, when compared to vehicle-treated MCAO rats. Also, the neurological deficits as assessed by different scoring methods reduced in OXY-treated MCAO rats. Histological analysis of apoptotic markers in the ischemic brain area revealed that OXY treatment diminished cyt c release from the mitochondria and decreased caspase-3 activation in MCAO rats. Also, staining for apoptotic DNA showed that the number of apoptotic nuclei in ischemic brain were reduced after OXY treatment as compared to the vehicle-treated MCAO rats. These findings demonstrate that OXY is neuroprotective in an in-vivo stroke model by limiting ischemia-induced brain injury. Taken together, we show here for the first time that the endogenous pineal hormone melatonin is a blocker of the mtPTP. Our data indicate that this property of melatonin contributes to its neuroprotective effects both, in-vitro and in-vivo. Furthermore, we established the naturally occurring hydroxystilbene, OXY as a potent neuroprotectant in a transient brain ischemia model, by demonstrating strongly reduced infarct volumes and neurological deficits upon its treatment after stroke insults. Our data show that both melatonin and OXY are potential drugs for the development of pharmacological intervention in stroke therapy.