Impaired regulation of mitochondrial dynamics, which shifts the balance towards fission, is associated with neuronal death in age-related neurodegenerative diseases, such as Alzheimer's disease or Parkinson's disease. A role for mitochondrial dynamics in acute brain injury, however, has not been elucidated to date. Here, we investigated the role of dynamin-related protein 1 (Drp1), one of the key regulators of mitochondrial fission, in neuronal cell death induced by glutamate toxicity or oxygen-glucose deprivation (OGD) in vitro, and after ischemic brain damage in vivo. Drp1 siRNA and small molecule inhibitors of Drp1 prevented mitochondrial fission, loss of mitochondrial membrane potential (MMP), and cell death induced by glutamate or tBid overexpression in immortalized hippocampal HT-22 neuronal cells. Further, Drp1 inhibitors protected primary neurons against glutamate excitotoxicity and OGD, and reduced the infarct volume in a mouse model of transient focal ischemia. Our data indicate that Drp1 translocation and associated mitochondrial fission are key features preceding the loss of MMP and neuronal cell death. Thus, inhibition of Drp1 is proposed as an efficient strategy of neuroprotection against glutamate toxicity and OGD in vitro and ischemic brain damage in vivo. Mitochondria play crucial roles in energy metabolism, regulation of free radical formation and calcium storage, thereby determining essential metabolic functions and cell survival. 1 Further, mitochondria are highly dynamic organelles that undergo constant fission and fusion and these morphological changes are required for efficient ATP production, calcium buffering, regulation of signal transduction and apoptosis. 2 In neurons, mitochondrial fission is also essential for axonal transport of the organelles into areas of high metabolic demand, 3 whereas mitochondrial fusion supports substitution and regeneration of mitochondrial proteins, mtDNA repair and functional recovery. 2,4 Consistent with the critical roles of mitochondrial dynamics in neurons, defects in mitochondrial fission and fusion proteins are associated with a wide array of inherited or acquired neurodegenerative diseases such as Charcot-Marie-Tooth disease or Alzheimer's disease, respectively. 2 Fission and fusion defects may limit mitochondrial motility, decrease energy production, promote oxidative stress and lead to accumulating of mtDNA defects, thereby promoting neuronal dysfunction and cell death. 1 Recently, enhanced mitochondrial fragmentation was associated with induction of neuronal death triggered by oxidative stress. 5 These data imply that during neuronal cell death, the tubular mitochondrial network is fragmented into smaller and functionally impaired organelles. 5 It is, however, a matter of ongoing controversy, whether mitochondrial fragmentation is cause or consequence in programmed cell death.Current knowledge of the mechanisms regulating mitochondrial dynamics indicates that fission and fusion of mitochondria are under control of highly conserved dynamin-relate...

A multicenter preclinical, randomized, controlled trial (pRCT) of a potential stroke treatment in mice demonstrates the feasibility of performing clinical trial–like investigations in animal models.

Rationale: Stroke is the third most common cause of death in industrialized countries. The main therapeutic target is the ischemic penumbra, potentially salvageable brain tissue that dies within the first few hours after blood flow cessation. Hence, strategies to keep the penumbra alive until reperfusion occurs are needed.Objective: To study the effect of inhaled nitric oxide on cerebral vessels and cerebral perfusion under physiological conditions and in different models of cerebral ischemia. Methods and Results:This experimental study demonstrates that inhaled nitric oxide (applied in 30% oxygen/70% air mixture) leads to the formation of nitric oxide carriers in blood that distribute throughout the body. This was ascertained by in vivo microscopy in adult mice. Although under normal conditions inhaled nitric oxide does not affect cerebral blood flow, after experimental cerebral ischemia induced by transient middle cerebral artery occlusion it selectively dilates arterioles in the ischemic penumbra, thereby increasing collateral blood flow and significantly reducing ischemic brain damage. This translates into significantly improved neurological outcome. These findings were validated in independent laboratories using two different mouse models of cerebral ischemia and in a clinically relevant large animal model of stroke. Key Words: collateral blood flow Ⅲ ischemic penumbra Ⅲ ischemic stroke Ⅲ nitric oxide inhalation E very year stroke is responsible for the death of 5.5 million people. 1 Despite its high incidence and mortality, clinical therapeutic options are still limited. 2 Research efforts to find novel treatment strategies focus primarily on rescuing the ischemic penumbra, the viable tissue surrounding the nonviable infarct core. In the penumbra, blood flow is critically reduced but still suffices to sustain neuronal integrity for several hours. The delayed nature of cell death in the penumbra leaves a unique window of opportunity for therapeutic interventions. If adequate cerebral perfusion is re-established sufficiently fast, then penumbral tissue can be effectively saved. 3 Therefore, penumbral reperfusion at the earliest possible time is the most critical factor in determining neurological outcome and in preventing mortality after stroke. 4 Conclusions:

Experimental stroke models producing clinically relevant functional deficits are often associated with high mortality. Because the mechanisms that underlie post-stroke mortality are largely unknown, results obtained using these models are often difficult to interpret, thereby limiting their translational potential. Given that specific forms of post-stroke care reduce mortality in patients, we hypothesized that inadequate food and water intake may underlie mortality following experimental stroke. C57BL/6 mice were subjected to 1 h of intraluminal filament middle cerebral artery occlusion. Nutritional support beginning on the second day after filament middle cerebral artery occlusion reduced the 14-day mortality rate from 59% to 15%. The surviving mice in the post-stroke support group had the same infarct size as non-surviving control mice, suggesting that post-stroke care was not neuroprotective and that inadequate food and/or water intake are the main reasons for filament middle cerebral artery occlusion-induced mortality. This notion was supported by the presence of significant hypoglycemia, ketonemia, and dehydration in control mice. Taken together, these data suggest that post-filament middle cerebral artery occlusion mortality in mice is not primarily caused by ischemic brain damage, but secondarily by inadequate food and/or water intake. Thus, providing nutritional support following filament middle cerebral artery occlusion greatly minimizes mortality bias and allows the study of long-term morphological and functional sequelae of stroke in mice.