Hypoxic preconditioning enhances the capacity of mesenchymal stem cells to repair infarcted myocardium, attributable to reduced cell death and apoptosis of implanted cells, increased angiogenesis/vascularization, and paracrine effects.

Hypoxic preconditioning of stem cells and neural progenitor cells has been tested for promoting cell survival after transplantation. The present investigation examined the hypothesis that hypoxic preconditioning of bone marrow mesenchymal stem cells (BMSCs) could not only enhance their survival but also reinforce regenerative properties of these cells. BMSCs from eGFP engineered rats or pre-labeled with BrdU were pre-treated with normoxia (20% O2, N-BMSCs) or sublethal hypoxia (0.5% O2. H-BMSCs). The hypoxia exposure up-regulated HIF-1α and trophic/growth factors in BMSCs, including brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), vascular endothelial growth factor (VEGF) and its receptor FIK-1, erythropoietin (EPO) and its receptor EPOR, stromal derived factor-1 (SDF-1) and its CXC chemokine receptor 4 (CXCR4). Meanwhile, many pro-inflammatory cytokines/chemokines were downregulated in H-BMSCs. N-BMSCs or H-BMSCs were intravenously injected into adult rats 24 hrs after 90-min middle cerebral artery occlusion. Comparing to N-BMSCs, transplantation of H-BMSCs showed greater effect of suppressing microglia activity in the brain. Significantly more NeuN-positive and Glut1-positive cells were seen in the ischemic core and peri-infarct regions of the animals received H-BMSC transplantation than that received N-BMSCs. Some NeuN-positive and Glut-1-positive cells showed eGFP or BrdU immunoflourescent reactivity, suggesting differentiation from exogenous BMSCs into neuronal and vascular endothelial cells. In Rota-rod test performed 15 days after stroke, animals received H-BMSCs showed better locomotion recovery compared with stroke control and N-BMSC groups. We suggest that hypoxic preconditioning of transplanted cells is an effective means of promoting their regenerative capability and therapeutic potential for the treatment of ischemic stroke.

Neural activation increases blood flow locally. This vascular signal is used by functional imaging techniques to infer the location and strength of neural activity 1,2 . However, the precise spatial scale over which neural and vascular signals are correlated is unknown. Furthermore, the relative role of synaptic and spiking activity in driving hemodynamic signals is controversial [3][4][5][6][7][8][9] . Prior studies recorded local field potentials (LFPs) as a measure of synaptic activity together with spiking activity and low-resolution hemodynamic imaging. Here we used two-photon microscopy to measure sensory-evoked responses of individual blood vessels (dilation, blood velocity) while imaging synaptic and spiking activity in the surrounding tissue using fluorescent glutamate and calcium sensors. In cat primary visual cortex, where neurons are clustered by their preference for stimulus orientation, we discovered new maps for excitatory synaptic activity, which were organized similar to spiking activity but were less selective for stimulus orientation and direction. We generated tuning curves for individual vessel responses for the first time and found that parenchymal vessels in cortical layer 2/3 were orientation selective. Neighboring penetrating arterioles had different orientation preferences. Pial surface arteries in cats, as well as surface arteries and penetrating arterioles in rat visual cortex (where orientation maps do not exist 10 ), responded to visual stimuli but had no orientation selectivity. We integrated synaptic or spiking responses around individual parenchymal vessels in cats and established that the vascular and neural responses had the same orientation preference. However, synaptic and spiking responses were more selective than vascular responses-vessels frequently responded robustly to stimuli that evoked little to no neural activity in the surrounding tissue. Thus, local neural and hemodynamic signals were partly decoupled. Together, these results indicate that intrinsic cortical properties, such as propagation of vascular dilation between neighboring columns, need to be accounted for when decoding hemodynamic signals.To determine how neural activity leads to changes in cerebral blood flow, the hemodynamic responses of individual vessels need to be compared to neural activity in the surrounding tissue 11 . While sensory-evoked responses of individual vessels have been measured in the Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

We demonstrate that Alexa Fluor 633 hydrazide (Alexa Fluor 633) selectively labels neocortical arteries and arterioles by binding to elastin fibers. We measured sensory stimulus–evoked arteriole dilation dynamics in mouse, rat and cat visual cortex using Alexa Fluor 633 together with neuronal activity using calcium indicators or blood flow using fluorescein dextran. Arteriole dilation decreased fluorescence recorded from immediately underlying neurons, representing a potential artifact during neuronal functional imaging experiments.

Restoration of local blood supply in the post-ischemic brain plays a critical role in tissue repair and functional recovery. The present investigation explored beneficial effects of recombinant human erythropoietin (rhEPO) on vascular endothelial cell survival, angiogenesis, and restoration of local cerebral blood flow (LCBF) after permanent focal cerebral ischemia in adult mice. Saline or rhEPO (5,000 U/kg, intraperitoneal) was administered 30 mins before ischemia and once daily after ischemic stroke. Immunohistochemistry showed an enhancing effect of rhEPO on expression of EPO receptor (EPOR) of endothelial cells in the penumbra region 3 to 21 days after the ischemic insult. The treatment with rhEPO decreased ischemia-induced cell death and infarct volume 3 days after stroke. Specifically, rhEPO reduced the number of terminal deoxynucleotidyl transferase biotin-dUPT nick end labeling- and caspase-3-positive endothelial cells in the penumbra region. Colocalization of the vessel marker glucose transporter-1 (Glut-1) and cell proliferation marker 5-bromo-2'-deoxyuridine indicated enhanced angiogenic activity in rhEPO-treated mice 7 to 21 days after stroke. Western blot showed upregulation of the expression of angiogenic factors Tie-2, Angiopoietin-2, and vascular endothelial growth factor in rhEPO-treated animals. Local cerebral blood flow was measured by laser scanning imaging 3 to 21 days after stroke. At 14 days, LCBF in the penumbra was recovered to preischemia levels in rhEPO-treated mice but not in control mice. Our data suggest that rhEPO treatment upregulates the EPOR level in vascular endothelial cells, confers neurovascular protection, and enhances angiogenesis. We further show a promoting effect of rhEPO on LCBF recovery in the ischemic brain. These rhEPO-induced effects may contribute to therapeutic benefits in the treatment of ischemic stroke.