Imaging the Impact of Cortical Microcirculation on Synaptic Structure and Sensory-Evoked Hemodynamic Responses In Vivo

Abstract

In vivo two-photon microscopy was used to image in real time dendrites and their spines in a mouse photothrombotic stroke model that reduced somatosensory cortex blood flow in discrete regions of cortical functional maps. This approach allowed us to define relationships between blood flow, cortical structure, and function on scales not previously achieved with macroscopic imaging techniques. Acute ischemic damage to dendrites was triggered within 30 min when blood flow over >0.2 mm2 of cortical surface was blocked. Rapid damage was not attributed to a subset of clotted or even leaking vessels (extravasation) alone. Assessment of stroke borders revealed a remarkably sharp transition between intact and damaged synaptic circuitry that occurred over tens of μm and was defined by a transition between flowing and blocked vessels. Although dendritic spines were normally ~13 μm from small flowing vessels, we show that intact dendritic structure can be maintained (in areas without flowing vessels) by blood flow from vessels that are on average 80 μm away. Functional imaging of intrinsic optical signals associated with activity-evoked hemodynamic responses in somatosensory cortex indicated that sensory-induced changes in signal were blocked in areas with damaged dendrites, but were present ~400 μm away from the border of dendritic damage. These results define the range of influence that blood flow can have on local cortical fine structure and function, as well as to demonstrate that peri-infarct tissues can be functional within the first few hours after stroke and well positioned to aid in poststroke recovery.

P2Y1R-Initiated, IP3R-Dependent Stimulation of Astrocyte Mitochondrial Metabolism Reduces and Partially Reverses Ischemic Neuronal Damage in Mouse

“…Thus, 2MeSDP treatment in the absence of reperfusion at least partially reversed ischemic dendritic damage. Consistent with previous reports, 13 we note that neither laser illumination nor the RB dye by itself affected dendrite beading (data not shown).…”

“…To test the impact of 19 Normal morphology can be rescued by early restoration of blood flow after ischemia. 13 In contrast, if left unchecked, progression of dendrite beading and swelling leads to dendritic loss and neuronal cell death. A key requirement for recovery appears to be an adequate energy supply.…”

Mesoscale infraslow spontaneous membrane potential fluctuations recapitulate high-frequency activity cortical motifs

“…For craniotomy surgery and for maintenance during imaging experiments, mice were anaesthetized with urethane as previously described 67 . Briefly, anaesthesia was induced with urethane (0.12% w/w) and body temperature was maintained at 37°C with a heating pad and feedback regulation from a rectal temperature probe.…”

Chronic Imaging of Cortical Blood Flow using Multi-Exposure Speckle Imaging

“…[16][17][18] Stroke studies in particular benefit from the intrinsic contrast obtained from imaging the effects of dynamic light scattering without introducing exogenous contrast agents into the bloodstream. 19 These studies range from providing a largely qualitative perspective of the presence or absence of flow 20 to the use of dynamic light scattering models to register a quantitative measure of CBF dynamics. 21 The flow estimates from traditional single-exposure LSCI are relative and sensitive to a number of nonflow related parameters, which affect the ability to establish a quantitative baseline.…”