Neurovascular coupling and CO interrogate distinct vascular regulations.

Neurovascular coupling (NVC), which mediates rapid increases in cerebral blood flow in response to neuronal activation, is commonly used to map brain activation or dysfunction. Here we tested the reemerging hypothesis that CO generated by neuronal metabolism contributes to NVC. We combined functional ultrasound and two-photon imaging in the mouse barrel cortex to specifically examine the onsets of local changes in vessel diameter, blood flow dynamics, vascular/perivascular/intracellular pH, and intracellular calcium signals along the vascular arbor in response to a short and strong CO challenge (10 s, 20%) and whisker stimulation.

Measurement of Blood Velocity With Laser Scanning Microscopy: Modeling and Comparison of Line-Scan Image-Processing Algorithms.

Laser scanning microscopy is widely used to measure blood hemodynamics with line-scans in physiological and pathological vessels. With scans of broken lines, i.e.

The oxygen initial dip in the brain of anesthetized and awake mice.

An ongoing controversy in brain metabolism is whether increases in neural activity cause a local and rapid decrease in oxygen concentration (i.e., the “initial dip”) preceding functional hyperemia.

IGF-1 is an independent predictor of retinal arterioles remodeling in subjects with uncontrolled acromegaly.

Context: Cardiovascular disease is one of the main causes of morbidity in active acromegaly due to the increased prevalence of risk factors and arterial consequences of increased growth hormone levels. No in vivo study has evaluated the consequences of acromegaly on the retinal microvasculature.

Objective: The aim of this study was to identify in vivo the presence of morphological alterations of retinal arterioles in subjects with acromegaly.

Cerebral oxygenation during locomotion is modulated by respiration.

In the brain, increased neural activity is correlated with increases of cerebral blood flow and tissue oxygenation. However, how cerebral oxygen dynamics are controlled in the behaving animal remains unclear. We investigated to what extent cerebral oxygenation varies during locomotion.

In vivo imaging with a water immersion objective affects brain temperature, blood flow and oxygenation.

Previously, we reported the first oxygen partial pressure (Po2) measurements in the brain of awake mice, by performing two-photon phosphorescence lifetime microscopy at micrometer resolution (Lyons et al., 2016). However, this study disregarded that imaging through a cranial window lowers brain temperature, an effect capable of affecting cerebral blood flow, the properties of the oxygen sensors and thus Po2 measurements.

Unbiased Analysis Method for Measurement of Red Blood Cell Size and Velocity With Laser Scanning Microscopy.

Two-photon laser scanning microscopy is widely used to measure blood hemodynamics in brain blood vessels. Still, the algorithms used so far to extract red blood cell (RBC) size and velocity from line-scan acquisitions have ignored the extent to which scanning speed influences the measurements. Here, we used a theoretical approach that takes into account the velocity and direction of both scanning mirrors and RBCs during acquisition to provide an algorithm that measures the real RBC size and velocity.

Vascular Compartmentalization of Functional Hyperemia from the Synapse to the Pia.

Functional hyperemia, a regional increase of blood flow triggered by local neural activation, is used to map brain activity in health and disease. However, the spatial-temporal dynamics of functional hyperemia remain unclear. Two-photon imaging of the entire vascular arbor in NG2-creERT2;GCaMP6f mice shows that local synaptic activation, measured via oligodendrocyte precursor cell (OPC) Ca signaling, generates a synchronous Ca drop in pericytes and smooth muscle cells (SMCs) enwrapping all upstream vessels feeding the activated synapses.

Two-Photon Holographic Stimulation of ReaChR.

Optogenetics provides a unique approach to remotely manipulate brain activity with light. Reaching the degree of spatiotemporal control necessary to dissect the role of individual cells in neuronal networks, some of which reside deep in the brain, requires joint progress in opsin engineering and light sculpting methods. Here we investigate for the first time two-photon stimulation of the red-shifted opsin ReaChR.

Impact of wavefront distortion and scattering on 2-photon microscopy in mammalian brain tissue.

Two-photon (2P) microscopy is widely used in neuroscience, but the optical properties of brain tissue are poorly understood. We have investigated the effect of brain tissue on the 2P point spread function (PSF₂p) by imaging fluorescent beads through living cortical slices. By combining this with measurements of the mean free path of the excitation light, adaptive optics and vector-based modeling that includes phase modulation and scattering, we show that tissue-induced wavefront distortions are the main determinant of enlargement and distortion of the PSF₂p at intermediate imaging depths.

Two-photon imaging of capillary blood flow in olfactory bulb glomeruli.

Two-photon laser scanning microscopy (TPLSM) is an efficient tool to study cerebral blood flow (CBF) and cellular activity in depth in the brain. We describe here the advantages and weaknesses of the olfactory bulb as a model to study neurovascular coupling using TPLSM. By combining intra- and extracellular recordings, TPLSM of CBF in individual capillaries, local application of drugs, we show that odor triggers odorant-specific and concentration-dependent increases in CBF.

The relationship between blood flow and neuronal activity in the rodent olfactory bulb.

In the brain, neuronal activation triggers an increase in cerebral blood flow (CBF). Here, we use two animal models and several techniques (two-photon imaging of CBF and neuronal calcium dynamics, intracellular and extracellular recordings, local pharmacology) to analyze the relationship between neuronal activity and local CBF during odor stimulation in the rodent olfactory bulb. Application of glutamate receptor antagonists or tetrodotoxin directly into single rat olfactory glomeruli blocked postsynaptic responses but did not affect the local odor-evoked CBF increases.

Two-photon imaging of capillary blood flow in olfactory bulb glomeruli.

Analysis of the spatiotemporal coupling between neuronal activity and cerebral blood flow requires the precise measurement of the dynamics of RBC flow in individual capillaries that irrigate activated neurons. Here, we use two-photon microscopy in vivo to image individual RBCs in glomerular capillaries in the rat dorsal olfactory bulb. We find that odor stimulation evokes capillary vascular responses that are odorant- and glomerulus-specific.