Biology subjects

Postnov, D. D.

Publications and source records attributed to Postnov, D. D..

14 recordsLinked to original sources

bioRxiv2026

Sex shapes capillary flows and oxygen extraction in the middle-aged mouse brain

Sex differences in brain aging are well documented, but their origin within the cerebrovascular hierarchy remains unclear. Here we show that cortical blood flow is higher in female than male mice at 15 months of age, at a point when an earlier sex difference in pulsatility and resistance indices has already converged, pial vessel diameter shows no difference between sexes, and estrogen levels are similar between sexes. Using an indicator-dilution and intravascular oxygen measurements using two-photon microscopy, we found that capillary transit-time heterogeneity (CTH) scales more steeply with mean transit time in females, consistent with a passively regulated capillary network, and that this is accompanied by reduced oxygen extraction fraction (OEF) without deficit in arterial oxygen delivery. Spatial transcriptomics reveals that sex differences are organized into distinct regional programs, most prominently in white matter, where a male-associated myelin and axonogenesis signature accompanies reduced white matter volume in females. These molecular and structural differences coincide with elevated hippocampal microglial reactivity and an altered spatial search strategy in females, without any detectable differences in circulating markers of stress, blood-brain barrier integrity, or immunity. Together, these findings indicate that sex differences in the aging brain are expressed at the level of capillary flow regulation and regional tissue programs rather than through bulk cerebral blood flow alone, and that elevated blood flow in females can mask, rather than reflect, adequate tissue oxygenation.

neuroscience↗

bioRxiv2026

Pial arteries bend with every heartbeat

Arterial pulsations are thought to drive perivascular transport by displacing vessel walls radially. In 11 awake mice, all pial arteries also bend with each heartbeat, displacing the wall by three times the pulse-related dilatation per wall, while veins barely move. The bend has a spatial period of about 20 diameters, arrives with the dilatation, at above 1.6 m/s, and dissipates 450 times less energy in the wall.

neuroscience↗

bioRxiv2026

Loss of contractile pericytes and their impaired calcium dynamics exacerbate brain ischemic stroke of awake mice in acute and chronic phases

Ischemic stroke disrupts neurovascular uncoupling, in which neuronal activity fails to evoke appropriate microvascular blood flow responses, despite successful recanalization of upstream arteries. The cellular mechanisms underlying this dysfunction remain poorly defined. We examined Ca{superscript 2} signaling and contractile dynamics of vascular smooth muscle cells, precapillary sphincters and contractile pericytes, using two-photon microscopy and laser speckle imaging in awake mice subjected to transient middle cerebral artery occlusion. During occlusion, precapillary sphincters exhibited pronounced Ca{superscript 2} elevations and constriction, amplifying downstream capillary resistance. Following reperfusion, elevated Ca{superscript 2} signals persisted without proportional diameter changes, indicating early uncoupling between Ca{superscript 2} dynamics and vascular responses. In the chronic phase, loss of precapillary sphincters-associated contractile pericytes was associated with capillary dilation and persistent neurovascular uncoupling. Although partial recovery of pericyte coverage and Ca{superscript 2} activity occurred, stimulus-evoked vascular responses remained blunted. These findings highlight precapillary sphincters as a key contributor to ischemia-induced microvascular dysfunction.

neuroscience↗

bioRxiv2024

Laser speckle imaging of hepatic microcirculation

The liver controls blood homeostasis and depends critically on adequate blood supply. While the global regulation of liver blood flow via the hepatic arterial buffer response is well established, the mechanisms governing hepatic sinusoidal hemodynamics remain elusive. We use laser speckle contrast imaging to investigate the hepatic microvascular blood flow in anesthetized rats. Laser speckle contrast imaging offers a spatial resolution of a few micrometers, enabling visualization of individual microvessels, and a temporal resolution sufficient to track flow dynamics. This allowed us to resolve individual sinusoids and venules on the liver surface and to detect a reduction of the blood flow following local Angiotensin-II injections. We show that the blood flow oscillates with frequencies within the range of 0.05-0.4 Hz, which may be linked to rhythmic contraction of upstream blood vessels. Our findings provide insights into vessel-specific liver microcirculation in vivo, offering new opportunities to explore vascular dysfunction mechanisms in metabolic liver diseases.

physiology↗

bioRxiv2024

Microvascular pulsatility of the ageing brain and confounding effects of anaesthesia

Microvascular pulsatility in the brain is crucial for sustaining the delicate balance between the brains metabolic demands and blood supply, as it affects nutrient exchange, waste removal and blood-brain barrier permeability. Abnormal pulsatility, associated with ageing or vascular risk factors, may impair the clearance of metabolic waste or contribute to conditions such as cerebral small vessel disease, ultimately leading to dementia and increasing the risk of stroke. In the present study, we introduce a new approach for robust full-field characterization of microvascular pulsatility and apply it to study cerebral perfusion and pulsatility across nearly the entire lifespan of awake and anaesthetized C57BL/6 mice. Our findings in awake animals reveal remarkably stable perfusion and pulsatility from 18 to 81 weeks, with pulsatility starting to change only in the final weeks of observation. In contrast, measurements taken under anaesthesia display a range of age-dependent and age-independent changes. We show that isoflurane affects the perfusion in an age-dependent manner, and both isoflurane and ketamine-xylazine, despite their distinct mechanisms, double the perfusion pulsatility and affect vascular diameter pulsatility in a complex manner, highlighting a previously overlooked detrimental effect of anaesthesia on assessing brain function.

physiology↗

bioRxiv2024

The neurovascular coupling response of the aged brain is brain-state dependent.

Brain aging lead to reduced cerebral blood flow and cognitive decline, but how normal aging affects neurovascular coupling (NVC) in the awake brain is unclear. Here, we investigated NVC in relation to calcium changes in vascular mural cells (VMCs) in awake adult and aged mice. We show that NVC responses are reduced and prolonged in the aged brain and that this is more pronounced at the capillary level than in arterioles. However, the overall NVC response, measured as the time integral of vasodilation, is the same in two age groups. In adult, but not in aged mice, the NVC response correlated with Ca2+ signaling in VMCs, while the overall Ca2+ kinetics were slower in aged than in adult mice. In particular, the rate of Ca2+ transport, and the Ca2+ sensitivity of VMCs were reduced in aged mice, explaining the reduced and prolonged vasodilation. Spontaneous locomotion was less frequent and reduced in aged mice as compared to young adult mice, and this was reflected in the slow but prolonged NVC and vascular Ca2+ responses. Taken together, our data characterize the NVC in the aged awake brain as slow but prolonged, and underscoring the importance of brain state in understanding age-related mechanisms.

neuroscience↗

bioRxiv2023

SorCS2 modulates neurovascular coupling via glutamatergic and calcium signaling in astrocytes

AO_SCPLOWBSTRACTC_SCPLOWSorCS2 is involved in trafficking of membrane receptors and transporters. SorCS2 is implicated in brain disorders, but the mechanism remains uncertain. We hypothesized that SorCS2 expression is important for neurovascular coupling. Brains from P8 and 2-month-old wild type mice were stained for SorCS2 and compared to SorCS2 knockouts (Sorcs2-/-). Changes in cerebral perfusion in response to sensory stimulation, i.e., neurovascular coupling, were compared in vivo. Neurovascular coupling was also assessed ex vivo in brain slices loaded with calcium-sensitive dye. Proteomics of astrocytes was analyzed for ingenuity pathways. SorCS2 was strongly expressed in astrocytic endfeet of P8 mice but only in few astrocytes from 2-month-old brains. Sorcs2-/- mice demonstrated reduced neurovascular coupling. This was associated with reduced astrocytic calcium response to neuronal excitation in Sorcs2-/- mice. No difference in cerebral artery caliber nor in endothelial function was seen between wild type and Sorcs2-/- mice. Proteomics indicated reduced glutamatergic signaling and suppressed calcium signaling in Sorcs2-/- astrocytes. We suggest that SorCS2 expression is important for neurovascular coupling due to modulation of glutamatergic and calcium signaling in astrocytes.

neuroscience↗

bioRxiv2022

The assessment of cortical hemodynamical responses induced by tubuloglomerular feedback using in vivo imaging

The tubuloglomerular feedback (TGF) mechanism is crucial in modulating renal hemodynamics and glomerular filtration rate in individual nephrons. Our study aimed to evaluate the TGF-induced vascular responses by comparing the effects of two transport inhibitors with different sites and mechanisms of action. We assessed cortical hemodynamics with high-resolution laser speckle contrast imaging, which enabled the evaluation of blood flow individual micro-vessels and analysis of their dynamical patterns in the time-frequency domain. We demonstrated that a systemic administration of a loop diuretic abolishes TGF-mediated hemodynamic responses. Furthermore, we showed that the local microcirculatory blood flow decreased, and the TGF reset in response to reduced proximal reabsorption elicited by systemic administration of a sodium-glucose co-transporter 2 inhibitor, phlorizin.

physiology↗

bioRxiv2021

Blood flow synchronization in renal microcirculation - a high-resolution imaging study.

AimsInternephron signalling and interaction are fundamental for kidney function. Earlier studies have shown that nephrons signal to each other over short distances and adjust their activity accordingly. Micropuncture experiments revealed synchronous clusters of 2-3 nephrons formed from such interactions, while imaging and modelling results suggested the possibility of larger clusters. Such clusters are expected to play an important role in renal autoregulation, but their presence has not been confirmed and their size has not been estimated. In this study, we present methodology for high resolution renal blood flow imaging and apply it to estimate frequency and phase angle differences in kidney blood vessels under normal conditions and after administration of the vasoactive agents angiotensin II and acetylcholine. Methods and resultsTo resolve signals from separate arterioles in a sufficiently large field of view, we developed a method for renal laser speckle contrast imaging. Our setup provides imaging of blood flow in the kidney cortex with a limit of image resolution at 0.8m per pixel and imaging frequency of 160Hz. We used the method to record from 1.5x1.5 mm2 sections of the renal surface in anaesthetised Sprague-Dawley rats in unstimulated conditions and during IV infusion of the vasoconstrictor angiotensin II or the vasodilator acetylcholine. In each section, we resolved and segmented 94.8{+/-}15.66 individual arterioles and venules, and analyzed blood flow using wavelet spectral analysis to identify clusters of synchronized blood vessels. ConclusionsWe observed spatial and temporal evolution of blood vessel clusters of various sizes, including the formation of large (>90 vessels) long-lived clusters (>10 periods) locked at the frequency of the tubular glomerular feedback (TGF) mechanism. The analysis showed that synchronization patterns and thus the co-operative dynamics of nephrons change significantly when either of the vasoactive agents is administered. On average, synchronization was stronger (larger clusters, longer duration) with angiotensin II administration than in the unstimulated state or with acetyl choline. While it weakens with distance, increased synchronization duration spanned the whole field of view, and likely, beyond it. Neighbouring vessels tend to demonstrate in-phase synchronization, especially in the vasoconstricted condition, which is expected to cause locally increased pressure variation. Our results confirm both the presence of the local synchronization in the renal microcirculatory blood flow and the fact that it changes depending on the condition of the vascular network and the blood pressure, which might have further implications for the role of such synchronization in pathologies development.

physiology↗

bioRxiv2021

Guidelines for obtaining an absolute blood flow index with laser speckle contrast imaging

Laser speckle contrast imaging (LSCI) is a technique broadly applied in research and clinical settings for full-field characterization of tissue perfusion. It is based on the analysis of speckle pattern contrast, which can be theoretically related to the decorrelation time - a quantitative measure of dynamics. A direct contrast to decorrelation time conversion, however, requires prior knowledge of specific parameters of the optical system and scattering media and thus is often impractical. For this reason, and because of the nature of some of the most common applications, LSCI is historically used to measure relative blood flow change. Over time, the belief that the absolute blood flow index measured with LSCI is not a reliable metric and thus should not be used has become more widespread. This belief has resulted from the use of LSCI to compare perfusion in different animal models and to obtain longitudinal blood flow index observations without proper consideration given to the stability of the measurement. Here, we aim to clarify the issues that give rise to variability in the repeatability of the quantitative blood flow index and to present guidelines on how to make robust absolute blood flow index measurements with conventional single-exposure LSCI. We also explain how to calibrate contrast to compare measurements from different systems and show examples of applications that are enabled by high repeatability.

bioengineering↗

bioRxiv2019

Rapid disruption of the cortical microcirculation after mild traumatic brain injury

Traumatic brain injury (TBI) is a major source of cognitive deficits affecting millions annually. The bulk of human injuries are mild, causing little or no macroscopic damage to neural tissue, yet can still lead to long-term neuropathology manifesting months or years later. Although the cellular stressors that ultimately lead to chronic pathology are poorly defined, one notable candidate is metabolic stress due to reduced cerebral blood flow (CBF), which is common to many forms of TBI. Here we used high-resolution in vivo intracranial imaging in a rodent injury model to characterize deficits in the cortical microcirculation during both acute and chronic phases after mild TBI. We found that CBF dropped precipitously during immediate post-injury periods, decreasing to less than half of baseline levels within minutes and remaining suppressed for 1.5-2 hours. Repeated time-lapse imaging of the cortical microvasculature revealed further striking flow deficits in the capillary network, where 18% of vessels were completely occluded for extended periods after injury, and an additional >50% showed substantial stoppages. Decreased CBF was paralleled by extensive vasoconstriction that is likely to contribute to loss of flow. Our data indicate a major role for vascular dysfunction in even mild forms of TBI, and suggest that acute post-injury periods may be key therapeutic windows for interventions that restore flow and mitigate metabolic stress.

neuroscience↗

bioRxiv2019

Neutrophil-mediated dynamic capillary stalls in ischemic penumbra: persistent traffic jams after reperfusion contribute to injury

Ever since the introduction of thrombolysis and the subsequent expansion of endovascular treatments for acute ischemic stroke, it remains to be identified why the actual outcomes are less favorable despite recanalization. Here, by high spatio-temporal resolution imaging of capillary circulation in mice, we introduce the pathological phenomenon of dynamic flow stalls in cerebral capillaries, occurring persistently in the salvageable penumbra after recanalization. These stalls, which are distinct from permanent cellular plugs that can lead to no-flow, were temporarily and repetitively occurring in the capillary network, impairing the overall circulation like small focal traffic jams. In vivo microscopy in the ischemic penumbra revealed leukocytes traveling through capillary lumen or getting stuck, while red blood cell flow was being disturbed in the neighboring segments, within 3 hours after stroke onset. Stall dynamics could be modulated, by injection of an anti-Ly6G antibody specifically targeting neutrophils. By decreasing the number and duration of stalls, we were able to improve the blood flow in the penumbra within 2-24 hours after reperfusion, increase capillary oxygenation, decrease cellular damage and improve functional outcome. Thereby the dynamic microcirculatory stall phenomenon contributes to the ongoing penumbral injury and is a potential hyperacute stage mechanism adding on previous observations of detrimental effects of activated neutrophils in ischemic stroke.\n\nSignificanceThis work provides in vivo evidence that, even in perfused capillaries, abnormal capillary flow patterns in the form of dynamic stalls can contribute to ongoing tissue injury in the salvageable penumbra in very early hours of cerebral ischemia. These events resembling micro traffic jams in a complex road network, are mediated by passage of neutrophils through the microcirculation and persist despite recanalization of the occluded artery.

neuroscience↗

bioRxiv2019

Functional ultrasound speckle decorrelation-based velocimetry of the brain

A high-speed, contrast free, quantitative ultrasound velocimetry (vUS) for blood flow velocity imaging throughout the rodent brain is developed based on the normalized first order temporal autocorrelation function of the ultrasound field signal. vUS is able to quantify blood flow velocity in both transverse and axial directions, and is validated with numerical simulation, phantom experiments, and in vivo measurements. The functional imaging ability of vUS is demonstrated by monitoring blood flow velocity changes during whisker stimulation in awake mice. Compared to existing power Doppler and color Doppler-based functional ultrasound imaging techniques, vUS shows quantitative accuracy in estimating both axial and transverse flow speeds and resistance to acoustic attenuation and high frequency noise.

bioengineering↗

bioRxiv2019

Dynamic Laser Speckle Imaging

Utilizing a high-speed camera and recording back-scattered laser light at more than 20,000 frames per second, we introduce the first wide-field dynamic laser speckle imaging (DLSI) in which we are able to quantify the laser speckleintensity temporal auto-correlation function g2({tau}) for every pixel individually to obtain a quantitative image of the dynamics of the light scattering particles in the sample. The ability to directly and quantitatively measure the intensity auto-correlation function allows us to solve the problem of how to quantitatively interpret data measured by laser speckle contrast imaging (LSCI), multi-exposure laser speckle imaging (MESI) and laser Doppler flowmetry (LDF). The intensity auto-correlation function is related to the field temporal auto-correlation function g1({tau}), which has been quantitatively related to the dynamics of the light scattering particles including flowing red blood cells. The form of g1({tau}) depends on the amount of light scattering (i.e. single or multiple scattering) and the type of particle motion (i.e. ordered or unordered). Although these forms of the field correlation functions have been established for over 30 years, there is no agreement nor experimental support on what scattering and motion regimes are relevant for the varied biomedical applications. We thus apply DLSI to image cerebral blood flow in mouse through a cranial window and show that the generally accepted form of g1({tau}), is applicable only to visible surface vessels of a specific size (20 - 200m). We demonstrate that for flow in smaller vessels and in parenchymal regions that the proper g1({tau}) form corresponds with multiple scattering light and unordered motion which was never considered to be relevant for these techniques. We show that the wrong assumption for the field auto-correlation model results in a severe underestimation of flow changes when measuring blood flow changes during ischemic stroke. Finally, we describe how DLSI can be integrated with other laser speckle methods to guide model selection, or how it can be used by itself as a quantitative blood flow imaging technique.

bioengineering↗