Neurovascular coupling is preserved in chronic stroke recovery after targeted photothrombosis

IGF-1 signaling pathway activation promotes axonal regeneration and repair: A mechanism study on catalpol-induced functional recovery after ischemic stroke

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese Medicine (TCM) theory, there is a concept of "tonifying the kidney and generating marrow, and marrow enriches and nourishes the brain ", which believes that tonifying the kidney and generating marrow can promote brain marrow repair and neurological function recovery. This theoretical framework has been substantiated by multiple modern medical studies. Catalpol, a bioactive iridoid glycoside extracted from Rehmannia glutinosa (Gaertn.) DC. has been traditionally employed in TCM for "kidney tonification, marrow generation, and brain nourishment". Regenerative remodeling of corticospinal tracts (CST) mediated by axonal regeneration, collateral formation, and neural network reconstruction is critical for neurological recovery after ischemic stroke. As the primary active component of Rehmannia glutinosa, catalpol may manifest the traditional medicinal effects of promoting neurological recovery through modern neuroregenerative mechanisms.

AIM OF THE STUDY

To verify whether catalpol promotes neurological recovery after ischemic stroke and elucidate its underlying mechanisms.

METHODS

Potential therapeutic targets of catalpol were first identified through network pharmacology coupled with cellular thermal shift assay (CETSA) validation. In vivo experiments utilized a photothrombotic (PT) stroke mouse model, in which catalpol's effects on neurological recovery were quantitatively assessed using behavioral tests. Axonal regeneration dynamics and IGF-1 pathway activation were systematically evaluated through functional magnetic resonance imaging (fMRI) for CST remodeling, growth-associated protein 43 (GAP43) and myelin basic protein (MBP) immunofluorescence for axonal sprouting quantification, and Western blotting for insulin-like growth factor-1 (IGF-1), insulin-like growth factor-1 receptor (IGF-1R), mammalian target of rapamycin (mTOR), and GAP43 expression profiling. Complementary in vitro studies employing oxygen-glucose deprived (OGD) neurons demonstrated catalpol's effects on proliferation, migration and axonal growth using Cell Counting Kit-8 (CCK-8), immunofluorescence, scratch wound assay and Western Blot. Mechanistic specificity was confirmed through pharmacological IGF-1R inhibition with linsitinib.

RESULTS

Catalpol was found to directly bind to IGF-1R, as evidenced by molecular docking (binding energy: -6.5 kcal/mol) and CETSA (ΔTm = 4.38 °C). In vivo, catalpol treatment significantly improved motor and sensory recovery in post-stroke mice, reducing error rates in irregular ladder walking (P = 0.014 vs. model) and shortening sticker removal times (P = 0.0043 vs. model), effects that were abolished by IGF-1R inhibition with linsitinib. Diffusion tensor imaging revealed enhanced fractional anisotropy (FA) values in corticospinal tract regions (e.g., dorsal fornix: P = 0.0496), alongside increased axonal markers GAP43 and MBP expression (P < 0.01) in peri-infarct tissues. In vitro, catalpol rescued oxygen-glucose deprivation (OGD)-induced neuronal damage, promoting SH-SY5Y cell viability (P < 0.01), neurite elongation (P < 0.0001), and scratch wound closure (P < 0.001). Mechanistically, catalpol upregulated IGF-1R phosphorylation, activated mTOR signaling, and suppressed phosphatase and tensin homolog deleted on chromosome ten (PTEN), thereby elevating GAP43, osteopontin (OPN), and p-S6 levels (P < 0.05-0.001). Co-treatment with linsitinib negated these effects, confirming the dependency on IGF-1R/mTOR/PTEN axis. These findings establish catalpol as a multimodal neuroregenerative agent targeting IGF-1 signaling to drive axonal repair and functional recovery post-stroke.

CONCLUSION

Our research elucidates that catalpol improves neurological recovery in ischemic stroke by regulating the IGF-1 signaling pathway to promote axonal regenerative repair, providing a new perspective for addressing the challenge of functional recovery in ischemic stroke.

Exploring neurovascular coupling in stroke patients: insights on linear and nonlinear dynamics using transfer entropy

Objective.The study of neurovascular coupling (NVC), the relationship between neuronal activity and cerebral blood flow, is essential for understanding brain physiology in both healthy and pathological states. Current methods to study NVC include neuroimaging techniques with limited temporal resolution and indirect neuronal activity measures. Methods including electroencephalographic (EEG) data are predominantly linear and display limitations that nonlinear methods address. Transfer entropy (TE) explores linear and nonlinear relationships simultaneously. This study hypothesizes that complex NVC interactions in stroke patients, both linear and nonlinear, can be detected using TE.Approach.TE between simultaneously recorded EEG and cerebral blood flow velocity (CBFV) signals was computed and analyzed in three settings: ipsilateral (EEG and CBFV from same hemisphere) stroke and nonstroke, and contralateral (EEG from stroke hemisphere, CBFV from nonstroke hemisphere). A surrogate analysis was performed to evaluate the significance of TE values and to identify the nature of the interactions.Main results.The results showed that EEG generally influenced CBFV. There were more linear+nonlinear interactions in the ipsilateral nonstroke setting and in the delta band in ipsilateral stroke and contralateral settings. Interactions between EEG and CBFV were stronger on the nonstroke side for linear+nonlinear dynamics. The strength and nature of the interactions were weakly correlated with clinical outcomes (e.g. delta band (p<0.05): infarct growth linear = -0.448, linear+nonlinear = -0.339; NIHSS linear = -0.473, linear+nonlinear = -0.457).Significance.This study exemplifies the benefits of using TE in linear and nonlinear NVC analysis to better understand the implications of these dynamics in stroke severity.

Neurovascular coupling over cortical brain areas and resting state network connectivity with and without rigidified carotid artery

Significance

Neurovascular coupling (NVC) is key to research as hemodynamics can reflect neuronal activation and is often used in studies regarding the resting state network (RSN). However, several circumstances, including diseases that reduce blood vessel elasticity, can diminish NVC. In these cases, hemodynamic proxies might not accurately reflect the neuronal RSN.

Aim

We aim to investigate in resting state if (1) NVC differs over brain regions, (2) NVC remains intact with a mild rigidification of the carotid artery, (3) hemodynamic-based RSN reflects neuronal-based RSN, and (4) RSN differs with a mildly rigidified artery.

Approach

We rigidified the right common carotid artery of mice ( n = 15 ) by applying aCaCl 2 -soaked cloth to it (NaCl for Sham, n = 17 ). With simultaneous GCaMP and intrinsic optical imaging, we compared neuronal activation to hemodynamic changes over the entire cortex.

Results

NVC parameters did not differ between the CaCl and Sham groups. Likewise, GCaMP and hemodynamic RSN showed similar connections in both groups. However, the parameters of NVC differed over brain regions. Retrosplenial regions had a slower response and a higher HbR peak than sensory and visual regions, and the motor cortex showed less HbO influx than sensory and visual regions.

Conclusions

NVC in a resting state differs over brain regions but is not altered by mild rigidification of the carotid artery.

From Mechanisms to Medicine: Neurovascular Coupling in the Diagnosis and Treatment of Cerebrovascular Disorders: A Narrative Review

Neurovascular coupling (NVC) refers to the process of local changes in cerebral blood flow (CBF) after neuronal activity, which ensures the timely and adequate supply of oxygen, glucose, and substrates to the active regions of the brain. Recent clinical imaging and experimental technology advancements have deepened our understanding of the cellular mechanisms underlying NVC. Pathological conditions such as stroke, subarachnoid hemorrhage, cerebral small vascular disease, and vascular cognitive impairment can disrupt NVC even before clinical symptoms appear. However, the complexity of the underlying mechanism remains unclear. This review discusses basic and clinical experimental evidence on how neural activity sensitively communicates with the vasculature to cause spatial changes in blood flow in cerebrovascular diseases. A deeper understanding of how neurovascular unit-related cells participate in NVC regulation is necessary to better understand blood flow and nerve activity recovery in cerebrovascular diseases.

Spatiotemporal relationships between neuronal, metabolic, and hemodynamic signals in the awake and anesthetized mouse brain

Neurovascular coupling (NVC) and neurometabolic coupling (NMC) provide the basis for functional magnetic resonance imaging and positron emission tomography to map brain neurophysiology. While increases in neuronal activity are often accompanied by increases in blood oxygen delivery and oxidative metabolism, these observations are not the rule. This decoupling is important when interpreting brain network organization (e.g., resting-state functional connectivity [RSFC]) because it is unclear whether changes in NMC/NVC affect RSFC measures. We leverage wide-field optical imaging in Thy1-jRGECO1a mice to map cortical calcium activity in pyramidal neurons, flavoprotein autofluorescence (representing oxidative metabolism), and hemodynamic activity during wake and ketamine/xylazine anesthesia. Spontaneous dynamics of all contrasts exhibit patterns consistent with RSFC. NMC/NVC relative to excitatory activity varies over the cortex. Ketamine/xylazine profoundly alters NVC but not NMC. Compared to awake RSFC, ketamine/xylazine affects metabolic-based connectomes moreso than hemodynamic-based measures of RSFC. Anesthesia-related differences in NMC/NVC timing do not appreciably alter RSFC structure.

Widefield in vivo imaging system with two fluorescence and two reflectance channels, a single sCMOS detector, and shielded illumination

Significance

Widefield microscopy of the entire dorsal part of mouse cerebral cortex enables large-scale ("mesoscopic") imaging of different aspects of neuronal activity with spectrally compatible fluorescent indicators as well as hemodynamics via oxy- and deoxyhemoglobin absorption. Versatile and cost-effective imaging systems are needed for large-scale, color-multiplexed imaging of multiple fluorescent and intrinsic contrasts.

Aim

We aim to develop a system for mesoscopic imaging of two fluorescent and two reflectance channels.

Approach

Excitation of red and green fluorescence is achieved through epi-illumination. Hemoglobin absorption imaging is achieved using 525- and 625-nm light-emitting diodes positioned around the objective lens. An aluminum hemisphere placed between objective and cranial window provides diffuse illumination of the brain. Signals are recorded sequentially by a single sCMOS detector.

Results

We demonstrate the performance of our imaging system by recording large-scale spontaneous and stimulus-evoked neuronal, cholinergic, and hemodynamic activity in awake, head-fixed mice with a curved "crystal skull" window expressing the red calcium indicator jRGECO1a and the green acetylcholine sensorGRAB ACh 3.0 . Shielding of illumination light through the aluminum hemisphere enables concurrent recording of pupil diameter changes.

Conclusions

Our widefield microscope design with a single camera can be used to acquire multiple aspects of brain physiology and is compatible with behavioral readouts of pupil diameter.

The novel imaging methods in diagnosis and assessment of cerebrovascular diseases: an overview

Cerebrovascular diseases, including ischemic strokes, hemorrhagic strokes, and vascular malformations, are major causes of morbidity and mortality worldwide. The advancements in neuroimaging techniques have revolutionized the field of cerebrovascular disease diagnosis and assessment. This comprehensive review aims to provide a detailed analysis of the novel imaging methods used in the diagnosis and assessment of cerebrovascular diseases. We discuss the applications of various imaging modalities, such as computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and angiography, highlighting their strengths and limitations. Furthermore, we delve into the emerging imaging techniques, including perfusion imaging, diffusion tensor imaging (DTI), and molecular imaging, exploring their potential contributions to the field. Understanding these novel imaging methods is necessary for accurate diagnosis, effective treatment planning, and monitoring the progression of cerebrovascular diseases.

High throughput detection of capillary stalling events with Bessel beam two-photon microscopy

Significance

Brief disruptions in capillary flow, commonly referred to as capillary "stalling," have gained interest recently for their potential role in disrupting cerebral blood flow and oxygen delivery. Approaches to studying this phenomenon have been hindered by limited volumetric imaging rates and cumbersome manual analysis. The ability to precisely and efficiently quantify the dynamics of these events will be key in understanding their potential role in stroke and neurodegenerative diseases, such as Alzheimer's disease.

Aim

Our study aimed to demonstrate that the fast volumetric imaging rates offered by Bessel beam two-photon microscopy combined with improved data analysis throughput allows for faster and more precise measurement of capillary stall dynamics.

Results

We found that while our analysis approach was unable to achieve full automation, we were able to cut analysis time in half while also finding stalling events that were missed in traditional blind manual analysis. The resulting data showed that our Bessel beam system was captured more stalling events compared to optical coherence tomography, particularly shorter stalling events. We then compare differences in stall dynamics between a young and old group of mice as well as a demonstrate changes in stalling before and after photothrombotic model of stroke. Finally, we also demonstrate the ability to monitor arteriole dynamics alongside stall dynamics.

Conclusions

Bessel beam two-photon microscopy combined with high throughput analysis is a powerful tool for studying capillary stalling due to its ability to monitor hundreds of capillaries simultaneously at high frame rates.