Biology subjects

Engelmann, S. A.

Publications and source records attributed to Engelmann, S. A..

4 recordsLinked to original sources

bioRxiv2023

Microvascular plasticity in stroke recovery: Longitudinal snapshots, network statistical analysis, and dynamics

This research article quantitatively investigates neuro-microvascular network remodeling dynamics following stroke using a novel in vivo two-photon angiography (cubic millimeter volume, weekly snapshots) and high throughput (thousands of connected capillaries) vascular vectorization method. The results suggest distinct temporal patterns of cere-brovascular plasticity, with acute remodeling peaking at one week post-stroke. The network architecture then gradually stabilizes, returning to a new steady state after four weeks. These findings align with previous literature on neuronal plasticity, highlighting the correlation between neuronal and neurovascular remodeling. Quantitative analysis of neurovascular networks using length- and strand-based statistical measures reveals intri-cate changes in network anatomy and topology. The distance and strand-length statistics show significant alterations, with a peak of plasticity observed at one week post-stroke, followed by a gradual return to baseline. The orientation statistic plasticity peaks at two weeks, gradually approaching the (conserved across subjects) stroke signature. The underlying mechanism of the vascular response (angiogenesis vs. tissue deformation), however, is yet unelucidated, requiring network registration advancements. Overall, the combination of two-photon angiography, vectorization, reconstruction/visualization, and statistical analysis enables both qualitative and quantitative assessments of neu-rovascular remodeling dynamics, demonstrating an impactful method for investigating neuro-microvascular network disorders and the therapeutic modes of action thereof. Understanding the timing and nature of neurovascular remodeling allows for optimized interventions, including personalized medicine for stroke rehabilitation. Additionally, the evaluation of pharmaceutical interventions using these tools may facilitate targeted drug development. Furthermore, neurovascular coupling dynamics have implications for neurodegenerative diseases, brain aging, and the field of brain-computer interfaces.

neuroscience↗

bioRxiv2023

Pulse train gating to improve signal generation for in vivo two-photon fluorescence microscopy

SignificanceTwo-photon microscopy is used routinely for in vivo imaging of neural and vascular structure and function in rodents with a high resolution. Image quality, however, often degrades in deeper portions of the cerebral cortex. Strategies to improve deep imaging are therefore needed. We introduce such a strategy using gates of high repetition rate ultrafast pulse trains to increase signal level. AimWe investigate how signal generation, signal-to-noise ratio (SNR), and signal-to-background ratio (SBR) improve with pulse gating while imaging in vivo mouse cerebral vasculature. ApproachAn electro-optic modulator is used with a high-power (6 W) 80 MHz repetition rate ytterbium fiber amplifier to create gates of pulses at a 1 MHz repetition rate. We first measure signal generation from a Texas Red solution in a cuvette to characterize the system with no gating and at a 50%, 25%, and 12.5% duty cycle. We then compare signal generation, SNR, and SBR when imaging Texas Red-labeled vasculature using these conditions. ResultsWe find up to a 6.73-fold increase in fluorescent signal from a cuvette when using a 12.5% duty cycle pulse gating excitation pattern as opposed to a constant 80 MHz pulse train. We verify similar increases for in vivo imaging to that observed in cuvette testing. For deep imaging we find pulse gating to result in a 2.95-fold increase in SNR and a 1.37-fold increase in SBR on average when imaging mouse cortical vasculature at depths ranging from 950 m to 1050 m. ConclusionsWe demonstrate that a pulse gating strategy can either be used to limit heating when imaging superficial brain regions or used to increase signal generation in deep regions. These findings should encourage others to adopt similar pulse gating excitation schemes for imaging neural structure through two-photon microscopy.

neuroscience↗

bioRxiv2021

An evaluation of resonant scanning as a high-speed imaging technique for two-photon imaging of cortical vasculature

We demonstrate a simple, low-cost two-photon microscope design with both galvo-galvo and resonant-galvo scanning capabilities. We quantify and compare the signal-to-noise ratios and imaging speeds of the galvo-galvo and resonant-galvo scanning modes when used for murine neurovascular imaging. The two scanning modes perform as expected under shot-noise limited detection and are found to achieve comparable signal-to-noise ratios. Resonant-galvo scanning is capable of reaching desired signal-to-noise ratios using less acquisition time when higher excitation power can be used. Given equal excitation power and total pixel dwell time between the two methods, galvo-galvo scanning outperforms resonant-galvo scanning in image quality when detection deviates from being shot-noise limited.

neuroscience↗

bioRxiv2021

Diamond Raman Laser and Yb Fiber Amplifier for In Vivo Multiphoton Fluorescence Microscopy

Here we introduce a fiber amplifier and a diamond Raman laser that output high powers (6.5 W, 1.3 W) at valuable wavelengths (1060 nm, 1250 nm) for multiphoton excitation of red-shifted fluorophores. These custom excitation sources are both simple to construct and cost-efficient in comparison to similar custom and commercial alternatives. Furthermore, they operate at a repetition rate (80 MHz) that allows fast image acquisition using resonant scanners. We demonstrate our systems compatibility with fast resonant scanning, the ability to acquire neuronal images, and the capability to image vasculature at deep locations (>1 mm) within the mouse cerebral cortex.

neuroscience↗