Xin Yu

Achieving precise spatiotemporal control over neuropeptide delivery in vivo remains a major challenge, as conventional approaches lack temporal resolution and control over release kinetics or have limitations for in vivo applications. Here, we demonstrate that photoswitchable azobenzene-containing lipid nanovesicles (“azosomes”) enable light-controlled release of neuropeptides in vivo in the brain of awake moving mice. Azosomes were infused into the hippocampus via optofluidic cannulas and activated using light stimulation in freely behaving mice. In vivo release kinetics were systematically characterized using calcein-loaded azosomes by varying light power, pulse duration, and post-infusion time. Oxytocin (OT)-loaded azosomes were used to assess bioactivity and receptor specificity using dual-color fiber photometry with the genetically encoded OT sensor (MTRIA _OT ), alongside pharmacological blockade with the oxytocin receptor antagonist OVTA (Ornithine-VasoTocin Analog). Azosomes enabled robust, repeatable, and light-dependent cargo release in vivo with tunable kinetics governed by stimulation parameters, with release efficiency controlled by light power and pulse duration. The system maintained functional stability for several hours post-infusion, with near-complete release achievable within a ∼2-hour window and minimal baseline leakage prior to stimulation. Controlled OT delivery produced rapid, receptor-specific increases in MTRIA _OT signals and modulated CA2 hippocampal circuit activity, reducing excitatory neuronal transient frequency and amplitude while altering social interaction dynamics, including decreased latency to initiate contact. These findings establish, for the first time, photoswitchable nanovesicles as a versatile platform for spatiotemporally precise delivery of neuropeptides in vivo , overcoming key limitations of existing delivery strategies and providing a broadly applicable framework for manipulating neuromodulatory signaling with high temporal precision.

Spontaneous vascular dynamics contribute fundamentally to functional MRI signals, but their intrinsic propagation structure remains unresolved at the systems level. Here, we combine 14 T cerebral blood volume (CBV)-weighted fMRI with space-frequency singular value decomposition (SF-SVD) to map vasodynamic propagation across the awake mouse cortex. High-resolution CBV-fMRI identified vessel-aligned, frequency-specific oscillatory modes, and ultra-fast CBV-fMRI enabled three-dimensional mapping of phase gradients across tangential and radial cortical axes. Vasodynamic propagation exhibited multiscale organization, with tangential gradients aligned with previously reported vasomotion traveling waves and radial gradients revealing slower laminar timing structure reflecting depth-dependent vascular regulation. At the group level, trial-wise 3D propagation speed maps revealed dominant cortex-wide patterns, while ROI-level analyses showed region-dependent differences in speed and directionality. These findings reframe intrinsic vascular fluctuations as a measurable system-level feature of brain physiology and establish CBV-fMRI-based propagation mapping as a framework for studying cerebrovascular organization and dysfunction.

Brain-wide, noninvasive methods that directly resolve neuronal activity on millisecond timescales are still lacking in neuroimaging. Hemodynamic fMRI ( ¹ H-based) provides whole-brain maps of activity, yet its vascular origin creates spatial and temporal displacements from neuronal events that complicate interpretation, especially in disease conditions where neurovascular coupling is altered. Here, we developed an ultrafast ²³ Na fMRI platform at 14 T that combines a reshuffled k-t 3D gradient echo readout (TR/TE, 10ms/1ms) with an implantable RF coil and respiration-gated acquisition. This configuration provides the sampling rate and SNR needed to probe quadrupolar T2*-weighted single quantum sodium dynamics on the neuronal timescale. Across rats and mice, somatosensory forepaw stimulation produced a localized ²³ Na signal decrease of ~2-3% in the FP-S1, peaking ~10-30 ms post-stimulus. The activity pattern is well matched with conventional BOLD-fMRI maps acquired in the same animals. Trial-by-trial measurements during simultaneous iGluSnFR glutamate fiber photometry demonstrated that larger evoked glutamate transients coincided with larger NARS decreases, supporting a neuronal origin of the NARS contrast. We interpret the negative NARS response as a transient activity-dependent redistribution of sodium ions toward restricted, protein-rich microdomains, where more restricted rotational dynamics may accelerate T2*short decay and produce a 2-3% signal decrease without requiring large changes in bulk sodium concentration. Together, these results establish neural activity-related sodium (NARS) fMRI as a viable approach for direct, mesoscale neuronal mapping with MRI at millisecond resolution. Graphical A reshuffled k-t 3D gradient echo (GRE) readout with an implantable figure-8 RF coil and respiration-gated trials captures a ~2-3% negative ²³ Na response peaking 10-30 ms after forepaw stimulation in the FP-S1. NARS fMRI responses co-localize with BOLD-fMRI and scale with iGluSnFR glutamate transients, consistent with activity-dependent shifts toward short-T ₂ * sodium microenvironments. Table of Contents (TOC) Blurb: Yu et al. introduce NARS-fMRI, an ultrafast ²³ Na method that resolves millisecond neuronal dynamics in rodent FP-S1. The negative sodium response (10-30 ms) co-localizes with BOLD and correlates with glutamate photometry, supporting a direct neuronal origin.

High spatial resolution sodium (23Na) imaging of brain lesions remains challenging due to the intrinsically low signal-to-noise ratio (SNR) of 23Na-MRI compared with conventional proton (1H) MRI. In this study, we established a high-resolution 23Na-MRI platform based on 14 T preclinical scanner using a dual-tuned head-implanted RF coil. This configuration enables the acquisition of 1H-based T2-weighted anatomical and diffusion-weighted imaging (DWI), as well as 23Na-MRI, from the same animal. Brain-wide 23Na-MRI with 300×300 μm2 in-plane resolution was performed within the first 4 hours after acute middle cerebral artery occlusion (MCAO) induced ischemic stroke induction. Hyperintense 23Na-MRI signals were observed in the ischemic brain regions, presenting a contrast-to-noise ratio (CNR) that exceeded that of T2-weighted images. Infarct regions can be well-identified in the elevated 23Na signal, which is spatially consistent with regions of reduced apparent diffusion coefficient (ADC) values, indicating water restriction in the ischemic core. This work established implanted double-tuned 1H/23Na RF coils as a powerful approach for high-resolution 23Na-MRI readout, facilitating the early detection of ischemic brain injury.

Background: Failure of cerebrovascular reserve is a fundamental determinant of ischemic vulnerability, yet the mechanisms by which vascular smooth muscle dysfunction compromises reserve and predisposes the brain to injury remain incompletely defined. We therefore tested whether a pathogenic smooth muscle mutation produces a baseline failure of cerebrovascular reserve sufficient to render the brain vulnerable to hypoperfusion, even in the absence of fixed arterial occlusion. Methods: We examined cerebrovascular structure, hemodynamics, and reserve in a genetically defined mouse model of ACTA2-associated multisystemic smooth muscle dysfunction syndrome with systemic or brain-restricted expression of the mutant allele. Cerebral artery morphology was assessed using magnetic resonance angiography and black ink angiography. Vascular smooth muscle phenotype was evaluated by immunohistochemistry and proliferation assays. Blood pressure reactivity and cerebral blood flow (CBF) were measured simultaneously using femoral arterial catheterization and laser speckle flowmetry during vasoactive challenges and controlled hypotension. Cerebrovascular stress responses were tested using unilateral common carotid artery occlusion. Downstream brain effects were assessed by histology, resting state functional connectivity imaging, and behavioral testing. Results: Impaired smooth muscle contractility drove rectification and narrowing of major cerebral arteries, downregulation of contractile markers, and increased vascular cell proliferation. These structural changes produced a distinct physiological phenotype: mutant mice exhibited blunted vasoreactivity, diminished spontaneous vasodynamic activity, and a downward shift in the blood pressure-CBF relationship across a wide range of arterial pressures, consistent with loss of cerebrovascular reserve. As a result, CBF was reduced at baseline and could not be maintained during hypotension or acute vascular stress. During carotid occlusion, mutant mice showed impaired compensatory perfusion, greater physiological instability, and worse behavioral outcomes. Chronic reserve failure coincided with white matter loss, reduced neuronal density, disrupted large-scale functional connectivity, and deficits in locomotion, anxiety-related behavior, and working memory. Conclusions: Pathogenic smooth muscle dysfunction caused by ACTA2 mutation produces a baseline failure of cerebrovascular reserve that renders the brain vulnerable to hypoperfusion and stress-induced ischemic injury. These findings establish cerebrovascular reserve failure as a central physiological mechanism linking vascular dysfunction to end-organ brain injury and identify reserve preservation as a critical, potentially actionable determinant of brain health in hypotension-prone vascular disease. Clinical Perspective: What Is New?: - ACTA2 smooth muscle dysfunction produces baseline cerebrovascular reserve impairment, with reduced cerebral blood flow and a downward-shifted pressure-flow relationship in the absence of critical large-vessel occlusion. - Vascular tone dysregulation is coupled to end-organ brain injury, including white matter and neuronal loss, disrupted functional connectivity, and behavioral deficits. - The results support complementary disease mechanisms in ACTA2 vasculopathy: baseline reserve limitation and injury-provoked occlusive remodeling. Clinical Implications: - Patients with ACTA2 vasculopathy may be vulnerable to ischemic brain injury during hypotension or systemic stress despite the absence of critical stenosis or occlusion on routine imaging. - Peri-procedural and acute-care management should emphasize preserving perfusion pressure and cerebrovascular reserve (e.g., during anesthesia, dehydration, or systemic illness). - More broadly, cerebrovascular reserve is a clinically relevant, potentially modifiable determinant of brain health in hypotension-prone vasculopathies and conditions characterized by impaired vascular reactivity.

Concurrent recording of electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) signals reveals cross-scale neurovascular dynamics crucial for explaining fundamental linkages between function and behaviors. However, MRI scanners generate artifacts for EEG detection. Despite existing denoising methods, cabled connections to EEG receivers are susceptible to environmental fluctuations inside MRI scanners, creating baseline drifts that complicate EEG signal retrieval from the noisy background. Here we show that a wireless integrated sensing detector for simultaneous EEG and MRI can encode fMRI and EEG signals on distinct sidebands of the detector’s oscillation wave for detection by a standard MRI console over the entire duration of the fMRI sequence. Local field potential and fMRI maps are retrieved through low-pass and high-pass filtering of frequency-demodulated signals. From optogenetically stimulated somatosensory cortex in ChR2-transfected Sprague Dawley rats, positive correlation between evoked local field potential and fMRI signals validates strong neurovascular coupling, enabling cross-scale brain mapping with this two-in-one transducer.

In the brain, vasomotor dynamics at infra-slow frequencies (∼0.1 Hz), driven by synchronized oscillations of smooth muscle cells in vessel walls, are thought to play a crucial role in regulating cerebral perfusion and underlie resting-state functional connectivity (FC), typically measured by correlated time courses of functional signals. In particular, rodent studies have demonstrated that vasomotor activity contributes to the coherence of blood oxygenation level dependent (BOLD) signal fluctuations. However, in humans, detecting this contribution non-invasively remains challenging due to the limited spatiotemporal sensitivity of functional magnetic resonance imaging (fMRI) to vasomotion. Given that prior studies have identified internal carotid artery stenosis (ICAS) as an informative conditional lesion model of vasomotor and hemodynamic impairments in humans, we investigated whether ICAS affects interhemispheric BOLD coherence at ∼0.1 Hz. Using a multi-modal fMRI framework integrating resting-state fMRI with quantitative mapping of cerebral blood volume, blood flow, oxygen metabolism, and BOLD time lag, we compared BOLD coherence between patients with asymptomatic unilateral ICAS and healthy controls. Frequency-specific analysis revealed significantly diminished interhemispheric BOLD coherence at ∼0.1 Hz across canonical resting-state networks in ICAS patients, while ultra-slow (<0.05 Hz) coherence remained largely preserved. This reduction was spatially widespread and particularly pronounced in watershed areas, i.e., border zones between major vascular territories, associated with significantly increased lateralization of cerebral blood volume (p < 0.01). Notably, coherence-based FC patterns at ∼0.1 Hz were heterogeneous within watershed areas but homogeneous outside, suggesting an interplay between compensatory mechanisms and cerebrovascular impairment. Taken together, our findings demonstrate that ICAS induces subtle, frequency-and region-specific alterations in interhemispheric FC, consistent with a model in which impaired vasomotor activity impacts on resting-state FC in the human brain.

Mild hypoxic-ischaemic encephalopathy is common in neonates, and there are no evidence-based therapies. By school age, 30–40% of those patients experience adverse neurodevelopmental outcomes. The nature and progression of mild injury is poorly understood. We studied the evolution of mild perinatal brain injury using longitudinal two-photon imaging of transgenic fluorescent calcium-sensitive and insensitive proteins to provide a novel readout of neuronal viability and activity at cellular resolution in vitro and in vivo. In vitro, perinatal organotypic hippocampal cultures underwent 15–20 min of oxygen-glucose deprivation. In vivo, mild hypoxia-ischaemia was completed at post-natal day 10 with carotid ligation and 15 min of hypoxia (FiO2, 0.08). Consistent with a mild injury, minimal immediate neuronal death was seen in vitro or in vivo, and there was no volumetric evidence of injury by ex vivo MRI 2.5 weeks after injury (n = 3 pups/group). However, in both the hippocampus and neocortex, these mild injuries resulted in delayed and progressive neuronal loss by the second week after injury compared to controls; measured by fluorophore quenching (n = 6 slices/group in vitro, P < 0.001; n = 8 pups/group in vivo, P < 0.01). Mild hypoxia-ischaemia transiently suppressed cortical network calcium activity in vivo for over 2 h after injury (versus sham, n = 13 pups/group; P < 0.01). No post-injury seizures were seen. By 24 h, network activity fully recovered, and there was no disruption in the development of normal cortical activity for 11 days (n = 8 pups/group). The participation in network activity of individual neurons destined to die in vivo was indistinguishable from those that survived up to 4 days post-injury (n = 8 pups/group). Despite a lack of significant immediate neuronal death and only transient disruptions of network activity, mild perinatal brain injury resulted in a delayed and progressive increase of neuronal death in the hippocampus and neocortex. Neurons that died late were functioning normally for days after injury, suggesting a new pathophysiology of neuronal death after mild injury. Critically, the neurons destined to die late demonstrated multiple biomarkers of viability long after mild injury, suggesting their later death may be modified with neuroprotective interventions.