Background: There is increasing interest in high-contrast cerebrospinal fluid (CSF) MRI for imaging perivascular spaces (PVSs). Dilated PVSs, associated with aging, dementia, and various other conditions, are readily detected within the white matter (WM), basal ganglia, and midbrain. While 7T MRI enables detection of smaller PVSs, cortical PVS burden has received limited attention despite its potential value for understanding neurological conditions. Purpose: To investigate the detectability of cortical PVS segments in healthy participants using heavily T2-weighted MRI at 7T. Materials and methods: A T2-weighted 3D-TSE sequence was optimized at 7T to detect CSF with high resolution and contrast-to-noise ratio (CNR) while minimizing signal from surrounding tissues. A semi-automated pipeline was developed to extract PVSs and quantify their density in the whole brain, including the cortex. Results: Seventeen healthy volunteers (40±14 years) were scanned at 7T. Optimized TSE achieved a CSF-to-tissue CNR of ∼180:1, enabling detection of small PVSs throughout the brain and leukocortical segments. About 20% of WM PVSs contained a leukocortical segment. WM PVSs with a leukocortical segment represented 70% of the total PVS volume. PVS density in the cortex was ∼0.7% (∼6-fold lower than WM), with highest in the insula and lowest in the auditory cortex. Conclusion: High-resolution CSF imaging using optimized 3D-TSE MRI at 7T allows detection and quantification of leukocortical PVS segments at the gray-white matter interface in healthy individuals. This study lays the groundwork for exploring regional PVS changes related to the cortex and their potential use in diagnosis or prognosis of neurological diseases.

PURPOSE:7T pseudo-continuous arterial spin labeling (PCASL) can benefit from combining 3D-EPI with high-performance background suppression (BS) pulses. However, the perfusion signal can be compromised by increased B1 and ∆ B0 inhomogeneity, and high SAR demands limiting the labeling duration (LD), labeling efficiency and BS inversion efficiency. METHODS:7T PCASL SNR efficiency (SNReff) was quantified using a range of LD (500-4000 ms) with optimized BS inversion pulses and 3D-EPI acquisitions. PCASL sensitivity to ∆ B0 was also investigated by measuring through-plane field variations along the feeding arteries and acquiring perfusion data across a range of PCASL mean gradients (Gmean, -0.8 to +0.8 mT/m) with in-plane ∆ B0 corrections. RESULTS:Optimized WURST BS pulses achieved ∼0.93 inversion efficiency. PCASL SNReff was maximized when employing a LD of ∼3 s (B1pcasl = 1 μ T, duty cycle = 60%), providing ∼25% higher SNReff than 1 s LD typically used at 7T. Arteries with strong negative though-plane ∆ B0 gradients ( G ∆ B 0 ) at the labeling plane generated low perfusion signal in the corresponding arterial territories when using a Gmean of 0.4 mT/m. In these cases, the perfusion signal increased ∼128% by using a higher Gmean of 0.8 mT/m. CONCLUSION:7T PCASL SNReff can be maximized with LD of ∼3 s when using 3D-EPI and optimized WURST BS pulses. A Gmean of 0.8 mT/m improved PCASL robustness to ∆ B0 field gradients along the feeding arteries without the need for subject specific corrections. Use of higher Gmean also offers benefits in cases with multiple G ∆ B 0 polarities and non-linear field variations.

Single cell transcriptomics supports both cell-specific characterization and the identification of responses to changes in neural activity. Unilateral whisker denervation in adult male and female mice activates post-critical period synaptic plasticity, but the transcriptional responses of neuronal subtypes remain unknown. Single nucleus RNA sequencing and multiplex fluorescence in situ hybridization identified previously unexplored plasticity mechanisms in layer 4 (L4) excitatory neurons in intact sensory cortex. We detected differentially expressed genes related to glutamate receptor signaling and synaptogenesis in thalamocortical (TC) recipient L4 sensory cortex neurons after whisker denervation. L4 excitatory neurons increase expression of glutamate receptors indicative of stabilized and potentiated TC synapses along the intact pathway. Immunohistochemistry and electrophysiology determined that intracortical connections to L4 neurons were specifically increased. Transcriptionally unique subtypes of L4 neurons responded uniformly to whisker denervation, likely responding to the global upregulation of activity in the intact sensory cortex after unilateral whisker denervation. These adaptations likely underlie the increased cortical activity responding to intact sensory inputs that are observed in rodents and humans after unilateral denervation injury.

Detecting changes in perivascular spaces (PVS) holds promise as a biomarker for neurodegenerative diseases. These spaces exhibit increased protein accumulation and dilatation in neurodegenerative diseases even preceding symptomatic stages. Advanced MRI techniques at high fields offer unparalleled clarity in visualizing these subtle structures. Notably, patients with Alzheimer’s disease (AD) show increased number of dilated PVS compared to healthy individuals in 7T MRI. While previous studies have primarily focused on white matter PVS due to their large size and visibility, cortical PVS remain relatively unexplored despite their potential diagnostic significance in diseases such as AD and motor neuron disease (MND). Recently, we optimized heavily T2-weighted Turbo Spin Echo (TSE) at 7T, exclusively highlighting cerebrospinal fluid (CSF) signals, thus enabling the visualization of cortical PVS for the first time in healthy individuals. Leveraging this ability to detect cortical PVS, we aim to investigate cortical PVS in neurodegenerative diseases. Seven MND and 5 AD/ADRD patients enrolled in an NIH IRB approved protocol (NCT03225144), and 20 healthy controls were scanned using Seimens Terra 7T MRI with our optimized T2-weighted TSE sequence (TR = 2430 ms, TE = 500 ms, ETL = 108, TA = 10 min) achieving an isotropic resolution of 0.5 mm (125 nl voxels). The optimized sequence achieved a CSF-to-tissue signal ratio of approximately 30:1. After thresholding above noise, it was possible to detect CSF volumes of 10 nanoliters per voxel. In controls, cortical perivascular spaces were detected with unique morphology and have a density of 1-2% of grey matter with the highest density in insular region. In one control, the CSF images revealed extensive PVS-like structures in a previously suspected cyst formation at the juxtacortical area (Figure 1). Furthermore, patients with MND exhibited multiple distinct cortical PVS, most pronounced in the motor cortex (Figure 2). Our findings underscore the utility of CSF-only MRI in uncovering intricate structural details of cortical PVS, which can be explored in neurodegenerative diseases. This non-invasive imaging modality holds promise as a sensitive biomarker for neurodegenerative diseases, with ongoing efforts aimed at quantifying disease-specific cortical PVS and elucidating clinical implications of changes on cortical PVS.

Abstract In a step towards generating switchable MRI cellular labels, we demonstrate in-situ field switching of micron scale metamagnetic Iron-Rhodium (FeRh) thin film particles. A thin-film (200 nm) FeRh sample was fabricated and patterned into an array of progressively smaller squares with sizes ranging from 500 μm down to 1 μm. The large first order phase change from antiferromagnetic to ferromagnetic state was characterized using vibrating sample magnetometry, magnetic force microscopy, and MRI. Room temperature MRI experiments sensitive to the local magnetic field surrounding the particles demonstrated the low moment state (OFF MRI contrast) at 4.7T and high moment state (ON MRI contrast) at 11.7T for the array where sizes down to 2–3 μm were observed in MRI at 50 μm resolution. The expected temperature dependent MRI contrast change was seen at 4.7T, where 10 μm particles could be observed at 150 μm resolution in the ON state. A shielded MRI insert, used to temporarily increase or decrease the magnetic field up to 0.77T amplitude, was used to reversibly switch the particle array at constant temperature and blink the particles ON and OFF at 4.7T. This work demonstrates the MRI contrast switching potential for FeRh particles with biological cell dimensions, and the use of magnetic field pulses for reversible MRI label contrast control.

Significance:Cocaine exerts effects on vascular and cellular functions in the brain. The interactions among cerebrovasculature, neurons, and astrocytes and their dynamic changes during exposure complicate the understanding of its effects. Therefore, there is a need for simultaneous, multiparameter in vivo measurements to accurately distinguish these effects. Aim:A multimodal optical imaging approach that is tailored to investigate cocaine's effects on cerebrovasculature, neurons, and astrocytes in high-spatiotemporal resolution and large field of view is presented with comparisons to other modalities. Approach:This approach integrates optical coherence tomography, fluorescence, and spectral absorption imaging to permit high-resolution imaging of 3D cerebrovessels, cerebral blood flow (CBF), changes in oxygenated/deoxygenated hemoglobin, and large-scale cellular activities via intracellular calcium fluorescence expressed through genetically encoded calcium indicators in the mouse cortex. Results:Results show that cocaine induces vasoconstriction and reduces CBF, thus increasing the susceptibility of the brain to ischemia with chronic exposure. Moreover, cocaine alters neuronal activity and frontal responses to deep brain stimulation. Conclusions:These findings on cocaine's effects on the neuro-astroglial-vascular network in the prefrontal cortex highlight the unique capacity of optical imaging to reveal the cellular and vascular mechanisms underlying cocaine's neurotoxic effects on brain function.

Neuroplasticity in sensory brain areas supports adaptation after nerve injury and fundamentally impacts sensation and movement. However, limited neuroplasticity in somatosensory areas due to the early critical period makes determining the role of thalamocortical (TC) inputs in sensorimotor signal processing challenging. Here, we demonstrated that reactivation of TC neuroplasticity was associated with an increase in the number of neurons in layer IV (L4) of the whisker primary somatosensory cortex (wS1) with a stable excitation-inhibition ratio. Highly synchronized neural activity in L4 propagated throughout the wS1 column and to the downstream areas, including whisker secondary somatosensory, primary motor cortices, and contralateral wS1. These results provide crucial evidence that TC inputs can alter the neural activity of sensory-motor pathways even after the critical period. Altogether, these enormous changes in sensorimotor circuit activity are important for adaptation following an injury such as limb loss, stroke, or other forms of neural injury.

Rationale: The brain remains a challenging organ for drug delivery. Earlier studies demonstrated that transcranial application of small molecular therapeutics and MRI contrast such as manganese ion (Mn2+) could serve as a new method for delivering molecules to the brain. In this earlier work using rats, manganese-enhanced MRI (MEMRI) demonstrated that Mn2+ passed most effectively through regions of the skull containing suture lines or dense vessel/marrow. In the present study, the delivery of Mn2+ to the brain using specific skull vessel/marrow pathways has been investigated. Methods: In-vivo microCT scans of rat skull was conducted to study the intricate geometry of vessel/marrow pathways connecting the outer skull surface and meninges. Specific vessel/marrow paths were identified. MnCl2 (500 mM) solution was pipetted directly on the skull bone surface above the target path. After 2 hr, rats were subjected to MRI. Results: High-resolution microCT images reveal that (a) there are "short paths" through the skull which have vessels on the outer surface of the skull, which directly pass through the vessel/marrow and then reach the meninges on the other side of the skull; (b) the skull above the cerebellum (interparietal bone) exhibits a significantly higher density of vessel/marrow compared to the frontal and parietal bone enabling testing whether direct application to skull enables transcranial movement and (c) thinning the skull in specific regions can lead to exposing vessel pathways from mid-skull to the meninges. Guided by microCT imaging, Mn2+ delivery to the brain could be accomplished as assayed with MEMRI through these different specific pathways. Two hours post pipetting MnCl2 solution onto the top of a short path through the intact skull, Mn2+ could be delivered readily to levels that produce detectable brain tissue enhancement by MEMRI. A T1 enhanced volume of 2.27 ± 1.47 mm3 was measured through the short path. Two hours post applying a MnCl2 solution to the intact skull above the cerebellum enabled MEMRI detection of a volume of enhanced brain tissue of 2.48 ± 2.66 mm3. Finally, in areas where surface short paths are absent but a path from mid skull to meninges is present, minimal thinning of the skull led to effective Mn2+ delivery, enabling MEMRI detection of volume of 4.68 ± 2.70 mm3. Conclusions: MicroCT-guided transcranial delivery via vessel/marrow pathways may offer a less invasive and more localized method for administering imaging probes and therapeutics to the brain.

Objective: We present a 500 MHz inductive birdcage RF resonator for imaging the human brain in an 11.7 T MRI scanner. Methods: A homogenous circularly polarized transmit field (B-1(+)) was generated by transmitting power to the resonator through four couplers driven in differential mode and with an incremental 90-degree phase delay. A detailed mechanical and electrical model of the hardware, loaded with different phantoms, was generated and its performance simulated using a finite-difference time-domain method. Results: The head-size inductively coupled birdcage presented a fundamental mode at 500 MHz. MR thermometry maps were in good agreement with heating profiles estimated from simulated SAR maps Conclusion: The model of the hardware was validated through both bench and MRI measurements. Significance: This validation is important for future analysis of radiofrequency safety and performance at ultra-high field MRI through the prediction of SAR and B-1(+) profiles across different human brain models at various positions inside the coil.

There has been renewed interest in neural transplantation of cells and tissues for brain repair. Recent studies have demonstrated the ability of transplanted neural precursor cells and in vitro grown organoids to mature and locally integrate into host brain circuitry. Most studies have focused on how the transplant behaves and functions after the procedure, but the extent to which the host brain can properly innervate the transplant, particularly in the context of aging, is largely unexplored. Here we report that transplantation of rat embryonic cortical precursor cells into the cerebrospinal fluid-subventricular zone (CSF-SVZ) interface of adult rat brains generates a brain-like tissue (BLT) at an ectopic site. This model allows for the assessment of precursor cell development, cellular interactions, and graft-host connectivity as a function of host age. We found that the transplanted precursor cells initially proliferated, then differentiated, and developed into mature BLTs, which received supportive cellular components from the host including blood vessels, microglia, astrocytes, and oligodendrocytes. There was integration of the BLT into the host brain which occurred at all ages studied, suggesting that host age does not affect the maturation and integration of the precursor cell-derived BLT. Long-range axonal projections from the BLT into the host brain were robust throughout the different aged recipients. However, long-distance innervation originating from the host brain into the BLT significantly declined with age. This work demonstrates the feasibility and utility of integrating new neural tissue structures at ectopic sites into adult brain circuits to study host-transplant interactions.

Magnetic Resonance Imaging (MRI) can provide the location and signal characteristics of pathological regions within a postmortem tissue block, thereby improving the efficiency of histopathological studies. However, such postmortem-MRI guided histopathological studies have so far only been performed on fixed samples as imaging tissue frozen at the time of extraction, while preserving its integrity, is significantly more challenging. Here we describe the development of cold-postmortem-MRI, which can preserve tissue integrity and help target techniques such as transcriptomics. As a first step, RNA integrity number (RIN) was used to determine the rate of tissue biomolecular degradation in mouse brains placed at various temperatures between -20 °C and +20 °C for up to 24 h. Then, human tissue frozen at the time of autopsy was immersed in 2-methylbutane, sealed in a bio-safe tissue chamber, and cooled in the MRI using a recirculating chiller to determine MRI signal characteristics. The optimal imaging temperature, which did not show significant RIN deterioration for over 12 h, at the same time giving robust MRI signal and contrast between brain tissue types was deemed to be -7 °C. Finally, MRI was performed on human tissue blocks at this optimal imaging temperatures using a magnetization-prepared rapid gradient echo (MPRAGE, isotropic resolution between 0.3-0.4 mm) revealing good gray-white matter contrast and revealing subpial, subcortical, and deep white matter lesions. RINs measured before and after imaging revealed no significant changes (n = 3, p = 0.18, paired t-test). In addition to improving efficiency of downstream processes, imaging tissue at sub-zero temperatures may also improve our understanding of compartment specificity of MRI signal.

PURPOSE:Gene-expression reporter systems, such as green fluorescent protein, have been instrumental to understanding biological processes in living organisms at organ system, tissue, cell, and molecular scales. More than 30 years of work on developing MRI-visible gene-expression reporter systems has resulted in a variety of clever application-specific methods. However, these techniques have not yet been widely adopted, so a general-purpose expression reporter is still required. Here, we demonstrate that the manganese ion transporter Zip14 is an in vivo MRI-visible, flexible, and robust gene-expression reporter to meet this need. METHODS:Plasmid constructs consisting of a cell type-specific promoter, gene coding for human Zip14, and a histology-visible tag were packaged into adeno-associated viruses. These viruses were intracranially injected into the mouse brain. Serial in vivo MRI was performed using a vendor-supplied 3D-MPRAGE sequence. No additional contrast agents were administered. Animals were sacrificed after the last imaging timepoint for immunohistological validation. RESULTS:Neuron-specific overexpression of Zip14 produced substantial and long-lasting changes in MRI contrast. Using appropriate viruses enabled both anterograde and retrograde neural tracing. Expression of Zip14 in astrocytes also enabled MRI of glia populations in the living mammalian brain. CONCLUSIONS:The flexibility of this system as an MRI-visible gene-expression reporter will enable many applications of serial, high-resolution imaging of gene expression for basic science and therapy development.

There has been renewed interest in neural transplantation of cells and tissues for brain repair. Recent studies have demonstrated the ability of transplanted neural precursor cells and in vitro grown organoids to mature and locally integrate into host brain neural circuitry. Much effort has focused on how the transplant behaves and functions after the procedure, but the extent to which the host brain can properly innervate the transplant, particularly in the context of aging, is largely unexplored. Here we report that transplantation of rat embryonic cortical precursor cells into the cerebrospinal fluid-subventricular zone (CSF-SVZ) of adult rat brains generates a brain-like tissue (BLT) at an ectopic site. This model allows for the assessment of long-range connectivity and cellular interactions between the transplant and the host brain as a function of host age. The transplanted precursor cells initially proliferate, then differentiate, and develop into mature BLTs, which receive supportive cellular components from the host including blood vessels, microglia, astrocytes, and oligodendrocytes. There was integration of the BLT into the host brain which occurred at all ages studied, suggesting that host age does not affect the maturation and integration of the transplant-derived BLT. Long-range axonal projections from the BLT into the host brain were robust throughout the different aged recipients. However, long-distance innervation originating from the host brain into the BLT significantly declined with age. This work demonstrates the feasibility and utility of integrating new neural tissue structures at ectopic sites into adult brain circuits to study host-transplant interactions.

Introduction Postmortem MRI provides insight into location of pathology within tissue blocks, enabling efficient targeting of histopathological studies. While postmortem imaging of fixed tissue is gaining popularity, imaging tissue frozen at the time of extraction is significantly more challenging. Methods Tissue integrity was examined using RNA integrity number (RIN), in mouse brains placed between -20 °C and 20 °C for up to 24 hours, to determine the highest temperature that could potentially be used for imaging without tissue degeneration. Human tissue frozen at the time of autopsy was sealed in a tissue chamber filled with 2-methylbutane to prevent contamination of the MRI components. The tissue was cooled to a range of temperatures in a 9.4T MRI using a recirculating aqueous ethylene glycol solution. MRI was performed using a magnetization-prepared rapid gradient echo (MPRAGE) sequence with inversion time of 1400 ms to null the signal from 2-methylbutane bath, isotropic resolution between 0.3-0.4 mm, and scan time of about 4 hours was used to study the anatomical details of the tissue block. Results and Discussion A temperature of -7 °C was chosen for imaging as it was below the highest temperature that did not show significant RIN deterioration for over 12 hours, at the same time gave robust imaging signal and contrast between brain tissue types. Imaging performed on various human tissue blocks revealed good gray-white matter contrast and revealing subpial, subcortical, and deep white matter lesions typical of multiple sclerosis enabling further spatially targeted studies. Conclusion Here, we describe a new method to image cold tissue, while maintaining tissue integrity and biosafety during scanning. In addition to improving efficiency of downstream processes, imaging tissue at sub-zero temperatures may also improve our understanding of compartment specificity of MRI signal.

Brain iron is important for normal function and aberrantly high iron is often associated with neuroinflammation and neurodegeneration. Oligodendrocytes are a major source of iron in brain as are iron-laden activated macrophages and microglia. T2*-weighted MRI detected a large decrease in signal at the olfactory nerve layer (ONL) in normal young mice over the period of 3 to 12 weeks of age, consistent with iron accumulation in this region. This signal change was most prominent in the inner nerve fiber layer (iNFL). Iron histochemistry, ferritin immunohistology and electron microscopy showed that there was high iron and ferritin in the olfactory ensheathing cells (OECs) in the iNFL of ONL. The iron concentration in the iNFL was calculated to be approximately 2-3 mM based on MRI T2* relaxivity. The glomerular region near the high-iron iNFL had evidence of neuroinflammation markers of activated microglia and lipofuscin. Lipofuscin was found within the activated microglia as early as 6 weeks. In rats, MRI T2* signal loss in the ONL and high iron levels and lipofuscin were only detected in older rats (11 months) but not in young rats. These results indicate that mouse OECs develop high levels of iron at an early age. It is not clear if this iron is important for mouse OEC function or a result of phagocytic activity of OECs. The relation between iron and inflammation may be interesting to study in these young, healthy mice.

Background: There is increasing interest in high-contrast cerebrospinal fluid (CSF) MRI to image perivascular spaces (PVSs). Dilated PVSs, associated with aging, dementia, and various other conditions, have been commonly detected within the white matter, basal ganglia, and midbrain. 7T MRI has enabled the early detection of smaller PVSs due to very high contrast and resolution. However, to date, PVSs in the cerebral cortex has received limited attention, despite that the identification of early changes in the cortical PVS could give valuable insight into neurological conditions. Purpose: To determine if PVSs can be detected within the cerebral cortex in healthy participants by using heavily T2-weighted MRI at 7T. Materials and Methods: A T2-weighted TSE sequence was optimized to detect CSF with high resolution and contrast at 7T while reducing the contribution from surrounding tissues. A semi-automated processing pipeline was used to extract PVSs and analyze their density in the whole brain including the cerebral cortex. Results: A total of 17 healthy volunteers were scanned at 7T (10 Males and 7 Females, aged 40±14 years). The optimized 3D-TSE sequence (0.125 mm3 volume, 0.5 mm isotropic resolution, 500 ms TE , 2.4 s TR and 10 min scan time) enabled a CNR of approximatively 180:1 after denoising, with a CSF volume detection limit of about 5 nL per voxel. At this sensitivity, average PVS density was found to be about 4.0% in white matter, 2.7% in deep gray matter and 1.3% in the cortex. Highest cortical PVS density was found to be in the insular cortex. Four characteristic classes of PVS morphology within the cortex or passing through the cortex were identified. Conclusion: High-resolution CSF imaging using optimized 3D-TSE MRI at 7T allows nanoliter scale volume detection of cortical PVSs in healthy individuals. This lays the groundwork for exploring cortical PVSs and their potential for use in diagnosis or prognosis of neurological diseases. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This research was supported by the Intramural Research Program of the National Institute of Neurological Disorders and Stroke at the National Institutes of Health. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The National Institutes of Health (NIH), Bethesda, Maryland, USA, Institutional Review Board gave ethical approval for this work under protocol number 00-N-0082 (ClinicalTrials.gov identifier: NCT 00004577). I confirm that all necessary participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. The study was supported by the of National Institute of Neurological Disorders and Stroke Intramural Research program. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced are available online on https://figshare.com [https://figshare.com/articles/dataset/Detection\_of\_Nanoliter-Scale\_Cortical\_Perivascular\_Spaces\_using\_Heavily\_T2-weighted\_MRI\_at_7T/26671444?file=48515059][1] [1]: https://figshare.com/articles/dataset/Detection_of_Nanoliter-Scale_Cortical_Perivascular_Spaces_using_Heavily_T2-weighted_MRI_at_7T/26671444?file=48515059

Unilateral whisker denervation activates plasticity mechanisms and circuit adaptations in adults. Single nucleus RNA sequencing and multiplex fluorescence in situ hybridization revealed differentially expressed genes related to altered glutamate receptor distributions and synaptogenesis in thalamocortical (TC) recipient layer 4 (L4) neurons of the sensory cortex, specifically those receiving input from the intact whiskers after whisker denervation. Electrophysiology detected increased spontaneous excitatory events at L4 neurons, confirming an increase in synaptic connections. Elevated expression levels of Gria2 mRNA and functional GluA2 subunit of AMPA receptors at the TC synapse indicate the presence of stabilized and potentiated TC synapses to L4 excitatory neurons along the intact pathway after unilateral whisker denervation. These adaptations likely underlie the increased cortical activity observed in rodents during intact whisker sensation after unilateral whisker denervation. Our findings provide new insights into the mechanisms by which the adult brain supports recovery after unilateral sensory loss.

Years before Alzheimer's disease (AD) is diagnosed, patients experience an impaired sense of smell, and β-amyloid plaques accumulate within the olfactory mucosa and olfactory bulb (OB). The olfactory vector hypothesis proposes that external agents cause β-amyloid to aggregate and spread from the OB to connected downstream brain regions. To reproduce the slow accumulation of β-amyloid that occurs in human AD, we investigated the progressive accumulation of β-amyloid across the brain using a conditional mouse model that overexpresses a humanized mutant form of the amyloid precursor protein (hAPP) in olfactory sensory neurons. Using design-based stereology, we show the progressive accumulation of β-amyloid plaques within the OB and cortical olfactory regions with age. We also observe reduced OB volumes in these mice when hAPP expression begins prior-to but not post-weaning which we tracked using manganese-enhanced MRI. We therefore conclude that the reduced OB volume does not represent progressive degeneration but rather disrupted OB development. Overall, our data demonstrate that hAPP expression in the olfactory epithelium can lead to the accumulation and spread of β-amyloid through the olfactory system into the hippocampus, consistent with an olfactory system role in the early stages of β-amyloid-related AD progression.

Cerebral blood flow (CBF) is widely used to assess brain function. However, most preclinical CBF studies have been performed under anesthesia, which confounds findings. High spatiotemporal-resolution CBF imaging of awake animals is challenging due to motion artifacts and background noise, particularly for Doppler-based flow imaging. Here, we report ultrahigh-resolution optical coherence Doppler tomography (µODT) for 3D imaging of CBF velocity (CBFv) dynamics in awake mice by developing self-supervised deep-learning for effective image denoising and motion-artifact removal. We compare cortical CBFv in awake vs. anesthetized mice and their dynamic responses in arteriolar, venular and capillary networks to acute cocaine (1 mg/kg, i.v .), a highly addictive drug associated with neurovascular toxicity. Compared with awake, isoflurane (2-2.5%) induces vasodilation and increases CBFv within 2-4 min, whereas dexmedetomidine (0.025 mg/kg, i.p .) does not change vessel diameters nor flow. Acute cocaine decreases CBFv to the same extent in dexmedetomidine and awake states, whereas decreases are larger under isoflurane, suggesting that isoflurane-induced vasodilation might have facilitated detection of cocaine-induced vasoconstriction. Awake mice after chronic cocaine show severe vasoconstriction, CBFv decreases and vascular adaptations with extended diving arteriolar/venular vessels that prioritize blood supply to deeper cortical capillaries. The 3D imaging platform we present provides a powerful tool to study dynamic changes in vessel diameters and morphology alongside CBFv networks in the brain of awake animals that can advance our understanding of the effects of drugs and disease conditions (ischemia, tumors, wound healing).