Biology subjects

Llano, D. A.

Publications and source records attributed to Llano, D. A..

At least 19 recordsLinked to original sources

bioRxiv2026

Task-Dependent and Cell-Type-Specific Modulation of the Mouse Dorsal Cortex of the Inferior Colliculus

Sensory responses in the auditory system are modulated by behavioral context, and this modulation extends as early as the inferior colliculus (IC). Where within the IC it occurs, which neurons it affects, what behavioral variables drive it, and whether it requires the auditory cortex remain unclear. We imaged the dorsal cortex of the IC (DCIC) with two-photon microscopy in head-fixed mice (n = 7) performing a two-alternative forced-choice tone-discrimination task, with blocks of passive listening to the same tones before and after, while recording orofacial movement, licking, and pupil diameter from synchronized video. Unsupervised clustering of sound-evoked responses in 1479 tracked neurons identified four functional response classes: onset-excited, sustained-inhibited, offset/motor-excited, and transient-inhibited. Task engagement modulated these classes in distinct and outcome-dependent ways, with the sustained-inhibited and transient-inhibited classes more suppressed and the offset/motor-excited class more excited during active trials, and with hit and miss trials driving most of the effect. Population activity discriminated active from passive trials above chance, and this discrimination outlasted the stimulus. A linear encoding model attributed a substantial share of the explained variance in three of the four classes to facial movement, whereas pupil diameter contributed little in any class. The correlation between orofacial motion and activity was itself context-dependent in the sustained-inhibited and transient-inhibited classes, but not in the offset/motor-excited class. Bilateral chemogenetic silencing of the auditory cortex (n = 3 mice, 171 matched neurons) altered task modulation only in the sustained-inhibited class. Task-related modulation in the DCIC is therefore heterogeneous across functionally defined neurons, is closely tied to movement, and depends on the auditory cortex in only one of these populations.

neuroscience↗

bioRxiv2026

Longitudinal Awake Mouse Brain Imaging Using Functional Ultrasound and Functional Ultrasound Localization Microscopy

Ultrafast ultrasound offers a unique route to cross-scale neurovascular phenotyping by integrating functional ultrasound (fUS), ultrasound localization microscopy (ULM), and functional ULM (fULM). Yet the baseline variability, longitudinal stability, and biological safety of such multimodal imaging in awake animals remain insufficiently defined, limiting its use for detecting subtle disease-associated neurovascular changes. Here, an awake longitudinal fUS-ULM-fULM framework is established and validated in mice over five months. Structural vascularity, microvascular flow velocity, mesoscale hemodynamic responses, and microvascular functional responses are repeatedly quantified in the same animals during monthly imaging sessions. Across all metrics, no significant longitudinal drift is detected (p > 0.60). Structural and flow-derived measures are markedly more reproducible than functional readouts, with within-subject coefficients of variation of 5.1% for mean flow velocity and 7.3% for vascularity, compared with 25.0% for fUS-derived cerebral blood volume responses and 53.2% for fULM-derived microvascular functional responses. Mean flow velocity shows the strongest longitudinal consistency (ICC = 0.70) and the lowest detection threshold. Behavioral testing and GFAP/Iba1 staining further reveal no memory impairment or chronic neuroinflammation. This study defines quantitative baselines, reproducibility limits, and safety evidence for awake cross-scale ultrasound imaging, providing a reference framework for longitudinal neurovascular phenotyping in preclinical disease models.

neuroscience↗

bioRxiv2026

Safety Signals Enable Single-Episode Active Avoidance paradigm and Expose Threat Generalization in Tuberous Sclerosis Complex

Animals must flexibly discriminate between threat and non-threat to deploy adaptive defensive strategies. We introduce a single-episode differential signaled active avoidance (DSAA) paradigm that temporally dissociates acquisition, consolidation, and retrieval of instrumental avoidance memory. Interleaving a behaviorally noncontingent neutral cue (CS-) with a threat-predictive, behaviorally contingent cue (CS+) enhanced long-term memory without altering acquisition, demonstrating that differential contingency structure selectively reinforces memory consolidation rather than influencing learning performance. Naive animals inferred contingencies within a single episode, and discrimination achieved during training predicted retrieval precision. However, discrimination operated within defined boundary conditions: overtraining or elevated threat intensity destabilized cue specificity and promoted persistent avoidance generalization. Under high-threat conditions, freezing and shuttling co-emerged as complementary defensive responses, indicating a shift from precise cue-based encoding to a generalized defensive state. Remote retrieval recruited oxytocin receptor-expressing cells in the medial prefrontal cortex and activated mTORC1-dependent translational signaling, implicating protein synthesis in maintenance of discriminative avoidance memory. In a Tuberous Sclerosis Complex model with Tsc2 haploinsufficiency in oxytocin-responsive cells, males displayed intact acquisition but generalized avoidance at both recent and remote time points, a deficit not rescued by additional training. These findings identify oxytocin-modulated translational control as a molecular gate stabilizing threat-safety discrimination and show that disruption of this axis - by excessive threat or reduced Tsc2 gene dosage - biases memory toward pathological generalization, providing a mechanistic framework for safety-learning deficits in neurodevelopmental and anxiety-related disorders.

animal behavior and cognition↗

bioRxiv2025

Modification and validation of a GAD-GFP mouse line without accelerated aging-related hearing loss.

GABAergic neurons in the inferior colliculus (IC) play a crucial role in auditory processing by extracting specific features of sounds (Ono et al., 2005). The Gad67-GFP mouse model developed by Tamamaki et al. in 2003 on a Swiss background facilitates studying these neurons by using a green fluorescent protein that is expressed endogenously via the GAD67 promoter. Unfortunately, this mouse suffers from accelerated aging-related hearing loss, limiting its utility in studying the auditory system. Here, we report the results of an 8-generation backcross of this line onto CBA/CaJ mice, which produces mice with stable low-threshold hearing while retaining GFP expression in GAD+ neurons. Additionally, this study investigates mechanisms that underlie hearing loss in the Gad67-GFP mouse model by focusing specifically on cochlear hair cells (HCs) and ribbon synapses, which may contribute to both model-specific hearing loss and clinical disorders like presbycusis. Findings revealed the newly generated F1 mouse model that resulted from the Gad67-GFP x CBA/CaJ backcross maintained better hearing thresholds when compared to ABR data for Gad67 and Swiss mice and very closely resembled those of the CBA/CaJ mice, mirroring progression of presbycusis in humans. Additionally, all morphological changes observed in cochlear structure correlated to ABR thresholds. F1 mice continued maintained expression of the GAD67 promoter in the IC via immunostaining.

neuroscience↗

bioRxiv2024

Combined Nanodrops Imaging and Ultrasound Localization Microscopy for Detecting Intracerebral Hemorrhage

ObjectiveAdvanced imaging methods are crucial for understanding stroke mechanisms and discovering effective treatments to reduce bleeding and enhance recovery. In preclinical in vivo stroke imaging, MRI, CT, and optical imaging are commonly used to evaluate stroke outcomes in rodent models. However, MRI and CT have limited spatial resolution for rodent brains, and optical imaging is hindered by limited imaging depth of penetration. Here we introduce a novel contrast-enhanced ultrasound imaging method to overcome these challenges and characterize intracerebral hemorrhage with unique insights. MethodsWe combined microbubble (MB)-based ultrasound localization microscopy (ULM) and nanodrop (ND)- based vessel leakage imaging to achieve simultaneous microvascular imaging and hemorrhage detection. ULM maps brain-wide cerebral vasculature with high spatial resolution and identifies microvascular impairments around hemorrhagic areas. NDs are sub-micron liquid-core particles which can extravasate due to blood-brain barrier (BBB) breakdown, serving as positive contrast agents to detect hemorrhage sites. ResultsOur findings demonstrate that NDs could effectively accumulate in the hemorrhagic site and reveal the location of the bleeding areas upon activation by focused ultrasound beams. ULM further reveals the microvascular damage manifested in the form of reduced vascularity and decreased blood flow velocity across areas affected by the hemorrhagic stroke. ConclusionThe results demonstrate that sequential ULM combined with ND imaging is a useful imaging tool for basic in vivo research in stroke with rodent models where brain-wide detection of active bleeding and microvascular impairment are essential.

bioengineering↗

bioRxiv2023

Longitudinal Awake Imaging of Deep Mouse Brain Microvasculature with Super-resolution Ultrasound Localization Microscopy

Ultrasound localization microscopy (ULM) is an emerging imaging modality that resolves microvasculature in deep tissues with high spatial resolution. However, existing preclinical ULM applications are largely constrained to anesthetized animals, introducing confounding vascular effects such as vasodilation and altered hemodynamics. As such, ULM quantifications (e.g., vessel diameter, density, and flow velocity) may be confounded by the use of anesthesia, undermining the usefulness of ULM in practice. Here we introduce a method to address this limitation and achieve ULM imaging in awake mouse brain. Pupillary monitoring was used to support the presence of the awake state during ULM imaging. Vasodilation induced by isoflurane was observed by ULM. Upon recovery to the awake state, reductions in vessel density and flow velocity were observed across different brain regions. In the cortex, the effects induced by isoflurane are more pronounced on venous flow than on arterial flow. In addition, serial in vivo imaging of the same animal brain at weekly intervals demonstrated the highly robust longitudinal imaging capability of the proposed technique. The consistency was further verified through quantitative analysis on individual vessels, cortical regions of arteries and veins, and subcortical regions. This study demonstrates longitudinal ULM imaging in the awake mouse brain, which is crucial for many ULM brain applications that require awake and behaving animals.

biophysics↗

bioRxiv2023

Developmental exposure to polychlorinated biphenyls prevents recovery from noise-induced hearing loss and disrupts the functional organization of the inferior colliculus

Exposure to combinations of environmental toxins is growing in prevalence, and therefore understanding their interactions is of increasing societal importance. Here, we examined the mechanisms by which two environmental toxins - polychlorinated biphenyls (PCBs) and high-amplitude acoustic noise - interact to produce dysfunction in central auditory processing. PCBs are well-established to impose negative developmental impacts on hearing. However, it is not known if developmental exposure to this ototoxin alters the sensitivity to other ototoxic exposures later in life. Here, male mice were exposed to PCBs in utero, and later as adults were exposed to 45 minutes of high-intensity noise. We then examined the impacts of the two exposures on hearing and the organization of the auditory midbrain using two-photon imaging and analysis of the expression of mediators of oxidative stress. We observed that developmental exposure to PCBs blocked hearing recovery from acoustic trauma. In vivo two-photon imaging of the inferior colliculus revealed that this lack of recovery was associated with disruption of the tonotopic organization and reduction of inhibition in the auditory midbrain. In addition, expression analysis in the inferior colliculus revealed that reduced GABAergic inhibition was more prominent in animals with a lower capacity to mitigate oxidative stress. These data suggest that combined PCBs and noise exposure act nonlinearly to damage hearing and that this damage is associated with synaptic reorganization, and reduced capacity to limit oxidative stress. In addition, this work provides a new paradigm by which to understand nonlinear interactions between combinations of environmental toxins. Significance statementExposure to common environmental toxins is a large and growing problem in the population. This work provides a new mechanistic understanding of how the pre-and postnatal developmental changes induced by polychlorinated biphenyls could negatively impact the resilience of the brain to noise-induced hearing loss later in adulthood. The use of state-of-the-art tools, including in vivo multiphoton microscopy of the midbrain helped in identifying the long-term central changes in the auditory system after the peripheral hearing damage induced by such environmental toxins. In addition, the novel combination of methods employed in this study will lead to additional advances in our understanding of mechanisms of central hearing loss in other contexts.

neuroscience↗

bioRxiv2022

Increased Pyramidal and VIP Neuronal Excitability in Primary Auditory Cortex Directly Correlates with Tinnitus Behavior

Tinnitus affects roughly 15-20% of the population while severely impacting 10% of those afflicted. Tinnitus pathology is multifactorial, generally initiated by damage to the auditory periphery, resulting in a cascade of maladaptive plastic changes at multiple levels of the central auditory neuraxis as well as limbic and non-auditory cortical centers. Using a well-established condition-suppression model of tinnitus, we measured tinnitus-related changes in the microcircuits of excitatory/inhibitory neurons onto layer 5 pyramidal neurons (PNs), as well as changes in the excitability of vasoactive intestinal peptide (VIP) neurons in primary auditory cortex (A1). Patch-clamp recordings from PNs in A1 slices showed tinnitus-related increases in spontaneous excitatory postsynaptic currents (sEPSCs) and decreases in spontaneous inhibitory postsynaptic currents (sIPSCs). Both measures were directly correlated to the rats behavioral evidence of tinnitus. Tinnitus-related changes in PN excitability were independent of changes in A1 excitatory or inhibitory cell numbers. VIP neurons, part of an A1 local circuit that can disinhibit layer 5 PNs, showed significant tinnitus-related increases in excitability that directly correlated with the rats behavioral tinnitus score. That PN and VIP changes directly correlated to tinnitus behavior, suggests an essential role in A1 tinnitus pathology. Tinnitus-related A1 changes were similar to findings in studies of neuropathic pain in somatosensory cortex suggesting a common pathology of these troublesome perceptual impairments. Improved understanding between excitatory, inhibitory and disinhibitory sensory cortical circuits can serve as a model for testing therapeutic approaches to the treatment of tinnitus and chronic pain. Key pointsO_LIIdentify tinnitus-related changes in synaptic function of specific neuronal subtypes in a reliable animal model of tinnitus. C_LIO_LIFinding show direct and indirect tinnitus-related losses of normal inhibitory function at A1 layer 5 pyramidal cells, and increased VIP excitability. C_LIO_LIFindings are similar to what has been shown for neuropathic pain suggesting that restoring normal inhibitory function at synaptic inputs onto A1 pyramidal neurons could conceptually reduce tinnitus discomfort. C_LI

neuroscience↗

bioRxiv2022

Highly branched and complementary distributions oflayer 5 and layer 6 auditory corticofugal axons in mouse.

The auditory cortex (AC) exerts a powerful, yet heterogeneous, effect on its subcortical targets. Auditory corticofugal projections emanate from distinct bands in layers 5 (L5) and 6 (L6), which have complementary anatomical and physiological properties. While several studies have suggested that corticofugal projections from L5 branch widely, others have suggested that there are multiple, mostly independent sets of L5 corticofugal projections. Even less is known about L6; no studies have examined whether the various L6 corticofugal projections are independent. Therefore, we examined branching patterns of L5 and L6 auditory corticofugal neurons, using the corticocollicular system as an index projection, using both traditional and novel approaches. We first confirmed that dual retrograde injections into the mouse inferior colliculus and auditory thalamus co-labeled subpopulations of L5 and L6 AC neurons. We then used an intersectional approach to selectively re-label L5 or L6 corticocollicular somata and found that both layers sent extensive branches to striatum, amygdala, superior colliculus, thalamus and nuclei of the lateral lemniscus. L5 corticocollicular axons also sent an unpaired projection to the superior olivary complex. Using a novel approach to separately label L5 and L6 axons in the same mouse, we found that L5/6 terminal distributions partially spatially overlapped and that a subset of giant terminals was only found in L5-derived axons. Overall, the high degree of branching and complementarity in the distributions of L5 vs. L6 axons suggest that corticofugal projections should be considered as two widespread systems of projections, rather than a collection of individual projections.

neuroscience↗

bioRxiv2022

Microprism-based two-photon imaging of the lateral cortex of the mouse inferior colliculus reveals novel organizational principles of the auditory midbrain

To navigate real-world listening conditions, the auditory system relies on the integration of multiple sources of information. However, to avoid inappropriate cross-talk between inputs, highly connected neural systems need to strike a balance between integration and segregation. Here, we develop a novel approach to examine how repeated neurochemical modules in the mouse inferior colliculus lateral cortex (LC) allow controlled integration of its multimodal inputs. The LC had been impossible to study via imaging because it is buried in a sulcus. Therefore we coupled two-photon microscopy with the use of a microprism to reveal the first-ever sagittal views of the LC to examine neuronal responses with respect to its neurochemical motifs under anesthetized and awake conditions. This approach revealed marked differences in the acoustic response properties of LC and neighboring nonlemniscal portions of the inferior colliculus. In addition, we observed that the module and matrix cellular motifs of the LC displayed distinct somatosensory and auditory responses. Specifically, neurons in modules demonstrated primarily offset responses to acoustic stimuli with enhancement in responses to bimodal stimuli, whereas matrix neurons showed onset response to acoustic stimuli and suppressed responses to bimodal stimulation. Thus, this new approach revealed that the repeated structural motifs of the LC permit functional integration of multimodal inputs while retaining distinct response properties.

neuroscience↗

bioRxiv2022

Super-resolution ultrasound imaging of cerebrovascular impairment in a mouse model of Alzheimer's disease

Increasing evidence has suggested a link between cerebrovascular disease and the cognitive impairment of patients with Alzheimers disease. However, cerebrovascular disease and Alzheimers disease share several risk factors making it unclear whether cerebrovascular deficiency and Alzheimers disease pathology have additive effects on cognition or if cerebrovascular impairment merely exacerbates existing Alzheimers disease-associated cognitive decline. Additionally, early-stage Alzheimers disease typically involves hippocampal atrophy, complicating most efforts to elucidate the interplay between cerebral microvascular function and Alzheimers disease progression due to the necessity of probing deep-brain structures. The purpose of this study was to demonstrate the use of ultrasound localization microscopy on the 5xFAD mouse model of Alzheimers disease (3-month and 6-month-old cohorts) in comparison to age-matched wild-type controls, revealing microvascular scale reconstructions throughout the whole brain depth, to visualize and quantify Alzheimers disease-associated vascular impairments. We found that functional decreases in hippocampal and entorhinal flow velocity preceded structural derangements in regional vascular density. In addition to providing global vascular quantifications of deep brain structures with a high local resolution, this technology also permitted hierarchical analysis of individual vessels and, in some cases, potentially allowed for decoupling of arteriole and venous flow contributions. Co-registered histological sectioning confirmed the regionalized hypo-perfusion deficits seen on ultrasound imaging, which were co-localized with amyloid beta plaque deposition. Significance statementThe study of the impact of cerebrovascular disease on Alzheimers disease pathology is complicated by the need to image deep-brain structures with high vascular fidelity. We demonstrate that ultrasound localization microscopy, a super-resolution acoustic imaging technique, is capable of imaging cerebrovasculature throughout the entire depth of the brain at a microvascular scale. This technology was applied to the 5xFAD mouse model of Alzheimers disease, where it was found that 5xFAD animals have significant impairments in vascular function in the entorhinal cortex and hippocampal region in comparison to age matched controls at the 3-month timepoint. Structural derangements in cerebrovasculature were only observed in the 6-month-old animal cohorts, with a maintained impairment in vascular function.

neuroscience↗

bioRxiv2022

Contrast-free Super-resolution Doppler (CS Doppler) based on Deep Generative Neural Networks

Super-resolution ultrasound microvessel imaging based on ultrasound localization microscopy (ULM) is an emerging imaging modality that is capable of resolving micron-scaled vessels deep into tissue. In practice, ULM is limited by the need for contrast injection, long data acquisition, and computationally expensive post-processing times. In this study, we present a contrast-free super-resolution Doppler (CS Doppler) technique that uses deep generative networks to achieve super-resolution with short data acquisition. The training dataset is comprised of spatiotemporal ultrafast ultrasound signals acquired from in vivo mouse brains, while the testing dataset includes in vivo mouse brain, chicken embryo chorioallantoic membrane (CAM), and healthy human subjects. The in vivo mouse imaging studies demonstrate that CS Doppler could achieve an approximate 2-fold improvement in spatial resolution when compared with conventional power Doppler. In addition, the microvascular images generated by CS Doppler showed good agreement with the corresponding ULM images as indicated by a structural similarity index of 0.7837 and a peak signal-to-noise ratio of 25.52. Moreover, CS Doppler was able to preserve the temporal profile of the blood flow (e.g., pulsatility) that is similar to conventional power Doppler. Finally, the generalizability of CS Doppler was demonstrated on testing data of different tissues using different imaging settings. The fast inference time of the proposed deep generative network also allows CS Doppler to be implemented for real-time imaging. These features of CS Doppler offer a practical, fast, and robust microvascular imaging solution for many preclinical and clinical applications of Doppler ultrasound.

bioengineering↗

bioRxiv2022

Curvelet Transform-based Sparsity Promoting Algorithm for Fast Ultrasound Localization Microscopy

Ultrasound localization microscopy (ULM) based on microbubble (MB) localization was recently introduced to overcome the resolution limit of conventional ultrasound. However, ULM is currently challenged by the requirement for long data acquisition times to accumulate adequate MB events to fully reconstruct vasculature. In this study, we present a curvelet transform-based sparsity promoting (CTSP) algorithm that improves ULM imaging speed by recovering missing MB localization signal from data with very short acquisition times. CTSP was first validated in a simulated microvessel model, followed by the chicken embryo chorioallantoic membrane (CAM), and finally, in the mouse brain. In the simulated microvessel study, CTSP robustly recovered the vessel model to achieve an 86.94% vessel filling percentage from a corrupted image with only 4.78% of the true vessel pixels. In the chicken embryo CAM study, CTSP effectively recovered the missing MB signal within the vasculature, leading to marked improvement in ULM imaging quality with a very short data acquisition. Taking the optical image as reference, the vessel filling percentage increased from 2.7% to 42.2% using 50ms of data acquisition after applying CTSP. CTSP used 80% less time to achieve the same 90% maximum saturation level as compared with conventional MB localization. We also applied CTSP on the microvessel flow speed maps and found that CTSP was able to use only 1.6s of microbubble data to recover flow speed images that have similar qualities as those constructed using 33.6s of data. In the mouse brain study, CTSP was able to reconstruct the majority of the cerebral vasculature using 1-2s of data acquisition. Additionally, CTSP only needed 3.2s of microbubble data to generate flow velocity maps that are comparable to those using 129.6s of data. These results suggest that CTSP can facilitate fast and robust ULM imaging especially under the circumstances of inadequate microbubble localizations.

bioengineering↗

bioRxiv2021

Improved Ultrasound Localization Microscopy based on Microbubble Uncoupling via Transmit Excitation (MUTE)

Ultrasound localization microscopy (ULM) demonstrates great potential for visualization of tissue microvasculature at depth with high spatial resolution. The success of ULM heavily depends on the robust localization of isolated microbubbles (MBs), which can be challenging in vivo especially within larger vessels where MBs can overlap and cluster close together. While MB dilution alleviates the issue of MB overlap to a certain extent, it drastically increases the data acquisition time needed for MBs to populate the microvasculature, which is already on the order of several minutes using recommended MB concentrations. Inspired by optical super-resolution imaging based on stimulated emission depletion (STED), here we propose a novel ULM imaging sequence based on microbubble uncoupling via transmit excitation (MUTE). MUTE "silences" MB signals by creating acoustic nulls to facilitate MB separation, which leads to robust localization of MBs especially under high concentrations. The efficiency of localization accomplished via the proposed technique was first evaluated in simulation studies with conventional ULM as a benchmark. Then an in vivo study based on the chorioallantoic membrane (CAM) of chicken embryos showed that MUTE could reduce the data acquisition time by half thanks to the enhanced MB separation and localization. Finally, the performance of MUTE was validated in an in vivo mouse brain study. These results demonstrate the high MB localization efficacy of MUTE-ULM, which contributes to a reduced data acquisition time and improved temporal resolution for ULM.

bioengineering↗

bioRxiv2021

Localization free super-resolution microbubble velocimetry using a long short-term memory neural network

Ultrasound localization microscopy is a super-resolution imaging technique that exploits the unique characteristics of contrast microbubbles to side-step the fundamental trade-off between imaging resolution and penetration depth. However, the conventional reconstruction technique is confined to low microbubble concentrations to avoid localization and tracking errors. Several research groups have introduced sparsity- and deep learning-based approaches to overcome this constraint to extract useful vascular structural information from overlapping microbubble signals, but these solutions have not been demonstrated to produce blood flow velocity maps of the microcirculation. Here, we introduce Deep-SMV, a localization free super-resolution microbubble velocimetry technique, based on a long short-term memory neural network, that provides high imaging speed and robustness to high microbubble concentrations, and directly outputs blood velocity measurements at a super-resolution. Deep-SMV is trained efficiently using microbubble flow simulation on real in vivo vascular data and demonstrates real-time velocity map reconstruction suitable for functional vascular imaging and pulsatility mapping at super-resolution. The technique is successfully applied to a wide variety of imaging scenarios, include flow channel phantoms, chicken embryo chorioallantoic membranes, and mouse kidney, tumor, and brain imaging.

bioengineering↗

bioRxiv2021

Aging-related cerebral microvascular changes visualized using Ultrasound Localization Microscopy in the living mouse

Aging-related cognitive decline is an emerging health crisis; however, no established unifying mechanism has been identified for the cognitive impairments seen in an aging population. A vascular hypothesis of cognitive decline has been proposed but is difficult to test given the contradictory radiologic needs of high-fidelity microvascular imaging resolution and a broad and deep brain imaging field of view. Super-resolution ultrasound localization microscopy (ULM) offers a potential solution by exploiting circulating microbubbles to achieve a vascular resolution approaching the capillary scale without sacrificing imaging depth. In this report, we apply ULM imaging to a mouse model of aging and quantify differences in cerebral vascularity, blood velocity, and vessel tortuosity across several brain regions. We found significant decreases in blood velocity, and significant increases in vascular tortuosity, across all brain regions in the aged cohort, and significant decreases in blood volume in the cortex. These data provide the first-ever measurements of subcortical microvascular dynamics in vivo and reveal that aging has a major impact on these measurements.

neuroscience↗

bioRxiv2020

Hearing loss in Alzheimer Disease is associated with altered serum lipidomic biomarker profiles

Recent data have found that aging-related hearing loss (ARHL) is associated with the development of Alzheimer Disease (AD). However, the nature of the relationship between these two disorders is not clear. There are multiple potential factors that link ARHL and AD, and previous investigators have speculated that shared metabolic dysregulation may underlie the propensity to develop both disorders. Here, we investigate the distribution of serum lipidomic biomarkers in AD subjects with or without hearing loss in a publicly available dataset. Serum levels of 349 known lipids from 16 lipid classes were measured in 185 AD patients. Using previously defined co-regulated sets of lipids, both age- and sex-adjusted, we found that lipid sets enriched in phosphatidylcholine and phosphatidylethanolamine showed a strong inverse association with hearing loss. Examination of biochemical classes confirmed these relationships and revealed that serum phosphatidylcholine levels were significantly lower in AD subjects with hearing loss. A similar relationship was not found in normal subjects. These data suggest that a synergistic relationship may exist between AD, hearing loss and metabolic biomarkers, such that in the context of a pathological state such as AD, alterations in serum metabolic profiles are associated with hearing loss. These data also point to a potential role for phosphatidylcholine, a molecule with antioxidant properties, in the underlying pathophysiology of ARHL in the context of AD, which has implications for our understanding and potential treatment of both disorders.

neuroscience↗

bioRxiv2020

Developmental PCB exposure disrupts synaptic transmission and connectivity in the rat auditory cortex, independent of its effects on peripheral hearing threshold

Polychlorinated biphenyls (PCBs) are enduring environmental toxicants and exposure is associated with neurodevelopmental deficits. The auditory system appears particularly sensitive, as previous work has shown that developmental PCB exposure causes both hearing loss and gross disruptions in the organization of the rat auditory cortex. However, the mechanisms underlying PCB-induced changes are not known, nor is it known if the central effects of PCBs are a consequence of peripheral hearing loss. Here, we study changes in both peripheral and central auditory function in rats with developmental PCB exposure using a combination of optical and electrophysiological approaches. Female rats were exposed to an environmental PCB mixture in utero and until weaning. At adulthood, auditory brainstem responses were measured, and synaptic currents were recorded in slices from auditory cortex layer 2/3 neurons. Spontaneous and miniature inhibitory postsynaptic currents (IPSCs) were more frequent in PCB-exposed rats compared to controls and the normal relationship between IPSC parameters and peripheral hearing was eliminated in PCB-exposed rats. No changes in spontaneous EPSCs were found. Conversely, when synaptic currents were evoked by laser photostimulation of caged-glutamate, PCB exposure did not affect evoked inhibitory transmission, but increased the total excitatory charge, the number and distance of sites that evoke a significant response. Together, these findings indicate that early developmental exposure to PCBs causes long-lasting changes in both inhibitory and excitatory neurotransmission in the auditory cortex that are independent of peripheral hearing changes, suggesting the effects are due to the direct impact of PCBs on the developing auditory cortex. Significance StatementThe mechanisms by which developmental exposure to polychlorinated biphenyls (PCBs) disrupt the central nervous system are not yet known. Here we show that developmental PCB exposure is associated with long-lasting dysregulation of both excitatory and inhibitory neurotransmission in the rodent brain. We further find that, unlike controls, synaptic parameters in the auditory cortex of PCB-exposed rats are independent of peripheral hearing changes. These data suggest that PCB-related changes in the auditory cortex are independent of their effects on the auditory periphery and that PCB exposure may disrupt the plastic mechanisms needed to restore normal processing in the auditory cortex after peripheral hearing loss.

neuroscience↗