Distinct Ventral Pallidal Neural Populations Mediate Separate Symptoms of Depression.

Major depressive disorder (MDD) patients display a common but often variable set of symptoms making successful, sustained treatment difficult to achieve. Separate depressive symptoms may be encoded by differential changes in distinct circuits in the brain, yet how discrete circuits underlie behavioral subsets of depression and how they adapt in response to stress has not been addressed. We identify two discrete circuits of parvalbumin-positive (PV) neurons in the ventral pallidum (VP) projecting to either the lateral habenula or ventral tegmental area contributing to depression. We find that these populations undergo different electrophysiological adaptations in response to social defeat stress, which are normalized by antidepressant treatment. Furthermore, manipulation of each population mediates either social withdrawal or behavioral despair, but not both. We propose that distinct components of the VP PV circuit can subserve related, yet separate depressive-like phenotypes in mice, which could ultimately provide a platform for symptom-specific treatments of depression.

Focused Ultrasound-mediated Liquid Biopsy in a Tauopathy Mouse Model.

Background Neurodegenerative disorders (such as Alzheimer disease) characterized by the deposition of various pathogenic forms of tau protein in the brain are collectively referred to as tauopathies. Identification of the molecular drivers and pathways of neurodegeneration is critical to individualized targeted treatment of these disorders. However, despite important advances in fluid biomarker detection, characterization of these molecular subtypes is limited by the blood-brain barrier. Purpose To evaluate the feasibility and safety of focused ultrasound-mediated liquid biopsy (sonobiopsy) in the detection of brain-derived protein biomarkers in a transgenic mouse model of tauopathy (PS19 mice). Materials and Methods Sonobiopsy was performed by sonicating the cerebral hemisphere in 2-month-old PS19 and wild-type mice, followed by measurement of plasma phosphorylated tau (p-tau) species (30 minutes after sonication in the sonobiopsy group). Next, spatially targeted sonobiopsy was performed by sonicating either the cerebral cortex or the hippocampus in 6-month-old PS19 mice. To detect changes in plasma neurofilament light chain (a biomarker of neurodegeneration) levels, blood samples were collected before and after sonication (15 and 45-60 minutes after sonication). Histologic staining was performed to evaluate tissue damage after sonobiopsy. The Shapiro-Wilk test, unpaired and paired t tests, and the Mann-Whitney U test were used. Results In the 2-month-old mice, sonobiopsy significantly increased the normalized levels of plasma p-tau species compared with the conventional blood-based liquid biopsy (p-tau-181-to-mouse tau [m-tau] ratio: 1.7-fold increase, P = .006; p-tau-231-to-m-tau ratio: 1.4-fold increase, P = .048). In the 6-month-old PS19 mice, spatially targeted sonobiopsy resulted in a 2.3-fold increase in plasma neurofilament light chain after sonication of the hippocampus and cerebral cortex (P < .001). After optimization of the sonobiopsy parameters, no excess microhemorrhage was observed in the treated cerebral hemisphere compared with the contralateral side. Conclusion This study showed the feasibility of sonobiopsy to release phosphorylated tau species and neurofilament light chain to the blood circulation, potentially facilitating diagnosis of neurodegenerative disorders. © RSNA, 2023 Supplemental material is available for this article. See also the editorial by Fowlkes in this issue.

Static Magnetic Fields Dampen Focused Ultrasound-mediated Blood-Brain Barrier Opening.

Background Focused ultrasound combined with microbubbles has been used in clinical studies for blood-brain barrier (BBB) opening in conjunction with MRI. However, the impact of the static magnetic field generated by an MRI scanner on the BBB opening outcome has not been evaluated. Purpose To determine the relationship of the static magnetic field of an MRI scanner on focused ultrasound combined with microbubble-induced BBB opening. Materials and Methods Thirty wild-type mice were divided into four groups. Mice from different groups were sonicated with focused ultrasound in different static magnetic fields (approximately 0, 1.5, 3.0, and 4.7 T), with all other experimental parameters kept the same. Focused ultrasound sonication was performed after intravenous injection of microbubbles. Microbubble cavitation activity, the fundamental -physical mechanism underlying focused ultrasound BBB opening, was monitored with passive cavitation detection. After sonication, contrast-enhanced T1-weighted MRI was performed to assess BBB opening outcome. Intravenously injected Evans blue was used as a model agent to evaluate trans-BBB delivery efficiency. Results The microbubble cavitation dose decreased by an average of 2.1 dB at 1.5 T (P = .05), 2.9 dB at 3.0 T (P = .01), and 3.0 dB at 4.7 T (P = .01) compared with that outside the magnetic field (approximately 0 T). The static magnetic field of an MRI scanner decreased BBB opening volume in mice by 3.2-fold at 1.5 T (P < .001), 4.5-fold at 3.0 T (P < .001), and 11.6-fold at 4.7 T (P <.001) compared with mice treated outside the magnetic field. It also decreased Evans blue trans-BBB delivery 1.4-fold at 1.5 T (P = .009), 1.6-fold at 3.0 T (P < .001), and 1.9-fold at 4.7 T (P < .001). Conclusion Static magnetic fields dampened microbubble cavitation activity and decreased trans-blood-brain barrier (BBB) delivery by focused ultrasound combined with microbubble-induced BBB opening. © RSNA, 2021 An earlier incorrect version of this article appeared online. This article was corrected on July 8, 2021.

Characterization of magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU)-induced large-volume hyperthermia in deep and superficial targets in a porcine model.

PURPOSE: To characterize temperature fields and tissue damage profiles of large-volume hyperthermia (HT) induced by magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) in deep and superficial targets in vivo in a porcine model. METHODS: Nineteen HT sessions were performed in vivo with a commercial MRgHIFU system (Sonalleve® V2, Profound Medical Inc., Mississauga, ON, Canada) in hind leg muscles of eight pigs with temperature fields of cross-sectional diameter of 58-mm. Temperature statistics evaluated in the target region-of-interest (tROI) included accuracy, temporal variation, and uniformity. The impact of the number and location of imaging planes for feedback-based temperature control were investigated. Temperature fields were characterized by time-in-range (TIR, the duration each voxel stays within 40-45 °C) maps. Tissue damage was characterized by contrast-enhanced MRI, and macroscopic and histopathological analysis. The performance of the Sonalleve® system was benchmarked against a commercial phantom. RESULTS: Across all HT sessions, the mean difference between the average temperature (Tavg) and the desired temperature was -0.4 ± 0.5 °C; the standard deviation of temperature 1.2 ± 0.2 °C; the temporal variation of Tavg for 30-min HT was 0.6 ± 0.2 °C, and the temperature uniformity was 1.5 ± 0.2 °C. A difference of 2.2-cm (in pig) and 1.5-cm (in phantom) in TIR dimensions was observed when applying feedback-based plane(s) at different locations. Histopathology showed 62.5% of examined HT sessions presenting myofiber degeneration/necrosis within the target volume. CONCLUSION: Large-volume MRgHIFU-mediated HT was successfully implemented and characterized in a porcine model in deep and superficial targets in vivo with heating distributions modifiable by user-definable parameters.

Blood-brain barrier opening in a large animal model using closed-loop microbubble cavitation-based feedback control of focused ultrasound sonication.

Focused ultrasound (FUS) in combination with microbubbles has been established as a promising technique for noninvasive and localized Blood-brain barrier (BBB) opening. Real-time passive cavitation detection (PCD)-based feedback control of the FUS sonication is critical to ensure effective BBB opening without causing hemorrhage. This study evaluated the performance of a closed-loop feedback controller in a porcine model. Calibration of the baseline cavitation level was performed for each targeted brain location by a FUS sonication in the presence of intravenously injected microbubbles at a low acoustic pressure without inducing BBB opening. The target cavitation level (TCL) was defined for each target based on the baseline cavitation level. FUS treatment was then performed under real-time PCD-based feedback controller to maintain the cavitation level at the TCL. After FUS treatment, contrast-enhanced MRI and ex vivo histological staining were performed to evaluate the BBB permeability and safety. Safe and effective BBB opening was achieved with the BBB opening volume increased from 3.8 ± 0.7 to 53.6 ± 23.3 mm3 as the TCL was increased from 0.25 to 1 dB. This study validated that effective and safe FUS-induced BBB opening in a large animal model can be achieved with closed-loop feedback control of the FUS sonication.

Mechanical and mechanothermal effects of focused ultrasound elicited distinct electromyographic responses in mice.

The objective of this study was to compare focused ultrasound (FUS) neuromodulation-induced motor responses under two physical mechanisms: mechanical and mechanothermal effects. Mice were divided into two groups. One group was subjected to short-duration FUS stimulation (0.3 s) that induced mechanical effects (mechanical group). The other group underwent long-duration FUS stimulation (15 s) that produced not only mechanical but also thermal effects (mechanothermal group). FUS was targeted at the deep cerebellar nucleus in the cerebellum to induce motor responses, which were evaluated by recording the evoked electromyographic (EMG) signals and tail movements. Brain tissue temperature rise associated with the FUS stimulation was quantified by noninvasive magnetic resonance thermometryin vivo. Temperature rise was negligible for the mechanical group (0.2 °C ± 0.1 °C) but did rise within the range of 0.6 °C ± 0.2 °C-3.3 °C ± 0.9 °C for the mechanothermal group. The elongated FUS beam also induced heating in the dorsal brain (below the top skull) and ventral brain (above the bottom skull) along the beam path for the mechanothermal group. Both mechanical and mechanothermal groups achieved successful FUS neuromodulation. EMG response latencies were within the range of 0.03-0.1 s at different intensity levels for the mechanical group. The mechanothermal effect of FUS could induce both short-latency EMG (0.2-1.4 s) and long-latency EMG (8.7-13.0 s) under the same intensity levels as the mechanical group. The different temporal dynamics of evoked EMG suggested that FUS-induced mechanical and mechanothermal effects could evoke different responses in the brain.

3-D Transcranial Microbubble Cavitation Localization by Four Sensors.

Cavitation is the fundamental physical mechanism of various focused ultrasound (FUS)-mediated therapies in the brain. Accurately knowing the three-dimensional (3-D) location of cavitation in real-time can improve the targeting accuracy and avoid off-target tissue damage. Existing techniques for 3-D passive transcranial cavitation detection require the use of expensive and complicated hemispherical phased arrays with 128 or 256 elements. The objective of this study was to investigate the feasibility of using four sensors for transcranial 3-D localization of cavitation. Differential microbubble cavitation detection combined with the time difference of arrival algorithm was developed for the localization using the four sensors. Numerical simulation using k-Wave toolbox was performed to validate the proposed method for transcranial cavitation source localization. The sensors with a center frequency of 2.25 MHz and a 6 dB bandwidth of 1.39 MHz were used to locate cavitation generated by FUS (500 kHz) sonication of microbubbles that were injected into a tube positioned inside an ex vivo human skullcap. Cavitation emissions from the microbubbles were detected transcranially using the four sensors. Both simulation and experimental studies found that the proposed method achieved accurate 3-D cavitation localization. When the cavitation source was located within 30 mm from the geometric center of the sensor network, the accuracy of the localization method with the skull was measured to be 1.9±1.0 mm, which was not significantly different from that without the skull (1.7 ± 0.5 mm). The accuracy decreased as the cavitation source was away from the geometric center of the sensor network. It also decreased as the pulse length increased. Its accuracy was not significantly affected by the sensor position relative to the skull. In summary, four sensors combined with the proposed localization algorithm offer a simple approach for 3-D transcranial cavitation localization.

Sonothermogenetics for noninvasive and cell-type specific deep brain neuromodulation.

BACKGROUND: Critical advances in the investigation of brain functions and treatment of brain disorders are hindered by our inability to selectively target neurons in a noninvasive manner in the deep brain. OBJECTIVE: This study aimed to develop sonothermogenetics for noninvasive, deep-penetrating, and cell-type-specific neuromodulation by combining a thermosensitive ion channel TRPV1 with focused ultrasound (FUS)-induced brief, non-noxious thermal effect. METHODS: The sensitivity of TRPV1 to FUS sonication was evaluated in vitro. It was followed by in vivo assessment of sonothermogenetics in the activation of genetically defined neurons in the mouse brain by two-photon calcium imaging. Behavioral response evoked by sonothermogenetic stimulation at a deep brain target was recorded in freely moving mice. Immunohistochemistry staining of ex vivo brain slices was performed to evaluate the safety of FUS sonication. RESULTS: TRPV1 was found to be an ultrasound-sensitive ion channel. FUS sonication at the mouse brain in vivo selectively activated neurons that were genetically modified to express TRPV1. Temporally precise activation of TRPV1-expressing neurons was achieved with its success rate linearly correlated with the peak temperature within the FUS-targeted brain region as measured by in vivo magnetic resonance thermometry. FUS stimulation of TRPV1-expressing neurons at the striatum repeatedly evoked locomotor behavior in freely moving mice. FUS sonication was confirmed to be safe based on inspection of neuronal integrity, inflammation, and apoptosis markers. CONCLUSIONS: This noninvasive and cell-type-specific neuromodulation approach with the capability to stimulate deep brain has the promise to advance the study of the intact nervous system and uncover new ways to treat neurological disorders.

Focused ultrasound for safe and effective release of brain tumor biomarkers into the peripheral circulation.

The development of noninvasive approaches for brain tumor diagnosis and monitoring continues to be a major medical challenge. Although blood-based liquid biopsy has received considerable attention in various cancers, limited progress has been made for brain tumors, at least partly due to the hindrance of tumor biomarker release into the peripheral circulation by the blood-brain barrier. Focused ultrasound (FUS) combined with microbubbles induced BBB disruption has been established as a promising technique for noninvasive and localized brain drug delivery. Building on this established technique, we propose to develop FUS-enabled liquid biopsy technique (FUS-LBx) to enhance the release of brain tumor biomarkers (e.g., DNA, RNA, and proteins) into the circulation. The objective of this study was to demonstrate that FUS-LBx could sufficiently increase plasma levels of brain tumor biomarkers without causing hemorrhage in the brain. Mice with orthotopic implantation of enhanced green fluorescent protein (eGFP)-transfected murine glioma cells were treated using magnetic resonance (MR)-guided FUS system in the presence of systemically injected microbubbles at three peak negative pressure levels (0.59, 1.29, and 1.58 MPa). Plasma eGFP mRNA levels were quantified with the quantitative polymerase chain reaction (qPCR). Contrast-enhanced MR images were acquired before and after the FUS sonication. FUS at 0.59 MPa resulted in an increased plasma eGFP mRNA level, comparable to those at higher acoustic pressures (1.29 MPa and 1.58 MPa). Microhemorrhage density associated with FUS at 0.59 MPa was significantly lower than that at higher acoustic pressures and not significantly different from the control group. MRI analysis revealed that post-sonication intratumoral and peritumoral hyperenhancement had strong correlations with the level of FUS-induced biomarker release and the extent of hemorrhage. This study suggests that FUS-LBx could be a safe and effective brain-tumor biomarker release technique, and MRI could be used to develop image-guided FUS-LBx.

Feasibility and safety of focused ultrasound-enabled liquid biopsy in the brain of a porcine model.

Although blood-based liquid biopsy is a promising noninvasive technique to acquire a comprehensive molecular tumor profile by detecting cancer-specific biomarkers (e.g. DNA, RNA, and proteins), there has been limited progress for brain tumor application partially because the low permeability of the blood-brain barrier (BBB) hinders the release of tumor biomarkers. We previously demonstrated focused ultrasound-enabled liquid biopsy (FUS-LBx) that uses FUS to increase BBB permeability in murine glioblastoma models and thus enhance the release of tumor-specific biomarkers into the bloodstream. The objective of this study was to evaluate the feasibility and safety of FUS-LBx in the normal brain tissue of a porcine model. Increased BBB permeability was confirmed by the significant increase (p = 0.0053) in Ktrans (the transfer coefficient from blood to brain extravascular extracellular space) when comparing the FUS-sonicated brain area with the contralateral non-sonicated area. Meanwhile, there was a significant increase in the blood concentrations of glial fibrillary acidic protein (GFAP, p = 0.0074) and myelin basic protein (MBP, p = 0.0039) after FUS sonication as compared with before FUS. There was no detectable tissue damage by T2*-weighted MRI and histological analysis. Findings from this study suggest that FUS-LBx is a promising technique for noninvasive and localized diagnosis of the molecular profiles of brain diseases with the potential to translate to the clinic.

Magnetic Resonance Imaging-Guided Focused Ultrasound-Based Delivery of Radiolabeled Copper Nanoclusters to Diffuse Intrinsic Pontine Glioma.

Diffuse intrinsic pontine glioma (DIPG) is an invasive pediatric brainstem malignancy exclusively in children without effective treatment due to the often-intact blood-brain tumor barrier (BBTB), an impediment to the delivery of therapeutics. Herein, we used focused ultrasound (FUS) to transiently open BBTB and delivered radiolabeled nanoclusters (64Cu-CuNCs) to tumors for positron emission tomography (PET) imaging and quantification in a mouse DIPG model. First, we optimized FUS acoustic pressure to open the blood-brain barrier (BBB) for effective delivery of 64Cu-CuNCs to pons in wildtype mice. Then the optimized FUS pressure was used to deliver radiolabeled agents in DIPG mouse. Magnetic resonance imaging (MRI)-guided FUS-induced BBTB opening was demonstrated using a low molecular weight, short-lived 68Ga-DOTA-ECL1i radiotracer and PET/CT before and after treatment. We then compared the delivery efficiency of 64Cu-CuNCs to DIPG tumor with and without FUS treatment and demonstrated the FUS-enhanced delivery and time-dependent diffusion of 64Cu-CuNCs within the tumor.

The Relationship between Saccades and Locomotion.

Human locomotion involves a complex interplay among multiple brain regions and depends on constant feedback from the visual system. We summarize here the current understanding of the relationship among fixations, saccades, and gait as observed in studies sampling eye movements during locomotion, through a review of the literature and a synthesis of the relevant knowledge on the topic. A significant overlap in locomotor and saccadic neural circuitry exists that may support this relationship. Several animal studies have identified potential integration nodes between these overlapping circuitries. Behavioral studies that explored the relationship of saccadic and gait-related impairments in normal conditions and in various disease states are also discussed. Eye movements and locomotion share many underlying neural circuits, and further studies can leverage this interplay for diagnostic and therapeutic purposes.