RESUMEN
Conscious perception is greatly diminished during sleep, but the underlying circuit mechanism is poorly understood. We show that cortical ignition-a brain process shown to be associated with conscious awareness in humans and non-human primates-is strongly suppressed during non-rapid-eye-movement (NREM) sleep in mice due to reduced cholinergic modulation and rapid inhibition of cortical responses. Brain-wide functional ultrasound imaging and cell-type-specific calcium imaging combined with optogenetics showed that activity propagation from visual to frontal cortex is markedly reduced during NREM sleep due to strong inhibition of frontal pyramidal neurons. Chemogenetic activation and inactivation of basal forebrain cholinergic neurons powerfully increased and decreased visual-to-frontal activity propagation, respectively. Furthermore, although multiple subtypes of dendrite-targeting GABAergic interneurons in the frontal cortex are more active during wakefulness, soma-targeting parvalbumin-expressing interneurons are more active during sleep. Chemogenetic manipulation of parvalbumin interneurons showed that sleep/wake-dependent cortical ignition is strongly modulated by perisomatic inhibition of pyramidal neurons.
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Electroencefalografía , Parvalbúminas , Sueño , Animales , Ratones , Neuronas Colinérgicas/fisiología , Lóbulo Frontal/metabolismo , Parvalbúminas/metabolismo , Sueño/fisiología , Vigilia/fisiologíaRESUMEN
Functional ultrasound (fUS) is a neuroimaging method that uses ultrasound to track changes in cerebral blood volume as an indirect readout of neuronal activity at high spatiotemporal resolution. fUS is capable of imaging head-fixed or freely behaving rodents and of producing volumetric images of the entire mouse brain. It has been applied to many species, including primates and humans. Now that fUS is reaching maturity, it is being adopted by the neuroscience community. However, the nature of the fUS signal and the different implementations of fUS are not necessarily accessible to nonspecialists. This review aims to introduce these ultrasound concepts to all neuroscientists. We explain the physical basis of the fUS signal and the principles of the method, present the state of the art of its hardware implementation, and give concrete examples of current applications in neuroscience. Finally, we suggest areas for improvement during the next few years.
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Encéfalo , Neuroimagen , Animales , Encéfalo/diagnóstico por imagen , Encéfalo/fisiología , RatonesRESUMEN
Innovative imaging methods help to investigate the complex relationship between brain activity and behavior in freely moving animals. Functional ultrasound (fUS) is an imaging modality suitable for recording cerebral blood volume (CBV) dynamics in the whole brain but has so far been used only in head-fixed and anesthetized rodents. We designed a fUS device for tethered brain imaging in freely moving rats based on a miniaturized ultrasound probe and a custom-made ultrasound scanner. We monitored CBV changes in rats during various behavioral states such as quiet rest, after whisker or visual stimulations, and in a food-reinforced operant task. We show that fUS imaging in freely moving rats could efficiently decode brain activity in real time.
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Mapeo Encefálico/instrumentación , Encéfalo/fisiología , Ecoencefalografía/instrumentación , Monitoreo Ambulatorio/instrumentación , Animales , Sistemas de Computación , Diseño de Equipo , Análisis de Falla de Equipo , Aprendizaje por Laberinto/fisiología , Miniaturización , Ratas , Ratas Sprague-Dawley , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
Functional ultrasound imaging is a method recently developed to assess brain activity via hemodynamics in rodents. Doppler ultrasound signals allow the measurement of cerebral blood volume (CBV) and red blood cells' (RBCs') velocity in small vessels. However, this technique originally requires performing a large craniotomy that limits its use to acute experiments only. Moreover, a detailed description of the hemodynamic changes that underlie functional ultrasound imaging has not been described but is essential for a better interpretation of neuroimaging data. To overcome the limitation of the craniotomy, we developed a dedicated thinned skull surgery for chronic imaging. This procedure did not induce brain inflammation nor neuronal death as confirmed by immunostaining. We successfully acquired both high-resolution images of the microvasculature and functional movies of the brain hemodynamics on the same animal at 0, 2, and 7 days without loss of quality. Then, we investigated the spatiotemporal evolution of the CBV hemodynamic response function (HRF) in response to sensory-evoked electrical stimulus (1 mA) ranging from 1 (200 µs) to 25 pulses (5s). Our results indicate that CBV HRF parameters such as the peak amplitude, the time to peak, the full width at half-maximum and the spatial extent of the activated area increase with stimulus duration. Functional ultrasound imaging was sensitive enough to detect hemodynamic responses evoked by only a single pulse stimulus. We also observed that the RBC velocity during activation could be separated in two distinct speed ranges with the fastest velocities located in the upper part of the cortex and slower velocities in deeper layers. For the first time, functional ultrasound imaging demonstrates its potential to image brain activity chronically in small animals and offers new insights into the spatiotemporal evolution of cerebral hemodynamics.
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Encéfalo/fisiología , Potenciales Evocados Somatosensoriales/fisiología , Neuroimagen Funcional/métodos , Hemodinámica/fisiología , Ultrasonografía Doppler Transcraneal/métodos , Animales , Volumen Sanguíneo/fisiología , Encéfalo/irrigación sanguínea , Corteza Cerebral/irrigación sanguínea , Corteza Cerebral/diagnóstico por imagen , Corteza Cerebral/fisiología , Estimulación Eléctrica/métodos , Eritrocitos/diagnóstico por imagen , Miembro Anterior/fisiología , Masculino , Ratas , Ratas Sprague-Dawley , Cráneo/cirugíaRESUMEN
Over the last decade, functional ultrasound (fUS) has risen as a critical tool in functional neuroimaging, leveraging hemodynamic changes to infer neural activity indirectly. Recent studies have established a strong correlation between neural spike rates (SR) and functional ultrasound signals. However, understanding their spatial distribution and variability across different brain areas is required to thoroughly interpret fUS signals. In this regard, we conducted simultaneous fUS imaging and Neuropixels recordings during stimulus-evoked activity in awake mice within three regions the visual pathway. Our findings indicate that the temporal dynamics of fUS and SR signals are linearly correlated, though the correlation coefficients vary among visual regions. Conversely, the spatial correlation between the two signals remains consistent across all regions with a spread of approximately 300 micrometers. Finally, we introduce a model that integrates the spatial and temporal components of the fUS signal, allowing for a more accurate interpretation of fUS images.
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Ischemic stroke occurs abruptly causing sudden neurologic deficits, and therefore, very little is known about hemodynamic perturbations in the brain immediately after stroke onset. Here, functional ultrasound imaging was used to monitor variations in relative cerebral blood volume (rCBV) compared to baseline. rCBV levels were analyzed brain-wide and continuously at high spatiotemporal resolution (100 µm, 2 Hz) until 70mins after stroke onset in rats. We compared two stroke models, with either a permanent occlusion of the middle cerebral artery (MCAo) or a tandem occlusion of both the common carotid and middle cerebral arteries (CCAo + MCAo). We observed a typical hemodynamic pattern, including a quick drop of the rCBV after MCAo, followed by spontaneous reperfusion of several brain regions located in the vicinity of the ischemic core. The severity and location of the ischemia were variable within groups. On average, the severity of the ischemia was in good agreement with the lesion volume (24 hrs after stroke) for MCAo group, while larger for the CCAo + MCAo model. For both groups, we observed that infarcts extended to initially non-ischemic regions located rostrally to the ischemic core. These regions strongly colocalize with the origin of transient hemodynamic events associated with spreading depolarizations.
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Isquemia Encefálica , Accidente Cerebrovascular Isquémico , Accidente Cerebrovascular , Ratas , Animales , Isquemia Encefálica/patología , Accidente Cerebrovascular Isquémico/patología , Encéfalo/patología , Accidente Cerebrovascular/patología , Isquemia/patología , Ultrasonografía , Hemodinámica , Modelos Animales de Enfermedad , Infarto de la Arteria Cerebral Media/patologíaRESUMEN
Positioning and navigation are essential components of neuroimaging as they improve the quality and reliability of data acquisition, leading to advances in diagnosis, treatment outcomes, and fundamental understanding of the brain. Functional ultrasound imaging is an emerging technology providing high-resolution images of the brain vasculature, allowing for the monitoring of brain activity. However, as the technology is relatively new, there is no standardized tool for inferring the position in the brain from the vascular images. In this study, we present a deep learning-based framework designed to address this challenge. Our approach uses an image classification task coupled with a regression on the resulting probabilities to determine the position of a single image. To evaluate its performance, we conducted experiments using a dataset of 51 rat brain scans. The training positions were extracted at intervals of 375 µm, resulting in a positioning error of 176 µm. Further GradCAM analysis revealed that the predictions were primarily driven by subcortical vascular structures. Finally, we assessed the robustness of our method in a cortical stroke where the brain vasculature is severely impaired. Remarkably, no specific increase in the number of misclassifications was observed, confirming the method's reliability in challenging conditions. Overall, our framework provides accurate and flexible positioning, not relying on a pre-registered reference but rather on conserved vascular patterns.
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Anesthesia is a major confounding factor in preclinical stroke research as stroke rarely occurs in sedated patients. Moreover, anesthesia affects both brain functions and the stroke outcome acting as neurotoxic or protective agents. So far, no approaches were well suited to induce stroke while imaging hemodynamics along with simultaneous large-scale recording of brain functions in awake animals. For this reason, the first critical hours following the stroke insult and associated functional alteration remain poorly understood. Here, we present a strategy to investigate both stroke hemodynamics and stroke-induced functional alterations without the confounding effect of anesthesia, i.e., under awake condition. Functional ultrasound (fUS) imaging was used to continuously monitor variations in cerebral blood volume (CBV) in +65 brain regions/hemispheres for up to 3 hr after stroke onset. The focal cortical ischemia was induced using a chemo-thrombotic agent suited for permanent middle cerebral artery occlusion in awake rats and followed by ipsi- and contralesional whiskers stimulation to investigate on the dynamic of the thalamocortical functions. Early (0-3 hr) and delayed (day 5) fUS recording enabled to characterize the features of the ischemia (location, CBV loss), spreading depolarizations (occurrence, amplitude) and functional alteration of the somatosensory thalamocortical circuits. Post-stroke thalamocortical functions were affected at both early and later time points (0-3 hr and 5 days) after stroke. Overall, our procedure facilitates early, continuous, and chronic assessments of hemodynamics and cerebral functions. When integrated with stroke studies or other pathological analyses, this approach seeks to enhance our comprehension of physiopathologies towards the development of pertinent therapeutic interventions.
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Anestesia , Accidente Cerebrovascular , Humanos , Ratas , Animales , Vigilia , Accidente Cerebrovascular/diagnóstico por imagen , Accidente Cerebrovascular/terapia , Infarto de la Arteria Cerebral Media , UltrasonografíaRESUMEN
PURPOSE: Performing drug-delivery with an ultrasonic imaging scanner in situ could drastically simplify treatment and improve its specificity. Our objective is to deliver large amounts of an encapsulated agent in vivo using a clinical ultrasound scanner with a millimetric resolution. This study describes the encapsulation of fluorescein within ultrasound-inducible composite droplets and its targeted release in predefined zones in the liver of rats. METHODS: An aqueous solution of fluorescein was encapsulated within perfluorocarbon liquid in 4 µm monodisperse droplets using a microfluidic system. The agent was then injected within the femoral vein of 12 rats. After exploratory ultrasound imaging, the sonographer defined five zones in the liver and a release sequence was initiated on the same apparatus. The surface of the liver was observed under fluorescence macroscopy and intraoperative fluorescence camera in vivo, before liver samples were sliced for pathology. RESULTS: Following the conversion of the droplets, a 25 dB increase in contrast was observed in the zones selected by the sonographer. These hyperechoic regions were colocalized with the bright fluorescent spots observed on the surface of the liver. A minimum peak-negative pressure of 2.6 MPa, which is within regulations for imaging pulses, was required for the delivery of the content of the droplets. The tissue and cellular structures were not affected by the exposure to the release sequence. CONCLUSIONS: Since composite droplets can carry various therapeutic and imaging agents, they could deliver such agents specifically in any organ accessible to ultrasound.
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Ultrasonido , Ultrasonografía/instrumentación , Ultrasonografía/métodos , Animales , Portadores de Fármacos , Sistemas de Liberación de Medicamentos , Fluoresceína/farmacología , Colorantes Fluorescentes/farmacología , Hígado/patología , Masculino , Microfluídica , Probabilidad , Ratas , Ratas Sprague-Dawley , Reproducibilidad de los Resultados , Factores de TiempoRESUMEN
Red blood cell velocity (RBCv), cerebral blood flow (CBF), and volume (CBV) are three key parameters when describing brain hemodynamics. Functional ultrasound imaging is a Doppler-based method allowing for real-time measurement of relative CBV at high spatiotemporal resolution (100 × 110 × 300 µm3, up to 10 Hz) and large scale. Nevertheless, the measure of RBCv and CBF in small cortical vessels with functional ultrasound imaging remains challenging because of their orientation and size, which impairs the ability to perform precise measurements. We designed a directional flow filter to overpass these limitations allowing us to measure RBCv in single vessels using a standard functional ultrasound imaging system without contrast agents (e.g., microbubbles). This method allows to quickly extract the number of vessels in the cortex that was estimated to be approximately 650/cm3 in adult rats, with a 55-45% ratio for penetrating arterioles versus ascending venules. Then, we analyzed the changes in RBCv in these vessels during forepaw stimulation. We observed that â¼40 vessels located in the primary somatosensory forelimb cortex display a significant increase of the RBCv (median ΔRBCv â¼15%, maximal ΔRBCv â¼60%). As expected, we show that RBCv was higher for penetrating arterioles located in the center than in the periphery of the activated area. The proposed approach extends the capabilities of functional ultrasound imaging, which may contribute to a better understanding of the neurovascular coupling at the brain-wide scale.
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Functional ultrasound imaging (fUSI) is an appealing method for measuring blood flow and thus infer brain activity, but it relies on the physiology of neurovascular coupling and requires extensive signal processing. To establish to what degree fUSI trial-by-trial signals reflect neural activity, we performed simultaneous fUSI and neural recordings with Neuropixels probes in awake mice. fUSI signals strongly correlated with the slow (<0.3 Hz) fluctuations in the local firing rate and were closely predicted by the smoothed firing rate of local neurons, particularly putative inhibitory neurons. The optimal smoothing filter had a width of â¼3 s, matched the hemodynamic response function of awake mice, was invariant across mice and stimulus conditions, and was similar in the cortex and hippocampus. fUSI signals also matched neural firing spatially: firing rates were as highly correlated across hemispheres as fUSI signals. Thus, blood flow measured by ultrasound bears a simple and accurate relationship to neuronal firing.
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Hemodinámica , Acoplamiento Neurovascular , Animales , Corteza Cerebral , Hemodinámica/fisiología , Ratones , Neuronas/fisiología , Ultrasonografía/métodosRESUMEN
Up to now, Psi formation in tRNAs was found to be catalysed by stand-alone enzymes. By computational analysis of archaeal genomes we detected putative H/ACA sRNAs, in four Sulfolobales species and in Aeropyrum pernix, that might guide Psi 35 formation in pre-tRNA(Tyr)(GUA). This modification is achieved by Pus7p in eukarya. The validity of the computational predictions was verified by in vitro reconstitution of H/ACA sRNPs using the identified Sulfolobus solfataricus H/ACA sRNA. Comparison of Pus7-like enzymes encoded by archaeal genomes revealed amino acid substitutions in motifs IIIa and II in Sulfolobales and A. pernix Pus7-like enzymes. These conserved RNA:Psi-synthase- motifs are essential for catalysis. As expected, the recombinant Pyrococcus abyssi aPus7 was fully active and acted at positions 35 and 13 and other positions in tRNAs, while the recombinant S. solfataricus aPus7 was only found to have a poor activity at position 13. We showed that the presence of an A residue 3' to the target U residue is required for P. abyssi aPus7 activity, and that this is not the case for the reconstituted S. solfataricus H/ACA sRNP. In agreement with the possible formation of Psi 35 in tRNA(Tyr)(GUA) by aPus7 in P. abyssi and by an H/ACA sRNP in S. solfataricus, the A36G mutation in the P. abyssi tRNA(Tyr)(GUA) abolished Psi 35 formation when using P. abyssi extract, whereas the A36G substitution in the S. solfataricus pre-tRNA(Tyr) did not affect Psi 35 formation in this RNA when using an S. solfataricus extract.
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Transferasas Intramoleculares/química , ARN de Archaea/química , ARN de Transferencia de Tirosina/química , Sulfolobales/enzimología , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Secuencia de Bases , Transferasas Intramoleculares/genética , Transferasas Intramoleculares/metabolismo , Datos de Secuencia Molecular , Pyrococcus abyssi/enzimología , Precursores del ARN/química , Precursores del ARN/metabolismo , ARN de Archaea/metabolismo , ARN Nucleolar Pequeño/química , ARN de Transferencia de Tirosina/metabolismo , Proteínas Recombinantes/metabolismo , Ribonucleoproteínas/metabolismo , Sulfolobales/genética , Sulfolobus solfataricus/enzimología , ARN Pequeño no TraducidoRESUMEN
Most brain functions engage a network of distributed regions. Full investigation of these functions thus requires assessment of whole brains; however, whole-brain functional imaging of behaving animals remains challenging. This protocol describes how to follow brain-wide activity in awake head-fixed mice using functional ultrasound imaging, a method that tracks cerebral blood volume dynamics. We describe how to set up a functional ultrasound imaging system with a provided acquisition software (miniScan), establish a chronic cranial window (timing surgery: ~3-4 h) and image brain-wide activity associated with a stimulus at high resolution (100 × 110 × 300 µm and 10 Hz per brain slice, which takes ~45 min per imaging session). We include codes that enable data to be registered to a reference atlas, production of 3D activity maps, extraction of the activity traces of ~250 brain regions and, finally, combination of data from multiple sessions (timing analysis averages ~2 h). This protocol enables neuroscientists to observe global brain processes in mice.
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Encéfalo/diagnóstico por imagen , Encéfalo/fisiología , Ultrasonografía , Vigilia/fisiología , Animales , Artefactos , Cabeza , Ratones Endogámicos C57BL , Factores de TiempoRESUMEN
Neuronal cell types are arranged in brain-wide circuits that guide behavior. In mice, the superior colliculus innervates a set of targets that direct orienting and defensive actions. We combined functional ultrasound imaging (fUSI) with optogenetics to reveal the network of brain regions functionally activated by four collicular cell types. Stimulating each neuronal group triggered different behaviors and activated distinct sets of brain nuclei. This included regions not previously thought to mediate defensive behaviors, for example, the posterior paralaminar nuclei of the thalamus (PPnT), which we show to play a role in suppressing habituation. Neuronal recordings with Neuropixels probes show that (1) patterns of spiking activity and fUSI signals correlate well in space and (2) neurons in downstream nuclei preferentially respond to innately threatening visual stimuli. This work provides insight into the functional organization of the networks governing innate behaviors and demonstrates an experimental approach to explore the whole-brain neuronal activity downstream of targeted cell types.
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Conducta Animal , Conectoma/métodos , Optogenética/métodos , Colículos Superiores/fisiología , Ultrasonografía/métodos , Animales , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Colículos Superiores/diagnóstico por imagen , Núcleos Talámicos/diagnóstico por imagen , Núcleos Talámicos/fisiologíaRESUMEN
Imaging large-scale circuit dynamics is crucial to understanding brain function, but most techniques have a limited depth of field. Here, we describe volumetric functional ultrasound imaging (vfUSI), a platform for brain-wide vfUSI of hemodynamic activity in awake head-fixed mice. We combined a high-frequency 1,024-channel 2D-array transducer with advanced multiplexing and high-performance computing for real-time 3D power Doppler imaging at a high spatiotemporal resolution (220 × 280 × 175 µm3, up to 6 Hz). We developed a standardized software pipeline for registration, segmentation, and temporal analysis in 268 individual brain regions based on the Allen Mouse Common Coordinate Framework. We demonstrated the high sensitivity of vfUSI under multiple experimental conditions, and we successfully imaged stimulus-evoked activity when only a few trials were averaged. We also mapped neural circuits in vivo across the whole brain during optogenetic activation of specific cell types. Moreover, we identified the sequential activation of sensory-motor networks during a grasping water-droplet task.
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Encéfalo/diagnóstico por imagen , Neuroimagen Funcional/métodos , Imagenología Tridimensional/métodos , Red Nerviosa/diagnóstico por imagen , Ultrasonografía Doppler/métodos , Vigilia , Animales , Encéfalo/fisiología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Red Nerviosa/fisiología , Optogenética/métodos , Estimulación Luminosa/métodos , Desempeño Psicomotor/fisiología , Ratas , Ratas Sprague-Dawley , Ultrasonografía/métodos , Vibrisas/fisiología , Vigilia/fisiologíaRESUMEN
Following middle cerebral artery (MCA) stroke, enhanced contralesional evoked responses have been consistently reported both in man and rodents as part of plastic processes thought to influence motor recovery. How early this marker of large-scale network reorganization develops has however been little addressed, yet has clinical relevance for rehabilitation strategies targeting plasticity. Previous work in mice has reported enhanced contralesional responses to unaffected-side forepaw stimulation as early as 45 min after MCA small branch occlusion. Using functional ultrasound imaging (fUSi) in anesthetized rats subjected to distal temporary MCA occlusion (MCAo), we assessed here (i) whether enhanced contralesional responses also occurred with unaffected-side whisker pad stimulation, and if so, how early after MCAo; and (ii) the time course of this abnormal response during occlusion and after reperfusion. We replicate in a more proximal MCA occlusion model the earlier findings of ultra-early enhanced contralesional evoked responses. In addition, we document this phenomenon within minutes after MCAo, and its persistence throughout the entire 90-min occlusion as well as 90-min reperfusion periods studied. These findings suggest that plastic processes may start within minutes following MCAo in rodents. If replicated in man, they might have implications regarding how early plasticity-enhancing therapies can be initiated after stroke.
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Estimulación Eléctrica , Lateralidad Funcional/fisiología , Infarto de la Arteria Cerebral Media/fisiopatología , Plasticidad Neuronal/fisiología , Animales , Masculino , Ratas , Ratas Sprague-Dawley , Ultrasonografía , Vibrisas/fisiologíaRESUMEN
Large numbers of brain regions are active during behaviors. A high-resolution, brain-wide activity map could identify brain regions involved in specific behaviors. We have developed functional ultrasound imaging to record whole-brain activity in behaving mice at a resolution of â¼100 µm. We detected 87 active brain regions during visual stimulation that evoked the optokinetic reflex, a visuomotor behavior that stabilizes the gaze both horizontally and vertically. Using a genetic mouse model of congenital nystagmus incapable of generating the horizontal reflex, we identified a subset of regions whose activity was reflex dependent. By blocking eye motion in control animals, we further separated regions whose activity depended on the reflex's motor output. Remarkably, all reflex-dependent but eye motion-independent regions were located in the thalamus. Our work identifies functional modules of brain regions involved in sensorimotor integration and provides an experimental approach to monitor whole-brain activity of mice in normal and disease states.
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Mapeo Encefálico/métodos , Encéfalo/fisiología , Percepción de Movimiento/fisiología , Nistagmo Optoquinético , Desempeño Psicomotor , Ultrasonografía/métodos , Animales , Encéfalo/fisiopatología , Masculino , Ratones Endogámicos C57BL , Ratones Transgénicos , Neuronas/fisiología , Nistagmo Congénito/fisiopatología , Estimulación Luminosa , ReflejoRESUMEN
Following middle cerebral artery occlusion, tissue outcome ranges from normal to infarcted depending on depth and duration of hypoperfusion as well as occurrence and efficiency of reperfusion. However, the precise time course of these changes in relation to tissue and behavioral outcome remains unsettled. To address these issues, a three-dimensional wide field-of-view and real-time quantitative functional imaging technique able to map perfusion in the rodent brain would be desirable. Here, we applied functional ultrasound imaging, a novel approach to map relative cerebral blood volume without contrast agent, in a rat model of brief proximal transient middle cerebral artery occlusion to assess perfusion in penetrating arterioles and venules acutely and over six days thanks to a thinned-skull preparation. Functional ultrasound imaging efficiently mapped the acute changes in relative cerebral blood volume during occlusion and following reperfusion with high spatial resolution (100 µm), notably documenting marked focal decreases during occlusion, and was able to chart the fine dynamics of tissue reperfusion (rate: one frame/5 s) in the individual rat. No behavioral and only mild post-mortem immunofluorescence changes were observed. Our study suggests functional ultrasound is a particularly well-adapted imaging technique to study cerebral perfusion in acute experimental stroke longitudinally from the hyper-acute up to the chronic stage in the same subject.
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Mapeo Encefálico/métodos , Neuroimagen Funcional/métodos , Infarto de la Arteria Cerebral Media/diagnóstico por imagen , Perfusión , Ultrasonografía/métodos , Animales , Volumen Sanguíneo Cerebral , Ataque Isquémico Transitorio/diagnóstico por imagen , Estudios Longitudinales , Ratas , ReperfusiónRESUMEN
Developing efficient brain imaging technologies by combining a high spatiotemporal resolution and a large penetration depth is a key step for better understanding the neurovascular interface that emerges as a main pathway to neurodegeneration in many pathologies such as dementia. This review focuses on the advances in two complementary techniques: multi-photon laser scanning microscopy (MPLSM) and functional ultrasound imaging (fUSi). MPLSM has become the gold standard for in vivo imaging of cellular dynamics and morphology, together with cerebral blood flow. fUSi is an innovative imaging modality based on Doppler ultrasound, capable of recording vascular brain activity over large scales (i.e., tens of cubic millimeters) at unprecedented spatial and temporal resolution for such volumes (up to 10µm pixel size at 10kHz). By merging these two technologies, researchers may have access to a more detailed view of the various processes taking place at the neurovascular interface. MPLSM and fUSi are also good candidates for addressing the major challenge of real-time delivery, monitoring, and in vivo evaluation of drugs in neuronal tissue.
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Encéfalo/fisiología , Circulación Cerebrovascular/fisiología , Neuronas/fisiología , Animales , Humanos , Microscopía Confocal/métodos , Ultrasonografía/métodosRESUMEN
Understanding the structure and function of cortical circuits requires the identification of and control over specific cell types in the cortex. To address these obstacles, recent optogenetic approaches have been developed. The capacity to activate, silence, or monitor specific cell types by combining genetics, virology, and optics will decipher the role of specific groups of neurons within circuits with a spatiotemporal resolution that overcomes standard approaches. In this review, the various strategies for selective genetic targeting of a defined neuronal population are discussed as well as the pros and cons of the use of transgenic animals and recombinant viral vectors for the expression of transgenes in a specific set of neurons.