In Vivo Imaging of Microglia With Multiphoton Microscopy

Abstract

Neuroimaging has become an unparalleled tool to understand the central nervous system (CNS) anatomy, physiology and neurological diseases. While an altered immune function and microglia hyperactivation are common neuropathological features for many CNS disorders and neurodegenerative diseases, direct assessment of the role of microglial cells remains a challenging task. Non-invasive neuroimaging techniques, including magnetic resonance imaging (MRI), positron emission tomography (PET) and single positron emission computed tomography (SPECT) are widely used for human clinical applications, and a variety of ligands are available to detect neuroinflammation. In animal models, intravital imaging has been largely used, and minimally invasive multiphoton microcopy (MPM) provides high resolution detection of single microglia cells, longitudinally, in living brain. In this study, we review in vivo real-time MPM approaches to assess microglia in preclinical studies, including individual cell responses in surveillance, support, protection and restoration of brain tissue integrity, synapse formation, homeostasis, as well as in different pathological situations. We focus on in vivo studies that assess the role of microglia in mouse models of Alzheimer’s disease (AD), analyzing microglial motility and recruitment, as well as the role of microglia in anti-amyloid-β treatment, as a key therapeutic approach to treat AD. Altogether, MPM provides a high contrast and high spatial resolution approach to follow microglia chronically in vivo in complex models, supporting MPM as a powerful tool for deep intravital tissue imaging.

Tools and Approaches for Studying Microglia In vivo

“…Several studies have since used twophoton imaging to study microglial dynamism in CNS disease models and aging (66)(67)(68). Most two-photon microglia imaging studies are performed on mice under general anesthesia through either a cranial window or thinned skull preparation [reviewed in detail in (69)]. The major advantage of this approach is that it is performed in live animals and therefore the cells are observed within their physiological environment.…”

“…Firstly, microglial arbor, surveillance territory and process dynamics are increased in anesthetized mice compared to awake mice ( 70 , 71 ) and methods to image microglia in awake mice may be required for some studies. Secondly, cranial window surgery and skull thinning procedures can induce CNS damage and subsequent microglial activation ( 69 ). Thirdly, not all brain regions are accessible using this approach.…”

The Role of Microglia in Perioperative Neurocognitive Disorders

“…There is a limited amount of data about changes in microglia in the perioperative period in clinical studies. Non-invasive neuroimaging techniques may provide opportunities to assess the role of microglia directly (Tronel et al, 2017 ; Hierro-Bujalance et al, 2018 ). For example, microglial activation can be measured by positron emission tomography using uptake of [ 11 C]PBR28, which binds to the translocator protein, a protein upregulated in activated microglia and astrocytes (Datta et al, 2017 ; Forsberg et al, 2017 ; Albrecht et al, 2019 ; Werry et al, 2019 ).…”

Shared Microglial Mechanisms Underpinning Depression and Fatigue and Their Comorbidities

“…A striking advance to this theory came from findings that showed microglial process motility in the living mouse by in vivo two-photon laser-scanning microscopy [28]. In these experiments, through a cranial window, microglial cells were observed in undisturbed CNS tissue, revealing that microglial processes show continuous fast movement at the order of 1 to 3 mm of extensions and retractions per minute [31,32].…”