Microglia are the brain's resident innate immune cells and also have a role in synaptic plasticity. Microglial processes continuously survey the brain parenchyma, interact with synaptic elements and maintain tissue homeostasis. However, the mechanisms that control surveillance and its role in synaptic plasticity are poorly understood. Microglial dynamics in vivo have been primarily studied in anesthetized animals. Here we report that microglial surveillance and injury response are reduced in awake mice compared to anesthetized mice, suggesting that arousal state modulates microglial function. Pharmacological stimulation of β2-adrenergic receptors recapitulated these observations and disrupted experience-dependent plasticity, and these effects required the presence Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:
Microglia are the innate immune cells of the central nervous system and are also important participants in normal development and synaptic plasticity. Here, we demonstrate that the microglia of the mouse cerebellum represent a unique population compared to cortical microglia. Microglia are more sparsely distributed within the cerebellum and have a markedly less ramified morphology compared to their cortical counterparts. Using time-lapse in vivo imaging, we found that these differences in distribution and morphology ultimately lead to decreased parenchymal surveillance by cerebellar microglia. We also observed a novel form of somal motility in cerebellar microglia in vivo, which has not been described in cortical populations. We captured microglial interactions with Purkinje neurons in vivo. Cerebellar microglia interact dynamically with both the dendritic arbors and somas of Purkinje neurons. These findings suggest that cerebellar microglia are physiologically distinct from cortical populations and that these differences may ultimately alter how they could contribute to plasticity and disease processes in the cerebellum. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 627-644, 2018.
The development of new therapeutics is critically dependent on an understanding of the molecular pathways, the disruption of which results in neurological symptoms. Genetic and biomarker studies have highlighted immune signalling as a pathway that is impaired in patients with neurodevelopmental disorders (NDDs), and several studies on animal models of aberrant neurodevelopment have implicated microglia, the brain’s immune cells, in the pathology of these diseases. Despite the increasing awareness of the role of immune responses and inflammation in the pathophysiology of NDDs, the testing of new drugs rarely considers their effects in microglia. In this brief review, we present evidence of how the study of microglia can be critical for understanding the mechanisms of action of candidate drugs for NDDs and for increasing their therapeutic effect.
Microglia are the innate immune cells of the brain with roles in neuroimmunology and synaptic plasticity. Microglial processes continuously survey the brain parenchyma interacting with synaptic elements and maintaining tissue homeostasis. However, the mechanisms that control surveillance and its role in synaptic plasticity are poorly understood. Microglial dynamics in vivo have been primarily studied in anesthetized animals, where slow-wave neural activity resembles sleep-like states. We report that microglial surveillance and injury response in awake animals are reduced compared to when animals are anesthetized, suggesting that arousal state profoundly modulates microglial roles in the physiological brain. Stimulating β2-adrenergic receptors recapitulated these observations and also disrupted experience-dependent plasticity only when intact β2-adrenergic receptors were present in microglia specifically. These results indicate that microglial roles in surveillance and synaptic plasticity in the healthy brain are modulated by noradrenergic fluctuations between arousal states and raises new considerations for sleep/wake disruption in neurodevelopment and neuropathology.
Alcohol exposure during gestation can lead to severe defects in brain development and lifelong physical, behavioral and learning deficits that are classified under the umbrella term fetal alcohol spectrum disorder (FASD). Sadly, FASD is diagnosed at an alarmingly high rate, affecting 2%-5% of live births in the United States, making it the most common non-heritable cause of mental disability. Currently, no standard therapies exist that are effective at battling FASD symptoms, highlighting a pressing need to better understand the underlying mechanisms by which alcohol affects the developing brain. While it is clear that sensory and cognitive deficits are driven by inappropriate development and remodeling of the neural circuits that mediate these processes, alcohol's actions acutely and long-term on the brain milieu are diverse and complex. Microglia, the brain's immune cells, have been thought to be a target for alcohol during development because of their exquisite ability to rapidly detect and respond to perturbations affecting the brain. Additionally, our view of these immune cells is rapidly changing, and recent studies have revealed a myriad of microglial physiological functions critical for normal brain development and long-term function. A clear and complete understanding of how microglial roles on this end of the spectrum may be altered in FASD is currently lacking. Such information could provide important insights toward novel therapeutic targets for FASD treatment. Here we review the literature that links microglia to neural circuit remodeling and provide a discussion of the current understanding of how developmental alcohol exposure affects microglial behavior in the context of developing brain circuits.
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