Microglia as a defensive arm of the nervous system emerged early in evolution. The surveilling microglia with motile and ramified processes are the main phenotype in the healthy CNS; the surveilling microglial patrol neuronal somata, dendrites, dendritic spines and axons. Increasing evidence suggests that microglia play fundamental roles in development, maturation and ageing of the brain, as well as contribute to a variety of physiological brain processes including sleep and circadian rhythm. Physiological state of microglia is tightly regulated by brain microenvironment and controlled by a sophisticated system of receptors and signalling cascades including ionotropic and metabotropic purinoceptors, pattern-recognition receptors, and receptors for chemokines and cytokines. Microglia also utilise ion channels and transporters in regulating ionic homeostasis and various aspects of microglial function. The major ion transporters expressed by microglia include Na⁺/H⁺ exchanger 1 and Na⁺/Ca²⁺ exchangers, which are involved in regulation of pH_i and Ca²⁺ homeostasis during microglial physiological responses. Microglial cells control development, maturation and plasticity of neuronal ensembles through controlled physiological phagocytosis of synapses or synaptic fragments - processes known as synaptic pruning and trogocytosis. This special issue on “Physiological roles of microglia” is an assembly of papers written by the leading experts in this research field. We start this special issue with this snapshot of microglial physiological functions as a prelude to the indepth discussion of microglia in physiological processes in the nervous system.

小胶质细胞作为神经系统的防御臂出现在进化的早期。具有运动和分枝过程的监视小胶质细胞是健康中枢神经系统的主要表型；监视小胶质细胞巡逻神经元胞体、树突、树突棘和轴突。越来越多的证据表明，小胶质细胞在大脑的发育、成熟和衰老中发挥着重要作用，并有助于包括睡眠和昼夜节律在内的各种大脑生理过程。小胶质细胞的生理状态受大脑微环境的严格调控，并受复杂的受体和信号级联系统控制，包括离子型和代谢型嘌呤受体、模式识别受体以及趋化因子和细胞因子受体。小胶质细胞还利用离子通道和转运蛋白来调节离子稳态和小胶质细胞功能的各个方面。小胶质细胞表达的主要离子转运蛋白包括 Na⁺ /H ⁺交换器 1 和 Na ⁺ /Ca ²⁺交换器，它们在小胶质细胞生理反应期间参与调节 pH _i和 Ca ²⁺稳态。小胶质细胞通过控制突触或突触片段的生理吞噬作用来控制神经元集合的发育、成熟和可塑性——这一过程被称为突触修剪和吞噬作用。本期“小胶质细胞的生理作用”特刊是该研究领域领先专家撰写的论文集。我们以小胶质细胞生理功能的快照作为本期特刊的开始，作为深入讨论小胶质细胞在神经系统生理过程中的序幕。