Table 1.

Different types of glial cells.

Number	Types of microglia	Concept	Function	Reference
1	“Satellite” microglia	“Satellite” microglia are located on the axon side of the neuronal cell body and overlap with the site where the neuronal potential starts, mainly in the cerebral cortex, thalamus, and hippocampus	“Satellite” glial cells are the most abundant in sensory ganglia and play a major role in sensory function; they are closely related to neuronal excitation	[15,23,44,45,62]
2	KSPG microglia	KSPG microglia are located in the extracellular matrix and cell surface; they are positive for keratin sulfate	Help cell axon growth and adhesion, establish boundaries for axonal growth in the developing brain and spinal cord and are a potential inhibitor of axon growth	[30,31,33,34]
3	Hoxb8 microglia	Hoxb8 glial cells are derived from the Hoxb8 lineage in the second wave (E8.5) hematopoiesis of the yolk sac	Loss of Hoxb8 glial function causes behaviors such as chronic anxiety and obsessive-compulsive disorder	[10,17,29,53,69,73]
4	CD11c microglia	CD11c expression is positive in these glial cells	Play an important role in myelin development and neurogenesis and are associated with Aβ protein deposition	[36,42,52]
5	Support neurons to form microglia	Glial cells associated with neurogenesis contribute to embryonic neurogenesis and neuronal differentiation and development	Critical for adult neurogenesis, removal of apoptotic neurons, learning-dependent synapse formation, synaptic and spinal remodeling, axon guidance, and survival and migration of neuroblasts	[32]
6	“Dark” microglia	Immunohistochemically appear as “dark” glial cells in transmission electron microscopy, which are often in contact with the synaptic cleft while extensively surrounding axon terminals	Interactions with blood vessels and synapses; they may be linked with the pathological remodeling in neural circuits that can impair learning, memory, and other basic cognitive functions	[4,63,64]