Figure 2:

Major cell types involved in pain in the DRG. Under physiological condition, DRG neurons are isolated from each other by SGCs and the neurons, glial cells and a small number of tissue resident immune cells form a microenvironment in dynamic balance. In chronic pain, macrophages are activated and release a milieu of inflammatory factors, and some blood-borne immune cells including neutrophils and T cells are recruited into the DRG. Sympathetic nerves, which usually terminate at the blood vessels, sprout into the DRG and form synaptic connection with DRG neurons, resulting in ectopic sensory activation. DRG, dorsal root ganglion; SGC, satellite glia cell.