Substance P-induced changes in cell genesis following diffuse traumatic brain injury

► Infusion of substance P (SP) after traumatic brain injury (TBI) promotes cellular proliferation. ► SP-induced cell proliferation after TBI was largely associated with microglial proliferation. ► Inhibition of SP activity after TBI with NK1 antagonists improves motor outcome. ► NK1 antagonists reduce microglial proliferation after TBI. ► Substance P-induced microglial proliferation after TBI is deleterious to functional outcome.