C3 and neurodegenerative disease: A previous study reported that the reduction of glial C3 production inhibits C3‐C3aR signaling‐mediated glial activation, potentially preventing synaptic loss, synaptic phagocytosis, and cognitive impairment.[21] The overactivated microglial phagocytosis of neurons and synapses leads to multiple neurodegenerative diseases and cognitive impairment.[37] Given our results and the reported findings, we hypothesized that anesthesia/surgery could activate hippocampal C3‐C3aR signaling‐mediated microglial phagocytosis of synapses.