PLPPR4 and bone neoplasm: To test for the role of hippocampal PRG-1 and P2X7 receptor in bone cancer pain, the virus vector LV-Plppr4 (PRG-1 overexpression), LV-Plppr4-RNAi (PRG-1 knock down) or LV-P2X7R-RNAi (P2X7 receptor knock down) was slowly injected unilaterally into the hippocampus area one week before BCP operation (Figure 4A).