We　investigated　the　antinociceptive　effect　of　local　intramuscular　injection　of　a　plasmid　encoding　human　proenlcephalin　(pVAX1-hPPE)　on　postoperative　pain　in　rats.　Male　Sprague-Dawley　rats　with　incision　induced　pain　were　intramuscularly　injected　into　injured　plantaris　muscle　with　empty　vector　(pVAX1)　or　pVAX1-hPPE,　respectively.　Paw　mechanical　threshold　and　thermal　latency　in　the　200　mu　g　pVAX1-hPPE　treated　rats　were　significantly　higher　at　6　h　and　on　1　day,　and　lasted　until　day　7　after　intramuscular　administration,　respectively.　The　analgesic　effects　were　reversed　by　methylnaltrexone,　suggesting　that　the　antinociceptive　effect　of　pVAX1-hPPE　was　mediated　through　peripheral　opioid　receptor　pathway.　In　contrast,　incisional　or　pVAX1-treated　rats　did　not　significantly　affect　pain　thresholds.　These　results　demonstrated　that　single　intramuscular　injection　of　pVAX1-hPPE　attenuated　incision-induced　pain　in　rats,　and　it　is　worthy　of　further　study　as　a　potential　gene　therapy　for　postoperative　pain.　(C)　2016　Elsevier　Ireland　Ltd.　All　rights　reserved.