Propofol produces preventive analgesia via GluN2B-containing NMDA Receptor/ERK1/2 Signaling Pathway in a rat model of inflammatory Pain

Propofol, an intravenous anaesthetic, has been shown to offer superior analgesic effect clinically. Whether propofol has preventive analgesic property remains unexplored. The present study investigated the antinociceptive effect of propofol and underlying molecular and cellular mechanisms via pre-emptive administration in a formalin-induced inflammatory pain model in rats. Male adult Sprague-Dawley rats were randomly allocated into 4 groups: naive (Group Naive), formalin injection only (Group Formalin), and formalin injection at 30 min (Group P-30min) or 2 h (Group P-2h) after intravenous infusion of propofol (0.6 mg kg(-1) min(-1)) for 1 h. Nociceptive responses and protein expression of phosphorylated- or pan-GluN2B, ERK1/2, p38 MAPK and JNK in the spinal dorsal horn was evaluated. Alteration of intracellular Ca2+ concentration induced by NMDA receptor agonists with or without pretreatment of propofol was measured using fluorometry in SH-SY5Y cells while neuronal activation in the spinal dorsal horn by immunofluorescence. Pre-emptive propofol reduced pain with a delayed response to formalin and a reduction in hypersensitivity that lasted at least for 2 h. The formalin-induced activation of spinal GluN2B and ERK1/2 but not p38 or JNK were also diminished by propofol treatment. Preconditioning treatment with 3 mu M and 10 mu M of propofol inhibited Ca2+ influx mediated through NMDA receptors in SH-SY5Y cells. Propofol also reduced the neuronal expression of c-Fos and p-ERK induced by formalin. These study shows that pre-emptive administration of propofol produces preventive analgesic effects on inflammatory pain through regulating neuronal GluN2B-containing NMDA receptor and ERK1/2 pathway in the spinal dorsal horn.