Role of GABA_A receptor in hyperalgesia induced by propofol injected into rostral ventromedial medulla in rats / 中华麻醉学杂志

ABSTRACT

Objective To investigate the effects of propofol injected into rostral ventromedial medulla (RVM) on nociceptive responses and examine whether GABA_A resceptor is involved in the mechanism. Methods Sixty-four pathogen free SD rats of both sexes aged 2-3 months weighing 250-300 g were randomly divided into 4 groups ( n = 16 each) group I control (group C) ; group Ⅱ propofol (group P) ; group Ⅲ bicuculline (group B) and group Ⅳ B + P (group BP) . The animals were anesthetized with intraperitoneal 1% pentobarbital 50 mg/kg. Their heads were fixed with stereotactic apparatus. An tracar was inserted into RVM for microinjection of propofol and/or bicuculline. The noxious responses were evaluated by hot plate test (response latency was measured) and formalin test (intraplantar injection of 2.0% formalin 100 μl) . Pain was scored (0 = no pain, 3 = severe pain) . Results Both hot plate test and formalin test showed that hyperalgesia was induced by microinjection of propofol into RVM. In hot plate test hyperalgesia induced by injection of propofol (4μg/0.4μl) into RVM was antagonized at 20 min after microinjection of bicuculline (10 ng/0.4μl) into RVM. In formalin test pain scores were significantly lower at 1, 5,10,20,30,40,50 and 60 min after intraplantar formalin injection in group BP than in group P.Conclusion GABA_A receptor in RVM partially mediates propofol-induced hyperalgesia.