GABA_B Receptor Mediate Rats Tibia Bone Cancer Pain And Spinal Mechanism

Part one: The effect of lntrathecal injection Baclofen and CGP35348 on mechanical hyperalgesia in tibia bone cancer pain rats .Objective To observe the effect of left hind limb on mechanical withdrawal threshold(MWT)by intrathecal injection agonist Baclofen and antagonist CGP35348 ofγ-aminobutyric acid B(GABAB) receptor in tabia bone cancer pain rats .Method We established rats model of tibia bone cancer by making Walker 256 breast carcinoma cells to inoculated into the left hind limb tibia medullaris cavity of the female unpregnancy SD rats. Use Von Frey fiber examine MWT every two days at 9:00-10:00. Set pipes into subarachnoid space of all rats after establishing model 3 d. Nine days after successfully model establishment, 32 SD rats was divided into experimental 4 groups (n=8) randomly including N1 group(NS, 10μl),B1 group(Baclofen, 0.1μg),C1 group(CGP35348, 60μg),D1 group(CGP35348, 60μg +Baclofen, 0.1μg).The day before making model (t0),0.5 h pre- (t1) and 0.5(t2),1,2,4,8,24 h post-dosage , MWT of the left posterior limb was record.Result After estalishing model 9 d, significant increase of the MWT was recognized comparing t1 with t0 (P<0.01).Comparing group B1 with group N1,reach peak in post dosage 0.5 h and persistent effect was achieved for 4 h post-dosage(P <0.01). But there were no significant difference of MWT with N1,C1 and D1 group (P>0.05) .Conclusion (1) Intrathecal injection Baclofen has significantly analgesic effect in rats of tibia bone cancer pain model. (2) Signally use CGP35348 could not influence the tibia bone cancer pain. (3) Combining CGP35348 with Baclofen can be inhibited the anti-nociceptive effect of the latter. (4) GABAB receptor maybe mediate the maintenance of tibia bone cancer pain.Part two: The effects of intrathecal injection Baclofen and CGP35348 on the expression of spinal cord dorsal horn p-ERK1/2 in rats model of tibia bone cancer painObjective To observe the effect of p-ERK1/2 expression in tibia bone cancer pain rats by intrathecal injection agonist Baclofen and antagonist CGP35348 of GABAB receptor and approach the spinal possible mechanism of GABAB receptor mediating tibia bone cancer pain.Methods We established rat model of bone cancer by using Walker256 breast carcinoma cells which was inoculated into the tibia medullaris cavity of the female unpregnancy SD rats. Use Von Frey fiber examine pain every two days at 9:00-10:00. Set pipes into subarachnoid space of all rats after establishing model 3 d. Nine days after successfully model establishment, 32 SD rats was divided into experimental 4 groups (n = 8) including N2 group(NS , 10μl),B2 group(Baclofen, 0.1μg),C2 group(CGP35348, 60μg),D2 group(CGP35348 60μg + Baclofen 0.1μg). The 4 days continues and regular dosage was administrated , one times per day. 6 h after the last dosage, all the rats were killed and took out of L3-L5 spinal cord with frozen section for p-ERK1/2 immunohistochemical test respectively.Results (1) In lumbar spinal cord significant decrease of the p-ERK1/2 positive cells(NUM) and integral optical density(IOD) was found between group B2 with group N2(P<0.05). (2) There were no significant difference of NUM and IOD with N2,C2 and D2 group (P>0.05).Conclusion (1) The p-ERK1/2 expresstion of spinal cord droal horn were reduced by intrathecal injection Baclofen in tibia bone cancer pain rats. (2) The reduction of p-ERK1/2 expression by Baclofen can be blocked by CGP35348. (3) The GABAB receptor may through control downstream p-ERK1/2 to mediate tibia bone cancer pain .