Objective To investigate the effect of melanocortin receptor antagonist HS014 on morphine tolerance and microglial activa-tion in the spinal cord of rats. Methods Thirty adult male SD rats were randomly divided into 5 groups( n=6 in each group) . The rats were injected with morphine(10 mg/kg,intraperitoneal administration)twice daily for 5 consecutive days in morphine group(M), and normal saline in N group. In HS014+morphine( HM) group and saline+morphine( NM) group,the rats were respectively injected in-trathecally with 5 μg of HS014 and 5 μl of saline 15 min before the second administration of morphine at each testing day. In HS014+saline( HN) group,the rats were injected intrathecally 5 μg of HS014 15 min prior to the second saline injection for 5 consecutive days. The withdrawal latency was measured by the hot-plate test 30 min after the second administration at each testing day. At day 5, the immu-nohistochemical technique was used to evaluate the microglial activation by examining positive cells of ox-42. Results At day 1 and 2, the paw withdrawal latency was higher in M group than in N group(P<0. 001). At day 3,the paw withdrawal latency began to decrease in M group, and there was no significant difference between M group and N group at day 5(P>0. 05). At day 3-5, the paw withdrawal la-tency was increased in HM group compared with M group(P<0. 05). Compared with N group, the OX-42 positive cells increased in the spinal cord in M group(P<0. 001). Compared with M group, the microglia activation was suppressed, and the OX-42 positive cells de-creased in the spinal cord in HM group(P<0. 001). Conclusion Chronic administration of morphine(10 mg/kg, twice daily for 5 d) could induce morphine tolerance and microglial activation in the spinal cord of rats. Combined administration of HS014 and mor-phine could inhibit the development of morphine tolerance and microglial activation,but HS014 alone could not show analgesic effect.%目的：探讨黑皮质素受体拮抗剂HS014对大鼠吗啡耐受及脊髓小胶质细胞激活的影响。方法健康雄性SD大鼠30只,随机分为5组(n=6)：吗啡组(M)、生理盐水组(N)、HS014+吗啡组(HM)、生理盐水+吗啡组(NM)和HS014+生理盐水组(HN)。 M组大鼠每次腹腔注射吗啡(10 mg/kg),2次/d；N组大鼠在相同条件下注射生理盐水； HS014+吗啡组(HM)、生理盐水+吗啡组( NM)大鼠每天第2次注射吗啡前15 min分别鞘内注射5μg HS014和5μl生理盐水；HS014+生理盐水组大鼠第2次注射生理盐水前15 min鞘内注射5μg HS014。各组均连续给药5 d,每天第2次给药后30 min进行热板测痛,于第5天采用免疫组织化学染色观察小胶质细胞标志物OX-42的表达。结果①在实验第1天和第2天,M组大鼠热痛觉阈值与N组比较,差异有统计学意义(P<0.001),此后M组热痛觉阈值开始下降,至第5天时M组大鼠热痛觉阈值与N组比较组间差异无统计学意义(P>0.05)。在第3-5天, HM组热痛觉阈值与M组比较明显增加,差异有统计学意义(P<0.05)。②与N组比较,M组大鼠脊髓OX-42阳性细胞计数明显增加(P<0.001)。与M组比较,HM组的小胶质细胞激活受到抑制,OX-42阳性细胞计数下降(P<0.001)。结论慢性应用吗啡(10 mg/kg,腹腔注射,2次/d,连续5 d)能够导致吗啡耐受和脊髓小胶质细胞激活；联合给予HS014和吗啡,能够抑制吗啡耐受和小胶质细胞的激活,但HS014本身无镇痛作用。
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