Calcagnetti D J, Helmstetter F J, Fanselow M S
Psychology Department, Dartmouth College, Hanover, NH 03755.
Pharmacol Biochem Behav. 1987 Jul;27(3):529-31. doi: 10.1016/0091-3057(87)90360-1.
Earlier research has demonstrated that when rats are placed in a context associated with mild electric shock (1 mA/0.75 sec), environmental cues alone can produce conditional analgesia that suppresses pain sensitivity on the formalin test. This analgesia appears to be mediated by endogenous opioids since it is reversed by the centrally active opioid antagonists naloxone and naltrexone. Two experiments attempted to determine if peripheral or central opioids mediate this analgesia by employing quaternary naltrexone (QNTX), an antagonist which does not readily penetrate the blood-brain barrier at moderate doses. Intracerebroventricularly administered QNTX (10 micrograms) significantly reversed conditional analgesia, whereas intraperitoneally injected QNTX did not affect formalin-induced behavior. These results suggest that the conditional analgesia produced by our procedures is mediated by central, not peripheral, opioid mechanism(s).
早期研究表明，当将大鼠置于与轻度电击（1毫安/0.75秒）相关的环境中时，仅环境线索就能产生条件性镇痛，从而抑制福尔马林试验中的疼痛敏感性。这种镇痛作用似乎是由内源性阿片类物质介导的，因为它会被中枢活性阿片类拮抗剂纳洛酮和纳曲酮逆转。两项实验试图通过使用季铵化纳曲酮（QNTX）来确定外周或中枢阿片类物质是否介导这种镇痛作用，QNTX是一种在中等剂量下不易穿透血脑屏障的拮抗剂。脑室内注射QNTX（10微克）能显著逆转条件性镇痛，而腹腔注射QNTX则不影响福尔马林诱导的行为。这些结果表明，我们的实验程序所产生的条件性镇痛是由中枢而非外周阿片类机制介导的。
