Fanselow M S, Bolles R C
J Comp Physiol Psychol. 1979 Aug;93(4):736-44. doi: 10.1037/h0077609.
The freezing behavior of the rat that occurs following painful electric shock was found to increase when the animal was pretreated with the opiate antagonist naloxone. Freezing was a positive linear function of drug dose and shock intensity (Experiment 2). Naloxone pretreatment enhanced freezing only when the animal was given two or three shocks but did not affect freezing when the animal was given only one shock or not shocked at all (Experiments 3, 4, and 5). Naloxone must be present during shock, nor just during the observation period, in order to increase freezing (Experiment 6). These results suggest that when an animal is shocked, it releases endogenous analgesics (endorphins) that make a subsequent shock less aversive. Naloxone, by blocking the endorphin system, makes the shock more aversive than it would normally be.
研究发现，当用阿片类拮抗剂纳洛酮对大鼠进行预处理时，大鼠在遭受痛苦电击后出现的僵住行为会增加。僵住程度是药物剂量和电击强度的正线性函数（实验2）。纳洛酮预处理仅在动物接受两到三次电击时增强僵住行为，但当动物仅接受一次电击或根本未接受电击时，对僵住行为没有影响（实验3、4和5）。为了增加僵住行为，纳洛酮必须在电击期间存在，而不仅仅是在观察期存在（实验6）。这些结果表明，当动物受到电击时，它会释放内源性镇痛剂（内啡肽），使随后的电击不那么令人厌恶。纳洛酮通过阻断内啡肽系统，使电击比正常情况更令人厌恶。
