Fanselow M S, Calcagnetti D J, Helmstetter F J
Psychology Department, Dartmouth College, Hanover, NH 03755.
Brain Res. 1988 Mar 15;444(1):147-52. doi: 10.1016/0006-8993(88)90921-3.
When rats are placed in a context with mild electric shock (1 mA/0.75 s), the environmental cues alone can provoke an immobile crouching behavior termed freezing. Freezing response is a Pavlovian conditional response provoked by stimuli that come to be associated with shock. Previous research has shown that peripheral injection of opioid antagonists can enhance this response. Two experiments were conducted to determine if peripheral and/or central opioid mechanisms are involved in this enhancement of freezing by employing quaternary naltrexone (QNTX), an opioid antagonist which does not readily penetrate the 'blood-brain barrier'. QNTX (5 and 10 micrograms/rat) administered i.c.v. prior to shock significantly enhanced freezing 24 h later, whereas i.p. injected QNTX, at doses as high as 20 mg/kg, had no effect. These results suggest that the enhancement of conditional freezing produced by QNTX is mediated by central, not peripheral, opioid mechanisms.
当将大鼠置于伴有轻度电击（1毫安/0.75秒）的环境中时，仅环境线索就能引发一种称为“僵住”的静止蹲伏行为。僵住反应是一种由与电击相关的刺激引发的巴甫洛夫条件反应。先前的研究表明，外周注射阿片类拮抗剂可增强这种反应。进行了两项实验，以确定外周和/或中枢阿片类机制是否参与了通过使用季铵型纳曲酮（QNTX，一种不易穿透“血脑屏障”的阿片类拮抗剂）增强僵住反应的过程。在电击前经脑室内注射QNTX（5微克/大鼠和10微克/大鼠）能显著增强24小时后的僵住反应，而腹腔注射高达20毫克/千克剂量的QNTX则没有效果。这些结果表明，QNTX产生的条件性僵住增强是由中枢而非外周阿片类机制介导的。
