Cassini Lindsey F, Flavell Charlotte R, Amaral Olavo B, Lee Jonathan L C
School of Psychology, University of Birmingham, Birmingham, B15 2TT, United Kingdom.
Institute of Medical Biochemistry Leopoldo de Meis, Federal University of Rio de Janeiro, Rio de Janeiro, 21941-902, Brazil.
Learn Mem. 2017 Aug 16;24(9):392-399. doi: 10.1101/lm.045724.117. Print 2017 Sep.
Retrieval of an associative memory can lead to different phenomena. Brief reexposure sessions tend to trigger reconsolidation, whereas more extended ones trigger extinction. In appetitive and fear cued Pavlovian memories, an intermediate "null point" period has been observed where neither process seems to be engaged. Here we investigated whether this phenomenon extends to contextual fear memory. Adult rats were subjected to a contextual fear conditioning paradigm, reexposed to the context 2 d later for 3, 5, 10, 20, or 30 min, with immediate injections of MK-801 or saline following reexposure, and tested on the following day. We observed a significant effect of MK-801 with the 3- and 30-min sessions, impairing reconsolidation and extinction, respectively. However, it did not have significant effects with 5-, 10-, or 20-min sessions, even though freezing decreased from reexposure to test. Further analyses indicated that this is not likely to be due to a variable transition point at the population level. In conclusion, the results show that in contextual fear memories there is a genuine "null point" between the parameters that induce reconsolidation and extinction, as defined by the effects of MK-801, although NMDA receptor-independent decreases in freezing can still occur in these conditions.
关联性记忆的提取会导致不同的现象。短暂的再次暴露会倾向于触发重新巩固，而较长时间的再次暴露则会触发消退。在基于奖赏和恐惧线索的巴甫洛夫式记忆中，已经观察到一个中间的“零点”期，在此期间似乎两种过程都未发生。在这里，我们研究了这种现象是否也适用于情境恐惧记忆。成年大鼠接受情境恐惧条件反射范式，在2天后再次暴露于该情境中3、5、10、20或30分钟，再次暴露后立即注射MK - 801或生理盐水，并在第二天进行测试。我们观察到，在3分钟和30分钟的再次暴露实验中，MK - 801分别对重新巩固和消退产生了显著影响，即损害了重新巩固和消退。然而，在5分钟、10分钟或20分钟的再次暴露实验中，它没有产生显著影响，尽管从再次暴露到测试期间，僵立行为有所减少。进一步分析表明，这不太可能是由于群体水平上的可变转换点所致。总之，结果表明，在情境恐惧记忆中，在由MK - 801的作用所定义的诱导重新巩固和消退的参数之间，存在一个真正的“零点”，尽管在这些条件下仍可能发生与NMDA受体无关的僵立行为减少。
