The Johns Hopkins University, 3400 North Charles, 126 Ames Hall, Baltimore, MD 21217, USA.
Behav Brain Res. 2010 Jul 29;211(1):111-7. doi: 10.1016/j.bbr.2010.03.020. Epub 2010 Mar 16.
In Pavlovian fear conditioning animals receive pairings of a neutral cue and an aversive stimulus such as an electric foot-shock. Through such pairings, the cue will come to elicit a central state of fear that produces a variety of autonomic and behavioral responses, among which are conditioned freezing and suppression of instrumental responding, termed conditioned suppression. The central nucleus of the amygdala (CeA) and the ventrolateral periaqueductal grey (vlPAG) has been strongly implicated in the acquisition and expression of conditioned fear. However, previous work suggests different roles for the CeA and vlPAG in fear learning maybe revealed when fear is assessed with conditioned freezing or conditioned suppression. To further explore this possibility we gave rats selective lesions of either the CeA or vlPAG and trained them in Pavlovian first-order fear conditioning as well as Pavlovian second-order fear conditioning. We concurrently assessed the acquisition of conditioned freezing and conditioned suppression. We found that vlPAG and CeA lesions impaired both first- and second-order conditioned freezing. VlPAG lesions did not impair, and CeA lesions only transiently impaired, first-order conditioned suppression. However, both vlPAG and CeA lesions impaired second-order conditioned suppression. These results suggest that the CeA and vlPAG are critically important to expressing fear through conditioned freezing but play different and less critical roles in expressing fear through conditioned suppression.
在巴甫洛夫式恐惧条件反射中，动物会接收到中性提示和厌恶刺激（如电击脚）的配对。通过这种配对，提示会引起一种中央恐惧状态，从而产生各种自主和行为反应，其中包括条件性冻结和工具性反应的抑制，称为条件性抑制。杏仁核中央核（CeA）和腹外侧导水管周围灰质（vlPAG）强烈参与了条件性恐惧的获得和表达。然而，以前的工作表明，CeA 和 vlPAG 在恐惧学习中的作用可能不同，当使用条件性冻结或条件性抑制来评估恐惧时会显露出来。为了进一步探索这种可能性，我们对大鼠进行了 CeA 或 vlPAG 的选择性损伤，并对它们进行了一阶和二阶恐惧条件反射训练。我们同时评估了条件性冻结和条件性抑制的获得。我们发现，vlPAG 和 CeA 损伤均损害了一阶和二阶条件性冻结。vlPAG 损伤不损害，而 CeA 损伤仅短暂损害了一阶条件性抑制。然而，vlPAG 和 CeA 损伤均损害了二阶条件性抑制。这些结果表明，CeA 和 vlPAG 对于通过条件性冻结表达恐惧至关重要，但在通过条件性抑制表达恐惧方面发挥着不同且不太关键的作用。
