Canadian Centre for Behavioural Neuroscience, University of Lethbridge, 4401 University Drive, Lethbridge, AB T1K 4N8, Canada.
Canadian Centre for Behavioural Neuroscience, University of Lethbridge, 4401 University Drive, Lethbridge, AB T1K 4N8, Canada.
Physiol Behav. 2019 Sep 1;208:112556. doi: 10.1016/j.physbeh.2019.05.017. Epub 2019 May 29.
For this series of experiments, we wanted to investigate issues related to stress and learning. First, we wanted to determine if unpredictable stress might foster generalized fear responses more than predictable stress. Second, we wanted to evaluate how repeated stress might influence a rat's ability to learn what context predicts and an aversive event. Our first hypothesis was that unpredictable stress would result in generalized fear responses compared to predictable stress and these effects would worsen over repeated stress cycles. Our second hypothesis was that stress, regardless of type, would result in enhanced discriminative fear conditioning to context, a measure of fear learning. Accordingly, two groups of rats received 14-day restraint stress with one group receiving predictable while the other group received unpredictable stress. Following these experimental manipulations, both groups were given a recovery period and then an assessment of fear-based context discriminative behaviour was performed. This stress-recovery cycle was repeated, and fear conditioning was again assessed. After a single stress-recovery cycle discriminative fear conditioning to context was not impaired for either group. However, we did find that unpredictable stress facilitated behavioural expression of fear in a fearful context. Following two stress-recovery cycles the unpredictable group exhibited discriminative freezing that was elevated within the paired context, whereas, surprisingly, the predictable group did not exhibit differentiated freezing and instead spent similar amounts of time freezing in both contexts. This pattern of effects suggests that unpredictable chronic stress fostered fearful behaviour in the presence of a threatening context, whereas generalized fear is brought about by repeated predictable stress. This result is the opposite of our hypothesis that unpredictable stress would result in generalized fear. Taken together these results show that certain types of stressful experiences (unpredictable) enhance discriminative fear conditioning to context and stress over a longer period can produce generalized fear, but surprisingly in the predictable and not unpredictable condition.
对于这一系列实验，我们希望研究与压力和学习相关的问题。首先，我们想确定不可预测的压力是否会比可预测的压力更容易产生普遍的恐惧反应。其次，我们想评估重复的压力如何影响大鼠学习什么环境预测和厌恶事件的能力。我们的第一个假设是，与可预测的压力相比，不可预测的压力会导致普遍的恐惧反应，并且这些影响会随着重复的压力周期而恶化。我们的第二个假设是，压力，无论类型如何，都会导致对环境的增强的辨别性恐惧条件作用，这是恐惧学习的一种衡量标准。因此，两组大鼠接受了为期 14 天的束缚应激，一组接受可预测的应激，另一组接受不可预测的应激。在进行这些实验操作后，两组都有一个恢复期，然后对基于恐惧的环境辨别行为进行评估。这个应激恢复循环重复进行，再次评估恐惧条件作用。在单次应激恢复循环后，两组的环境辨别性恐惧条件作用都没有受损。然而，我们确实发现不可预测的压力促进了在恐惧环境中恐惧行为的表达。经过两个应激恢复周期后，不可预测组在配对环境中表现出显著的冻结行为，而令人惊讶的是，可预测组没有表现出差异冻结，而是在两个环境中冻结的时间相似。这种效应模式表明，不可预测的慢性应激在存在威胁性环境的情况下促进了恐惧行为，而重复的可预测应激则导致了普遍的恐惧。这一结果与我们的假设相反，即不可预测的压力会导致普遍的恐惧。总的来说，这些结果表明，某些类型的压力体验（不可预测性）增强了对环境的辨别性恐惧条件作用，而较长时间的压力会产生普遍的恐惧，但令人惊讶的是，这种情况发生在可预测的而非不可预测的条件下。
