Department of Biology, Stanford University, Stanford, CA 94305, USA.
Stress. 2009 Jul;12(4):305-12. doi: 10.1080/10253890802379955.
The ability to discriminate between spatial contexts is crucial for survival. This ability can be succinctly tested in the paradigm of fear renewal. In this paradigm, a change of spatial context results in robust renewal of conditioned fear, even if the conditioned fear has been previously extinguished. Chronic stress and environmental enrichment are known to affect learning and memory in opposite directions, with the former generally being deleterious. In this study, we examined the effects of chronic stress and enrichment on fear renewal in rats. Fear was evaluated as freezing responses to an auditory conditioning stimulus initially associated with footshocks in context A; fear extinction was evaluated in a novel spatial context (B) without the conditioned stimulus, and renewal in a third context (C) with the auditory cue. Specifically, we aimed to test if environmental enrichment can oppose the effects of chronic stress on fear renewal. We exposed different groups of adult male Wistar rats (6-12 per group) to 10 days of chronic stress (immobilization for 2 h daily), 14 days of enrichment, or a combination of both. We report that chronic stress compromised fear extinction and renewal. In contrast, enrichment re-established fear renewal in chronically stressed rats. Enhanced contextual modulation of fear memories in animals experiencing environmental enrichment while stressed could reflect an adaptive response. This could allow greater flexibility to optimize vigilance in differing spatial contexts.
辨别空间环境的能力对生存至关重要。这种能力可以在恐惧再现范式中简洁地进行测试。在这种范式中，即使条件恐惧已经被消除，空间环境的改变也会导致条件恐惧的强烈再现。慢性应激和环境丰富已知以相反的方式影响学习和记忆，前者通常是有害的。在这项研究中，我们研究了慢性应激和丰富对大鼠恐惧再现的影响。恐惧是通过对听觉条件刺激的冻结反应来评估的，该听觉条件刺激最初与 A 环境中的电击相关联；在没有条件刺激的新空间环境（B）中评估恐惧消退，在第三个环境（C）中评估听觉线索的再现。具体来说，我们旨在测试环境丰富是否可以对抗慢性应激对恐惧再现的影响。我们让不同组的成年雄性 Wistar 大鼠（每组 6-12 只）暴露于 10 天的慢性应激（每天固定 2 小时）、14 天的丰富或两者的组合中。我们报告说，慢性应激会损害恐惧的消退和再现。相比之下，丰富在慢性应激大鼠中重新建立了恐惧再现。在经历环境丰富的同时感到压力的动物中，增强了对恐惧记忆的上下文调制，这可能反映了一种适应性反应。这可以使在不同的空间环境中保持警觉的灵活性得到提高。
