Mikami Kaori, Kiyokawa Yasushi, Takeuchi Yukari, Mori Yuji
Laboratory of Veterinary Ethology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Physiol Behav. 2016 Sep 1;163:123-128. doi: 10.1016/j.physbeh.2016.05.001. Epub 2016 May 5.
In social species, the phenomenon in which the presence of conspecific animals mitigates stress responses is called social buffering. We previously reported that social buffering in male rats ameliorated behavioral fear responses, as well as hypothalamic-pituitary-adrenal axis activation, elicited by an auditory conditioned stimulus (CS). However, after social buffering, it is not clear whether rats exhibit fear responses when they are re-exposed to the same CS in the absence of another rat. In the present study, we addressed this issue using an experimental model of extinction. High stress levels during extinction training impaired extinction, suggesting that extinction is enhanced when stress levels during extinction training are low. Therefore, we hypothesized that rats that had received social buffering during extinction training would not show fear responses to a CS, even in the absence of another rat, because social buffering had enhanced the extinction of conditioned fear responses. To test this, we subjected male fear-conditioned rats to extinction training either alone or with a non-conditioned male rat. The subjects were then individually re-exposed to the CS in a recall test. When the subjects individually underwent extinction training, no responses were suppressed in the recall test. Conversely, when the subjects received social buffering during extinction training, freezing and Fos expression in the paraventricular nucleus of the hypothalamus and lateral amygdala were suppressed. Additionally, the effects of social buffering were absent when the recall test was conducted in a different context from the extinction training. The present results suggest that social buffering enhances extinction of conditioned fear responses.
在群居物种中，同种动物的存在减轻应激反应的现象被称为社会缓冲。我们之前报道过，雄性大鼠中的社会缓冲改善了由听觉条件刺激（CS）引发的行为恐惧反应以及下丘脑-垂体-肾上腺轴的激活。然而，在经历社会缓冲后，尚不清楚大鼠在没有其他大鼠的情况下再次暴露于相同的条件刺激时是否会表现出恐惧反应。在本研究中，我们使用消退实验模型解决了这个问题。消退训练期间的高应激水平会损害消退，这表明当消退训练期间的应激水平较低时，消退会增强。因此，我们假设在消退训练期间接受过社会缓冲的大鼠即使在没有其他大鼠的情况下也不会对条件刺激表现出恐惧反应，因为社会缓冲增强了条件恐惧反应的消退。为了验证这一点，我们让雄性恐惧条件化大鼠单独或与一只非条件化雄性大鼠一起接受消退训练。然后在回忆测试中让这些大鼠个体再次暴露于条件刺激。当大鼠个体接受消退训练时，回忆测试中没有反应受到抑制。相反，当大鼠在消退训练期间接受社会缓冲时，下丘脑室旁核和杏仁核外侧的僵立和Fos表达受到抑制。此外，当回忆测试在与消退训练不同的环境中进行时，社会缓冲的效果不存在。目前的结果表明，社会缓冲增强了条件恐惧反应的消退。
