Neurobiology of Stress ( IF 5 ) Pub Date : 2019-04-10 , DOI: 10.1016/j.ynstr.2019.100163 Andrea Cardenas 1 , Michelle Blanca 1 , Eugene Dimitrov 1
Ensembles of principal neurons in the basolateral amygdala (BLA) generate the initial engrams for fear memories, while projections from the BLA to the medial prefrontal cortex (mPFC) are essential for the encoding, transfer and storage of remote fear memories. We tested the effects of chronic pain on remote fear memories in mice.
Male mice underwent classic fear conditioning by pairing a single tone (conditional stimulus, CS) with a single electric foot shock (unconditional stimulus, US). Sciatic nerve constriction was used to induce neuropathic pain at various time points before or after the fear conditioning. The mice with sciatic nerve cuffs implanted 48 h after the fear conditioning showed an increased freezing response to CS when compared to mice without cuffs or when compared to mice in which the nerve cuffing was performed 48 h before the fear conditioning. The enhancing effect of pain on consolidated fear memory was further tested and mice in which the nerve cuffing was performed 14 days after the fear conditioning also showed an increased fear response when tested 56 days later.
We used immunostaining to detect morphological changes in the BLA that could suggest a mechanism for the observed increase in fear response. We found an increased number of calbindin/parvalbumin positive neurons in the BLA and increased perisomatic density of GAD65 on projection neurons that connect BLA to mPFC in mice with nerve cuffs. Despite the strong increase of c-Fos expression in BLA and mPFC that was induced by fear recall, neither the BLA to mPFC nor the mPFC to BLA projection neurons were activated in mice with nerve cuffs. Furthermore, non-injured mice had an increased fear response when BLA to mPFC projections were inhibited by a chemogenetic method.
In conclusion, this study provides evidence that persistent pain has a significant impact on consolidated fear memories. Very likely the underlying mechanism for this phenomenon is increased inhibitory input onto the BLA to mPFC projection neurons, possibly from neurons with induced parvalbumin expression. Conceivably, the increased fear response to consolidated fear memory is a harbinger for the later development of anxiety and depression symptoms associated with chronic pain.
中文翻译:
持续的疼痛加剧了巩固恐惧记忆的回忆。
基底外侧杏仁核(BLA)中主要神经元的集合生成恐惧记忆的初始字母,而从BLA到内侧前额叶皮层(mPFC)的投影对于远程恐惧记忆的编码,传递和存储至关重要。我们测试了慢性疼痛对小鼠远程恐惧记忆的影响。
雄性小鼠通过将单音(有条件刺激,CS)与单足电击(无条件刺激,美国)配对来进行经典的恐惧条件调节。在恐惧调节之前或之后的各个时间点,使用坐骨神经收缩来诱发神经性疼痛。与没有袖带的小鼠相比,或与在恐惧条件发生前48小时进行神经束缚的小鼠相比,在恐惧条件发生后48 h植入坐骨神经袖带的小鼠表现出对CS的冷冻反应增加。进一步测试了疼痛对巩固恐惧记忆的增强作用,在恐惧条件治疗后14天进行神经套扎的小鼠在56天后进行测试时,其恐惧反应也有所增强。
我们使用免疫染色检测BLA的形态变化,这可能表明观察到的恐惧反应增加的机制。我们发现BLA中钙结合蛋白/小白蛋白阳性神经元的数量增加,而将BLA连接至mPFC的投射神经元的GAD65的过密度增加。尽管恐惧召回引起了BLA和mPFC中c-Fos表达的强烈增加,但在具有神经袖套的小鼠中,BLA到mPFC或mPFC到BLA投射神经元均未激活。此外,当通过化学生成方法抑制对mPFC投影的BLA时,未受伤的小鼠的恐惧反应增强。
总而言之,这项研究提供了证据表明持续性疼痛对巩固恐惧记忆有重大影响。这种现象的潜在机制很可能是增加了对mPFC投射神经元的BLA抑制性输入,可能是来自具有诱导的小白蛋白表达的神经元。可以想象,对合并的恐惧记忆的恐惧反应增强是与慢性疼痛相关的焦虑和抑郁症状后来发展的先兆。