Robinson-Drummer P A, Chakraborty T, Heroux N A, Rosen J B, Stanton M E
Department of Psychological and Brain Sciences, University of Delaware, Newark, DE 19716, United States.
Department of Psychological and Brain Sciences, University of Delaware, Newark, DE 19716, United States.
Neurobiol Learn Mem. 2018 Apr;150:1-12. doi: 10.1016/j.nlm.2018.02.008. Epub 2018 Feb 13.
The context preexposure facilitation effect (CPFE) is a variant of contextual fear conditioning in which acquisition of the contextual representation and association of the retrieved contextual memory with an immediate foot-shock are separated by 24 h. During the CPFE, learning- related expression patterns of the early growth response-1 gene (Egr-1) vary based on training phase and brain sub-region in adult and adolescent rats (Asok, Schreiber, Jablonski, Rosen, & Stanton, 2013; Schreiber, Asok, Jablonski, Rosen, & Stanton, 2014; Chakraborty, Asok, Stanton, & Rosen, 2016). The current experiments extended our previous findings by examining Egr-1 expression in infant (PD17) and juvenile (PD24) rats during the CPFE using preexposure protocols involving single-exposure (SE) or multiple-exposure (ME) to context. Following a 5 min preexposure to the training context (i.e. the SE protocol), Egr-1 expression in the medial prefrontal cortex (mPFC), dorsal hippocampus (dHPC) and lateral nucleus of the amygdala (LA) was differentially increased in PD24 rats relative to PD17 rats. In contrast, increased Egr-1 expression following an immediate foot-shock (2s, 1.5 mA) did not differ between PD17 and PD24 rats, and was not learning-related. Interestingly, increasing the number of exposures to the training chamber on the preexposure day (i.e. ME protocol) altered training-day expression such that a learning-related increase in expression was observed in the mPFC in PD24 but not PD17 rats. Together, these results illustrate a clear maturation of Egr-1 expression that is both age- and experience-dependent. In addition, the data suggest that regional activity and plasticity within the mPFC on the preexposure but not the training day may contribute to the ontogenetic profile of the effect. Further studies are necessary to elucidate the causal role of sub-region-specific neuroplasticity in the ontogeny of the CPFE.
情境暴露前促进效应（CPFE）是情境恐惧条件反射的一种变体，其中情境表征的习得以及检索到的情境记忆与即时足部电击的关联被分隔24小时。在CPFE过程中，成年和青春期大鼠中早期生长反应-1基因（Egr-1）与学习相关的表达模式会因训练阶段和脑区的不同而有所变化（阿索克、施赖伯、雅布隆斯基、罗森和斯坦顿，2013年；施赖伯、阿索克、雅布隆斯基、罗森和斯坦顿，2014年；查克拉博蒂、阿索克、斯坦顿和罗森，2016年）。当前的实验通过在CPFE过程中，使用涉及单次暴露（SE）或多次暴露（ME）于情境的暴露前方案，检测婴儿期（出生后第17天，PD17）和幼年期（出生后第24天，PD24）大鼠的Egr-1表达，扩展了我们之前的研究结果。在对训练情境进行5分钟的预暴露（即SE方案）后，与PD17大鼠相比，PD24大鼠内侧前额叶皮质（mPFC）、背侧海马体（dHPC）和杏仁核外侧核（LA）中的Egr-1表达有不同程度的增加。相比之下，在即时足部电击（2秒，1.5毫安）后Egr-1表达的增加在PD17和PD24大鼠之间没有差异，且与学习无关。有趣的是，在预暴露日增加对训练室的暴露次数（即ME方案）会改变训练日的表达，使得在PD24大鼠而非PD17大鼠的mPFC中观察到与学习相关的表达增加。总之，这些结果表明Egr-1表达存在明显的成熟过程，这既依赖于年龄也依赖于经验。此外，数据表明，在预暴露日而非训练日mPFC内的区域活动和可塑性可能有助于该效应的个体发育特征。有必要进行进一步研究以阐明特定脑区神经可塑性在CPFE个体发育中的因果作用。
