microRNA regulation related to the protective effects of environmental enrichment against cocaine-seeking behavior

MicroRNAs are “master regulators” of gene expression. To investigate microRNAs involved in the incentive motivation for cocaine elicited by exposure to cocaine-associated cues, we conducted NanoString nCounter analyses of microRNA expression in the nucleus accumbens shell of male rats that had been tested for cue reactivity in a previous study. These rats had been trained to self-administer cocaine while living in isolate housing, then during a subsequent 21-day forced abstinence period they either stayed under isolate housing or switched to environmental enrichment (EE), as this EE intervention is known to decrease cocaine seeking. This allowed us to create groups of “high” and “low” cocaine seekers using a median split of cocaine-seeking behavior. We conducted a differential expression analysis across these two groups that identified 33 miRNAs that were differentially altered in the nucleus accumbens shell. Predicted mRNA targets of these microRNAs are implicated in synaptic plasticity and neuronal signaling. Some of these microRNAs have previously been implicated in substance use disorders, while others are predicted to target large numbers of cocaine-related genes. Of the 33 differentially expressed microRNAs, 8 were specifically downregulated in the low-seeking group and another set of 8 had expression levels that were significantly correlated with cocaine-seeking. These findings suggest that processes involved in cocaine-seeking behavior may alter, or be altered by, multiple microRNAs. Further research examining the mechanisms involved in these microRNA changes and their effects on signaling may reveal novel therapeutic targets for attenuating drug craving.微小RNA（microRNAs）是基因表达的主控调控因子。为探究参与可卡因相关线索暴露引发的可卡因诱因动机的微小RNA，我们对此前一项研究中经线索反应性测试的雄性大鼠伏隔核壳区的微小RNA表达开展了NanoString nCounter分析。这些大鼠曾在隔离饲养条件下接受可卡因自身给药训练，随后在为期21天的强制戒断阶段中，一部分大鼠维持隔离饲养，另一部分则转换为环境丰富化（Environmental Enrichment, EE）饲养——已知该EE干预可降低可卡因寻求行为。我们通过对可卡因寻求行为进行中位数拆分，构建了“高可卡因寻求者”与“低可卡因寻求者”两组样本。对这两组样本开展差异表达分析后，我们鉴定出33个在伏隔核壳区存在差异表达的微小RNA。这些微小RNA的预测mRNA靶点涉及突触可塑性与神经元信号传导过程。其中部分微小RNA此前已被证实与物质使用障碍（substance use disorders）相关，其余微小RNA则被预测可靶向大量可卡因相关基因。在这33个差异表达的微小RNA中，有8个在低寻求组中特异性下调，另有8个的表达水平与可卡因寻求行为显著相关。本研究结果提示，可卡因寻求行为相关的生物学过程可能改变多种微小RNA的表达，或受多种微小RNA表达变化的调控。后续针对这些微小RNA表达变化的调控机制及其对信号传导的影响开展研究，或可发现用于减弱药物渴求的新型治疗靶点。