Transcriptome of accumbens nuclei from mice having low scores of cocaine-dependent conditioned place preference. Mus musculus

Molecular basis of transition to addiction in vulnerable individuals is largely unknown. We hypothesized that human susceptibility genes can be identified on the basis of conserved molecular mechanisms in rodent brains. We used a short-term cocaine-dependent conditioned place preference (CPP) to identify genetic hallmarks of early steps of reward memory in basal ganglia including accumbens nucleus (NAc), globus pallidus (GP) and subthalamic nucleus (STN). Using genome-wide microarray analysis and CPP as a quantitative trait, we found that synaptic plasticity-related genes are deregulated in these three structures. A significant enrichment in bona fide transcripts involved in dendritic spine local translation was evidenced. mGluR5 is transcriptionally deregulated in Acc and GP of cocaine-treated animals. Grin3a that encodes a NMDA receptor subunit involved in Ca++ permeability is deregulated in NAc. Furthermore, Orexin/Hcrt transcript level is decreased in STN, a region known to be involved in discriminating addictive drugs and natural rewards. We also found that mGluR5 and Grin3a expression deregulation is sufficient to induce changes in synaptic plasticity-related genes. Altogether, these results suggest that a combined deregulation of mGluR5 and Grin3A pathway in NAc, mGluR5 in GP and orexin system in STN may generate an incentive memory contrasted between addictive drugs and natural rewards. Such pathways may include clusters of genes that are potential susceptibility genes for transition to addiction. Overall design: Agilent Whole Mouse Genome oligomicroarrays (GEO accession no. GPL2872, Agilent Technologies, Palo Alto, CA) were used. They contain 60-mer DNA probes synthesized in situ in a 44k format. Of 44,290 spots, 2756 are controls. The remaining 41,534 spots represent 33,661 unique transcripts which correspond to 20,202 unique human genes. Five independent (five accumbens nuclei from mice treated with cocaine and having a low score of conditioned place preference compared to five accumbens nuclei from mice treated with saline solution) measurements were carried out for each group of biological conditions using exchanged dye-labeled RNA targets (i.e., Cy3 and Cy5 dyeswapping experiments).

易感个体向成瘾转化的分子机制迄今尚未完全阐明。本研究假设，可基于啮齿类动物大脑中保守的分子机制，鉴定人类成瘾易感基因。本研究采用短期可卡因依赖型条件位置偏爱（conditioned place preference, CPP）模型，对基底神经节（含伏隔核（accumbens nucleus, NAc）、苍白球（globus pallidus, GP）与丘脑底核（subthalamic nucleus, STN））内奖励记忆早期阶段的遗传标记进行鉴定。以全基因组微阵列分析为手段，将CPP作为数量性状，本研究发现上述三个脑区中与突触可塑性相关的基因均存在表达失调现象。研究证实，参与树突棘局部翻译的功能性转录本存在显著富集。经可卡因处理的动物的伏隔核与苍白球中，代谢型谷氨酸受体5（metabotropic glutamate receptor 5, mGluR5）存在转录水平失调。编码参与钙离子通透性调控的N-甲基-D-天冬氨酸（N-methyl-D-aspartate, NMDA）受体亚基的Grin3a基因在伏隔核中存在表达失调。此外，食欲素/下丘脑泌素（Orexin/Hcrt）的转录本水平在丘脑底核中出现下调，而丘脑底核是已知参与区分成瘾性药物与天然奖赏的脑区。本研究同时证实，mGluR5与Grin3a的表达失调足以诱导突触可塑性相关基因的表达改变。综上，上述结果表明，伏隔核中mGluR5与Grin3A通路的协同失调、苍白球中mGluR5的表达失调，以及丘脑底核中食欲素系统的失调，可能共同促成可区分成瘾性药物与天然奖赏的动机性记忆形成。此类通路所包含的基因簇，或可成为成瘾转化过程中的潜在易感基因。
整体实验设计：本研究使用安捷伦全小鼠基因组寡核苷酸微阵列（Agilent Whole Mouse Genome oligomicroarrays，GEO登录号：GPL2872，安捷伦科技公司，加利福尼亚州帕洛阿尔托），该芯片采用44k格式，包含原位合成的60聚体DNA探针。44290个斑点中，2756个为对照斑点，剩余41534个斑点对应33661个独特转录本，涵盖20202个人类独特基因。针对两组生物学条件（分别为5个经可卡因处理且条件位置偏爱评分较低的小鼠伏隔核，与5个经生理盐水处理的小鼠伏隔核），本研究采用交换染料标记的RNA靶标（即Cy3与Cy5染料互换实验）进行了5次独立重复测量。