内侧前额叶皮层-基底外侧杏仁核投射神经元分层亚群的解剖学研究

Anatomical structure of laminar specific subtypes of medial prefrontal cortex-basolateral amygdala projection neurons

目的·从脑区特异性和皮层分层特异性水平上精细解析小鼠内侧前额叶皮层(medial prefrontal cortex,mPFC)-基底外侧杏仁核(basolateral amygdala,BLA)投射神经元亚群的解剖学结构。方法·给C57BL/6小鼠BLA注射逆向示踪腺相关病毒,21 d后,心脏灌流并取脑。使用冰冻切片机制作mPFC的连续冠状切片,利用荧光显微镜采集脑片图像,选取具有mPFC分区代表性的脑片,统计分析病毒标记的胞体在mPFC内不同亚区的分布情况。采用转基因小鼠(Tbr2-CreER::LSL-Flp小鼠和Rbp4-Cre小鼠)与重组酶(Flp和Cre)依赖的腺相关病毒,特异性地荧光标记小鼠mPFC第2层与第5层投射神经元的胞体及其在BLA内的投射轴突;病毒注射28 d后,同样灌流、取脑,收集BLA的连续冠状切片,免疫荧光染色标记后在荧光显微镜下采集脑片图像;通过测定BLA内不同区域投射轴突的荧光强度,比较mPFC第2层与第5层神经元在BLA投射轴突的空间分布情况。结果·荧光显微镜观察及定量分析结果表明:BLA投射神经元的胞体在包含前扣带回皮层和前边缘皮层的背内侧前额叶皮层(dorsal medial prefrontal cortex,dmPFC)中分布较多,且主要分布在第2层和第5层;而在包含内侧眶额叶皮层和下边缘皮层的腹内侧前额叶皮层(ventral medial prefrontal cortex,vmPFC)中分布较少,且没有观察到明显的分层现象。随后,在研究dmPFC的2个分层投射神经元的轴突分布时发现:在BLA内,第2层投射神经元的轴突分布较为均匀,而第5层投射神经元的轴突则更多分布在背侧区。结论·mPFC-BLA投射神经元的胞体分布具有脑区分布特异性和层分布特异性,dmPFC中不同层神经元的轴突投射在BLA也具有相应的脑区特异性。

Objective·To dissect the fine anatomical structure of medial prefrontal cortex(mPFC)-basolateral amygdala(BLA) projection neurons based on regional and laminar specificity in the cortex in mice. Methods·The retrograde tracer of adenoassociated viral(AAV) vectors were injected into BLA of C57BL/6 mice. Twenty-one days after the injection, the mice were sacrificed and the brains were harvested. The coronal sections containing mPFC were prepared by using a cryostat microtome. The images were taken by fluorescence microscopy. Then the representative brain slices containing mPFC were selected and the distribution of virus-labeled cell bodies in different subregions of mPFC was analyzed. By using transgenic mouse lines(Tbr2-CreER:: LSL-Flp mice and Rbp4-Cre mice) with Flp-or Cre-dependent AAV, layer 2(L2) and layer 5(L5) projection neurons in mPFC and their axons in BLA were marked, respectively. Twenty-eight days after the injection, the mice were sacrificed and the brains were also harvested. Coronal sections of the BLA were collected. The brain slices were imaged by fluorescence microscopy after immunofluorescence staining. By measuring the fluorescence intensity of projecting axons in different regions within BLA, the spatial distributions of the axons in BLA of mPFC L2 and L5 projection neurons were compared. Results·Through fluorescence microscopy and quantitative analysis, it was found that the cell bodies of BLA projection neurons were mainly located at L2 and L5in the dorsal mPFC(dmPFC) which contains anterior cingulate cortex and prelimbic cortex. However, the distribution of BLA projection neurons in the ventral mPFC(vmPFC) including medial orbital cortex and infralimbic cortex did not exhibit the similar distribution. When studying the axonal distribution of dmPFC projection neurons in two layers, it was found that the axons of L2projection neurons dispersed in the BLA, while the axons of L5 projection neurons were mainly located in the dorsal region of BLA. Conclusion·The cell body distribution of mPFC-BLA projection neurons shows regional specificity and laminar specificity.The axon projections initiated from different layers of dmPFC also exhibit regional specificity in BLA.