Department of Pharmacology and Therapeutics.
Center for Smell and Taste, University of Florida, Gainesville, FL 32610.
eNeuro. 2019 Feb 7;6(1). doi: 10.1523/ENEURO.0390-18.2019. eCollection 2019 Jan-Feb.
The inter-regional connectivity of sensory structures in the brain allows for the modulation of sensory processing in manners important for perception. In the olfactory system, odor representations in the olfactory bulb (OB) are modulated by feedback centrifugal innervation from several olfactory cortices, including the piriform cortex (PCX) and anterior olfactory nucleus (AON). Previous studies reported that an additional olfactory cortex, the olfactory tubercle (OT), also centrifugally innervates the OB and may even shape the activity of OB output neurons. In an attempt to identify the cell types of this centrifugal innervation, we performed retrograde tracing experiments in mice utilizing three unique strategies, including retrobeads, retrograde adeno-associated virus (AAV) driving a fluorescent reporter, and retrograde AAV driving Cre-expression in the Ai9-floxed transgenic reporter line. Our results replicated the standing literature and uncovered robustly labeled neurons in the ipsilateral PCX, AON, and numerous other structures known to innervate the OB. Surprisingly, consistent throughout all of our approaches, no labeled soma were observed in the OT. These findings indicate that the OT is unique among other olfactory cortices in that it does not innervate the OB, which refines our understanding of the centrifugal modulation of the OB.
大脑中感觉结构的区域间连接允许以对感知重要的方式调节感觉处理。在嗅觉系统中，嗅球（OB）中的气味表示被来自几个嗅觉皮质的反馈离心神经支配所调制，包括梨状皮质（PCX）和前嗅核（AON）。先前的研究报告称，另一个嗅觉皮质，嗅结节（OT）也离心神经支配 OB，甚至可能塑造 OB 输出神经元的活动。为了鉴定这种离心神经支配的细胞类型，我们在小鼠中使用三种独特的策略进行逆行示踪实验，包括逆行微珠、逆行腺相关病毒（AAV）驱动荧光报告基因和逆行 AAV 在 Ai9-floxed 转基因报告系中驱动 Cre 表达。我们的结果复制了已有的文献，并在同侧 PCX、AON 和许多已知支配 OB 的其他结构中发现了强烈标记的神经元。令人惊讶的是，在所有方法中，在 OT 中均未观察到标记的胞体。这些发现表明，OT 在不向 OB 神经支配方面与其他嗅觉皮质不同，这细化了我们对 OB 的离心调制的理解。
