State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Center for Magnetic Resonance, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China.
Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China.
Int J Mol Sci. 2023 Feb 26;24(5):4579. doi: 10.3390/ijms24054579.
Centrifugal projections in the olfactory system are critical to both olfactory processing and behavior. The olfactory bulb (OB), the first relay station in odor processing, receives a substantial number of centrifugal inputs from the central brain regions. However, the anatomical organization of these centrifugal connections has not been fully elucidated, especially for the excitatory projection neurons of the OB, the mitral/tufted cells (M/TCs). Using rabies virus-mediated retrograde monosynaptic tracing in Thy1-Cre mice, we identified that the three most prominent inputs of the M/TCs came from the anterior olfactory nucleus (AON), the piriform cortex (PC), and the basal forebrain (BF), similar to the granule cells (GCs), the most abundant population of inhibitory interneurons in the OB. However, M/TCs received proportionally less input from the primary olfactory cortical areas, including the AON and PC, but more input from the BF and contralateral brain regions than GCs. Unlike organizationally distinct inputs from the primary olfactory cortical areas to these two types of OB neurons, inputs from the BF were organized similarly. Furthermore, individual BF cholinergic neurons innervated multiple layers of the OB, forming synapses on both M/TCs and GCs. Taken together, our results indicate that the centrifugal projections to different types of OB neurons may provide complementary and coordinated strategies in olfactory processing and behavior.
离心投射在嗅觉系统中对嗅觉处理和行为都至关重要。嗅觉球（OB）是嗅觉处理的第一个中继站，从中枢脑区接收大量的离心输入。然而，这些离心连接的解剖组织尚未完全阐明，特别是对于 OB 的兴奋性投射神经元，即僧帽/丛状细胞（M/TCs）。我们使用 Thy1-Cre 小鼠中的狂犬病毒介导的逆行单突触追踪技术，发现 M/TCs 的三个最主要的输入源来自于前嗅核（AON）、梨状皮层（PC）和基底前脑（BF），与颗粒细胞（GCs）相似，GCs 是 OB 中最丰富的抑制性中间神经元群体。然而，M/TCs 从中枢嗅觉皮质区域（包括 AON 和 PC）接收的输入比例较低，但从 BF 和对侧脑区接收的输入比例较高。与这两种 OB 神经元从初级嗅觉皮质区域传入的组织上不同的输入不同，来自 BF 的输入组织相似。此外，单个 BF 胆碱能神经元支配着 OB 的多个层，在 M/TCs 和 GCs 上形成突触。总的来说，我们的结果表明，不同类型的 OB 神经元的离心投射可能为嗅觉处理和行为提供互补和协调的策略。
