Department of Biological Sciences, University of Windsor, Windsor, Ontario, Canada.
PLoS One. 2013 Jul 29;8(7):e69525. doi: 10.1371/journal.pone.0069525. Print 2013.
Although there is abundant evidence for segregated processing in the olfactory system across vertebrate taxa, the spatial relationship between the second order projection neurons (PNs) of olfactory subsystems connecting sensory input to higher brain structures is less clear. In the sea lamprey, there is tight coupling between olfaction and locomotion via PNs extending to the posterior tuberculum from the medial region of the olfactory bulb. This medial region receives peripheral input predominantly from the accessory olfactory organ. However, the axons from olfactory sensory neurons residing in the main olfactory epithelium extend to non-medial regions of the olfactory bulb, and the non-medial bulbar PNs extend their axons to the lateral pallium. It is not known if the receptive fields of the PNs in the two output pathways overlap; nor has the morphology of these PNs been investigated. In this study, retrograde labelling was utilized to investigate the PNs belonging to medial and non-medial projections. The dendrites and somata of the medial PNs were confined to medial glomerular neuropil, and dendrites of non-medial PNs did not enter this territory. The cell bodies and dendrites of the non-medial PNs were predominantly located below the glomeruli (frequently deeper in the olfactory bulb). While PNs in both locations contained single or multiple primary dendrites, the somal size was greater for medial than for non-medial PNs. When considered with the evidence-to-date, this study shows different neuroanatomical organization for medial olfactory bulb PNs extending to locomotor control centers and non-medial PNs extending to the lateral pallium in this vertebrate.
尽管在脊椎动物分类中，嗅觉系统的分隔处理有大量证据，但连接感觉输入和大脑更高结构的嗅觉子系统的二级投射神经元 (PN) 的空间关系则不太清楚。在海七鳃鳗中，PN 从嗅球的内侧区域延伸到后结节，将嗅觉和运动紧密地联系在一起。这个内侧区域主要接收来自副嗅器官的外周输入。然而，主嗅上皮中的嗅觉感觉神经元的轴突延伸到嗅球的非内侧区域，而非内侧嗅球的 PN 将其轴突延伸到外侧脑皮层。目前还不知道这两个输出通路的 PN 的感受野是否重叠；也没有研究这些 PN 的形态。在这项研究中，逆行标记被用来研究属于内侧和非内侧投射的 PN。内侧 PN 的树突和体仅局限于内侧肾小球神经丛，而非内侧 PN 的树突则不会进入这个区域。非内侧 PN 的胞体和树突主要位于肾小球下方（嗅球中较深的位置）。虽然这两个位置的 PN 都包含单个或多个主树突，但内侧 PN 的体大小比非内侧 PN 大。考虑到迄今为止的证据，这项研究显示在这种脊椎动物中，延伸到运动控制中心的内侧嗅球 PN 和延伸到外侧脑皮层的非内侧 PN 具有不同的神经解剖组织。
