Department of Medical Neurobiology, Faculty of Medicine and IMRIC, The Hebrew University of Jerusalem, 9112102 Jerusalem, Israel.
Department of Medical Neurobiology, Faculty of Medicine and IMRIC, The Hebrew University of Jerusalem, 9112102 Jerusalem, Israel.
Curr Biol. 2023 Nov 20;33(22):4857-4868.e6. doi: 10.1016/j.cub.2023.09.061. Epub 2023 Oct 18.
The olfactory bulb (OB) is a critical component of mammalian olfactory neuroanatomy. Beyond being the first and sole relay station for olfactory information to the rest of the brain, it also contains elaborate stereotypical circuitry that is considered essential for olfaction. Indeed, substantial lesions of the OB in rodents lead to anosmia. Here, we examined the circuitry that underlies olfaction in a mouse model with severe developmental degeneration of the OB. These mice could perform odor-guided tasks and even responded normally to innate olfactory cues. Despite the near total loss of the OB, piriform cortices in these mice responded to odors, and its neural activity sufficed to decode odor identity. We found that sensory neurons express the full repertoire of olfactory receptors, and their axons project primarily to the rudiments of the OB but also, ectopically, to olfactory cortical regions. Within the OB, the number of principal neurons was greatly reduced, and the morphology of their dendrites was abnormal, extending over large regions within the OB. Glomerular organization was totally lost in the severe cases of OB degeneration and altered in the more conserved OBs. This study shows that olfactory functionality can be preserved despite reduced and aberrant circuitry that is missing many of the elements believed to be essential for olfaction, and it may explain reported retention of olfaction in humans with degenerated OBs.
嗅球（OB）是哺乳动物嗅觉神经解剖结构的关键组成部分。它不仅是嗅觉信息传递到大脑其他部位的第一个也是唯一的中继站，还包含着精细的刻板的回路，这些回路被认为对嗅觉至关重要。事实上，啮齿动物嗅球的大量损伤会导致嗅觉丧失。在这里，我们研究了一种在 OB 严重发育退化的小鼠模型中嗅觉所依赖的回路。这些老鼠能够完成气味导向的任务，甚至对先天的嗅觉线索有正常的反应。尽管 OB 几乎完全丧失，但这些老鼠的梨状皮层对气味有反应，其神经活动足以解码气味的身份。我们发现感觉神经元表达了完整的嗅觉受体谱，它们的轴突主要投射到 OB 的原始部分，但也异位投射到嗅觉皮质区域。在 OB 内，主神经元的数量大大减少，其树突的形态异常，在 OB 内的大片区域内延伸。在 OB 退化的严重情况下，肾小球组织完全丧失，而在更保守的 OB 中则发生改变。这项研究表明，尽管嗅觉功能回路减少且异常，缺失了许多被认为对嗅觉至关重要的元素，但仍能保持嗅觉功能，这可能解释了报道的 OB 退化的人类嗅觉保留现象。
