Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA.
Department of Neuroscience, Yale University, New Haven, CT, USA; The John B. Pierce Laboratory, New Haven, CT, USA.
Neuroimage. 2020 May 15;212:116664. doi: 10.1016/j.neuroimage.2020.116664. Epub 2020 Feb 20.
Odorants can reach olfactory receptor neurons (ORNs) by two routes: orthonasally, when volatiles enter the nasal cavity during inhalation/sniffing, and retronasally, when food volatiles released in the mouth pass into the nasal cavity during exhalation/eating. Previous work in humans has shown that both delivery routes of the same odorant can evoke distinct perceptions and patterns of neural responses in the brain. Each delivery route is known to influence specific responses across the dorsal region of the glomerular sheet in the olfactory bulb (OB), but spatial distributions across the entire glomerular sheet throughout the whole OB remain largely unexplored. We used functional MRI (fMRI) to measure and compare activations across the entire glomerular sheet in rat OB resulting from both orthonasal and retronasal stimulations of the same odors. We observed reproducible fMRI activation maps of the whole OB during both orthonasal and retronasal stimuli. However, retronasal stimuli required double the orthonasal odor concentration for similar response amplitudes. Regardless, both the magnitude and spatial extent of activity were larger during orthonasal versus retronasal stimuli for the same odor. Orthonasal and retronasal response patterns show overlap as well as some route-specific dominance. Orthonasal maps were dominant in dorsal-medial regions, whereas retronasal maps were dominant in caudal and lateral regions. These different whole OB encodings likely underlie differences in odor perception between these biologically important routes for odorants among mammals. These results establish the relationships between orthonasal and retronasal odor representations in the rat OB.
气味可以通过两条途径到达嗅觉受体神经元 (ORNs)：经鼻，当挥发性物质在吸入/嗅探时进入鼻腔，以及经鼻后，当食物挥发性物质在呼气/进食时从口腔进入鼻腔。先前在人类中的工作表明，同一种气味的两种传递途径都可以在大脑中引起不同的感知和神经反应模式。据了解，每种传递途径都会影响嗅球 (OB) 中背侧区域的特定反应，但整个 OB 中整个嗅球的空间分布在很大程度上仍未得到探索。我们使用功能磁共振成像 (fMRI) 来测量和比较经鼻和经鼻后刺激同一种气味时在大鼠 OB 中整个嗅球的激活情况。我们观察到在经鼻和经鼻后刺激时整个 OB 的可重复 fMRI 激活图。然而，经鼻后刺激需要两倍的经鼻气味浓度才能产生相似的反应幅度。尽管如此，对于相同的气味，经鼻刺激的活动幅度和空间范围都大于经鼻后刺激。经鼻和经鼻后反应模式既存在重叠，也存在一些特定途径的优势。经鼻地图在背侧-内侧区域占主导地位，而经鼻后地图在尾部和外侧区域占主导地位。这些不同的整个 OB 编码可能是哺乳动物中这些对气味很重要的途径之间气味感知差异的基础。这些结果确立了大鼠 OB 中经鼻和经鼻后气味表示之间的关系。
