A common feature of the primary processing structures of sensory systems is the presence of parallel output “channels” that convey different information about a stimulus. In the mammalian olfactory bulb, this is reflected in the mitral cells (MCs) and tufted cells (TCs) that have differing sensitivities to odors, with TCs being more sensitive than MCs. In this study, we examined potential mechanisms underlying the different responses of MCs vs. TCs. For TCs, we focused on superficial TCs (sTCs), which are a population of output TCs that reside in the superficial-most portion of the external plexiform layer, along with external tufted cells (eTCs), which are glutamatergic interneurons in the glomerular layer. Using whole-cell patch-clamp recordings in mouse bulb slices, we first measured excitatory currents in MCs, sTCs, and eTCs following olfactory sensory neuron (OSN) stimulation, separating the responses into a fast, monosynaptic component reflecting direct inputs from OSNs and a prolonged component partially reflecting eTC-mediated feedforward excitation. Responses were measured to a wide range of OSN stimulation intensities, simulating the different levels of OSN activity that would be expected to be produced by varying odor concentrations in vivo. Over a range of stimulation intensities, we found that the monosynaptic current varied significantly between the cell types, in the order of eTC > sTC > MC. The prolonged component was smaller in sTCs vs. both MCs and eTCs. sTCs also had much higher whole-cell input resistances than MCs, reflecting their smaller size and greater membrane resistivity. To evaluate how these different electrophysiological aspects contributed to spiking of the output MCs and sTCs, we used computational modeling. By exchanging the different cell properties in our modeled MCs and sTCs, we could evaluate each property's contribution to spiking differences between these cell types. This analysis suggested that the higher sensitivity of spiking in sTCs vs. MCs reflected both their larger monosynaptic OSN signal as well as their higher input resistance, while their smaller prolonged currents had a modest opposing effect. Taken together, our results indicate that both synaptic and intrinsic cellular features contribute to the production of parallel output channels in the olfactory bulb.

感觉系统主要处理结构的一个共同特征是存在传递有关刺激的不同信息的并行输出“通道”。在哺乳动物嗅球中，这反映在对气味具有不同敏感性的二尖瓣细胞 (MC) 和簇状细胞 (TC) 上，其中 TC 比 MC 更敏感。在这项研究中，我们研究了 MC 与 TC 不同反应的潜在机制。对于 TC，我们重点关注浅表 TC (sTC)，它们是驻留在外部丛状层最表层部分的输出 TC 群体，以及外部簇状细胞 (eTC)，它们是肾小球层中的谷氨酸能中间神经元。使用小鼠灯泡切片中的全细胞膜片钳记录，我们首先测量了 MC、sTC、嗅觉感觉神经元 (OSN) 刺激后的 eTC，将反应分为反映 OSN 直接输入的快速单突触成分和部分反映 eTC 介导的前馈兴奋的延长成分。测量了对各种 OSN 刺激强度的反应，模拟了不同气味浓度预期产生的不同水平的 OSN 活性体内。在一系列刺激强度下，我们发现不同细胞类型的单突触电流差异显着，顺序为 eTC > sTC > MC。与 MC 和 eTC 相比，sTC 中的延长成分较小。sTC 的全细胞输入电阻也比 MC 高得多，这反映出它们的尺寸更小，膜电阻率更大。为了评估这些不同的电生理学方面如何影响输出 MC 和 sTC 的尖峰，我们使用了计算模型。通过交换我们建模的 MC 和 sTC 中的不同细胞特性，我们可以评估每种特性对这些细胞类型之间尖峰差异的贡献。该分析表明，与 MC 相比，sTC 的尖峰敏感性更高，反映出它们更大的单突触 OSN 信号以及更高的输入电阻，而它们较小的持续电流则产生了适度的相反效果。综上所述，我们的结果表明，突触和内在细胞特征都有助于嗅球中并行输出通道的产生。