Burton Shawn D, Urban Nathaniel N
Department of Biological Sciences, Center for the Neural Basis of Cognition, Carnegie Mellon University, Pittsburgh, PA, 15213, USA.
Department of Biological Sciences, Center for the Neural Basis of Cognition, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
J Physiol. 2014 May 15;592(10):2097-118. doi: 10.1113/jphysiol.2013.269886. Epub 2014 Mar 10.
Mitral and tufted cells, the two classes of principal neurons in the mammalian main olfactory bulb, exhibit morphological differences but remain widely viewed as functionally equivalent. Results from several recent studies, however, suggest that these two cell classes may encode complementary olfactory information in their distinct patterns of afferent-evoked activity. To understand how these differences in activity arise, we have performed the first systematic comparison of synaptic and intrinsic properties between mitral and tufted cells. Consistent with previous studies, we found that tufted cells fire with higher probability and rates and shorter latencies than mitral cells in response to physiological afferent stimulation. This stronger response of tufted cells could be partially attributed to synaptic differences, as tufted cells received stronger afferent-evoked excitation than mitral cells. However, differences in intrinsic excitability also contributed to the differences between mitral and tufted cell activity. Compared to mitral cells, tufted cells exhibited twofold greater excitability and peak instantaneous firing rates. These differences in excitability probably arise from differential expression of voltage-gated potassium currents, as tufted cells exhibited faster action potential repolarization and afterhyperpolarizations than mitral cells. Surprisingly, mitral and tufted cells also showed firing mode differences. While both cell classes exhibited regular firing and irregular stuttering of action potential clusters, tufted cells demonstrated a greater propensity to stutter than mitral cells. Collectively, stronger afferent-evoked excitation, greater intrinsic excitability and more irregular firing in tufted cells can combine to drive distinct responses of mitral and tufted cells to afferent-evoked input.
二尖瓣细胞和簇状细胞是哺乳动物主嗅球中的两类主要神经元，它们在形态上存在差异，但人们普遍认为它们在功能上是等效的。然而，最近几项研究的结果表明，这两类细胞可能通过其不同的传入诱发活动模式编码互补的嗅觉信息。为了了解这些活动差异是如何产生的，我们首次对二尖瓣细胞和簇状细胞的突触特性和内在特性进行了系统比较。与先前的研究一致，我们发现，在受到生理传入刺激时，簇状细胞比二尖瓣细胞具有更高的放电概率、放电频率和更短的潜伏期。簇状细胞的这种更强反应可能部分归因于突触差异，因为簇状细胞比二尖瓣细胞接收到更强的传入诱发兴奋。然而，内在兴奋性的差异也导致了二尖瓣细胞和簇状细胞活动的差异。与二尖瓣细胞相比，簇状细胞的兴奋性和峰值瞬时放电频率高出两倍。这些兴奋性差异可能源于电压门控钾电流的差异表达，因为簇状细胞比二尖瓣细胞表现出更快的动作电位复极化和超极化后电位。令人惊讶的是，二尖瓣细胞和簇状细胞还表现出放电模式的差异。虽然这两类细胞都表现出规则放电和动作电位簇的不规则口吃现象，但簇状细胞比二尖瓣细胞表现出更大的口吃倾向。总的来说，簇状细胞中更强的传入诱发兴奋、更高的内在兴奋性和更不规则的放电可以共同驱动二尖瓣细胞和簇状细胞对传入诱发输入的不同反应。
