Functional role of NMDA autoreceptors in olfactory mitral cells
Functional role of NMDA autoreceptors in olfactory mitral cells
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DOI：
10.1152/jn.2000.84.1.39
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发表时间：
2000-07-01
影响因子：
2.5
通讯作者：
Strowbridge, BW
中科院分区：
文献类型：
--
作者：
Friedman, D;Strowbridge, BW
嗅球的输出是由突触电位与二尖瓣细胞的固有电导的相互作用决定的。虽然僧帽细胞通常被认为是简单的中继神经元，将嗅觉受体细胞的活动传递到梨状皮质，但有强有力的生理和行为证据表明，嗅球内的局部突触相互作用调节僧帽细胞放电并促进气味辨别。了解嗅球的电路是复杂的，因为这个区域的大多数树突都是突触前和突触后的。反馈抑制通过二尖瓣细胞次级树突和GABA能颗粒细胞之间的相互树-树突触介导。在这里，我们表明，从二尖瓣细胞树突释放谷氨酸也激活本地N-甲基-D-天冬氨酸（NMDA）的自身受体，产生一个内向的尾电流后去极化电压步骤。自身受体介导的自激是钙依赖性的，可以在镁存在下由单个动作电位诱发，并且用一连串尖峰的数量分级。我们发现，树突状抑制也引起了单一的动作电位，但在重复放电迅速饱和。自激也是钾通道阻断后二尖瓣细胞明显延长后放电的基础。后放电和自身受体介导的尾电流坚持TTX，这表明它们是由本地而不是谷氨酸的多突触作用。用2-氨基-5-磷酸戊酸（APV）阻断NMDA自身受体可降低动作电位簇内的放电频率。自激的快速动力学表明NMDA自身受体在延长二尖瓣细胞的阶段性放电期间中的功能作用。
The output of the olfactory bulb is governed by the interaction of synaptic potentials with the intrinsic conductances of mitral cells. While mitral cells often are considered as simple relay neurons, conveying activity in olfactory receptor cells to the piriform cortex, there is strong physiological and behavioral evidence that local synaptic interactions within the olfactory bulb modulate mitral cell discharges and facilitate odorant discrimination. Understanding the circuitry of the olfactory bulb is complicated by the fact that most dendrites in this region are both pre- and postsynaptic. Feedback inhibition is mediated through reciprocal dendrodendritic synapses between the secondary dendrites of mitral cells and GABAergic granule cells. Here we show that glutamate released from mitral cell dendrites also activates local N-methyl-D-aspartate (NMDA) autoreceptors, generating an inward tail current following depolarizing voltage steps. Autoreceptor-mediated self-excitation is calcium dependent, can be evoked by single action potentials in the presence of magnesium, and is graded with the number of spikes in a train. We find that dendrodendritic inhibition also is evoked by single action potentials but saturates rapidly during repetitive discharges. Self-excitation also underlies the prolonged afterdischarges apparent in mitral cells following potassium channel blockade. Both afterdischarges and autoreceptor-mediated tail currents persist in TTX, suggesting that they are produced by local rather than polysynaptic actions of glutamate. Blockade of NMDA autoreceptors with 2-amino-5-phosphonovaleric acid (APV) reduces the firing frequency within action potential cluster. The rapid kinetics of self-excitation suggests a functional role of NMDA autoreceptors in prolonging periods of phasic firing in mitral cells.