Huang Jie, Spier Avron D, Pickel Virginia M
Division of Neurobiology, Department of Neurology and Neuroscience, Weill Medical College of Cornell University, 411 East 69th Street, New York, NY 10021, USA.
Brain Res. 2004 Dec 3;1028(2):156-69. doi: 10.1016/j.brainres.2004.09.009.
The 5-hydroxytryptamine 3 (5HT3) receptor is a serotonin-gated ion channel implicated in reflex regulation of autonomic functions within the nucleus of the solitary tract (NTS). To determine the relevant sites for 5-HT3 receptor mediated transmission in this region, we used electron microscopic immunocytochemistry to examine the subcellular distribution of the 5HT3 receptor subunit A (5HT3A) in relation to the serotonin transporter (SERT) in the intermediate medial NTS (mNTS) of rat brain. The 5HT3A immunolabeling was detected in many axonal as well as somatodendritic and glial profiles. The axonal profiles included small axons and axon terminals in which the 5HT3A immunoreactivity was localized to membranes of synaptic vesicles and extrasynaptic plasma membranes. In dendrites and glia, the 5HT3A immunoreactivity was located on the plasma membranes or in association with membranous cytoplasmic organelles. The dendritic plasmalemmal 5HT3A labeling was prominent within and near excitatory-type synapses from terminals including those that resemble vagal afferents. The 5HT3A-labeled glial processes apposed 5HT3A-immunoreactive axonal and dendritic profiles, some of which also contained SERT. Terminals containing 5-HT3A and/or SERT were among those providing synaptic input to 5HT3A-labeled dendrites. Thus, 5HT3A has a subcellular distribution consistent with the involvement of 5-HT3 receptors in modulation of both presynaptic release and postsynaptic responses of mNTS neurons, some of which are serotonergic. The results further suggest that the neuronal as well as glial 5HT3 receptors can be activated by release of serotonin from presynaptic terminals or by diffusion facilitated by SERT distribution at a distant from the synapse.
5-羟色胺3（5HT3）受体是一种5-羟色胺门控离子通道，与孤束核（NTS）内自主功能的反射调节有关。为了确定该区域中5-HT3受体介导传递的相关位点，我们采用电子显微镜免疫细胞化学方法，研究大鼠脑中间内侧NTS（mNTS）中5HT3受体亚基A（5HT3A）与5-羟色胺转运体（SERT）相关的亚细胞分布。在许多轴突以及躯体树突和神经胶质细胞形态中均检测到5HT3A免疫标记。轴突形态包括小轴突和轴突终末，其中5HT3A免疫反应性定位于突触小泡膜和突触外质膜。在树突和神经胶质细胞中，5HT3A免疫反应性位于质膜上或与膜性细胞质细胞器相关。树突质膜上的5HT3A标记在包括类似迷走神经传入终末的兴奋性突触内及附近很突出。5HT3A标记的神经胶质细胞突起与5HT3A免疫反应性轴突和树突形态相邻，其中一些还含有SERT。含有5-HT3A和/或SERT的终末是向5HT3A标记的树突提供突触输入的终末之一。因此，5HT3A的亚细胞分布与5-HT3受体参与调节mNTS神经元的突触前释放和突触后反应一致，其中一些神经元是5-羟色胺能的。结果进一步表明，神经元和神经胶质细胞的5HT3受体可被突触前终末释放的5-羟色胺激活，或被SERT在远离突触处的分布促进扩散而激活。
