Li C S, Smith D V
Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore 21201-1509, USA.
J Neurophysiol. 1997 Mar;77(3):1514-25. doi: 10.1152/jn.1997.77.3.1514.
The effects of excitatory amino acid (EAA) receptor antagonists in blocking the synaptic transmission between gustatory fibers of the chorda tympani (CT) nerve and taste-responsive neurons within the nucleus of the solitary tract (NST) were examined electrophysiologically in urethan-anesthetized hamsters. Single neurons in the NST were recorded extracellularly and drugs were microinjected into the vicinity of the cell with the use of a multibarrel pipette assembly. The activity of each cell was recorded in response to lingual stimulation with 0.032 M NaCl, 0.032 M sucrose, 0.0032 M citric acid, 0.032 M quinine hydrochloride, and/or 25 microA anodal current pulses. Once a cell was identified as a taste-responsive neuron, one or more EAA receptor antagonists were administered by microinjection. Approximately 27 nl of 50 mM kynurenic acid (KYN), a broad-spectrum EAA receptor antagonist; 0.5 or 2.0 mM DL-2-amino-5-phosphonovalerate (APV), an N-methyl-D-aspartate (NMDA) receptor antagonist; 0.05 or 0.5 mM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonist; or phosphate-buffered physiological saline was applied to the neuron. Responses to chemical stimulation of the anterior tongue were obtained before and after drug administration and again after recovery; responses to anodal current stimulation (0.1 Hz) were obtained continually throughout the drug administration protocol. Microinjection of KYN completely and reversibly abolished responses elicited by both anodal current and chemical stimulation of the anterior tongue. The excitatory responses of cells in the NST to chemical and electrical stimulation of the anterior tongue were also completely and reversibly blocked by CNQX, implicating the involvement of an AMPA/kainate receptor. Microinjection of APV was generally less effective and partially reduced the responses of some taste-responsive NST cells to chemical stimulation of the anterior tongue. There were no effects following microinjection of a 27-nl bolus of phosphate-buffered saline. None of these EAA receptor antagonists had a differential effect on responses to different taste stimuli. The responses to all tastants were completely blocked by both KYN and CNQX; there was no apparent relationship between the response to any particular tastant and the limited effects of APV. These data implicate glutamate as an excitatory neurotransmitter between CT gustatory fibers and taste-responsive NST cells and suggest that it acts primarily on AMPA/kainate receptors, with some contribution from NMDA receptors. This conclusion is strengthened by other data obtained from in vitro slice preparations, which show that responses of cells in the rostral NST to solitary tract stimulation are blocked by both NMDA and AMPA/kainate receptor antagonists.
在经乌拉坦麻醉的仓鼠中，采用电生理学方法研究了兴奋性氨基酸（EAA）受体拮抗剂阻断鼓索神经（CT）味觉纤维与孤束核（NST）内味觉反应神经元之间突触传递的作用。细胞外记录NST中的单个神经元，并使用多管移液管组件将药物微量注射到细胞附近。记录每个细胞对0.032M氯化钠、0.032M蔗糖、0.0032M柠檬酸、0.032M盐酸奎宁和/或25微安阳极电流脉冲的舌部刺激的反应。一旦确定一个细胞为味觉反应神经元，就通过微量注射给予一种或多种EAA受体拮抗剂。大约27纳升50毫摩尔的犬尿喹啉酸（KYN），一种广谱EAA受体拮抗剂；0.5或2.0毫摩尔的DL-2-氨基-5-磷酸戊酸（APV），一种N-甲基-D-天冬氨酸（NMDA）受体拮抗剂；0.05或0.5毫摩尔的6-氰基-7-硝基喹喔啉-2,3-二酮（CNQX），一种α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）/海人藻酸受体拮抗剂；或磷酸盐缓冲生理盐水应用于神经元。在给药前和给药后以及恢复后再次获得对舌前部化学刺激的反应；在整个给药过程中持续获得对阳极电流刺激（0.1赫兹）的反应。微量注射KYN完全且可逆地消除了阳极电流和舌前部化学刺激所引发的反应。CNQX也完全且可逆地阻断了NST中细胞对舌前部化学和电刺激的兴奋性反应，这表明AMPA/海人藻酸受体参与其中。微量注射APV通常效果较差，部分降低了一些味觉反应性NST细胞对舌前部化学刺激的反应。微量注射27纳升磷酸盐缓冲生理盐水后没有效果。这些EAA受体拮抗剂对不同味觉刺激的反应均无差异作用。KYN和CNQX均完全阻断了对所有味觉剂的反应；对任何特定味觉剂的反应与APV的有限作用之间没有明显关系。这些数据表明谷氨酸是CT味觉纤维和味觉反应性NST细胞之间的兴奋性神经递质，并表明它主要作用于AMPA/海人藻酸受体，NMDA受体也有一定作用。从体外脑片制备获得的其他数据强化了这一结论，这些数据表明延髓头端NST中细胞对孤束刺激的反应被NMDA和AMPA/海人藻酸受体拮抗剂所阻断。
