We previously reported the immunoreactivity for the vesicular glutamate transporter 2 (VGLUT2) in afferent nerve terminals attached to chemoreceptor type I cells of the carotid body (CB), suggesting that glutamate is released from afferent terminals to stimulate these cells. In the present study, we examined the immunoreactivity for the glutamate-binding subunits of N-methyl-D-aspartate (NMDA) receptors, GluN2A and GluN2B in the rat CB, and the immunohistochemical relationships between these subunits and VGLUT2. Immunoreactivities for GluN2A and GluN2B were predominant in a subpopulation of tyrosine hydroxylase-immunoreactive type I cells rather than those of dopamine beta-hydroxylase-immunoreactive cells. Punctate VGLUT2-immunoreactive products were attached to GluN2A- and GluN2B-immunoreactive type I cells. Bassoon-immunoreactive products were localized between VGLUT2-immunoreactive puncta and type I cells immunoreactive for GluN2A and GluN2B. These results suggest that afferent nerve terminals release glutamate by exocytosis to modulate chemosensory activity of a subpopulation of type I cells via GluN2A- and GluN2B subunits-containing NMDA receptors.

我们之前报道了连接到颈动脉体 (CB) 的 I 型化学感受器细胞的传入神经末梢中囊泡谷氨酸转运蛋白 2 (VGLUT2) 的免疫反应性，表明谷氨酸从传入末梢释放以刺激这些细胞。在本研究中，我们检查了N-甲基-D的谷氨酸结合亚基的免疫反应性-天冬氨酸 (NMDA) 受体、大鼠 CB 中的 GluN2A 和 GluN2B，以及这些亚基与 VGLUT2 之间的免疫组织化学关系。GluN2A 和 GluN2B 的免疫反应性在酪氨酸羟化酶免疫反应性 I 型细胞亚群中占主导地位，而不是多巴胺 β-羟化酶免疫反应性细胞亚群。点状 VGLUT2 免疫反应产物附着在 GluN2A 和 GluN2B 免疫反应性 I 型细胞上。巴松管免疫反应产物位于 VGLUT2 免疫反应性斑点和对 GluN2A 和 GluN2B 具有免疫反应性的 I 型细胞之间。这些结果表明，传入神经末梢通过胞吐作用释放谷氨酸盐，以通过含有 GluN2A 和 GluN2B 亚基的 NMDA 受体调节 I 型细胞亚群的化学感应活性。