Department of Otorhinolaryngology, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan.
Brain Res. 2010 Mar 10;1319:60-9. doi: 10.1016/j.brainres.2010.01.016. Epub 2010 Jan 14.
TRPM8 and TRPA1 are cold-activated transient receptor potential (TRP) cation channels. TRPM8 is activated by moderate cooling, while TRPA1 is activated by extreme, noxious cold temperatures. These cold receptors are expressed in different subpopulations of primary afferent neurons. TRPA1 is co-expressed in a subpopulation of somatosensory neurons expressing TRPV1, which is activated by heat. However, the distribution and co-expression of these channels in the nodose-petrosal ganglion complex, which contains the jugular (JG), petrosal (PG), and nodose ganglia (NG) (mainly involved in putative somatic, chemo- and somato-sensation, and somato and visceral sensation, respectively), remain unknown. Here, we conducted in situ hybridization analysis of the rat nodose-petrosal ganglion complex using specific riboprobes for TRPM8, TRPA1, and TRPV1 to compare the features of the cranial sensory ganglia. Hybridization signals for TRPA1 were diffusely observed throughout these ganglia, whereas TRPM8 transcripts were seen in the JG and PG but not in the NG. We retrogradely labeled cranial nerve X with Fast Blue (fluorescent dye) and found TRPM8 transcripts in the jugular-vagal ganglion but not the NG neurons. TRPA1 transcripts were not detected in TRPM8-expressing neurons but were present in the subpopulation of TRPV1-expressing visceral sensory neurons. Taken together, these findings support that in the vagal system the expression of cold-activated TRP channels differs between nodose- and jugular-ganglion neurons suggesting different mechanisms of cold-transduction and that the TRPA1 distribution is consistent with its proposed function as a cold-sensing receptor in the visceral system.
TRPM8 和 TRPA1 是冷激活瞬时受体电位 (TRP) 阳离子通道。TRPM8 被中等冷却激活，而 TRPA1 被极冷、有害的冷温度激活。这些冷受体表达在初级传入神经元的不同亚群中。TRPA1 与表达 TRPV1 的感觉神经元亚群共同表达，TRPV1 被热激活。然而，这些通道在包含颈静脉 (JG)、岩骨 (PG) 和结状神经节 (NG) 的结状 - 岩骨神经节复合体中的分布和共表达仍然未知（主要涉及假定的躯体感觉、化学感觉和躯体感觉，以及躯体和内脏感觉）。在这里，我们使用针对 TRPM8、TRPA1 和 TRPV1 的特异性核糖探针对大鼠结状 - 岩骨神经节复合体进行了原位杂交分析，以比较颅神经节的特征。TRPA1 的杂交信号在这些神经节中弥漫观察到，而 TRPM8 转录本仅在 JG 和 PG 中可见，而在 NG 中不可见。我们用 Fast Blue（荧光染料）逆行标记颅神经 X，发现 TRPM8 转录本存在于颈静脉 - 迷走神经节中，但不存在于 NG 神经元中。TRPA1 转录本未在表达 TRPM8 的神经元中检测到，但存在于表达 TRPV1 的内脏感觉神经元的亚群中。综上所述，这些发现支持在迷走神经系统中，结状神经节和颈静脉神经节神经元中冷激活 TRP 通道的表达不同，提示冷传导的不同机制，并且 TRPA1 的分布与其在内脏系统中作为冷感觉受体的拟议功能一致。
