Characterization of a cell bridge variant connecting the nodose and superior cervical ganglia in the mouse: Prevalence, anatomical features, and practical implications

While autonomic ganglia have been extensively studied in rats instead of mice, there is renewed interest in the anatomy of the mouse autonomic nervous system. This study examined the prevalence and anatomical features of a cell bridge linking two autonomic ganglia of the neck, namely, the nodose ganglion (NG) and the superior cervical ganglion (SCG) in a cohort of C57BL/6J mice. We identified a cell bridge between the NG and the cranial pole of the SCG. This cell bridge was tubular shaped with an average length and width of 700 and 240 μm, respectively. The cell bridge was frequently unilateral and significantly more prevalent in the ganglionic masses from males (38%) than females (21%). On each of its extremities, it contained a mixed of vagal afferents and postganglionic sympathetic neurons. The two populations of neurons abruptly replaced each other in the middle of the cell bridge. We examined the mRNA expression for selected autonomic markers in samples of the NG with or without cell bridge. Our results indicated that the cell bridge was enriched in both markers of postganglionic sympathetic and vagal afferents neurons. Lastly, using FluoroGold microinjection into the NG, we found that the existence of a cell bridge may occasionally lead to the inadvertent contamination of the SCG. In summary, this study describes the anatomy of a cell bridge variant consisting of the fusion of the mouse NG and SCG. The practical implications of our observations are discussed with respect to studies of the mouse vagal afferents, an area of research of increasing popularity.