Mediolateral and rostrocaudal topographic organization of the sympathetic preganglionic cell pool in the spinal cord of Xenopus laevis

Abstract

The sympathetic preganglionic cell pool in Xenopus laevis can be divided into four parts, i.e., the intercalated nucleus (IC) and the intermediolateral nucleus (IML) located respectively at the medial and the lateral borders of the lateral field, the lateral funiculus, and the ventral field within the thoracolumbar spinal segments. We compared the location of the preganglionic cells labeled following tracer application to the paravertebral sympathetic chain with those labeled following application to the celiac ganglion (CG), the adrenal gland (AG), and the splanchnic nerves (SNs) and found that their relative contribution differs depending on the sites. In tracer application to the paravertebral chain ganglia and the sympathetic trunk, 31.4-41.9% and 43.9-58.4% of labeled cells were detected respectively in the IC and in the IML, whereas application to the CG, AG, and on all the SNs, revealed that more than 84% of labeled cells were found in the IML and in the lateral funiculus with less than 8.6% in the IC. The contribution of the ventral field cells was less than 7.5% in all experiments. This type of topographic cytoarchitecture is a character shared with the mammalian preganglionic cell pool, but what distinguishes it from that of mammals is its systematic form throughout the entire longitudinal extent of the pool. In Xenopus, differences of mean soma areas and dendritic projections of labeled cells also suggest that the cell pools are distinguished not only by their location and axonal projections, but also by the morphology of their cells.