Sympathetic renal nerve ultrastructure: Comparative analysis between adult mice and rats.

Abstract

The renal nerves exhibit efferent and afferent sympathetic fibers, crucial for regulation of renal function and input of sensory information from the kidneys to the central nervous system. The intrinsic renal innervation was widely described in rats. However, few reports deal with renal extrinsic innervation in rats and mice, and comparative studies between species have not been reported. We aimed to compare the ultrastructural and morphometric characteristics of the extrinsic renal nerves of adult rats and mice. A total of 15 left renal nerves, 5 from adult male C57BL/6 mice and 10 from adult male Wistar rats were used. The renal nerves were dissected and prepared for light and electron microscopy morphometry. As expected, the difference of the fascicular area and diameter was significant, being the nerves of mice smaller than rats. The myelinated fibers of rats were larger (diameter and area) compared to mice, but the number and density of these fibers were not different between species. No morphological differences were observed (number, area, diameter, and size distribution) on the unmyelinated fibers between species. Our results indicate that fascicle and myelinated fibers sizes accompany the animal size. The unmyelinated fibers, mainly responsible for the sympathetic functions of the renal nerve, do not differ between species in size and number, suggesting the absence of functional differences.