Hind Limb Sensory Innervation in Rats: Comparison between Sural and Saphenous Nerve Morphometry

Abstract

NERI, L. O.; DE AMORIM, M. M.; CAMPOS, S. A. R.; SANADA, L. S. & FAZAN, V. P. S. Hind limb sensory innervation in rats:Comparison between sural and saphenous nerve morphometry. Int. J. Morphol., 33(2):743-750, 2015. SUMMARY:Although numerous studies investigate sensory recovery of the hind paw of the rat after nerve damage, still no comprehensive overview of its normal innervation is present in the literature. We investigated the morphometry of myelinated fibers in the sural and saphenous nerves and analyzed their size distributions in young rats. Six 30-day-old female Wistar rats were perfused with 2.5% glutaraldehyde and their right and left sural and saphenous nerves were prepared for light microscopy and morphometry. Morphometric data were compared between segments (proximal versus distal) and sides (right versus left) for the same nerves. Also, segments from right or left sides were compared between nerves (sural versus saphenous). Both, the sural and saphenous nerves, exhibited proximal to distal symmetry on both sides as well as left-right symmetry. Histograms of the diameter of the myelinated fibers were unimodal in both nerves, regardless of segments or sides with the peaks of the fibers size occurring between 2.5 and 4.0 µm. The axon distributions reflected the myelinated fiber distributions, with the sural and saphenous nerves peaking between 1.5 and 2.0 µm. The G ratio (the ratio between the axon and fiber diameters) distributions were also unimodal, with peaks at 0.6 for both nerves. This study contributes to the literature with information on the myelinated fibers morphometry from the two sensory nerves responsible for the rat hind limb innervation. This information is valuable for a better understanding of the possible contribution of collateral sprouting from the sural or saphenous nerves on the paw sensory territory recovery observed after one of these nerves is damaged.

Feasibility study of greater occipital nerve blocks by focused ultrasound – an animal study

“…The rat GON contains, on average, 900 myelinated and 3300 unmyelinated afferent axons, and the majority of myelinated axons are also Aδ fibers (mean diameter: 3.5 µm, mean G ratio: 0.47) [23,28]. Although the number and myelination of Aδ fibers are slightly different in the sural nerve and the GON, the percentage of the GON occupied by myelinated fibers (61%) is much higher than that in the sural nerve (33%) [23,27]. Moreover, myelin primarily comprises lipids and can absorb ultrasound very efficiently [29].…”

“…The rat sural nerve generally contains 1100 myelinated and 2800 unmyelinated afferent axons and 1500 unmyelinated sympathetic axons [26]. Most of the myelinated axons are Aδ fibers (diameter range: 2.5-4.0 µm, mean G ratio: 0.52) [27]. The rat GON contains, on average, 900 myelinated and 3300 unmyelinated afferent axons, and the majority of myelinated axons are also Aδ fibers (mean diameter: 3.5 µm, mean G ratio: 0.47) [23,28].…”

Focused ultrasound enhances the anesthetic effects of topical lidocaine in rats

“…Ultrasound gel (Aquasonic, Parker Laboratories, Fairfield, NJ, USA) was applied between PVA hydrogel and transducer surface. The zone encompassing the sciatic nerve in the thigh was chosen over the distal sural and saphenous nerves (which directly innervate the hind paw [27]) due to its proximity to the brain and ease of anatomy-based identification/sonication. Except for the time needed for the application of the topical lidocaine, the transducer remained in position throughout the SSEP measurement.…”