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.

Previous studies form our laboratory [1,2] in spontaneously hypertensive rats (SHR) have demonstrated morphological alterations on the aortic depressor nerve (ADN), known to contain mainly barorreceptor fibers. Nevertheless, those studies used male and female rats indistinctly. We are investigating if there are morphological differences related to gender in the ADN of adult rats. Male and female SHR aged 20‐week were anesthetized for arterial pressure (AP) and heart rate (HR) recordings, together with the ADN spontaneous activity. After the recordings, the left ADN were prepared for light microscopy and morphometry. Comparisons were made between proximal and distal segments in the same gender and between genders. Males are significantly heavier than females but no differences in AP and HR between genders were found. There was a tendency towards larger fascicle values on males compared to females. Interestingly, this tendency was inverted on the myelinated fibers and respective axons sizes. Nevertheless, no significant differences were observed between genders on the morphometric parameters. We conclude that adult males and females can be used indistinctly for morphometric studies of the ADN if physiological parameters are similar between genders.

Aortic depressor nerve (ADN) is an afferent nerve that contains myelinated (fast conducting) and unmyelinated (slow conduction) fibers that send information from aortic mechanoreceptors to central nervous system [1]. Previous studies form our laboratory [2,3] in spontaneously hypertensive rats (SHR) have demonstrated morphological alterations on the ADN in SHR, using male and female animals indistinctively. In this study we investigated the ADN fiber distribution comparing male and female adult (20 weeks old) SHR. After the (AP) and heart rate (HR) recordings, together with the ADN spontaneous activity, the left ADN were prepared for light microscopy and morphometry. Myelinated fiber distributions were compared between proximal and distal segments in the same gender and between genders. Myelinated axon and G ratio distributions were also investigated. Myelinated fiber diameter range from 1 to 5 µm, with peak (~40% of fibers) at 2 µm while myelinated axon size range from 0.5 to 4 µm, with peak (~50% of axons) at 1.5 µm. No differences were observed between segments or genders. This indicates that gender does not influence on the ADN myelinated fiber size, allowing the use of male and females for morphological studies. [1] Krieger and Marseillan, Am J Physiol, 1963:205; [2] Fazan et. al, J Auton Nerv Syst 77, 1999:133; [3] Fazan et. al, Am J Physiol Heart Circ Physiol 280,2001:H1560. Grant Funding Source: FAPESP, CAPES, CNPq and FAEPA