Hind limb sensory innervation in rats: comparison between sural and saphenous nerve morphometry / Inervación sensorial de los miembros posteriores en ratas: comparación morfométrica entre los nervios sural y safeno

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.

Aunque numerosos estudios investigan la recuperación sensorial del miembro pélvico o posterior de la rata después del daño en los nervios, aún no existe en la literatura una visión global de su inervación normal. Investigamos la morfometría de fibras mielínicas de los nervios sural y safeno y analizamos sus distribuciones de tamaño en ratas jóvenes. Seis ratas Wistar de 30 días de edad fueron perfundidas con 2,5% de glutaraldehído, se prepararon los nervios sural y safeno derecho e izquierdo para microscopía de luz y morfometría. Datos morfométricos fueron comparados entre los segmentos (proximal vs distal) y laterales (derecho vs izquierdo) para los mismos nervios. Además, los segmentos de los lados derecho e izquierdo se compararon entre los nervios (sural vs safeno). Ambos nervios sural y safeno exhibieron una simetría proximal a distal en ambos lados, así como una simetría izquierda-derecha. Histogramas del diámetro de las fibras mielinizadas eran unimodales en ambos nervios, independientemente de los segmentos o de los lados, siendo los peaks del tamaño de las fibras entre 2,5 y 4,0 micras. Las distribuciones de los axones reflejan las distribuciones de fibras mielinizadas, de los nervios sural y safeno que alcanzaban entre 1,5 and 2,0 µm. La relación de G (relación entre los diámetros de los axones y de fibra) eran también unimodales, alcanzando 0,6 para ambos nervios. Este estudio contribuye a la literatura con los datos de la morfometría de fibras mielinizadas de ambos nervios sensoriales responsables de la inervación de la extremidad pélvica de la rata. Esta información es valiosa para una mejor comprensión de los nervios sural y safeno en la recuperación sensorial del miembro después de que uno de estos nervios ha sido dañado.

Transmission electron microscopy studies of the vestibulocochlear nerve in chronic diabetic rats / Estudios de microscopía electrónica de transmisión del nervio vestibulococlear en ratas diabéticas crónicas

It is widely described in the literature that diabetic patients present hearing impairment. Despite the histological alterations of the internal ear structures in these patients as well as in experimental models of diabetes, to the best of our knowledge, an histological evaluation of the vestibulocochlear nerve have not been performed. In the present study, ultrastructural alterations are described and compared between a spinal nerves and a cranial nerve in rats with chronic induced diabetes. Male Wistar rats (n = 12), fed with standard diet from the animal care facility at 42 days of age were used. Induced diabetic animals (n=6) were fasted for 12 hours prior to being injected intraperitoneally with streptozotocin (STZ - 60mg/kg) in a single dose. Control animals (n=6) received (0.01 mol/l citrate buffer, pH 4.5) vehicle alone. Ten weeks after STZ injection the animals were perfused intracardially with Karnovsky solution. Right and left vestibulocochlear nerves were dissected and histologically processed for epoxy resin embedding. Samples were imaged with the transmission electron microscope. Large myelinated fibers with morphological signs of axonal atrophy in the vestibulocochlear nerves were readily observed. These results suggest that chronic STZ-induced diabetes in rats caused alterations in the myelinated fibers and Schwann cells, compatible to the classic diabetes signs and symptoms. Morphological alterations of the vestibulocochlear nerve in diabetes is described for the first time and contributes information for a better understanding of why there are changes in hearing observed in diabetic patients.

Se ha descrito ampliamente en la literatura que los pacientes diabéticos presentan discapacidad auditiva. En estos pacientes, a pesar de las alteraciones histológicas de las estructuras del oído interno, así como en modelos experimentales de diabetes, que mejoran nuestro conocimiento, la evaluación histológica del nervio vestibulococlear no ha sido realizada. Se describen y comparan las alteraciones ultraestructurales entre un nervio espinal y uno craneal en ratas con diabetes crónica inducida. Fueron utilizadas 12 ratas Wistar machos, de 42 días de edad, alimentadas con dieta estándar. Los animales diabéticos inducidos (n = 6) se mantuvieron en ayuno por 12 horas antes de ser inyectados por vía intraperitoneal con estreptozotocina (STZ - 60mg/kg) en una sola dosis. Los animales control (n = 6) sólo recibieron inyección de 0.01 mol/l buffer, citrato pH 4,5. Diez semanas después de la inyección de STZ, los animales fueron perfundidos intracardiacamente con solución de Karnovsky. Los nervios vestibulococlear derecho e izquierdo fueron disecados y procesados histológicamente para ser incluidos en resina epoxy. Las muestras fueron estudiadas con microscopio electrónico de transmisión. Fueron observadas fácilmente, grandes fibras mielinizadas con signos morfológicos de atrofia axonal en los nervios vestibulococlear. Estos resultados sugieren que la diabetes crónica inducida por STZ en ratas causó alteraciones en las fibras mielínicas y células del neurilema, compatible, con los signos y síntomas clásicos de la diabetes. Alteraciones morfológicas del nervio vestibulococlear en la diabetes son descritas por primera vez, lo que aporta información para una mejor comprensión de por qué hay cambios en la audición en los pacientes diabéticos.

Sex differences of short-term enriched environment on myelinated nerve fibers in the hippocampal formation of middle-aged rats / 第三军医大学学报

Objective To investigate the sex differences of the myelinated nerve fibers in the hippocampal formation of mid-aged standard and enriched rats. Methods Twenty 14-month Sprague-Dawley (SD) rats, 10 female and 10 male rats, were randomly divided into enriched group and standard group. Enriched rats were reared in enriched environment and standard rats were reared in standard environment for 4 months. Then, the total volume of the hippocampal formation and the myelinated nerve fibers in the hippocampus were quantitatively estimated by transmission electron microscopy and stereological methods. Results The total volume and mean diameter of the myelinated nerve fibers in the hippocampal formation of standard female rats were significantly bigger than those of standard male rats (P0.05). The mean diameter of the myelinated nerve fibers in the hippocampal formation of enriched female rats was significantly smaller than that of enriched male rats (P0.05). Conclusion The sex differences of the myelinated nerve fibers in the hippocampal formation of mid-aged standard and enriched rats are significantly different, which indicates the response to the enriched environment in the mid-aged male and female rats is different.