Unmyelinated nerve fibre analysis of the human lesser splanchnic nerve

The aim of the present study is to analyse unmyelinated nerve fibres of the human lesser splanchnic nerve in relation to the ageing process. With the help of an image-analyser, we examined 30 human lesser splanchnic nerves. The analysis was conducted with the use of a new staining method that makes it possible to discriminate various structures of the nervous tissue. Our report provides for the first time information on the ageing process of the human lesser splanchnic nerve fibres. The results indicate that a decrease in transverse area and perimeter of unmyelinated axons is one of the important changes occurring in the human lesser splanchnic nerve during the ageing process.     

Morphometric analysis of myelinated axons in the human vagus nerve

Myelinated axons of the human vagus nerve were analyzed morphometrically on 30 cadavers (16 males and 14 females). The result showed that the transverse area and perimeter of myelinated axons decreased with age, although the total number of their axons did not change.     

Unmyelinated nerve fiber analysis of the human oculomotor nerve

Unmyelinated nerve fibers of the oculomotor nerve have occasionally been observed in experimental animals with the use of electron microscopes, but no details concerning normal oculomotor nerves in humans have been published. We measured and analyzed unmyelinated nerve fibers in the human oculomotor nerve with an image analyzer and a computer, using a new staining method, the Luxol fast blue-periodic acid-Schiff-hematoxylin (LPH) discriminative staining method which is the only one suitable for morphometric research on nervous tissues. We studied the numbers and transverse areas of unmyelinated fibers of the oculomotor nerve in 20 cadavers. The number of unmyelinated axons did not change with age, but the mean transverse area decreased with age. These fibers were distributed diffusely in the transverse area of the oculomotor nerve, not localized in any part of the nerve. These findings may be important for the analysis of clinical and neurological signs in relation to aging and ophthalmologic functions.     

Morphometric analysis of the human trigeminal nerve.

We evaluated the components of nerve fibers of the motor and sensory roots of the trigeminal nerve by morphometric analysis. Trigeminal nerves were obtained from 5 cadavers (males, aged 67-95) were stained by Masson-Goldner-Goto method and examined under the microscope using a morphometric image-analyzer. The area and perimeter of axons were larger in the motor root than in the sensory root. The size distribution of axons was wider in the motor root than in the sensory root and the distribution pattern was unimodal type. These findings suggested that nerve fibers of the human trigeminal nerve gave similar findings to those of other peripheral nerves, regarding axonal size distribution and relative size of motor and sensory nerve axons.     

Morphometric nerve fiber analysis and aging process of the human inferior alveolar nerve.

We studied morphometric nerve fiber analysis and the aging process of the inferior alveolar nerve (IAN). Human IANs were resected at the mandibular foramen. The preparation of sections involved fixation, washing, dehydration, embedding, sectioning and staining as described in our previous reports. We estimated the total number of myelinated axons in the IAN being average 26,200, the transverse area of those being average 37.1 microns 2, the average perimeter of those being 23.0 microns, the average circularity ratio of those being 0.85, respectively. According to these results, the IAN did not demonstrate notable age-relation change in any measured item. The IAN differed from not only our previous data on the human motor peripheral nerves but also those on the human sensory peripheral nerves. With regard to the aging process, the IAN indicated morphological features compared with other peripheral nerves.     

Morphometric nerve fiber analysis of the human inferior alveolar nerve: lateral asymmetry

We studied morphometric nerve fiber analysis and the lateral asymmetry of the inferior alveolar nerve (IAN). Human IANs were resected at the mandibular foramen. The preparation of sections involved fixation, washing, dehydration, embedding, sectioning and staining as described in our previous reports. We estimated the average total number of myelinated axons in the right IAN to be 22,808, with an average transverse area of 37.6 microm2, an average perimeter of 23.0 microm, and average circularity ratio of 0.85, with the same measurements in the left IAN being 24,289, 33.9 microm2, 21.6 microm, and 0.86, respectively. Morphological differences between the right and left side were analyzed by applying parametric tests (unpaired t-test) to all measured items. According to these results, the IAN did not demonstrate notable lateral asymmetry in any measured item. We considered that these results were caused by using subjects with the same dentulous condition in both sides.     

Morphometric analysis of the human tibial nerve and the ageing process.

We analysed numbers and sizes of the human tibial nerve branch innervating the soleus muscle. The material was taken from 13 cadavers aged from 67 to 98 years. A linear regression analysis disclosed a significant age-related decrease in the mean number per unit area and the mean transverse area of axons. Such decreases with age may indicate atrophy and loss of motoneurons. Our results could help in understanding the correlation between morphology and function during the ageing process.     

Functional development of the visual system in normal and protein-deprived rats. VIII. Post-natal development of optic nerve axons

Protein deprivation results in a persistent impairment of transmission of impulses from the specific cortical projection within the visual cortex. In order to evaluate changes in subcortical structures during pre-weaning development, a study was made on number, calibre and myelination of optic nerve axons in control (C) and protein-deprived (PD) rats 5, 12, 20 and 30 days of age. Protein deprivation was induced by giving rat mothers a diet containing 7% protein by weight (control diet 14%, during gestation and lactation. The cross-sectional area of the nerve was measured on a digitizer. Between 3000 and 4000 axons collected from 7-13 field areas sampled by a random, systematic procedure from a cross-shaped area of the nerve were counted and measured. Between 5 and 12 days after birth, the number of axons was reduced by 50% in C rats. The total number of optic nerve axons was not significantly different in PD compared to C rats, indicating that protein deprivation does not affect the formation or naturally occurring nerve cell death of retinal ganglion cells. At all ages examined there were significant reductions in the number of axons larger than 0.52 micron as well as the number of myelinated axons. The rates of growth/maturation and myelination of axons in C rats and PD rats suggested that the reductions seen in PD rats up to 20 days of age may represent a developmental delay of approximately 4 days. At 30 days, a delay or a distortion of development may present. The retarded development of optic nerve axons is discussed in relation to delays, distortions and deficits during visual system maturation in protein-deprived rats.     

Functional development of the visual system in normal and protein-deprived rats. VIM. Post-natal development of optic nerve axons

Protein deprivation results in a persistent impairment of transmission of impulses from the specific cortical projection within the visual cortex. In order to evaluate changes in subcortical structures during pre-weaning development, a study was made on number, calibre and myelination of optic nerve axons in control (C) and protein-deprived (PD) rats 5, 12, 20 and 30 days of age. Protein deprivation was induced by giving rat mothers a diet containing 7% protein by weight (control diet 14%, during gestation and lactation. The cross-sectional area of the nerve was measured on a digitizer. Between 3000 and 4000 axons collected from 7–13 field areas sampled by a random, systematic procedure from a cross-shaped area of the nerve were counted and measured. Between 5 and 12 days after birth, the number of axons was reduced by 50% in C rats. The total number of optic nerve axons was not significantly different in PD compared to C rats, indicating that protein deprivation does not affect the formation or naturally occurring nerve cell death of retinal ganglion cells. At all ages examined there were significant reductions in the number of axons larger than 0.52μm as well as the number of myelinated axons. The rates of growth/maturation and myelination of axons in C rats and PD rats suggested that the reductions seen in PD rats up to 20 days of age may represent a developmental delay of approximately 4 days. At 30 days, a delay or a distortion of development may be present. The retarded development of optic nerve axons is discussed in relation to delays, distortions and deficits during visual system maturation in protein-deprived rats.     

Morphometric difference in the human maxillary nerve fibers between dentulous and edentulous jaw subjects

This study was conducted to quantify the change in the number and size of myelinated nerve fibers of the maxillary nerve with tooth loss in humans. We carried out a morphometric analysis to compare the number and size of myelinated nerve fibers in the human maxillary nerve between four dentulous and four edentulous jaw cases. Our results indicated that the number of axons decreased by approximately 13,000 with tooth loss. The average size of axons remained unchanged, but there was a change in the fiber size distribution, namely the loss of a large number of small-sized axons was accompanied by the total disappearance of small number of large-sized axons.     

Morphometric analysis of the human femoral nerve and its ageing process

We analysed the sizes of nerve fibres in the human femoral nerve which innervates the quadriceps femoris muscles. The material was taken from 14 cadavers aged from 61 to 97 years. A linear regression analysis disclosed a significant age-related decrease of the mean transverse area of axons. Such decrease with age may be an indication of motoneuron atrophy. Our results could help in the understanding of the correlation between morphology and function during the ageing process.     

Different multiple regeneration capacities of motor and sensory axons in peripheral nerve

Abstract After peripheral nerve injury, axons often project sprouts from the node of Ranvier proximal to the damage site. It is well known that one parent axon can sprout and maintain several regenerating axons. If enough endoneurial tubes in the distal stump are present for the regenerating axons to grow along, then the number of mature myelinated nerve fibers in the distal stump will be greater than the number in the proximal stump. "Multiple regeneration" is used to describe this phenomenon in the peripheral nerve. According to previous studies, a prominent nerve containing many axons can be repaired by the multiple regenerating axons sprouting from another nerve that contains fewer axons. Most peripheral nerves contain a mixture of myelinated motor and sensory axons as well as unmyelinated sensory and autonomic axons. In this study, a multiple regeneration animal model was developed by bridging the proximal common peroneal nerve with the distal common peroneal nerve and the tibial nerve. Differences in the multiple regeneration ratio of motor and sensory nerves were evaluated using histomorphometry one month after ablating the dorsal root ganglion (DRGs) and ventral roots, respectively. The results suggest that the motor nerves have a significantly larger multiple regeneration ratio than the sensory nerves at two different time points.     

Aging process of myelinated nerve fibers in the human Lissauer tract

We calculated numbers and axonal areas of myelinated nerve fibers in the Lissauer tract of the human lumbar spinal cord (L1) from the viewpoint of the aging process. We examined 20 human spinal cords from 13 males and 7 females, age ranging from 41 to 88 years old. We found that, although the number of nerve fibers showed no significant change in relation to the age of the subject, the axonal area of myelinated nerve fiber in the Lissauer tract did decrease with age.     

Peripheral nerve regeneration using acellular nerve grafts

Long gap peripheral nerve injuries usually require a graft to facilitate axonal regeneration into the distal nerve stump. The use of autografts is often limited because of graft availability and donor-site morbidity. We investigated whether acellular nerve allografts would provide an appropriate channel for the promotion and induction of sciatic nerve regeneration in rats. Axons sprouted from the proximal portion and reached the distal portion in the 1 cm-long grafts by 1 month. The number of axons in the regenerated nerves was similar to that of normal nerves at 1 month. Loading the grafts with betaNGF and VEGF increased the number and mean diameter of axons and neovascularization in the regenerated nerves at 1 month. The motor conduction velocity increased over time and reached 63 +/- 10% of that of normal nerves at 6 months. The nerve injuries treated with the acellular grafts had a significant improvement in motor, nociception, and proprioception function compared to untreated nerves. The results from this study suggest that acellular nerve allografts may be a useful biomaterial for functional peripheral nerve regeneration.     

Unmyelinated nerve fibers of the human mandibular nerve

The aim of this research is to find and to evaluate morphometorically the unmyelinated nerve fibers in the human mandibular nerve using a light microscope. Our report demonstrates for the first time the presence of the unmyelinated nerve fibers of the human mandibular nerve stained by a special method. Our results also indicate that there is a morphometric change with aging in the unmyelinated axons of the nerve.     

Axon diameter distributions across the monkey's optic nerve

The distribution of axons according to diameter has been examined in the optic nerve of old world monkeys. Axon diameters were measured from electron micrographs, and histograms were constructed at regular intervals across a section through the optic nerve to reveal the local axon diameter distribution. The total axon diameter distribution was also estimated. Fine-calibre optic axons (less than 2.0 micron in diameter) are found at all locations across the optic nerve. They are most frequent centrotemporally, where very few coarse optic axons can be found, but also make up the majority at the optic nerve's periphery. Coarse optic axons (greater than 2.0 microns in diameter) are increasingly common at progressively peripheral positions in the nerve. Around the nerve's circumference, these coarse optic axons are least numerous temporally, and most common dorsonasally. The axon diameter distribution peaks around 1.25 microns at most locations across the optic nerve, but there are more, slightly larger (1.5-2.0 microns), optic axons dorsally than ventrally. The estimated total axon diameter distribution is unimodal, peaking at 1.0-1.25 microns, with an extended tail towards larger diameters. This centroperipheral gradient of increasing axon diameters across the optic nerve is not substantial enough to account for the partial segregation of axons by size in the monkey's optic tract: there, coarse optic axons form a conspicuously greater proportion of the local axon diameter distribution along the tract's superficial (sub-pial) border, and fine optic axons are the only axons present near the tract's deep border. Hence, the fibre distribution in the optic tract cannot be formed by a simple combination of the fibre distributions of the two respective half-nerves, as described in the classic neuro-ophthalmologic literature. Rather, the present results, in conjunction with previous results from the optic tract, demonstrate that there must be a reorganization of axons by size in or near the optic chiasm.     

Association fibers of cortical representation zones 1 and 2 of the splanchnic nerve in the cat

Summary The presence of bilateral anatomical relation between the 1 and 2 cortical zones of the splanchnic nerve was established by the method of terminal degeneration. There is a difference in the reciprocal interchange of fibers between the cortical zones of the splanchnic nerve: a much greater number of fibers enters the 2 zone from the 1. A considerable part of the fibers belongs to horizontal systems, whereas the fibers coming from the 2 zone to the 1 zone belong mainly to radial fibers. Thus, the interrelations between the connecting systems of the 1 and 2 splanchnic nerve zones are such that the number of fibers coming from one zone into another one are different.(Presented by Academician V. N. Chernigovskii) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 55, No. 3, pp. 114–117, March, 1963.     

Functional segregation within the pelvic nerve of male rats: a meso- and microscopic analysis

The pelvic splanchnic nerves are essential for pelvic organ function and have been proposed as targets for neuromodulation. We have focused on the rodent homologue of these nerves, the pelvic nerves. Our goal was to define within the pelvic nerve the projections of organ-specific sensory axons labelled by microinjection of neural tracer (cholera toxin, subunit B) into the bladder, urethra or rectum. We also examined the location of peptidergic sensory axons within the pelvic nerves to determine whether they aggregated separately from sacral preganglionic and paravertebral sympathetic postganglionic axons travelling in the same nerve. To address these aims, microscopy was performed on the major pelvic ganglion (MPG) with attached pelvic nerves, microdissected from young adult male Sprague–Dawley rats (6–8 weeks old) and processed as whole mounts for fluorescence immunohistochemistry. The pelvic nerves were typically composed of five discrete fascicles. Each fascicle contained peptidergic sensory, cholinergic preganglionic and noradrenergic postganglionic axons. Sensory axons innervating the lower urinary tract (LUT) consistently projected in specific fascicles within the pelvic nerves, whereas sensory axons innervating the rectum projected in a complementary group of fascicles. These discrete aggregations of organ-specific sensory projections could be followed along the full length of the pelvic nerves. From the junction of the pelvic nerve with the MPG, sensory axons immunoreactive for calcitonin gene-related peptide (CGRP) showed several distinct patterns of projection: some projected directly to the cavernous nerve, others projected directly across the surface of the MPG to the accessory nerves and a third class entered the MPG, encircling specific cholinergic neurons projecting to the LUT. A subpopulation of preganglionic inputs to noradrenergic MPG neurons also showed CGRP immunoreactivity. Together, these studies reveal new molecular and structural features of the pelvic nerves and suggest functional targets of sensory nerves in the MPG. These anatomical data will facilitate the design of experimental bioengineering strategies to specifically modulate each axon class.     

Quantitative study of the apical nerve fibers of adult and juvenile rat molars

The rat molar has become an important model for studies of interactions between nerves and the pulp-dentin complex, yet there is only limited quantitative information on the number and size distribution of axons entering the roots of this tooth. This study was undertaken to provide such a detailed characterization of the apical innervation of the rat molar. An additional objective was to compare the apical nerve composition of young, recently erupted rat molars with that of mature teeth in order to determine whether there is ongoing maturation of the innervation after the teeth have attained functional occlusion. A complete census was made of the nerve fibers entering the roots of both mature and recently erupted juvenile mandibular first molars in Sprague-Dawley rats. Each of the four roots of the first molars was processed for electron microscopy of thin sections near the apex. The majority of intradental nerve fibers entered the molar via the two larger (mesial and distal) roots. Within the apical root pulp, most, but not all, axons occurred within well-defined fascicles associated with blood vessels. Molars from adult animals (age 4 months) had a mean total of 232 (S.D. = 49, N = 7 teeth) myelinated fibers and 806 (S.D. = 143) unmyelinated axons entering the four roots. Fibers exceeding the Aδ size range (circumference ≥ 19 μm) accounted for only 4% of the myelinated axons at the apex. Molars from juvenile animals (age 4 weeks) had fewer myelinated fibers (mean 176, S.D. 18, N = 8), but more unmyelinated axons (mean 1,174, S.D. 160) than adults. The mean ratio of unmyelinated axons to myelinated axons was 6.6:1 for juveniles compared to 3.5:1 for adults. Juvenile teeth contained no myelinated fibers that exceeded 19 μm in circumference. These results indicate that the innervation of the rat molar resembles that of teeth of non-rodent mammals in that (1) innervation density is high, (2) there is a high ratio of unmyelinated axons, and (3) most of the myelinated fibers are of thin caliber. Furthermore, it appears that after the molar erupts, maturation of the nerve fiber composition continues with processes that include both a marked decrease in the number of unmyelinated axons and an increase in the number and size heterogeneity of myelinated fibers. © 1994 Wiley-Liss, Inc.     

Functional development of the visual system in normal and protein deprived rats. II. Morphometric and biochemical studies on adult optic nerve

The optic nerve of normal (C) and protein deprived (PD) adult rats was examined by morphometry and biochemistry. The mean cross-sectional area of the optic nerve was reduced by 15% and the number of axons per unit area increased by 17% in the PD rats. Calibre spectrum analysis of axons revealed a reduction in median diameter from 0.49 micron in controls to 0.45 micron in PD rats. The number of axons with a diameter larger than 1 micron was reduced by 35% in PD rats. These reductions were probably due to a general reduction in size, since the calculated total number of axons in the optic nerve was almost identical in C and PD rats (126 X 10(3) and 124 X 10(3), respectively). The increased packing density of axons in the nerve was not only due to thinner axons. The biochemical measurements showed a marked reduction in myelin basic protein in the optic nerves of PD rats, without an alteration in the composition of the total protein. This confirms the persistent hypomyelination which has been reported previously in other malnutrition models. The possible relations between the structural and biochemical changes affecting optic nerve fibres and physiological findings on cortical visual evoked response and on optic nerve in vitro in PD rats are discussed.