Size Of Myelinated Fibers Research Articles

Effect of protein calorie malnutrition on peripheral nerves. A clinical, electrophysiological and histopathological study.

Forty-three children (aged 7 to 62 months) with protein calorie malnutrition (PCM) were studied; 13 had mild to moderate PCM and 30 severe PCM. A reduction of motor nerve conduction velocity and abnormalities of sensory conduction were present in both groups. The abnormality of motor nerve conduction was directly related to the severity of PCM and the presence of hypotonia and/or hyporeflexia. Sural nerve biopsies from both groups were studied for myelinated fibre density, fibre size spectrum, relationship of internodal length with diameter and qualitative light microscopic changes. The biopsies from children with mild to moderate PCM were characterized by a normal developmental change in myelinated fibres with an increasing proportion of medium and large size fibres, a transition from a unimodal to a bimodal distribution and an appropriate relationship of internodal length to fibre diameter. Evidence of mild segmental demyelination was observed in only one patient of this group. In contrast, in the biopsies from children with severe PCM, the normal developmental pattern for myelinated fibre size distribution was impaired with a persistence of small myelinated fibres, and there was a failure of internodal segments on large fibres to elongate with increase in age and significant segmental demyelination in about 50 per cent of cases. Retarded myelination and segmental demyelination probably form the morphological basis for impaired peripheral nerve function in PCM. Short internodes on large diameter fibres may also contribute to this effect.

Postnatal development of conduction velocity and fibre size in the rat tibial nerve

The maximum conduction velocity (CV) and fibre diameters (D) were determined in the tibial nerve of developing rats. In 1-day-old rats CV of the fastest motor and sensory fibres (assessed separately) was 1.4 m/sec on the average and increased to 35 m/sec by postnatal day 30. The maximum conduction rate in adult rats ranged from 60 to 84 m/sec. Diameters of at least 100 nerve fibres in each age group were measured in electronmicrographs. The calibre of myelinating fibres in 1-day-old rats was 0.5–1.5 μm. By day 90 after birth the range of myelinated fibre size extended to 1.5–12.5 μm. The factor relating conduction rate and total fibre diameter of the largest fibres (i.e. the value of CVD) was found to vary with age, increasing from 1.1 to 6.2 between postnatal days 1 and 90. These results indicate that functional and morphological properties of peripheral nerve fibres in the rat undergo considerable changes during postnatal ontogeny until they reach adult values.

Peripheral nerve abnormalities in the diabetic mutant mouse.

Observations were made on the genetically diabetic C57BL/Ks (db/db) mouse. Morphometric observations were performed on the tibial nerve at 6, 9, and 15 mo and compared with those from nondiabetic (m/m) controls. Myelinated fiber size was less in the diabetic animals at all stages and affected cross-sectional axon area and myelin thickness equally. Unmyelinated axons were unaffected. The index of circularity of myelinated axons did not differ between diabetic and control animals. No definite absolute reduction in fiber size occurred and degenerative changes, which were slight, were equally frequent in the diabetic and control nerves. Axonal glycogenosomes, polyglucosan particles, and Schwann cell/axon networks, and Schwann cell Reich granules increased with age in both groups, but only glycogenosomes were consistently more numerous in the diabetic animals. Counts of membrane associated particles in both P and E faces revealed that these were reduced in number in the diabetic animals in myelin and in axolemma of unmyelinated axons, but not in the axolemma of myelinated fibers. Growth in tibial length was also reduced in the diabetic animals and this suggested that the reduced fiber diameter probably represented a maturational deficit. The absence of a selective reduction in axonal size did not favor a primary axonopathy as the cause.

Effects of sciatic nerve resection on L7 spinal roots and dorsal root ganglia in adult cats

The size, distribution, and number of nerve fibers and neuronal perikarya in the L7 spinal roots and ganglia of adult cats were examined 35, 90, and 190 days after ipsilateral sciatic nerve resection. With increasing survival time the size spectra of myelinated ventral root nerve fibers showed a progressive flattening of the alpha peak. In the dorsal roots the myelinated fiber size distribution exhibited a marked shift toward smaller sizes. The reduction in the proportion of large myelinated axons was particularly evident in the dorsal roots. Less clearcut changes were found in the size distribution of spinal ganglion neuronal perikarya. No significant loss of axons could be detected in ventral or dorsal roots. There was, however, a marked reduction in the number of dorsal root ganglion neurons. This discrepancy suggested the possibility that an initial loss of dorsal root axons was concealed by recurrent sprouting of axons from the proximal nerve stump. However, neuroma excision 90 days after nerve resection did not lead to any reduction in dorsal root axon numbers. Thus, any ingrowth of new axons to the dorsal root should occur from levels proximal to the neuroma. In comparison with previous findings in kittens, peripheral nerve resection in adult cats had significantly smaller effects on sizes and numbers of spinal root nerve fibers as well as of dorsal root ganglion neurons. Therefore, the potential for restitution of the peripheral innervation by axon regeneration appeared to be basically greater in mature than in immature animals.

Changes in shape and size of cat spinal root myelinated nerve fibers during fixation and Vestopal-W embedding for electron microscopy

The influence of glutaraldehyde fixation, osmication, acetone dehydration, and Vestopal-W embedding on shape and dimensions of cat myelinated lumbar spinal root nerve fibers was investigated using light and electron microscopy. Glutaraldehyde fixation gave no clear changes in nerve fiber shape or dimensions. The subsequent preparative steps introduced a decrease in the whole fiber “diameter” of about 10% irrespective of the original fiber “diameter”. Myelin sheath thickness decreased by about 30–35%. With this background it was calculated that axon “diameter” should change with the g value of the fiber; viz., Y = (X − Z)/g + Z, where X, Y, and Z are terms expressing the change (%) in values for fiber “diameter”, axon “diameter”, and myelin sheath thickness, respectively. It was noted that the axon “diameter” of fibers with g values of 0.4, 0.5, 0.6, and 0.7, changed by +20, +15, +5 and 0%, respectively. Experimental data confirmed these calculations. The most striking preparatory change at the nodes of Ranvier was widening of the node gaps.

In vivo effect of methylcobalamin on the peripheral nerve structure in streptozotocin diabetic rats.

To study in vivo effect of methylcobalamin (CH3-B12) on the peripheral nerve structures, rats with experimental diabetes induced by streptozotocin were administered with daily intramuscular injection of CH3-B12 (500 microgram/kg) for 16 weeks. By isolated nerve fiber studies, CH3-B12-treated diabetic rats showed less incidence of paranodal demyelination as an early sign of segmental demyelination than non-treated diabetic rats. From morphometrical analysis on sural nerves, the reduction in the density of myelinated nerve fibers, nerve fiber size and axon size of myelinated fibers was definitely protected in treated diabetic rats. The results suggested that continuous treatment with CH3-B12 had an ameliorative effect on the peripheral nerve lesions in experimental diabetic neuropathy.

Imaging system for nerve and fiber tract morphometry: components, approaches, performance, and results.

This report describes the imaging system that was developed to recognize, count, size, and evaluate shapes of transverse myelinated fiber (MF) profiles in nerves and fiber tracts automatically and by operator interaction. Automatic analysis, without operator interaction, will either miss a variable percentage of small MFs (using thresholds that discriminate against all other tissue profiles) or include most MFs but spuriously detect other tissue profiles (using more sensitive thresholds). Systems such as this must therefore be operator-interactive. The system that was developed will, in a favorable histologic section, automatically detect and border myelin in more than 85% of MFs without inclusion of other tissue elements. The remainder of the MFs are then identified by the operator with the digitizer pen, and the myelin is automatically bordered or, in rare cases, drawn in. Very reliable, reproducible, and rapid measurements of MF number, size, and shape can be obtained with this system. From evaluation of the size and shape of MFs in semithin sections in the light microscope as compared with the same fibers in adjacent thin sections in the electron microscope, measurements by this system can be expressed as if they were obtained on thin sections. Evaluations can be analyzed statistically, with results printed out, displayed on a video screen, and graphed. Such a system will be useful in evaluating and following morphologic changes in number, size, and shape of MFs in development, aging, regeneration, neurotoxicity, and various diseases.

Reduced perikaryal volume of lower motor and primary sensory neurons in early experimental diabetes.

The volume of nerve cell bodies of the anterior horn of the fifth lumbar segment and of the fifth lumbar dorsal root ganglion were measured by stereological methods in rats with 4-wk duration of streptozotocin diabetes and in age-matched controls. The perikaryal volume of motor and sensory neurons was reduced by 18% in diabetic rats and a shift between the number of A- and B-cells was observed in the dorsal root ganglion. The findings are in accordance with our earlier observation of reduced axonal size of myelinated fibers in the common peroneal nerve. Furthermore, the data lead us to suppose that the nervous system abnormalities in early diabetes are not exclusively restricted to the peripheral nerves.

Histological studies of experimental interfascicular graft repairs

Biopsies of sutured and grafted primate peripheral nerves were examined by light and electron microscopy after the final set of electrical measurements had been recorded. Inspection of all proximal stumps showed the expected regenerative activity which was not affected by the nature of the nerve repair. Transverse sections through the epineurial, interfascicular, and graft suture lines showed a similar pattern in all animals and at this site nerves sutured by epineurial technique could only be distinguished from those sutured by fascicular technique by loci of the non-absorbable suture. Fascicular repairs, whether done fascicle-to-fascicle or with interposition of grafts, had a more lengthy neuroma than did the epineurial repairs. Maintenance of fascicular architecture through the course of the grafts was variable. Fascicular structure was frequently absent in the central graft segments and in segments close to the second suture site. The method of repair used more proximally could not be distinguished by evaluation of distal stump segments. Measurements of myelinated fiber size made of distal stump axons revealed no statistical difference between the methods of repair.

Nerve fibers of the eighth nerve and their distribution to sensory nerves of inner ear in the bullfrog

The number of both myelinated and unmyelinated nerve fibers has been determined for the eighth nerve and each of its sensory branches in the bullfrog. No significant differences were found in the size distribution of the myelinated nerve fibers among the three ampullary nerves or between the saccular and lagenar nerves. Comparison of these two functional groups also showed no significant differences in the myelinated nerve fiber size distribution between the angular acceleration and otolithic receptors, collectively the equilibrium receptors. The wide variability, that was found not only among the animals but also between the right and left sides, most likely resulted in the absence of differences. Highly significant differences were noted when the myelinated nerve fiber diameter distributions to the acoustic organs were compared to those of the equilibrium organs. The most notable difference was the absence of any myelinated nerve fibers whose diameters were greater than 8 micrometer.

QUANTITATIVE HISTOLOGY OF NERVE IN PROTEIN‐CALORIE MALNUTRITION AND WELL‐NOURISHED CHILDREN*

Dastur D.K., Dewan A., Manghani D.K. & Udani P.M. (1977) Neuropathology Applied Neurobiology 3, 405–422Quantitative histology of nerve in protein‐calorie malnutrition and well‐nourished childrenQuantitative histological data is presented on the sural nerve from four well‐nourished control children between the ages of 5 months and 10 years. The average myelinated nerve fibre density was 14 460/mm2 with a range of 13 020/mm2 to 15 700/mm2, and bore no relation to chronological age, both the oldest and the youngest, children showing high counts. An age‐related increase in size of myelinated fibres was seen in the histograms to become bimodal at age 1 year and then remained essentially unchanged until 10 years. One well‐nourished 9‐month‐old infant born 2 months preterm showed features suggesting retardation in myelination and nerve fibre growth, medium‐sized nerve fibres (> 5μm) having not yet developed, while the fibre density was greater (17 420/mm2). Quantitative histological data on the sural nerve is also presented in 8 of 14 children with protein‐calorie malnutrition (PCM), varying in age from 1.5 to 9 years, either with protein deficiency (kwashiorkor) predominating or with calorie malnutrition predominating. The majority had acquired some secondary infection as well. Twelve of the fourteen children suffered from severe malnutrition or marasmus (grade III or IV according to Harvard standards). The myelinated nerve fibre densities varied from 7940 to 22 820/mmz with a mean of 16 199/mm2, not significantly different from the mean densities in the four comparable control children. The histograms, however, showed a persistence of small diameter fibres (<5 μm) in children with PCM especially those above 2 years of age, suggesting an arrest of, or delay in, myelination. This arrest, and the frequent paucity of thick axons in silver stained preparations, suggested a lack of development of medium and large myelinated nerve fibres. There was also an inverse relationship betweeen the size of myelinated fibres and the grade of malnutrition as also the age of the patients.

Fibers in monkey posterior articular nerves

The distribution of axons in the posterior articular nerves in rhesus monkey has been studied in terms of ratio of myelinated to unmyelinated fibers, and size of myelinated fibers. Conduction velocity measurements were also made. The nerves contained 2,000 to 2,200 unmyelinated fibers of 0.2 to 1.2 mum diameter. They contained 399 to 478 myelinated fibers, varying in size from 1.4 to 12.3 mum. Thus 80 to 85% of fibers in these nerves were unmyelinated. The maximum conduction velocity of 70 to 80 meters per second corresponded to an initial small deflection, with most fibers conducting at slower rates. These results are compared to previous reports which severely underestimated the number of unmyelinated fibers because electron microscope counts were not utilized. It is suggested that pain fibers from the knee joint of monkey make up much of this large population of unmyelinated axons. An unknown number of post-ganglionic sympathetic fibers is also included in the unmyelinated fiber group.

Fiber components of the recurrent laryngeal nerve in the cat.

Experimental neuroanatomical methods were employed in 21 adult cats to determine 1) the number and size of myelinated motor and sensory fibers in the recurrent laryngeal nerve (RLN), and 2) the fiber components originating in the nucleus ambiguus (NA) and retrofacial nucleus (RFN) of the brain stem. Intracranial transection of the X and XI cranial nerves and selective destruction of the NA or RFN were the experimental lesions inflicted in order to obtain the following results. About 55% (312) of the right RLN (565 fibers) is composed of myelinated motor nerve fibers which measure 4 mu - 9 mu in diameter. Nine percent come from the RFN and are smaller (4-6 mu) than the 46% which emanate from the NA and measure 6-9 mu in diameter. The remaining 45% of the RLN is made up of sensory neurons which can be divided into three groups. 1) The largest numerical group (32%) is very small in caliber (1-3 mu) and supplies extralaryngeal regions (trachea, esophagus). 2) The intermediate size fiber group (4-9 mu) comprises 11% of the RLN and probably supplies the subglottic mucosa. 3) The smallest group (2%) of sensory fibers is the largest in diameter (10-15 mu) and may represent either the innervation of muscle spindles or afferents from the superior laryngeal nerve coursing down into the chest.

Myelinated nerve fibers: computed effect of myelin thickness on conduction velocity.

Myelinated nerve fibers: computed effect of myelin thickness on conduction velocity.

An electron microscopic study of the relationship between axon diameter and the initiation of myelin production in the peripheral nervous system.

AbstractMid‐thoracic dorsal and ventral roots from adult rats, cats and cows were prepared for electron microscopy using standard techniques. Axon diameters were measured on photographs of known magnification. Minimal diameters of the unmyelinated fibers in the spinal cords of these animals were measured also. With the exception of a few overlapping diameters unmyelinated fibers were smaller than the smallest myelinated fibers in all the material examined. In the dorsal roots of the cow, the unmyelinated fibers, as a group, were larger than those of the rat and cat, and very few were enclosed by any one Schwann cell. The largest unmyelinated fibers were singly enclosed. In addition, the dorsal root of the cow contains many more small myelinated fibers than those of the other two species. In the ventral roots, a progressive increase in the size and relative numbers of myelinated preganglionic fibers from rat through cat to cow was noted. These facts indicated that myelination is directly dependent on fiber diameter irrespective of age, species or function although less precisely than was indicated by the earlier studies of Duncan ('34). Although the critical diameter for myelination in the peripheral nervous system is about one micron, in the central nervous system it is 0.3 μ or less.

The number and size of myelinated fibres in the inferior alveolar nerve of a young sheep

Sections of the inferior alveolar nerve of a young sheep were taken at four levels along the mandibular canal, and stained with osmium tetroxide. The myelinated fibres were counted by projection of the negatives of photomicrographs on millimetre paper at a magnification of 1000 diameters. From the most proximal section to the most distal the number of fibres increased: the four counts were 13,151, 13,479, 14,312 and 16,641. In the same direction the mean fibre diameter decreased: the four determinations were 4.22, 4.16, 4.01 and 3.72μ. The observations support the doctrine of patterns as a more satisfactory postulate of afferent neural organization than the doctrine of specific energy. The high degree of branching within the mandibular canal is consistent with an economy of adjustment to tooth loss and succession, and with a minimal effect of such adjustment on centripetal impulses.