Composition of the medial and posterior articular nerves of the mouse knee joint

The number and the distribution of fiber size in the medial (MAN) and posterior (PAN) articular nerves of the mouse knee joint were studied by electron microscopy. The MAN contained 75 &#45 28 nerve fibers consisting of 63 &#45 24 unmyelinated and 12 &#45 6 myelinated fibers. The PAN was composed of 195 &#45 50 nerve fibers, namely 129 &#45 28 unmyelinated and 66 &#45 24 myelinated fibers. A skewed unimodal distribution of the unmyelinated nerve fiber diameters was seen in both nerves ranging from 0.1 to 1.2 &#119 m with a maximum between 0.3 and 0.6 &#119 m. The myelinated nerve fibers in the MAN ranged from 1 to 8 &#119 m with a peak between 2 and 5 &#119 m. In the PAN, their diameters ranged from 1 to 12 &#119 m with a clearly visible peak at 4-5 &#119 m and a plateau at 8-9 &#119 m that may represent a second maximum. These data show that the knee joint innervation of the mouse is comparable to those of the cat and rat concerning the types of nerve fibers and the composition of the two nerves. However, in relation to the much smaller area of tissue to be innervated the total number of primary afferents is considerable smaller in the mouse.     

Conduction velocities and fiber diameters in a cutaneous nerve of the pigeon

Summary The characteristics of fibers of a cutaneous nerve supplying the wing skin of the pigeon have been investigated with electrophysiological and electron microscopic techniques.Recordings of the compound action potential showed four distinct peaks with conduction velocities of about 30 m/s, 12 m/s, 4 m/s and 0.5 m/s.From electron micrographs both fiber diameters and thickness of myelin sheath were assessed and used as criteria for segregating various fiber populations. Altogether four groups could be discerned: large thickly myelinated fibers, small thickly myelinated fibers, small thinly myelinated fibers, and unmyelinated or C-fibers. The subdivision of the thickly myelinated fibers into two populations is evidenced mainly by corresponding peaks in the compound action potential. The thinly myelinated fibers with a mean diameter of 2 m contributed about 90% of all myelinated fibers in this nerve.When comparing fiber dimensions and conduction velocities of this avian nerve with those of mammalian cutaneous nerves, the lower CV's of avian nerve fibers can be explained by smaller diameters and thinner myelin sheaths.The results of this investigation are a prerequisite for latency considerations in central somatosensory pathways in birds.Abbreviations CAP compound action potential - CV conduction velocity - D fiber diameter - d axon diameter - g ratio d/D - m thickness of myelin sheath     

扬子鳄视神经的研究

本文研究了扬子鳄的视神经。结果明明,视神经中可见有髓纤维和无髓纤维。有髓纤维分布均匀,无髓纤维常聚集成团;胶质细胞核,在视神经中可看到两种类型,有髓纤维总数为２００,０００－３００,０００根,纤维直径范围为０．４１－６．６６μｍ,只有一个峰值,峰直径为１．３１μｍ;纤维轴突径与纤维直径之比（ｄ／Ｄ）约为０．７３－０．７５。经统计分析,同个体左右侧神经纤维数目有差异,同一神经中周围区与中央区数目分布     

Morphometry and ultrastructure of the squirrel monkey (Saimiri sciureus) vestibular nerve

Vestibular nerves of squirrel monkeys (Saimiri sciureus) embedded in plastics and epoxies were examined with light microscopy (LM) and transmission electron microscopy (TEM), and computerized measures were obtained and analyzed statistically. An average of 12,412 perikarya and 12,005 myelinated nerve fibers was obtained. Approximately 0.7% of the perikarya appeared unmyelinated under LM. About 500 unmyelinated fibers were counted. The cross-sectional area of 1,864 perikarya was 200-650 micron 2. The cross-sectional area of 1,346 nerve fibers was 3-11 micron 2 for the axoplasm and 11-12 micron 2 for the myelin sheath of the same fiber. Myelin thickness was directly proportional to the axoplasm cross-sectional area of the nerve fibers. The cross-sectional area of central axons and peripheral dendrites differed significantly (p less than 0.001). The initial segments of peripheral dendrites were usually smaller, but longer than the initial segments of the central axons. Both initial segments increased in diameter after the first node of Ranvier. Schmidt-Lantermann incisures were more abundant in thick and heavily myelinated fibers than in thin and lightly myelinated fibers. Larger perikarya usually had larger fibers and vice versa, within the first 100-200 micron from the first node of Ranvier. No major ultrastructural differences were found between myelinated and unmyelinated perikarya, except at the hillock region. The Nissl substance was preferentially located in the peripheral cytoplasm.     

A quantitative electron microscope analysis of peripheral nerve in the urodele amphibian in relation to limb regenerative capacity

An approximate 1:1 ratio of myelinated to unmyelinated fibers was established in counts from electron micrograph montages in nerves of the newt, Triturus (Notophthalmus) viridescens. The number of myelinated fibers correspond to the number counted with the light microscope after osmium fixation. Light microscope counts of silver impregnated sections yielded a value slightly higher suggesting that, except for bundles of unmyelinated fibers, the silver technique revealed mainly myelinated fibers. The results were used to reassess previous quantitative studies on the relation between number of nerve fibers and the control which nerves exert on regeneration. For a truer estimate of the number of axons affecting regeneration, fiber values previously reported should now be doubled to include the large number of unmyelinated fibers. However, calculations show that the unmyelinated fibers contribute less than 3% of the total neuroplasm in the peripheral nerve. Finally, counts made of Schwann cells and fibroblasts show that the latter are few in number.     

The chorda tympani and glossopharyngeal nerves in the adult hamster

The numbers and diameters of axons in the intact chorda tympani(CT) and lingual branch of the glossopharyngeal nerve (GN) arequantified with the use of electron microscopic photomontages.The cross-sectional diameters of the CT and GN average 68 and86 microns, respectively. The intact CT contains {small tilde}1050 fibers, 63% are unmyelinated and 37% are myelinated. TheGN contains {small tilde} 1600 fibers, 79% are unmyelinatedand 21% are myelinated. Both nerves are made up of relativelysmall unmyelinated and myelinated fibers, although the GN showsa broader distribution of diameters for its myelinated fibersdue to the presence of general somatosensory fibers. Followingde-efferentation, there is a 48% reduction in the number ofunmyelinated fibers in the CT. Fifty-two per cent of the unmyelinatedfibers are sensory. The number of myelinated fibers is not significantlyreduced and nearly all of the myelinated fibers are sensory.Sixty-seven per cent of the fibers within the CT are sensory.The de-efferented CT contains an equal number of unmyelinatedand myelinated axons and a total of {small tilde} 700 fibers.Comparable data in the rat indicate that its intact and de-efferentedCT are organized differently in regards to the numbers of sensoryand motor, and myelinated versus unmyelinated fibers. The findingsof the present study, together with the available data fromother species, suggest that anatomical differences in the make-upof the major gustatory nerves do not contribute in any obviousway to the known differences in the response properties betweenthe rat and hamster CT, and that the number of myelinated fibersin the visceral motor component of the CT varies considerablyacross species.     

Acetylcholinesterase activity of motor and sensory nerve fibers in the spinal nerve roots of the rat

Summary The histochemical and cytochemical distribution of acetylcholinesterase activity in the anterior and posterior spinal nerve roots and ganglia of the rat was demonstrated by the Karnovsky method using acetyl and butyrylthiocholine as substrates and eserine and DFP as inhibitors. Light and electron microscopic examination of transverse frozen sections enabled the simultaneous visualization of end product in relationship to the various fiber components of each nerve root. While the enzymatic activity of the anterior roots was consistantly observed in the large extrafusal and small intrafusal motor fibers a relatively greater amount of precipitate occurred in aggregates of myelinated and unmyelinated fibers believed to represent preganglionic sympathetic nerves. In contrast, no significant enzymatic activity could be demonstrated in the myelinated nerve fibers of the posterior root. In the sensory sytem, the limited enzymatic precipitate was largely restricted to the unmyelinated afferent fibers and to their small cell bodies in the dorsal root ganglia. The ultrastructural distribution of enzymatic activity was located in the granular endoplasmic reticulum and perinuclear spaces of the ganglion cells. Within peripheral nerves this end product occurred between the apposing axonal and Schwann cell membranes and along the membranous aspect of occasional axoplasmic vesicles of both myelinated and unmyelinated nerve fibers.This study was supported by grants NB 04161-04 and NB 04161-05 of the National Institute of Neurological Diseases and Blindness. — The author would like to thank MissMaria C. la Valle for her skillful technical assistance.     

Quantitative studies on the motor root of the mouse facial nerve. An electron-microscopic study.

Fiber count analysis was performed with the electron microscope on the motor root of the facial nerve in six mice. On an average, 3,433 (84.9%) of the total nerve fibers (4,046) were myelinated and 592 (14.6%) unmyelinated. The motor root consisted mostly of large myelinated fibers (large fiber group), but a part of the root consisted of small myelinated and unmyelinated fibers (small fiber group). The nerve fibers of the small fiber group appear to correspond with those of the intermediate nerve, and to pass through the motor root and enter the intermediate nerve near the geniculate ganglion.     

Acetylcholinesterase: a histochemical identification of motor and sensory fascicles in human peripheral nerve and its use during operation

To evaluate the precision of acetylcholinesterase histochemical identification of motor and sensory fascicles, this study presents a systematic observation of human peripheral nerves by Karnovsky and Roots' histochemical method. The results indicate that either of the enzymatic activities of myelinated and unmyelinated fibers was different between motor and sensory fascicles. Fifty-seven percent of the myelinated fibers showed enzymatic activity in the motor fascicles, while none of the myelinated fibers in the sensory fascicles showed enzymatic activity. The unmyelinated fibers showing enzymatic activity in the sensory fascicles were far denser than those in the motor fascicles. Our study demonstrated that the unmyelinated fibers were sympathetic postganglionic unmyelinated fibers. From these results it is concluded that the motor and sensory fascicles may be identified not only according to the enzymatic activities of the myelinated fibers, but also according to the enzymatic activities of the sympathetic postganglionic unmyelinated fibers. An improved histochemical method was suggested for its applicability as a method of intraoperative nerve fascicle identification. Simulated experiments were done on the radial nerves and the median nerves in human cadavers. This improved histochemical process can be completed within 50 minutes and can be used in intraoperative nerve fascicle identification.     

Quantitative studies on the regeneration of myelinated nerve fibers. I. Variations in the number and the size of myelinated fibers in the nerves of normal rats]

The number and size of myelinated nerve fibers have been determined at standard levels in the nerve to medial head of right and left gastrocnemius muscles of 24 normal rats (11 males and 13 females). The mean values of all results were comparable on right and left sides. Thus, 271 +/- 5 myelinated nerve fibers were found in the right nerve and 272 +/- 4 in the left; their mean diameter were respectively 8.1 +/- 0.1 and 8.0 +/- 0.1 micron. There were 60.1% of large nerve fibers on the right side and 59,9% on the left, their mean diameters being 10.5 and 10.6 micron. Some variations occured in all these values, depending of the weight and sex of the animals. Nevertheless, the differences between both sides of a same rat were negligible and the histograms of both nerves could be superposed. Accordingly, in the operated animals, the contralateral nerve may be used as control.     

Localization of Phospholipid Synthesis to Schwann Cells and Axons

Quantitative electron microscopic autoradiography was used to detect and characterize endoneurial sites of lipid synthesis in mouse sciatic nerve. Six tritiated phospholipid precursors (choline, serine, methionine, inositol, glycerol, and ethanolamine) and a protein precursor (proline) were individually injected into exposed nerves and after 2 h the mice were perfused with buffered aldehyde. The labeled segments of nerve were prepared for autoradiography with procedures that selectively remove nonincorporated precursors and other aqueous metabolites, while preserving nerve lipids (and proteins). At both the light and electron microscope levels, the major site of phospholipid and protein synthesis was the crescent-shaped perinuclear cytoplasm of myelinating Schwann cells. Other internodal Schwann cell cytoplasm, including that in surface channels, Schmidt-Lanterman incisures, and paranodal regions, was less well labeled than the perinuclear region. Newly formed proteins were selectively located in the Schwann cell nucleus. Lipid and protein formation was also detected in unmyelinated fiber bundles and in endoneurial and perineurial cells. Tritiated inositol was selectively incorporated into phospholipids in both myelinated axons and unmyelinated fibers. Like inositol, glycerol incorporation appeared particularly active in unmyelinated fibers. Quantitative autoradiographic analyses substantiated the following points: myelinating Schwann cells dominate phospholipid and protein synthesis, myelinated axons selectively incorporate tritiated inositol, phospholipid precursors label myelin sheaths and myelinated axons better than proline.     

Neurogenic inflammation of gingivomucosal tissue in streptozotocin-diabetic rat

Previously it was assumed that nerve fibres are involved in the neurogenic inflammation induced by mechanical or chemical irriations. It has been also suggested that in diabetes mellitus the unmyelinated small diameter fibers are impaired as a result of diabetic neuropathy. Therefore, our aim was to study the alterations of the nerve processes in the gingivomucosal tissue in streptozotocin (STZ)-diabetic rats. Light- and electronmicroscopical examinations were made to analyze the changes in nerve fibres. After one week of steptozotocin treatment, the gingivomucosal tissue had inflammatory cell infiltration and some degenerated nerve fibres were also observed. Dense mitochondria, disorganization of cell organelles, and appearance of myelin-like dense bodies were found in the axons of degenerared nerve fibres. Semiquantitative analysis showed that 14 +/- 4% of the unmyelinated nerve fibres degenerated after one week of STZ treatment. However, degeneration of the myelinated nerve fibers was not observed. Two weeks after STZ treatment, most of the unmyelinated and myelinated nerve fibers showed degeneration (86 +/- 5%) and the placement of the ligature revealed a non-inflammatory connective tissue adjacent to a normal epithelium. The myelin sheath was disrupted and dark axoplasm with cytolysosomes became manifest. These findings demonstrated that both unmyelinated and myelinated nerve fibers are altered and inflammatory reaction exists in the gingivomucosal tissue only in the early stage of diabetes mellitus.     

Electron-microscopic analysis of the mouse facial nerve near the geniculate ganglion

An electron-microscopic analysis of the mouse facial nerve near the geniculate ganglion shows that there are, on the everage, 603 more nerve fibers in the portion of the nerve distal to the geniculate ganglion than there are in the part proximal to the ganglion. The average distal increase in the number of unmyelinated fibers is 444 and that in the myelinated fibers is 165. The somatic motor nerve fibers and the parasympathetic fibers in the mouse facial nerve may not contribute to the distal excess. It is possible that the increase in the number of unmyelinated fibers distal to the geniculate ganglion is mainly due to the presence of postganglionic sympathetic fibers in the facial trunk distal to the geniculate ganglion and the greater petrosal nerve. The distal increase in the number of myelinated fibers may be mainly contributed by the sensory fibers.     

Quantitative studies on the intermediate nerve of the mouse with the electron microscope.

Quantitative counts of the intermediate nerve fibers of the mouse with electron microscope have shown that, on an average, 1,267 (79.3%) and 301 (18.9%) of the total nerve fibers (1,597) were myelinated and unmyelinated fibers, respectively. The number of unmyelinated fibers in the intermediate nerve was less than one-half the number of unmyelinated fibers in the greater petrosal nerve found in previous studies. Therefore, it is postulated that some of the unmyelinated fibers in the greater petrosal nerve may come from the intermediate nerve, while the rest may be derived from another source.     

Adenosine triphosphatase activity of cutaneous nerve fibers

Summary The histochemical study of Mg⁺⁺-activated adenosine triphosphatase (Mg⁺⁺-ATPase) activity was carried out on the peripheral nerves of mouse digital skin by light and electron microscopy. Under the light microscope, the ATPase activity was clearly demonstrated on the nerve fibers as a fine network in the subepidermal regions. Under the electron microscope, the reaction product of enzyme activity was located in the interspace between axolemma and the surrounding Schwann cells of the unmyelinated nerve fibers. No reaction product was observed in the space between the axolemma and the Schwann cells associated with myelinated nerve fibers. Demonstrable activity was absent at the nodes of Ranvier as well as on the para- and internodal regions of these myelinated axons. The part of the axolemma lacking a Schwann cell sheath failed to show a reaction product. The perineural epithelial cells surrounding the nerve fibers displayed reaction product in the caveolae. These results suggest a functional difference in the axon-Schwann interface of myelinated as compared to unmyelinated nerve fibers. The function of the perineural epithelial cell would be expected to be a regulatory one in transferring materials across the epithelium to keep the proper humoral environment around nerve fibers.     

Distribution of myelinated nerves in ascending nerves and myenteric plexus of cat colon

The parts of the colon differ in motor function and in responses to extrinsic and intrinsic nerve stimulation. The distribution of myelinated nerve fibers in the colonic myenteric plexus is not known. Because these fibers might be largely extrinsic in origin, their distribution might indicate the domain of influence of extrinsic nerves and help to explain the different behaviors of the different parts of the colon. Myelinated fibers were examined by electron microscopy in cross sections of the ascending nerves and in myelin-stained whole-mount preparations in the colon. The ascending nerves are much like one another. They have the structure of peripheral nerves, not that of myenteric plexus. The proportion of myelinated fibers in the ascending nerves declines rostrad with no uniform change in total nerve fiber number. Cross-sectional areas of ascending nerves, 3,304 to 7,448 microns 2; total number of nerve fibers per profile, 703-2,651; and mean myelin coat thickness, 0.45 +/- 0.01 micron, do not change uniformly along the ascending nerves. Myelinated fibers are about 2% of total fibers in the extramural colonic nerves, 7-9% in the ascending nerves in the sigmoid colon, and 2-3% at the rostrad ends of the ascending nerves in the transverse colon. Blood vessels lie at the core of each ascending nerve and on the nerve sheath. Myelinated fibers in the ascending nerves degenerate after section of colonic branches of the pelvic plexus and after section of the pudendal nerves, indicating that myelinated nerves reach the colon through both pathways.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gliogenesis and myelination in the optic nerve of trisomy 19 mice. A quantitative electron-microscopic study

Trisomy 19 (ts19) of the mouse permits detailed studies on the influence of an extra autosome upon the postnatal development of the central nervous system. To examine gliogenesis and myelinogenesis, the optic nerves of 19 ts19 pugs aged 1-15 days have been examined by light and electron microscopy and compared to those of litter-mate controls. Differentiation of astrocytes and oligodendrocytes, myelinogenesis as well as the opening of the eyes are each delayed by about 2 days. Myelin sheaths are normally structured in ts19. There is a decrease in the percentage of myelinated fibres. The cross-sectional area of the ts19 optic nerve is reduced. The fibre density, which decreases with age both in ts19 and control mice, is higher in ts19 mice. Both with ts19 and control animals, the distribution of fibre diameters of myelinated axons overlaps with that of promyelinated and unmyelinated fibres, but myelinated axons cannot be observed below a diameter of 0.3 micron, and unmyelinated axons are always smaller than 1 micron. The mean diameter of promyelinated axons is identical in ts19 and control animals. Myelination is therefore not severely disturbed in the ts19 optic nerve. As retinal differentiation in ts19 is delayed by 2 days as well, reports on an asynchronous development of neurons and myelin sheaths cannot be confirmed for the visual system.     

Fiber size and sensory endings of the middle cardiac nerve of the domestic fowl (Gallus domesticus)

The middle cardiac nerve, a branch of the vagus, innervates the ventricles of the avian heart. Of 533 myelinated sensory fibers, the size range was 2 micron. The ratio of myelinated to unmyelinated sensory fibers ranged from 2.17 to 3.48. Sensory endings resembled a network pattern with no distinct receptor-like endings. Frequency of nerve population increased from apex to base of the heart.     

Ultrastructure and functional characteristics of the optic nerve of Rana temporaria L. in the norm and during degeneration

Results of electron microscopy and electrophysiological studies of the frog optic nerve are presented. The nerve contains 96% unmyelinated (about 210,000) and 4% myelinated (8700–14,800) fibers. The peripheral zone of the nerve (20–30 µm) has relatively few myelinated fibers, whereas in other zones these fibers are distributed uniformly (counting area 300–400 µm²). The curve of the distribution of the diameters of myelinated fibers has a number of peaks: a main peak at 1 µm and additional peaks at 0.6 and 1.6 µm (the latter is more prominent). Individual fibers have a diameter of 0.4–3.9 µm. The diameter of the unmyelinated fibers are 0.1–0.4 µm; 64% of these fibers have a diameter of 0.2 µm. Most fibers at a temperature of 18–20° conduct at 0.3–0.4 m/sec and a few (myelinated with a diameter of 1.0–1.6 µm) at 3 and 6 m/sec. After enucleation the myelinated fibers degenerate at first and are phagocytized by neuroglia; the ultrastructure and function of the unmyelinated fibers at 18–20° remain unchanged up to 100 days postoperation.A. N. Severtsov Institute of Evolutionary Animal Morphology and Ecology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 627–635, November–December, 1970.     

Pathological changes of human unmyelinated nerve fibers: a review

In the cutaneous nerves, unmyelinated nerve fibers outnumber the myelinated ones but are scarcely analyzed, especially at autopsy. This indifference toward the pathology of unmyelinated nerve fibers may be due to the necessity of electron microscopic analyses and, more importantly, the obscurity of pathological alteration of unmyelinated nerve fibers in aging as well as in peripheral nerve disorders. The aim of this article is to review (1) the normal appearance including postmortem changes, (2) the age-related changes, and (3) the pathological alteration in various neuropathic and non-neuropathic conditions, of unmyelinated nerve fibers in the sural nerve. For the complete analyses of sural nerve, qualitative and quantitative estimation of unmyelinated nerve fibers in all specimens should be recommended and it sometimes has an important diagnostic value.