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.     

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.     

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 +/- 28 nerve fibers consisting of 63 +/- 24 unmyelinated and 12 +/- 6 myelinated fibers. The PAN was composed of 195 +/- 50 nerve fibers, namely 129 +/- 28 unmyelinated and 66 +/- 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 microm with a maximum between 0.3 and 0.6 microm. The myelinated nerve fibers in the MAN ranged from 1 to 8 microm with a peak between 2 and 5 microm. In the PAN, their diameters ranged from 1 to 12 microm with a clearly visible peak at 4-5 microm and a plateau at 8-9 microm 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.     

Cochlear and lagenar ganglia of the chicken

Cochlear and lagenar components of the statoacoustical ganglion in the inner ear of one chicken were studied quantitatively in the TEM. Both myelinated and unmyelinated nerve fibers were present in these two parts of the ganglion and in a putative efferent bundle within the ganglion. The cochlear portion had the lowest, the efferent bundle the highest percentage of unmyelinated fibers. Compared to the other parts of the ganglia, the cochlear fibers had a high degree of homogeneity, especially in fiber size. Some gradients in the baso-apical direction were found, such as an increase in the size of myelinated cochlear fibers from the base to the apex. Based on the ultrastructure of cellular components, no distinct populations of cell bodies within the statoacoustical ganglion were definable. The ganglion contained some 8,000 cochlear and about 1,200–2,000 lagenar neurons. The putative efferent bundle had only 150–200 fibers. This cannot be the total number of efferents to the hair cells in both the basilar papilla and the lagena. A large number of efferent fibers to the auditory papillae presumably run mingled among the afferent fibers. © 1994 Wiley-Liss, Inc.     

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.     

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.     

Normal and abnormal pathfinding of facial nerve fibers in the chick embryo

Development of the facial nerve was studied in normal chicken embryos and after surgical disruption of ingrowing sensory facial nerve fibers at 38–72 h of incubation. Disruption of facial nerve fibers by otocyst removal often induced a rostral deviation of the facial nerve and ganglion to the level of the trigeminal ganglion. Cell bodies of the geniculate ganglion trailed their deviating neurites and occupied an abnormal rostral position adjacent to the trigeminal ganglion. Deviating facial nerve fibers were labeled with the carbocyanine fluorescent tracer Dil in fixed tissue. Labeled fibers penetrated the cranium adjacent to the trigeminal ganglion, but they did not follow the trigeminal nerve fibers into the brain stem. Rather, after entering the cranium, they projected caudally to their usual site of entrance and proceeded towards their normal targets. This rostral deviation of the facial nerve was observed only after surgery at 48–72 h of incubation, but not in cases with early otocyst removal (38–48 h). A rostral deviation of the facial nerve was seen in cases with partial otocyst removal when the vestibular nerve was absent. The facial nerve followed its normal course when the vestibular nerve persisted. We conclude that disruption of the devloping facial pathway altered the routes of navigating axons, but did not prevent pathfinding and innervation of the normal targets. Pathfinding abilities may not be restricted to pioneering axons of the facial nerve; later-developing facial nerve fibers also appeared to have positional information. Our findings are consistent with the hypothesis that navigating axons may respond to multiple guidance cues during development. These cues appear to differ as a function of position of the navigating axon. © 1992 John Wiley & Sons, Inc.     

Normal and abnormal pathfinding of facial nerve fibers in the chick embryo.

Development of the facial nerve was studied in normal chicken embryos and after surgical disruption of ingrowing sensory facial nerve fibers at 38-72 h of incubation. Disruption of facial nerve fibers by otocyst removal often induced a rostral deviation of the facial nerve and ganglion to the level of the trigeminal ganglion. Cell bodies of the geniculate ganglion trailed their deviating neurites and occupied an abnormal rostral position adjacent to the trigeminal ganglion. Deviating facial nerve fibers were labeled with the carbocyanine fluorescent tracer DiI in fixed tissue. Labeled fibers penetrated the cranium adjacent to the trigeminal ganglion, but they did not follow the trigeminal nerve fibers into the brain stem. Rather, after entering the cranium, they projected caudally to their usual site of entrance and proceeded towards their normal targets. This rostral deviation of the facial nerve was observed only after surgery at 48-72 h of incubation, but not in cases with early otocyst removal (38-48 h). A rostral deviation of the facial nerve was seen in cases with partial otocyst removal when the vestibular nerve was absent. The facial nerve followed its normal course when the vestibular nerve persisted. We conclude that disruption of the developing facial pathway altered the routes of navigating axons, but did not prevent pathfinding and innervation of the normal targets. Pathfinding abilities may not be restricted to pioneering axons of the facial nerve; later-developing facial nerve fibers also appeared to have positional information. Our findings are consistent with the hypothesis that navigating axons may respond to multiple guidance cues during development. These cues appear to differ as a function of position of the navigating axon.     

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.     

Light and electron microscopic studies on the pineal tract of rainbow trout, Salmo gairdneri.

The pineal tract of rainbow trout from the pineal end vesicle to the posterior commissure was studied by light and electron microscopy. Five types of nerve fibres (photoreceptor basal process, ganglion cell dendrite, electron-lucent fibre and synaptic vesicles, myelinated and unmyelinated axons) and two modes of synapses (photoreceptor basal process ganglion cell dendrite and axon terminal with synaptic vesicles-photoreceptor basal process synapses) are distinguishable in the proximal region of end vesicle. The two distinct synaptic associations with the photoreceptor basal process suggest two different (excitatory and inhibitory) control of pineal sensory activity. At the distal portion of stalk about two thousand nerve fibres converge into dorsal and ventral bundles. Posterior to the habenular commissure several small branches run out laterally from the ventral bundles to the basal margin of the ependyma, but not into the habenular commissure. The dorsal bundle passes through the dorsal side of the subcommissural organ and runs ventral to the posterior commissure. The pineal tract is composed of unmyelinated axons, electron-lucent nerve fibres and myelinated axons. The number of fibres increases throughout the stalk and reaches the maximum number at the opening of pineal lumen to IIIrd ventricle, however, the number of fibres then decreases through the subcommissural organ and posterior commissure. This increase and decrease of nerve fibres suggest the continuous participation of axonal fibres of pineal nerve cells and the ramification or branching of pineal tract, respectively.     

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.     

Morpho-functional characteristics of the optic nerve of the steppe turtle Agrionemys horsfieldi]

The optic nerve of the tortoise Agrionemys horsfieldi contains about 400,000 fibers (90% unmyelinated and 10% myelinated ones). the diameter of unmyelinated fibers varies from 0.3 to 1.1 mu, mean value being equal to 0.5 mu; fibers with a diameter 0.4-0.7 comprise 77%. The diameter of myelinated fibers varies within 0.3-3.0 mu, average value being 0.5-0.8 nu; fibers with a diameter 0.5-0.9 mu amount to 62%. Electrogram of the optic nerve consists of two components which are equal in their amplitudes. These components presumably reflect summary firings of modal groups of unmyelinated and myelinated fibers. The velocity of propagation of excitation along the fibers producing the first component is equal to 1.3 m/sec, wheras that in fibers producing the second component - to 0.5 m/sec. The data obtained are compared with those related for the other tortoise - Emys orbicularis.     

Myelinated axons of ganglion cells in the retinae of teleosts

Summary In the retina of the goldfish and the rainbow trout, the axons of ganglion cells belong to the unmyelinated or the myelinated types. The unmyelinated fibers are either arranged in bundles in direct contact with neighboring fibers or they are separated by intervening lamellae of oligodendroglial cytoplasm. The myelin sheaths of the myelinated fibers differ greatly in thickness. Most fibers show 3 to 5 myelin layers; single fiber elements, however, show 10 or even more layers.     

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.     

NUCLEOSIDE PHOSPHATASE AND CHOLINESTERASE ACTIVITIES IN DORSAL ROOT GANGLIA AND PERIPHERAL NERVE

In dorsal root ganglia and peripheral nerve of the rat and other species, nucleoside phosphatase and unspecific cholinesterase reaction products are found in the plasma membranes and spaces between them at two sites: (1) Schwann cell-axon interfaces and mesaxons of unmyelinated fibers, and (2) sheath cell-perikaryon interfaces and interfaces between adjacent sheath cells. Acetylcholinesterase reaction product is found in the perikaryon (within the endoplasmic reticulum) and the axon (axoplasmic surface). Nucleoside phosphatase reaction product is also found in the numerous vacuoles at the surface of perineurium cells, ganglion sheath cells, and cells surrounding some ganglion blood vessels. Nucleoside phosphatase activities in the sections fail to respond, in the manner described for "transport ATPase," to diisopropylphosphofluoridate, sodium and potassium ions, and ouabain. Nucleoside diphosphates are hydrolyzed more slowly than triphosphates in unmyelinated fibers, and are not hydrolyzed at the perikaryon surface. Nucleoside monophosphates are either not hydrolyzed or hydrolyzed very slowly. In contrast to these localizations, which are believed to demonstrate sites of enzyme activity, it is considered likely that diffusion artifacts account for the nucleoside phosphatase reaction product frequently found along the outer surfaces of myelinated fibers and within vacuoles at the Schwann cell surfaces of these fibers. The diffuse reaction product seen in basement membranes of ganglion and nerve may also be artifact.     

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.     

Morphometric analysis of the sciatic nerve and its principal branches in the pigeon (Columba livia)]

The methodological approach used in this study is to characterize the number, the density and the diameter distribution of myelinated fibers (MFs) and unmyelinated fibers (UMFs) in sciatic nerve and its main branches of pigeon. The results have shown that the fiber composition is quite variable because in pigeon there are relatively MF with thin myelin sheaths and MF with thicker sheaths. Our data suggest that morphometric analysis could represent a helpful methodological approach to better characterize these systems.     

The influence of an unmyelinated terminal on repetitive firing of a mammalian receptor afferent fiber

The distal end of a myelinated receptor afferent fiber consists of an unmyelinated terminal membrane which is assumed to be the site of sensory transduction, whereas the action potential encoding appears at a distal node of Ranvier. In the present paper a model of a mammalian myelinated nerve fiber was augmented by an unmyelinated terminal segment into which stimulating current was injected thus modelling the situation at a myelinated receptor afferent fiber. It was found that the introduction of the unmyelinated terminal reduces the repetitive firing rate shown by the model. However, also the amplitude of the spikes at the site of action potential generation diminishes through the large electrical load which the unmyelinated terminal imposes onto the active parts of the nerve fiber model. This "loss" of spike amplitude can abolish the ability of the model to show repetitive activity, if the unmyelinated terminal increases in size. On the other hand, the incorporation of sodium channels into the terminal membrane compensates the spike amplitude reduction introduced by the electrical load of that membrane. This allows repetitive firing at a lower frequency than would be possible for a model with an equivalent sodium-channel-free terminal. The results show that the unmyelinated terminal present at the distal end of myelinated receptor afferent fibers has not only the ability to provide sensory transduction but evokes also a reduction in the discharge rate of the encoding membrane.     

Microtubule stability along mammalian peripheral nerves

Microtubule (MT) number, axonal area, and MT density were examined in unmyelinated axons of rat cervical vagus nerve. Study of nerve regions proximal (1-5 mm) and distal (35-40 mm) to the nodosum ganglion in controls (incubation at 37 degrees C for 1 h) showed that the number of MT per axon is significantly less in distal than in proximal nerve regions. Cooling (incubation at 0 degree C for 1 h) caused a significant reduction in the number of MT per axon in both nerve regions. The unmyelinated axons from both nerve regions showed a comparable reduction in MT number by cooling, indicating that axonal MT stability to cold was not significantly different between these two nerve regions. In these nerves no detectable changes were found in cross-axonal area of unmyelinated axons between distal and proximal nerve regions. In another experimental series, in distal nerve regions (35-40 mm from the nodosum ganglion) the number of MT was not further reduced in nerves incubated at 0 degree C by increasing the incubation time. Similar results were obtained from colchicine treated nerves (incubation at 37 degrees C, with 10 mM colchicine for 1 and 2 h). Distal nerve regions (35-40 mm from the nodosum ganglion) showed a similar reduction in the number of MT per axon when nerves were incubated at 0 degree C or with colchicine, suggesting that this drug, as well as cold, may be affecting a similar population of axonal MT, i.e., MT susceptible to anti-MT agents. These results indicate that approximately one-half of the axonal MT are stable to cold as well as to colchicine in rat unmyelinated axons.     

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