Myelinated nerve fiber analysis of the human greater splanchnic nerve.

The purpose of the present study is to analyze the human greater splanchnic nerve in relation to aging. We adopted a new staining method which makes it possible to discriminate various structures of the nervous tissue. We examined 25 human greater splanchnic nerves from cadavers for anatomy dissection. We measured the number, area and perimeter of axons. The results reveal that: (1) there is no correlation between age and the number of axons; (2) the mean area and perimeter of axons increase with age, but not the total area and perimeter. We compared these results with those for the lesser splanchnic nerve. These morphological changes in the greater splanchnic nerve may indicate a kind of compensation through axon hypertrophy for hypofunctions in abdominal organ control.     

Morphometric and ultrastructural changes with ageing in mouse peripheral nerve

Qualitative and quantitative information is reported on the morphological changes that occur in nerve fibres and nonneuronal cells of peripheral nerve during the lifetime of the mouse. Tibial nerves of mice aged 6–33 mo were studied. With ageing, collagen accumulates in the perineurium and lipid droplets in the perineurial cells. Macrophages and mast cells increase in number, and onion bulbs and collagen pockets are frequently present. Schwann cells associated with myelinated fibres (MF) slightly decrease in number in parallel with an increase of the internodal length from 6 to 12 mo, but increase in older nerves when demyelination and remyelination are common. The unmyelinated axon to myelinated fibre (UA/MF) ratio was about 2 until 12 mo, decreasing to 1.6 by 27 mo. In older mice, the loss of nerve fibres involves UA (50% loss of 27–33 mo cf. 6 mo) more markedly than MF (35%). In aged nerves wide incisures and infolded or outfolded myelin loops are frequent, resulting in an increased irregularity in the morphology of fibres along the internodes. In the mouse there is an adult time period, 12–20 mo, during which several features of degeneration progressively appear, and an ageing period from 20 mo upwards when the nerve suffers a general disorganisation and marked fibre loss.     

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.     

Fibre composition in the interosseous nerve of the pigeon

The interosseous nerve of birds innervates a string of Herbst corpuscles located near the interosseous membrane between the tibia and fibula. Fibre composition of this nerve was assessed including both myelinated and unmyelinated axons. The diameter of the whole nerve is ∼100 μm. Complete data were obtained for 3 nerves. The mean total number of myelinated fibres and unmyelinated axons was 2872±53. The mean number of myelinated fibres was 280±20 and that for unmyelinated axons was 2600±47. There was a broad distribution of diameters for myelinated fibres ranging from ∼2 μm to 10 μm with a distinct peak at ∼3–5 μm and a less prominent second peak at 6–8 μm. Similarly, myelin sheath thickness distribution showed 2 peaks, one at 0.6–0.8 μm and another at 1.4–1.6 μm. It is suggested that the group represented by the second peak innervates the Herbst corpuscles. The group of smaller myelinated fibres and the unmyelinated axons are assumed to innervate other types of receptors, some of which may be nociceptors.     

Regeneration and retrograde degeneration of axons in the rat optic nerve

Summary The retinal stump of the rat optic nerve was examined histologically 1–64 weeks after intracranial section of the nerve with or without grafting of autologous peripheral nerve segments. Single unmyelinated axons and bundles of unmyelinated axons appeared in cut optic nerves and were most abundant 2–4 weeks after section. With light and electron microscope radioautography after injection of tritiated amino acids into the globe, it was confirmed that many unmyelinated fibres arose from the optic nerve rather than from nearby peripheral nerves and it was estimated that some axons regenerated as far as 0.5 mm. At or near the end of retinofugal axons, structures resembling growth cones were seen at 2 weeks and vesicle-containing swellings similar to synapses were found at 1–2 months. Outgrowth from optic nerve axons was not obviously enhanced by peripheral nerve grafts although a few retinofugal axons became ensheathed by Schwann cells. Retrograde axonal degeneration was rapid in both cut and grafted optic nerves, the number of nerve fibres near the globe falling to less than 10% of normal after 4 weeks. A few myelinated and unmyelinated fibres were still present 64 weeks after nerve transection. In conclusion, some cut axons in the rat optic nerve display a transient regenerative response before undergoing retrograde degeneration.     

Anatomy of the rat knee joint and fibre composition of a major articular nerve

Several recent reports discuss the role of joint nerves in arthritis. Many of these are based on studies in the rat. The aim of this study is to examine the anatomy of the rat knee joint, in search for a primary articular nerve, and to analyze the fibre composition of that nerve. The results show that the structure of the joint differs in some respects from the human knee. At the upper end of the bony patella a cartilaginous patella extends proximally, forming the anterior wall of the suprapatellar bursa. Distinct collateral ligaments are integrated in the joint capsule. The extensor digitorum longus muscle bridges the knee joint, originating from the lateral femoral epicondyle. The well-developed menisci contain pyramid-shaped ossicles. The cruciate ligaments are arranged like in the human knee. A large posterior (PAN) and a small medial (MAN) articular nerve can be identified. The PAN is composed of some 400 axons, about 80% of which are unmyelinated. All myelinated fibres are sensory. They present a unimodal size spectrum with a size range of 1-8 microns, and a predominance of small fibres. Specific denervations indicate that about 1/3 of the unmyelinated axons represent afferents, and some 2/3 are sympathetic efferents. Interestingly, neonatal capsaicin treatment did not influence the number of unmyelinated PAN axons. The functional significance of the numerous unmyelinated sympathetic and sensory PAN axons in the normal knee joint remains to be elucidated.     

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.     

人周围神经内乙酰胆碱酯酶活性与神经束性质的鉴别

本文用Karnovsky乙酰胆碱酯酶组织化学方法,系统地观察了成人周围神经中乙酰胆碱酯酶的分布。材料包括20侧上肢主要神经干及其分支、部分下肢神经的肌支和皮支、6侧C_7脊神经前后根。皮神经内,有髓纤维酶反应阴性;大量无髓纤维显示强阳性酶反应,呈群块状分布。肌支神经内58%的有髓纤维酶反应阳性,酶活性局限于轴索内,髓鞘不显酶活性;示强阳性酶反应的无髓纤维远较皮神经少。C_7脊神经前根87%有髓纤维酶反应阳性,与肌支内酶反应阳性有髓纤维相似;后根纤维酶反应阴性;灰交通支内酶反应强阳性,与皮支内阳性无髓纤维酶染色强度一致。本文结果表明,周围神经运动束和感觉束内,有髓及无髓纤维酶活性都有明显不同;明确提出,酶染色有髓纤维来源脊神经前根运动纤维,具有强酶活性的无髓纤维是交感神经节后纤维。     

Neuritis of the cauda equina in the horse

Ultrastructural lesions of the cranial nerves and their ganglia and the autonomic nervous system from 5 cases of neuritis of the cauda equina in the horse are described. They include lysosomal inclusions within the semilunar, geniculate and sympathetic chain ganglia, granulomatous involvement of the coeliaco-mesenteric ganglion and accumulation of axonal organelles in unmyelinated fibres of the great splanchnic nerve, sympathetic chain and oesophageal vagus.     

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.     

Absence of large-diameter sensory fibres in a nerve to the cat humerus

A fine branch of the median nerve innervates the periosteum and medullary cavity of the cat humerus. After branching to innervate the periosteum on the medial surface of the humerus, the nerve enters and supplies the medullary cavity via a nutrient foramen, accompanied by a small artery and vein. The composition of the fibres in the nerve was examined using electron microscopy. Myelinated fibres with diameters of 0.8-6.6 microm and unmyelinated fibres with diameters of 0.1-1.4 microm were observed. These diameters indicate that afferent fibres of this nerve are confined within the Group III and IV categories, and may therefore be nociceptive or mechanoreceptive in function. In addition, autonomic efferent fibres may also be present in these fibre groups. As no fibre diameters greater than 7 microm were noted, it appears that Group I and II fibres are absent in this nerve. The fibre distribution suggests that the principal role of this nerve is to relay bone-related nociceptive or mechanoreceptive information to the central nervous system and to provide autonomic regulatory influences on the bone.     

Axo-glial relations in the retina-optic nerve junction of the adult rat: freeze-fracture observations on axon membrane structure

Summary The axolemmal ultrastructure of nerve fibres within the retina-optic nerve junction (ROJ) from adult rats was examined by freeze-fracture electron microscopy. In the juxtaocular (proximal) region of the ROJ, all fibres are unmyelinated. The axons generally have a membrane ultrastructure similar to that of retinal nerve fibre layer axons, with a high density of intramembranous particles (IMPs) on the P-fracture face and a low density of IMPs on the E-face. However, along some axons in this region of the ROJ, localized aggregations of E-face IMPs are observed. At levels of the ROJ closer to the optic nerve proper, the unmyelinated fibres enter a transition zone in which the axons acquire myelin sheaths. By the distal boundary of the transitional zone (optic nerve proper), virtually all fibres are myelinated. Within the transitional zone, conventional axo-glial associations and axolemmal ultrastructure is present at nodes of Ranvier. In addition, atypical axo-glial relationships and atypical nodal segments are observed in this region. At some nodes, an isolated oligodendroglial process traverses obliquely across the nodal membrane. Beneath the oligodendroglial process, the axolemma usually displays a paranodal-like ultrastructure. Finger-like oligodendroglial processes were also observed in association with non-nodal unmyelinated axon membrane. At these sites of association, the axon membrane tends to be indented and may have a paranodal-like morphology. Nodal axolemma may exhibit several atypical forms in the transition zone. At some nodes, the nodal axolemma has a low density of E-face particles. Also, nodes of extended linear length (2m) exhibit a lower-than-normal density of P-face IMPs. At heminodes, the axolemma immediately adjacent to the terminal loops lacks the usual nodal characteristics of high IMP density and high percentage of large particles. The results show that aberrant axo-glial associations accompanied by unusual ultrastructural characteristics of the axolemma are present in the ROJ of normal adult rats.     

Potential of Schwann cells from unmyelinated nerves to produce myelin: a quantitative ultrastructural and radiographic study

Summary In adult mice, most nerve fibres in the cervical sympathetic trunk (CST) are unmyelinated whereas a large proportion of sural nerve fibres are myelinated. This study of nerve grafts in syngeneic mice was designed to determine if Schwann cells originating from the unmyelinated CST would produce myelin when in contact with regenerating axons of the sural nerve. Quantitative microscopy of tritiated thymidine-labelled CST segments grafted to unlabelled sural nerve stumps revealed that, one month after grafting, previously unmyelinated grafts contained many myelinated fibres. By phase and electron microscope radioautography, nearly 40% of the myelin-producing cells in the reinnervated graft were shown to have originated in the unmyelinated CST. These findings indicate that Schwann cells originating from unmyelinated fibres are able to differentiate into myelin producing cells.     

Studies on the termination of sinus nerve afferents

Summary Compound action potentials evoked by electrical stimulation in the brainstem of anaesthetized, paralyzed cats and rabbits were recorded distally in the carotid sinus nerve. The latencies of the components of the responses were indicative of fibres with conduction velocities between 0.5 and 32 m/s. These include both myelinated and unmyelinated fibres. Using histological reconstructions of the responsive sites, the termination of the primary afferent fibres of the sinus nerve within the medulla was mapped.In both cat and rabbit these responsive sites were restricted to thedorsomedial medulla in the vicinity of the NTS 0–3 mm rostral to the obex. Although in the cat the fast conducting myelinated fibres (conduction velocities >12.5 m/s) were discretely localized to the ventrolateral area of the NTS, the slower conducting myelinated and unmyelinated fibres were found more diffusely, spreading into areas dorsal and medial to the NTS. In the rabbit the terminals of all types of fibre were mainly confined to the NTS although some C fibres appeared to be grouped in the juxta-alar region. Responses were never evoked from the medial reticular formation or nucleus ambiguus in either cats or rabbits.The organization of the sinus nerve input to the medulla is discussed in the light of these results.     

Constitution of the greater splanchnic nerve in the rat

The greater splanchnic nerve originating from the sympathetic ganglia between the 10th and 12th ribs on the dorsal thoracic wall passes through the diaphragm between its medial and lateral erura, to form the celiac plexus around the celiac trunk and superior mesenteric artery in the abdominal cavity. The nerve consists of about 10,000 of nerve fibers and of 25,000 of ganglion cells in its whole length of 2.5 cm; nerve fibers can be divided into myelinated fibers, accounting for less than 6% of total numbers, and unmyelinated fibers, which amount to more 90%. Special attention was not paid to the numerous ganglion cells in terms of their shapes, sizes, and cell organelles except for a small number of binucleate cells. However, the nerve contains remarkable synapses that connect between axon showing flat, elliptical, and cored vesicles and dendrite, between another type of axon having elliptical and cored vesicles and dendrite, and even between dendrite and cell body, in which synaptic vesicles are small spherical and elliptical. These facts can suggest that the greater splanchnic nerve contains more complex structure than has been hitherto described.     

Nerve fiber analysis and age-related changes of the human mandibular nerve

We morphometrically analyzed nerve fibers of the human mandibular nerve with a discriminative staining method that makes it possible to separate nerve fibers into myelinated and unmyelinated fibers. We counted numbers and transverse areas of myelinated axons under the microscope using an on-line image-analyzer. This study revealed the morphometric changes which affect the human mandibular nerve during the aging process.     

Radial and tibial nerve pathology of two lactating ewes with "kangaroo gait"

Radial and tibial nerves of two ewes with clinical signs of chronic "kangaroo gait" were examined by qualitative and quantitative techniques and compared to the same nerves of a clinically normal ewe in late lactation. In affected ewes, there was extensive axonal degeneration of myelinated fibres in the radial nerve. Large and small myelinated fibres were affected equally and unmyelinated fibres were normal. Nerve fibre regeneration was present. In contrast, tibial nerve changes in the "kangaroo gait" ewes were minimal. The chronic nature of the radial nerve pathology was consistent with the clinical time course of "kangaroo gait". Regeneration may account for gradual improvement with eventual recovery in most chronically affected ewes. An episode of bilateral severe compression of a proximal radial nerve site is proposed as an explanation for the neuropathy, although the specific mechanism of this trauma is not known.     

Morphology of human intracardiac nerves: an electron microscope study

Since many human heart diseases involve both the intrinsic cardiac neurons and nerves, their detailed normal ultrastructure was examined in material from autopsy cases without cardiac complications obtained no more than 8 h after death. Many intracardiac nerves were covered by epineurium, the thickness of which was related to nerve diameter. The perineurial sheath varied from nerve to nerve and, depending on nerve diameter, contained up to 12 layers of perineurial cells. The sheaths of the intracardiac nerves therefore become progressively attenuated during their course in the heart. The intraneural capillaries of the human heart differ from those in animals in possessing an increased number of endothelial cells. A proportion of the intraneural capillaries were fenestrated. The number of unmyelinated axons within unmyelinated nerve fibres was related to nerve diameter, thin cardiac nerves possessing fewer axons. The most distinctive feature was the presence of stacks of laminated Schwann cell processes unassociated with axons that were more frequent in older subjects. Most unmyelinated and myelinated nerve fibres showed normal ultrastructure, although a number of profiles displayed a variety of different axoplasmic contents. Collectively, the data provide baseline information on the normal structure of intracardiac nerves in healthy humans which may be useful for assessing the degree of nerve damage both in autonomic and sensory neuropathies in the human heart.     

The projection of splanchnic afferents on the cerebellum of the cat

1. The projections of the ipsilateral and contralateral splanchnic nerves on the cerebellum were studied in cats under sodium thiopentone anaesthesia.2. The splanchnic nerves were electrically stimulated. Evoked potentials and single unit discharges were recorded by means of 2.5 M-NaCl-filled glass micropipettes. A responsive region was found in the intermediate cortex of lobules Vb to f of the anterior lobe.3. The Agammadelta fibres of the splanchnic nerve had a bilateral cerebellar representation. The Abeta fibres were represented only on the ipsilateral side.4. At the level of the upper cervical spinal cord, fibres from the ipsilateral splanchnic nerve were conveyed in both the dorsal and lateral funiculi; fibres from the contralateral nerve were restricted to the ipsilateral lateral funiculus.5. On the basis of the characteristic potential fields generated in the cerebellar cortex, it is concluded that the majority of the splanchnic afferents studied terminate in the cerebellum as climbing fibres. A few responses of short latency may have been due to a mossy fibre input.6. In interaction experiments, a conditioning stimulus to one splanchnic nerve depressed the response to stimulation of the other nerve for up to 80-100 msec, the effect being most pronounced at 40-50 msec. During this period, spontaneous activity of the cerebellar unit was also suppressed.7. The organization of the splanchnic pathways to the cerebellum and their terminal connexions are discussed.     

Properties of afferent nerve fibres supplying the saphenous vein in the cat.

1. We examined the responses of primary afferent neurones supplying a vascularly isolated segment of the saphenous vein to mechanical and chemical stimuli in anaesthetized cats. Activity was recorded from centrally cut axons of afferent nerve fibres which were isolated from the saphenous nerve near its junction with the femoral nerve. 2. A total of thirty units responded to one of these stimuli and twenty-three of them were activated by local mechanical stimulation of the venous wall. Most receptive fields were circular spots. The response of the isolated venous segment to distension was tested in fifteen out of thirty units and eight out of fifteen were activated. Intravasal threshold pressures inducing discharges were in the range of 35-250 mmHg with a mean of 120 mmHg. 3. Twenty-seven out of the thirty units were tested for both mechano- and chemosensitivity. Thirteen were classified as A fibres and fourteen as C fibres with conduction velocities of 5-30 m s-1 and less than 2.5 m s-1 respectively. Twenty fibres (12/13 A, 8/14 C) were mechanosensitive. Two-thirds of the mechanosensitive A (8/12) and all of the mechanosensitive C fibres (8/8) responded to at least one of the chemical stimuli used: hypertonic saline, bradykinin (BK) or capsaicin. 4. The remaining seven units (6 C, 1 A) were activated by injection of BK into the isolated venous segment but failed to respond to mechanical stimuli. Six were found during five experiments in which BK was used as a search stimulus. Injection of bradykinin into the isolated venous segment repeatedly induced an increase in systemic blood pressure. 5. The proportion of unmyelinated fibres responding to mechanical stimulation of the venous segment was systematically examined in three experiments and amounted to about 1% of the unmyelinated afferents in the saphenous nerve. 6. In conclusion, a small proportion of afferent nerve fibres in the saphenous nerve responds to presumably noxious mechanical and/or chemical stimuli applied to the saphenous vein. These fibres, together with some chemospecific venous afferents, may be capable of encoding nociceptive information from the vein especially under pathological conditions.