Non-myelinated Nerve Fibres Research Articles

Ultrastructure of the rat pineal stalk.

The ultrastructure of the rat pineal stalk was described. The pineal stalk contained few pinealocytes, glial cells and numerous nerve fibers. The last were mostly non-myelinated axons, although a few myelinated ones were also observed. Glial cells showed many filaments, mostly in the processes which presented a longitudinal orientation. Other more lamellar processes were found enclosing the axons. The pineal stalk became wider as it reached the body of the gland. Ultrastructurally, this wide region resembled more the pineal body. Bundles of non-myelinated nerve fibers were seen around the pineal stalk.

Freeze-fracture electron microscopy of non-myelinated nerve fibres in the human dental pulp

Freeze-fracture replicas from the subodontoblast region gave a good three-dimensional comprehension of the structure of non-myelinated nerve fibres. Each Schwann cell ensheathed 1–15 axons with a mean diameter of 0.4 μm (0.1–1.2 μm). Many axons were not entirely ensheathed but were exposed to the extracellular space to various degrees. Tightening membrane specializations were not found in the mesaxons. The Schwann-cell plasmalemma exhibited caveolae with necks surrounded by evenly-sized intramembranous particles, typical of endocytosis. The nuclear envelope of Schwann cells showed a few typical pores and perinuclear cisterna. In tangential fractures, the axolemma displayed intramembranous particles evenly distributed over the axolemmal fracture planes. There was a marked difference in particle density between the P (600–650/μm 2) and E (150–200/μm 2) faces.

Skin biopsy as a beneficial procedure for morphological evaluation of diabetic neuropathy.

In an attempt to evaluate the morphological abnormalities of dermal non-myelinated nerve fibers of diabetics and elucidate the pathogenesis of diabetic peripheral neuropathy, the terminal part of peripheral nerve in the upper dermis was observed on electron microscopy using skin samples biopsied in 10 diabetics with symptomatic neuropathy and 6 age-matched controls. In diabetics, the density of nerve fibers was significantly lower than in controls. In addition, swelling, lytic change and vacuolation in the axon, multiplication of basement membrane of the Schwann cell and Schwann cell cluster devoid of axon were more frequently observed in diabetics. The Schwann cell did not show significant structural alterations. These findings suggest that the axon is primarily involved, at least in the terminal region of nerve fiber, in diabetic peripheral neuropathy. It is also concluded that the skin biopsy technique is harmless, cosmetically not troublesome and might be beneficial for studying peripheral neuropathies including diabetic neuropathy.

Involvement of intracellular calcium in the phosphate efflux from mammalian nonmyelinated nerve fibers.

Phosphate efflux was measured as the fractional rate of loss of radioactivity from desheathed rabbit vagus nerves after loading with radiophosphate . The effects of strategies designed to increase intracellular calcium were investigated. At the same time, the exchangeable calcium content was measured using 45Ca. Application of calcium ionophore A23187 increased phosphate efflux in the presence of external calcium in parallel with an increase in calcium content. In the absence of external calcium, there was only a late, small increase in phosphate efflux. For nerves already treated with the calcium ionophore, the phosphate efflux was sensitive to small changes in external calcium, in the range 0.2 to 2 mM calcium, whereas similar increases in calcium in absence of ionophore gave much smaller increases in phosphate efflux. Removal of external sodium (choline substitution) produced an initial increase in phosphate efflux followed by a fall. The initial increase in phosphate efflux was much larger in the presence of calcium, than in its absence. The difference was again paralleled by an increase in calcium content of the preparation, thought to be due to inhibition of Na/Ca exchange by removal of external sodium. Measurements of ATP content and ATP, ADP, phosphate and creatine phosphate ratios did not indicate significant metabolic changes when the calcium content was increased. Stimulation of phosphate efflux by an increase in intracellular calcium may be due to stimulation of phospholipid metabolism. Alternatively, it is suggested that stimulation of phosphate efflux is associated with the stimulation of calcium efflux, possibly by cotransport of calcium and phosphate.

The effect of some new aminopyridines on mammalian non-myelinated nerve fibres

We evaluated the action of 2,4-, 3,4-diaminopyridine and 3-[(dimethylamino)carbonyl]amino,4-aminopyridine (LF-14) on non-myelinated fibres of the guinea-pig vagus nerve. The amplitude and duration of the compound action potential were enhanced similarly by all of the aminopyridines. The propagation velocity of the compound action potential and electrogenic sodium pumping were not changed by the aminopyridines. The results show that 2,4-diAP and LF-14 affect non-myelinated nerve fibres of the guinea-pig in the same way as does 3,4-diAP; sodium pumping was not modified by the aminopyridines.

Effects of 4-aminopyridine on rapidly and slowly conducting axons of rat corpus callosum

The action potentials of some normal mammalian peripheral myelinated and non-myelinated nerve fibers are known to differ with respect to the role of voltage-dependent potassium currents in membrane repolarization. Because comparable differences have not been fully established for mammalian cerebral axons, the present work examined the influence of the potassium blocker, 4-aminopyridine (4-AP), on field potentials in the rat corpus callosum. Three successive negative waves could be detected in field potentials obtained with recording electrodes positioned several millimeters from the site of callosal stimulation. Spatial and functional properties of these field components indicated that the two shorter-latency waves were due to activity in callosal fibers. Furthermore, the discontinuity of the first and second waves, not only with respect to latency but also in pattern of recruitment and in refractoriness, suggested that they largely reflected activity in respective myelinated and nonmyelinated groups of callosal fibers. When 4-AP was injected into the callosum, or superfused onto surgically exposed callosal fibers, the duration and amplitude of the second negative wave were markedly increased. The first negative wave either was not affected or was reduced in amplitude by 4-AP application. This contrasting effect was identical to that known to distinguish normal myelinated and nonmyelinated mammalian peripheral nerve fibers and provided some evidence suggesting that mammalian cerebral axons have a functional organization similar to that of peripheral fibers.

Effects of the venom of the Brazilian scorpion (Tityus serrulatus) on the compound action potential of the rabbit vagus nerve fibres.

1 The effects of the venom of the scorpion (Tityus serrulatus) on nerve fibres of the rabbit cervical vagus were studied by the single sucrose-gap technique. Scorpion venom (1 microgram/ml) increased irreversibly the duration of the B component of the compound action potential of the vagus nerves, leaving the C component with its normal configuration. Tetrodotoxin (200 nM) suppressed the prolongation of the action potential duration in venom-treated B fibres. 2 At the same concentration (1 microgram/ml), scorpion venom reduced the amplitude and the rate constant of decay of the hyperpolarization produced by tetanic stimulation of non-myelinated nerve fibres. 3 A lower concentration (0.2 micrograms/ml) blocked completely the hyperpolarization of the potassium-activated response. After washing, the potassium-activated response partially recovered its amplitude but there was a significant increase in the time constant of the decay of hyperpolarization. 4 It is suggested that scorpion venom may modify the sodium pumping mechanism within fibres as well as affecting the passive and active sodium permeability systems.

Structure of the glomic arteries.

The structure of the arteries which supply blood tp the carotid bodies was examined in five cases in which the weights of the cardiac ventricles were normal and in which hypoxaemia due to emphysema or systemic hypertension were absent. The right glomic arteries were studied by light microscopy, and the left by electron microscopy. A sixth case, also free from myocardial hypertrophy, was used solely for an examination of the common carotid artery, the carotid sinus and the internal carotid artery by light and electron microscopy. The glomic arteries resembled the carotid sinus in being highly elastic with a rich supply of non-myelinated nerve fibres and thus had a structure consistent with having a baroreceptor function.

Histologic and fine-structural anatomy of the adrenorenal portal vessels in the dog.

Reflex vasoconstriction that occurs in the kidney of the dog can be the result of activation of catecholamine flow reaching the kidney directly from the adrenal medulla via adrenorenal portal vessels. This study was undertaken to learn more about the histologic and fine-structural anatomy of these unusual vessels. We found that they are thin-walled vessels (200-500 micrometers) which are accompanied by many capillaries. These portal vessels have distinctive valves and have sparse, longitudinally arranged musculature which is denser at the base of the valves. The valves in the portal vessels are arranged to permit flow in the direction from the adrenal gland toward the kidney. Smooth muscle at the base of the valve is in close proximity to non-myelinated nerve fibers, suggesting that the opening of these valves may in part be neurally mediated. These unique anatomical features distinguish the adrenorenal portal vessels from other blood vessels and likely have functional importance in control of the adrenorenal circulation.

Pulmonary and respiratory tract receptors.

Nervous receptors in the lungs and respiratory tract can be grouped into four general categories. 1. Deep, slowly adapting end-organs, which respond to stretch of the airway wall and have large-diameter myelinated fibres; those in the lungs are responsible for the Breuer-Hering reflex. 2. Endings in and under the epithelium which respond to a variety of chemical and mechanical stimuli (i.e. are polymodal), usually with a rapidly adapting discharge, and with small-diameter myelinated fibres; they are responsible for defensive reflexes such as cough and sneeze, and for the reflex actions to inhaled irritants and to some respiratory disease processes. 3. Receptors with nonmyelinated nerve fibres which, being polymodal, are stimulated by tissue damage and oedema and by the mediators released in these conditions; these receptors may be similar in function to 'nociceptors' in other viscera, and set up appropriate reflexes as a reaction to respiratory damage. 4. Specialized receptors such as those for taste and swallowing, and those around joints and in skeletal muscle. Stimulation of any group of receptors may cause reflex changes in breathing (including defensive reflexes), bronchomotor tone, airway mucus secretion, the cardiovascular system (including the vascular bed of the airways), laryngeal calibre, spinal reflexes and sensation. The total pattern of motor responses is unique for each group of receptors, although it is probably unusual for one type of receptor to be stimulated in isolation. The variety of patterns of motor responses must reflect the complexity of brainstem organization of these systems.

Varicose axons bearing "synaptic" vesicles on the basal lamina of the human seminiferous tubules.

Normal (infant and adult) and pathological testes were examined by electron microscopy in order to study testicular innervation. Nerves composed of non-myelinated fibres were abundant in the tunica vasculosa of the tunica albuginea. These nerves penetrated into the testicular septa reaching the interstitial tissue. This showed numerous non-myelinated nerve fibres running among the Leydig cells and blood vessels. Single axons or small groups of them, partially surrounded by Schwann cells, approached: 1) the Leydig cells, 2) the interstitial blood vessels, and 3) the seminiferous tubules. Single naked axons were also observed primarily in the proximity of the seminiferous tubules. These axons showed varicosities containing both small and large "synaptic" vesicles. The latter were less numerous and contained a central dense core. Small vesicles were agranular. Some varicose axons ran across the myofibroblast layer of the tunica propria reaching the basal lamina of the seminiferous tubules at the level of the Sertoli cells but not at the level of the spermatogonia. The intercellular space between Sertoli cell and axon membrane was about 150-200 nm.

Numbers and sizes of nerve fibres in mouse spinal roots.

The numbers of myelinated and non-myelinated nerve fibres in the spinal roots of one strain of mouse have been counted from electron micrographs and the accuracy of counting procedures assessed. Non-myelinated nerve fibres are present in the ventral roots at all levels though the largest number are found inthe thoracic and L1, L5, L6 and S1 ventral roots. The number is very small in L2, L3, and L4 ventral roots which are those supplying the hind limb. Fibre diameter histograms were obtained from measurements of cross sectional area for myelinated and non-myelinated fibres in L1 and L4 ventral roots. The relationship of myelin thickness to axon diameter shows that to a near approximation the myelin thickness is 1/5 to 1/4 the axon diameter. A measure of circularity was calculated, the ratio of the measured cross-sectional area to the area calculated from the measured perimeter assuming the fibre to be circular, and plotted against the axon perimeter fo L1 and L4 ventral root myelinated fibres, This showed a tendency for larger fibres to be less circular than smaller fibres.

"Extraepithelial enterochromaffin cell--nerve-fibre complexes" in the normal human appendix, and in neurogenic appendicopathy.

Extraepithelial, extraglandular endocrine cells of types EC1 and EC2 occur in the lamina propria of the normal appendix. They are more numerous in intramucosal neurogenic appendicopathy. Ultrastructurally there is invariably a close association between the cells and non-myelinated nerve fibres of the mucous plexus. Together they form a complex surrounded by a common basal lamina, and the term enterochromaffin cell-nerve fibre complex (ECC-NF) is suggested for this morphological and functional unit. The derivation of extraepithelial EC cells from the glandular epithelial cells could not be established and the existence of the complexes is held to support an origin from neuroendocrine-programmed ectoblasts.

Effects of calcium and lanthanum on phosphate efflux from nonmyelinated nerve fibers.

Phosphate efflux was measured as the fractional rate of loss of radioactivity from rabbit vagus loaded with radiophosphate. The effects of changes in extracellular calcium and of lanthanum have been investigated. In Locke solution with normal, 0.9 mM, calcium and without phosphate, the fractional rate of loss was 1.62 X 10(-3) min-1 at 120 min after the beginning of the washing period and fell slowly (9% hr-1) during washing from 2 to 6 hr. Addition of calcium to the Locke solution produced a transient increase followed by a reversible maintained increase in phosphate efflux. The latter was 40 and 75% above efflux in normal calcium for 20 and 50 mM calcium, respectively. Removal of calcium, with or without addition of EGTA, produced only a transient increase in phosphate efflux, with no subsequent maintained change. Addition of low concentrations of lanthanum produced a reversible inhibition of phosphate efflux. Half-maximal inhibition was at 3.5 micro M lanthanum and appeared to be due to binding of lanthanum to more than one, probably two, sites. Measurements of inhibition by lanthanum at different calcium concentrations did not indicate any competition between calcium and lanthanum. It is suggested that a least a part of phosphate efflux depends on internal calcium and that lanthanum acts by preventing release of phosphate from the phosphate transport mechanism.

Uptake of adenosine and release of adenine derivatives in mammalian non-myelinated nerve fibres at rest and during activity.

1. Influx of adenosine into rabbit non-myelinated nerve fibres was measured using [2-(3)H]adenosine. The uptake of radioactivity increased linearly with duration of incubation for up to 60 min and adenosine concentration up to 200 mum. The uptake at different adenosine concentrations showed a saturable component with a half-maximal activation at 17.1 mum and a linear part.2. The radioactivity taken up was rapidly incorporated into AMP, ADP and ATP. Isotopic equilibrium between the nucleotides was achieved within 15 min.3. The uptake of (3)H from 0.2 mum-adenosine was almost completely inhibited by addition of 200 mum-adenosine and to a similar extent by 200 mum-tubercidin and AMP; a 70% inhibition was found with ATP and ADP; alpha, beta methylene-ADP had no effect.4. ATP, ADP and AMP added to the extracellular medium of a desheathed vagus were slowly hydrolysed.5. In preparations loaded with [2-(3)H]adenosine and then washed with adenosine and label-free solution there was a steady efflux of radioactivity amounting to 0.18 x 10(-3)/min. Addition of adenosine or tubercidin transiently increased the efflux.6. Electrical stimulation caused an extra release of radioactivity. The extra fractional loss was 21.8 x 10(-6)/impulse in preparations that had rested for several hours; it decreased to 2.3 x 10(-6)/impulse when stimulation was applied after a 30 min rest.7. The radioactivity of the resting efflux and of the extra efflux after stimulation was found mostly in inosine and hypoxanthine; adenosine and adenine accounted for only 3%, and the nucleotides for less than 1% of the efflux.8. Adenosine added to the external medium of a desheathed nerve was slowly deaminated.9. It is concluded that inosine and hypoxanthine found in the effluent from desheathed vagus nerve trunk result from release of these compounds from nerve fibres and not from extracellular breakdown of released ATP or adenosine.10. Electrical activity in non-myelinated nerve fibres of the nerve trunk thus causes the release of metabolites (inosine and hypoxanthine) together with small amounts of adenosine and adenine, while release of ATP and other nucleotides is almost completely absent.

Hilus cells from human postmenopausal ovaries: gonadotrophin sensitivity, steroid and cyclic AMP production.

Strips of ovarian hilar tissue taken from 11 post-menopausal women were examined histologically and found to contain clusters of hilus cells in contiguity with non-myelinated nerve fibers. No other steroidogenically active structures were found. Specimens from these strips were incubated for 30 and 240 minutes in Krebs bicarbonate buffer containing 5.5 mM glucose and 1% bovine serum albumin. The specimens produced measureable amounts of androstenedione, estradiol-17 beta and progesterone in vitro. The major steroid formed was androstenedione, and this pattern of steroidogenesis appeared similar to that of postmenopausal ovarian stroma. However, the amounts of steroids formed were considerably higher than in stromal tissue. This implies that the hilus cells possibly may be of greater importance, qualitatively, than the stroma cells for steroidogenesis in the postmenopausal ovary. Addition of hCG to the incubated specimens elicited increase in both cyclic AMP formation and steroid synthesis, especially of estradiol-17 beta, indicating a preserved responsiveness to gonadotrophin in hilus cells from postmenopasual ovaries.

Morphological studies on the vomeronasal organ in the golden hamster.

Morphological features of the vomeronasal organ in the golden hamster were examined by light and electron microscopy. This organ consisted of a 7 mm long tubular structure situated bilaterally in the anteroventral nasal septum and enclosed completely by a bony capsule. Posteriorly it ended blindly, whereas anteriorly it communicated with the nasal cavity through an orifice at its rostral end. The sensory epithelium lining the medial wall of the lumen of this organ showed a cell configuration similar to that of the olfactory epithelium except the basal cells. Free surface of the sensory cells in the sensory epithelium was covered with structures intermediate between cilia and microvilli. Capillaries often penetrated into the sensory epithelium, and the vomeronasal nerve observed under the sensory epithelium consisted of nonmyelinated nerve fibers. The respiratory epithelium lining the lateral wall of the lumen of this organ was typically ciliated and pseudostratified, devoid of goblet cells. Mucous and serous acini of Jacobson's glands were distributed on the dorsolateral and ventromedial sides of the lumen. The glands were PAS-positive, different from alcian blue-positive olfactory glands of Bowman. Myelinated and nonmyelinated nerve fibers were often distributed among the acini.

Ultrastructural observations on the central innervation of the guinea-pig pineal gland.

In the present study the central innervation of the guinea-pig pineal gland was investigated. The habenulae and the pineal stalk contain myelinated and non-myelinated nerve fibres with few dense-cored and electron-lucent vesicles. Some myelinated fibres leave the main nerve fibre bundles, lose their myelin-sheaths and terminate in the pineal gland. Although direct proof is lacking, the non-myelinated fibres appear to end near the site where the bulk of the myelinated fibres are located. Here a neuropil area exists where synapses between non-myelinated fibre elements are abundant. Neurosecretory fibres were also seen. The results support the concept of functional interrelationships between hypothalamus, epithalamus and the pineal gland.

The nature of atrial receptors responsible for the increase in urine flow caused by distension of the left atrium in the dog.

In dogs anaesthetized with alpha-chloralose the effects of distension of a large balloon in the lumen of the left atrium on the discharge of action potentials in vagal fibres and on urine flow were studied with the cervical vagi cooled at 18 and 12 degrees C. Distension of the balloon in seven dogs resulted in an increase in urine flow. Cooling the cervical vagi to 18 degrees C reduced the response to 70% of that obtained at 37 degrees C, and at 12 degrees C the response was reduced to 28%. In a second group of dogs, the effect of distension of the balloon on atrial receptors which discharged into myelinated nerve fibres of the vagi, i.e. Paintal type A and type B receptors, was examined. The increase in the activity of these receptors was reduced to 68% when the vagus nerve was cooled to 18 degrees C and was reduced further to 25% at 12 degrees C., In a third group of dogs, the effect of distension of the balloon on receptors which discharged into non-myelinated nerve fibres in the vagi was examined. Cooling of the cervical vagi also reduced the evoked increase in activity in these fibres; this reduction in activity occurred over a wider range of temperature, unlike the effect of cooling on the response in myelinated vagal fibres. It is concluded that the increase in urine flow caused by distension of a balloon in the left atrium is mediated solely by the Paintal-type atrial receptors which discharge into the myelinated fibres in the vagi.

Myelinated nerve fibers in the parathyroid gland of the dog: a light and electron-microscopic study.

The distribution of myelinated and non-myelinated nerve fibers in the parathyroid glands of the dog was studied by light and electron microscopy. The mixed fasciculi with myelinated nerve fibers (average diameter 7.0 micron) and unmyelinated fibers were present independent of the adventitia of the arterioles. The mixed fasciculi were accompanied by large amounts of collagen fibrils running in the direction of the nerve fibers. The fasciculi were surrounded by a complete sleeve composed of a perineural epithelial sheath which a basal lamina on both sides. The possibility that these fibers might represent an afferent pathway is discussed.