Modifications in the type distribution of muscle fibers induced by repeated local freezings the rat sciatic nerve]

In the Rat, after a localized freezing of the sciatic nerve inducing a complete denervation of the medial head of the gastrocnemius muscle, the reinnervation took place within 16-18 days under our experimental conditions. After only one freezing, a limited and stable "type-grouping" of muscle fibres is observed from 30 to 360 days. After 2 to 5 freezing repeated every three weeks, the muscular changes observed one month after the last freezing are much more pronounced than when only one freezing is performed. These changes consist of a progressive increase in the number of type I and type II C fibres. This transformation is not stable: 3 months after the 3rd freezing, the muscle pattern does not differ from that which is noted after a single freezing.     

The conduction velocity, number, and diameter of unmyelinated fibers in Remak's nerve

Remak's nerve in the chicken was examined ultrastructurally and electrophysiologically to determine the characteristics of fibers in the nerve trunk. The ration of unmyelinated fibers to myelinated ones was 111:1. The mean number of unmyelinated fibers was 3555 plus/minus 232 (SEM, n=5) and they had a mean diameter of 0.502 plus/minus 0.034 (SEM) micron. The compound action potential consisted almost entirely of a large diphasic waveform which had a mean peak conduction velocity of 0.62 plus/minus 0.031 (SEM, n=5) m.s-1 at 37 degrees C.     

The conduction velocity,number and diameter of unmyelinated fibers in Remak's nerve

Summary Remak's nerve in the chicken was examined ultrastructurally and electrophysiologically to determine the characteristics of fibers in the nerve trunk. The ratio of unmyelinated fibers to myelinated ones was 1111. The mean number of unmyelinated fibers was 3555±232 (SEM, n=5) and they had a mean diameter of 0.502±0.034 (SEM) m. The compound action potential consisted almost entirely of a large diphasic waveform which had a mean peak conduction velocity of 0.62±0.031 (SEM, n=5) m·s^–1 at 37°C.     

Geschwindigkeit der Nervenleitung innerhalb der Netzhaut

Summary The conduction velocity of the unmyelinated portion of the optic nerve fibres within the cat's retina was measured by shifting a microelectrode from the blind spot outwards and stimulating antidromically in the lateral geniculate body. The mean conduction velocities were 2.8 m/s for the fast, and 1.7 m/s for the slow group of optic nerve fibres, as compared with maxima of 70 and 23 m/s respectively for the same groups in the myelinated extrabulbar portion.     

Changes in gastric parietal cells during prolonged intermittent corticosteroid treatment

Summary Immature A/J mice were treated for up to 7 weeks with intermittent doses of triamcinolone hexacetonide and were thereafter allowed to recover for 7 weeks. Structural examinations and morphological measurements were performed on the parietal cells in the gastric mucosa. By the 3rd injection a significant decrease was noted in the number of the above cells—a feature that lasted throughout the experimental period. In contrast, the diameter of the parietal cells increased. However, following recovery, the latter returned to their normal size.The authors wish to thank Mrs M. Brenman for her excellent technical assistance.     

Endothelial nerve fibres in the cornea of the frogRana ridibunda

Summary The ultrastructural study of the frog cornea revealed the existence of intraendothelial nerve fibres. These nerve fibres are unmyelinated elements but surrounded by cytoplasmic lamellae of Schwann cells.Supported by D.C.I.N.P. Grant 78-77.     

Elemental distribution of Na,P, Cl and K in different structures of myelinated nerve ofRana esculenta

Summary Measurements of the distribution of Na, P, Cl and K were performed in different structures of the myelinated nerve. Whereas the axon shows a typical intracellular distribution pattern for Na, Cl and K, the interstitial space and the myelin sheath show a typical extracellular pattern. These measurements have demonstrated that Na is present in the myelin sheath close to the node of Ranvier.     

Elemental distribution of Na, P, Cl and K in different structures of myelinated nerve of Rana esculenta.

Measurements of the distribution of Na, P, Cl and K were performed in different structures of the myelinated nerve. Whereas the axon shows a typical intracellular distribution pattern for Na, Cl and K, the interstitial space and the myelin sheath show a typical extracellular pattern. These measurements have demonstrated that Na is present in the myelin sheath close to the node of Ranvier.     

An analysis of the distribution of the myelinated nerve fibers in the optic fascicle of a beagle dog

The composition of both optic fascicles of a Beagle dog was studied in topographically oriented, semithin transections of whole nerve stained with toluidine blue. About 165,000 myelinated fibers were present in each nerve, their maximum caliber reaching 11 micron; large, less densely arranged fibers occurred especially in the dorso-temporal region.     

Formation of cutaneous nerve trunks in the chick. Ultrastructural and quantitative analysis]

In chick skin structuration of nervous trunks takes place at 14-15 days of incubation, at the time of formation of the adult pattern of cutaneous innervation. At this same stage, myelogenesis begins, but develops mainly after hatching: only 4% of axons are myelinated at hatching, 40% in 6-week old Chickens and 60% in adults. This "critical" stage (14-15 days of incubation) apparently corresponds to the stabilization of cutaneous nerve supply.     

Prostaglandin E2 increases mechanically evoked potentials in the peripheral nerve

Summary Subdermal injections of PGE₂ (5 g) in the rat foot lead to increases in the potentials evoked in sensory nerve branches by the mechanical stimulation of the skin. This sensitization of both A and C fibres complements the previously described hyperalgesic effects of prostaglandins of the E series.     

Interaction between bradykinin and voltage-sensitive sodium channels in myelinated nerve fibers

The effects of externally and internally applied bradykinin on the excitability of single myelinated nerve fibers were studied. External bradykinin (10 microM) slightly prolongs the action potential of a single myelinated nerve fiber; hence, when the fibers are stimulated by long-lasting pulses, this raises the frequency of repetitive firing in sensory fibers and evokes repetitive activity in motor fibers. Under voltage-clamp conditions, sodium channel inactivation is slowed, while sodium channel activation remains unaffected. Prolonged depolarization of the membrane leads to a maintained sodium current. The voltage dependence of the steady-state sodium current inactivation (h infinity) is shifted in the depolarized direction by approximately 10 mV. Internally applied bradykinin produces a frequency-dependent block of the sodium current. The phenomena described here imply that more than one site on the sodium channel is modified by bradykinin.     

Immunohistochemical localization by electron microscopy of GnRH in the median eminence of Xenopus laevis daud]

Using antibodies against mammalian LHRH with the unlabeled antibody enzyme method immunoreactive nerve fibres were localized in the median eminence of Xenopus laevis at the electron microscopic level. These fibres contain irregularly shaped neurosecretory granules with an average diameter of 890 A.     

Nerve-growth promoting action of isaxonine in rat

Summary After sciatic nerve lesion by freezing, the length of the most rapidly regenerating fibres was significantly increased by i.p. injection of isaxonine (N-isopropyl-amino-2-pyrimidine orthophosphate) in the rat. A dose-effect relationship was demonstrated. Both sensory and motor function returned earlier in treated animals.     

Nerve-growth promoting action of isaxonine in rat.

After sciatic nerve lesion by freezing, the length of the most rapidly regenerating fibres was significantly increased by i.p. injection of isaxonine (N-isopropyl-amino-2-pyrimidine orthophosphate) in the rat. A dose-effect relationship was demonstrated. Both sensory and motor function returned earlier in treated animals.     

An analysis of the distribution of the myelinated nerve fibers in the optic fascicle of a Beagle dog

Summary The composition of both optic fascicles of a Beagle dog was studied in topographically oriented, semithin transections of whole nerve stained with toluidine blue. About 165,000 myelinated fibers were present in each nerve, their maximum caliber reaching 11 m; large, less densely arranged fibers occurred especially in the dorso-temporal region.We are grateful to Dr D.C. Naylor, Mrs K. Schnider, Mr F. da Silva and Mr K. Traber for their aid.     

Zur wirkung hypertoner Lösungen auf die markhaltige Nervenfaser

Summary The effect of hypertonic solutions on the action potential of single myelinated nerve fibres is described. Hypertonicity mainly changes the duration of the action potential: Short action potentials obtained in normal Ringer's solution at room temperature are prolonged, long action potentials due to 0.1–1.0 mM NiCl₂-Ringer's solution and low temperature are shortened by hypertonicity. The changes in action potential duration are accompanied by small changes in action potential amplitude. In addition, hypertonicity reduces the depolarization produced by 20 mM KCl; inactivation of the sodium-carrying system under cathodal polarization is enhanced.

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Die Untersuchungen wurden mit Unterstützung der Deutschen Forschungsgemeinschaft ausgeführt.     

A simple silver nitrate impregnation of nerve fibres with preservation of acetylcholinesterase activity at the motor end-plate

A rapid silver nitrate impregnation of nerve fibres has been devised to maintain a histochemically detectable acetylcholinesterase activity at the motor end-plates.     

Role of grafted Schwann cells in the regeneration of intraspinal nerve fibers when peripheral nerve, skeletal muscle or submandibular gland fragments are transplanted into the spinal cord of the mouse

Small pieces of peripheral nerve, skeletal muscle or submandibular gland, taken from young or new-born mice, were grafted into the non-transected spinal cord of young albino mice, at the thoracic level, through a punctiform meningeal opening. Neighbouring intraspinal nerve fibres, severed during the grafting process, regenerate into and eventually throughout the transplants. In this regenerative process, sedentary or migrating Schwann cells of the transplants probably have a prominent influence in guiding the growth of the axonal sprouts they ensheathe and eventually myelinate.     

Schwann cell mitochondria as key regulators in the development and maintenance of peripheral nerve axons

Formation of myelin sheaths by Schwann cells (SCs) enables rapid and efficient transmission of action potentials in peripheral axons, and disruption of myelination results in disorders that involve decreased sensory and motor functions. Given that construction of SC myelin requires high levels of lipid and protein synthesis, mitochondria, which are pivotal in cellular metabolism, may be potential regulators of the formation and maintenance of SC myelin. Supporting this notion, abnormal mitochondria are found in SCs of neuropathic peripheral nerves in both human patients and the relevant animal models. However, evidence for the importance of SC mitochondria in myelination has been limited, until recently. Several studies have recently used genetic approaches that allow SC-specific ablation of mitochondrial metabolic activity in living animals to show the critical roles of SC mitochondria in the development and maintenance of peripheral nerve axons. Here, we review current knowledge about the involvement of SC mitochondria in the formation and dysfunction of myelinated axons in the peripheral nervous system.