The Nerve Fiber as a System in Continuous Flow: Microcinematographic and Electronmicroscopic Demonstrations

The origin and nature of beading: a reversible transformation of the shape of nerve fibers

Nerve fibers which appear beaded (varicose, spindle-shaped, etc.) are often considered the result of pathology, or a preparation artifact. However, beading can be promptly elicited in fresh normal nerve by a mild stretch and revealed by fast-freezing and freeze-substitution, or by aldehyde fixating at a temperature near 0 degree C (cold-fixation). The key change in beading are the constrictions, wherein the axon is much reduced in diameter. Axoplasmic fluid and soluble components are shifted from the constrictions into the expansions leaving behind compacted microtubules and neurofilaments. Labeled cytoskeletal proteins carried down by slow axonal transport are seen to move with the soluble components and not to have been incorporated into and remain with, the cytoskeletal organelles on beading the fibers. Lipids and other components of the myelin sheath are also shifted from the constrictions into the expansions, with preservation of its fine structure and thickness. Additionally, myelin intrusions into the axons are produced and a localized bulging into the axon termed "leafing". The beading constrictions do not arise from the myelin sheath: beading occurs in the axons of unmyelinated fibers. It does not depend on the axonal cytoskeleton: exposure of nerves in vitro to beta, beta'-iminodipropionitrile (IDPN) disaggregates the cytoskeletal organelles and even augments beading. The hypothesis advanced was that the beading constrictions are due to the membrane skeleton; the subaxolemmal network comprised of spectrin/fodrin, actin, ankyrin, integrins and other transmembrane proteins. The mechanism can be activated directly by neurotoxins, metabolic changes, and by an interruption of axoplasmic transport producing Wallerian degeneration.

Slow pulsatile movements of Schwann cells in vitro: a time-lapse cinemicrographic study

Slow pulsatile movements of Schwann cells in vitro were studied quantitatively by using time-lapse cinemicrography. Schwann cells from peripheral nerves of 3-day-old rats were cultured in serum-free medium. Most Schwann cells showed intermittent episodes of pulsatile movement; each episode consisted of one or several contractile pulses. About half of the episodes consisted of a single pulse, and episodes with more than four pulses were rare. The average episode of activity lasted 2.6 min, while the average duration of a single pulse was 1.5 min. The mean quiescent interval between episodes of activity was 3.7 min. Some cells showed no pulsatile activity. Active cells averaged 6.6 episodes/h. The fraction of time which a Schwann cell spent in pulsatile activity varied widely, with an average of 28%. Behavior of Schwann cells in HEPES-buffered Hanks saline was generally similar to that in the complete medium. Raising K+ to 40 mM or Ca++ to 10 mM did not markedly affect the time course of the pulsatile motility, although the contractions were more vigorous in the high Ca++. Pulsatile movement was reversibly inhibited by cytochalasin B and appeared to be potentiated by drugs that disrupt microtubules.

Scar prevention in peripheral nerve surgery

Constriction of a peripheral nerve may precipitate a primary problem of prevent recovery from a pre-existing one. Any surgical technique to minimize subsequent constrictive scar formation would be advantageous. In this study, using rat femoral nerves, various modes of protection were evaluated. Wrapping the nerve with free fat seemed to offer the best prophylaxis.

Electrically-induced mechanical activity of the isolated guinea-pig sciatic nerve. Influences of calcium and anoxia

The electrically-induced motility of isolated segments of guinea-pig sciatic nerves is reported. This motility was characterized by waves of tensional variations. The removal of Ca2+ from the suspending solution, the addition of EDTA as well as anoxia, resulted in a decrement of tension accompanied by a prolonged duration of the cycles of mechanical activity.

Neuronal dynamics and axonal flow: axonal peristalsis

By time-lapse, phase-contrast cinemicrography of sensory nerve fibers of young mice, isolated with their originating spinal ganglia in nutrient solution, the postulated peristaltic surface drive of the cellulifugal propulsion of the semisolid axonal column at a rate of the order of 1 mm/day (1 mum/min) could be verified and quantitatively analyzed. The pulse waves follow each other at about 30-min intervals, regardless of whether the continuity of the axon is preserved or disrupted by degenerative fragmentation. Even when the axonal flow is obstructed, surface peristalsis continues.

Movement of choline acetyltransferase in axons disconnected from their cell bodies

1. Phrenic nerves of rats were cut out and divided into two parts of equal length, one proximal and one distal. The activity of choline acetyltransferase of the two pieces was estimated. Four groups of rats were studied: (1) normal rats, and rats in which 3 days earlier, (2) the right nerve had been cut in the uppermost part of the thorax, (3) a ligature had been tied round the right nerve just above the diaphragm, and (4) these two procedures had been combined.2. In normal rats the activity of the enzyme was about the same in proximal and distal pieces. Ligation of the nerve caused an increase of the activity, of about 50%, in the distal but not in the proximal segment.3. After section of the nerve the activity below the section was 18% of normal in the proximal, and 9% in the distal piece.4. When the nerve was both cut and tied the activity decreased to the same level in both pieces, and this was about the level of the proximal piece after mere section of the nerve.5. It is concluded that choline acetyltransferase can move for some time along the axons to the nerve terminals even when the connexion with the soma has been interrupted.

A neuropathy in goats caused by experimental coyotiool (Karwinskia humboldtiana) poisoning. IV. Light and electron microscopic lesions in peripheral nerves

Lesions in peripheral nerves from 12 goats poisoned experimentally with coyotillo were studied by light and electron microscopy. The goats were poisoned with daily oral doses of the ground coyotillo fruits and killed at various times after the first day of dosing.

Lesions at a mid-femoral site of the sciatic nerve included swelling of Schwann cells, degeneration of mitochondria, depletion of glycogen, splitting of myelin, segmental demyelination, and Wallerian degeneration. The results were suggestive of primary mitochondrial injury in Schwann cells with resultant impaired active transport, intracellular edema, splitting of myelin, and segmental demyelination.

The organization of synaptic axcplasm in the lamprey (petromyzon marinus) central nervous system

The fine structure of synapses in the central nervous system of lamprey (Petromyzon marinus) ammocoetes has been investigated. Both synapses within the neuropil and synaptic links between giant fibers (including Müller cells) and small postsynaptic units are described. The distribution of neurofilaments and microtubules in nerve profiles over a wide diameter range is described, and the possible role of these structures in intracellular transport is discussed. Electron micrographs indicate that small lucent "synaptic vesicles" occur sparsely throughout the axoplasm and in regular arrays in association with microtubules in the vicinity of synapses. Within a synaptic focus, immediately adjoining the presynaptic membrane, vesicles are randomly arranged and are not associated with microtubules. Neurofilaments are present, generally in large numbers, but these are not associated with vesicles or other particulates. The structural findings are considered in terms of current concepts of fast and slow transport in neurons and the mechanochemical control of intracellular movement of materials.

Brain monoamine oxidase in mice after exposure to aggression and defeat

Effects on the monoamine Oxidase activity of the hypothalamus, amygdala, and frontal cortex of untrained mice exposed to repeated defeat by trained fighters for two 5-minute periods a day for 0, 1, 2, 4, 8, 14, or 20 days were studied. Activity in the hypothalamus increased significantly during the first 2 days of fighting, while the activity in the amygdala and frontal cortex remained essentially unchanged. After 8 days, activity in all three brain areas declined. After 14 days of fighting the monoamine Oxidase activity returned to normal, but another decrease was observed in the three areas after 20 days of fighting.

Novas observações sôbre as fibras nervosas que repopulam o segmento distal de nervos com mais de seis meses de secção completa

Com base em dados experimentais, publicados em trabalhos anteriores, são apresentados e discutidos, aspectos histológicos que, analisados em seqüência (figs. 1 a 8), sugerem uma possível via de reorganização progressiva com conseqüente regeneração de fibras nervosas, nos segmentos intermédio e distal de nervos, completamente separados por transecção, entre si e do côto proximal, há mais de seis meses, mas mantidos em seus leitos conectivos naturais.

Pulsatile and myelin-forming activities of Schwann cells in vitro

1. Sympathetic and dorsal root ganglia from young mice and new-born rats were cultured in vitro. The activity of the outgrowing Schwann cells was studied with time-lapse photography.2. Schwann cells exhibited a pulsatile activity with a contraction rate varying from 1 to 12 min. The occurrence of pulsations depended on the mode of attachment of cells to their surroundings.3. Fibres of various materials were introduced into the cultures in an attempt to simulate conditions obtaining in vivo. Schwann cells attached themselves to these fibres and rotated about them depositing myelin. Polarized light and histochemical studies showed that myelin was formed as early as four days in vitro.4. The possible significance of the behaviour of Schwann cells in vitro is discussed.

Demonstration of axonal flow by the movement of tritium-labeled protein in mature optic nerve fibers

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