Reiko Yokota

Schwann cell basal lamina and nerve regeneration

Nerve segments approximately 7 mm long were excised from the predegenerated sciatic nerves of mice, and treated 5 times by repetitive freezing and thawing to kill the Schwann cells. Such treated nerve segments were grafted into the original places so as to be in contact with the proximal stumps. The animals were sacrificed 1, 2, 3, 5, 7 and 10 days after the grafting. The grafts were examined by electron microscopy in the middle part of the graft, i.e. 3-4 mm distal to the proximal end and/or near the proximal and distal ends of the graft. In other instances, the predegenerated nerve segments were minced with a razor blade after repetitive freezing and thawing. Such minced nerves were placed in contact with the proximal stumps of the same nerves. The animals were sacrificed 10 days after the grafting. Within 1-2 days after grafting, the dead Schwann cells had disintegrated into fragments. They were then gradually phagocytosed by macrophages. The basal laminae of Schwann cells, which were not attacked by macrophages, remained as empty tubes (basal lamina scaffolds). In the grafts we examined, no Schwann cells survived the freezing and thawing process. The regenerating axons always grew out through such basal lamina scaffolds, being in contact with the inner surface of the basal lamina (i.e. the side originally facing the Schwann cell plasma membrane). No axons were found outside of the scaffolds. One to two days after grafting, the regenerating axons were not associated with Schwann cells, but after 5-7 days they were accompanied by Schwann cells which were presumed to be migrating along axons from the proximal stumps. Ten days after grafting, proliferating Schwann cells observed in the middle part of the grafts had begun to sort out axons. In the grafts of minced nerves, the fragmented basal laminae of the Schwann cells re-arranged themselves into thicker strands or small aggregations of basal laminae. The regenerating axons, without exception, attached to one side of such modified basal laminae. Collagen fibrils were in contact with the other side, indicating that these modified basal laminae had the same polarity in terms of cell attachment as seen in the ordinary basal laminae of the scaffolds.(ABSTRACT TRUNCATED AT 400 WORDS)

The granule-containing cell somata in the superior cervical ganglion of the rat, as studied by a serial sampling method for electron microscopy

SummaryThe surface of 4 granule-containing cells, in a cluster within the rat superior cervical ganglion, was studied by a serial sampling technique for electron microscopy. The result shows that all the 4 cells receive one, or three afferent synaptic boutons from the preganglionic fibers impinging upon their somata, and a somatic efferent synapse exists at two locations on each soma of the 2 of these cells. The postsynaptic element of the efferent synapse is observed to be represented by non-vesiculated and vesiculated segments of dendrites, soma and a possible axon collateral of the adrenergic principal neuron of the ganglion. There is a remarkably constant development of the attachment plaque between the granule-containing cells themselves, representing 1.7–2.3% of surface area for each cell. The surface area exposed to the extracellular space (covered only by a basal lamina) varies from 0.1 to 2.3% of the total perikaryal surface of the 4 cells. A tendency is noted that those cells without efferent synapses possess a more extensive area exposed to extracellular space than those forming somatic efferent synapse to the postganglionic elements.

Reciprocal synapses between cholinergic postganglionic axon and adrenergic interneuron in the cardiac ganglion of the turtle

Electron microscopy of the cardiac ganglion from normal and bilaterally vagotomized turtles revealed the occurrence of reciprocal synapses between the postganglionic cholinergic axon and the granule-containing cell (adrenergic interneuron). In the synaptic zone polarized from cholinergic to adrenergic elements, agranular intraaxonal vesicles are concentrated toward the presynaptic membrane, but no granular vesicles of the adrenergic interneuron are gathered on the postsynaptic side. In the synaptic zone polarized from adrenergic to cholinergic elements, granular vesicles are accumulated beneath the presynaptic membrane but no vesicles are associated with the postsynaptic axolemma. The membrane thickening is asymmetrical, and larger on the presynaptic than the postsynaptic side in both cases of polarization at reciprocal synapses. The intercellular cleft at the adrenergic interneuron to cholinergic axon synapse is slightly wider than that at the synapse with opposite polarity. These findings appear to provide a basis for a disinhibition device incorporated within the inhibitory feedback system of the ganglion.

Nearest-neighbor distance of intermediate filaments in axons and schwann cells

SummaryTo distinguish axons from Schwann cell processes in the denervated (Büngners bands) and reinnervated peripheral nerves, the nearest-neighbor distance of intermediate filaments (NND) was measured in axons and Schwann cells from denervated and subsequent regenerating peripheral nerves. It was revealed that the NND was much larger in regenerating axons (41.9±14.1 nm) than in Schwann cell processes (23.1±7.1 nm in regeneration and 19.7±5.8 nm in denervation).In addition, the NND was also measured in the normal adult and developing peripheral nerves, and it became clear that in all cases the NND in axons (29.0–41.9 nm) was larger than in Schwann cells (19.7–23.1 nm). Thus, it can be generally considered that the NND is larger in axons than in Schwann cells. This fact can be used for the distinction between axons and Schwann cell processes, when the latter have a profile similar to that of the former as in Büngners bands and in the regenerating nerves.

Occurrence of long non-myelinated axonal segments intercalated in myelinated, presumably sensory axons: electron microscopic observations in the dog atrial endocardium

SummaryElectron microscopy of serial sections revealed the occurrence of long non-myelinated segments in myelinated, presumably sensory axons running in the left atrial endocardium of normal adult dogs. Four such non-myelinated segments were analysed in three myelinated axons. They varied from 20 to 150 μm in length, and differed from nodes of Ranvier in being invested by Schwarm cells in the manner of unmyelinated nerve fibres. Short non-myelinated portions (20–25 μm long) were associated with a single Schwann cell, whereas the longest such segment (150 gmm) had five. The non-myelinated axonal segments were non-varicose and similar in diameter (1.2–3.0 μm) to adjacent myelinated segments, which had myelin sheaths 6–25 lamellae thick. The cytoplasm of the non-myelinated axonal segments contained numerous neurofilaments and microtubules, some mitochondria and smooth endoplasmic reticulum. The short non-myelinated segments were enclosed by perineurium, whereas the long non-myelinated segment was devoid of perineurium at its mid-portion; instead fibroblast-like cells made a loose boundary around the axon at this level. The significance of these non-myelinated segments was discussed with special emphasis on the question of whether they result from focal degeneration of the myelin sheath (demyelination) or are generally present in the preterminal regions of some axons.

Distribution of anionic sites on the basal lamina of Schwann cells

Basal laminae (BL) were separated from Schwann cells of rat sciatic nerves by means of weak sonication, and the anionic sites of the BL were demonstrated by using cationized ferritin (CF) or ruthenium red (RR). CF particles were deposited in clusters at intervals of 100-150 nm on the interstitial side of the BL facing the connective tissue, while the cellular side facing the Schwann cell plasmalemma showed only an occasional deposition of CF particles. RR-positive sites were found only on the interstitial side with a pattern of distribution comparable to that of CF-binding sites. These results indicate that the patterns of anionic site distribution are different between the inner and outer surfaces of the Schwann cell BL.

The long-term influence of decentralisation or preganglionic hypogastric nerve stimulation in vivo on the reinnervation of minced vas deferens in the guinea-pig

SummaryPrevious studies have shown that minced regenerating smooth muscle of the guinea-pig vas deferens becomes reinnervated by nerves growing in from the surrounding intact vas deferens. Using electron microscopy, we have examined the effect of altering activity in the preganglionic nerves, either by decentralisation, or by chronic stimulation of the hypogastric nerve, in vivo, on the reinnervation of regenerating smooth muscle cells. Chronic stimulation induced earlier reinnervation than that seen in unstimulated (sham-operated) or decentralised preparations; the number of nerve profiles present in four preparations stimulated for up to 7 days was approximately 10–20 times that seen in unstimulated or decentralised preparations. However, electron micrographs revealed that “empty” nerve terminals were a feature following stimulation for longer periods. Decentralised preparations showed little change of reinnervation, at least up to 7 weeks. Compensatory changes in the density of innervation were found in the unstimulated contralateral vas deferens.

Schwann cell basal lamina and central nerve regeneration

It has been demonstrated that the basal lamina scaffolds of Sehwann cells are effective pathways for regenerating peripheral nerves (Ide, et al, 1988). The present study was carried out to examine whether the Schwann cell basal laminae can be effective for regenerating fibers of the central nervous system. The rat sciatic nerve was transected for predegeneration, and after one week a part of the distal portion of the transected nerve was excised and treated several times by freezing and thawing to kill the Schwann cells. The treated nerve segment was then implanted into the spinal cord of the same animal. About 7 days after implantation, macrophages phagocytized dead Schwann cells, leaving basal lamina scaffolds of Schwann cells in the implant. Regenerating fibers entered such basal lamina scaffolds, being accompanied by cells resembling Schwann cells in appearance. After 20 days, most of the regenerating fibers were myelinated. The cells forming myelin sheaths resembled Schwann cells, being surrounded with basal laminae. Some astrocytic processes were found within the basal lamina scaffolds, enclosing one to several myelinated f~bers of the central nerve type. These findings suggest at least the possibility of the effectiveness of Schwann cell basal laminae for central nerve regeneration.