An electron microscopic study of the early changes proximal to a constriction in sympathetic nerves

Abstract

The ultrastructural changes, proximal to a constriction, in unmyelinated postganglionic sympathetic axons have been studied in the cat splenic and hypogastric nerves. They were con stricted with a fine ligature, which was left in situ , and examined at intervals up to 24h after operation. Immediately after tying the ligature there were definite changes in the morphology and organelle content of the axons adjacent to the constriction. These were due to the mechanical trauma produced by tying the ligature. From 10 min onwards there was a rapid accumulation of organelles in axons, which became progressively more swollen. Eventually the plasma membranes of both axons and Schwann cells broke down and later the Sclrwann cell basement membrane ruptured , allowing axonal organelles to escape into the interstitial spaces. The accumulating organelles included vesicles with an electron dense core, mitochondria, large vacuoles and myelin figures. Filamentous structures and both fine and wide tubules were more prominent and more numerous after operation. These were accompanied by a marked increase in the number of agranular vesicles. Tubular structures, morphologically similar to both the agranular vesicles and the vacuoles, were also very numerous. This similarity in appearance and the fact that many of these agranular vesicles, vacuoles and tubules were found joined together by either filaments or fine tubules suggests that they are part of the same system . At all times the greatest accumulation of organelles and the most marked axonal swelling was found in the first 0.5 to 1 mm segment of nerve immediately adjacent to the constriction. Less marked changes, affecting principally the agranular vesicles and finer tubules to gether with focal accumulations of mitochondria were seen at more proximal levels from 4h onwards. It is suggested that the axonal swelling is due to the accumulation of axoplasm and organelles. Two possible interpretations are discussed: (1) that this represents the effects of obstructing the normal flow of axoplasm from the cell body to the periphery, and (2) that some features, in particular the increase in the size and number of the various tubules may be indicative of an active reaction to the effects of axonal injury. These two phenomena probably take place simultaneously and are accompanied by degenerative changes.

Nerve growth factor induces volume increase and enhances tyrosine hydroxylase synthesis in chemically axotomized sympathetic ganglia of newborn rats.

“…As shown in Table 1, treatment with NGF alone produced a 4-fold increase in TH activity, demonstrating that the response to NGF is not confined to the adrenergic cell body but also involves the peripheral parts of the adrenergic neurons. In contrast to the superior cervical ganglion, the effect of combined treatment with NGF and 6-OHdopamine did not differ from that with 6-OHdopamine alone, i.e., the (22,23). The striking increase of TH in the rat sympathetic ganglia after combined treatment with NGF and 6-OHdopamine, as opposed to the severe reduction of this enzyme in peripheral tissues, demonstrates that the selective effect of NGF on this enzyme in the cell body and axons is also increased by concomitant administration of 6-OHdopamine.…”

Morphology and serotonergic innervation of physiologically identified cells of the guinea pig's myenteric plexus

“…It now seems likely that these structures are not specialized nerve terminals but retraction bulbs formed by the resealing of the cut ends of damaged fibers. In electron micrographs of these structures filled with HRP, an accumulation of organelles and smooth membranous elements is found and is identical in appearance to that of the proximal stumps of axons constricted in order to interrupt axonal transport (Kapellar and Mayor, 1969). In fact, electron microscopy made it evident that considerable damage is done to the input to myenteric ganglia in the preparation and the immobilization of the myenteric plexus for intracellular recording.…”

Axonal transport of noradrenaline, protein and glycoprotein in cat hypogastric nerves in vitro under conditions of high extracellular glucose

“…The hypogastric nerves of the cat comprise about 85% non-myelinated fibres, a large proportion of which contain accumulated noradrenaline after constriction [12,13,22]. The remainder are myelinated fibres which would not be expected to arise from cell bodies in the inferior mesenteric ganglion since decentralisation of the ganglion causes these fibres to degenerate [22].…”