Degeneration of axons in the ureteric and duodenal nerve plexuses of the adult rat following in vivo treatment with capsaicin.

The fine structure of the ureteric and duodenal nerve plexuses was studied in specimens taken from adult rats 24 h after subcutaneous injection of 50 mg/kg capsaicin and in specimens taken from rats injected with the vehicle used to emulsify the capsaicin. In specimens from capsaicin-treated rats, there was extensive degeneration of axons in the ureteric plexuses and widespread, but much smaller amounts of degeneration of axons in the duodenal plexuses. Comparison of the fine structure of the plexuses in the capsaicin-treated rats with that of the plexuses in the control rats indicated that the degeneration was confined to axons with terminals containing mainly large dense-cored vesicles.

Effect of capsaicin on the intraperitoneal axons of the rat trachea.

In vitro exposure of specimens of rat trachea to capsaicin at a concentration of 2 x 10(-4) g/ml was followed by a significant increase in the diameter and major changes in the vesicle content of intraepithelial axons with terminals containing a high proportion of large dense-cored vesicles and only scattered small vesicles, but had no effect on axons with terminals containing large numbers of closely-packed small vesicles. Twenty-four hours after in vivo treatment of rats with capsaicin at dose levels of 50 mg/kg, there was a highly significant reduction in the number of axons/unit length in the tracheal epithelium. This was attributed to similar patterns of degeneration of axons with terminals containing a high proportion of large dense-cored vesicles to those seen in the ureter and to the early elimination of the degenerating axons by phagocytosis by the epithelial cells.

Effect of 5-hydroxydopamine on the large dense-cored vesicles in the axon terminals of the myenteric ganglia of the guinea-pig stomach.

Quantitative ultrastructural analysis revealed that the large dense-cored vesicles in the axon terminals in the myenteric ganglia of the guinea-pig stomach tend to be concentrated towards the ends of the terminals. In guinea-pigs treated with 50 mg/kg 5-hydroxydopamine, diameters of the vesicles were increased and their distribution in the terminals was altered. Treatment with reserpine prior to 5-hydroxydopamine increased the proportion of large dense-cored vesicles and decreased the overall number of vesicles in the terminals. The diameter of the vesicles was increased both in the terminal profiles and in the non-terminal segments of the axons. These observations are consistent with the view that uptake of 5-hydroxydopamine into small vesicles is followed by their transformation into large dense-cored vesicles.

Distribution and diameter of large dense-cored vesicles in axon terminals in the myenteric ganglia of the mouse and hamster stomach.

The distribution and diameter of the large dense-cored vesicles in axon terminals in the myenteric ganglia of the mouse and hamster stomach were analyzed in electron micrographs of groups of 150 terminal profiles. In the mouse, the vesicles were proportionately more numerous and larger than in the hamster; they were also larger in terminal profiles containing more than 20% of the vesicles. There was no evidence of bimodality of the distribution curve of the proportion of large dense-cored vesicles/profile in either animal. The presence of a significant degree of skew of the distribution curves was indicative of uneven distribution of the vesicles in the terminals, and the occurrence of a significant inverse correlation between the proportion of large dense-cored vesicles/profile and both the diameter of the profiles and the total number of vesicles/profile was in agreement with subjective evidence of a tendency towards accumulation of the vesicles at the ends of the terminals.

Parameters of fixation of the putative pain afferents in the ureter: preservation of the dense cores of the large vesicles in the axonal terminals.

A study has been undertaken of the effects of a number of fixation procedures on the appearance of axons in the ureteric plexuses of the rat, and especially on the appearance of the dense-cored vesicles in those axons which have recently been characterized as pain afferents. Terminals were readily identified in material fixed by perfusion with glutaraldehyde, and many of them contained few if any vesicles. After fixation by immersion in cold glutaraldehyde terminals were not easy to identify because of the loss of microtubules. Immersion fixation in glutaraldehyde produced changes in the number and distribution of the vesicles in the axons which accentuated the similarity of the 'vesicle-containing regions' to the terminals of so-called 'purinergic' axons. Few of the dense-cored vesicles seen in glutaraldehyde-fixed material were preserved by fixation in permanganate, osmium or paraformaldehyde. The way dense-cored vesicles were or were not preserved by the various fixatives used indicated major differences between such cores and those of the vesicles in adrenergic axons. There was also evidence from the study of osmium-fixed material that both the number and appearance of the vesicles can be affected by the type of buffer used: the presence of more vesicles after fixation in osmium buffered with veronal than after osmium buffered in other ways was attributed to the membrane-stabilizing properties of veronal.

On the calibre of the ureteric lumen.

The cross sectional appearances of the lumen of rat ureter were compared in specimens fixed by perfusion and by immersion and processed for electron microscopy. After efficient perfusion fixation in untreated animals, and in animals previously injected with 6-hydroxydopamine, there was substantial dilatation of the ureter, and the lumen was approximately circular in section. In inadequately perfused and immersion-fixed material the lumen was usually narrowed, and was either slit-like or stellate in appearance. Ultrastructural examination indicated that closure of the lumen was accompanied by the development in the cells of the muscle coat of the features usually associated with contraction, and the possibility that the appearance of the ureter in well perfused specimens approximated to its state in vivo was discussed.

Generalised smooth-muscle disease with defective muscarinic-receptor function.

A patient with widespread smooth-muscle disease presented with chronic intestinal pseudo-obstruction but had in addition defects of the bladder, pupils, sweating, and cardiovascular function. There was no evidence of a primary neural lesion, and minor changes in the muscle did not resemble those of a myopathy. In each organ affected muscarinic cholinergic function was at fault, but instead of supersensitivity to cholinergic drugs, which occurs in postganglionic autonomic neuropathies, there was a lack of response to cholinergic drugs and anticholinesterases. It was therefore concluded that the patient had a new type of defect of muscarinic-receptor function. The cause was unknown, but it may have been an autoimmune disease resembling myasthenia, in which there is a postjunctional defect of muscarinic receptors. In similar cases binding of muscarinic agonists and antagonists should be tested. When antibodies to purified human muscarinic receptors become available different patterns of smooth-muscle defect may be identifiable, enabling the lesion to be defined more precisely.

Ultrastructure of the perivascular nerve plexuses of the rat pancreas.

The fine structure of the arteriolar perivascular and capillary nerve plexuses of the pancreas was studied in the rat. In perfusion-fixed control specimens, occasional profiles which contained accumulations of large dense-cored vesicles and numerous profiles which contained mainly small vesicles were seen in sections of the nerves. Counts of degenerating axons in specimens from rats treated with 6-hydroxydopamine and of profiles in which the small vesicles contained dense cores in specimens fixed by immersion after incubation in buffer indicated that the arteriolar perivascular plexus contains much larger numbers of adrenergic axons than the plexus associated with the capillaries. The presence in specimens fixed by immersion after incubation in buffer containing 5-hydroxydopamine of a considerable increase in the percentage of profiles in which the small vesicles contained dense material indicated that the plexuses contain a second type of axon capable of taking up 5-hydroxydopamine. Profiles in which all of the small vesicles remained clear after incubation in 5-hydroxydopamine were regarded as sections through cholinergic axonal terminals. Such profiles were most numerous in the capillary plexus.

Axonal terminal ultrastructure in the myenteric ganglia of the guinea-pig stomach.

The ultrastructure of the vesicle-containing axon profiles in the myenteric ganglia of the guinea-pig stomach was studied in specimens fixed by vascular perfusion and in specimens fixed by immersion in cold fixative after incubation in 5-hydroxydopamine. Three major types of vesicle-containing axon profile were identified in the ganglia: 1. Profiles containing numerous small, mainly shperical vesicles and only limited numbers of large dense-cored vesicles. In perfusion-fixed specimens, the small vesicles in these profiles were all clear. In specimens fixed by immersion after incubation in 5-hydroxydopamine, the profiles could be divided into three types: a) profiles containing small clear vesicles; b) profiles containing small dense-cored vesicles; c) profiles in which the small vesicles contained a peripheral rim of dense material. In these profiles, large vesicles which contained dense cores were rare. The mean diameter of the vesicles in the profiles was also significantly higher than in the profiles containing small clear vesicles. 2. Profiles containing flattened membrane-bounded structures. Reconstructions prepared from serial sections suggested that these structures represented sections through networks of smooth endoplasmic reticulum-like tubules rather than flattened vesicles. 3. Profiles containing many large dense-cored vesicles and few small clear vesicles. In perfusion-fixed specimens, the diameter of the dense-cored vesicles in these profiles was significantly higher than in the type 1 profiles. Type 1a and type 1c profiles were much more numerous than either type 2 or type 3 profiles. and type 1b profiles were few. Synaptic juctions were found in association only with type 1a profiles. Type 1a and type 1b profiles resembled cholinergic and adrenergic axon terminals. The remaining profiles may represent the terminals of different forms of peptidergic axon or of other as yet unidentified types of axon.

Innervation of the trachealis muscle in the guinea-pig: a quantitative ultrastructural study.

The fine structure and composition of the nerve plexuses associated with the cervical and the thoracic parts of the trachealis muscle were studied in two groups of six guinea-pigs. One group of animals was perfused with fixative before removal of the specimens. In the second, the specimens were incubated in 5-hydroxydopamine before cold immersion fixation. In both the cervical and the thoracic trachea, plexuses of nerves were found within and between the fascicles of muscle cells. The number of intrafascicular nerves/1000 micrometer 2 was low, and only a small proportion of the nerves contained more than five axons. Interfascicular nerves were more numerous and the mean number of axons/nerve was significantly higher than within the muscle. The number of efferent terminal profiles/100 axonal profiles was higher in the intrafascicular than in the interfascicular plexus, but in neither case was there evidence of a very close approximation of exposed terminal membranes to the membranes of adjacent muscle cells. Terminals classified as those of autonomic efferent axons were present in much greater numbers in the nerves than any other type of terminal. Examination of 5-hydroxydopamine-incubated specimens showed that less than half of these terminals were the terminals of adrenergic axons. Terminals of the type considered to represent the terminals of purinergic axons were also found in the nerves but were present in much smaller numbers than in the nerves of the submucous plexuses. The presence in the nerves of mitochondria-containing terminals with features similar to those of mechanosensitive nerve endings was related to physiological evidence of the location of stretch receptors in the muscle.

Morphology and response to vagus nerve section of the intra-epithelial axons of the rat trachea. A quantitative ultrastructural study.

The fine structure and distribution of the axons in the epithelium of the left and right sides of the trachea were studied in control rats and in rats subjected to unilateral cervical vagotomy. In control rats, the axons possessed similar ultrastructural features to the vesicle-containing axons which have been identified in the cornea and in the submucous plexus of the ureter. Stereological analysis showed that there are considerable differences in the degree of orientation of the axons and in the density of the intra-epithelial plexus on the two sides of the trachea. Degenerating axons were most numerous in the epithelium one day after vagotomy and degeneration and elimination of the axons by phagocytosis by the epithelial cells was completed within three days of section of the nerve. Comparison of the figures for the numbers of axons/grid hole obtained from specimens taken three days after vagotomy with those obtained from control specimens indicated that almost all the axons are derived directly from the vagus and that, although the majority of the axons in the epithelium on one side of the trachea are derived from the ipsilateral nerve, approximately one fifth are derived from the nerve on the contralateral side.

Degeneration and phagocytosis of smooth muscle cells in the neonatal rat ureter.

It was shown by ultrastructural investigation that, during the early stages of postnatal development of the rat ureter, some of the cells of the muscle coat undergo degeneration. These cells were rapidly eliminated by phagocytosis, mainly by other muscle cells. Following their incorporation into other muscle cells, the cells gradually became transformed into heterogeneous electron-dense bodies with the features of heterophagosomes.

Fine structure and composition of the submucous nerve plexus of the guinea-pig trachea.

The ultrastructure of the nerves forming the submucous plexus of cervical and thoracic parts of the trachea was studied in the guinea-pig. Specimens were obtained from 6 animals perfused with warm fixative and from 6 animals in which pieces of trachea were incubated in buffer containing 5-hydroxydopamine before immersed in cold fixative. Of the two types of axonal terminal identified in the nerves, one contained mainly large dense-cored vesicles, and the second contained numerous small vesicles. In specimens incubated in 5-hydroxydopamine, the small vesicles of the latter terminals exhibited the electron-dense cores which are characteristic of adrenergic axonal terminals. Counts made on perfused specimens showed that, in both the thoracic and cervical parts of the trachea, the density of adrenergic terminals was higher than that of terminals containing mainly large dense-cored vesicles. Overall terminal density was, however, higher in the thoracic than in the cervical part of the trachea, and estimates of nerve size showed that this was associated with the presence in the thoracic plexus of a substantially greater proportion of nerves with less than 6 axons. The possible function of the nerves in the control of the calibre of the submucous blood vessels was discussed.

Fine structure of the extraganglionic nerve plexuses of the guniea-pig stomach.

The fine structure of the perivascular and the other extraganglionic nerve plexuses in the muscularis externa and the mucosa of the guinea-pig stomach was studied in specimens fixed by perfusion and in specimens fixed by immersion after in vitro incubation in 5-hydroxydopamine. In each of the plexuses, over 50% of the nerves contained ten axons or less; terminal profiles were also much more numerous in sections of nerves of this size than in sections of the larger nerves. Five types of axon terminal were identified in the nerves. Terminals containing mainly large dense-cored vesicles were few, but were more numerous in the perivascular than in the other plexuses. Terminals containing small clear vesicles and large dense-cored vesicles approximately 140 nm in diameter were also few and were confined to the plexuses in the muscularis externa. The remaining types of terminal could be clearly differentiated only in specimens incubated in 5-hydroxydopamine. Terminals containing small clear vesicles were present in large numbers in the plexuses in the muscularis externa and the mucosa. Terminals containing small dense-cored vesicles constituted all but a small proportion of those seen in the perivascular plexuses. They were also seen in small numbers in each of the other plexuses. The remaining type of terminal contained small vesicles which were larger than in the other types and which contained halos of electron-dense material. Such terminals were present in the plexuses in the muscularis externa and were concentrated in nerves located close to the myenteric plexus.

Ultrastructure of the corneal nerves in the rat.

The ultrastructure of the corneal nerves of the rat was studied in tissue fixed by immersion in and by perfusion with glutaraldehyde-containing fixatives. Of the four types of axonal terminal identified in the nerves, those with the features of adrenergic and cholinergic terminals were confined to the nerves at the limbus and were concentrated in the perivascular plexuses. The remaining two types of terminal were found on axons located in all parts of the cornea and on both intraepithelial axons located in all parts of the cornea and on both intraepithelial axons and axons in the stromal nerves. Of these, one contained the numerous mitochondria which occur in the terminals of axons associated with known mechanoreceptors and the second contained variable and often small numbers of both clear and large dense-cored vesicles. While most of the mitochondria-containing terminals were seen in nerves located near the periphery,vesicle-containing terminals were numerous in all of the nerves,and especially in those in the avascular cornea. In material fixed by immersion in glutaraldehyde-paraformaldehyde,the vesicle-containing terminals appeared to be dilated,but in material fixed by perfusion there was little evidence of any increase in the diameter of the axons in the terminal regions. The structure of the terminals was compared with that of the terminals of axons identified in the nerves of the skin and the urinary tract and the differences in the vesicle content of the terminals to those reported in other studies of the corneal nerves was related to the use of different fixation procedures. The possibility that axons possessing such terminals are identical with the beaded axons and both the cholinesterase-positive and fluorescent axons demonstrated in light microscopical studies of the corneal nerves is discussed, and the widespread distribution of the axons in the cornea is equated with the hypothesis that they are afferent in nature and represent the peripheral receptors for pain impulses.

The fine structure of haemopoiesis in the human fetal liver. II. Origin and differentiation of the megakaryocyte.

The differentiation of the megakaryocyte was studied at the ultrastructural level in the liver of human fetuses of between 49 and 134 mm crown-rump length. The development of the cells was traced from lymphoid elements with the features of haemopoietic stem cells and was divided on the basis of nuclear morphology into three stages. Granule formation commenced during the first stage and demarcation membrances could be demonstrated in the perinuclear cytoplasm early in the second stage. Late stage 2 cells often contained more than one nucleus, and the possibility that this was due to cellular fusion is discussed. The third stage was characterized by the appearance of cytoplasmic zoning and by the gradual extension of the demarcation system throughout the cytoplasm. There was evidence that the demarcation membrances were initially formed directly from the Golgi apparatus, but that their further development was due to the incorporation of elements of the agranular endoplasmic reticulum. The surface projections associated with platelet release were observed only in fully developed cells, and the formation of a zone of clear cytoplasm at the periphery was related to events occurring during the later stages of platelet release.

Comparative ultrastructure of the nerves innervating the muscle of the body of the bladder.

The distribution and structure of the nerves supplying the muscle of the body of the bladder in mammals such as the mouse, guinea-pig, rabbit, cat and dog was compared with that previously demonstrated in the rat. The muscle of the arterioles located between the muscle bundles is innervated by a fine perivascular plexus and the nerves forming the muscular plexus can be divided into inter- and intra-fascicular nerves and the intrafascicular nerves are characterised by large numbers of terminals with the features of those of cholinergic axons. In addition to many small clear vesicles, the cholinergic terminals contained some small dense-cored vesicles, and it is suggested that, as in the rat, these contain a second transmitter which is released with acetylcholine at the terminals during impulse transmission. Adrenergic term-nals are more common in the muscular plexuses of the guinea-pig, dog and cat than in those of the other animals studied and there is evidence for the presence of two types of such terminal in the nerves. Of these, one contains a much smaller proportion of small vesicles with dense cores and many more large dense-dored vesicles than the second, and the possibility of a relationship between such terminals and those of short adrenergic neurones and neurones associated with non-adrenergic patterns of impulse transmission is discussed.

Location in the nodose ganglion of the perikarya of neurons whose axons distribute in the epithelium of the rat trachea.

The numbers of axons/unit length and of axons/group in the epithelium of the right and left sides of the trachea were determined in longitudinally orientated sections of specimens taken from five control rats, and from groups of five or six rats three days after section of the left vagus nerve above or below the nodose ganglion or section of the superior laryngeal and pharyngeal branches of the left vagus. After section of the vagus nerve below the nodose ganglion, there was a highly significant reduction in the number of axons/unit length in the epithelium of the ipsilateral side of the trachea, a significant reduction in the number of axons/group on this side and a small reduction in the number of axons/unit length on the contralateral side. The absence of similar changes in specimens from rats in which the vagus nerve was sectioned above the nodose ganglion, and in rats in which the branches from the ganglion were sectioned, indicated that the intraepithelial axons are derived from neurons whose perikarya are located in the ganglion and is consistent with the view that the axons are afferent. In addition to axons with terminals which resembled those which, in other tissues, have been defined as pain afferents, occasional axons with terminals containing numerous small clear vesicles were identified in the epithelium. The absence of these axons from the epithelium only in specimens taken from the ipsilateral side of the trachea after infranodose section of the left vagus nerve suggests that these may also be afferent.