Architecture of the caudal vena cava wall of the dog at the level of the liver caudate lobe

The vascular segment of the caudal vena cava of the dog at the level of the caudate lobe was shown to be intimately related to hepatic tissue through the hepatic capsule and parenchyma. The tunica adventitia of the caudal vena cava was formed mainly by smooth muscle cells with collagen and elastic fibers arranged in bundles. The thin tunica media of the vein was also formed by smooth muscle cells, collagen and elastic fibers arranged in bundles. The tunica intima presented an elastic subendothelial network. The hepatic segment of the caudal vena cava showed a myoconnective architecture and propulsive characteristics in terms of its hemodynamic pattern.     

A study of excitatory neuromuscular transmission in the bovine trachea

1. The excitatory innervation of bovine tracheal smooth muscle has been studied with the sucrose-gap apparatus.2. Single 2 ms electrical stimuli applied to the whole tissue excited intrinsic nerves, and produced a small transient depolarization of the smooth muscle, the excitatory junction potential (e.j.p.). The e.j.p. caused a twitch-type contraction; twitches and e.j.p.s summated during repetitive stimulation but facilitation was not observed, and action potentials were never elicited.3. The effects of electrical stimulation could be abolished by atropine (5 x 10(-7) mol/l) and augmented by neostigmine (4 x 10(-6) mol/l), and were mimicked by exogenous acetylcholine (1.0 mug/ml).4. With the electron microscope, the density of innervation was found to be low (one axon per ninety smooth muscle cells). Axons were found in small groups in the clefts between bundles of cells, but no axons penetrated within the muscle bundles. Naked axon varicosities containing agranular vesicles were seen, but no axon approached within 200 nm of a smooth muscle cell.5. It is difficult to reconcile the sparsity of innervation with the dependence of the tissue on nerve excitation to initiate activity.     

The structure and mechanical properties of collecting lymphatic vessels: an investigation using multimodal nonlinear microscopy

This study employed nonlinear microscopy on fresh, unstained and unfixed collecting lymphatic vessels to determine the wall structure and its relationships to the mechanical properties of the tissue. Fresh bovine mesenteric collecting lymphatic vessels were mounted in a vessel bath and imaged under different luminal pressures (0–30 cmH₂O pressure head), and longitudinal tensions. The entire wall thickness was imaged, using two‐photon fluorescence to visualize elastin, second harmonic generation to image the collagen, and coherent anti‐Stokes Raman scattering to image the cell membrane. The adventitial fat cells were coupled to the wall within the elastin‐rich network of fibres. The medial smooth muscle cells were too densely packed to resolve the boundaries of individual cells in en face images, but in tissue sections their appearance was consistent with electron microscopic data. Two distinct populations of collagen fibre were revealed. Large fibre (15–25 μm diameter) bundles were present in the inner media and small fibres (2–5 μm diameter) were distributed throughout the wall. The responses to longitudinal tension and luminal pressure indicated that the larger fibres resist the longitudinal strain and the smaller oppose pressure forces. Individual elastin fibres were of uniform thickness (1–3 μm) and interwove amongst themselves and between the collagen fibres. The network was probably too sparse directly to support mechanical loads and we speculate that its main function is to maintain the organization of collagen bundles during recovery from contraction.     

A comparison of the spindles in two different muscles of the frog

1. The responses of spindles in the iliofibularis muscle of frogs to stretch during either small motor nerve fibre stimulation or the application of suxamethonium were compared.2. All spindles which were excited by small motor nerve fibre stimulation were also excited by suxamethonium, and their responses to these two methods of excitation were very similar. The drug dose was usually 5-10 mug/ml. but smaller and larger doses were effective. Large doses (> 100 mug/ml.) could sometimes lead to a reversible partial block of the spindle response to stretch.3. Suxamethonium also caused a prolonged contraction in extrafusal slow muscle fibres. This contraction was not responsible for the effect on the spindle, because the time course of its action on the muscle tension and on the spindle afferent was different.4. It was concluded that suxamethonium stimulated prolonged contraction in the small intrafusal muscle fibres, which are known to be innervated by the small motor nerve fibres.5. Only about half of the spindles in the iliofibularis muscle were excited by suxamethonium.6. In the sartorius muscle which has no slow extrafusal muscle fibres, no spindles were found to be excited by suxamethonium in the way characteristic of that due to small intrafusal muscle fibre contraction.7. It is concluded that, in frog muscles which have no slow extrafusal fibres, the muscle spindles do not have small intrafusal muscle fibres of the kind found in the iliofibularis muscle.     

Complex structure of the common carotid artery of sheep

Background: Mechanical properties of blood vessels are dictated by the vessel wall structure. In many large conduit vessels the tunica media is a sheath of circular musculature and the tunica adventitia a layer of fibrous connective tissue with limited longitudinal extensibility. In contrast, the carotid artery of the sheep displays in each tunica a more complex architecture of muscle and connective tissue. Methods: Vessels collected from ewes were measured and processed for light microscopy and for transmission electron microscopy. Results: Layers of histologically different materials are found within the tunica intima, media and adventitia. (1) The tunica media is made of circumferentially arranged muscle cells markedly different at different depths. In the innermost third of the media. muscle cells are small and with irregular profiles, the cells are widely separated, and the extracellular material is abundant and composed mainly of elastic fibres. In the outermost third, muscle cells are larger and with more regular profiles, the cells are relatively close to each other and the extracellular material is sparse and consists mainly of collagen fibrils. (2) A small number of fibroblasts is found in all parts of the media amongst the preponderant muscle cells. (3) The intima contains fibroblast-like cells and longitudinally arranged muscle cells. (4) The adventitia contains a thick layer of collagen and elastic fibres; external to this, it displays a conspicuous musculature, made of large bundles of longitudinal muscle. Conclusions: The carotid artery of the sheep presents in all three coats of its wall features which are at variance from those in the better known vessels of small laboratory animals. The presence of many layers of material within the wall, the heterogeneity of the tissues found, and the occurrence of an extensive longitudinal musculature, have important effects on the mechanical properties of the vessel. © 1995 Wiley-Liss, Inc.     

Electrical and mechanical response of arteries to stimulation of sympathetic nerves

1. When common carotid arteries of sheep were studied in vitro by the sucrose-gap method, application of acetylcholine or nicotine caused small irregular spikes of depolarization. The discharge was prevented by hexamethonium, Hydergine, phentolamine, or chronic denervation, indicating that it represented electrical activity of groups of smooth muscle cells induced by the stimulation of sympathetic nerve fibres.2. The size of spikes produced by acetylcholine or nicotine, together with counts of the total number of smooth muscle cells in cross-sections of the arterial strips, indicated that the larger groups of smooth muscle cells activated by one sympathetic nerve fibre contained approximately 1300 cells.3. Sections of arteries treated with hot formaldehyde vapour contained numerous fluorescent fibres which were intensified by previous injection of noradrenaline into the animal and were scanty or absent after chronic sympathetic denervation. They are therefore believed to be post-ganglionic sympathetic nerve fibres.4. Most of these fibres ran circularly in the outer (1/2)-(3/4) of the media. A few ran longitudinally in the adventitia. There were none in the inner (1/4)-(1/2) of the media.5. Electrical stimulation of the cervical sympathetic nerve of anaesthetized sheep caused large contractions of the common carotid artery of the same side, reducing its external diameter by 30-39%.     

The vascular anatomy of the liver of the monitor lizard (genus varanus)

The gross and microscopic anatomy of the vasculature of the monitor lizard liver was studied. The portal vein has a peculiar arrangement of smooth muscle. The tunical media of the entering portal vein has bundles of smooth muscle cells separated by large numbers of collagenous fibers. The amount of smooth muscle decreases as the vessel decreases in diameter and soon one finds intermittent broad, thin bands of smooth muscle. As the caliber of the vessels continues to decrease, the smooth muscle bands become narrower and thicker so that they appear as doughnut-shaped sphincters. The sphincters are usually found at the beginning of each branch of the portal vein as well as along the course of veins between areas of branching. Some sphincters are found in direct contact with the outer capsule of the liver. Sphincters occur in the terminal branches of the portal vein just proximal to the sinusoids. Small numbers of scattered smooth muscle cells were seen arranged longitudinally, obliquely, or circularly in the smaller hepatic veins. Even the large hepatic veins had only small amounts of smooth muscle. At no place along the course of hepatic veins could smooth muscle sphincters equivalent to those seen around portal veins be found. The monitor lizard should be an excellent subject for physiological and pharmacological studies of regulation of intrahepatic portal vein blood flow.     

Coexistence of Dense and Sparse Areas in the Longitudinal Smooth Muscle of the Anal Canal: Anatomical and Histological Analyses Inspired by Magnetic Resonance Images

Magnetic resonance images of the anal canal show small, circular, low-intensity areas arranged in a row and a high-intensity area surrounding them internally and externally in the longitudinal muscle layer that cannot be explained by current anatomical findings. The purpose of this study was to elucidate the detailed structure of the longitudinal smooth muscle of the anal canal and to interpret the magnetic resonance image of the longitudinal muscle. Specimens for macroscopic anatomy and histology were obtained from six and seven cadavers, respectively. The histological nature of the longitudinal muscle was examined by staining serial transverse and coronal sections of the lateral wall of the anal canal with Masson's trichrome stain and using immunohistochemistry for smooth and skeletal muscle fibers. Dense and sparse areas of smooth muscle fibers coexisted in the longitudinal muscle layer. The dense areas formed columnar muscle bundles approximately 1.0–1.5 mm in diameter, and they continued from the longitudinal muscle bundles of the rectum. The columnar muscle bundles of the longitudinal anal muscle were internally and externally surrounded by sparsely arranged smooth muscle fibers that ran longitudinally. The coexistence of dense and sparse areas of smooth muscle fibers suggests that the structure of the smooth muscle is optimized for its function. This histological nature is probably reflected in the magnetic resonance image of the longitudinal muscle as the coexistence of low- and high-intensity areas. Clin. Anat. 33:619–626, 2020. © 2019 Wiley Periodicals, Inc.     

The innervation of sheep mesenteric veins

1. An isolated preparation of sheep mesenteric vein is described from which contractions of the longitudinal smooth muscle of the adventitia have been recorded in response to stimulation of intramural and periarterial nerves.2. The preparation did not respond to single stimuli but the relation between amplitude of response and frequency of stimulation was characteristic of that described for other smooth muscles innervated by sympathetic nerves.3. Responses were blocked by tetrodotoxin, guanethidine, and by a number of alpha-receptor blocking drugs. Responses to peri-arterial stimulation were unaffected by hexamethonium. It was concluded that the longitudinal smooth muscle is supplied with post-ganglionic noradrenergic motor nerves and the presence of such fibres in the adventitia was confirmed by fluorescence microscopy.4. Acetylcholine also caused contractions. Although a direct excitatory action on the smooth muscle could not be excluded, results suggest that acetylcholine may release noradrenaline from the axons of the sympathetic ground plexus.     

Scanning electron microscopic studies of the vascular smooth muscle cells and pericytes in the rat heart

The cytoarchitecture of smooth muscle cells and pericytes in the rat cardiac vessels was studied by scanning electron microscopy after the removal of connective tissue matrices using a modified KOH-collagenase digestion method. The initial stem of the coronary arteries had groups of smooth muscle cells which ran in various directions on the outermost layer of the media. Although smooth muscle cells in coronary arteries of more than 100 microm in the outer diameter were arranged in a rough circle around the vessel axis, oblique and/or longitudinal muscle bundles were often present in the medio-adventitial border of the vessels. The presence of irregularly oriented muscular bundles is probably connected with resistance against the stretching force induced by the beating of the heart. As the vessel size decreased toward the periphery, almost all of the smooth muscle cells became spindle-shaped with several tiny processes and ran circularly or helicaly to the vessel axis. In the precapillary arterioles (6-12 microm), smooth muscle cells acquired various cytoplasmic processes which helicaly surrounded endothelial cells. Unmyelinated nerves were often associated with arterioles. Blood capillaries were morphologically divided into three segments: arterial capillaries which had pericytes with wide and circularly oriented processes, true capillaries whose pericytes extended long and thin primary processes bilaterally along the vessel axis, and venous capillaries surrounded irregularly and loosely by wide pericytic processes. The stellate pericytes in the postcapillary venules (10-30 microm) gradually changed into flat tape-like smooth muscle cells, which ran circularly in the collecting venules and veins (30-200 microm). The large collecting veins were finally overwhelmed by superficial thin layer of the myocardium, their own smooth muscle cells being very sparse. This suggests that large veins have poor ability to contract by themselves but are influenced by the surrounding myocardial cells.     

Excitation of Mytilus smooth muscle

1. Membrane potentials and tension were recorded during nerve stimulation and direct stimulation of smooth muscle cells of the anterior byssus retractor muscle of Mytilus edulis L.

2. The resting potential averaged 65 mV (range 55-72 mV).

3. Junction potentials reached 25 mV and decayed to one half maximum amplitude in 500 msec. Spatial summation and facilitation of junction potentials were observed.

4. Action potentials, 50 msec in duration and up to 50 mV in amplitude were fired at a membrane potential of 35-40 mV. No overshoot was observed.

5. Contraction in response to neural stimulation was associated with spike discharge. Measurement of tension and depolarization in muscle bundles at high K⁺ indicated that tension is only produced at membrane potentials similar to those achieved by spike discharge.

6. Blocking of junction potentials, spike discharge and contraction by methantheline, an acetylcholine antagonist, supports the hypothesis that the muscle is excited by cholinergic nerves. However, evidence of a presynaptic action of methantheline complicates this argument.

     

Longitudinal smooth muscle in pulmonary arteries

Summary In lung biopsy specimens of 19 patients with congenital heart disease and pulmonary hypertension, in addition to the common features of plexogenic arteriopathy, longitudinal smooth muscle cells were found in small pulmonary arteries. These cells were arranged in bundles or layers, particularly in the intima but sometimes within the media or adventitia of the arteries. They often caused severe narrowing of the lumen. Corrective surgery of the cardiac defect was performed in 14 patients. The results suggested that even when these changes are wide-spread and severe, they do not stand in the way of a favourable postoperative course. In one patient who underwent a banding procedure of the pulmonary artery, virtually complete regression of the smooth muscle layers could be demonstrated in a second biopsy, taken 5 years later during a corrective operation.     

A light microscope study of the distribution of muscle in the frog esophagus and stomach.

The present study reports light microscopical observations of the distribution of muscle in the esophagus and stomach of both the bull frog (Rana catesbeiana) and the African clawed frog (Xenopus laevis). The external muscle coat of the upper half of the esophagus in both species had several collagen coated bundles of striated muscle fibres around the circumference. These striated muscle bundles ran longitudinally from the pharynx to around the vicinity of the center of the esophagus. Beneath these striated muscle bundles was an inner circular layer of smooth muscle. In both species, the inner circular layer of smooth muscle was particularly thick in the region close to the pharynx. In the bull frog, the lower half of the esophagus lacked striated muscle. However, the circular smooth muscle layer, extending from the upper half of the esophagus, was also observed throughout the lower half of the esophagus. An outer longitudinal layer of smooth muscle developed towards the terminal portion of the esophagus such that in this region, both outer longitudinal and inner circular layers of smooth muscle were observed. Similarly in the African clawed frog, the inner circular layer of smooth muscle was continuous along the full length of the esophagus. Again, no striated muscle bundles were observed in the lower half of the esophagus. However, the outer longitudinal layer of smooth muscle was seen to develop in the middle region of the esophagus. Its muscle layer extended to the terminal portion of the esophagus. Thus, both outer longitudinal and inner circular layers of smooth muscle were observed throughout the lower half of the esophagus. In both frogs, the thickness of the outer longitudinal and inner circular layers of smooth muscle changed before and after the esophago-gastric junction. In both frogs, no muscularis mucosa was observed in the esophageal wall. However, in the lower half of the esophagus of the African clawed frog, small bundles of smooth muscle were observed here and there in the submucosa. A fully developed muscularis mucosa with both outer longitudinal and inner circular layers was observed in the upper stomach of both frogs.     

Fine structure of the mouse portal vein in relation to its peristaltic movement

The hepatic portal vein has been known to make a spontaneous peristaltic movement in some mammals, including the mouse and rat. To investigate the fine structure of the portal vein in relation to its physiological characteristics, we observed the mouse portal vein by using various histological techniques including conventional light microscopy, videomicroscopy, transmission and scanning electron microscopy, and real-time confocal laser scanning microscopy. The mouse hepatic portal vein was provided with a spiral fold which was produced by the inner layer, i.e. the endothelium and smooth muscles of the wall protruding into the lumen. Longitudinal smooth muscle cells spanned the interval of the fold, like a spirally arranged palisade around the vessel wall. The longitudinal muscle fibers ended at the spiral fold, being partly connected with a network of irregularly shaped smooth muscle cells. This network, hitherto unknown, was recognized to be restricted to the fold in distribution and characterized by numerous gap junctions connecting the muscle cells. Real-time confocal laser scanning microscopy using a Ca2+ sensitive fluorescent dye revealed that a transient and periodic increase in Ca2+ concentration occurred in the longitudinal smooth muscle cells and was transmitted spirally from the intestinal to the hepatic side. These findings indicate that, during the peristaltic movement, the contraction of smooth muscle cells is transmitted along the longitudinal smooth muscles of the portal vein wall toward the liver, presumably controlled by the network of the irregularly-shaped smooth muscle cells in the fold of the portal vein. Light microscopic observation in some specimens indicated an occurrence of cardiac muscle cells outside the smooth muscle layer. Restricted to the site of the porta hepatis in distribution, their involvement in the peristaltic contraction of the portal vein seemed unlikely.     

An electron microscopic study of intimal cushions in intracranial arteries of the cat

Subendothelial protuberances associated with the tunica intima have been described by light microscopy at branching sites of arteries in various animal species. These structures are termed intimal cushions or intimal pads. Some investigators regard them as being pathologic, preceding the appearance of atherosclerosis in the vessel wall. This fine structural study was done because of the possible role of intimal cushions in the regulation of cerebral blood flow at branching sites of intracranial arteries. The internal elastic lamina is split at the margins of a cushion to enclose irregularly arranged bundles of smooth muscle cells and collagenous fibrils. These smooth muscle cells are generally arranged at a right angle to smooth muscle cells in the underlying media. The outermost layer of the internal elastic lamina forms a boundary between the body of the cushion and the media; however, areas of discontinuity cause this border to be poorly defined in some instances. Perivascular autonomic nerves do not extend into either media or intimal cushions. Intercellular contacts between smooth muscle cells are observed within cushions as well as in the media, suggesting that cushions may be contractile and capable of modifying cerebral blood flow.     

Histological and electrophysiological investigation of lizard skeletal muscle

1. The patterns of innervation and electrical properties of muscle fibres in a skeletal muscle of the blue tongue lizard Tiliqua nigrolutea have been investigated.2. Gold impregnation of nerve terminals and staining of muscle fibre junctional areas for cholinesterase showed that there are two histological types of muscle fibre in scalenus muscles of the lizard: (a) those usually receiving single en plaque innervation, and (b) those that receive multiple en grappe terminations.3. In normal solution and in solutions to which small doses of curare were added, two types of subthreshold post-junctional response were recorded following nerve stimulation, (a) potentials with rapid rates of rise and a half-decay time of less than 10 msec and (b) responses with fast rise times and long half-decay times (50 msec or more).4. Fast time course subthreshold responses often gave rise to propagated action potentials. In curarized preparations ((+)-tubocurarine 0.4-1.0 mug/ml.) action potentials failed, giving way to junction potentials of decreasing amplitude, when stimulation was maintained at rates of 5/sec or more. The decay phases of fast time course potentials were closely approximated by error functions.5. Slow time course responses summated during repetitive stimulation, but action potentials were never produced. The decays of slow junction potentials were well fitted by exponentials. It is suggested that fibres in which they were recorded received distributed, en grappe innervation.6. Fibres in which fast time course junction potentials were recorded were excited by direct stimulation via an intracellular micro-electrode. They had apparent membrane resistance and capacity of about 4000 Omega. cm(2) and 7 muF/cm(2).7. Fibres exhibiting slow junction potentials could not be excited directly, even when depolarizing pulses were preceded by hyperpolarizations of 50 mV or more for more than 20 msec. Such fibres had an apparent membrane resistance of 31 x 10(3) Omega.cm(2) (mean) and a capacity of less than 3 muF/cm(2) (eight fibres).8. Curarized muscles developed tension in response to nerve stimulation at frequencies of 5/sec or more. The tension profile was smooth at even the lowest frequencies at which a response was elicited. Normal fusion frequency was around 50/sec.9. It is suggested that fibres exhibiting slow junction potentials were functionally similar to amphibian tonic fibres.10. Some fibres were found in which action potentials could be elicited by stimulation of one or more axons. Their subthreshold responses and passive properties were not determined and it remains uncertain to which of the two structural types they belong.     

Three-dimensional cytoarchitecture of the media of arteriovenous anastomoses in the rabbit ear

Arteriovenous anastomoses in the rabbit ear were examined with scanning electron microscopy to elucidate the structural differentiation of the media of the shunt. Arterial, intermediate, and venous segments in the shunt and two layers of the media in the intermediate segment were differentiated based on cell shape and cell organization. In the arterial segment, smooth muscle cells were spindle-shaped, either elongated or short, with a few branches, and were arranged circularly or diagonally with respect to the vessel's long axis. There were also stellate muscle cells with radiating processes. In the intermediate segment, the smooth muscle cells of the outer layer of the media were also arranged circularly and resembled the elongated cells in the arterial segments, but they were more irregular in shape and had more processes than those of the arterial segment. The epithelioid cells of the inner layer of the media were oval or polygonal and oriented irregularly with respect to the vessel's long axis, clustering to form longitudinal plicae. The smooth muscle cells of the venous segment were flat with many lateral processes and formed a thin, discontinuous layer. The smooth muscle cells in the arterial segment and those of the outer layer of the intermediate segment exhibited a highly rugged surface texture, indicating their strong contractility; the epithelioid cells and the smooth muscle cells in the venous segment exhibited a generally smooth surface, indicating less contractility. The intermediate segments were supplied with a dense nerve plexus. The intermediate segments, therefore, may be actively involved in the regulation of blood flow under neuronal influence.     

Dynamic association between α-actinin and β-integrin regulates contraction of canine tracheal smooth muscle

The adhesion junctions of smooth muscle cells may be dynamically regulated during smooth muscle contraction, and this dynamic regulation may be important for the development of active tension. In the present study, the role of α-actinin during smooth muscle contraction was evaluated in tracheal smooth muscle tissues and freshly dissociated cells. Stimulation with acetylcholine (ACh) increased the localization of α-actinin at the membrane of freshly dissociated smooth muscle cells, and increased the amount of β₁ integrin that coprecipitated with α-actinin from muscle tissue homogenates. GFP-α-actinin fusion proteins were expressed in muscle tissues and visualized in live freshly dissociated cells. GFP-α-actinin translocated to the membrane within seconds of stimulation of the cells with ACh. Expression of the integrin-binding rod domain of α-actinin in smooth muscle tissues depressed active contraction in response to ACh. Expression of the α-actinin rod domain also inhibited the translocation of endogenous α-actinin to the membrane, and inhibited the association of endogenous α-actinin with β₁-integrin in α-actinin immunoprecipitates from tissue extracts. However, the expression of α-actinin rod domain peptides did not inhibit increases in myosin light chain phosphorylation or actin polymerization in response to stimulation with ACh. Results suggest that contractile stimulation of smooth muscle causes the rapid recruitment of α-actinin to β-integrin complexes at the membrane, and that the recruitment of α-actinin to integrin complexes is necessary for active tension development in smooth muscle.     

Electron microscopic study of the characteristics of skeletogenic tissue differentiation during distraction osteosynthesis]

Electron microscopic examination of the regenerating tissue was performed after distractional osteosynthesis carried out by the method of G. A. Ilizarov. The results showed osteogenesis to occur on the basis of the fibrous tissue formed in diastasis. The observed zones of the regeneration typical of distractional osteosynthesis are due to functional stimulation (tension) resulting in the arrangement of collagen fiber bundles and bone trabeculae in the direction of the extension forces. Cells of the skeletogenic tissue, between the bone fragments are also arranged with their longitudinal axis along the collagen fibril bundles. The ultrastructural pattern of the osteogenesis after distractional osteosynthesis reflects the intensification of the synthesis of glycosaminoglycan-protein complexes forming the main substance of the bone tissue.