Structure of the digestive tract of the pluteus larva of Dendraster excentricus (Echinodermata: Echinoida)

Summary Histological and ultrastructural observations of the digestive tract of eight-armed plutei of Dendraster excentricus are reported. The esophagus is divided into two regions. The uppermost is a narrow tube comprised of ciliated cells that assist in transporting food to the more bulbous lower esophagus where food particles are formed into a bolus prior to entering the stomach. The esophagus is surrounded by a network of smooth muscle fibers that are predominantly oriented circumferentially in the upper esophagus, and longitudinally in the lower esophagus. The musculature of the upper esophagus produces peristaltic contractions, whereas contractions of the muscle of the lower esophagus open the cardiac sphincter and force food from the lower esophagus into the stomach. Axons are associated with the ciliated cells and the muscles of the upper esophagus. The cardiac sphincter consists of a ring of myoepithelium, with cross-striated myofibrils oriented around the bases of the cells. The gastric epithelium is comprised of two cell types. Type I cells, which predominate, absorb and store nutrients, and may be the source of secreted digestive enzymes. Type II cells apparently phagocytize and intracellularly digest whole algal cells. The intestine is comprised of relatively unspecialized cells and probably functions primarily as a conductive tube for the elimination of undigested materials.     

Reconstruction of the muscle system in Antygomonas sp. (Kinorhyncha,Cyclorhagida) by means of phalloidin labeling and cLSM

In the present investigation the entire muscle system of the cyclorhagid kinorhynch Antygomonas sp. was three-dimensionally reconstructed from whole mounts by means of FITC-phalloidin labeling and confocal scanning microscopy. With this technique, which proved to be especially useful for microscopically small species, we wanted to reinvestigate and supplement the findings obtained by histological and electron microscopical methods. The organization of the major muscle systems can be summarized as follows: 1) All muscle fibers, apart from the intestinal ones, the spine, and the mouth cone muscles, show a cross-striated pattern; 2) Dorsal longitudinal muscle fibers as well as segmentally arranged dorsoventral fibers occur from segment III to XIII; 3) Diagonal muscle fibers are located laterally in segments III to X; 4) Two rings of circular fibers are present in segment II, forming the closing apparatus in Cyclorhagida. Further circular muscles are present in segment I, forming the mouth cone and the eversible introvert, and in the pharyngeal bulb.     

New muscle formation following transplantation of muscle treated with trypan blue]

The sources and mechanism of muscle formation de novo were investigated under the transplantation of skeletal muscle fibers treated in the 1% water solution of Trypan Blue for 48 hrs after Levander under skin and in omentum in rabbits and rats. In some cases the pieces of Trypan Blue stained muscles were placed in the diffusion chambers. Besides, 3H-thymidine autoradiography was used. It was established that after the above described treatment the muscles appeared morphologically as necrotized. They do not develop in the diffusion chambers in which cells do not penetrate. Under the transplantation of such muscles under skin and in omentum, they are phagocytized and disintegrate and in the close neighbourhood myoblasts arise which transform into muscle tubules and differentiated cross-striated muscle fibers. If prior to the transplantation the rats--recipients were labeled by 3H-thymidine, the muscle fibers formed de novo with the labeled nuclei, i. e. from the recipient cells in omentum where there are no muscles, apparently from polyblasts. Under the definite experimental conditions, myoblasts appear to arise from cells of non-myogenic origin by means of induction.     

Diversity of Striated Muscle

A broad comparative survey has been made correlating ultrastructureof cross-striated fibers with contractile properties in bothinvertebrates and vertebrates. Most of the muscles were foundto be heterogeneous in fiber-composition as indicated by: lengthof sarcomere, extent of SR, number of invaginating tubules,numbers of mitochondria, etc. Z discs and M bands have markedlydifferent structures in different fibers. The general conceptof the "fibrillar" nature of striated muscle is challenged.It is suggested that following excitation the responses of individualsarcomeres, or parts of sarcomeres, are relatively independent.The possibility that all striated muscles contain a very thinelastic filament in parallel with actin and myosin, which mayalso be contractile, is raised.     

The ultrastructure of normal and denervated human facial muscle

The ultrastructure of normal human facial muscles from 25 nonparalytic and 17 paralytic patients revealed normal features in nondenervated human facial muscles, identical to the fine structure of other normal human and mammalian cross-striated muscle fibers. However, in denervated facial muscle, a broad spectrum of ultrastructural lesions had affected sarcomeres, abnormal inclusions, and organelles. A large variety of inclusion bodies, some of which have not been described, were also found. The spectrum of ultrastructural changes showed no dependence on the length of the denervation period. There were no inclusion bodies in all the normal facial muscle biopsies. To our knowledge, this study represents the first systematic electron microscopic investigation of normal and denervated human facial muscles.     

Limitations on locomotor performance in squid

An empirical equation relating O2 consumption (power input) to pressure production during jet-propelled swimming in the squid (Illex illecebrosus) is compared with hydrodynamic estimates of the pressure-flow power output also calculated from pressure data. Resulting estimates of efficiency and stress indicate that the circularly arranged obliquely striated muscles in squid mantle produce maximum tensions about half those of vertebrate cross-striated muscle, that "anaerobic" fibers contribute to aerobic swimming, and that peak pressure production requires an instantaneous power output higher than is thought possible for muscle. Radial muscles probably contribute additional energy via elastic storage in circular collagen fibers. Although higher rates of aerobic power consumption are only found in terrestrial animals at much higher temperatures, the constraint on squid performance is circulation, not ventilation. Anaerobic power consumption is also among the highest ever measured, but the division of labor between "aerobic" and "anaerobic" fibers suggests a system designed to optimize the limited capacity of the circulation.     

The fine structure of the drum muscles of the Tigerfish,Therapon jarbua,as compared with the trunk musculature

Summary The fibers of drum and trunk muscles of the Tigerfish, Therapon jarbua, differ greatly in diameter. The myofibrils of the trunk muscles are irregularly oriented, while those of the drum muscles are rolled into spiral or concentric bands. Both muscle types possess the sarcomere structure typical of cross-striated musculature. However, the myofibrils of the drum muscles differ greatly in sarcomere length and width from those in the trunk musculature. The trunk muscles contain few mitochondria, whereas in the drum muscles mitochondria are abundant. The sarcoplasmic reticulum (SR) of the drum muscles takes the form of elongated tubes in both the A and the I region; that of the trunk musculature consists of small vesicles. Of the two muscle types, the drum muscle contains more SR. With respect to the form of the T system, the trunk musculature is of the Z type and the drum muscles of the A-I type. The drum muscle displays a considerably greater number of motor endplates; these lack typical junctional folds and have mitochondria with very few cristae. No fat could be demonstrated in either the drum or the trunk muscles. However, the concentration of glycogen is higher in the drum muscle than in the musculature of the trunk.This work was accomplished with support from the Deutsche Forschungsgemeinschaft and is gratefully dedicated to Prof. R. Danneel on the occasion of his 75th birthday.     

The musculature of horsehair worm larvae (<Emphasis Type="Italic">Gordius aquaticus</Emphasis>,<Emphasis Type="Italic"> Paragordius varius</Emphasis>, Nematomorpha): F-actin staining and reconstruction by cLSM and TEM

The musculature of larvae of Gordius aquaticus was investigated by laser-scanning microscopy and compared to transmission electron microscopic data for the larva of Paragordius varius. In the anterior portion of the body, the preseptum, four different muscle groups can be distinguished: (1) 12 anterior parietal muscles in the body wall, (2) six oblique muscles that function as retractors of the introvert, (3) six proboscideal muscles, which function as retractors for the proboscis, and (4) six muscles associated with spines of the outermost of the three rings of spines. The posterior portion of the body, the postseptum, possesses four pairs of longitudinal muscle strands in G. aquaticus, the postseptal parietal muscles, that are located dorsolaterally and ventrolaterally. These are not clearly visible in P. varius, where instead three pairs of parietal muscles are present. Additional small muscles are associated with the terminal spines and with the duct running from the pseudointestine to the body wall. All fibers show a cross-striated pattern although this striation is less obvious at the ends of the fibers.     

Morphohistochemical characteristics of structures of the esophageal cross-striated muscle tissue]

On the bases of histochemical enzymatic studies and morphometric investigations, some differences were revealed between cross-striated esophageal muscular tissue and other skeletal muscles of mammals. A peculiar feature of the esophageal musculature is prevalence of unitypical fibres with small diameter and possessing high activity of oxidating enzymes. According to these signs, esophageal myons can be ascribed to the first type of muscular fibres. Simultaneously, a high activity of myofibrillar ATPh is revealed in them. Thus, according to histochemical indices, cross-striated esophageal muscular fibres of mammals are quick and slowly fatiqued fibres.     

Ultrastructural Studies of the Visceral Muscles of Chaetognaths

The visceral musculature of Chaetognaths was studied with special attention given to the digestive apparatus muscle. In the head the digestive apparatus muscle is relatively thick; individual muscles are difficult to distinguish at the anatomical level; in the anterior part of the oesophagus discontinuous bundles and layers of cross-striated fibers are found. As a group however, the oesophageal musculature completely covers the oesophageal epithelium. The prominent muscle layers around the oesophagus probably help to force food into the intestine against the turgor pressure of the trunk cavity which tends to collapse the intestine. Around the intestine the musculature is largely circular and smooth. The intestinal epithelium is ciliated despite its muscular covering. Muscle fibers are not individually innervated. They form myoepithelial structures with various intercellular junction types. In the intestinal muscle the fibers show myoendothelial-like junctions. Sphincters composed of myoepidermal cells surround the anus and the female gonopores. The somatic side of the general cavity is lined with a polymorphic squamous epithelium. Sometimes myoepithelial cells are found, with the occasional presence of extracellular matrix basal to the layer of the squamous epithelium. The ontogenetic relations between the polymorphic epithelium and the composite ‘mesenteries’ remain to be established. We have now some idea about the architecture of the body of Chaetognaths in relation to contractile structures.     

Differentiation of slow and fast fibers in tentacles of Sepia officinalis (Mollusca)

The tentacles of Sepia officinalis are cylindrical muscular structures that can be quickly everted and elongated to capture prey. The combination of both velocity and extensive elongation of the tentacles is due to the presence of both cross-striated and helical muscles. The complex organization and differentiation of different fibers has been studied in cuttlefish extracted from egg gel coats at different developmental stages, and in completely developed animals. Tentacle muscles start to differentiate centrifugally from the area close to the axial nervous system, where two types of myocytes can be recognized. These populations of myocytes, which may be distinguished morphologically and which express different myosin isoforms, give rise to fast and slow muscles. The presence in molluscs of slow and fast muscles arising from different populations of myocytes, as in vertebrate muscle development, could be considered as an example of evolutionary conservation.     

Age-related alterations of mitochondria from muscle tissue

The ultrastructure of mitochondria of cross-striated muscles during aging was studied by electron microscopy. Mitochondrial ultrastructure was analyzed in the flight muscle of D. melanogaster (1- and 36-day-old) and in the cardiomyocytes and skeletal muscle of young and senile Wistar and OXYS rats (3- and 25-month-old). The mitochondria in the flight muscle samples of senile D. melanogaster flies were shown to have several types of peculiar age-related mitochondrial abnormalities corresponding to those described previously. Previously unknown changes were revealed in the ultrastructure of cardiomyocyte mitochondria in senile rats (both Wistar and OXYS). Substantial changes in the ultrastructure of subsarcolemmal mitochondria were found in the fibers of red skeletal muscle of senile OXYS rats. It has been shown that the subsarcolemmal mitochondria of red muscle fibers are a peculiar population of mitochondria with atypical ultrastructure. Initial changes in the ultrastructure of subsarcolemmal mitochondria were revealed even in 3-month-old OXYS rats. At the same time, the skeletal muscle mitochondria of senile Wistar rats maintain their morphological characteristics, and their ultrastructure corresponds to that of skeletal muscle mitochondria in 3-month-old Wistar rats.     

Destructive changes in the muscles of sportsmen during dynamic cyclic exercise of different intensities

An electron microscopic investigation of bioptates from the external vast femoral muscle in sportsmen performing cyclic activity of various power has been performed: sprinters to middle distances, short-distance skaters and rowing-sportsmen--work in the zone of submaximal power; skaters to the distance of 3,000-10,000 m and racing skiers to the distance of 5-10 km--work of great power; racing skiers to long distances--prolonged work of moderate power. When working in the zone of the submaximal power, the signs of destruction of contracting structures in the muscle fiber are poorly manifested. When the work is of greater power and of greater duration with moderate power, necrotized fibers are found in the sportsmen's muscles. In muscle fibers with sublethal lesions, increasing autophagic processes are noted. The destructive changes of various degree of manifestation, revealed in muscle fibers predetermine the programme of adaptive changes in the muscles of the sportsmen specialized in different sports.     

Motor innervation by enteric nerve fibers containing both nitric oxide synthase and galanin immunoreactivities in the striated muscle of the rat esophagus

The relationship between nitric oxide synthase (NOS)- and galanin-immunoreactive nerve terminals and the origin of NOS-immunoreactive nerve terminals on the motor endplates in the striated muscles of the rat esophagus was investigated. Double immunohistochemical staining revealed a dual innervation of motor endplates by calcitonin gene-related peptide (CGRP)-immunoreactive axons and by axons that were immunoreactive for both NOS and galanin. On average, 91% of NOS terminals were galanin immunoreactive. NOS-immunoreactive fibers were revealed at 67% of endplates, identified by the presence of CGRP terminals. The left vagus and superior laryngeal nerve were cut and 15 days allowed for terminals to degenerate. This caused a significant loss of CGRP fibers, but did not affect the density of innervation of the striated muscle by NOS-immunoreactive fibers. Thus the NOS/galanin fibers are deduced to originate from ganglia in the esophageal wall. This is supported by our observation of numerous NOS-immunoreactive nerve cell bodies in the myenteric ganglia of the esophagus, 74% of which were galanin immunoreactive. There were no CGRP-immunoreactive nerve cell bodies in the wall of the esophagus.     

Ultrastructure of the tail appendage in microphallid cercariae (Trematoda, Microphallidae)

The tail structure of larvae of Maritrema subdolum and Microphallus claviformes is similar in essence. Its wall is made by the tegument and underlying layers of muscles. The syncytial anucleated tegumental lamina with the only type of secretory inclusions forms regular circular folds along the tail. The outer muscle layer is formed by the smooth muscular cells. It is underlaid by the longitudinal cross-striated muscles with the strongly pronounced sarcomere organization. The nucleus-containing bodies of the muscle cells occupy the axial part of the tail excepting the central cavity. The functional joining of tail and body musculatures is provided by thick muscle bundles in the caudal department of the larval body.     

Innervation regulates the metamorphic fates of larval abdominal muscles in the moth, Manduca sexta

 With the onset of metamorphosis, the abdominal muscles of the moth, Manduca sexta, follow one of three developmental fates: maintenance, respecification, or death. The maintained muscles retain their larval size and morphology throughout adult development. The respecified and dying muscles dedifferentiate, which involves regression, nuclear degeneration, and myofibril breakdown. Nuclei in both dying and respecified muscles also proliferate. The amount of nuclear degeneration is greater in the dying muscle fibers, and the amount of nuclear proliferation is greater in the respecified muscles. Four to ten days after pupation, the sizes of the respecified muscles stabilize while the dying muscles are lost. During regression, a subset of the respecified muscle fibers die. The surviving respecified muscle fibers grow and differentiate during the last half of adult development. In respecified muscles, denervation triggers an increased amount of nuclear degeneration and a decreased amount of nuclear proliferation. As a result, denervated respecified fibers experience increased muscle regression including an increased loss of muscle fibers and sometimes muscle death. Surviving respecified fibers still grow and differentiate yet are only 5 to 12% of the control size. Denervation triggers dedifferentiation in maintained muscles, resulting in fiber loss and occasionally muscle death. The percentage of fibers which dedifferentiate varies between different muscles. Denervation also triggers nuclear proliferation, with the amount of nuclear proliferation correlated with the extent of dedifferentiation of the individual muscle fibers. The dedifferentiated maintained fibers subsequently undergo differentiation in the absence of muscle growth. Received: 10 July 1997 / Accepted: 21 April 1998     

Histochemical fiber types characteristics in the normal and the persistent levator ani muscle of the rat

Summary Morphological features of the persistent levator ani (LA) muscle of the female rat normally undergoing involution but maintained by application of testosterone propionate to newborn animals were compared with that of the normal LA muscle of untreated male rat. The two muscles differ in number and size of muscle fibers.Using histochemical methods for myofibrillar adenosine triphosphatase (ATPase), mitochondrial -glycerophosphate dehydrogenase (-GPDH) and succinic dehydrogenase (SDH) the distribution of these enzymes in individual muscle fiber types was studied.ATPase and -GPDH activities show a homogenously positive reaction in the muscle fibers of the male rat, whereas a small portion of fibers with low activity is found in the persistent muscle of female rat.The most pronounced difference concerns SDH activity, i.e. two kinds of fibre types are barely discernible with prolonged incubation in LA muscle of male rat, but three basic fibre types (white, intermediate and red) are clearly distinguished in LA muscle of the female rat.The results are discussed in relation to neural and hormonal influences on histochemical features in cross-striated muscle.This work was supported by a grant from the Muscular Dystrophy Association of America to the Institute of General Pathology, University of Padua, Italy.     

Pharynx, esophagus, and associated structures in the booklouse, Liposcelis divinatorius

Abstract. Ultrastructural features of the pharynx, esophagus, and associated intrinsic visceral muscular and nervous structures of the booklouse, Liposcelis divinatorius , were studied to determine whether the anatomical arrangements of these structures differed from the general pattern found in insects. The results are compared with previous light microscope studies of this tiny insect. Variations from the usual arrangement reported for intrinsic visceral muscles associated with the pharynx in insects are described. Intrinsic visceral muscles include a narrow band of circularly disposed fibers and both extra-circular and intra-circular longitudinally disposed fibers. This represents a departure from the slightly developed inner longitudinal and more prominent outer circular fibers seen in most insects. The outer surface of some circular muscle cells has apparently unique pouches packed with mitochondria, which contain many cristae. Numerous bacteroids appear in the esophageal epithelial cells and in the sub-esophageal ganglion. Nerve processes associated with the foregut contain neurotubules, synaptic vesicles, and electron-dense granules.     

The skeletal muscles of rotifers and their innervation

The skeletal muscles of rotifers are monocellular or occasionally bicellular. They display great diversity of cytological features correlated to their functional differentiation. The cross-striated fibers of some retractors are fast contracting and relaxing, with A-band lengths of 0.7 µm to 1.6 µm, abundant sarcoplasmic reticulum and dyads. Other retractors and the circular muscles are tonic fibers (A band > 3 µm), stronger (large volume of myoplasm) or with greater endurance (superior volume of mitochondria/ myoplasm). All of these retractor muscles are coupled by gap junctions and are innervated at two symmetrical points; they constitute two motor units implicated in withdrawal behaviour.The muscles inserted on the ciliary roots of the cingulum control swimming. They are multi-innervated and each of them constitute one motor unit. They have characteristics of very fast fibers; the shortest A-band length is 0.5 µm in Asplanchna.All the skeletal muscles of bdelloids are smooth or obliquely striated as are some skeletal muscles of monogononts. These muscles are well suited for maximum shortening and are either phasic or tonic fibers.All rotifer skeletal muscles originate from ectoderm and contain thin and thick myofilaments whose diameters are identical to those of actin and myosin filaments in vertebrate fast muscles or in insect flight muscles. There are no paramyosinic features in the thick myofilaments. The insertion, innervation, coupling by gap junctions and other cytological differentiations of rotifer skeletal muscles are reviewed and their phylogeny discussed.