Histological organization of the intestine in the crayfish Procambarus clarkii

Six longitudinal ridges span the length of the intestine in the crayfish Procambarus clarkii. A simple columnar epithelium with tetralaminar cuticle lines the lumen. Folds of the epithelium overlie a dense irregular connective tissue packed with mixed acinar (alveolar) glands. Mucous secretions are probably involved with formation and lubrication of faecal strings; neither the nature nor the role of the serous secretions is immediately apparent. Aggregations of cells with large cytoplasmic vacuoles, called bladder cells, appear in the subepithelial connective tissue near the tops of the intestinal ridges. The bladder cells are suitably positioned to bolster the integrity of the ridges. Striated muscle of the intestine occurs in inner longitudinal and outer circular layers. The inner longitudinal layer consists of six strips, with one strip associated with the base of each intestinal ridge. The outer circular layer is essentially complete, but there are periodic apertures in this layer on the left and right sides of the intestine, providing nerves and haemolymph vessels with access to the interior of the gut. Based on histological features, and consistent with reports on other crayfish, we conclude that the intestine of P. clarkii has a proctodeal (ectodermal) origin.     

Direct and indirect innervation of smooth muscle cells of rat stomach,with special reference to the interstitial cells of Cajal

Interstitial cells of Cajal in the circular (ICC-CM) and longitudinal (ICC-LM) muscle layer of the rat gastric antrum and their innervation were studied ultrastructurally. Both ICC-CM and ICC-LM are characterized by many mitochondria, rough and smooth endoplasmic reticulum, caveolae, and formation of gap junctions with each other and with muscle cells, though ICC-LM tend to show more variable cytoplasmic features depending on section profiles. Close contacts between nerve terminals and both ICC-CM and ICC-LM are observed. These possible synaptic structures are characterized by: (1) accumulation of synaptic vesicles in nerve varicosities, (2) a narrow gap (about 20 nm) between pre- and postjunctional membranes, (3) lack of a basal lamina between pre- and postjunctional membranes, and (4) the presence of an electron-dense lining on the inner aspect of prejunctional membranes. Almost the same characteristics are observed between the nerve terminals and the muscle cells of both circular and longitudinal muscle layers of the same specimens. Therefore, we conclude that the smooth muscle cells of both circular and longitudinal layers of the rat antrum are directly and indirectly innervated via ICC. Their functional significance is discussed.     

Characterization of interstitial cells of Cajal in the subserosal layer of the guinea-pig colon

Interstitial cells of Cajal in the subserosa (ICC-SS) of the guinea-pig proximal colon were studied by immunohistochemistry for c-Kit receptors and by transmission electron microscopy. These cells were distributed within a thin layer of connective tissue space immediately beneath the mesothelium and were multipolar with about five primary cytoplasmic processes that divided further into secondary and tertiary processes to form a two-dimensional network. Ultrastructural observations revealed that ICC-SS were connected to each other via gap junctions. They also formed close contacts and peg-and-socket junctions with smooth muscle cells. Three-dimensional analysis of confocal micrographs revealed that the cytoplasmic processes of ICC-SS had contacts with interstitial cells in the longitudinal muscle layer. Taking account of the location and peculiar arrangement of the ICC-SS and the main functions of the proximal colon, i.e. the absorption and transport of fluids, we suggest that the superficial network of ICC-SS acts as a stretch receptor to detect circumferential expansion and swelling of the colon wall and triggers the contraction of the longitudinal muscle to accelerate the drainage of fluids from the colon.     

Structural characterization of interstitial cells of Cajal in myenteric plexus and muscle layers of canine colon

We have carried out a detailed ultrastructural study of the interstitial cells near the myenteric plexus of the canine colon and defined the structural characteristics which distinguish them from other resident non-neural cells. We have also examined the interconnections of these interstitial cells with nerves, the longitudinal muscle, and the circular muscle. In addition, we sought connections between interstitial cells of the myenteric plexus and those described earlier at the inner border of the circular muscle in proximal and distal colon. The interstitial cells of the myenteric plexus were structurally distinctive, and made gap junctions with one another and occasionally with smooth muscle. There seemed to be two subsets of these interstitial cells, one associated with the longitudinal muscle and the other with the circular muscle. Cells of both subsets were often close (less than or equal to 20 nm) to nerve profiles. The interstitial cells near the longitudinal muscle layer penetrated slightly into the muscle layer, but those near the circular muscle did not and neither set contacted the other. Moreover, interstitial cells of Cajal located near the myenteric plexus were never observed to contact those at the inner border of circular muscle. The interstitial cells of Cajal at the canine colon myenteric plexus are structurally organized to provide independent pacemaking activities for the longitudinal and adjacent circular muscle. Their dense innervation suggests that they mediate neural modulation of intestinal pacemaker activities. Moreover, they lack direct contacts with the interstitial cell network at the inner border of circular muscle, which is essential for the primary pacemaking activity of circular muscle. The structural organization of interstitial cells in canine colon is consistent with their proposed role in pacemaking activity of the two muscle layers.     

Scanning electron microscopy of the muscle coat of the guinea-pig small intestine

Summary We have studied the layers of the muscular coat of the guinea-pig small intestine after enzymatic and chemical removal of extracellular connective tissue. The cells of the longitudinal muscle layer are wider, have rougher surfaces, more finger-like processes and more complex terminations, but fewer intercellular junctions than cells in the circular muscle layer. A special layer of wide, flat cells with a dense innervation exists at the inner margin of the circular muscle layer, facing the submucosa. The ganglia of the myenteric and submucosal plexuses are covered by a smooth basal lamina, a delicate feltwork of collagen fibrils, and innumerable connective tissue cells. The neuronal and glial cell processes at the surface of ganglia form an interlocking mosaic, which is loosely packed in newborn and young animals, but becomes tightly packed in adults. The arrangement of glial cells becomes progressively looser along finer nerve bundles. Single varicose nerve fibres are rarely exposed, but multiaxonal bundles are common. Fibroblast-like cells of characteristic shape and orientation are found in the serosa; around nerve ganglia; in the intermuscular connective tissue layer and in the circular muscle, where they bridge nerve bundles and muscle cells; at the submucosal face of the special, flattened inner circular muscle layer; and in the submucosa. Some of these fibroblast like cells correspond to interstitial cells of Cajal. Other structures readily visualized by scanning electron microscopy are blood and lymphatic vessels and their periendothelial cells. The relationship of cellular elements to connective tissue was studied with three different preparative procedures: (1) freeze-cracked specimens of intact, undigested intestine; (2) stretch preparations of longitudinal muscle with adhering myenteric plexus; (3) sheets of submucosal collagen bundles from which all cellular elements had been removed by prolonged detergent extraction.     

Electrical coupling in the circular muscles of dog jejunum.

Two distinct layers of circular muscle have previously been demonstrated in dog jejunum, the main circular layer containing many gap junction contacts, and an inner dense muscle layer where no gap junctions have been found. Length constants were determined for these muscle layers and no significant difference was found between these values. The main circular muscle cells had lower membrane potentials and may have had abnormally low space constants owing to injury. It was concluded that the absence of gap junctions in the inner dense layer does not reduce the spread of passive current as might be expected of electrically isolated cells, and it is suggested that an alternate pathway for passive current exists in this layer.     

Further observations on upper urinary tract smooth muscle

Summary Light and electron microscopic techniques have been employed to study the arrangement and distribution of two types of muscle in the upper urinary tract of the rat. An outer layer of cells has been identified in the wall of the renal calix and pelvis. These cells are separated by connective tissue but possess numerous processes which make close contacts with adjacent cells. A layer of similar cells has not been observed in the wall of the upper ureter. The inner layer of muscle in the calix and pelvis is composed of larger cells similar to and apparently continuous with ureteric muscle. These cells are closely related to one another without intervening connective tissue and possess numerous bundles of myofilaments which extend along the length of the cell. The two types of muscle are closely related and, in the junctional region, cells of the outer layer are arranged along the length and make close contacts with one or more of the inner smooth muscle cells. A quantitative estimation has been made of nerve bundles associated with smooth muscle forming the outer layer of the calix and pelvis and with the muscle of the ureter. The results have shown a five fold increase in nerves associated with the caliceal muscle when compared with the ureter. The results are discussed in relation to the concept of a ureteric pacemaker.The authors wish to thank Professor G. A. G. Mitchell for his useful advice and encouragement.     

A new genus and species of heteronemertean from the Changjiang (Yangtze) River Estuary

A new genus and species of heteronemertean, Yinia pratensis gen. nov. and sp. nov., collected from low salinity waters (salinity 0.2–0.4 ‰) at Changjiang River Estuary, is described and illustrated. The species possesses a proboscis with an outer circular and an inner longitudinal muscle layer, and is placed in family Lineidae sensu Gibson. The following combination of morphological features distinguishes the new species from any other genera in this family: proboscis with two muscle crosses; dermis without connective tissue layer between gland cells and body wall outer longitudinal muscle layer; rhynchocoel wall circular muscles not interweaving with adjacent body wall longitudinal muscles; foregut with circular somatic muscles and subepithelial gland cell layer; neurochord cells present in central nervous system; caudal cirrus missing; blood system developed into alimentary plexus extending almost the full length of the body. Another significant character is that the lobular excretory cells are extremely well developed which may represent adaptation to water of low salinity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Histologic, morphometric, and immunocytochemical analysis of myometrial development in rats and mice: I. Normal development

Myometrial development from the prenatal to adult period was examined in rats and mice 1) by histologic and immunocytochemical methods with anti-actin, -vimentin, and -laminin to assess cytodifferentiation of smooth muscle and fibroblastic cells; and 2) by morphometric procedures to assess quantitatively the expression of cellular orientation in the emerging inner circular myometrial layer. Uterine mesenchymal cells initially were uniformly vimentin-positive, undifferentiated, and randomly oriented during the late fetal period. By the early neonatal period, three mesenchymal layers became recognizable histologically, the middle one of which (prospective circular myometrium) developed distinct circular orientation and differentiated into a layer composed of actin-positive smooth muscle cells. The cells of the inner mesenchymal layer initially exhibited radial orientation. By 10 days postpartum, the outer longitudinal mesenchymal layer differentiated into bundles of smooth muscle cells representing the longitudinal myometrium. The inner mesenchymal layer remained vimentin-positive and differentiated into the randomly ordered endometrial stroma. The cells of the middle and outer mesenchymal layers that were destined to form myometrium initially expressed vimentin throughout and then coexpressed vimentin and actin, but with time vimentin staining disappeared in the maturing smooth muscle cells as they expressed actin.     

A new genus and species of monostiliferous hoplonemertean (Nemertea: Enopla: Monostilifera) from Japan

A new genus and species of monostiliferous hoplonemertean, Diopsonemertes acanthocephala gen. et sp. nov., is described from Otsuchi Bay, Japan. Significant anatomical features of the new form include a body wall longitudinal musculature anteriorly divided into inner and outer layers by connective tissue, no pre-cerebral septum, the presence of a thin coat of diagonal muscle fibres between the body wall longitudinal and circular muscle layers in the foregut body region, cephalic retractor muscles derived only from the inner portion of the divided longitudinal muscles and a rhynchocoel more than half the body length.     

Ovipositor ultrastructure of the striped bitterling Acheilognathus yamatsutae (Teleostei: Acheilognathinae) during spawning season

The ovipositor of striped bitterling Acheilognathus yamatsutae was subjected to ultrastructure and histochemical analysis during spawning season using light and electron microscopy. Although the ovipositor of A. yamatsutae is a long cylindrical tube with smooth external surface, it was possible to confirm the presence of well-developed fingerprint structure using scanning electron microscopy. Internal aspect analysis of ovipositor revealed formation of 5–8 longitudinal folds. Cross section analysis revealed that the ovipositor is composed of an outer epithelial layer, a mid connective tissue layer, and an inner epithelial layer. The outer epithelial layer contains 7–9 cell layers composed mainly of epithelial and mucous cells. Result of AB–PAS (pH 2.5) and AF–AB reaction showed that mucous cells contained mainly acidic carboxylated mucosubstances. The connective tissue layer was loose and made mainly of collagen fibers and some muscle fibers, along with blood vessels and a small number of chromatophores. The inner epithelial layer, which is a single layer, is composed of columnar epithelia. Observation under transmission electron microscope enabled distinction of the outer epithelial layer into superficial, intermediate and basal layers. Although the types of cells in the superficial tissue layer were diverse, they all shared the development of glycocalyx covered microridges. The majority of epithelial cells in the intermediate layer were cuboidal shaped, while those in the basal layer were columnar. Two types (A and B) of secretory cells were observed in the outer epithelial layer. The connective tissue layer had two types of chromatophores including xantophore and melanophore, in addition to a well-developed nerve fiber bundles. Columnar epithelial cells, mitochondria-rich cells and rodlet cells were observed in the inner epithelial layer. Microvilli were well developed on the free surface of columnar epithelial cells.     

Some ultrastructural features of the muscular coat of human small intestine

The muscular coat of human small intestine is constituted by a 'special' layer, by the main component of the circular layer, by the region between the circular and the longitudinal layers and by the longitudinal layer. The 'special' layer is made up of the innermost 4-6 rows of muscle cells of the circular layer and is separated from the main component of the circular layer by a space in which an abundant connective tissue and numerous nerve fibers rich in nerve endings are located. Cells identified as interstitial cells of Cajal are located inside the 'special' layer, the space between it and the main component of the circular layer and in the region between the circular and the longitudinal layers. In this region small bundles of obliquely orientated muscle cells, apparently bridging the circular to the longitudinal layer, are found.     

Immunohistochemical and ultrastructural characteristics of interstitial cells of Cajal in the rabbit duodenum. Presence of a single cilium

Santiago Ramón y Cajal discovered a new type of cell related to the myenteric plexus and also to the smooth muscle cells of the circular muscle layer of the intestine. Based on their morphology, relationships and staining characteristics, he considered these cells as primitive neurons. One century later, despite major improvements in cell biology, the interstitial cells of Cajal (ICCs) are still controversial for many researchers. The aim of study was to perform an immunohistochemical and ultrastructural characterization of the ICCs in the rabbit duodenum. We have found interstitial cells that are positive for c-Kit, CD34 and nestin and are also positive for Ki67 protein, tightly associated with somatic cell proliferation. By means of electron microscopy, we describe ICCs around enteric ganglia. They present triangular or spindle forms and a very voluminous nucleus with scarce perinuclear chromatin surrounded by a thin perinuclear cytoplasm that expands with long cytoplasmic processes. ICC processes penetrate among the smooth muscle cells and couple with the processes of other ICCs located in the connective tissue of the circular muscle layer and establish a three-dimensional network. Intercellular contacts by means of gap-like junctions are frequent. ICCs also establish gap-like junctions with smooth muscle cells. We also observe a population of interstitial cells of stellate morphology in the connective tissue that sur-rounds the muscle bundles in the circular muscle layer, usually close to nervous trunks. These cells establish different types of contacts with the muscle cells around them. In addition, the presence of a single cilium showing a structure 9 + 0 in an ICC is demonstrated for the first time. In conclusion, we report positive staining c-Kit, CD34, nestin and Ki 67. ICCs fulfilled the usual transmission electron microscopy (TEM) criteria. A new ultrastructural characteristic of at least some ICCs is demonstrated: the presence of a single cilium. Some populations of ICCs in the rabbit duodenum present certain immunohistochemical and ultrastructural characteristics that often are present in progenitor cells.     

日本血吸虫尾蚴发育的超微结构观察：Ⅲ.肌肉

在超微结构水平对日本血吸虫发育期尾蚴的主要肌肉包括体壁、头器、腹吸盘和尾部等进行观察,首次证明发育期体壁肌层组织最早见于Ｓ２,在原始基膜（ＰＢＬ）下方有１￣２层类似纤丝胞质块,为早期肌细胞管状胞质延伸至原始基膜下的结构,Ｓ３这种现象更为明显;典型体壁外环肌与内纵肌在Ｓ４与Ｓ５已形成。腹吸盘早期原始肌细胞的分化见于Ｓ３,至Ｓ５强大的腹吸盘肌纤维已形成。文章首次提出内间质层在Ｓ３、Ｓ４的体部存在及Ｓ５     

Immunohistochemical localization of a gap junction protein (connexin43) in the muscularis externa of murine,canine, and human intestine

Electron-microscopic studies have revealed a heterogeneous distribution of gap junctions in the muscularis externa of mammalian intestines. This heterogeneity is observed at four different levels: among species; between small and large intestines; between longitudinal and circular muscle layers; and between subdivisions of the circular muscle layer. We correlated results obtained with two immunomethods, using an antibody to the known gap-junctional protein (connexin43) with ultrastructural findings, and further evaluated the respective sensitivity of these two approaches. For comparative reasons we also included the vascular smooth muscle of coronary arteries into our study. Two versions of the immunotechnique (peroxidase-antiperoxidase and fluorescence methods) were applied to frozen sections of murine, canine, and human small and large intestines, as well as to pig coronary artery. In the small intestine of all three species a very strong reactivity marked the outer main division of the circular muscle layer, while the longitudinal muscle layer as well as the inner thin division of the circular muscle layer were negative. In murine and human colon both muscle layers were negative, while in canine colon the border layer between the circular muscle and the submucosa reacted strongly, and scattered activity was found in the portion of the circular muscle layer (one tenth of its thickness) closest to the submucosa. The remainder of the circular muscle layer and the entire longitudinal muscle layer were negative in the canine colon. In the coronary artery we could not confirm the positive, specific labeling reported by other investigators (l.c.). In conclusion, we found close correlations at all four above-mentioned levels in the distribution of gap junctions in the gut musculature, as determined by binding of anticonnexin43 in comparison to conventional ultrastructural studies. Since no significant immunostaining was found in (i) the outer border of the circular muscle layer of the canine colon and (ii) the border layer between the submucosa and the circular muscle layer of human colon, where rare gap junctions have been identified at the ultrastructural level, we conclude that the electron-microscopic analysis is the more sensitive of the two methods.     

Ultrastructure of the dorsal hemal vessel in the sea-cucumber Parastichopus tremulus (Echinodermata: Holothuroidea)

The dorsal hemal vessel in Parastichopus consists of three distinct layers: An outer flagellated epithelium, an intermediate circular muscle layer and an inner connective tissue layer which nearly fills the lumen. Between the outer and intermediate layer runs strands of nerve fibers. Each coelomic epithelial cell has one flagellum and some microvilli. It contains a number of different vacuoles and a few bundles of tonofilaments. One special type of vacuole which contains well organized myofilaments is described. Each muscle cell contains one myofibril of a non-striated type consisting of thick and thin filaments and no dense bodies. The sarcoplasmic reticulum is poorly developed, but peripheral coupling are frequently found. The muscle cells in the dorsal hemal vessel of Parastichopus are compared with other muscles in echinoderms and muscle types described in other phyla.     

Histological and histochemical studies on regeneration and tissue differentiation in the crab Menippe rumphii (Fabricius) (Crustacea: Brachyura)

In the process of regeneration the crab secretes an outer three-layered fibrous exoskeleton, consisting of outer thin parenchymatous vacuolated layer, an elastin layer, and a collagen layer. The origin and synthesis of these layers have been discussed. Similarly a two-layered inner cuticle is also secreted during the process of regeneration. Together with this, tissue differentiation takes place inside the growing limb bud. The rôles of the cells responsible for the secretion of the outer and inner cuticular layers have been discussed. Various histochemical tests have been employed to study the chemical nature of the cuticular layers, connective tissue cells, tegumental glands, and haemocytes. Two types of connective tissue cells and four types of haemocytes were identified. The rôles of the haemocytes, tegumental glands, and connective tissue cells in tissue differentiation are also discussed.     

Musculature of the penial complex: A new criterion in unravelling the phylogeny of Hygrophila (Gastropoda: Pulmonata)

The taxonomy of freshwater pulmonates (Hygrophila) has been in a fluid state warranting the search for new morphological criteria that may show congruence with molecular phylogenetic data. We examined the muscle arrangement in the penial complex (penis and penis sheath) of most major groups of freshwater pulmonates to explore to which extent the copulatory musculature can serve as a source of phylogenetic information for Hygrophila. The penises of Acroloxus lacustris (Acroloxidae), Radix auricularia (Lymnaeidae), and Physella acuta (Physidae) posses inner and outer layers of circular muscles and an intermediate layer of longitudinal muscles. The inner and outer muscle layers in the penis of Biomphalaria glabrata consist of circular muscles, but this species has two intermediate longitudinal layers separated by a lacunar space, which is crossed by radial and transverse fibers. The muscular wall of the penis of Planorbella duryi is composed of transverse and longitudinal fibers, with circular muscles as the outer layer. In Planorbidae, the penial musculature consists of inner and outer layers of longitudinal muscles and an intermediate layer of radial muscles. The penis sheath shows more variation in muscle patterns: its muscular wall has two layers in A. lacustris, P. acuta, and P. duryi, three layers in R. auricularia and Planorbinae and four layers in B. glabrata. To trace the evolution of the penial musculature, we mapped the muscle characters on a molecular phylogeny constructed from the concatenated 18S and mtCOI data set. The most convincing synapomorphies were found for Planorbinae (inner and outer penis layers of longitudinal muscles, three-layered wall of the penis sheath). A larger clade coinciding with Planorbidae is defined by the presence of radial muscles and two longitudinal layers in the penis. The comparative analysis of the penial musculature appears to be a promising tool in unraveling the phylogeny of Hygrophila.     

Histology and Ultrastructure of the Body Wall in the Phoronid Phoronopsis harmeri

The histology and ultrastructure of the body wall in Phoronopsis harmeriwere studied using light microscopy and TEM. The ectoderm epithelium of tentacles, anterior body region, and ampulla consists of monociliary cells. Gram-negative bacteria were found between microvilli, in the protocuticle of the anterior region, and in the ampulla. The epithelium of the posterior body region lacks both monociliary cells and bacteria. The bundles of nerve fibers run between the layer of epithelial cells and basal membrane. The musculature of the body wall comprises circular and longitudinal muscles. The circular muscle fibers are applied to the basal membrane and constitute a solid layer extending almost throughout the length of the body. This pattern is broken in the posterior body region, where there is no solid layer of circular musculature, and the latter is arranged in isolated muscle bands. In the ampullar (terminal) body region, the inversion of circular and longitudinal muscle layers takes place, so that the latter appears to be pressed against the basal membrane. The apical surfaces of longitudinal muscle cells bear cytoplasmic processes; some of the cells have a flagellum. The basal portion of the longitudinal muscle cells forms a cytoplasmic process containing bundles of tonofilaments. The processes of all cells making up the muscle bands are interwoven and anchored to the basal membrane.     

Histological description of the midgut and the pyloric valve of Tropidacris collaris (Stoll, 1813) (Orthopetera: Romaleidae).

The present research describes the histology of the midgut, gastric caeca, and pyloric valve of Tropidacris collaris (Stoll, 1813), (Orthopetera: Romaleidae). We used light microscopy, staining (Gomori's trichrome and periodic acid-Schiff (PAS)), and a routine histological analysis method (hematoxilin-eosin). The insects were obtained from, and also bred in, the Laboratory of Entomology, Department of Biology, of the Rural Federal University of Pernambuco (UFRPE). The collected material was fixed in alcoholic Botüin and embedded in paraplast. The results demonstrated that the midgut wall is composed of an inner epithelial layer and two outer layers of striate muscles: one internal (circular) and the other external (longitudinal), with connective tissue between the muscle fibers. The epithelium is single-layered, with two cell types: regenerative and elongated columnar. The gastric caeca presents muscle layers similar to those of the midgut. Simple columnar epithelium lines the gastric caeca, which presents villi and projects towards the lumen. The pyloric valve is of striate muscle tissue, covered by a single epithelial-cell layer.