Leucine aminopeptidase activity in the digestive tract of perch, Perca fluviatilis L.

The distribution of the enzyme leucine aminopeptidase (LAP, EC 3.4.1.1) in the digestive tract of perch, Perca fluviatilis L., was investigated histochemically. The enzyme was present in the mucosa of the entire intestine and was absent in the oesophagus, stomach and pyloric sphincter. In the intestine, the enzyme was localized in the supranuclear cytoplasm of the columnar cells and was strongest in the brush border area. Enzyme activity was also present in the lumen of the intestine. The activity of the enzyme in the intestine decreased slightly towards the rectum. In perch, the final digestion of peptides and aminopeptides is both extracellular and intracellular and takes place along the entire length of the intestine.     

Gross morphology and histology of the alimentary tract of the convict cichlid Amatitlania nigrofasciata

The primary objectives of this study were to document the macroscopic and histological structure of the alimentary tract (AT) of the convict cichlid Amatitlania nigrofasciata, because there are no data available for this omnivorous freshwater fish of the family Cichlidae. The morphology of the AT of A. nigrofasciata resembles that of related species. While having morphological criteria of the AT typical of most omnivorous fishes, such as a blind sac stomach and medium length intestine, A. nigrofasciata also has some structural peculiarities: the oesophagus is lined by a uniform stratified squamous epithelial layer with interspersed goblet cells along its entire length. Additionally, it has well‐developed layers of the tunica muscularis including muscle fibre bundles that ascend into its mucosal folds. Occasionally, taste buds are present. In the transitional area between oesophagus and stomach, a prominent torus‐like closure device is present. The mucosa of the stomach cannot be divided into different regions according to mucosal and morphological properties. The simple pattern of intestinal loops of A. nigrofasciata has few variations, irrespective of sex, mass and length of the individual fish. The first segment of the intestine is characterized by the largest mucososerosal ratio and the most complex mucosal surface architecture. A distinction of midgut and hindgut was not possible in A. nigrofasciata due to lack of defining structural components as described for other fish species.     

Visualization of calcium transients controlling orientation of ciliary beat

To image changes in intraciliary Ca controlling ciliary motility, we microinjected Ca Green dextran, a visible wavelength fluorescent Ca indicator, into eggs or two cell stages of the ctenophore Mnemiopsis leidyi. The embryos developed normally into free-swimming, approximately 0.5 mm cydippid larvae with cells and ciliary comb plates (approximately 100 microns long) loaded with the dye. Comb plates of larvae, like those of adult ctenophores, undergo spontaneous or electrically stimulated reversal of beat direction, triggered by Ca influx through voltage-sensitive Ca channels. Comb plates of larvae loaded with Ca Green dextran emit spontaneous or electrically stimulated fluorescent flashes along the entire length of their cilia, correlated with ciliary reversal. Fluorescence intensity peaks rapidly (34-50 ms), then slowly falls to resting level in approximately 1 s. Electrically stimulated Ca Green emissions often increase in steps to a maximum value near the end of the stimulus pulse train, and slowly decline in 1-2 s. In both spontaneous and electrically stimulated flashes, measurements at multiple sites along a single comb plate show that Ca Green fluorescence rises within 17 ms (1 video field) and to a similar relative extent above resting level from base to tip of the cilia. The decline of fluorescence intensity also begins simultaneously and proceeds at similar rates along the ciliary length. Ca-free sea water reversibly abolishes spontaneous and electrically stimulated Ca Green ciliary emissions as well as reversed beating. Calculations of Ca diffusion from the ciliary base show that Ca must enter the comb plate along the entire length of the ciliary membranes. The voltage-dependent Ca channels mediating changes in beat direction are therefore distributed over the length of the comb plate cilia. The observed rapid and virtually instantaneous Ca signal throughout the intraciliary space may be necessary for reprogramming the pattern of dynein activity responsible for reorientation of the ciliary beat cycle.     

Seasonal changes in morphology and function of the gastrointestinal tract of free-living alpine marmots (Marmota marmota)

The gastrointestinal tracts of 76 free-living alpine marmots ( Marmota marmota) shot during a population control program in Switzerland were collected and analysed for patterns of change in morphology and function over the period from emergence from hibernation in April to just before re-entry into hibernation in September. Between first emergence and mid-summer (July) the fresh tissue mass of the stomach increased by 105%, the small intestine by 259% (among the largest recorded for a mammal), caecum by 185%, proximal colon by 138%, and distal colon by 144%. Mitotic activity was greatest in the small intestine; the mitotic index was high (40%) compared with indexes in the stomach and hindgut (approximately 4%) even at emergence, and increased to approximately 60% by mid-summer. Microbial activity in the caecum was also significant at emergence. The stomach (length) and caecum (length and fresh mass) increased in response to ingested food earlier than did the small intestine. Between mid-summer and September there were decreases in small intestinal tissue mass and mitotic activity. It is concluded that the gastrointestinal tract of alpine marmots probably continues to function throughout hibernation at a low level, with a mid-winter trough as part of an endogenous circannual rhythm. However, after emergence in spring, increases in size and activity of the tract appear to be a response to ingested food rather than to an endogenous signal. The early signs of down-regulation of the small intestine before re-entry into hibernation, together with its delayed up-regulation in response to food in spring, are consistent with the high costs of maintaining this section of the digestive system.     

光唇鱼消化道的形态结构特征

采用解剖及石蜡切片显微技术,观察研究了光唇鱼消化道的形态结构特征。消化道由口咽腔、食道、肠构成。口下位、马蹄形,无颌齿,具咽齿,齿式为4/4。舌较小,前端游离,舌粘膜表层为复层鳞状上皮,有较多的杯状细胞和味蕾。食道及肠均由粘膜层、粘膜下层、肌层及外膜构成。食道内皱襞发达,粘膜层有大量杯状细胞。肠道盘曲,由前、中、后肠组成,肠长/体长为1.84±0.24;前肠管腔较大,中、后肠管腔渐变小;前、中肠皱襞及纹状缘比后肠发达;前肠及后肠杯状细胞较少,中肠杯状细胞较多。光唇鱼消化道的形态结构特征与其食性相适应。     

Does diet variation determine the digestive tract length of Capoeta banarescui Turan,Kottelat, Ekmekci and Imamoglu, 2006?

This study tested the spatial variations in the digestive/intestine tract length of Capoeta banarescui, with regard to their diets in different habitats. Highly varied diets observed in a previous study within the same river system posed the question whether this flexibility is reflected in the digestive tract and intestine length of the species in the Ye?il?rmak River, Turkey. Totals of 382 specimens (standard length 4.6–19.1 cm) were captured by electro‐fishing along the river in September 2012 at 11 locations spanning elevations from 34 to 992 m. The stomach, intestine and total digestive tract lengths were measured, and stomach contents analysed from 196 specimens. For statistical analyses, the stomach, intestine and total digestive tract length were expressed as percentages of total weight and standard length. The data provided evidence that the digestive tract and intestine lengths varied significantly among locations in association with the diet. Fish having dominantly carnivorous diets (e.g. chironomid larvae/invertebrates) in two locations had significantly shorter intestines and digestive tracts than those with diets dominated by benthic algae and other plants. The data indicated that C. banarescui showed broad flexibility in their feeding habits. Feeding heavily on plant materials might lead to the development of longer digestive tracts, increasing the active surface area for digestion; alternatively, there may be less invested in development of the digestive tract when feeding primarily on carnivorous diets where the respective digestive enzymes are readily available. The data suggest that phenotypic plasticity in the digestive tract length of C. banarescui is associated more with the abundant protein‐rich carnivorous food sources in the studied habitats. Whether this digestive tract plasticity has a genetic background remains to be verified in future studies.     

Arousal and re-feeding rapidly restores digestive tract morphology following aestivation in green-striped burrowing frogs

During aestivation, the gut of the green-striped burrowing frog, Cyclorana alboguttata undergoes significant morphological down-regulation. Despite the potential impact such changes might have on the re-feeding efficiency of these animals following aestivation, they appear to be as efficient at digesting their first meals as active, non-aestivating animals. Such efficiency might come about by the rapid restoration of intestinal morphology with both arousal from aestivation and the initial stages of re-feeding. Consequently, this study sought to determine what morphological changes to the intestine accompany arousal and re-feeding following 3 months of aestivation. Arousal from aestivation alone had a marked impact on many morphological parameters, including small and large intestine masses, small intestinal length, LF heights, enterocyte cross-sectional area and microvilli height and density. In addition, the onset of re-feeding was correlated with an immediate reversal of many morphological parameters affected by 3 months of aestivation. Those parameters that had not returned to control levels within 36 h of feeding generally had returned to control values by the completion of digestion (i.e. defecation of the meal). Re-feeding was also associated with several changes in enterocyte morphology including the incorporation in intracytoplasmic lipid droplets and the return of enterocyte nuclear material to the 'active' euchromatin state. In conclusion, morphological changes to the gut of aestivating frogs which occur during aestivation are transitory and rapidly reversible with both arousal from aestivation and re-feeding. The proximate causes behind these transitions and their functional significance are discussed.     

Seasonal changes in pH values in the intestine of fish from Lake Chany (West Siberia)

The pH values are determined in the digestive tract of nine fish species in Lake Chany (West Siberia). Seasonal changes in pH values are found along the intestine of fish. Intestinal pH values decrease in summer as the temperature rises and increase during the cold season as the temperature drops. The hypothesis has been advanced that temperature-dependent pH changes in the intestine may serve as a regulatory mechanism that maintains the activity of hydrolytic enzymes at the level required for successful digestive processes due to some adaptive modifications of the medium where these enzymes operate.     

The unique ultrastructure of the uterus of the Gyrocotylidea Poche, 1926 (Cestoda) and its phylogenetic implications

The members of the order Gyrocotylidea are monozoic tapeworms and generally considered to be the most primitive group of the Cestoda in terms of the evolution of this platyhelminth class. As part of a series of ultrastructural studies on Gyrocotyle urna (Wagener, 1852), three regions of the uterus were distinguished. The proximal region of the uterus is characterised by underlying perikarya, the presence of septate junctions within the epithelial wall and two types of specialised outer coverings, lamellae and cilia. The middle, syncytial region of the uterus is covered by short lamellae and marked by a concentration of sunken glandular perikarya (uterine glands). Glandular spheroidal granules (c.0.45 μm in diameter) of moderately dense content and a fine fibrillar texture are liberated by migration through the luminal membrane. The epithelium of the sac-shaped, distal region of the uterine duct is interrupted by cytoplasmic processes of sunken epithelial bodies, covered with lamellae and contains septate junctions. A muscular sphincter surrounds the narrow, terminal region of the distal uterine duct. The ultrastructural pattern of the uterus of the Gyrocotylidea has important discriminating traits (i.e. the presence of sunken perikarya along its entire length, septate junctions within the uterine epithelial cytoplasm of the proximal and distal regions, and cilia on the surface of its proximal region) unique among the Neodermata and which may represent autapomorphic character states for the group.     

Effects of long-term exposure to different salinities on the location and activity of Na+-K+-ATPase in the gills of juvenile mitten crab, Eriocheir sinensis

The euryhalinity of mitten crab, Eriocheir sinensis, is based on osmoregulation, and thus on the activity of Na(+)-K(+)-ATPase. We studied location and activity of this enzyme in gills of juvenile crabs exposed to 5 per thousand, 25 per thousand, and 40 per thousand salinity. The posterior gills showed always a high number of immunopositive cells (IPC), staining with fluorescent antibody against Na(+)-K(+)-ATPase, covering at 5 per thousand the entire lamellae. At 25 per thousand, they showed fewer IPC which occurred only at the bases of the lamellae. Enzyme activity was consistently higher in posterior than in anterior gills. Low salinity stimulated the activity only in posterior gills. Both histochemical and enzymatic results are consistent with previous ultrastructural observations showing that the epithelial cells of the posterior, but not the anterior gills exhibit typical traits of ionocytes. While an increase in Na(+)-K(+)-ATPase activity at a reduced salinity is consistent with a strong hyper-osmoregulatory capacity in juvenile crabs, a low activity at an enhanced salinity suggests a physiological response, directed towards a reduction of Na(+) uptake. The activity increase of ion-transporting enzymes is directly related to spatial changes in their distribution along the osmoregulatory tissue, i.e. an enhanced number of IPC scattered along the entire lamellae. In juveniles, this allows for successful development and growth at reduced salinities.     

Morphological characterization of the alimentary tract of Antarctic fishes and its relation to feeding habits

Summary Morphological and morphometric characteristics of the alimentary tract in 22 species of carnivorous antarctic fishes were studied. It is shown that all of these species have similar, well-developed Y-shaped stomachs with generally thick (0.5–1.0 mm) walls. The relative stomach lengths are also similar, ranging from 9.8 to 22.2% of body length. Relative intestine lengths, a characteristic frequently used as an indicator of the kind of food eaten by a species, are also remarkably similar among most species (31 to 67%). Notothenia gibberifrons, a conspicuous benthos feeder, has a significantly longer intestine (91%), probably as an adaptation to the quantity of undigestible material (mud) incorporated with its faunal prey. These values fit within or below the limits (60–150$) of relative intestine length described in the literature for carnivorous fishes. The number of pyloric caecae is in general relatively low and fairly constant in each species. It is concluded that the morphological features studied could represent similar adaptations of these antarctic fishes to a similar carnivorous diet.     

洞庭湖区社鼠消化道长度和质量的季节变化

对洞庭湖区社鼠（Niviventer confucianus）自然种群四季的消化道各器官的长度和质量进行了测定。结果表明。消化道指标季节变化明显。总体消化道含内容鲜质量、净鲜质量与干质量均具有显著的季节变化。以冬、春季较高。夏、秋季较低。消化道各器官的变化与总消化道不尽相同。其中,以胃的变化相对比较稳定。仅长度的变化达显著水平,以冬季最短,夏、秋季较长。这是动物为适应繁殖季节能量需求而增加摄食量的反应,也与夏秋季食物丰富度有关。小肠、盲肠、大肠的长度和质量指标（内容鲜质量、净鲜质量和干质量）以冬、春季较高。夏、秋季较低。这是该鼠对冬、春季低温和食物匮乏的适应性反应。总体来说。洞庭湖区社鼠为适应夏、秋季繁殖盛期能量需求增加的主要对策是增加摄食量;而为适应冬、春季低温环境和食物数量和质量减少的主要对策是增大消化道。提高消化效率。     

Localization of cystathionine β-synthase in digestive tract of the masu salmon <Emphasis Type="Italic">Onchorhynchus masou</Emphasis> (Teleostei)

By immunohistochemical method the hydrogen sulfide (H₂S)-producing system was studied in digestive tract in fry and adult masu salmon Onchorhynchus masou. The general and agerelated peculiarities have been revealed in morphology, distribution, and the amount of enteric cystathionine β-synthase (CBS)-immunopositive neurons. They have been established to be present in fry only in esophagus and stomach, while in adult fish—along the entire length of the digestive tract, the number of marked cells in esophagus, stomach, and distal intestine exceeding that in the proximal and middle intestine. In fry and in adult fish, the neurons and nerve fibers are located in branches of vagus, in intermuscular and submucosal nerve plexuses, in serosal and muscle layers. There are detected uni-, bi-, and, much seldom, multipolar neurons surrounded by numerous poorly or undifferentiated nerve cells. Besides, the CBS-immunopositive nerve fibers were present in the subepithelial area of the duct of swim bladder.     

Spatial and salinity-induced alterations in claudin-3 isoform mRNA along the gastrointestinal tract of the pufferfish Tetraodon nigroviridis

In fishes, variation in paracellular permeability is important for regulating salt and water balance. Paracellular permeability is maintained by TJs in vertebrate epithelia. This study examined the spatial distribution and effects of salinity on claudin-3 isoform mRNA expression and abundance along the gastrointestinal (GI) tract of the euryhaline puffer fish (Tetraodon nigroviridis) and related these to morphological heterogeneity of the TJ complex. The puffer fish GI tract was divided into three regions (anterior, middle and posterior) and four isoforms of claudin-3 (Tncldn3a, Tncldn3b, Tncldn3c and Tncldn3d) were found to be expressed in each section. The effect of freshwater (FW) or seawater (SW) acclimation on regional 1) Tncldn3 isoform mRNA abundance, 2) TJ complex morphology and 3) Na⁺–K⁺-ATPase (NKA) activity was examined. In situ hybridization indicated that all Tncldn3 isoforms localized to the mucosal epithelium in the intestine. The mRNA abundance of Tncldn3 isoforms varied spatially along the GI tract. Furthermore, region as well as isoform specific alterations in mRNA abundance could be observed along the GI tract in response to salinity change. Qualitative TEM observations suggested that the depth of TJ complexes increased from anterior to posterior along the GI tract and that TJ complexes in the GI tract of FW fish were deeper than those in SW. NKA activity increased from anterior to posterior in fish acclimated to FW, whereas activity in fish acclimated to SW was uniformly high along the length of the intestine. Taken together data; (1) suggest a progressive decrease in epithelial permeability from anterior to posterior along the longitudinal axis of the puffer fish GI tract, (2) indicate that claudin-3 protein isoforms may play a role in regulating paracellular movement of solutes across this epithelium, and (3) provide further evidence that claudin-3 proteins are involved in the homeostatic control of salt and water balance in fishes.     

Digestive flexibility in females of the subterranean rodent ctenomys talarum in their natural habitat

We studied the occurrence of digestive strategies at different levels in females of the subterranean herbivorous rodent Ctenomys talarum living in their natural habitat. We determined the dimensions of different parts of the gastrointestinal tract and organs along as the activity of key digestive enzymes(sucrase, maltase and N-aminopeptidase) in small intestine in females seasonally caught. Females of C. talarum did not show seasonal variations in the mass of the different parts of the gastrointestinal tract. In nonreproductive females large intestine was longer in autumn, whereas reproductive females did not show seasonal variations in the length of the different parts of the gut. Females of C. talarum exhibited a high sucrose, maltase and N-aminopeptidase activity in small intestine, although these activities were higher in small intestine of females caught in autumn (nonreproductive) than in females caught in winter (reproductive). The results show that C. talarum females exhibit characteristics in the gut at the morphological and biochemical level, which could represent digestive strategies to face the constraints imposed by their costly particular way of life.     

On the morphology of the alimentary tract of flatfishes (Pleuronectiformes)

The changes during the life cycle in the relative length of certain parts of the alimentary tract, buccal-pharyngeal cavity, oesophagus-stomach, intestine, rectum—are investigated in the five North Sea flatfish species, viz. turbot, brill, plaice, dab, sole. According to the average ratio between the length of the alimentary tract and the food preference three main groups are distinguished.     

Morphological adaptations of the digestive tract of tropical cyprinids and cichlids to diet

Eight cyprinids with four different feeding habits fall into two distinct groups according to morphological adaptations of the intestine: (i) carnivorous and omnivorous cyprinids with large gut diameter and large mucosal surface which decreases from the foregut to the hindgut; (ii) benthivorous and phytoplanktivorous cyprinids with small gut diameter and small mucosal surface which is more or less uniformly built along the intestine, although relative gut length may vary considerably (1.45–6.10). Although the intestine of phytoplanktivorous cyprinids is extremely elongated, it appears less adapted for processing a refractory diet than that of cichlids with similar feeding habits.