Ultrastructure of the midgut and blood meal digestion in the adult tickDermacentor variabilis

Digestive cells in the midgut of male and femaleDermacentor variabilis (Say) took up the blood meal in coated vesicles and smooth flask-shaped vesicles, and deposited it in endosomes which were digested via heterophagy. Iron was concentrated in residual bodies.Digestion occurred in three distinct phases in mated females: (1) continuous digestion (initiated by feeding) occurred during slow engorgement; (2) reduced digestion (initiated by mating) occurred in mated females during the period of rapid engorgement; (3) a second continuous digestion phase (initiated by detachment from the host) occurred throughout the post-feeding periods of preoviposition and oviposition.It is proposed that the stem cells in the midguts of unfed females were progenitors of digestive, replacement, and presumed vitellogenic cells in midguts of mated feeding females. Digestive cells were present in all three digestion phases. Only during the first continuous digestion phase did digestive cells fill up with residual bodies, rupture and slough into the lumen, or did whole cells slough into the lumen. During the other two digestion phases no sloughing of digestive cells was observed. At the end of oviposition the digestive cells were filled with residual bodies. Replacement cells were present only during the first continuous-digestion phase. Presumed vitellogenic cells were present only during the reduced-digestion phase and during the second continuous-digestion phase. Stem cells in unfed males developed only into digestive cells in feeding males. Fed males and fed unmated females had only the first continuous-digestion phase. After being hand-detached from the host, unmated 13-day-fed females went through cellular changes associated with the reduced-digestion phase and second continuous-digestion phase of fed mated females, then began ovipositing. Maximum development of the basal labyrinth system and lateral spaces matched the known time of maximum water and ion movement across the midgut epithelia.Spectrophotometric analyses of lumen contents and midgut cells, sampled after detachment from the host, showed that concentrations of protein and hemoglobin at day 1 post-detachment decreased by one-half at the beginning of oviposition, while hematin increased about twofold by the end of oviposition. This supported the idea of the presence of a second continuous-digestion phase.     

Morphological aspects of blood digestion in a parasitic mite Bakericheyla chanayi

All life stages of B. chanayi (Acariformes: Cheyletidae) are characterized by occasional bloodsucking and a long period of digestion. No newly engorged mites were found during the period of their host birds' migration. The fine structure of the digestive tract of a blood-feeding acariform mite is described for the first time. The anterior midgut (AMG) is a place of blood digestion, while the posterior midgut (PMG) is involved in nitrogen metabolism forming guanine crystals as the main end-product. The AMG epithelium consists of digestive cells that probably arise from mitotically active basal cells with high synthesizing activity.As observed in ticks, blood digestion is accompanied by the formation of huge endosomes that serve as places of storage and sorting of ingested material. Digestive cells show different types of endocytotic activity as well as various late endosomes, which implies different subcellular pathways for different blood components. In both midgut regions, elimination of the excretory material occurs by apocrine secretion or by discharging of apical cell fragments (loaded with lysosomes) into the gut lumen. The formation of guanine granules occurs inside the lysosomes of PMG epithelial cells thus having much in common with intracellular digestion. Peculiarities of intracellular blood digestion were analyzed according to the modern hypothesis of endocytosis and compared to what is known in ticks.     

Digestion of host immunoglobulin and activity of midgut proteases in the buffalo fly Haematobia irritans exigua

The digestion of blood by the buffalo fly (Haematobia irritans exigua) was monitored for 6h at 33 degrees C after a single meal. Following the meal, the concentration of soluble protein within the midgut increased to a peak at 2 hours then decreased steadily over the next 4h. The magnitude of the increase in soluble protein at 2h indicated a release of protein from another source; most likely from lysed red blood cells. The immunoglobulin (IgG) fraction of the blood meal was digested rapidly (50% within one hour of feeding) and fully digested within 4h. This is indicative of its accessibility to digestive enzymes within the midgut. In contrast, when flies had continuous access to blood, the concentration of IgG in the midgut remained at a more constant level. The loss of antigen-binding activity of a specific antibody was more rapid than complete degradation of the IgG, with 70% of binding activity lost within one hour of feeding. The level of trypsin activity in the midgut increased from pre-feeding levels to reach a peak at 2h before returning to basal levels after 6h. The pattern of trypsin activity follows closely that of the concentration of soluble protein in the midgut (r=0.88). The activity of leucine aminopeptidase in the midgut also increased immediately after feeding and remained elevated for 4 h before declining to a basal level after 6h. The rapid digestion of IgG and subsequent loss of antibody activity suggests that for a specific anti-buffalo fly antibody to be effective it would need to be able to either evade the digestive system or induce a rapid response.     

银盾革蜱的中肠上皮变化与血餐消化

用光学显微镜及电子显微镜对不同生理状况下银盾革蜱Dermacentor niveus Neumann雌虫中肠上皮及血餐消化进行了研究.饿蜱的中肠只由一种干细胞组成,脂滴作为饿蜱营养的贮藏形式.非滞育蜱消化分三个阶段,即第一连续消化阶段,减慢消化阶段及第二连续消化阶段.吸血后中肠上皮共观察到四种细胞类型,即替代细胞、分泌细胞、消化细胞及卵赞原细胞.滞育蜱第一连续消化阶段延长.饱血后60天到120天,消化作用几近停止,为停滞消化阶段.卵黄原细胞的超微结构有明显改变.滞育解除后,开始进行减慢消化阶段及第二连续消化阶段.     

Ultrastructural studies on the midgut epithelium and digestion in the female tickArgas (Persicargas) arboreus (Ixodoidea: Argasidae)

The ultrastructure of the midgut epithelium and digestion in the female tickArgas (Persicargas) arboreus are described before and after feeding, up to oviposition. The epithelium consists of secretory cells, digestive cells (DI and DII), and regenerative cells which may differentiate into any of the other cell types. In unfed ticks, the midgut wall consists mainly of type DII digestive cells retained from a previous feeding, and a few regenerative cells. Within 3 days after the tick feeding, haemolysis of the host blood components occurs in the midgut lumen. Secretory cells, the first differentiation of the regenerative cells, are presumed to produce a haemolysin and an anticoagulant which are released by merocrine and holocrine secretions. The DII cells seen in unfed ticks, and secretory cells which have completed their secretory cycle, start to have a specialized surface for endocytosis characteristic of type DI digestive cells. From 5 to 7 days after feeding up to the female oviposition, type DI cells which have completed their endocytosis are transformed into type DII digestive cells specialized for intracellular digestion and the storage of reserve nutrients required by the tick for long starvation. The various phases of the digestive cycle are considered according to ultrastructural changes of the midgut epithelium.     

Morphofunctional changes in the midgut of tick nymphs of the genus Ixodes (Acarina: Ixodidae) during and after feeding

The midgut epithelium of feeding nymph is represented by the digestive cells of larval phase. Digestion of the main part of feed is performed by the one generation of digestive cells of nymphal phase after detachment, during moult. This period precedes the apolysis. The generation of secretory cells is absent on the nymphal phase. Secretory vacuoles are formed in the digestive cells of larval phase. All functioning cells form a peritrophic matrix on their apical surface. The replacement of the digestive cells of larval phase by the digestive cells of nymphal phase proceeds gradually, during the first 5-10 days after detachment. The beginning of the accumulation of digestive inclusions in the young digestive cells of nymphal phase takes place in the 10-15 days after detachment.     

Morphofunctional changes in the midgut of tick females of the genus Ixodes (Acari: Ixodidae) during and after feeding

Cyclic changes of the midgut epithelium were observed in females of 5 ticks species of the genus Ixodes during 7-10 days of feeding. The midgut epithelium of unfed females is represented by the digestive cells of nymphal phase and stem cells. The digestive cells of nymphal phase are functional during 1.5-2 days after attachment of the tick, and then, after the tearing away they go into the gut lumen. The secretory cells substitute the digestive cells of nymphal phase and finish their growth during the 4-4.5 days. Secretion of digestive enzymes is performed by the holocrine type with tearing away a whole cell. Intracellular digestion takes place in the digestive cells of four consequent generations. The secretory and digestive cells form a peritrophic matrix on their surface. The presence of peritrophic matrix gives an evidence the maturity and functional activity of the secretory and digestive cells. We suggest, that the peritrophic matrix takes part in intracellular digestion, namely in the process of micropinocytosis. The phagocytosis was not found in the ticks investigated. Digestion in the midgut lumen is performed by enzymes of the ruptured secretory and digestive cells, that is proved by the haemolysis of erythrocytes in the zone of their contact with these cells. The digestive cells of each generation functioned almost synchronously, with largest difference in starting about 12 hours.     

Nutrient-induced alpha-amylase and protease activity is regulated by crustacean cardioactive peptide (CCAP) in the cockroach midgut

The midgut plays a major role in digestion and absorption of nutrients in insects, and contains endocrine cells throughout the epithelial layer that express neuropeptides, including crustacean cardioactive peptide (CCAP). In the present study, we demonstrate regulation of digestive enzyme activities by CCAP in response to nutrient ingestion in the cockroach, Periplaneta americana. The midgut of the cockroach exhibits maximal alpha-amylase and protease activities 3 h after intake of either starch or casein, but not of non-nutrients. Similar time-dependent responses of CCAP expression in midgut endocrine cells were observed after feeding starch and casein, but not after non-nutrients. We also show that incubation of the dissected midgut with CCAP leads to an increase in alpha-amylase and protease activity in a time-dependent manner, with the maximal activity at 2 h. Taken together, our data indicate the existence of an inducible mechanism where endocrine cells in the midgut are stimulated to synthesize and secrete CCAP by nutrients, and CCAP then up-regulates the activity of digestive enzymes.     

Morphofunctional changes in the midgut of the Ixodes females (Acari: Ixodidae) during the immunizing feedings

The changes of the midgut in the females of the tick species Ixodes persulcatus and I. ricinus during the second and third immunizing feeding on rabbits were studied by the histological technics. The alternation of one generation of the digestive cells of nymphal stage and two generations of the digestive cells of adult stage was observed. The generation of secretory cells is absent. The tick completes feeding and drop off when the last generation of the digestive cells is on the initial activity stages. The amount of the blood consumed is not enough for the rhythmical functioning of the midgut. The feeding of tick is broken on the second phase and full satiation does not take place. It is apparently an effect of the interruption of the blood entrance into the midgut cavity of feeding tick as a probable result of anti-ticks resistance of unnatural hosts.     

The fine structure of the midgut of mite Myobia murismusculi

The pattern of digestion in females of Myobia murismusculi was studied with light and electron microscopy. The midgut consists of a stomach and two pairs of blind caeca. The stomach is connected dorsoposteriorly with the excretory organ, that leads externally to an anal opening via the cuticle-lined rectum. No differences were found between the stomach and its caeca. The midgut epithelial cells are of a single type. Their fine structure and gut contents greatly vary depending on different physiological conditions of the mite. Four stages of digestion can be shown with electron microscope. Pino- and phagocytose takes place in the same cells. At an active stage of digestion numerous pinocytic canals were observed in the midgut cells. At each stage of the digestive cycle groups of flat cells are present in the midgut epithelium. They do not take part in the intracellular digestion of food material. Cytoplasmic processes from the underlying cells of coxal glands project into the midgut cells through the orifices in the gut basal lamina.     

The interactive effects of exercise and feeding on oxygen uptake, activity levels, and gastric processing in the graceful crab Cancer gracilis

Exercise and digestive processes are known to elevate the metabolic rate of organisms independently. In this study, the effects of simultaneous exercise and digestion were examined in the graceful crab Cancer gracilis. This species exhibited resting oxygen uptake levels between 29 and 42 mg O(2) kg(-1) h(-1). In postprandial crabs, oxygen uptake was approximately double that of unfed crabs. During exercise, oxygen uptake increased three- to fourfold, reaching maximal levels of more than 130 mg O(2) kg(-1 ) h(-1). However, there was no difference in oxygen uptake during activity between unfed and postprandial animals. There was also no difference in exercise endurance levels between unfed and postprandial animals; both sets of animals were unable to right themselves after being turned on their backs, reaching exhaustion after 13-15 attempts. To determine whether increased activity affected gastric processes, the passage of a meal through the digestive system was followed using a fluoroscope. Passage of digesta through the gut system was slower in active animals than in resting crabs. Resting crabs cleared the foregut after approximately 18 h, which was significantly faster than the 34.5 h for constantly active animals. Likewise, the midgut region of resting animals was cleared at a faster rate than that of active animals. Because of residual amounts of digesta remaining in the hindgut, no difference in clearance rates of this section of the gut was evident. The slower clearance times of the foregut were due to a significantly slower rate of mastication of food, as evidenced by a lower cardiac stomach contraction rate. Contraction of the pyloric region of the foregut functions to move the digesta along the midgut, and there was a direct correlation between slower contraction rates of this region and the increased time of passage for digesta through the midgut of active animals. Because increased activity levels affected gastric processing, the crabs exhibited a behavioral response. During a 24-h period after feeding, there was a significant reduction in locomotor activity. The findings of this study suggest a prioritization of metabolic responses toward activity at the expense of digestion. This is discussed in relation to the ability of the crabs to balance the demands of competing physiological systems.     

Ultrastructural changes in the abdominal midgut of the mosquito, Culiseta melanura, during the gonotrophic cycle

Abdominal midguts of the mosquito, Culiseta melanura, were examined by light and electron microscopy 1 hr-14 days days after blood feeding. Epithelial cells were drastically altered from columnar to squamous in form after engorgement, and returned to columnar by day 4 after feeding. Accumulation of mitochondria along brush borders of digestive cells, followed by the appearance of large secondary lysosomes, accompanied blood digestion. Evidence was obtained that myelin-like material in the lysosomes, probably the result of mitochondrial autolysis, is extruded into the lumen. Digestive cells resumed their pre-blood meal appearance by 10-14 days post-engorgement. Regenerative cells were scattered throughout the basal portion of the epithelium, along with endocrine cells. Other midgut cells containing large, microvilli-lined apical cavities were identified in most specimens. No evidence of division or differentiation was obtained for any cell types.     

Changes in the digestive gland of the loliginid squid Sepioteuthis lessoniana (Lesson 1830) associated with feeding

Changes associated with feeding in the histological and cytological structure of the digestive gland of the loliginid squid Sepioteuthis lessoniana were examined, along with the nature of both the intracellular and extracellular enzymes produced by the gland. The timing of the release of the extracellular enzymes during the digestive cycle was also determined using a quantitative experimental program. Like that of all coleoid cephalopods, the digestive gland was characterised by one type of cell with several functional stages. As is the case for other loliginid squids, however, the digestive cells did not contain the large enzyme-carrying boules that characterise the digestive glands of most cephalopods. Instead, smaller secretory granules were found in the digestive cells and these may be the enzyme carriers. The prominent rough endoplasmic reticulum, large mitochondria and active Golgi complexes present in the digestive cells are characteristic of cephalopods and indicate a high metabolic activity. Like that of other cephalopods, endocytotic absorption of nutrients and intracellular digestion occurs in the digestive gland of this squid. From quantitative and qualitative examinations of structural changes in the digestive gland of S. lessoniana after feeding, a schedule of its function during the course of digestion was proposed. This indicated that digestion was very rapid, being completed in as little as 4 h in S. lessoniana. Extracellular digestive enzymes were only released after the first hour following feeding, which implies that they are stored in the stomach between meals to increase digestive efficiency.     

The antioxidant role of xanthurenic acid in the Aedes aegypti midgut during digestion of a blood meal

In the midgut of the mosquito Aedes aegypti, a vector of dengue and yellow fever, an intense release of heme and iron takes place during the digestion of a blood meal. Here, we demonstrated via chromatography, light absorption and mass spectrometry that xanthurenic acid (XA), a product of the oxidative metabolism of tryptophan, is produced in the digestive apparatus after the ingestion of a blood meal and reaches milimolar levels after 24 h, the period of maximal digestive activity. XA formation does not occur in the White Eye (WE) strain, which lacks kynurenine hydroxylase and accumulates kynurenic acid. The formation of XA can be diminished by feeding the insect with 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl] benzenesulfonamide (Ro-61-8048), an inhibitor of XA biosynthesis. Moreover, XA inhibits the phospholipid oxidation induced by heme or iron. A major fraction of this antioxidant activity is due to the capacity of XA to bind both heme and iron, which occurs at a slightly alkaline pH (7.5-8.0), a condition found in the insect midgut. The midgut epithelial cells of the WE mosquito has a marked increase in occurrence of cell death, which is reversed to levels similar to the wild type mosquitoes by feeding the insects with blood supplemented with XA, confirming the protective role of this molecule. Collectively, these results suggest a new role for XA as a heme and iron chelator that provides protection as an antioxidant and may help these animals adapt to a blood feeding habit.     

Digestive cells in the midgut of Triatoma vitticeps (Stal, 1859) in different starvation periods

Triatoma vitticeps (Stal, 1859) is a hematophagous Hemiptera that, although being considered wild, can be found in households, being a potential Chagas’ disease vector. This work describes the histology and ultrastructure of the midgut of T. vitticeps under different starvation periods. Fifteen adults of both sexes starved for 3, 7, 20 and 25 days were studied. In general, digestive cells had apical microvilli, basal plasma membrane infoldings and central nucleus. The perimicrovillar membrane was found in all insects examined. Digestive cells of anterior midgut had lipid droplets, glycogen granules, developed basal labyrinth associated with mitochondria suggesting their role in nutrient storage and in fluid and ion transport. The cells of median and posterior regions of the midgut were rich in rough endoplasmic reticulum, lysosomes, vesicles and granules with different electron-densities. Moreover, cells of the posterior portion of the midgut had hemozoyn granules and mitochondria in the apical cytoplasm close to microvilli, suggesting their role in blood digestion and active nutrient absorption. The midgut of T. vitticeps showed differences in digestive cells associated with the time after feeding, and the increase of vesicles amount in long starvation periods, which suggests enzyme storage, which is readily used after a blood meal.     

Morphofunctional changes in the midgut of the Ixodes ricinus nymphs (Acari: Ixodidae) during developmental diapause

Changes in the midgut of the Ixodes ricinus nymphs at the stage of developmental diapause were studied. It is established, that the midgut of the tick nymphs undergoes the identical and synchronous changes at the development without diapause and in the state of diapause. In 7-8 months after feeding the midgut of the nymphs containes the digestive cells with gematine and food inclusions, as well as reserve cells, like the midgut of unengorged moulted female. But the midgut of diapausing nymphs retaines such condition during the whole period of diapause.     

Morphometric analysis of Rhodnius prolixus Stal (Hemiptera:Reduviidae) midgut cells during blood digestion

Post-feeding ultrastructural modifications to the midgut cells of Rhodnius prolixus are quantified using morphometry. Changes in relative and absolute volumes and/or surface areas are demonstrated for the whole cells, nuclei, mitochondria, rough endoplasmic reticulum, lysosomes, Golgi apparatus, storage vesicles, glycogen, microvilli, and basal labyrinth, before and during blood digestion. These parameters are separately determined for cells from each of the three midgut regions, and are correlated against previously published cycles of digestive enzyme activities. The results support the proposed division of the midgut of R. prolixus into three functional regions: the anterior midgut or crop is the site of water transport immediately after feeding, and of lipid and glycogen storage. No protein digestion occurs in this region. The anterior intestine is the site of most proteinase synthesis and secretion, although limited absorption and nutrient storage also occurs. The posterior intestine is responsible for some secretory activity, but is also implicated as the most important region for absorption of digested nutrients and for carbohydrate absorption and storage.     

Specialization of midgut cells for synthesis of male isoprenoid pheromone components in two scolytid beetles,Dendroctonus jeffreyi and Ips pini

Endodermal or midgut cells have only recently been recognized as the site of pheromone synthesis in bark beetles. Midgut cells are not only specialized for digestion, but they have also been recruited to form isoprenoid compounds that function as pheromone components in Ips pini and Dendroctonus jeffreyi. Male bark beetle midgut cells are competent to produce isoprenoid pheromones after feeding or stimulation by juvenile hormone (JH) III. Competent midgut cells share many ultrastructural features with cells that do not secrete isoprenoid pheromone, but they are distinguished from these by abundant and highly ordered arrays of smooth endoplasmic reticula. During secretion, both midgut cells that produce pheromone and cells that do not are characterized by the presence of apical extrusions (apocrine secretion) rather than the presence of vesicles that fuse with the apical membrane and undergo exocytosis (eccrine secretion). Pheromone-producing cells of the midgut do not represent a population of cells that are distinct from cells involved in digestion. All, or most, midgut cells of male I. pini and D. jeffreyi can secrete pheromones as well as digestive enzymes.     

Long-Term Starvation and Posterior Feeding Effects on Biochemical and Physiological Responses of Midgut Gland of Cherax quadricarinatus Juveniles (Parastacidae)

We investigated the effect of long-term starvation and posterior feeding on energetic reserves, oxidative stress, digestive enzymes, and histology of C. quadricarinatus midgut gland. The crayfish (6.27 g) were randomly assigned to one of three feeding protocols: continuous feeding throughout 80 day, continuous starvation until 80 day, and continuous starvation throughout 50 day and then feeding for the following 30 days. Juveniles from each protocol were weighed, and sacrificed at day 15, 30, 50 or 80. The lipids, glycogen, reduced glutathione (GSH), soluble protein, lipid peroxidation (TBARS), protein oxidation (PO), catalase (CAT), lipase and proteinase activities, and histology were measured on midgut gland. Starved crayfish had a lower hepatosomatic index, number of molts, specific growth rate, lipids, glycogen, and GSH levels than fed animals at all assay times. The starvation did not affect the soluble protein, TBARS, PO levels and CAT. In starved juveniles the lipase activity decreased as starvation time increased, whereas proteinase activity decreased only at day 80. The histological analysis of the starved animals showed several signs of structural alterations. After 30 days of feeding, the starved-feeding animals exhibited a striking recovery of hepatosomatic index, number of molts, lipids and glycogen, GSH, lipase activity and midgut gland structure.     

Fine structure of the midgut gland of Phalangium opilio (Chelicerata,Phalangida)

Summary The fine structure of the midgut gland and the changes in composition associated with the digestive activity were examined in Phalangium opilio. In the epithelium four different types of cells are present: ferment cells, resorption cells, and digestion cells which probably turn into excretion cells, as can be seen by many intermediate stages. Ferment cells are found only in the midgut gland and in no other epithelia; therefore they should be regarded as a cell type. The relationship between digestion and resorption cells is not yet clear. No regeneration zone or single regeneration cells could be identified.The ultrastructural changes in these different cells during digestion are described, and their functional aspects are discussed. A hypothetical digestive cycle is constructed from these data. The results are compared with those on other chelicerate midgut glands.