The effect of ethoxyzolamide, an analogue of insect juvenile hormone, nor-adrenaline and iodine on changes in the optical path difference in the excretory cells and oesophagus during exsheathment in Haemonchus contortus

Davey K. G., Sommerville R. I. and Rogers W. P. 1982. The effect of ethoxyzolamide, an analogue of insect juvenile hormone, nor-adrenaline and iodine on changes in the optical path difference in the excretory cells and oesophagus during exsheathment in Haemonchus contortus. International Journal for Parasitology12: 509–513. Ethoxyzolamide, an inhibitor of carbonic anhydrase, markedly inhibits exsheathment of Haemonchus when the larvae are subsequently exposed to an exsheathing stimulus of CO₂ at 38.5°C. Ethoxyzolamide at 2 × 10^?5M does not prevent the increase in optical path difference in the oesophageal region which normally accompanies exsheathment, but markedly inhibits the increase in optical path difference in the excretory cells. An analogue of juvenile hormone (JHA; the methyl ester of 3,7,11 trimethyl-7,11-dichloro-2-dodecenic acid) does not affect the optical path difference in either the oesophagus or the excretory cells of ensheathed worms. When worms are artificially desheathed by exposure to NaOCl, a procedure which mimics the effect of CO₂ upon the oesophagus, but which does not affect the excretory cells, subsequent exposure to JHA at room temperature increases the optical path difference in the excretory cells. This increase is enhanced by subsequent incubation of the worms at 38.5°C at 30–60 min and further enhanced when CO₂ is present during the incubation at 38.5°C. The stimulation of the excretory cells by JHA is inhibited by ethoxyzolamide at 2 × 10^?5M. Noradrenaline at 10^?3M has no effect on ensheathed larvae, but causes an increase in optical path difference in the excretory cells of larvae desheathed with NaOCl. This increase is inhibited by ethoxyzolamide. A brief exposure to I₂ blocks the response of the excretory cells of both CO₂ and JHA, but does not significantly reduce the effect of nor-adrenaline. On the basis of these and previous results, it is proposed that both CO₂ and JHA stimulate a hypothetical CO₂ receptor which leads to the release of nor-adrenaline. The noradrenaline in turn stimulates, either directly or indirectly, the excretory cells.     

The structure of the excretory system of the infective larva of Haemonchus contortus

The excretory system of the infective larva of Haemonchus contortus consists of a tubular H-system with two excretory cells. The excretory cells contain electron-dense granules which may be a source of exsheathing fluid. Video microscopy indicates that the pulsation of the excretory ampulla is due to a cycle of filling and emptying controlled by the excretory valve. The apparent functional similarity between this system and the contractile vacuole complex of protozoa is discussed.     

Changes in water content and volume accompanying exsheathment of Haemonchus contortus

Davey K. G. and Rogers W. P. 1982. Changes in water content and volume accompanying exsheathment of Haemonchus contortus, International Journal for Parasitology12: 93–96. The exchange water volume was determined for ensheathed larvae, for larvae exsheathed by exposure to CO₂ and for larvae desheathed by exposure to a solution of NaOCl. Larvae exsheathed by exposure to CO₂ lose approx. 66 pl. of water while those desheathed by exposure to NaOCl lose approx. 50 pl. Larvae first desheathed by exposure to NaOCl lose a further 20 pl of water when subsequently exposed to CO₂. Volumes calculated from linear measurements of larvae demonstrate that larvae exsheathed by exposure to CO₂ lose about 69 pl of their total volume, while those desheathed by NaOCl lose about 54 pl. It is concluded that exsheathment may involve at least two parallel processes. Both processes are initiated by CO₂, while one is mimicked by exposure to NaOCl.     

The relationship between the rapid rejection of Haemonchus contortus larvae with cells and mediators in abomasal tissues in immune sheep

Rapid rejection or immune exclusion of challenge larvae is a well recognised phenomenon in sheep hypersensitised by repeated infection with gastrointestinal nematodes. While mast cells and globule leukocytes (GLs) are typically associated with this rapid rejection response, the exact mechanisms and mediators involved are not known. This study has adapted a recently developed ex vivo tissue explant model to examine in more detail the cells and mediators involved in preventing establishment of Haemonchus contortus L3s in abomasal tissue of sensitised sheep. Hypersensitisation of sheep by repeated larval infection resulted in a significant inhibition of larval establishment in abomasal tissue cultures and the extent of inhibition was dependent on the sensitisation dose. Both mast cells and GLs, but not eosinophils, were increased in abomasal tissues of hypersensitised sheep. Globule leucocyte numbers decreased significantly after 3 h of culture, independent of the addition of L3s. In contrast, mast cell numbers only decreased after addition of L3s to the tissue cultures and this was associated with an increased release of histamine in tissue washes after incubation with L3s. Although, there was no significant difference in the number of tissue eosinophils between the groups, there was a marked increase in the eosinophil-specific protein, galectin-14, in tissue washes of the hypersensitised sheep after culture, suggesting eosinophils and their products may play a hitherto unrecognised role in the rapid rejection response. Further studies using specific inhibitors in this ex vivo tissue explant model may delineate the relative role of each cell population and mediator in the rapid rejection process.     

Leucine aminopeptidase and exsheathing activity in preparations from Haemonchus contortus

Rogers W.P. and Brooks F. 1978. Leucine aminopeptidase and exsheathing activity in preparations from Haemonchus contortus. International Journal for Parasitology 8: 449–452. Exsheathing activity relative to leucine aminopeptidase activity (LAP) was greater in exsheathing fluid of infective juveniles of Haemonchus contortus than extracts of homogenates of the same organism. In both preparations the biological and enzyme activities were precipitated with acetone 20 v/v and ammonium sulphate, 40% saturation. Broad peaks of exsheathing and LAP activities obtained by sucrose density-gradient centrifugation and on Sephadex G150 overlapped but the peak of biological activity was always found on the low mol. wt. side of the LAP peak. LAP in exsheathing fluid was separated into two sharp peaks in polyacrylamide gradient-pore electrophoresis. In four experiments the major peak gave a mol. wt. within the limits 345,000–354,500. A minor peak was obtained at 1,800,000. Exsheathing activity remained broadly distributed but fell mostly on the low mol. wt. side of the major LAP peak.It is concluded that LAP cannot be the sole agent involved in exsheathment a lipase may be necessary to expose the substrate attacked by LAP.     

The interaction of Trypanosoma congolense and Haemonchus contortus in Djallonké sheep

The interaction between Trypanosoma congolense and Haemonchus contortus was studied in 5 groups of 8 Djallonké sheep. Two groups received a single infection with either H. contortus or T. congolense, and 2 groups were infected with T. congolense followed by H. contortus (TH) or vice versa (HT). One group was kept as uninfected controls. Mortality due to infection was observed only in the dual infection groups. In the TH group, the effects were more acute whereas in the HT group they were more chronic. No significant differences in weight gain could be demonstrated between infected and control groups. Djallonké sheep are able to withstand a single infection with either T. congolense or H. contortus, which confirms their trypanotolerant nature and provides preliminary indication of resistance against helminth infections. However, when exposed to successive infections with both parasites, some of the animals lose this tolerance.     

Further investigations of the primary mechanism of benzimidazole resistance in Haemonchus contortus

The binding of the [³H] benzimidazole carbamates (BZCs)—albendazole (ABZ), oxibendazole (OBZ), parbendazole (PBZ), mebendazole (MBZ), fenbendazole (FBZ) and oxfendazole (OFZ)—to tubulin from three ecologically-related isolates of adult Haemonchus contortus has been examined. The extent of binding of each BZC was inversely proportional to the known resistance status of the isolate. Biochemically, the change in the formation of the BZC-tubulin complex was due to a reduction in the amount of drug bound to resistant tubulin, with no significant change in the association constant of the complex. The resistance factors derived from the binding data support the hypothesis that the complex is ligand-dependent, with the aryl-substituted BZCs—MBZ, OFZ and FBZ—demonstrating lower resistance factors than those of the alkyl-substituted BZCs—ABZ, OBZ and PBZ. Examination of the slope derived from plots of binding against protein concentration demonstrated that the failure of resistant or partially resistant isolates to bind was due to either a decrease in the number of binding sites or, more likely, to reduced stability of the BZC-tubulin complex rendering it unstable to charcoal extraction.     

Observations on the self-cure reaction and other forms of immunological responsiveness against Haemonchus contortus in sheep

Self-cure reactions and immunological responses preventing establishment of Haemonchus contortus in sheep may operate as separate entities. In one experiment, self-cure occurred when challenge infection with 5000 larvae was superimposed on an infection with 5000 larvae given to worm-free sheep 6 weeks previously. Resident worms were rejected and establishment of infection by incoming larvae was impeded. The latter effect was not observed in sheep treated similarly but with resident parasites removed by treatment with oxfendazole before challenge. In another experiment, younger worm-free sheep primed by three infections with 2000 larvae at intervals of 2 weeks or a single infection with 6000 larvae were challenged with 10,000 larvae 6 weeks after the first priming infection. Self-cure was not incited but establishment of infection was impeded in sheep primed with three divided doses of larvae whether or not priming infections had been removed by oxfendazole. Infection regimes used for priming did not influence numbers of arrested fourth-stage larvae derived from challenge infection. However, more arrested larvae were present when challenge was superimposed on extant infections, indicating that resident worms or a factor activated by their presence induced developmental arrest. In a third experiment, large burdens with H. contortus were established in sheep immunosuppressed with the corticosteroid, dexamethasone, at the time of infection. Self-cure was not triggered by a challenge infection given 32 days later either in these sheep, or in sheep with a smaller worm burden derived from infection given without immunosuppression. Faecal egg counts, however, indicated that development of the challenge infection was prevented in both groups of sheep.

Investigation of self-cure is restricted by lack of a predictable system for reproducing the phenomenon. Self-cure was induced by a single infection with 5000 larvae in mature sheep but not with 6000 larvae in immature sheep. Three infections with 3000 larvae given at intervals of 2 weeks to mature sheep did not prime for self-cure. Procedures aimed at heightening immediate hypersensitivity, i.e. treatment with pertussis vaccine or concurrent infections with Ostertagia circumcincta, did not promote self-cure reactivity in the latter situation.     

Genetics of vulvar morph types in Haemonchus contortus: Haemonchus contortus from the Northern Tablelands of New South Wales

Le Jambre L. F. and Royal W. M. 1977. Genetics of vulvar morph types in Haemonchus contortus: Haemonchus contortus from the Northern Tablelands of New South Wales. International Journal for Parasitology7: 481–487. The inheritance of the vulvar morph types, smooth, knobbed, linguiform A-right, linguiform A-left and linguiform C-type was studied in Haemonchus contortus from the Northern Tablelands of New South Wales. The dominance hierarchy of these characters was found to be smooth > knobbed > linguiform. The linguiform phenotype was the most common in the wild type population. The modifications on the linguiform phenotype were found to be highly heritable with A-right responding most to selection. Realised heritabilities for these characters was A-right 0.37, A-left 0.15, and C-type 0.21. It appeared that the dominance of a phenotype increased following selection.     

A stochastic development fraction model for predicting the development of the nematode parasite of sheep, Haemonchus contortus from egg to infective larvae under the influence of temperature

1. 1 Regression models for predicting the minimum, the median and the maximum period of development of the parasite H. contortus from egg to the infective stage of constant temperature were described.

2. 2. Simulations were used to study the development of the parasite to the infective stage.

3. 3. Further, an analytic Stochastic Development Fraction Model was used to reproduce the development of the parasite obtained by simulations.

4. 4. The Stochastic Development Fraction Model was compared with the Deterministic Development Fraction Model to expose its potentials for predicting the development of parasites on pasture where varying temperature prevail.

Glutamate synthase, but not GABA shunt enzymes, contributes to nitrogen metabolism of the sheep abomasal nematode parasites Haemonchus contortus and Teladorsagia circumcincta

Glutamate synthase (E.C. 1.4.1.14) (GOGAT) activity was not detectable in L3 Haemonchus contortus, but was present in L3 Teladorsagia circumcincta and adult worms of both species. GOGAT activity was inhibited by 80% by azaserine. Activity (nmol min⁻¹ mg⁻¹ protein) was 33–59 in adult H. contortus, 51–91 in adult T. circumcincta and 24–41 in L3 T. circumcincta, probably depending on exposure to ammonia, as incubation with 1 mM NH₄Cl doubled GOGAT activity. The pH optimum was 7.5 in both species. Either NAD or NADP acted as co-factor. The mean apparent K_m for 2-oxoglutarate was 0.7 (0.5–0.9) mM and for glutamine was 1.0 (0.5–1.7) mM for different homogenates. There was no detectable activity in whole parasite homogenates of glutamate decarboxylase (E.C. 4.1.1.15) or succinic semialdehyde dehydrogenase (E.C. 1.2.1.24), the first and third enzymes of the GABA shunt, respectively, suggesting that the GABA shunt is not important in general metabolism in these species.     

Changes in polysome content during development after diapause of Bombyx mori embryos

Undegraded polysomes could be extracted from eggs of Bombyx mori by cutting egg shells with a blade in a buffer containing high salt. The polysome content as measured by this method increased steeply during post-diapause development, which was commenced by long term chilling followed by hot HCl treatment of diapausing eggs. At the 24th hr of the post-diapause development the polysome content became 2.6-times the level at 0 h. The alteration of the polysome content paralleled that of the incorporation of [¹⁴C]leucine into acid-insoluble fractions investigated by modified Takami's embryonic culture system.     

Expression of genes in gastrointestinal and lymphatic tissues during parasite infection in sheep genetically resistant or susceptible to Trichostrongylus colubriformis and Haemonchus contortus

Resistance to an acute gastrointestinal nematode (GIN) infection is dependent on the ability of the host to recognise the parasite and mount a protective Th2 response. It is hypothesised that lambs which are genetically susceptible to GIN will differentially up-regulate Th1-type genes and therefore remain susceptible to chronic parasitism compared with genetically resistant lambs which will differentially up-regulate Th2-type genes and clear the parasite infection. Two selection flocks, in which lines of Merino sheep produced lambs genetically resistant or susceptible to GIN, were acutely challenged once or thrice with either Haemonchus contortus or Trichostrongylus colubriformis. Faecal-egg counts (FECs), and plasma and tissue anti-parasite (H. contortus or T. colubriformis) antibody isotype responses showed that resistant animals challenged three times with T. colubriformis established a protective Th2 response (negligible FEC, IgG1 and IgE) whereas susceptible animals required multiple challenges to establish a significant IgG1 response despite FECs remaining high. Trichostrongylus colubriformis elicited a more pronounced host response than H. contortus. RNA extracted from tissues at the site of each parasite infection and associated lymph nodes were interrogated by microarray and quantitative PCR analyses to correlate host gene expression to FECs and antibody responses. The IFN-γ inducible gene cxcl10 was up-regulated in the susceptible line of the Trichostrongylus selection flock sheep after a tertiary challenge with the parasites H. contortus and T. colubriformis. However, a uniform pattern of genes was not up-regulated in resistant animals from both selection flocks during both parasite infections, suggesting that the mode of host resistance to these parasites is different, although some similarities in host susceptibility were apparent.     

Changes in the dynamics of structured water and metabolite contents in early developing stages of eggs of turbot (Psetta maxima)

The dynamics of structured water and the contents in main metabolites were determined using two techniques of nuclear magnetic resonance (NMR) for the developing eggs of the flatfish Psetta maxima. The unfrozen water (structured water), and its thermodynamic properties were modified during embryogenesis, especially in two developmental stages, from ova to morula (8 h), and from organogenesis (70 h) to the pre-hatching stage (128 h). These modifications were closely related to the metabolization of vitelloproteins and consequently to the concentration of aminoacid and choline compounds.     

Changes of the caecal villi during postnatal development in rats

Summary The villi of the caecal mucosa in postnatal rats were studied using both scanning electron and light microscopy.On the day of birth, numerous villi of various sizes and shapes were present on the caecal mucosa. After the 5th day, the villi decreased very rapidly in length and in number. A strong constriction was observed at the basal region of the caecal villi. During postnatal days 5 9 the villi probably separated and disappeared from the caecal mucosa. No villi were observed in rats that were over 10 days of age.     

紫花含笑花被呈色过程中色素含量与超微结构的变化特征

为了探究色素含量以及细胞结构在紫花含笑花被呈色过程中的作用机理,该研究以绿色和紫色花被为材料,测定其花被色素含量,运用逐步回归方程分析花被呈色与色素含量的关系,采用石蜡切片及超薄切片技术观察花被细胞超显微结构变化。结果表明:(1)在紫花含笑花被呈色过程中,紫色花被表面明度L^*值降低,a^*值上升,b^*值降低;花被花青素苷的积累量以及类胡萝卜素和类黄酮等含量增加,同时伴随着叶绿素的降解及其含量降低。(2)a^*与花青素、类黄酮、类胡萝卜素等色素含量以及花青素/类黄酮、花青素/叶绿素呈显著正相关关系,b^*与叶绿素含量和花青素/类胡萝卜素呈显著正相关关系。(3)在细胞结构上,随着花被由绿转紫,其上表皮细胞由扁平型向圆锥凸起型变化,单个细胞长宽比增大,细胞垂周壁出现褶皱,紫色花被上表皮结构向增加入射光吸收面积变化;液泡体积增大与叶绿体向有色体转化是主要的细胞器变化。研究发现,花被呈色是多因素作用的结果,花青素含量的产生与积累以及类胡萝卜素和类黄酮等含量增加辅助增色可能是紫花含笑呈紫色的主要...     

Changes in replicon behaviour during the S period in Sorex araneus cells in culture

The parameters of DNA replicon synthesis have been examined at successive stages in the S period of synchronised Sorex araneus (S3/4) cells in culture by DNA fibre autoradiography. Both mean rate of chain growth and distance between initiation sites remain constant. There is, however, an indication that during mid-S, when cells are subjected to the maximum utilization of the DNA-elongating system, there is a slight reduction in the rate of chain elongation, particularly among the faster growing chains of DNA.     

Schistosoma japonicum (Chinese): Changes of the tegument surface in cercariae, schistosomula and juvenile parasites during development

, , , and 1988. Schistosoma japonicum (Chinese): changes of the tegument surface in cercariae, schistosomula and juvenile parasites during development. International Journal for Parasitology18: 1093–1104. The surface of cercariae of S. japonicum (Chinese) and changes following their transformation into schistosomula were observed at 0.5,1, 3,6,12,24 and 48 hand 5,7,10 and 15 days by scanning electron microscopy. The cercarial surface shows two distinct regions: on the head and the body it is mildly undulating and covered throughout with numerous spines that are partially embedded in a thick layer of glycocalyx; on the tail it is highly folded into tall and thin circumferential ridges, spines are confined to the dorsal and ventral aspects and are prominent due to a thinner glycocalyx. Between 0.5 and 12 h following skin penetration, the surface of schistosomula is gradually cleared of glycocalyx, while small blebs and slender microvilli project out from the glycocalyx-free area and from spines. Subsequently, these structures are detached from the surface and thus responsible for the shedding of the original cercarial membrane and glycocalyx. Between 24 and 48 h, schistosomula show little change in the body size in comparison to earlier stages, and most of the surface is still covered with spines but devoid of blebs and microvilli. From day 2 onwards schistosomula are lengthened but with little net growth. Spines decrease in the middle region of the body; and the surface is invaginated by small pits and folded into thin ridges, which result in rapid increase of the surface area. Between days 5 and 7 schistosomula elongate further, and the disappearance of the spines in the middle region becomes even more pronounced, while those remaining are confined only to the anterior and posterior extremities. Ridges and pits are more developed, and the former begin to show regular foldings throughout all parts of the body. Between days 7 and 10 schistosomula grow rapidly and the body is quadrupled in size. Between days 10 and 15 sexes can be differentiated. The male has a flat ovoid shape body, whose ridges and pitting on the surface are highly developed almost to the same extent as in adult parasites, while spines remain mostly on the posterior end. Sensory papillae greatly increase in number, especially on the ventral and lateral aspects and around the suckers. The surface of the female is relatively smooth; ridges are developed only on the posterior part, while the remaining surface is flat and extensively pitted. Spines are present throughout but less concentrated in the middle region.     

Nippostrongylus brasiliensis and Haemonchus contortus: Function of the excretory ampulla of the third-stage larva

An improved technique for measuring the water content of nematodes is described using an electronic interferometer. Changes in phase of a laser beam passing through a known pathlength of the nematode have been used to measure the refractive index and hence the water content and relative volume of the animal. Third-stage larvae of Nippostrongylus brasiliensis and Haemonchus contortus which possess an excretory ampulla, differed from second-stage larvae lacking this ampulla in requiring a greater fall in the osmolarity of artificial tap water before there was a significant increase in their water content. Increases in the pulsation frequency of the ampulla also occurred in less hypotonic solutions than those required to increase the water content of the third-stage larvae. The ampulla pulsation frequency of third-stage larvae of N. brasiliensis increased after locomotor activity in hypotonic tap water and locomotory wave frequency of third-stage larvae of N. brasiliensis was independent of the extent of hypotonicity for a range of solutions that reduced wave propogation by its second-stage larva. The results suggest that the ampulla is an adaptation to hypotonic conditions favouring a volume homeostasis that is required for optimal locomotor activity of the third-stage infective larvae of these nematodes.