Occurrence of Bucephaloides gracilescens metacercariae in three species of gadoid fish

Bucephaloides gracilescens metacercaria is a common encysted trematode parasite of whiting, Merlangius merlangus (L), haddock, Melanogrammus aeglefinus (L), and hake, Merluccius merluccius (L), in the Irish Sea. The incidence of infection over an 18-month period was uniformly high (whiting, 95%; haddock and hake, 100%). The major site of infection in all three hosts was the cranial fluid surrounding the brain. Large numbers of cysts were also found embedded in the spinal nerves posterior to the anus in haddock and hake and in the auditory capsules in whiting and haddock. Other sites of infection included the spinal canal, cranial nerves (V, VII, VIII, X), eye muscles, orbits and nasal region. Results are discussed in the light of previous records of gasterostome trematodes in the Gadidae.     

Accumulation of the lipophilic environmental contaminant lindane in metacercariae of Bucephaloides gracilescens (Trematoda, Bucephalidae) in the central nervous system of bullrout Myoxocephalus scorpius

Bucephaloides gracilescens is a common parasite in the intestine of the angler fish Lophiuspiscatorius, and the metacercariae have been recorded from a number of gadoid intermediate hosts. In a toxicokinetic study of lindane (gamma-hexachlorocyclohexane) in bullrout Myoxocephalus scorpius, metacercariae of B. gracilescens were found in the central nervous system (CNS). Furthermore, the metacercariae accumulated concentrations of lindane that were higher than in the surrounding CNS tissue. This is the first report of metacercariae of B. gracilescens in bullrout. In addition the present results contribute knowledge of the disposition of an important environmental contaminant in the metacercarial stage of a trematode that has been pointed out as a promising sentinel species of pollution in the marine environment.     

The occurrence of metacercariae of Bucephaloides gracilescens (Digenea: Gasterostomata) in an intermediate host, the four-bearded rockling, Enchelyopus cimbrius (Gadidae)

Infections with metacercariae of Bucephaloides gracilescens in the four-bearded rockling Enchelyopus cimbrius were studied for a year in a Norwegian fjord. The prevalence was at all times high, but abundance showed a marked decline in spring to a low level during summer. A rise in abundance, variance-to-mean ratio and frequency of smaller metacercariae in early autumn (August-September) shows infection to have occurred mainly in autumn. There were no differences in level of infection between host sexes, but a highly significant positive correlation of parasite burden with host length. No influence on the condition factor of the host was revealed, the parasite cysts in the central nervous system are believed to have low pathogenicity. A detailed account of the distribution of metacercarial cysts is given. No support for infection being via the lateral line canals is revealed, cercarial penetration is believed to be through the general surface of the head and through the unpaired fins of the trunk and tail.     

An ultrastructural study of the early cercarial development in Prosorhynchoides borealis (Digenea: Bucephalidae) with special reference to formation of the primitive epithelium

Primitive epithelium and outer tegumental layer formation during early cercarial development was studied in Prosorhynchoides borealis using electron microscopy. It demonstrated that germinal cells freely floating in the sporocyst body cavity divide to give rise to naked cell aggregates. These early embryos are highly irregular in outline and are composed of blastomeres differing in size and structure. In embryos consisting of about 12-14 cells a few (possibly only two) superficial macromeres become concave and produce thin extensions which envelop the embryonic mass before fusing to form a syncytial primitive epithelium. This primitive epithelium forms syncytial connections with underlying embryonic cells. Primordial tegumental cells become apparent in late germinal balls below the primitive epithelium. These cells expand and fuse to give rise to an embryonic nucleated tegument. The embryonic tegument is connected to peripheral embryonic cells by thin cytoplasmic bridges until the basement lamina is formed. Subsequently, the primitive epithelium is shed by the embryos and the nuclei in the embryonic tegument undergo pyknotic degeneration. These results are analysed and compared with data from studies on other trematode species and it is concluded that the primitive epithelium is derived from the embryo in at least the majority of digeneans.     

Schistosoma manonsi: cercarial penetration of host epidermis at the ultrastructural level

Invasion of the outer layers of the epidermis of mouse ear skin by cercariae of Schistosoma mansoni within 7 min of their application to it has been studied with the optical and the scanning and transmission electron microscopes.Entrance of cercariae was under the edges of the dead flattened keratinized cells of the horny layer (squames), and penetration through this layer was by disarticulation of the stacks of squames at their interdigitations. Mucus from the postacetabular glands was recognized with the light and electron microscopes on the skin surface, especially at squame edges and between layers of squames and along the keratogenous zone. The findings suggested that disarticulation of the squames was not effected solely by the muscular probing and pushing of the parasite, but that it might be aided by swelling of the mucus secretion deposited in the area from the postacetabular glands. Loosening of the interlocked edges of the squames by enzymatic action is also a possibility, but was not evaluated for this report.The migration path along the keratongenous zone was marked by extensive damage to the transitional cells of the granular layer subjacent to the squames. Packets of secretion from the cercarial preacetabular glands were identified below the horny layer in the cytoplasm of these cells. It was considered that the host tissue damage in this area was the result not only of tearing of the tissues by passage of the spiny schistosomules, but also of enzymatic activity, the enzyme source being the granules in the packets of preacetabular gland secretion.     

Mechanisms involved in parasitic castration: in vitro effects of the trematode Prosorhynchus squamatus on the gametogenesis and the nutrient storage metabolism of the marine bivalve mollusc Mytilus edulis

The mechanisms involved in the parasitic castration of the marine mussel Mytilus edulis by the trematode parasite Prosorhynchus squamatus Odhner, 1905, have been investigated in vitro with two bioassays employing dissociated host tissues. There is no conclusive evidence that P. squamatus affects the secretion of two host neuroendocrine factors, viz., gonial mitosis-stimulating factor and glycogen mobilization hormone, involved in the gametogenesis/nutrient storage cycles of the mussel. In contrast, extracts of P. squamatus sporocysts and cercariae significantly stimulated glycogen mobilization in host glycogen cells and strongly inhibited host gonial mitosis. A gonial mitosis-inhibiting factor (GMIF) was found in the hemolymph of parasitized mussels. The existence of an endogenous GMIF in mantle tissue of uninfected mussels has been demonstrated. This factor appeared to be secreted into the hemolymph during the period of sexual maturity. Whether the parasite acts directly on the host gonia, or by provoking the liberation of this endogenous GMIF, has yet to be ascertained. It would appear, however, that the parasite acts directly on host glycogen cells.     

An ultrastructural study of osmiophilia in the human rectum

Synopsis Rectal biopsies from subjects with a normal rectum and from patients with various forms of inflammatory bowel disease were studied by the prolonged osmication technique. No consistent ultrastructural differences were observed between these groups, but there were striking differences between individual epithelial cells in the same biopsy and between the epithelium and the cells of the lamina propria. The Golgi apparatus was demonstrated occasionally in the epithelium, often in endothelium. Endoplasmic reticulum, perinuclear cisterna and mitochondria were variably outlined. In plasma cells, there were striking differences in osmiophilia.The underlying mechanism of the different staining patterns is not clear. The findings do not appear to help in the differential diagnosis of inflammatory bowel disease nor to shed any new light on their underlying pathogenic mechanisms.     

An ultrastructural and cytochemical study of the digestive system in Oxyposthia praedator (Turbellaria,Acoela)

The central parenchyma in Oxyposthia praedator consists of multifunctional cells. These cells digest food material intracellularly, can effect extracellular digestion through release of digestive enzymes by cell lysis and clasmatosis, and synthesize reserve nutritional substances.     

Morphogenesis of the hydrogenosome: An ultrastructural study

Summary— The morphogenesis of hydrogenosomes in several trichomonad species (Tritrichomonas foetus, Trichomonas vaginalis, Tritrichomonas suis, Trichomonas gallinae, Tritrichomonas augusta and Monocercomonas sp) was investigated by transmission electron microscopy of thin sections and freeze-fracture replicas of whole cells or the isolated organelle. Close proximity, and even continuity, between endoplasmic reticulum and hydrogenosomes was observed. Structures were seen connecting hydrogenosomes to each other and to cytoplasmic structures. Morphological evidence is presented showing that in all the trichomonads here studied, hydrogenosomes, like mitochondria, may divide by two distinct processes: segmentation and partition. In the segmentation process, the hydrogenosome grows, becoming enlongated with the appearance of a constriction in the central portion. Microfibrillar structures appear to help the furrowing process, ending with a total fission of the organelle. In the partition process, the division begins by an invagination of the inner hydrogenosome membrane, forming a transversal septum, separating the organelle matrix into two compartments. We suggest that myelin-like structures seen either in close contact with or in the vicinity of the hydrogenosomes may be a source of membrane lipids for hydrogenosome growth.     

An ultrastructural study of the human micropolycystic ovary

The basement membrane of follicles in the micropolycystic ovaries of infertile women was thickened compared to that in the ovaries of normal women or those with typical polycystic ovaries.     

Effects of treatment with noradrenaline and isoproterenol on the excretory portion of the submaxillary gland in the rat: an ultrastructural study

The aim of this study is to evaluate the modification of the excretory portion and its comparison with the acinus, on stimulating the rat submaxillary gland with noradrenaline and isoproterenol. Stimulation of the submaxillary gland with these drugs for a period of 10 min produces different effects in the acinus and excretory portion. The secretory granules do not show reorganisation of their contents after stimulation with isoproterenol, while in the acinus the material is reorganised forming concentric laminae. After stimulation with noradrenaline, the acinar lumen increases its diameter with respect to the control groups, while this same stimulus does not modify the diameter of the ductal lumen. After stimulation with noradrenaline, the extracellular spaces are consistently obliterated in all ducts except the striated duct, in which the behaviour is variable as in the acinus. In these two latter cases, the extracellular spaces are visible in some cases and not in others. Stimulation with noradrenaline is a potent stimulus of synthesis in both the granular undulated duct and the striated undulated duct, while in the acinus this effect is produced by isoproterenol.     

An ultrastructural study of oogenesis in the polychaeteNephtys hombergi Savigny

The polychaeteNephtys hombergi has an annual cycle of reproduction. Ovaries were fixed for electron microscopy during the gametogenic phase from September to March, and during the breeding and post-breeding periol. Oogenesis takes place entirely within the ovary, the integrity of which is maintained by a network of simple follicle cells. Previtellogenic oocytes have close contacts with the peri-vasal cells which surround the genital blood capillaries. These contacts are lost as the oocytes enter vitellogenesis. The vitellogenic oocytes have a cytology typical of oocytes which are thought to undergo autosynthetic production of protein yolk. Biochemical studies would be required to establish whether heterosynthesis of yolk also occurs. As the oocytes proceed through vitellogenesis, cortical material is laid down near the periphery of the oocyte and a microvillous surface is developed. When the microvillous surface is complete the oocytes, by then hormone independent, are ovulated from the ovary and are ready to be spawned.