Ecology,development and pathogenicity of Buddenbrockia plumatellae Schröder, 1910 (Myxozoa,Malacosporea) (syn. Tetracapsula bryozoides) and establishment of Tetracapsuloides n. gen. for Tetracapsula bryosalmonae

Buddenbrockia plumatellae, an enigmatic worm-like myxozoan, was observed as continuously writhing free and attached 'worms' and as free mature spores in the coelom of the freshwater bryozoans Plumatella fungosa, Hyalinella punctata, and Fredericella sp. 'Worm' numbers could double every three days. 'Worms' and spores could be expelled from colonies by external pressure. Some mature 'worms' exited actively, entraining release of free spores, and gradually ceased movement outside the host. Bryozoans sealed off infected regions of the colony. Infected colonies grew slowly, produced no statoblasts, and eventually regressed and died. Transmission was not achieved and prevalence was low. Electron microscopy of 'worms' revealed a single layer of mural cells on a fibrous basal lamina overlying four longitudinal muscle blocks and an inner sheet of two types of proliferating cells, an organization indicative of the bilaterian ancestry of the Myxozoa. Primary type A cells were attached directly by striated tubules to mural cells at positions between muscle blocks. Secondary type A cells had a secretory function. Type B cells underwent meiosis and subsequently developed to typical malacosporean myxozoan spores filling the internal cavity of the 'worms'. External tubes were formed during capsulogenesis in 'worms' from Fredericella sp. Tetracapsula bryozoides is synonymised with Buddenbrockia plumatellae and a new genus is proposed for Tetracapsula bryosalmonae.     

A new class and order of myxozoans to accommodate parasites of bryozoans with ultrastructural observations on Tetracapsula bryosalmonae (PKX organism)

Tetracapsula bryosalmonae, formerly PKX organism, is a myxozoan parasite that causes proliferative kidney disease in salmonid fish. Its primary hosts, in which it undergoes a sexual phase, are phylactolaemate bryozoans. It develops in the bryozoan coelomic cavity as freely floating sacs which contain two types of cells, stellate cells and sporoplasmogenic cells, which become organised as spores. Eight stellate cells differentiate as four capsulogenic cells and four valve cells which surround a single sporoplasmogenic cell. The sporoplasmogenic cell undergoes meiosis and cytoplasmic fission to produce two sporoplasms with haploid nuclei. Sporoplasms contain secondary cells. The unusual development supports previously obtained data from 18S rDNA sequences, indicating that species of Tetracapsula form a clade. It diverged early in the evolution of the Myxozoa, before the radiation that gave rise to the better known genera belonging to the two orders in the single class Myxosporea. The genus Tetracapsula as seen in bryozoans shares some of the characters unique to the myxosporean phase and others typical of the actinosporean phase of genera belonging to the class Myxosporea. However, it exhibits other features which are not found in either phase. A new class Malacosporea and order Malacovalvulida are proposed to accommodate the family Saccosporidae and genus Tetracapsula. Special features of the new class are the sac-like proliferative body, valve cells not covering the exit point of the polar filament, lack of a stopper-like structure sealing the exit, maintenance of valve cell integrity even at spore maturity, absence of hardened spore walls and unique structure of sporoplasmosomes in the sporoplasms.     

Serious doubts over “Eggs forever?”

A recent commentary in this journal by Byskov et al. (2005) claims that, despite published results from numerous independent lines of investigation from our laboratory and others, there does not "exist any evidence for neo-folliculogenesis in the adult mammalian ovary." While we agree with Byskov et al. that our work represents a radical departure from the age-old dogma that mammalian females permanently lose the capacity for oocyte and follicle production during the perinatal period, careful examination of all of the available data leaves no doubt that adult female mammals retain the capacity for oogenesis and folliculogenesis. These findings do not change the fact that exhaustion of the oocyte pool occurs with advancing chronological age--a process responsible for driving the menopause in women--but rather question the basic mechanism underlying age-related ovarian failure. In this regard, studies of aging male mice have demonstrated that testicular atrophy is associated with a dramatic decline in the number, activity and quality of germline stem cells that maintain spermatogenesis during adulthood (Zhang et al., 2006). Therefore, to the contrary of the opinion of Byskov et al. that such a process would be "considered exceptional among stem cells," it is certainly reasonable to hypothesize that a similar deterioration of female germline stem cell function underlies the decline in oocyte quality and the onset of ovarian failure in aging females. Further, while we accept that a departure from conventional thinking can take years to gain widespread acceptance, we feel this resistance to change should not be construed as the sole means to voice opinions about the validity of our data or the maturity of our principal conclusion.     

Ultrastructure of Buddenbrockia allmani n. sp. (Myxozoa, Malacosporea), a parasite of Lophopus crystallinus (Bryozoa, Phylactolaemata)

Development of a new species of malacosporean myxozoan (Buddenbrockia allmani n. sp.) in the bryozoan Lophopus crystallinus is described. Early stages, represented by isolated cells or small groups, were observed in the host's body wall or body cavity. Multiplication and rearrangement of cells gave an outer cell layer around a central mass. The outer cells made contact by filopodia and established adherens junctions. Sporoplasmosomes were a notable feature of early stages, but these were lost in subsequent development. Typical malacosporean sacs were formed from these groups by attachment of the inner (luminal) cells by a basal lamina to the outer layer (mural cells). Division of luminal cells gave rise to a population of cells that was liberated into the lumen of the sac. Mitotic spindles in open mitosis and prophase stages of meiosis were observed in luminal cells. Centrioles were absent. Detached luminal cells assembled to form spores with four polar capsules and several valve cells surrounding two sporoplasms with secondary cells. Restoration of sporoplasmosomes occurred in primary sporoplasms. A second type of sac was observed with highly irregular mural cells and stellate luminal cells. A radially striated layer and dense granules in the polar capsule wall, and previous data on 18 rDNA sequences enabled assignment of the species to the genus Buddenbrockia, while specific diagnosis relied on the rDNA data and on sac shape and size.     

Further observations on the ultrastructure of Cystosporogenes operophterae (Canning, 1960) (phylum Microsporidia) parasitic in Operophtera brumata L. (Lepidoptera, Geometridae)

Reinvestigation of Cystosporogenes operophterae [J. Parasitol. 46 (1960) 755] by electron microscopy confirmed that development in host cells takes place in a vacuole with a single membrane at its boundary. Although ribosomes were not clustered on this membrane, it is hypothesised that it originates from host endoplasmic reticulum. The dome-shaped anchoring disc, the morphology of the polaroplast and the separation of the polar tube coils from the ribosome-packed cytoplasm are newly described details of spore structure. The polaroplast consists of an outer region of compact lamellae forming 'arms' surrounding an inner region of widely spaced lamellae. The 'arms' extends back into the region of an elongate nucleus. The genera Cystosporogenes and Endoreticulatus were differentiated by their positions in a previously obtained 16S rDNA phylogeny and on the new ultrastructural data.     

Differential effects of airway afferent nerve subtypes on cough and respiration in anesthetized guinea pigs

The hypothesis that respiratory reflexes, such as cough, reflect the net and often opposing effects of activation of multiple afferent nerve subpopulations throughout the airways was evaluated. Laryngeal and tracheal mucosal challenge with either citric acid or mechanical probing reliably evoked coughing in anesthetized guinea pigs. No other stimulus reliably evoked coughing in these animals, regardless of route of administration and despite some profound effects on respiration. Selectively activating vagal C-fibers arising from the nodose ganglia with either adenosine or 2-methyl-5-HT evoked only tachypnea. Selectively activating vagal afferents arising from the jugular ganglia induced respiratory slowing and apnea. Nasal afferent nerve activation by capsaicin, citric acid, hypertonic saline, or histamine evoked only respiratory slowing. Histamine, which activates intrapulmonary rapidly adapting receptors but not airway or lung C-fibers or tracheal bronchial cough receptors induced bronchospasm and tachypnea, but no coughing. The results indicate that the reflexes initiated by stimuli thought to be selective for some afferent nerve subtypes will likely depend on the net and potentially opposing effects of multiple afferent nerve subpopulations throughout the airways. The data also provide further evidence that the afferent nerves regulating cough in anesthetized guinea pigs are distinct from either C-fibers or intrapulmonary rapidly adapting receptors.     

Orphan worms and homeless parasites enhance bilaterian diversity

Microscopic endoparasites belonging to the Phylum Myxozoa provide a striking example of how much there is still to be learned about the diversity of the Metazoa. Recent research on myxozoans has provided new insights into evolution within the Bilateria, revealing unparalleled levels of morphological simplification associated with parasitism, a home for an orphan worm, and a hypothesis of the endosymbiotic origin(s) for extrusible intracellular organelles in myxozoans and cnidarians. In addition, discovery of the source of a devastating disease of salmonid fish has enabled researchers to identify two ancient clades within the Myxozoa, and has exposed new mysteries concerning myxozoan life-cycle evolution and evolutionary diversification. This plethora of new insights exemplifies the fundamental value of studying obscure organisms.     

Potassium-sparing Agents during Diuretic Therapy in Hypertension

Three pharmacological agents in use as “potassium-sparing” drugs have been tested by serial measurements of total exchangeable potassium (K_E) during 4 to 12 weeks of oral diuretic therapy in hypertensive subjects. Triamterene seemed ineffective in the dosage used (50 mg twice daily). Spironolactone (25 mg twice daily) reduced K loss to a considerable extent, while Slow-K (32 mEq daily) completely reversed previous K_E deficits. Plasma K levels were a poor indication of degree of K_E restoration.     

Light and electron microscope observations on Unikaryon legeri (Microsporida,Nosematidae), a parasite of the metacercaria of Meigymnophallus minutus in Cardium edule

Nosema legeri from the metacercariae of Meigymnophallus minutus in Cardium edule has been shown by light and electron microscopy to be disporous and to lack nuclei in diplokaryon form throughout its development. Although its ultrastructure resembles that of Encephalitozoon cuniculi and mature spores often lay in vacuoles surrounded by host membranes, dividing stages were never present in a common vacuole. Sporoblasts showed a cytoplasmic protuberance suggestive of a locomotory organelle. It is possible that movement of these stages disrupts the host cell cytoplasm and creates the vacuole in which the spores mature. The species has been transferred to the genus Unikaryon Canning, Lai and Lie and named Unikaryon legeri(Dollfus, 1912).