SPHAEROPHRYA SOL (CILIATA: SUCTORIA) PARASITIC IN SOME MEXICAN CILIATES.
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The anterior dorsal fin in rocklings consists of a fringe of 50-80 delicate, vibratile rays, which are densely beset with epidermal chemosensory cells. The innervation of these cells is from the dorsal branch of the recurrent facial nerve, which also innervates all other fins and the skin of the trunk. This nerve carries at least three classes of fibres: small (0.5-1.5 micron in diameter), medium (1.5-4 micron), and large (greater than 4 micron). Approximately 12,000 small and weakly myelinated nerve fibres from the recurrent facial nerve innervate the anterior dorsal fin organ. Application of HRP at different locations of the recurrent facial nerve labelled three different sizes of sensory perikarya within the geniculate ganglion--small (6-15 micron in diameter), medium (18-24 micron), and large (greater than 25 micron)--which corresponds to the different size classes of fibres present within the nerve. Retrograde transganglionic transport of HRP revealed somatotopy within the brainstem facial lobe: the delicate nerve fibres innervating the chemosensory anterior dorsal fin terminate exclusively in a distinct, dorsal portion of the facial lobe. Fibres innervating the posterior dorsal fin, the anal and caudal fins, as well as the skin of the trunk terminate within caudal and dorsal areas of the ventral facial lobe; pectoral and pelvic fins are represented in the ventral and caudal portions of the ventral facial lobe. Innervation by a distinct type of fibre and exclusive representation within a distinct, dorsal part of the facial lobe may indicate a peculiar biological role in the anterior dorsal fin chemosensory organ in the rocklings.
PHA, Con-A, or anti-tubulin antibodies inhibit homotypic pair formation, in B, intermedium mating type-I cells in the presence of suboptimal concentrations of gamone II. The inhibition is dependent on the dose of gamone added; the structural conformation and the relative concentration of the inhibitor; and the time of addition of the inhibitor. The block can be selectively prevented by competitive inhibitors of each ligand. The receptors for the inhibitors are distinctive and there is no cross-reaction between the ligands. It is concluded that ligand binding and subsequent receptor-ligand aggregation must induce a change within the cell-surface membrane, which distorts the distribution and/or affects an optimal conformational aspect of a specific membrane-receptor system for the gamon, a prerequisite for cell pair formation.
Solitary chemosensory cells (SCCs) are secondary sensory cells present in the epidermis of most primary aquatic vertebrates. In rocklings, the epidermis of the anterior dorsal fin (ADF) contains approximately 5 million SCCs. High-voltage electron microscopy and three-dimensional reconstructions from serial sections were used to examine the ultrastructure, arrangement, and synaptic contacts of the SCCs in the rockling ADF. Approximately 15% of all cells in the fin ray epidermis are SCCs, which occupy roughly 30% of the epidermal volume. These spindle-shaped cells are 25-30 microm long and up to 10 microm wide and terminate apically in a microvillus protruding 2-5 microm above the epidermal surface. SCCs contain abundant endoplasmic reticulum and a large Golgi apparatus in their proximal regions. The distal parts of SCCs contain characteristic vesicles, elongate mitochondria, and longitudinal strands of intermediate filaments. Synapses between SCCs and nerves resemble those found in teleost taste buds. One to four synaptic contacts per SCC were found. We hypothesize that the apparent secretory activity of the SCCs serves to replenish the apical membrane and mucus. Furthermore, parallel sampling of several hundred SCCs by single nerve fibers may serve low-threshold detection rather than stimulus localization.
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The three-dimensional (3D) organization of nucleoli in the somatic nuclei (macronuclei) of recently fed and starved Didinium nasutum was reconstructed on the basis of serial ultra-thin sections. It was shown that nucleoli, looking on the single sections like individual separate structures, appeared to be parts of the large complicated branchy nucleolar networks. A 30 h starvation did not lead to disintegration of this network, but stimulated formation of numerous vacuoles in the granular component of nucleoli, which becomes more condensed. Unlike starved D. nasutum, in fed ciliates numerous holes appeared in the fibrillar component located at the periphery of nucleoli. These holes may presumably serve as channels for transporting newly synthesized rRNA. To our knowledge, this is the first report of a 3D reconstruction of the nucleolar apparatus in ciliates.
This study, conducted in the Dnieper-Bug Canal in Belarus, is the first to monitor the seasonal (June-November) dynamics of infection with the parasitic ciliate Ophryoglena sp. in a zebra mussel (Dreissena polymorpha) population. Mean population prevalence and intensity of infection varied, respectively, from 11 to 62% and from 0.9 to 24.1 ciliates/mussel. Mean prevalence was highly correlated with mussel length in mussels <20 mm (R(2)=0.97) and was lower in larger mussels. Mean infection intensity in mussels 1-25 mm long was similarly correlated with their size (R=0.98), reached a maximum in the 20-25 mm size-class, and then sharply decreased, thus providing evidence, albeit limited, that high intensity of infection might be lethal. Transinfection of zebra mussels by Ophryoglena sp. was achieved in the laboratory-a first for a protozoan parasite of D. polymorpha; from an initial complete lack of infection, mean prevalence and intensity rose, respectively, to 86.7% and 8.3 ciliates/mussel.
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