Some implications of helical fibres in worm cuticles

The cuticles of many worms contain a cylindrical trellis made of layers of collagen fibres wound round the body in left- and right-hand helices. This kind of extensible skeletal structure imposes various constraints on a worm's behaviour, and some of these are examined, using the nematomorph Parachordodes woltersforffii as the main example. Upon extension or shortening of the cuticle, neighbouring fibres in one layer will eventually touch and so limit further movement; this in turn affects the extent of shortening, elongation, bending and coiling of the whole worm. Simple equations relate: the angle between a fibre and the worm's long axis; fibre spacing and radius; worm body radius and radius of curvature. The relevance to the life of the worm of fibre arrangement, matrix properties and volume changes is discussed.     

Parallel Induction of Nitric Oxide and Tetrahydrobiopterin Synthesis by Cytokines in Rat Glial Cells

Abstract: Activation of monocyte-derived macrophages with cytokines leads to the induction of nitric oxide synthase. Much less is known about the effects of cytokines on microglia, resident brain macrophages, or on astrocytes. In this study, we compared the induction by lipopolysaccharide, interferon-γ, and tumor necrosis factor-α of nitric oxide production and synthesis of tetrahydrobiopterin, the required cofactor for nitric oxide synthase, in microglia and peritoneal macrophages. Activation of microglia induced parallel increases in nitric oxide and intracellular tetrahydrobiopterin levels, although induction of the latter appears to be somewhat more sensitive to diverse stimulators. As with macrophages, inducible nitric oxide production in microglia was blocked by inhibitors of tetrahydrobiopterin biosynthesis. Interleukin-2, an important component of the neuroimmunomodulatory system, was only a weak activator of microglia by itself but potently synergized with interferon-γ to stimulate production of both nitric oxide and tetrahydrobiopterin. Astrocytes were also activated by lipopolysaccharide and combinations of cytokines but showed a somewhat different pattern of responses than microglia. Biopterin synthesis was increased to higher levels in astrocytes than in microglia, but maximal induction of nitric oxide production required higher concentrations of cytokines than microglia and the response was much lower. These results suggest that tetrahydrobiopterin synthesis in glial cells is a potential target for therapeutic intervention in acute CNS infections whose pathology may be mediated by overproduction of nitric oxide.     

The action of the anterior feeding apparatus of Caenorhabditis elegans (Nematoda: Rhabditida)

From analysis of ciné film, combined with ultrastructural observations, the anterior feeding structures and their behaviour in the free-living microbivorous nematode Caenorhabditis elegans during ingestion in dense and sparse suspensions of Escherichia coli are described In dense suspensions bacteria accumulate in the buccal cavity against the three metastomal flaps that nearly close it, and are then swallowed down the three tubular apical expansions of the triradiate oesophageal lumen when the flaps open. Excess medium is then expelled, as the oesophageal lumen closes and traps the swallowed bacteria. The flaps and oesophagus operate by contractions in the seven most anterior oesophageal muscle cells, probably coordinated via proprioceptive nerve endings between the cells. About one million nematode hours are needed to extract 1 g of bacteria from 30 ml of medium. With few or no bacteria, the head moves more, the metastomal flaps do not close and medium seems to pass in and out of the buccal cavity, probably as part of the widespread exploration phase of food-finding behaviour. Abnormal feeding behaviour, control and functions of the metastomal flaps and associated structures, and control of food intake volume are discussed.     

Dispersal of the lycaenid Plebejus argus in response to patches of its mutualist ant Lasius niger

We examined the movement rates of individuals of an obligate myrmecophilous butterfly, Plebejus argus (Lycaenidae: Lepidoptera), in relation to a patch of its mutualist ant, Lasius niger . Marked male and female P. argus from local (resident), fragmented and continuous populations were released into and away from (>100m) a patch of L. niger , and subsequently searched for in a 500×500 m area. Recaptures of males and females from all populations were strongly associated with the target patch of mutualist ants. First day recapture displacements were significantly higher for releases away from the target patch for males, but not for females. Mutualist ant presence was shown to be more important than nectar source density in determining persistence of P. argus in release squares. There was no significant difference in displacement distances or recapture frequencies (standardised for search effort) in the target patch of individuals from local (resident of target patch), fragmented and continuous populations. The recapture frequency in the target patch of males from the local population released outside the target patch was greater than expected from a null model of random straight line movement, suggesting non-random (systematic or orientated) search behaviour. The number of males remaining in the target patch following release into the target patch was greater than expected from a simple diffusion model, suggesting a behavioural response to patch boundaries or other cues related to the patch.     

Humidity‐terminated diapause in the tropical braconid parasitoid Microplitis demolitor

1. Microplitis demolitor, a solitary braconid parasitoid of Helicoverpa armigera and Helicoverpa punctigera, uses an increase in relative humidity to signal the end of diapause and the re‐establishment of direct development. 2. Photoperiod and temperature changes appear not to have a direct influence on the duration or termination of diapause in this species. 3. Once diapause termination is signalled, the adult parasitoids emerge approximately 38 days later. 4. The cue for diapause termination in M. demolitor is different from that used by its hosts and ensures that the parasitoid emerges to find a population of nonmigrating hosts. 5. It appears that the cocoon surrounding the diapausing parasitoid plays a role in diapause termination; parasitoids emerge earlier from diapause if the cocoon is removed but the weight of the intact cocoon does not appear to influence the length of time the parasitoid is in diapause.     

Long-term effects of gamma-irradiation on cultured human thyroid cells

When differentiated 15-day-old cultures of human thyroid glands were irradiated they exhibited a high degree of radiosensitivity, an absence of split-dose recovery, an increase in the number of non-senescent colonies observed over four passages, increased focus formation on the confluent postirradiation monolayer and a shift in the isozyme pattern of LDH towards the anaerobic form (LD 5). The effects are similar to those previously observed for irradiated sheep thyroid cultures, but occurred at lower radiation doses.