Kinetics of contractile activation in voltage clamped frog skeletal muscle fibers.

Excitation-contraction coupling events leading to the onset of contraction were studied in single skeletal frog muscle fibers. This entailed the simultaneous measurement of the changes in intracellular calcium concentration using antipyrylazo III and fura-2, isometric force, and clamp voltage in a modified single vaseline gap chamber for the first time. The calcium transients were incorporated into an analysis of calcium binding to regulatory sites of troponin C (TnC) that permitted both a linear and a cooperative interaction. The analysis assumed that the onset of mechanical activation corresponds with a particular TnC saturation with calcium setting constraints for the calcium binding parameters of the regulatory sites. Using a simple model that successfully reproduced both the time course and the relative amplitudes of the measured isometric force transients over a wide membrane potential range, k(off) of TnC was calculated to be 78 s(-1) for the cooperative model at 10 degrees C. Together with the above constraints this gave a dissociation constant of 8.8 +/- 2.5 microM and a relative TnC saturation at the threshold (Sth) that would cause just detectable movement of 0.17 +/- 0.03 (n = 13; mean +/- SE). The predictions were found to be independent of the history of calcium binding to the regulatory sites. The observed delay between reaching Sth and the onset of fiber movement (8.7 +/- 1.0 ms; mean +/- SE, n = 37; from seven fibers) was independent of the membrane potential giving an upper estimate for the delay in myofilament activation. We thus emerge with quantitative values for the calcium binding to the regulatory sites on TnC under maintained structural conditions close to those in vivo.     

Feather mites (Acari: Astigmata) and body condition of their avian hosts: a large correlative study

Feather mites are arthropods that live on or in the feathers of birds, and are among the commonest avian ectosymbionts. However, the nature of the ecological interaction between feather mites and birds remains unclear, some studies reporting negative effects of feather mites on their hosts and others reporting positive or no effects. Here we use a large dataset comprising 20 189 measurements taken from 83 species of birds collected during 22 yr in 151 localities from seven countries in Europe and North Africa to explore the correlation between feather mite abundance and body condition of their hosts. We predicted that, if wing‐dwelling feather mites are parasites, a negative correlation with host body condition should be found, while a mutualistic interaction should yield positive correlation. Although negative relationships between feather mite abundance and host body condition were found in a few species of birds, the sign of the correlation was positive in most bird species (69%). The overall effect size was only slightly positive (r =0.066). The effect of feather mite abundance explained <10% of variance in body condition in most species (87%). Results suggest that feather mites are not parasites of birds, but rather that they hold a commensalistic relationship where feather mites may benefit from feeding on uropygial gland secretions of their hosts and birds do not seem to obtain a great benefit from the presence of feather mites.     

The cell adhesion molecule NrCAM is crucial for growth cone behaviour and pathfinding of retinal ganglion cell axons

We investigated the role of the cell adhesion molecule NrCAM for axonal growth and pathfinding in the developing retina. Analysis of the distribution pattern of NrCAM in chick embryo retina sections and flat-mounts shows its presence during extension of retinal ganglion cell (RGC) axons; NrCAM is selectively present on RGC axons and is absent from the soma. Single cell cultures show an enrichment of NrCAM in the distal axon and growth cone. When offered as a substrate in addition to Laminin, NrCAM promotes RGC axon extension and the formation of growth cone protrusions. In substrate stripe assays, mimicking the NrCAM-displaying optic fibre layer and the Laminin-rich basal lamina, RGC axons preferentially grow on NrCAM lanes. The three-dimensional analysis of RGC growth cones in retina flat-mounts reveals that they are enlarged and form more protrusions extending away from the correct pathway under conditions of NrCAM-inhibition. Time-lapse analyses show that these growth cones pause longer to explore their environment, proceed for shorter time spans, and retract more often than under control conditions; in addition, they often deviate from the correct pathway towards the optic fissure. Inhibition of NrCAM in organ-cultured intact eyes causes RGC axons to misroute at the optic fissure; instead of diving into the optic nerve head, these axons cross onto the opposite side of the retina. Our results demonstrate a crucial role for NrCAM in the navigation of RGC axons in the developing retina towards the optic fissure, and also for pathfinding into the optic nerve.     

Sex differences in the response of postprandial lipemia to a change from a low-fat low-cholesterol diet to a high-fat high-cholesterol diet

To determine whether a short-term change in dietary habits affects postprandial lipemia in men and women in the same way, postprandial triglyceridemia was measured in age- and BMI-matched young healthy men and women after two weeks on the self-selected low-fat low-cholesterol (LF) diet and after another two weeks on the self-selected high-fat high-cholesterol (HF) diet. After a standardized challenge meal (1.4 g fat/kg of body weight), men had higher postprandial triglyceridemia than women on the HF diet but no such difference was observed on the LF diet. The results of this preliminary study suggest that there may be important sex differences in the mechanisms regulating the postprandial lipemia response to different diets, women being able to adapt better to the HF diet with respect to postprandial lipemia.     

Subsequent effect of subacute T-2 toxicosis on spermatozoa, seminal plasma and testosterone production in rabbits

Pannon White (n=12) male rabbits (weight: 4050 to 4500 g, age: 9 months) received 2 ml of a suspension containing purified T-2 toxin by gavage for 3 days. The daily toxin intake was 4 mg/animal (0.78 to 0.99 mg/kg body weight (BW)). Control animals (n=12) received toxin-free suspension for 3 days. Since a feed-refusal effect was observed on the second day after T-2 administration, a group of bucks (n=10) were kept as controls (no toxin treatment) but on a restricted feeding schedule, that is, the same amount of feed was provided to them as was consumed by the exposed animals. On day 51 of the experiment (i.e. 48 days after the 3-day toxin treatment), semen was collected, and pH, concentration, motility and morphology of the spermatozoa, as well as concentration of citric acid, zinc and fructose in the seminal plasma, were measured. After gonadotropin-releasing hormone (GnRH) analogue treatment, the testosterone level was examined. One day of T-2 toxin treatment dramatically decreased voluntary feed intake (by 27% compared to control, P<0.05) and remained lower (P<0.05) during the first 2 weeks after the withdrawal of the toxin. BW of the contaminated rabbits decreased by 88% on days 17 and 29 compared to controls (P<0.05). No effect of toxin treatment was detected on pH and quantity of the semen or concentration of spermatozoa. The ratio of spermatozoa showing progressive forward motility decreased from 65% to 53% in the semen samples of toxin-treated animals compared to controls (P>0.05). The ratio of spermatozoa with abnormal morphology increased (P<0.05) in the ejaculates collected from the toxin-treated animals. T-2 toxin applied in high doses decreased the concentration of citric acid in seminal plasma (P<0.05). No effect of T-2 toxin on the concentrations of the other seminal plasma parameters (fructose and zinc) was observed. T-2 toxin decreased the basic testosterone level by 45% compared to control (P<0.01) and resulted in lower (P<0.05) GnRH-induced testosterone concentration. Feed restriction, that is, less nutrient intake, resulted in more morphologically abnormal spermatozoa in the semen, but it did not cause significant loss in BW, motility of the spermatozoa, composition of the seminal plasma or testosterone concentration--its effect needs further examination.     

Dose-related effects of cysteamine treatment on hypothalamic and striatal dopamine, noradrenaline and serotonin neurotransmission

The dose-related effects of cysteamine treatment on hypothalamic and striatal neurotransmission were investigated. Cysteamine pretreatment with a dose of 150 mg/kg slightly increased the dopamine, and markedly decreased the noradrenaline, content of the hypothalamus in a dose-related manner. The serotonin levels of the hypothalamus and striatum were not affected. Cysteamine pretreatment with a higher dose (300 mg/kg sc) slightly increased the uptake of noradrenaline into hypothalamic slices. The drug did not influence dopamine and serotonin uptake into hypothalamus and striatal slices. These results suggest that cysteamine decreases rather selectively the noradrenaline content of the hypothalamus.     

Glycosylation changes in different developmental stages of Trichinella

The in situ identification of carbohydrate structures in Trichinella spiralis intestinal larvae, adults and L1 muscular larvae was carried out by lectin histochemistry, with emphasis on the O-linked glycans. The absence of reactivity with two lectins-TML and MAL indicated that Trichinella spiralis does not synthesize sialic acid. Reactivity with HPA, VVL-B4, PNA and UEA-I staining suggested that T. spiralis synthesizes and expresses on its cuticle O-linked glycans analogous to Tn-antigen (GalNAc-α-Ser/Thr), T-antigen (Gal-β1,3-GalNAc-α-Ser/Thr) and also structures analogous to A-blood group antigens (GalNAc-α1,3-Gal-β1,3(4)-(Fuc-α1,2-)-R). Expression of the saccharidic moieties is stage-specific. Blood group-A and T-antigen structures were identified on the cuticle of the intestinal and muscular larvae. The Tn-antigen structure was missing in the intestinal larvae. Appropriate ligands for WGA were not identified in the adult individuals. The obtained results may contribute to a better understanding of the glycobiology of this parasitic nematode in relation to occupation of its intracellular niche. The presence of saccharidic structures analogous to some of those expressed on the intestinal epithelial cells may serve as a protective shield on the surface of the parasite.