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Sperm-oviduct binding is an essential step in the capacitation process preparing the sperm for fertilization in several mammalian species. In many species, capacitation can be induced in vitro by exposing spermatozoa to bicarbonate, Ca2+, and albumin; however, these conditions are insufficient in the horse. We hypothesized that binding to the oviduct epithelium is an essential requirement for the induction of capacitation in stallion spermatozoa. Sperm-oviduct binding was established by coincubating equine oviduct explants for 2 h with stallion spermatozoa (2 × 106 spermatozoa/ml), during which it transpired that the highest density (per mm2) of oviduct-bound spermatozoa was achieved under noncapacitating conditions. In subsequent experiments, sperm-oviduct incubations were performed for 6 h under noncapacitating versus capacitating conditions. The oviduct-bound spermatozoa showed a time-dependent protein tyrosine phosphorylation response, which was not observed in unbound spermatozoa or spermatozoa incubated in oviduct explant conditioned medium. Both oviduct-bound and unbound sperm remained motile with intact plasma membrane and acrosome. Since protein tyrosine phosphorylation can be induced in equine spermatozoa by media with high pH, the intracellular pH (pHi) of oviduct explant cells and bound spermatozoa was monitored fluorometrically after staining with BCECF-AM dye. The epithelial secretory cells contained large, alkaline vesicles. Moreover, oviduct-bound spermatozoa showed a gradual increase in pHi, presumably due to an alkaline local microenvironment created by the secretory epithelial cells, given that unbound spermatozoa did not show pHi changes. Thus, sperm-oviduct interaction appears to facilitate equine sperm capacitation by creating an alkaline local environment that triggers intracellular protein tyrosine phosphorylation in bound sperm.

Date du colloque: 01/2008

The aim of the present study was to evaluate the efficacy of ElastoguardTM silver-releasing rubber in preventing Pseudomonas aeruginosa biofilm formation in water. Biofilm formation by P. aeruginosa under various conditions in an in vitro model system was compared for silver-releasing and conventional rubber. Under most conditions tested, the numbers of sessile cells attached to silver-releasing rubber were considerably lower with reference to conventional rubber, although the effect diminished with increasing volumes. The release of silver also resulted in a decrease in planktonic cells. By exposing both materials simultaneously to conditions for biofilm growth, it became obvious that the antibiofilm effect was due to a reduction in the number of planktonic cells, rather than to contact-dependent killing of sessile cells. The data demonstrate that the use of silver-releasing rubber reduces P. aeruginosa biofilm in water and reduces the number of planktonic cells present in the surrounding solution.

Two series of feeding experiments were conducted to study the feasibility of using decapsulated Artemia cysts for direct feeding to ornamental fish. The first series evaluated the dietary values of the dried and the brine decapsulated Artemia cysts against two conventional live feeds, Artemia nauplii and Moina for adults and fry of the guppy, Poecilia reticulata Peters. In the second series, brine cysts were used for feeding to fry of four other important ornamental fish species, viz. platy, Xiphophorus maculatus (Guenther), swordtail, X. helleri (Heckel), molly, P. sphenops Cuvier & Valenciennes and black neon tetra, Hyphessobrycon herbertaxelrodi Gery, and the results were compared with those fed Moina. Evaluation of the performance of the fish fed the various diets was based on stress resistance, growth and survival of the fish. Our findings indicated that decapsulated cysts could be used as a substitute for Artemia nauplii or Moina in freshwater ornamental fish culture. Apart from being a hygienic off-the-shelf feed, the direct use of the cysts also signifies a new area of application for low-hatch cysts in the ornamental fish industry, with concomitant saving in feed costs.

Variations in the concentrations of ascorbic acid (AA) and tocopherols in association with the gonadal development of the freshwater prawn Macrobrachium rosenbergii were investigated in females captured in the Mae Klong River, Thailand. Mean ovarian AA levels ranged from 210 to 540 µg/g dry weight (dw) and were at least 11-fold higher than midgut gland (MG) levels. Variations in ovarian AA levels are believed to be related to the biosynthesis of steroid hormones, the formation of collagen, and the deposition of egg yolk compounds. alpha-Tocopherol (alpha-T) was the predominant form of vitamin E in prawn tissues and eggs. The level of alpha-T in the MG was constant, whereas in the ovaries, it ranged from 143 to 425 µg/g dw. The incorporation of a-T into the ovary was highly correlated (r² = 0.87) to ovarian lipid levels, which probably reflects the role of this vitamin as a major antioxidant agent. The present results provide further evidence of the essentiality of these vitamins in crustacean reproduction.