Synaptophysin (p38) immunolabelling at the mouse neuromuscular junction.

The synaptophysin (p38), a transmembrane glycoprotein of synaptic vesicles, has been used as a marker in order to study the membrane events that take place during transmitter release at the mouse neuromuscular junction (NMJ). p38 has been labelled by immunofluorescence using a monoclonal anti-p38 antibody and fluorescein-conjugated IgG on dissociated muscle fibres (biceps brachialis m.). Its localization has been compared to that of the acetylcholine (ACh) receptors labelled with rhodaminated alpha-bungarotoxin. A weak labelling was obtained in nerve-muscle preparations at rest only when the muscle fibres were permeabilized with Triton X-100. By contrast, an intense immunofluorescence of the NMJ was observed after an exhaustive ACh release induced by Cd2+ in Ca(2+)-free medium, which leads to a synaptic vesicle depletion and an increase in the membranous structures in nerve terminals. Treatment with Cd2+ in Ca(2+)-free solution leads to both synaptic vesicle depletion and p38 immunolabelling, which is in favour of synaptic vesicle fusion and incorporation into the axolemma.

Changes in large dense-core vesicles during maturation of the rat neuromuscular junction.

The proportion of large dense-core vesicles (LDCVs) in motor nerve terminals of the rat biceps brachialis muscle was evaluated from embryonic day 20 to 4 weeks postpartum as well as in the adult. A progressive decrease was observed up to 3 weeks postpartum when maturation of the endplates is achieved. Differences compared with the adult were no longer significant at 4 weeks postpartum. Three types of LDVCs, classified according to their size and the core density, were detected. Their relative proportion did not vary significantly during the period of life examined. The high proportion of LDCVs during early development and their persistence at a low level in the adult suggest that they might play a role in the maturation and maintenance of the endplates.

Large dense-core vesicles at the frog neuromuscular junction: characteristics and exocytosis.

The population of large dense-core vesicles (LDCVs) in motor nerve terminals of the frog cutaneous pectoris muscle was analysed after various experimental protocols leading to large acetylcholine release. Three types of LDCVs classified according to their size and the core density were detected. Vesicles, 100-150 nm in diameter, with a large and very dense core (type 1) or with an irregular and diffuse dense core (type 2) were present in similar proportions (45 and 50% respectively) in controls. Smaller vesicles, 50-80 nm in diameter, with a very dense core (type 3) were rare, representing around 5% of the cored vesicles. The relative proportion of type 1 and type 2 LDCVs was not modified after prolonged treatment with 25 mM K+. In contrast, the proportion of type 2 LDCVs significantly increased whereas that of type 1 LDCVs decreased after two or three series of 20 Hz electrical stimuli applied to the nerve at 5 s intervals. These changes suggest that type 2 LDCVs are newly recycled LDCVs in the process of reloading. Images of fusion of LDCVs with the axolemma in regions facing Schwann cell digitations were observed both in K(+)- and in electrically stimulated preparations. They indicate that exocytosis of LDCVs at the frog neuromuscular junction takes place preferentially away from the active zones. The presence of a clathrin-like coat on large pockets still containing a core and of both type 1 and type 2 LDCVs in the vicinity of coated pockets strongly suggests that LDCVs might undergo a combined process of exo-endocytosis at the same site.

[Coagulation of the hemolymph in Macropipus puber (L)., Crustacea, Decapoda. Electrophoretic demonstration of a plasma component intervening in hemostasis]. / Coagulation de l'hémolymphe chez Macropipus puber (L.). Crustacé décapode. Mise en évidence par électrophorèse d'un composant plasmatique intervenant dans l'hémostase.

Electrophoretical and immuno-electrophoretical analysis of plasma, serum and some plasmatic extracts of Macropipus puber (L). have evidenced the presence in the plasma of a component absent in the serum. This component which disappears from the plasmatic extracts after their coagulation must therefore plays a role in the clotting processes.