Journal de physiologie最新文献

1. On a substrate consisting of alternating lanes of anterior and posterior tectal membranes, temporal retinal axons have a strong tendency to grow on the lanes of anterior membranes and to avoid the lanes of posterior membranes. 2. Temporal axons do extend neurites on posterior material, and in equivalent numbers and lengths to that of anterior membranes if the substrate consists of pure anterior or posterior membranes. 3. Inactivation of posterior membranes by heat or the enzyme phosphatidylinositol-specific phospholipase C (PI-PLC) abolishes their ability to induce the avoidance reaction of temporal axons. It is concluded that the posterior membranes contain a repulsive component for temporal retinal axons. 4. Growth cones growing on anterior membranes, which encounter posterior membranes at the strip boundary, in general do not become reduced in their growth rate. 5. These results are most easily explained by a "gradient-reading model" similar to chemotaxis where the steering of a growth cone is independent on the growth rate. 6. According to the model, a gradient of a guiding component outside the growth cone is transformed into an internal gradient which gives the growth cone its directionality. 7. Other models like growth inhibition cannot be ruled out but need at least two additional assumptions like habituation for growth on the putative posterior inhibitory substrate and a strong local restriction of the inhibitory effect within the growth cone which contacts the posterior material.

Botulinum neurotoxin type A (BoNTx) inhibits the release of acetylcholine (ACh) from Torpedo electric organ synaptosomes. We have studied several biochemical and morphological aspects in order to characterize the molecular interactions of BoNTx intoxication in our preparation. 1. We are describing for the first time an electrophoretic band from cholinergic presynaptic plasma membrane (PSPM) that is recognized by 125I-BoNTx as a putative BoNTx receptor. 2. Furthermore we describe direct interaction of botulinum toxin-gold complexes with synaptic vesicles through the three-step model of the BoNTx intoxication.

1. Mammalian cells can produce bacterial beta-galactosidase when they carry the lacZ gene under the control of mammalian regulatory elements. The single cell resolution of the beta-galactosidase histochemical detection method makes this molecule an excellent marker in studies of development at the cellular and molecular level. Different lacZ fusion genes can be engineered to study the histological diversification of cell lineages, the developmental regulation of isolated genes, or to recognize and clone genes with new expression profile. 2. Transgenic mice carrying lacZ gene fusions provide information on the cell type, developmental stage and spatial specificity of cis-acting regulatory regions linked to a mammalian homeobox gene. We describe our strategy for designing the gene fusions. 3. The scord region of the Hox 1.3 gene is sufficient to determine spatially restricted expression of a heterologous protein in the midgestational spinal cord. We propose to use this region to alter the expression pattern of other homeobox gene products. Developmental alterations due to a variant expression pattern would point to the function of the misexpressed gene.

In vertebrates, the peripheral nervous system arises from the neural crest by a multistep process involving epithelium-mesenchyme interconversions and cell migrations. These successive events are associated with profound and controlled reorganization of the expression of both cell-cell and cell-substratum adhesion molecules responsible for the direct interaction of neural crest cells with their neighbours or the extracellular matrix. Thus, at the onset of emigration of neural crest cells from the neural tube, the cell-cell adhesion systems mediated by N-cadherin and N-CAM are lost by cells. This is accompanied by the complete reorganization of the extracellular matrix in the immediate environment of neural crest cells and by changes in cell shape. Later, as crest cells undergo migration towards their differentiation sites, they are found associated with fibronectin. Cell adhesion molecules are reaquired by neural crest cells following specific sequences as they coalesce into primordia of the various ganglia. In vitro, fibronectin constitutes the most appropriate substrate for migration of neural crest cells. The migration-promoting effect of fibronectin can be specifically inhibited both in vivo and in vitro by antibodies to fibronectin, integrin receptors, or by peptides containing the Arg-Gly-Asp-Ser sequence. Neural crest cells recognize two major adhesion sites along fibronectin molecules; these are the Arg-Gly-Asp-Ser sequence located in the medial part of the molecule and the CS1 site situated in the alternatively spliced IIICS region. These two sequences are required to permit full motile behavior of cells.(ABSTRACT TRUNCATED AT 250 WORDS)

1. With the aim of gaining insight into the mechanism of Ca2(+)-dependent secretion, inhibition of transmitter release by botulinum neurotoxins or their fragments was studied at mammalian motor nerve terminals, cerebrocortical synaptosomes and PC-12 cells. 2. Relative to BoNT type A, the feeble neuromuscular paralytic activity of its two chains and the lack of activity observed with a proteolytic fragment, H2L (lacking H1, the C-terminal half of the heavy chain) highlight a requirement of the intact, disulphide-linked dichain protein for efficient targetting (binding/uptake) to peripheral cholinergic nerve endings. 3. In PC-12 cells, the renatured light chain alone proved equally potent as the whole toxin in reducing Ca2(+)-evoked noradrenaline release, when digitonin-permeabilization was used to overcome the uptake barrier. Treatment of BoNT A with 10 mM dithiothreitol, under non-denaturing conditions, was not very effective in reducing its inter-chain disulphide bond(s) and had little influence on the level of inhibition seen. 4. Altering the intra-synaptosomal concentrations of cyclic nucleotides (c-AMP, c-GMP) or protein kinase C activity failed to affect the reduction of Ca2(+)-dependent K(+)-stimulated noradrenaline release caused by BoNT A or B. On the other hand, raising the cytosolic Ca2+ concentration with the ionophore A23187 reversed the inhibitory effect of BoNT A to a greater extent than that of type B, revealing differences in their actions. 5. Whereas BoNT-induced decrease of Ca2(+)-dependent K(+)-evoked release of noradrenaline was unaffected by destruction of the actin-based cytoskeleton in synaptosomes with cytochalasin D, disassembly of microtubules with colchicine, nocodazole or griseofulvin antagonised the intracellular action of type B but not A. It is speculated that BoNT B blocks transmitter release by interfering with the proposed detachment of synaptic vesicles from microtubules. Establishing the precise involvement of tubulin in the toxin's action may provide a valuable clue to the mechanism of neurotransmitter release or its control.

1. Botulinum C1 toxin and C3 exoenzyme were purified from the culture filtrate of type C Clostridium botulinum strain 003-9, and specific antibodies were raised against each protein. Immunochemical analysis using these antibodies revealed the presence of minute amount of a C3-like molecule in C1 toxin preparation which tightly binds to the toxin component(s). This enzyme complex was separated from the major neurotoxin. Thus, the ADP-ribosyltransferases in C1 and D toxins and C3 exoenzyme appear to come from the same origin, and should be called together botulinum C3 enzyme. 2. Botulinum C3 enzyme ADP-ribosylates the rho and rac gene products, a family of small molecular weight GTP-binding proteins homologous to ras p21s. This ADP-ribosylation occurs at Asn41 of the rho products which is located in their putative effector domain, suggesting that it interferes interaction of these GTP binding proteins with their effector molecules. 3. When incubated with PC-12 cells, the enzyme inhibits cell growth and induces neurites and acetylcholine esterase. Several lines of evidence suggest that the ADP-ribosylation of the rho/rac proteins is responsible for these changes.

1. This article summarizes some of the recent advances in the understanding of structural and functional properties of isolated small synaptic vesicles (SSV) from mammalian brain. 2. SSV contain a set of integral membrane proteins which are highly specific for this organelle and which occur on all SSV of the central and peripheral nervous system irrespective of their transmitter content. In contrast, these proteins are absent from the membrane of peptide-containing large dense-core vesicles indicating that the two types of organelle have a different membrane composition. The availability of antibodies for these proteins has allowed the evaluation of the purity of vesicle preparations which is instrumental for functional studies. 3. Recent advances in the study of neurotransmitter uptake have revealed that SSV contain specific carrier systems for glutamate and GABA. They are different from the transporters of the plasma membrane, and are dependent on the energy of a proton electrochemical gradient. The uptake of glutamate has been characterized in some detail and the mechanistic and physiological implications of these findings are discussed.

The results of the treatment with botulinum toxin A injection of 234 patients with blepharospasm and 73 with hemifacial spasm were reviewed. Visual function improved in the majority of patients with blepharospasm, and the improvement was sustained for up to 40 sets of injections. Mid and lower facial movements were also reduced in a minority of patients. However, a sub-group with pre-tarsal blepharospasm or persistent levator inhibition after treatment had a poor response. An average 75% reduction in abnormal movements was seen in cases of hemifacial spasm. Side effects of the treatment were usually mild and short lived.

1. The development of the mouse trigeminal system is outlined and its advantages for studying the synthesis of low-abundance regulatory proteins are described. 2. The onset of NGF gene expression and NGF synthesis in the cutaneous target field of the trigeminal ganglion coincide with the arrival of the earliest nerve fibres. 3. The distribution and magnitude of NGF synthesis within the target field are related to its final innervation density. 4. NGF receptors are first detected on trigeminal neurons when their peripheral axons reach the target field. 5. Neither NGF synthesis nor NGF receptor expression are dependent on nerve-target contact but appear to occur as part of an intrinsic developmental program in the target field and neurons, respectively. 6. The time-course of NGF synthesis and NGF receptor expression indicate that NGF does not play a role in guiding axons to their target fields in development.

1. Recent experiments on the development of neural segmentation in chick embryos are reviewed. 2. Segmentation of the spinal peripheral nerves is governed by a subdivision of the somite-derived sclerotome into anterior and posterior halves. Migrating neural crest cells and outgrowing motor axons are confined to the anterior sclerotome as a result, in part, of inhibitory interactions with posterior sclerotome cells. 3. The sclerotomal distribution of certain molecules known to influence growing nerve cells in vitro, namely laminin, fibronectin, N-CAM, N-Cadherin and J1/tenascin/cytotactin, suggest that these molecules play no critical role in determining the preference of nerve cells for anterior sclerotome. 4. Peanut agglutinin (PNA) recognises cell surface-associated components on posterior cells which, when incorporated into liposomes, cause the abrupt collapse of sensory growth cones in vitro. The PNA receptor(s) may be inhibitory for nerve cells in vivo. 5. The chick hindbrain epithelium is segmented early in its development. Each branchiomotor nucleus in the series of cranial nerves V, VII and IX derives from a pair of segments lying in register with an adjacent branchial arch. Neurogenesis of motor and reticular axons begins in alternate segments, suggesting parallels with insect pattern formation.