Synaptosome

About: Synaptosome is a research topic. Over the lifetime, 2012 publications have been published within this topic receiving 67743 citations.

Botulinum neurotoxin A selectively cleaves the synaptic protein SNAP-25

Abstract: Neurotransmitter release is potently blocked by a group of structurally related toxin proteins produced by Clostridium botulinum. Botulinum neurotoxin type B (BoNT/B) and tetanus toxin (TeTx) are zinc-dependent proteases that specifically cleave synaptobrevin (VAMP), a membrane protein of synaptic vesicles. Here we report that inhibition of transmitter release from synaptosomes caused by botulinum neurotoxin A (BoNT/A) is associated with the selective proteolysis of the synaptic protein SNAP-25. Furthermore, isolated or recombinant L chain of BoNT/A cleaves SNAP-25 in vitro. Cleavage occurred near the carboxyterminus and was sensitive to divalent cation chelators. In addition, a glutamate residue in the BoNT/A L chain, presumably required to stabilize a water molecule in the zinc-containing catalytic centre, was required for proteolytic activity. These findings demonstrate that BoNT/A acts as a zinc-dependent protease that selectively cleaves SNAP-25. Thus, a second component of the putative fusion complex mediating synaptic vesicle exocytosis is targeted by a clostridial neurotoxin.

Rim is a putative Rab3 effector in regulating synaptic-vesicle fusion

Abstract: Rab3 is a neuronal GTP-binding protein that regulates fusion of synaptic vesicles and is essential for long-term potentiation of hippocampal mossy fibre synapses1,2,3,4,5 More than thirty Rab GTP-binding proteins are known to function in diverse membrane transport pathways, although their mechanisms of action are unclear We have now identified a putative Rab3-effector protein called Rim Rim is composed of an amino-terminal zinc-finger motif and carboxy-terminal PDZ and C2 domains It binds only to GTP (but not to GDP)-complexed Rab3, and interacts with no other Rab protein tested There is enrichment of Rab3 and Rim in neurons, where they have complementary distributions Rab3 is found only on synaptic vesicles, whereas Rim is localized to presynaptic active zones in conventional synapses, and to presynaptic ribbons in ribbon synapses Transfection of PC12 cells with the amino-terminal domains of Rim greatly enhances regulated exocytosis in a Rab3-dependent manner We propose that Rim serves as a Rab3-dependent regulator of synaptic-vesicle fusion by forming a GTP-dependent complex between synaptic plasma membranes and docked synaptic vesicles

Calcium-Dependent and-Independent Release of Glutamate from Synaptosomes Monitored by Continuous Fluorometry

Abstract: An enzyme-linked fluorometric assay is described for the continuous monitoring of the unidirectional efflux of glutamate from guinea-pig synaptosomes. Glutamate efflux from freshly suspended, polarized synaptosomes occurs at 0.35–0.39 nmol min−1 mg of protein−1 and is not significantly affected by external Ca2+. KC1 depolarization (30 mM KCI) in the absence of Ca2+ doubles this rate, whereas in the presence of Ca2+, the initial kinetics of the assay are consistent with the release in the first 5 s of 0.6 nmol mg of protein−1. The final extent of Ca2+-dependent release amounts to 1.9 nmol mg of protein−1, or 8.5% of the total intrasynaptosomal glutamate content. Preincubation of synaptosomes at 30°C for 2 h before depolarization leads to a decrease in Ca2+-independent release and an increase in Ca2+-dependent release, consistent with an intrasynaptosomal relocation of the amino acid.

Glial cell function: uptake of transmitter substances

Abstract: Rabbit-brain fractions enriched in neuronal cell bodies and in glial cells accumulated norepinephrine, serotonin, dopamine, and γ-aminobutyric acid, substances believed to serve as neurotransmitters in the central nervous system. Both neurons and glia were able to concentrate the monoamine transmitters about 4-fold from a medium containing 0.1-1 μM concentrations. However, the glial-cell fraction concentrated aminobutyrate over a 100-fold from the medium, in contrast to the neuronal fraction, which concentrated this amino acid only 4-fold. The uptake of aminobutyrate by glial cells was 30-50% of that of synaptosome preparations. Its uptake in all fractions was temperature sensitive, sensitive to metabolic inhibitors, and exhibited Km values of 0.72 μM for the neuronal fraction, 0.42 μM for the synaptosomal fraction, and 0.27 μM for the glial-cell fraction. These results are interpreted as evidence that the glial cell is involved in limiting the extracellular build-up of substances that might trigger synaptic transmission by removing any transmitters that may diffuse out of the synaptic cleft during the transmission of impulses. The possible function of the enormous ability of glia and synaptosomes to accumulate aminobutyrate is discussed in light of the actions and distribution of this substance in the central nervous system.