Ca‐dependence of synaptic vesicle exocytosis and endocytosis at the hippocampal mossy fibre terminal

The number and morphology of synaptic ribbons at photoreceptor and bipolar cell terminals has been reported to change on a circadian cycle. Here we sought to determine whether this phenomenon exists at goldfish Mb-type bipolar cell terminals with the aim of exploring the role of ribbons in transmitter release. We examined the physiology and ultrastructure of this terminal around two time points: midday and midnight. Nystatin perforated-patch recordings of membrane capacitance ( Cm) revealed that synaptic vesicle exocytosis evoked by short depolarizations was reduced at night, even though Ca2+ currents were larger. The efficiency of exocytosis (measured as the Δ Cm jump per total Ca2+ charge influx) was thus significantly lower at night. The paired-pulse ratio remained unchanged, however, suggesting that release probability was not altered. Hence the decreased exocytosis likely reflects a smaller readily releasable vesicle pool at night. Electron microscopy of single sections from intact retinas averaged 65% fewer ribbons at night. Interestingly, the number of active zones did not change from day to night, only the probability of finding a ribbon at an active zone. Additionally, synaptic vesicle halos surrounding the ribbons were more completely filled at night when these on-type bipolar cells are more hyperpolarized. There was no change, however, in the physical dimensions of synaptic ribbons from day to night. These results suggest that the size of the readily releasable vesicle pool and the efficiency of exocytosis are reduced at night when fewer ribbons are present at bipolar cell terminal active zones.

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A Tripartite Protein Complex with the Potential to Couple Synaptic Vesicle Exocytosis to Cell Adhesion in Brain

Cell ◽

10.1016/s0092-8674(00)81736-5 ◽

1998 ◽

Vol 94 (6) ◽

pp. 773-782 ◽

Cited By ~ 363

Author(s):

Stefan Butz ◽

Masaya Okamoto ◽

Thomas C Südhof

Keyword(s):

Cell Adhesion ◽

Synaptic Vesicle ◽

Protein Complex ◽

Synaptic Vesicle Exocytosis ◽

Vesicle Exocytosis

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The synaptic vesicle SNARE neuronal Synaptobrevin promotes endolysosomal degradation and prevents neurodegeneration

The Journal of Cell Biology ◽

10.1083/jcb.201108088 ◽

2012 ◽

Vol 196 (2) ◽

pp. 261-276 ◽

Cited By ~ 25

Author(s):

Adam Haberman ◽

W. Ryan Williamson ◽

Daniel Epstein ◽

Dong Wang ◽

Srisha Rina ◽

...

Keyword(s):

Synaptic Vesicle ◽

Transmembrane Protein ◽

Primary Defect ◽

Endosomal Sorting ◽

Synaptic Vesicle Exocytosis ◽

Cathepsin Proteases ◽

Core Proteins ◽

Protein Receptors ◽

Vesicle Exocytosis ◽

Photoreceptor Neurons

Soluble NSF attachment protein receptors (SNAREs) are the core proteins in membrane fusion. The neuron-specific synaptic v-SNARE n-syb (neuronal Synaptobrevin) plays a key role during synaptic vesicle exocytosis. In this paper, we report that loss of n-syb caused slow neurodegeneration independent of its role in neurotransmitter release in adult Drosophila melanogaster photoreceptor neurons. In addition to synaptic vesicles, n-Syb localized to endosomal vesicles. Loss of n-syb lead to endosomal accumulations, transmembrane protein degradation defects, and a secondary increase in autophagy. Our evidence suggests a primary defect of impaired delivery of vesicles that contain degradation proteins, including the acidification-activated Cathepsin proteases and the neuron-specific proton pump and V0 adenosine triphosphatase component V100. Overexpressing V100 partially rescued n-syb–dependent degeneration through an acidification-independent endosomal sorting mechanism. Collectively, these findings reveal a role for n-Syb in a neuron-specific sort-and-degrade mechanism that protects neurons from degeneration. Our findings further shed light on which intraneuronal compartments exhibit increased or decreased neurotoxicity.

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