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Sequential changes in synaptic vesicle pools and endosome-like organelles during depolarization near the active zone of central nerve terminals.

Abstract：

:During periods of high-frequency stimulation the maintenance of synaptic transmission depends on a continued supply of synaptic vesicles. Local recycling in the terminals ensures synaptic vesicle replenishment, but the intermediate steps are still a matter of debate. We analyzed changes in synaptic vesicle pools and endosome-like organelles near the active zone in central nerve terminals during depolarization at the ultrastructural level by electron microscopy. A short, 100 ms, depolarization-induced recruitment of synaptic vesicles was observed from a reserve pool to a recruited pool, within 150 nm of the active zone, and the docked pool at the active zone was increased as well. Prolonged, 15 s or 3 min, depolarization decreased the total amount of synaptic vesicles, which was accompanied by a parallel increase in size and amount of endosome-like organelles. After a period of rest, the number of endosome-like organelles decreased and the amount of synaptic vesicles was restored to control level. The endocytotic nature of part of the endosome-like organelles after 15 s and 3 min depolarization was indicated by their labeling with extracellularly added horseradish peroxidase (HRP). In addition, a small number of synaptic vesicles entrapped HRP under these conditions. After repolarization, the number of HRP-loaded endosome-like structures decreased. Simultaneously, a strong increase in amount of HRP-loaded small vesicles did occur. These results indicate that during sub-second depolarization, synaptic vesicles were rapidly recruited from the reserve pool to replenish the releasable pool, whereas prolonged depolarization (s-min) induced local endocytosis in at least two ways, i.e. either directly as vesicles or via endosome-like organelles from which synaptic vesicles were reformed.

journal_name

Neuroscience

journal_title

Neuroscience

authors

Leenders AG,Scholten G,de Lange RP,Lopes da Silva FH,Ghijsen WE

doi

10.1016/s0306-4522(01)00450-x

keywords:

subject

Has Abstract

pub_date

2002-01-01 00:00:00

pages

195-206

issue

eissn

0306-4522

issn

1873-7544

pii

S030645220100450X

journal_volume

109

pub_type

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Sequential changes in synaptic vesicle pools and endosome-like organelles during depolarization near the active zone of central nerve terminals.