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Synaptic vesicle recycling at two classes of release sites in giant nerve terminals of the embryonic chicken ciliary ganglion
Author(s) -
Nguyen Don,
Sargent Peter B.
Publication year - 2002
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.10237
Subject(s) - ciliary ganglion , biology , synaptic vesicle , active zone , postsynaptic potential , neurotransmission , horseradish peroxidase , neuroscience , stimulation , vesicle , cholinergic , microbiology and biotechnology , anatomy , biophysics , receptor , biochemistry , membrane , enzyme
Rapid synaptic transmission in the embryonic chicken ciliary ganglion occurs through the activation of two distinct classes of nicotinic acetylcholine receptors (AChRs): those containing α3 subunits (α 3*‐AChRs) and those containing α7 subunits (α 7*‐AChRs). α3*‐AChRs are found on ciliary neurons in clusters at synaptic sites on the cell body, whereas α7* ‐AChRs are found on somatic spines, which historically were thought not to have release sites in the embryo. However, Shoop et al. (Shoop et al. [1999] J. Neurosci. 19:692–704) recently described release sites having pre‐ and postsynaptic densities on somatic spines. We used transmission electron microscopy to compare the structure of synaptic sites on spines with those on the smooth surfaced part of the cell. We find that the two populations of sites are similar in active zone length, number of vesicles, and distance between vesicles and active zone. To study the functional properties of these sites, we examined their stimulation‐dependent uptake and release of the extracellular tracer horseradish peroxidase (HRP). We found that each class of release sites both took up and released HRP in a stimulation‐ and calcium‐dependent manner. The mean fraction of synaptic vesicles labeled with tracer was similar for the two populations, both after loading (∼45%) and after unloading (∼ 7%). Thus we detect no differences between these two anatomically distinct classes of release sites, other than their incidence: sites on spines occurred only 12% as often as those on the cell body. The release sites on somatic spines presumably underlie synaptic responses attributable to α7*‐AChRs. J. Comp. Neurol. 448:128–137, 2002. © 2002 Wiley‐Liss, Inc.