Rare and spatially segregated release sites mediate a synaptic interaction between two identified network neurons
J. Neurobiol.. 2002-01-08; 50(2): 150-163
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Cabirol-Pol MJ(1), Combes D, Fénelon VS, Simmers J, Meyrand P.
(1)Laboratoire de Neurobiologie des Réseaux, Université Bordeaux 1 & Centre
National de la Recherche Scientifique-Unité Mixte de Recherche 5816, Avenue des
Facultés, 33405 Talence, France.
Laser-scanning confocal microscopy (LSCM), electron microcopy (EM), and cellular
electrophysiology were used in combination to study the structural basis of an
inhibitory synapse between two identified neurons of the same network. To achieve
this, we examined the chemical inhibitory synapse between identified neurons
belonging to the lobster (Homarus gammarus) pyloric network: the pyloric dilator
(PD) and the lateral pyloric (LP) neurons. In order to visualize simultaneously
these two neurons, we used intrasomatic injection of Lucifer Yellow (LY) in one
and rhodamine/horseradish peroxydase (HRP) in the other. Under LSCM, we found
only two zones of close apposition in a restricted part of the neuritic tree of
the two network neurons. Then, within these two zones, the synaptic release sites
were searched using EM. To this end, photoconversion of LY with immunogold and
development of HRP with DAB were performed on the previously observed
preparations. Structural evidence was found for only one release site per zone.
To confirm this result, and because the zones of contact were always segregated
in a restricted part of the dendrites, we used laser photoablation to selectively
delete, either pre- or postsynaptically, the branches on which the release sites
were located. In both cases, such restrictive ablation completely abolished the
functional interaction between these neurons. Our results therefore demonstrate
that an inhibitory synapse that is essential for the operation of a neural
network relies on only very few sites of contact localized in a highly restricted
part of each neuron’s dendritic arbor.
Copyright 2002 John Wiley & Sons, Inc. J Neurobiol 50: 150-163, 2002; DOI
PMID: 11793361 [Indexed for MEDLINE]