Journal of Neuroscience, Vol 8, 4319-4333, Copyright © 1988 by Society for Neuroscience
Distribution of glycine receptors on the membrane of a central neuron: an immunoelectron microscopy study
T Seitanidou, A Triller and H Korn
INSERM U261, Departement des Biotechnologies, Institut Pasteur, Paris, France.
The distribution of glycine receptors on the plasmalemma of the teleost
Mauthner cell was examined with light and electron microscopy using
monoclonal antibodies raised against the glycine receptors of the rat.
These immunoglobulins recognize a peptide of 93 kDa associated with the
intracellular side of the receptor complex. With indirect
immunofluorescence, labeling appeared as small clusters over the whole
surface of the neuron. This distribution indicates that, unlike other
neurons, the Mauthner cell can express glycine receptors at the dendritic
and at the somatic level as well. Vestibular or reticular neurons lying in
the proximity of the Mauthner cell were also stained. At the
ultrastructural level, the immunoenzymatic reaction product, localized in
front of the presynaptic active zones, slightly overextends the limits of
the synaptic complex. This observation may account for vesicular exocytosis
at the border of the presynaptic grid. More generally, inside and outside
the axon-cap, stained postsynaptic membranes were apposed to terminals
identified as unmyelinated club endings and some small vesicle boutons,
respectively. Each of them could establish classical flat synapses or
spinelike contacts, the latter being described here for the first time.
Patches of membrane remained unstained, however, particularly along the
lateral and ventral dendrites of the cell; they corresponded to the contact
sites of excitatory afferents. In order to enhance the penetration of
immunoreactive substances, a particular fixation procedure was used; its
effect on the shape of the synaptic vesicles is described. Our results
support the notion that glycine is responsible for both somatic and remote
dendritic Cl- -dependent inhibition of the Mauthner cell. The first one is
produced by the so-called PHP exhibiting neurons, which correspond to cells
of recurrent collateral network and vestibulovestibular pathway. In
contrast, cells giving rise to the more distal inhibitory synapses on both
dendrites are not yet characterized.