Journal of Neuroscience, Vol 8, 4640-4645, Copyright © 1988 by Society for Neuroscience
Secretory function of the vestibular nerve calyx suggested by presence of vesicles, synapsin I, and synaptophysin
E Scarfone, D Dememes, R Jahn, P De Camilli and A Sans
INSERM, U 254, Laboratoire de Neurophysiologie Sensorielle, U.S.T.L., Montpellier, France.
Type I sensory hair cells of the vestibular epithelium are nearly
completely ensheathed by an afferent nerve ending, the vestibular nerve
calyx. We have recently reported that the nerve calyx, and, in particular,
its apical portions surrounding the neck of the hair cell, are
immunoreactive for synapsin I (Favre et al., 1986), a major membrane
component of small synaptic vesicles of axonal endings. We have now found,
by electron microscopy, that the same region of the calyx is densely
populated by microvesicles morphologically similar to typical presynaptic
small synaptic vesicles. Furthermore, we have established by light
microscopy immunocytochemistry that this region of the calyx also contains
a high concentration of synaptophysin, another well-characterized major
component of small synaptic vesicle membranes. These results suggest that
the upper portion of the calyx is equipped with the machinery that in
presynaptic terminals is involved in the release of neurotransmitters and
raise the possibility that the calyx, via secretion of neurotransmitterlike
substances, might modulate the function of type I hair cells.