26 research outputs found
Role for a Novel Usher Protein Complex in Hair Cell Synaptic Maturation
The molecular mechanisms underlying hair cell synaptic maturation are not well understood. Cadherin-23 (CDH23), protocadherin-15 (PCDH15) and the very large G-protein coupled receptor 1 (VLGR1) have been implicated in the development of cochlear hair cell stereocilia, while clarin-1 has been suggested to also play a role in synaptogenesis. Mutations in CDH23, PCDH15, VLGR1 and clarin-1 cause Usher syndrome, characterized by congenital deafness, vestibular dysfunction and retinitis pigmentosa. Here we show developmental expression of these Usher proteins in afferent spiral ganglion neurons and hair cell synapses. We identify a novel synaptic Usher complex comprised of clarin-1 and specific isoforms of CDH23, PCDH15 and VLGR1. To establish the in vivo relevance of this complex, we performed morphological and quantitative analysis of the neuronal fibers and their synapses in the Clrn1−/− mouse, which was generated by incomplete deletion of the gene. These mice showed a delay in neuronal/synaptic maturation by both immunostaining and electron microscopy. Analysis of the ribbon synapses in Ames waltzerav3J mice also suggests a delay in hair cell synaptogenesis. Collectively, these results show that, in addition to the well documented role for Usher proteins in stereocilia development, Usher protein complexes comprised of specific protein isoforms likely function in synaptic maturation as well
Synaptophysin immunoreactivity in the cat cochlear nuclei
The presence of synaptophysin, a presynaptic ca2+ binding glycoprotein, has been analyzed in the cochlear nucleus complex of the adult cat using an antisynaptophysin monoclonal antibody. Synaptophysin immunoreactivity was differently distributed between regions of cochlear nuclei. Terminal boutons contacting directly with neurons (cell bodies and dendrites) or in the neuropil of ventral and dorsal cochlear nuclei appeared immunostained. In the ventral cochlear nucleus, synaptophysin-labelled boutons were clearly defined in contact with spherical, globular, multipolar, octopus and cochlear-nerve root neurons. However, the dorsal cochlear nucleus showed a dense immunostained network of synaptophysin-labelled puncta, inside which some neuron cell bodies were observed. The present findings show a differential distribution of synaptophysin- immunostained boutons between the ventral and the dorsal cochlear nuclei of the cat. The present description of the different synaptophysin-labelled terminal boutons in the cochlear nuclei complex and their pattern of distribution, will be useful for further studies on development, degeneration or regeneration of the peripheral auditory pathway
Synaptophysin immunoreactivity in the cat cochlear nuclei
The presence of synaptophysin, a presynaptic
ca2+ binding glycoprotein, has been analyzed in the
cochlear nucleus complex of the adult cat using an antisynaptophysin
monoclonal antibody. Synaptophysin
immunoreactivity was differently distributed between
regions of cochlear nuclei. Terminal boutons contacting
directly with neurons (cell bodies and dendrites) or in
the neuropil of ventral and dorsal cochlear nuclei
appeared immunostained. In the ventral cochlear
nucleus, synaptophysin-labelled boutons were clearly
defined in contact with spherical, globular, multipolar,
octopus and cochlear-nerve root neurons. However, the
dorsal cochlear nucleus showed a dense immunostained
network of synaptophysin-labelled puncta, inside which
some neuron cell bodies were observed. The present
findings show a differential distribution of synaptophysin-
immunostained boutons between the ventral and
the dorsal cochlear nuclei of the cat. The present
description of the different synaptophysin-labelled
terminal boutons in the cochlear nuclei complex and
their pattern of distribution, will be useful for further
studies on development, degeneration or regeneration of
the peripheral auditory pathway
Transitional expression of OX-2 and GAP-43 glycoproteins in developing rat cochlear nerve fibers
The OX-2 and GAP-43 glycoproteins are
two proteins involved in neuronal cell-to-cell interaction
and/or growing of dendrites and axons. Therefore, for
the auditory receptor the expression of these proteins
could provide information on the afferent and eff e r e n t
nerve fiber organization. The expression and distribution
of OX-2 and GAP-43 were analyzed during the auditory
receptor development and maturation (from embryonic
day E13 to postnatal day P22). Both glycoproteins were
early recognized in the cochleae of E13 rats. Then, they
slowly but progressively disappeared, being absent when
the animals reached the P22 postnatal day. At E13, a
weak OX-2 expression was restricted to the perikaryon
of the spiral ganglion neurons, while in the same period
a strong GAP-43 immunostaining was found in both the
neuronal perikaryon and the neurites. During the rat
embryonic period (E13 to birth) the expression of both
glycoproteins appeared progressively restricted to the
neurites. During the rat postnatal period (P0 to P22),
OX-2 and GAP-43 exhibited a dissimilar distribution
pattern. The OX-2 glycoprotein appeared in the afferent,
efferent and fibers of the auditory nerve, while the GAP-
43 glycoprotein only appeared in the efferent nerve
fibers. Present data suggest that OX-2 and GAP-43
could act as two complementary glycoproteins during
the development, organization, and maturation of the
cochlear nerve fibers. While both glycoproteins could
participate in axonal growing and orientation, OX-2
could also be involved in a similar process for auditory
dendrites
Immunocytochemical detection of synaptophysin in C57BL/6 mice cochlea during aging process
Aged mammals frequently exhibit a bilateral, progressive, and symmetric deafness related to the degeneration of auditory receptor. However, little is still known about aging effects on synapses in this receptor. Synaptophysin (Syp) is a 38 kDa Ca2+ binding glycoprotein widely found in presynaptic membrane and vesicles. The Syp has been found in presynaptic buttons of efferent auditory fibers, within the developing and adult auditory receptor. The detection of Syp in aged cochleae could provide relevant information about synaptic changes and receptor degeneration process observed in old animals. This paper focuses on aging linked changes related to the presence of Syp in cochleae of C57BL/6J mice (from 1 to 24 months old). Results showed that during the first months of age, no significant changes were observed in the Syp distribution under the basal pole of inner (IHCs) neither the outer (OHCs) hair cells. At six months of age, a significant decrease of Syp immunocytochemical detection appeared in fibers under the most external row of OHCs, but restricted to the cochlear basal coil. Only a very scarce reduction of Syp was noted under the IHC and the other OHC rows, also at the basal coil. From mice 9 months old on, a progressive decrease of the presence of Syp was found under IHC and all OHC rows starting at the basal coil and reaching the apical coil in the oldest mice. All these data could indicate that the cochlea aging process early affects to presynaptic membrane proteins of efferent endings fibers. This early alteration of cochleae efferent synapses could be involved in the whole degeneration of the Corti's organ
Abnormal cochlea linked to deafness in transgenic mice expressing human cytokeratin K8
The cytokeratin intermediate filaments have
a relevant role in the proliferation and differentiation
processes of epithelial cells. To provide information
about the role of K8 cytokeratin during the auditory
receptor differentiation, two groups of adult mice were
used: TGK8-4 transgenic and control animals. The
TGK8-4 transgenic mice contained 12 kb of K8 human
cytokeratin (HK8) locus (Casanova et al., 1995, 1999).
The functional activity of the auditory receptor was
analyzed by auditory thresholds. Morphological studies
demonstrate that the auditory receptors of the TGK8-4
transgenic mice are highly immature.
Immunocytochemical studies were made by using two
monoclonal antibodies: CAM 5-2 (recognizing K8
human cytokeratin) and Troma-1 (recognizing both
mouse and human K8 cytokeratin). These demonstrated
significant differences between the auditory receptors of
the transgenic mice and the control mice. These
functional and morphological differences clearly suggest
that K8 cytokeratin has a relevant role during the
differentiation and tridimensional organization of the
sensory and the supporting cells of the auditory receptor
Dopamine transporter is essential for the maintenance of spontaneous activity of auditory nerve neurones and their responsiveness to sound stimulation.
International audienceDopamine, a neurotransmitter released by the lateral olivocochlear efferents, has been shown tonically to inhibit the spontaneous and sound-evoked activity of auditory nerve fibres. This permanent inhibition probably requires the presence of an efficient transporter to remove dopamine from the synaptic cleft. Here, we report that the dopamine transporter is located in the lateral efferent fibres both below the inner hair cells and in the inner spiral bundle. Perilymphatic perfusion of the dopamine transporter inhibitors nomifensine and N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine into the cochlea reduced the spontaneous neural noise and the sound-evoked compound action potential of the auditory nerve in a dose-dependent manner, leading to both neural responses being completely abolished. We observed no significant change in cochlear responses generated by sensory hair cells (cochlear microphonic, summating potential, distortion products otoacoustic emissions) or in the endocochlear potential reflecting the functional state of the stria vascularis. This is consistent with a selective action of dopamine transporter inhibitors on auditory nerve activity. Capillary electrophoresis with laser-induced fluorescence (EC-LIF) measurements showed that nomifensine-induced inhibition of auditory nerve responses was due to increased extracellular dopamine levels in the cochlea. Altogether, these results show that the dopamine transporter is essential for maintaining the spontaneous activity of auditory nerve neurones and their responsiveness to sound stimulation