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M Eybalin

Publications and source records attributed to M Eybalin.

At least 55 records · Page 3Linked to original sources
PubMed1989

Cochlear neuroactive substances.

We have reviewed the experiments done in our laboratory concerning various cochlear neuroactive substances. Data using chemical neuroanatomy and neurochemical techniques are described. They allow the identification and localization of neuroactive substances which could act as neurotransmitters and/or neuromodulators at the different types of synapses in the organ of Corti. Three hypotheses are presented: (1) the inner hair cells use glutamate as a neurotransmitter, but in addition to its excitatory properties, glutamate may also be involved in pathophysiological events affecting afferent auditory dendrites: (2) subpopulations of both the lateral and medial olivocochlear efferent systems can be differentiated by the neuroactive substances they may use: (3) the base and the apex of the cochlea can be distinguished on the basis of neurochemical data.

Animals↗
PubMed1989

[Application of an immunofluorescent technique on a guinea pig cochlear section for the study of endocochlear pathologies].

Experimental evidence suggests the existence of autoimmune mechanisms in the appearance of cochlear pathologies. Following a recall of studies made previously by different authors, we will present an immunofluorescent technique on a guinea pig cochlear section applied to the study of 22 serums of patients with endocochlear pathologies. The goal of this test is to identify the patients with immunologic disorders in order to adapt treatment using immunosuppressive medication. The findings show the existence of antibodies directed against the cell nuclei, or against the endothelium of the cochlear vessels, or against the endosteum of the inner ear. The importance of these findings has yet to be established.

Animals↗
PubMed1988

Met-enkephalin and Met-enkephalin-Arg6-Gly7-Leu8 immunofluorescence in the developing guinea-pig organ of Corti.

The immunofluorescence technique has been applied to the organ of Corti from developing guinea pigs to detect the immunoreactions to antibodies directed against Met-enkephalin and Met-enkephalin-Arg6-Gly7-Leu8. Four stages of gestation were studied (30, 41, 50 and 62 days). On days 30 and 41 of gestation, no specific fluorescence to both antibodies was seen in the organ of Corti. On day 50, the inner spiral bundle and the tunnel spiral bundle, two areas displaying anti-enkephalin immunoreactivity in the adult, showed a specific immunofluorescence to either the anti-Met-enkephalin and the anti-Met-enkephalin-Arg6-Gly7-Leu8 antibodies. On day 62, these two structures showed an immunofluorescence whose intensity was slightly increased compared with that seen on day 50. In no case, was an immunoreaction in the outer hair cell area seen. These results suggest that the enkephalins, which have been proposed as putative neurotransmitters or neuromodulators of neurons belonging to the lateral olivocochlear system, are present in the organ of Corti at about the time of onset of cochlear function. Thus, the enkephalin-containing lateral efferents may play a role in the early control of cochlear potentials.

Animals↗
PubMed1988

Immunoelectron microscopy identifies several types of GABA-containing efferent synapses in the guinea-pig organ of Corti.

Using an immunoperoxidase technique, we have localized by light and electron microscopy GABA-immunostained fibers within a component of the efferent innervation of the organ of Corti. At the light microscopic level, GABA-immunostained fibers were observed within the inner spiral bundle (below the inner hair cells) and the tunnel spiral bundle. The immunostaining was clearly more intense in the upper turns than in the basal turns. Mostly in the upper turns, GABA-immunostained fibers were seen crossing the tunnel of Corti to reach the outer hair cells where they formed large immunostained patches at the base of the cells. Unevenly distributed throughout these upper turns, immunostained fibers were seen climbing along the outer hair cells and traveling near the non-sensorineural Hensen's cells. The electron microscopic observations of GABA-immunostained fibers in the upper turns allowed us to identify within the inner spiral bundle vesiculated varicosities synapsing with radial dendrites connected to the inner hair cells. In the outer hair cell area, the GABA-immunostained fibers made several kinds of synaptic contacts. They included a minor population of the large axosomatic synapses with the basal pole of the outer hair cells and many axodendritic synapses with the spiral dendrites connected to these cells. Occasionally, the GABA-immunostained climbing fibers also synapsed with the outer hair cells at a supranuclear level. These result confirm previous light microscopic data dealing with the projection of the GABA-immunostained fibers along the cochlear partition. Moreover, they extend them in characterizing several kinds of GABA-immunostained synapses. These latter findings agree with previous neurochemical electrophysiological data which suggests an efferent neurotransmitter role for GABA. Nevertheless, such an existence of an efferent innervation predominantly projecting to the upper turns of the cochlea adds another criterion distinguishing the "apical" from the "basal" cochlea.

Animals↗
PubMed1987

Opioid receptors inhibit the adenylate cyclase in guinea pig cochleas.

The effects of mu- and delta-preferring agonists on adenylate cyclase activity have been investigated in vitro in homogenates of guinea pig cochleas. Morphine, Leu-enkephalin, D-Ala2, N-methyl-Phe4, Gly-ol5-enkephalin (DAGO) and D-Ser2-Leu-enkephalin-Thr (DSLET) each inhibited the synthesis of cyclic AMP. This effect was reversed by naloxone which had a greater affinity in blocking the effect of the mu-preferring agonists (morphine, DAGO) than in blocking the effect of the delta-preferring agonists (Leu-enkephalin, DSLET). Finally, no additive effects were observed when various combinations of two agonists were used. These results indicate that opioid receptors exist in the guinea pig cochlea and that they are negatively linked to adenylate cyclase. The different affinities shown by naloxone to reverse the inhibition induced by the mu- and delta-preferring agonists suggest that morphine and DAGO act through mu-receptors, whereas Leu-enkephalin and DSLET act through delta-receptors. Since no additive effects have been found when combining two different agonists, it can be hypothesized that the mu- and delta-receptors are coupled to the same pool of adenylate cyclase. It may be proposed from these findings that in vivo enkephalins inhibit the synthesis of cyclic AMP via mu- and delta-receptors. However, whether this effect occurs at a presynaptic level (within opioid-containing olivocochlear varicosities) or at the postsynaptic level (within dendrites of the primary auditory neurons) remains to be determined.

Adenylyl Cyclases↗
PubMed1987

Effect of noise level on the Met-enkephalin content of the guinea pig cochlea.

Using a highly sensitive and specific radioimmunoassay for Met-enkephalin, we have monitored in two series of experiments the changes of the Met-enkephalin content of guinea pig cochleas following a 60 min exposure to different intensities of white noise (70 dB SPL, 90 dB SPL, 110 dB SPL). Our results indicate that the Met-enkephalin content was significantly lower after noise exposures than after exposure to the silence of a sound attenuated chamber. After a stimulation at 70 dB SPL, the levels of Met-enkephalin were 70% (series I) and 61% (series II) of those obtained after a period of silence. After a 110 dB SPL stimulation, these values fell to 41% (series I) and 55% (series II) of those in silence. These results strengthen the hypothesis that enkephalins are olivocochlear neuroactive substances. They suggest that the enkephalin-containing lateral olivocochlear system discharges with noise stimuli of moderate intensity.

Acoustic Stimulation↗
PubMed1987

Choline acetyltransferase (ChAT) immunoelectron microscopy distinguishes at least three types of efferent synapses in the organ of Corti.

Using anatomical criteria, the olivo-cochlear fibers ending in the organ of Corti (efferent fibers) have recently been separated into two systems: a lateral system innervating principally the inner hair cell (IHC) area and a medial system innervating mainly the outer hair cells (OHCs). Electrophysiological and biochemical experiments suggest that acetylcholine may be a neurotransmitter of these efferent fibers. However, efferent synapses that use acetylcholine as neurotransmitter have not yet been identified at the electron microscopic level. Using a pre-embedding immunoelectron microscopic technique with a monoclonal antibody against choline acetyltransferase (ChAT), we localized ChAT-immunostained fibers below both the IHCs and OHCs. In the inner spiral bundle, one type of ChAT-immunostained fibers was vesiculated and formed axo-dendritic synapses with the afferent auditory dendrites contacting the inner hair cells. A second type of ChAT-immunostained fibers seen in the inner spiral bundle was unvesiculated. Unstained vesiculated varicosities synapsing with the auditory dendrites were also seen in the inner spiral bundle. At the OHC level, ChAT immunostaining was found in nearly all the terminals synapsing with the OHCs. The finding of two types of ChAT-immunostained efferent synapses in the organ of Corti, i.e. axo-dendritic synapses in the inner spiral bundle and axo-somatic synapses with the OHCs, supports the hypothesis that both the lateral and the medial olivo-cochlear systems use acetylcholine as a neurotransmitter. The finding of numerous unstained synapses in the inner spiral bundle, and some below OHCs, together with previous data about putative cochlear neurotransmitters, suggests the possibility of additional non-cholinergic olivo-cochlear systems. It might soon appear useful to reclassify efferents according to the nature of the different neurotransmitters/co-transmitters found in the various efferent synapses of the organ of Corti.

Animals↗
PubMed1987

Coexistence of putative neuroactive substances in lateral olivocochlear neurons of rat and guinea pig.

We have used the retrograde axonal transport of Fast Blue, injected intra-cochlearly, to identify in the rat lateral superior olive (LSO) neurons which belong to the lateral olivocochlear system (LOCS). Using immunohistofluorescence technique, we have localized within Fast Blue-labeled neurons immunostainings for enkephalins (Met-enkephalin, Met-enkephalin-Arg6-Gly7-Leu8), dynorphins (alpha-neo-endorphin, dynorphin 1-17) or choline acetyltransferase (ChAT). Many Fast Blue-labeled neurons did not show any immunostaining, but all the immunostained neurons found in the LSO were Fast Blue-labeled. In immunohistofluorescence colocalization experiments of two antigens, we could colocalize within the same neurons of the rat LSO immunostainings for ChAT and enkephalins and for ChAT and dynorphins. In each case, neurons only immunostained for ChAT, enkephalins or dynorphins could also be observed. A colocalization of the immunostainings for Met-enkephalin and dynorphins within neurons of the guinea pig and rat LSO was also found. However, in this case, neurons which did not show colocalization were only Met-enkephalin-immunoreactive, thus suggesting that all the dynorphins immunoreactive LSO neurons also contain enkephalins. These findings support the idea that the neurons of the LSO which contain ChAT-, enkephalin- or dynorphin-immunostainings project to the cochlea and belong to the LOCS. It can also be concluded that acetylcholine, enkephalins and dynorphins coexist within a same population of neurons of the LOCS, although other patterns of co-containment of neuroactive substances within LOCS neurons may also exist.

Animals↗
PubMed1985

Electron microscopic localization of N-terminal proenkephalin (synenkephalin) immunostaining in the guinea pig organ of Corti.

Using a pre-embedding immunoelectron microscopic technique, anti-synenkephalin immunostaining has been demonstrated within efferent varicosities (originating from the brainstem) of the inner spiral bundle and the tunnel spiral bundle of the organ of Corti. Axodendritic synapses were observed between the anti-synenkephalin immunostained varicosities and auditory dendrites connected to inner hair cells. No anti-synenkephalin immunostaining was found in any efferents at the outer hair cell level. We suggest that this immunolocalization of synenkephalin in the organ of Corti allows a better differentiation of the cochlear efferent systems on a neurochemical basis. The whole lateral system, or at least a significant part of it, could be referred to as the 'enkephalin-containing efferent system'.

Animals↗
PubMed1985

Met-enkephalin-Arg6-Gly7-Leu8 in the organ of Corti: high performance liquid chromatography and immunoelectron microscopy.

The opioid octapeptide Met-enkephalin-Arg6-Gly7-Leu8 (MERGL) was identified and quantified in the guinea pig cochlea using high performance liquid chromatography and a specific radioimmunoassay. The presence of MERGL immunostaining in efferent endings (coming from the brainstem) within the inner spiral bundle and the tunnel spiral bundle was demonstrated using a pre-embedding immunoelectronmicroscopic technique. Axo-dendritic synapses were observed between the MERGL immunostained varicosities and auditory dendrites. It is hypothesized that MERGL could act, together with Met-enkephalin and other pro-enkephalin A-related peptides, as an efferent neuromodulator or neurotransmitter in the organ of Corti.

Animals↗
PubMed1985

Kainic acid selectively alters auditory dendrites connected with cochlear inner hair cells.

Cochleas of adult guinea pigs and rats, and 6-day-old rat pups, were injected, through the round window, with 2 microliters of artificial classical Konishi perilymph containing 1 nmol kainic acid (KA). 5 min later, they were fixed, removed, and processed for electron microscopy. In all KA-treated cochleas, the injection resulted in a severe swelling of auditory dendrites below the inner hair cells (IHCs). Below the outer hair cells (OHCs), the swelling appeared only in the 6-day-old rats, not in adult animals. These results are significant in three different ways: (1) They confirm the strong difference between afferents innervating the IHCs and the OHCs in adult cochleas. (2) They shed some light on the synaptic plasticity found at the OHC level during synaptogenesis. (3) They support the hypothesis that glutamate, or a related substance, is the IHC neurotransmitter.

Age Factors↗
PubMed1985

[Immunolocalization of choline acetyltransferase in 2 types of efferent synapses of the organ of Corti].

The efferent (olivo-cochlear) innervation of the organ of Corti was studied using a monoclonal antibody against choline acetyltransferase (ChAT). In the inner spiral bundle (ISB), below the inner hair cells (IHCs), the anti-ChAT immunoreactivity was observed within unvesiculated fibers and vesiculated varicosities. Unreactive varicosities, at least as numerous as the immunoreactive ones, were also detected. Both types of vesiculated varicosities synapsed with the dendrites of the primary auditory neurons (afferent fibers) connected to the IHCs. At the outer hair cell (OHC) level, nearly all the vesiculated terminals making axo-somatic synapses with the OHCs were anti-ChAT immunoreactive. Only few terminals synapsing with the OHCs were unreactive. These findings allowed the differentiation of at least three types of efferent synapses in the organ of Corti. In the ISB, a first population of axo-dendritic synapses seems to be cholinergic whereas a second population might use another neurotransmitter. At the OHC level, our results support the hypothesis that acetylcholine is the neurotransmitter of nearly all the large axo-somatic synapses. The rare unreactive axo-somatic synapses could constitute a fourth and minor type of efferent synapse. Thus, it would be helpful to subclassify the efferent innervations of the organ of Corti according to their neurochemical nature. A re-evaluation of the whole body of available electrophysiological data would be also necessary, as until now, acetylcholine was considered as being the only efferent cochlear neurotransmitter.

Animals↗
PubMed1984

Met-enkephalin characterization in the cochlea: high-performance liquid chromatography and immunoelectron microscopy.

The present paper extends and refines previous observations of enkephalin-like immunoreactivity in the guinea-pig cochlea. Firstly, Met-enkephalin was identified and a quantitative evaluation was made by combining high-performance liquid chromatography (HPLC) and a specific radioimmunoassay. Both the antibody specificity and the HPLC purification allowed us to demonstrate the co-existence, in the cochlea, of at least 3 opioid peptides: Met-enkephalin, Leu-enkephalin and Met-enkephalin-Arg6-Phe7. Secondly, a pre-embedding immunoperoxidase technique was used on whole or dissected cochleas. Immunoreactivity was localized in efferent fibers (coming from the brainstem) in the inner spiral bundle, tunnel spiral bundle and intraganglionic spiral bundle. In the inner spiral bundle vesiculated Met-enkephalin-immunoreactive fibers could be seen synapsing with afferent auditory dendrites. It is hypothesized that these Met-enkephalin immunoreactive fibers (belonging to the lateral efferent system) could be responsible for an inhibitory effect upon the gross cochlear action potential.

Animals↗
PubMed1984

Quantitation and localization of Met-enkephalin-Arg-Gly-Leu in rat brain using highly sensitive antibodies.

Met-enkephalin-Arg-Gly-Leu is an endogenous opioid peptide recently identified in bovine adrenal medulla. In the present study, we describe the production of highly sensitive and specific antibodies against this octapeptide. The sensibility of the radioimmunoassay procedure allows us to quantify at the femtomole level, the Met-enkephalin-Arg-Gly-Leu in individual parts of the brain without prior purification or concentration. The antibodies are highly specific for the C terminal part of the molecule, and did not cross-react with the other opioid peptides. Immunochemical techniques were used also to determine the histological location of the immunoreactive substances in individual structures of the brain. In the present paper, the comparative regional distribution of Met-enkephalin-Arg-Gly-Leu and of Met-enkephalin in rat brain are described. Our results are in good agreement with the biosynthetic relationship between Met-enkephalin and Met-enkephalin-Arg-Gly-Leu.

Animals↗
PubMed1984

Immunofluorescence with Met-enkephalin and Leu-enkephalin antibodies in the guinea pig cochlea.

We have applied an indirect immunofluorescence technique to cryostat sections of guinea pig cochleas using Met-enkephalin and Leu-enkephalin antisera. With both antisera, high immunofluorescence was seen in the inner spiral bundle, the tunnel spiral bundle and the intraganglionic spiral bundle. Immunoreactivity persisted to a dilution of 1/50 000. In three out of the twelve guinea pigs, immunoreactivity was observed under the outer hair cells, but only with the Met-enkephalin antiserum. Immunoreactivity of medium intensity was seen when the Met-enkephalin antiserum was pre-adsorbed by Leu-enkephalin. No immunoreactivity was seen when the Leu-enkephalin antiserum was pre-adsorbed by Met-enkephalin. After treatment of cochlear sections with acidic permanganate, immunoreactivity of medium intensity was still observed with the Leu-enkephalin antiserum. These observations indicate that Met-enkephalin and Leu-enkephalin co-exist in the cochlea in regions where efferent terminals are located, particularly in the inner spiral bundle below the inner hair cells.

Animals↗
PubMed1983

[Ultrastructural localization of immune reactions to met-enkephalin antibodies in the organ of Corti].

Using a pre-embedding immunoperoxidase technique, enkephalin-like substances were described, at the ultrastructural level, in efferent terminals of the guinea pig cochlea. These fibers were located in the inner spiral bundle and the tunnel spiral bundle. No immunoreaction was detected under the outer hair cells. Most of the immunoreactive fibers contacted afferent dendrites; synaptic differentiations were seen, suggesting a possible inhibitory effect of the enkephalin immunoreactive efferents upon the auditory afferents.

Animals↗
PubMedDate not supplied

Morphological and molecular changes in the inner hair cell region of the rat cochlea after amikacin treatment.

This study investigates the morphological and molecular changes that occur in the inner hair cell area of the rat cochlea following aminoglycoside treatment. Rats were injected daily with 500 mg/kg of amikacin between postnatal day 9 (PND9) and PND16. Cochleae were examined at PND16 to PND120 using both scanning and transmission electron microscopy and molecular fluorescent labeling. The inner hair cells showed obvious signs of apoptosis in response to amikacin treatment and most of them were missing by one week after the end of the aminoglycoside exposure period. Concomitantly, the epithelium became scarred as the surrounding supporting cells expanded and filled the space vacated by the missing IHCs. The mid-basolateral region of these modified supporting cells was surrounded by many afferent and efferent terminals. However, these cells expressed neither calbindin nor SNAP25, proteins that are both expressed by IHCs in the normal, untreated organ of Corti in the rat. In addition, these supporting cells remained attached to the basal lamina by a thin cytoplasmic process. The supporting cells surrounding the inner hair cells therefore appear unable to convert directly into inner hair cells following aminoglycoside induced hair-cell loss but may be able to provide trophic support for the remaining afferent and efferent neurites.

Actins↗