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M Eybalin

Publications and source records attributed to M Eybalin.

At least 19 recordsLinked to original sources
PubMed1992

Implication of non-NMDA and NMDA receptors in cochlear ischemia.

We have investigated the hypothesis that the acute ischemic swelling of the radial dendrites connected to the inner hair cells (IHCs) is mediated by glutamatergic receptors. In control cochleas, after 20 min ischemia all the dendrites were dramatically swollen. Conversely, after a perfusion of 50 microM 6-7-dinitroquinoxaline-2,3-dione (DNQX) before ischemia, most dendrites were protected although those contacting the IHCs on their modiolar side frequently swelled. After 50 microM of D-2-amino-5-phosphonopentanoate (D-AP5), no dendrite protection could be obtained. Finally, after DNQX and D-AP5, no dendrite swelling occurred. These results suggest that, in the cochlea, the acute ischemic swelling of dendrites primarily occurs via non-NMDA receptors. However, in radial dendrites contacting the IHCs on their modiolar side, NMDA receptors may contribute to excitotoxicity.

2-Amino-5-phosphonovalerate↗
PubMed1992

Co-expression of NMDA and AMPA/kainate receptor mRNAs in cochlear neurones.

The co-expression of NMDAR-1 and GluR1-4 mRNAs in spiral ganglions of rat and guinea-pig cochleas was checked using a non-radioactive in situ hybridization technique. NMDAR-1, GluR2 and GluR3 mRNAs were expressed in the large neurones (type I) of the ganglion which innervate inner hair cells (IHCs), a sensory cell type likely to use an excitatory amino acid as a neurotransmitter. The labelling was very intense with the GluR2 and GluR3 oligoprobes while it remained moderate with the NMDAR-1 oligoprobe. This is consistent with the predominant implication of AMPA/kainate receptors in the physiological and early pathophysiological aspects of the IHC neurotransmission. Spiral ganglion neurones did not express GluR1 and GluR4 mRNAs, but a glial expression of GluR4 mRNAs was observed.

Animals↗
PubMed1992

Monoclonal antiidiotypic antibodies against delta opioid receptors as an electron microscopy probe.

Four different rat monoclonal antibodies were produced against delta opioid receptor using an antiidiotypic approach in which antibodies directed against the opioid agonist DADLE were used as immunogen. In the first step, seven hybridomas were selected on the basis of their ability to inhibit the DADLE-anti-DADLE antibody interaction. After purification from ascitic fluids, these monoclonal antibodies were characterized. Four antiidiotypic antibodies, named 5, 11, 16, and 51, directed toward different epitopes, recognized the delta opioid receptor: (i) they bound directly to the NG108-15 cells, (ii) they inhibited the [3H]DADLE binding on the NG108-15 cells, (iii) they immunoprecipitated a 52,500 dalton protein present on the surface of the NG108-15 cells. The four monoclonal antiidiotypic anti-opioid receptor antibodies were used to immunocytologically detect the opioid receptors under light and electron microscopy in the rat spinal cord. The regional distribution of the immunoreactivity corresponded to layers known to be rich delta opioid receptor subtype. Moreover, at the ultrastructural level, the labeling was located mainly on plasma membranes, especially on non-synaptic zones. Our results show that monoclonal antiidiotypic antibodies constitute a valuable tool for visualizing cell surface receptors.

Animals↗
PubMed1991

Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid electrophysiological and neurotoxic effects in the guinea-pig cochlea.

We have recorded cochlear potentials after perilymphatic perfusion of cumulative doses of the excitatory amino acid alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) which selectively recognizes the non-N-methyl-D-aspartate ionotropic receptor formerly known as the quisqualate receptor. Our results show that AMPA (1-80 microM) caused a significant suppression of the amplitude of the compound action potential evoked by acoustic stimulation. A total elimination of this potential at the 100 microM concentration was observed in all animals. In no case was the cochlear microphonic potential, a hair cell receptor potential, affected by AMPA. Histological examinations were performed either at the end of the physiological studies or on cochleas perfused for 10 min with a single dose of AMPA (50 or 100 microM). In both experimental conditions, a selective dendritic swelling or radial afferent nerve endings under the sensory inner hair cells was observed. No damage was found in both types of hair cells supporting cells, lateral and medial efferent fibers and spiral afferent nerve ending on the outer hair cells. The occurrence of the radial dendrite swelling was prevented when 6,7-dinitroquinoxaline-2,3-dione (500 microM) was perfused in the cochlea 10 min prior, then concomitantly with AMPA. The present study strongly suggests that non-N-methyl-D-aspartate receptors, possibly of the AMPA subtype, are involved in the synaptic transmission between the inner hair cells and the primary auditory neurons. They provide further support for the hypothesis that L-glutamate, or another excitatory amino acid, acts as an inner hair cell neurotransmitter.

Acoustic Stimulation↗
PubMed1991

Electrophysiological evidence for the presence of NMDA receptors in the guinea pig cochlea.

An excitatory amino acid, possibly L-glutamate, which probably acts as a neurotransmitter at the inner hair cell-afferent fiber synapses in the cochlea. In the present study, we have used an electrophysiological approach to investigate at this level the presence of a major type of excitatory amino acid receptor, namely the glutamatergic receptor for which N-methyl-D-aspartate is a selective agonist. Our results show that, when N-methyl-D-aspartate and the antagonist 2-amino-5-phosphonovalerate are perfused through the perilymphatic scalae, they induced, by different mechanisms, a significant reduction of the amplitude of the compound action potential and an increase of the N1 latency, both predominant at high intensity tone burst stimulations. No significant difference was found in the presence or absence of Mg2+ in the artificial perilymph used as a vehicle. A further slight N-methyl-D-aspartate-induced decrease of the amplitude of the compound action potential, although non significant, was observed when the Mg2(+)-free perilymph contained 100 or 1000 microM glycine. In all the experimental conditions, no effect was observed on the cochlear microphonic potential. This observation is consistent with an action of N-methyl-D-aspartate and 2-amino-5-phosphonovalerate at receptors located on the auditory nerve dendrites contacting the inner hair cells. In conclusion, our results suggest the presence of N-methyl-D-aspartate receptors in the cochlea.

2-Amino-5-phosphonovalerate↗
PubMed1990

Immunoelectron microscopic localization of neurotransmitters in the cochlea.

This paper presents the works and methods of our respective laboratories using electron microscopic immunocytochemistry to identify and localize cochlear neurotransmitters. Antibodies to various prospective neurotransmitters and associated enzymes have been used to study the ultrastructural localization of several candidates for olivocochlear efferent neurotransmitters previously suggested by light microscopic immunocytochemistry. Antibodies against enkephalins label lateral olivocochlear efferent fibers. Antibodies against choline acetyltransferase (ChAT) (an enzyme marker for acetylcholine) label a major population of both lateral and medial efferent fibers and terminals, whereas antibodies to gamma-aminobutyric acid (GABA) label what might be a small subpopulation of both the lateral and medial efferent systems. The GABA-like immunostained medial efferent fibers are preferentially located in the upper turns of the guinea pig cochlea, particularly the third turn. Immunoelectron microscopy shows that neither GABA nor ChAT immunolabels all medial efferent terminals, regardless of cochlear turn. All the different types of immunolabeled efferent terminals have been observed to make characteristic synaptic contacts; lateral efferent terminals on afferent dendrites and medial efferent terminals on outer hair cells and occasionally on type II afferent dendrites. Other types of contacts involving GABA-like, and sometimes met-enkephalin-like, immunostained fibers are occasionally seen particularly in the upper turns of the cochlea. Immunoelectron microscopic results suggest that both medial and lateral efferent systems might be further subdivided on the basis of differences in neurotransmitters. Future trends of immunocytochemical research on cochlear neurotransmitters are proposed, particularly colocalization studies, which show a complex pattern of coexistence of neurotransmitters in the lateral efferent system.

Animals↗
PubMed1990

Ontogeny of glutamate decarboxylase and gamma-aminobutyric acid immunoreactivities in the rat cochlea.

gamma-Aminobutyric acid (GABA)-ergic efferent nerve fibers were studied during the postnatal development of the rat cochlea, using light microscopic immunocytochemical techniques. Antibodies against GABA and its synthesizing enzyme, glutamate decarboxylase (GAD), were used. Immunoreactivity to GAD is already present at birth (postnatal day 1) and could be found below the inner hair cells of the basal turn. Immunoreactivity progressively extends toward the apical turn until day 3. GAD-like immunoreactivity appears under the outer hair cells on postnatal day 15 and is only found in the upper part of the second turn and in the apical turn. The distribution of GABA-like immunoreactivity closely corresponds to that observed with the anti-glutamate decarboxylase antibody. However, the GABA-like immunoreactivity appears about 1-2 days after GAD-like immunoreactivity. At the beginning of the 3rd postnatal week, an adult pattern of GABA- and GAD-like immunoreactivity is established. These results suggest that GABA, which appears under the inner hair cells largely before the onset of hearing, may play a neurotrophic function during cochlear maturation and participate in the regulation of the first cochlear potentials as soon as they appear.

Aging↗
PubMed1990

Immunocytochemical detection of calcitonin gene-related peptide in the postnatal developing rat cochlea.

Using the immunofluorescence technique, three populations of fibers staining for calcitonin gene-related peptide are identified in postnatal developing cochleas and in adult rat cochleas. During the maturation of the cochlea, the immunostaining first appears in the basal turn and then extends toward the apex of the cochlea. The first population of immunostained fibers belongs to the lateral olivocochlear innervation. It is observed at postnatal day 4 within the inner spiral bundle of the organ of Corti. The second population of calcitonin gene-related peptide-like immunostained fibers belongs to the medial olivocochlear innervation. It is first identified at postnatal day 6 under the outer hair cells, generally in the first row. In the older stages, this population of fibers progressively extends toward the external row of outer hair cells. Finally, the third population of immunostained fibers belongs to the sympathetic supply of the cochlea. They can be identified at postnatal day 6 around the cochlear artery and its branches, and also within the entire modiolus. Our results confirm the presence of calcitonin gene-related peptide in fibers of the lateral and medial efferent innervations of the cochlea. They indicate an early appearance of calcitonin gene-related peptide in the developing cochlea, before the onset of the cochlear function, suggesting for this peptide either a neurotrophic function or a regulation of the early cochlear potentials at the level of the lateral efferent synapses.

Aging↗
PubMed1990

Immunocytochemical detection of glutamate decarboxylase in the postnatal developing rat organ of Corti.

Using a fluorescent avidin-biotin technique, we have immunolocalized the GABA synthesizing enzyme, glutamate decarboxylase, in postnatal developing and adult rat organs of Corti. At birth, the glutamate decarboxylase-like immunoreactivity is already present in the basal turn below the inner hair cells, i.e. within lateral olivocochlear efferent fibers of the inner spiral bundle. In the apical turn, the inner spiral bundle displays an immunoreactivity as early as postnatal day 3. Only the outer hair cells of the upper second turn and apex receive fibers immunostained for glutamate decarboxylase that most probably belong to the medial olivocochlear efferent innervation. They first appear at this level at postnatal day 15. Within these two regions of the organ of Corti, the glutamate decarboxylase-like immunoreactivity reaches an adult-like pattern at postnatal days 17-18. These results strengthen the hypothesis that GABA is a putative neurotransmitter that could be used by subpopulations of the two olivocochlear innervations. They also suggest that GABA either plays a neurotrophic function or participates in the regulation of the first cochlear potentials at the level of lateral efferent synapses.

Aging↗
PubMed1990

Glutamate neurotoxicity in the cochlea: a possible consequence of ischaemic or anoxic conditions occurring in ageing.

Glutamate is considered to be one of the most common neurotransmitters in the fast excitatory synapses in the central nervous system. On the other hand, its excitotoxic properties are increasingly cited to explain some of the brain damage linked with hypoxia and ischaemia: i.e., those that occur frequently in ageing. An excess release of glutamate could, either directly or indirectly, activate receptors on the postsynaptic neuron, causing ion influxes accompanied by a massive entry of water, which would lead to an acute swelling of dendrites. In addition, calcium influx deregulates calcium homeostasis, which could lead to cell death. In the cochlea, glutamate is now considered to be one of the best candidates to mediate neurotransmission between inner hair cells (IHCs) and the auditory nerve dendrites. Among the variety of anatomical and physiological findings supporting the glutamate hypothesis, is the striking similarity of acute damage in the organ of Corti caused by exposure to a glutamate analogue (kainic acid), or by hypoxia, or even by an intense loud noise. In all cases an immediate swelling is observed, specifically affecting the radial afferents below the IHCs. The best explanation for this swelling is related to glutamate (or glutamate analogue) excitotoxicity. Thus, some of the cochlear damage that occur with ageing, especially the loss of the radial afferent fibres and type I ganglion cells, might well be attributed to glutamate excitotoxicity linked to vascular atrophy. The present paper discusses this hypothesis.

Aging↗
PubMed1990

[Immunolocalization of parvalbumin in two glutamatergic cell types of the guinea pig cochlea: inner hair cells and spinal ganglion neurons].

Immunoreactions to a monoclonal antibody raised against parvalbumin, a calcium-binding protein, have been detected in the inner hair cells of the organ of Corti and in the spiral ganglion neurons connected to them (type I neurons). Both cell types probably use an excitatory amino acid as a neurotransmitter (glutamate and/or aspartate). No immunoreactivity was found within the second sensory cell type (outer hair cells) nor in the olivocochlear (efferent) fibers or endings in the cochlea. In the central nervous system, parvalbumin may be involved in calcium-dependent mechanisms leading to neurotransmitter release. It could thus be hypothesized that parvalbumin also have similar implications at the level of the inner hair cell and type I neuron synapses. Additional functions could also be hypothesized for this protein in the cochlea. Within the inner hair cells, parvalbumin may be involved in the ionic regulation following potassium entry during the transduction process. Within type I neurons, by buffering sudden increases in the intracellular calcium concentration, it may allow an adaptation of the firing rate to variations in the intensity of sound stimuli.

Animals↗
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↗