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Publications and source records attributed to A Sans.

At least 37 records · Page 2Linked to original sources
PubMed1999

K+-dependence of Na+-Ca2+ exchange in type I vestibular sensory cells of guinea-pig.

The properties of the vestibular Na+-Ca2+ exchanger in mammalian type I vestibular sensory cells were studied using fura-2 fluorescence and immunocytochemical techniques. In the absence of external Na+, the activation of Na+-Ca2+ exchange in reverse mode required the presence of external K+ (K+o) and depended on K+o concentration. Alkali cations Rb+ and NH4+ but not Li+ or Cs+ substituted for K+o to activate the exchange. For pressure applications of 10 mm K+, the contribution of voltage-sensitive calcium channels to the increase in [Ca2+]i was < 15%. The dependence of the exchange on [K+]o was also recorded when the membrane potential was clamped using carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP) and monensin ionophores. In these conditions, where there was no intracellular Na+, the increase in [Ca2+]i was completely blocked. These physiological results suggest that in reverse mode, Ca2+ entry is driven by both an outward transport of Na+ and an inward transport of K+. The dependence of the vestibular Na+-Ca2+ exchanger on K+ is more reminiscent of the properties of the retinal type Na+-Ca2+ exchanger than those of the more widely distributed cardiac type exchanger. Moreover, the immunocytochemical localization of both types of exchange proteins in the vestibular sensory epithelium confirmed the presence in the vestibular sensory cells of a Na+-Ca2+ exchanger which is recognized by an antibody raised against retinal type and not by an antibody raised against the cardiac type.

Alkalies↗
PubMed1998

A role for BDNF in early postnatal rat vestibular epithelia maturation: implication of supporting cells.

The early development of the inner ear is largely determined by two members of the neurotrophic family: brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3). Little information is available on the role of these neurotrophins during the late stages of vestibular development in the rat which take place during the first postnatal weeks. At this period where terminal synaptogenesis and maturation occur, we have investigated the expression and the activity of BDNF, the most important neurotrophin in the vestibular system. Using different experimental approaches, we show that BDNF is released by vestibular epithelia on postnatal day 3 (P3) and continues to have a trophic effect on vestibular neurones in vitro. Immunocytochemistry coupled to confocal microscopy revealed a remarkable evolution in BDNF localization during later stages of development. Whereas BDNF is present in both supporting cells and hair cells at P3, its distribution gradually changed and is highly compartmentalized within the upper part of supporting cells at P8 and P15. In parallel, we observed the presence of a truncated form of the BDNF receptor in sensory hair cells. These results suggest an original role for supporting cells, which could be involved in the release of BDNF during the late stages of synaptogenesis in mammalian vestibular epithelia. In particular, BDNF could participate to the set up of the calyx, a specific nerve structure surrounding type I vestibular hair cells.

Animals↗
PubMed1998

Potassium depolarization of mammalian vestibular sensory cells increases [Ca2+]i through voltage-sensitive calcium channels.

The existence of voltage-sensitive Ca2+ channels in type I vestibular hair cells of mammals has not been conclusively proven. Furthermore, Ca2+ channels present in type II vestibular hair cells of mammals have not been pharmacologically identified. Fura-2 fluorescence was used to estimate, in both cell types, intracellular Ca2+ concentration ([Ca2+]i) variations induced by K+ depolarization and modified by specific Ca2+ channel agonists and antagonists. At rest, [Ca2+]i was 90 +/- 20 nM in both cell types. Microperifusion of high-K+ solution (50 mM) for 1 s increased [Ca2+]i to 290 +/- 50 nM in type I (n = 20) and to 440 +/- 50 nM in type II cells (n = 10). In Ca2+-free medium, K+ did not alter [Ca2+]i. The specific L-type Ca2+ channel agonist, Bay K, and antagonist, nitrendipine, modified in a dose-dependent manner the K+-induced [Ca2+]i increase in both cell types with maximum effect at 2 microM and 400 nM, respectively. Ni2+, a T-type Ca2+ channel blocker, reduced K+-evoked Ca2+ responses in a dose-dependent manner. For elevated Ni2+ concentrations, the response was differently affected by Ni2+ alone, or combined to nitrendipine (500 nM). In optimal conditions, nitrendipine and Ni2+ strongly depressed by 95% the [Ca2+]i increases. By contrast, neither omega-agatoxin IVA (1 microM), a specific P- and Q-type blocker, nor omega-conotoxin GVIA (1 microM), a specific N-type blocker, affected K+-evoked Ca2+i responses. These results provide the first direct evidence that L- and probably T-type channels control the K+-induced Ca2+ influx in both types of sensory cells.

Animals↗
PubMed1997

Short-term response of postnatal rat vestibular neurons following brain-derived neurotrophic factor or neurotrophin-3 application.

The effects of the application of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) neurotrophins on the intracellular calcium level ([Ca2+]i) were studied in vestibular ganglion neurons (VGNs) from postnatal day 3 (P3) rats cultured for 50 hr. We first assessed the expression of trkB and trkC mRNA receptors in cultured VGNs. Immunobloting and immunocytochemistry confirmed the presence of the neurotrophin receptors on neurons. Both neurotrophins induced transient [Ca2+]i elevations in VGNs: BDNF-treated neurons responded in 65% and NT-3-treated neurons in 56%. The responses could be inhibited by anti-BDNF or anti-NT-3 antibodies. The [Ca2+]i elevation was dependent on extracellular calcium since it was abolished in calcium-free medium but also implicates the release of calcium from intracellular stores as tested by prior depletion with thapsigargin. Our results suggest the implication of a short-term calcium regulation in VGNs, which could reflect specific fast effects of neurotrophins in the early postnatal rat vestibular system.

Animals↗
PubMed1997

Voltage-activated sodium currents in acutely isolated mouse vestibular ganglion neurones.

Voltage-activated sodium currents (INa) in vestibular ganglion neurones acutely isolated from postnatal mice were investigated using the whole-cell configuration of the patch-clamp technique. Under recording conditions designed to allow the complete isolation of INa depolarizations from a holding potential of -80 mV revealed a fast inactivating inward current which was activated around -60 mV and exhibited maximum peak current around -30 mV. This current was eliminated when the cells were perifused with a Na(+)-free solution and almost totally blocked by application of 100 nM tetrodotoxin (TTX). These properties identify this inward current as TTX-sensitive INa. The half-maximum activation potential of INa was -46 mV and its half-maximum inactivation potential was -69 mV. This is the first report of voltage-activated sodium currents in vestibular primary neurones.

Animals↗
PubMed1997

Multiple voltage-dependent calcium currents in acutely isolated mouse vestibular neurons.

We investigated the presence of voltage-gated calcium currents in vestibular neurons acutely isolated from postnatal mice vestibular ganglions using the whole-cell patch-clamp technique. The neuronal origin of the recorded cells was confirmed by immunohistochemical detection of neurofilaments and calretinin. High and low voltage-activated calcium currents were recorded. High voltage-activated currents were present in all investigated neurons. Low voltage-activated currents were recorded in only a few large vestibular neurons. High and low voltage-activated currents were distinguished by their thresholds of activation and their ability to run-up during early recordings. Among high voltage-activated currents. L-, N- and P-type currents were identified by their sensitivity to, respectively, the dihydropyridines agonist Bay K 8644 (3 microM) and antagonist nitrendipine (3 microM), the co-conotoxin GVIA (3 microM) and the omega-agatoxin IVA at low concentration (50 nM). An inactivating current sensitive to 1 microM omega-agatoxin IVA with characteristics similar to those of the Q-type current was also recorded in vestibular neurons. When L-, N-, P-, Q-type barium currents were blocked, a residual high voltage-activated current defined by its resistance to saturating concentrations of all above blockers was detected. This residual current was completely blocked by 0.5 mM nickel and cadmium. Our results reveal that primary vestibular neurons express a variety of voltage-activated calcium currents with distinct physiological and pharmacological properties. This diversity could be related both with their functional synaptic characteristic, and with the intrinsic physiological properties of each class of vestibular afferents.

Animals↗
PubMed1997

Regulation of NMDA receptor subunit mRNA expression in the guinea pig vestibular nuclei following unilateral labyrinthectomy.

The localization of neurons expressing mRNAs for the NR1 and NR2A-D subunits of the glutamatergic NMDA receptor was examined by non-radioactive in situ hybridization throughout the guinea pig vestibular nuclei. After deafferentation of the vestibular nuclei by unilateral labyrinthectomy, modifications of the mRNA distributions were followed for 30 days. A quantitative analysis was performed in the medial vestibular nucleus by comparison of the labelled neurons in the ipsi- and contra-lateral nuclei. In vestibular nuclei, the NR1 subunit mRNA was found in various populations of neurons. The NR2A and NR2C subunit mRNAs were less widely distributed, whereas little NR2D mRNA was detected and only rare cells contained NR2B mRNA. NR1 and NR2A-D mRNAs were colocalized in some but not other neuronal types. Twenty hours after the lesion, there was a transient ipsilateral increase of NR1 mRNA level in the medial vestibular nucleus, followed by a decrease 48 h after the lesion and, at 3 days, by recovery to the control level. An ipsilateral increase in the mRNA level of NR2C subunit was detected 20 h after lesion and maintained at 48 h. No significant changes were apparent in NR2A, NR2B and NR2D mRNA levels. The distributions and the differential signal intensities of NR2A-D mRNAs suggest various subunit organizations of the NMDA receptors in different neurons of the vestibular nuclei. Neuronal plasticity reorganizations in the vestibular nuclei following unilateral labyrinthectomy appear to include only changes in NR1 and NR2C mRNA levels modifying the functional diversity of the NMDA receptor in the ipsilateral medial vestibular nucleus neurons. The transient changes in NR1 and the NR2C subunit mRNA expressions in response to sensory deprivation are consistent with an active role for NMDA receptors in the appearance and development of the vestibular compensatory process.

Animals↗
PubMed1997

[Late onset of pseudobulbar paralysis and dystonia in a case of hemispheric cortical dysplasia].

The atypical clinical course of a young male with encephalopathy due to right hemispheric cortical dysplasia (pachygiria) is described. From the first months of life the course of the disease was a static encephalopathy with left hemiparesis, epilepsy and mild mental retardation. When he was 14 years old a subacute pseudobulbar palsy, dystonia and spread of the paresis to the right side occurred. Epileptic seizures, paroxysmal EEG abnormalities and drug ingestion were excluded. Neuropsychological studies showed a low level of cognitive functions, probably related to the malformative encephalopathy and expressive language deficit due to the pseudobulbar paresis. We speculate that this case could be an atypical case of delayed onset dyskiesia.

Adult↗
PubMed1996

Histopathology of the peripheral vestibular system in small vestibular schwannomas.

Gadolinium-enhanced magnetic resonance imaging can be used to detect small vestibular schwannomas/acoustic neuromas. Early detection raises the question of the necessity of their surgical removal. Do all tumors induce lesions in the vestibule and to what extent? We thus investigated the ultrastructure of peripheral vestibular systems in grades I and II schwannomas. Vestibular tissues were fixed as soon as they were removed during the resection of tumors, by the translabyrinthine approach, and then processed for transmission electron microscope observations. In neurosensory epithelia, hair cells lost stereocilia, whereas cuticular plates disaggregated. The cytoplasm of hair cells degenerated in either a dense or vacuolated manner, and cytoplasmic blisters extended into the endolymph. In some cases, supporting cells extended processes covering the apical surface of hair cells. Nerve fibers massively disappeared from epithelia, only few nerve fibers contacted type I and type II hair cells, and both afferent and efferent terminals were abnormal. In vestibular nerves, axons degenerated, and myelin sheaths disaggregated. Glycogen was present in both intracellular and extracellular spaces. Luse bodies associated with collagen bundles were found between fibers. Scarpa ganglion neurons contained lysosomes/lipofuscin granules and vacuoles. Tumor cells were found in both the ganglion and the vestibular nerve. Thus small tumors induce extensive degeneration of vestibular tissues. The various hallmarks of schwannomas are already present in small acoustic neuromas. Moreover, different types of degeneration of hair cells and neurons were observed, together with the covering of hair cells by supporting cells and the accumulation of glycogen in the vestibular nerve.

Adult↗
PubMed1995

Immunocytochemical localization of the GTP-binding protein G0 alpha in the vestibular epithelium and ganglion of the guinea-pig.

The guanine nucleotide binding protein G0 alpha was immunolocalized in the guinea-pig vestibular system by confocal and electron microscopy. The vestibular sensory epithelia consist of the macula utriculi, macula sacculi and cristae ampullaris of the semicircular canals. Two types of hair cells are present in these epithelia. Type I hair cells are surrounded by an afferent nerve calyx that receives efferent innervation and type II hair cells are innervated directly by the afferent and efferent nerves. G0 alpha protein was observed on the inner face of the afferent calyceal membrane surrounding type I hair cells and in nerve endings in contact with type II hair cells. No labelling was found in the stereocilia and cuticular plate of type I and type II hair cells whereas the cytoplasmic matrix displayed a diffuse labelling. The plasma membrane of the supporting cells showed discreet labelling in the confocal microscope that are still confirmed by electron microscopy. A positive reaction was also observed along the plasma membrane of the vestibular ganglion neurons. Immunoblotting with affinity-purified polyclonal rabbit antibodies selective for the 39 kDa alpha subunit of G0 indicated that G0 alpha protein was present in both the vestibular ganglion. That G0 alpha labelling was observed in the cytoplasm of vestibular hair cells and in nerve endings contacting hair cells suggests that G0 may be involved in the modulation of vestibular neurotransmission.

Animals↗
PubMed1995

Transient increase in cytosolic free calcium evoked by repolarization in type I vestibular hair cells of rats.

Simultaneous whole-cell patch clamp and Fura-2 microfluorimetric recordings of membrane currents and intracellular free calcium concentration ([Ca2+]i) were made from type I vestibular hair cells isolated from cristae ampullares of adult rats. Cells held between -110 or -70 mV and depolarized up to -20 mV did not evoke any [Ca2+]i changes for any duration of the membrane depolarization (up to 3 s). Returning the membrane to repolarizing potential induced a transient [Ca2+]i increase. At the pulse break, an inward current was evoked. The [Ca2+]i increase and inward current amplitude were dependent on the duration and the amplitude of the previous depolarization. A liminar value of membrane depolarization of -55 +/- 3 mV (mean resting potential -62 +/- 7 mv) had to be applied to induce [Ca2+]i increase upon subsequent repolarization. [Ca2+]i response and inward current could not be evoked in calcium-free solution. Both responses were restored when calcium was added to the medium.

Animals↗
PubMed1995

Calcium homeostasis in guinea pig type-I vestibular hair cell: possible involvement of an Na(+)-Ca2+ exchanger.

In type-I vestibular hair cells (VHCs), the mechanisms involved in intracellular calcium homeostasis have not yet been established. In order to investigate the involvement of an Na(+)-dependent ionic exchanger in the regulation of cytosolic free calcium concentration, we analyzed the effect of the removal of external sodium on the cytosolic concentration of calcium ions ([Ca2+]i), sodium ions ([Na+]i), and protons (pHi). These concentrations were measured in type-I VHCs isolated from guinea pig labyrinth, using Fura-2, sodium benzofuran isophtalate (SBFI), and 1,4 diacetoxy-2,3 dicyanobenzol (ADB) respectively. Complete replacement of Na+ in the superfusion solution with N-methyl-D-glucamine (NMDG+), reversibly increased [Ca2+]i by 276 +/- 89% (n = 46) and decreased [Na+]i by 23 +/- 6% (n = 14). Both responses were prevented by removing external Ca2+ or chelating internal Ca2+. This suggests the presence of coupled Ca2+ and Na+ transport. The [Ca2+]i increase evoked by Na(+)-free solution was reduced by about 55% with the application of amiloride derivatives and was totally abolished in the presence of high [Mg2+]o. No pHi variation was detected during [Na+]o reduction. In the absence of external K+, the Na(+)-free solution failed to induce [Ca2+]i increase; the readmission of external K+ restored the [Ca2+]i response. These results are consistent with a Na(+)-Ca2+ exchanger operating in reverse mode. An K+ dependence of this exchange is also suggested.

Animals↗
PubMed1995

[Treatment and outcome of infantile cholesteatoma surgery].

Infantile Cholesteatoma has been lately the aim of a large number of papers dealing with its natural history and optimal treatment. The outcome of 26 cases of ear surgery, done between 1990 and 1991, are reviewed. The etiology of Cholesteatoma was congenital in 2 cases, iatrogenic in an other one and unknown for the remainder (88%). Fifteen (15) closed surgical procedures and 11 open were carry out, achieving global removal of lesions in 76 percent of cases. Ninety-one (91%) of open tympanoplasties and 66 percent of closed procedures. Six cases evolved to recidivation (and later reoperatively reconverted in open cases) owing either to the erosion of the ossicular chain or encroachment of the recessus. Reconstructions of the ossicular chain was undertaken in 61.5 percent of cases and the hearing preserved in all instances and improved in 35 percent of reconstructions.

Adolescent↗
PubMed1994

Intracellular calcium variations evoked by mechanical stimulation of mammalian isolated vestibular type I hair cells.

The variations of intracellular free calcium concentration ([Ca2+]i) were recorded on-line from guinea-pig isolated vestibular sensory cells using a fura-2 fast fluorescent photometry system, during mechanical displacements of the hair bundle. Repetitive displacements of the hair bundle towards the kinocilium (positive stimulation 7 degrees, 300 ms, 2Hz for 10 s), revealed [Ca2+]i variations detectable only in the cuticular plate. [Ca2+]i increased from 105 to 145 nM. Single mechanical displacements of the hair bundle (7 degrees, 200 ms, 0.5 Hz) evoked increases of [Ca2+]i from 50 +/- 23 nM to 139 +/- 79 (n = 12). In the opposite direction, the mechanical stimulations (8 degrees, 400 ms, 0.5 Hz) evoked a decrease of [Ca2+]i from 68 +/- 17 nM to 37 +/- 12 nM (n = 8). The variations of [Ca2+]i detected in the cuticular plate during positive displacements of the hair bundle were reversibly abolished in the presence of 100 microM gentamicin and they could not be evoked in 0.1 mM calcium in the external medium. From these experiments, it has been concluded that the [Ca2+]i variations recorded in the cuticular plate were due to a limited entry of calcium ions through transduction channels localized in the hair bundle. The typical kinetics of variations of [Ca2+]i evoked during positive displacements of the hair bundle should account for the presence of strong calcium regulation systems in the hair bundle and cuticular plate.

Animals↗
PubMed1994

Cholinergic agonists increase intracellular calcium concentration in frog vestibular hair cells.

Acetylcholine (ACh) is usually considered to be the neurotransmitter of the efferent vestibular system. The nature and the localization of cholinergic receptors have been investigated on frog isolated vestibular hair cells (VHCs), by measuring variations of intracellular calcium concentration ([Ca2+]i), using calcium sensitive dye fura-2. Focal iontophoretic ACh (1 M, 300 nA.40 ms) application induced a rapid increase in [Ca2+]i, reaching a peak in 20 s and representing about 5-fold the resting level (from 61 +/- 6 to 320 +/- 26 nM). Applications of muscarinic agonists as methacholine and carbachol induced weaker calcium responses (from 78 +/- 25 to 238 +/- 53 nM) than the one obtained with ACh applications. These muscarinic agonists were efficient only in precise zones. Desensitization of muscarinic receptors to successive stimulations was significant. Perfusion of nicotine or 1,1-dimethyl-4-phenyl-piperazinium (DMPP), a nicotinic agonist, induced an increase in [Ca2+]i only in some cells (4/28 with DMPP). These results indicated the presence of cholinergic receptors on frog VHCs: muscarinic receptors were more responsive than nicotinic receptors. Presence of muscarinic and nicotinic receptors in the membrane of VHCs could indicate different modulations of VHCs activity mediated by [Ca2+]i and involving an efferent control which represents a central regulation of the vestibular afferent message.

Acetylcholine↗