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A Sans

Publications and source records attributed to A Sans.

At least 55 records · Page 3Linked to original sources
PubMed1994

The vestibular type I hair cells: a self-regulated system?

In this study the functional role of afferent nerve calyx surrounding the type I vestibular hair cells was investigated. Synaptic microvesicles were present at the apex of the calyx in the vestibular epithelium of human foetuses at 9 weeks from gestation. Whole cell clamped type I hair cells isolated from guinea pig epithelium presented active movements as shortening of the neck and tilting of the cuticular plate at the cessation of the depolarising step. These movements were calcium dependent. With the aim of establishing the kinetics of calcium influx during the cell depolarisation, intracellular free calcium rate variations were investigated by coupling cytofluorimetry technique with whole cell patch clamp. An increase of intracellular calcium was only observed at the repolarisation of type I hair cells. Thus, a regulatory short-loop is thought to exist to control adaptation phenomena at the upper part of the type I hair cell. It is suggested that this occurs through the release of a neurotransmitter from the apex of the afferent calyx.

Afferent Pathways↗
PubMed1994

The toxicity of IDPN on the vestibular system of the rat: new insights on its effects on behavior and neurofilament transport.

3,3'-Iminodipropionitrile (IDPN) causes a permanent syndrome of abnormalities in spontaneous behavior and a deficit in the axonal transport of neurofilaments (NF). Male Long-Evans rats were given IDPN (0, 200, 400, 600, or 1000 mg/kg, ip, in saline) and assessed for behaviors indicative of vestibular function at 1 week post-dosing. The morphology of the peripheral vestibular system in animals dosed with 0, 200, 400, 600, 800, or 1000 mg/kg of IDPN was assessed at 4 days post-dosing by light microscopy on semithin sections. Animals receiving 1000, 1500, or 2000 mg/kg of IDPN were assessed for morphological alterations in the vestibular ganglion at 8 days post-dosing. Behavioral data indicated a dose-dependent loss of vestibular function after IDPN, the vestibular deficits first appearing at the 400 mg/kg dose level. IDPN exposure was also observed to result in degeneration of the vestibular sensory hair cells. Degenerative changes were already found at the 400 mg/kg dose level, and were extensive after 1000 mg/kg. In the ganglion neurons, no effects were observed after 1000 mg/kg of IDPN, but perikaryal accumulations of NF were found after 1500 or 2000 mg/kg. In conclusion, the data showed that low doses of IDPN are toxic to the vestibular hair cells, and suggest a link between this action and the effects of the chemical on spontaneous behavior. In addition, doses of IDPN larger than those required for toxicity to the vestibular sensory cells, induced accumulations of NF in the myelinated cell bodies of the vestibular ganglion neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Glutamate receptors on type I vestibular hair cells of guinea-pig.

Afferent nerve calyces which surround type I vestibular hair cells (VHCI) have recently been shown to contain synaptic-like vesicles and to be immunoreactive to glutamate antibodies. In order to understand the physiological significance of these observations, the presence of glutamate receptors on type I vestibular sensory cells has been investigated. The effect of excitatory amino acids applied by iontophoresis was examined by spectrofluorimetry using fura-2 sensitive dye. Glutamate application caused a rapid and transient increase in intracellular calcium concentration ([Ca2+]i), in a dose-dependent manner. The ionotropic glutamate receptors agonists N-methyl-D-aspartic acid (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and quisqualic acid (QA) induced an increase of [Ca2+]i. The NMDA receptor antagonist 2-amino-5-phosphonovaleric acid and the AMPA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione partially blocked the glutamate response, by 39 +/- 10 and 53 +/- 11% respectively. Metabotropic receptors were also revealed by the specific agonist trans-1-amino-cyclopentyl-1,3-dicarboxylate. The presence of different glutamate receptors on the VHCI membrane suggests two kinds of feedback. (i) At the base of the sensory cell, autoreceptors may locally control the synaptic transmission. (ii) At the apex, postsynaptic receptors may modulate sensory transduction from glutamate release at the upper part of the afferent nerve calyx. These feedbacks suggest presynaptic modulation of the vestibular hair cell response which could affect its sensitivity.

Animals↗
PubMed1993

Inward potassium rectifier current in type I vestibular hair cells isolated from guinea pig.

Large inward current activated by hyperpolarization was studied using whole cell patch clamp technique in type I vestibular hair cells of guinea pig. Near the resting membrane potential, at an holding potential of -60 mV (HP -60), this current increased with hyperpolarizing steps and showed time-dependent decay for steps below -80 mV. This current was progressively inactivated at more negative holding potential and was totally abolished at HP -90 mV. The underlying conductance was a K+ conductance as indicated by: (i) its dependence on the external potassium concentration; (ii) its tail currents, which reversed at about -90 mV in solutions with a normal gradient for K+ ions. Pharmacological studies revealed that external application of 4-aminopyridine (5 mM) reversibly blocked (95%) the total inward current, while external application of tetraethylammonium (10 mM) or cesium (2 mM) did not significantly affect the amplitude of this current. This potassium inward rectifier current could contribute to restoration of the resting membrane potential during negative stimulations.

4-Aminopyridine↗
PubMed1993

The behavioral syndrome caused by 3,3'-iminodipropionitrile and related nitriles in the rat is associated with degeneration of the vestibular sensory hair cells.

Animals exposed to 3,3'-iminodipropionitrile (IDPN) or to several similar nitriles develop a permanent syndrome of behavioral abnormalities. The present work addressed the hypothesis that this syndrome is caused by a toxic effect of these nitriles on the peripheral vestibular system. Male Long-Evans rats were given acute doses of IDPN (0, 200, 400, 600, or 1000 mg/kg, ip) and assessed for a number of behaviors indicative of vestibular function at postdosing times ranging from 1 day to 9 weeks. The pathological effects of IDPN on the morphology of the vestibular sensory epithelia were studied by scanning electron microscopy at 1,2,4, and 21 days after exposure. The behavioral study revealed dose-dependent deficits in vestibular function after IDPN. Alterations in vestibular morphology occurred at the same doses of IDPN that induced behavioral changes (400-1000 mg/kg). The pathological alterations after IDPN consisted of degeneration of the vestibular sensory hair cells, and no hair cells remained in the vestibular receptors 3 weeks after the 1000 mg/kg dose. A good correlation was also found for the time-course characteristics of the behavioral and the morphopathological effects of IDPN. The vestibular sensory epithelia displayed a regional pattern of differential sensitivity to the toxic effect of IDPN. Both intraepithelial and interepithelial differences in sensitivity were found. Crotonitrile (250 mg/kg, ip), which induces the same behavioral syndrome, was found to induce also degeneration of the vestibular hair cells. We conclude that IDPN and the similar nitriles that cause the same behavioral abnormalities are toxic to the peripheral vestibular system.

Animals↗
PubMed1993

Potassium currents in type II vestibular hair cells isolated from the guinea-pig's crista ampullaris.

Type II vestibular hair cells were isolated from cristae ampullares of guinea-pig and maintained in vitro for 2-3 h. Outward membrane currents were studied under whole-cell voltage-clamp conditions. Type II hair cells had resting potentials of about -45 mV. Depolarizing voltage steps from a holding potential of -80 or -90 mV induced time- and voltage-dependent outward currents which slowly decayed to a sustained level. Tail currents reversed at about -70 mV, indicating that the outward currents were mainly carried by potassium ions. The currents had an activation threshold around -50 mV. The transient component was completely removed by a depolarizing pre-pulse positive to -10 mV. While bath application of 4-aminopyridine (5 mM) reduced both components, extracellular tetraethylammonium (10 mM) or zero calcium preferentially diminished the sustained current. We conclude that at least two potassium conductances are present, a delayed rectifier with a relatively fast inactivation and a calcium-dependent potassium current. Depolarizing current injections induced an electrical resonance in the voltage responses, with a frequency of 25-100 Hz, larger currents causing higher frequencies.

4-Aminopyridine↗
PubMed1993

Non-typical K(+)-current in cesium-loaded guinea pig type I vestibular hair cell.

Isolated guinea pig type I vestibular hair cells were voltage clamped at HP-110 mV in whole cell clamp configuration and depolarized up to +20 mV. Increasing depolarizations elicited large outward currents. These currents were replaced, in cesium-loaded cells, by inward/outward currents that reversed at membrane potentials between -55 and -30 mV. The reversal potential varied from cell to cell, and appeared to depend on the intracellular potassium cesium ratio. The current remaining in the presence of intracellular cesium was essentially due to a non-typical potassium conductance, which decreased in the presence of 4-AP and was blocked by 4-AP plus TEA. This current appeared as soon as the membrane was depolarized, showing the high potassium permeability of type I vestibular hair cells. A small part of this current was a strictly calcium inward current, sensitive to flunarizine, with a leakage component in the hyperpolarized state and a voltage component when the cell was depolarized.

Animals↗
PubMed1993

Voltage dependent reversible movements of the apex in isolated guinea pig vestibular hair cells.

Type I vestibular hair cells isolated from guinea pig were placed in the whole cell clamp configuration, and electrically stimulated by depolarizing voltage pulses. The voltage dependent reversible movements of the cell apex affected the length of the cell neck, the position of the cuticular plate, and the tilting and bending of the stereocilia. The cell neck shortened when the membrane was depolarized by 10 mV while cuticular plate and the stereocilia tilting did not begin until 20 mV. The shortening was 0.5 to 1 micron, and the cuticular plate tilting was up to 15 degrees for depolarization amplitudes of 20-40 mV. These movements were reversed within a few seconds. More complex, larger movements were induced by stronger depolarizations. The cuticular plate tilting and the hair bundle bending were always in the opposite direction to the kinocilium position. The small reversible movements of the mammalian type I vestibular hair cells are discussed in terms of mechanical adaptation processes and morphological features. It is suggested that such active movements of the vestibular hair cells occur in vivo.

Animals↗
PubMed1991

Motile responses of isolated guinea pig vestibular hair cells.

Vestibular hair cells were isolated from the guinea pig vestibule by a micromechanical non-enzymatic procedure. Perfusion with 125 mM K+ solution induced irreversible slow shortening of the necks in 42.8% of the hair cells tested. Mechanical stimulation, creating a displacement of the hair bundle towards the kinocilium, induced either irreversible coiling or tilting of the neck of the cells, or reversible fast tilting of the cuticular plate (44.5% of tested cells). The response to the Ca2+ antagonist, Flunarizine, suggested that these movements were calcium-dependent. We propose several explanations of the physiological role of these mechanisms and discuss the possibility that fast tilting of the cuticular plate is a physiological movement involving the hair cells at the periphery of the vestibular receptors. The regulation of the vestibular message at the apex of type I hair cells is also considered.

Animals↗
PubMed1991

Intracellular free calcium in isolated vestibular hair cells and potassium iontophoresis.

The resting free calcium level was measured in 128 isolated mammalian vestibular sensory cells using the calcium-sensitive dye fura-2. Iontophoresis was used to apply short, localised and limited pulses of K+ which evoked dynamic changes in intracellular free calcium concentration. While most of the type I hair cells tested showed brief reversible and specific calcium responses, some were unresponsive. The changes in intracellular free calcium were also measured by videomicroscopic analysis. Iontophoretic application of K+ ions is shown to be a suitable method for inducing fast, transient changes in intracellular free calcium in vestibular hair cells. This technique could be useful for applying several ions and charged molecules such as amino acids in in-vitro cellular methods.

Animals↗
PubMed1991

Dedifferentiation phenomena after denervation of mammalian adult vestibular receptors.

The effect of transecting the vestibular nerve on the vestibular sensory epithelium was studied in adult guinea-pigs. When denervation was complete, after fifteen days, the vestibular hair cells began to show morphological features of immaturity. After two months, the majority of hair cells showed a supporting cell phenotype. By four months, both hair cells and supporting cells had become morphologically similar to the epithelial cells which line the vestibular cavities. When denervation was incomplete, hair cells and supporting cells retained their normal phenotype. This, plus the dedifferentiation after complete denervation, indicates that the phenotypes of the hair cells and supporting cells are innervation-dependent.

Age Factors↗
PubMed1991

Synapsin I and Synaptophysin expression during ontogenesis of the mouse peripheral vestibular system.

Synapsin I and Synaptophysin are selectively localized in axonal endings of CNS neurons where they are associated with small synaptic vesicle membranes. The development of expression of these 2 proteins was studied by immunocytochemistry during ontogenesis of the peripheral vestibular system in the mouse. Both proteins are localized in vestibular ganglion neurons and in their peripheral sensory extensions as early as gestational day 14. While the entire periphery of these fibers is labeled during embryogenesis, both proteins are subject to relocation during the postnatal maturation of these fibers. In the mature vestibular receptors they disappear from the fibers themselves but are found concentrated in their intraepithelial endings and in the neuronal cell body. These observations show that the distribution pattern of Synapsin I and Synaptophysin in peripheral extensions of vestibular afferent neurons during development is identical to that described in axonal processes of CNS neurons. This suggests that the peripheral processes of the vestibular afferent neurons present structural and biochemical characteristics of axons. These characteristics are consistent with a bimodal sensory and secretory function of mature endings.

Aging↗
PubMed1990

Afferent innervation patterns in crista ampullaris of the mouse during ontogenesis.

The development of vestibular afferent innervation patterns was studied by labeling the peripheral terminations between gestation day 17 and postnatal day 10. Extracellular injections of horseradish peroxidase were performed into vestibular ganglia in mouse otocysts maintained in vitro for several hours. At gestation days 17 and 18, the afferent innervation patterns were characterized by the presence of a few collaterals that arose from the parent fiber and sometimes ended by swellings or by enlargement extended by filopods rising to the epithelium surface. At the 20th gestation day the first endings differentiated into boutons or calyces were seen. At birth, the afferent innervation consisted of collaterals that could terminate either in boutons or in incomplete thin calyces. Starting on postnatal days 1 and 2, boutons and calyces became more pronounced and 3 afferent innervation patterns could be distinguished, i.e., calyx, dimorphic, and bouton. By postnatal day 5, the filopods had disappeared and the characteristic endings on type I or II cells were clearly individualized. On postnatal day 10, the afferent innervation patterns were comparable to those in the adult. These results are discussed in relation to ultrastructural data concerning the synaptogenesis and to the physiological development that have been described during the first postnatal days.

Aging↗
PubMed1990

Glutamate-like immunoreactivity in the peripheral vestibular system of mammals.

Using a specific antibody raised against glutamate (Glu) conjugated to bovine serum albumin with glutaraldehyde, the distribution of Glu-like immunoreactivity was studied by postembedding staining in semithin sections of nonosmicated or osmicated tissue through the vestibular sensory epithelia and ganglia of different mammalian species (mouse, rat and cat). Strong immunoreactive staining was found in all ganglion neurons and their peripheral and central nerve processes as well as in the two types of sensory hair cells whereas, in contrast, supporting cells were devoid of immunoreactivity. Glu-like immunoreactivity found in vestibular fibers and ganglion neurons, is in good agreement with the proposition of glutamate as the neurotransmitter involved in vestibular nerve transmission. In sensory hair cells, glutamate, apart from its metabolic function, may play a role in synaptic transmission between the sensory cells and the vestibular afferent fibers.

Afferent Pathways↗
PubMed1989

Immunocytochemical localization of myosin, tropomyosin and actin in vestibular hair cells of human fetuses and cats.

Semithin sections (1 micron) of human fetuses and young cat vestibular epithelium embedded in Epon were reacted with primary antibodies raised against myosin, tropomyosin, and actin. The results were very similar in the two species. Myosin and tropomyosin were colocalized and strictly limited to an apical superficial corona arranged in a punctiform pattern. The stereocilia and cuticular plate were unreactive to myosin and tropomyosin antibodies. Actin antibodies stained the stereocilia, cuticular plate, and a marginal ring surrounding and underlying the cuticular plate. At this level, myosin and tropomyosin were not detected. This result suggests that the circumferential actin ring has a structural role. Colocalization of myosin, tropomyosin, and actin in a superficial area around the stereocilia bundle and along the apical surface of the hair cell imply that active processes could exist at the apex of certain sensory vestibular hair cells. The specificity of myosin antibodies and their cross-reactivity with different types of myosin are discussed.

Actins↗
PubMed1989

Immunocytological characterization of the expression of cell adhesion molecule L1 during early innervation of mouse otocysts.

Doubts exist as to whether afferent nerve fibers exert a neurotrophic effect on the differentiation of sensory cells in the developing vestibular neuroepithelium. To determine whether innervation of hair cells precedes their differentiation, we have used the L1 adhesion molecule as a marker for axons. The detection of L1 on afferent axons in the otic vesicle of mouse embryos on gestation day 11 shows that nerve fibers penetrate the neuroepithelium before the sensory cells differentiate. L1-immunoreactivity of nerve endings also reveals the considerable fiber ramification on gestation days 14 and 15, i.e., corresponding to the first stages of sensory cell differentiation. The expression of L1 at successive stages of nerve fiber growth in the neuroepithelium, such as fasciculation and ramification, is not consistent with the previous role proposed for L1 as a fascicule-promoting factor and raises the possibility that other mechanisms are involved in L1 mediated adhesion.

Animals↗