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At least 865 records · Page 48Linked to original sources
PubMed1999

Opioid peptides as possible neuromodulators of the afferent synaptic transmission in the frog semicircular canal.

Vestibular receptors of the frog, Rana temporaria, were examined for the effect of bath-applied opioid peptide leu-enkephalin, its synthetic analogue dalargin and the specific opiate antagonist naloxone. Multiunit afferent activity of the whole vestibular nerve was recorded in an in vitro preparation. Leu-enkephalin (0.005-100 nM) and dalargin (0.1-100 nM) depress the resting discharge frequency. Naloxone (10 nM-1 microM) antagonizes responses induced by leu-enkephalin and dalargin that suggests a specific action of opioid peptides. Leu-enkephalin and delargin inhibit the excitatory action of L-glutamate. The effects of opioid peptides on L-glutamate-induced responses are unaffected by Co2+ block of transmitter release from hair cells that could speak in favour of the postsynaptic nature of these responses. At the same time, the other possible site of action of opioid peptides, such as efferent system, can not be excluded. The results indicate that opiate receptors are present in hair cells and that the neurotransmitter L-glutamate is involved in opiate action at the peripheral vestibular system of the frog. We suggest that opioid peptides may act as a neuromodulator in this system.

Animals↗
PubMed1975

Functional organization of vestibulofastigial projection in the horizontal semicircular canal system in the cat.

Spike potentials of fastigial nucleus neurons were recorded extracellularly in decerebrate, unanesthetized cats. The neurons responding to head rotation in the horizontal plane with a type I fashion were located mainly in the middle and caudal regions of the fastigial nucleus. Three fourth of these fastigial type I neurons were antidromically activated by stimulation of the contralateral vestibular nuclei. These neurons were excited transsynaptically from the ipsilateral vestibular nerve or nuclei. Intra cellular recordings were made from those neurons which were located in the caudal half of the fastigial nucleus and were activated antidromically from the contralateral vestibular nuclei. Stimulation of the ipsilateral vestibular nerve produced EPSPs in these neurons with latencies of 1.0-6.6 msec. The shortest conduction time along primary vestibular aggerents from the labyrinth to the ipsilateral fastigial nucleus was 0,7 msec. The EPSPs with the shortest latency of 1.0 msec were therefore postulated to be due to monosynaptic connections of primary vestibular afferents with fastigial neurons. Stimulation of ipsilateral vestibular nuclei also produced monosynaptic EPSPs in fastigial neurons. These EPSPs were facilitated by conditioning stimulation of the ipsilateral vestibular nerve, indicating the existence of polysynaptic activation of fastigial neurons from the ipsilateral vestibular nerve through the vestibular nuclei.

Animals↗
PubMed1993

GABAB-mediated modulation of ionic conductances in type I hair cells isolated from guinea-pig semicircular canals.

Mammalian vestibular type I hair cells (VIHCs) are innervated by an afferent synaptic calyx which contains vesicles and is immunoreactive for GABA. We describe here the effects of GABA on electrophysiological properties and on cytosolic free-calcium levels ([Ca2+]i) of VIHCs isolated from guinea-pig ampullae. Whole-cell tight-seal macroscopic currents recorded from VIHCs showed that 100 microM GABA induced a decrease in the outward currents elicited by depolarizing membrane potentials. These are known to comprise potassium calcium-dependent currents. This effect was mimicked by baclofen, a GABAB agonist, and was not affected by picrotoxin, a GABAA antagonist. GABA also induced an increase in the inward current elicited at hyperpolarized membrane potentials in 50% of the tested cells. Single channel recording in cell-attached patches revealed that externally applied GABA produced a decrease and an increase in the open probability of 170 pS and 45 pS and of 15 pS channels, respectively. In imaging experiments using the dye Fura-2 to measure [Ca2+]i, the only reversible modulation of [Ca2+]i observed in response to GABA application was a decrease. These results demonstrate a modulation of calcium and potassium conductances by GABA, via GABAB receptors, in guinea-pig VIHCs.

Animals↗
PubMed1999

Vestibular semicircular canal epithelium of the rat in culture on filter support: polarity and barrier properties.

The inner ear of mammals contains the vestibular apparatus which is involved in the maintenance of posture and balance. The tubular structure of the apparatus is bathed by the potassium-rich endolymph and sodium-rich perilymph in the luminal and abluminal compartments, respectively. The luminal compartment is lined by a continuous epithelium with islets of receptor organs, which separates the luminal from the abluminal compartment. The present work focuses on the epithelium, without the receptor organs, and shows that it can be reconstituted in culture. The epithelium from 4-day-old Wistar rats was grown on microporous membranes. High transepithelial electrical resistances (4000-6000 Omega.cm2) were achieved after 4-8 days in culture. The epithelium was characterized by the presence of cytokeratin, ZO-1 protein, occludin, and the presence of tight junctions and kinocilia. The transepithelial resistance of the cell monolayer withstood endolymph/perilymph dual bathing when the apical pole of the cells was in contact with endolymph, but collapsed in the reverse configuration. Weak but statistically highly significant basal to apical rubidium (86Rb) transport was observed. These findings show that this epithelium maintains its in vivo polarity and could enhance the potassium composition of endolymph up to maturity. This new culture model, in which dual bathing is possible, should enable further in vitro studies of the sensory vestibular epithelia.

Animals↗
PubMed1977

Post-synaptic potentials recorded from afferent nerve fibres of the posterior semicircular canal in the frog.

Glass microelectrode recordings were made from single fibres of the posterior ampullary nerve in the isolated labyrinth of the frog (Rana esculenta). Potentials were recorded both at rest and during rotatory stimulation of the canal. At rest, the tracings revealed an intense background of small, largely summated potentials (0.5-10 mV amplitude, 3-6 msec duration), which underlay the discharge of spikes in all the impaled units. The frequency of the subthreshold events was related to the frequency of the propagated spikes, the latter ranging from 0 to 40/sec. Stimulation modulated the frequency of both spikes and subthreshold potentials, whose summation during excitation led to a positive shift of the fibre membrane potential. The small potentials proved to be dependent on Ca2+ and Mg2+ levels in the bath. Antidromic-stimulation of the posterior ampullary nerve indicated that the observed events do not represent an artifact due to extracellular field interference related to spike activity in the neighbouring fibres. Tetrodotoxin (10(-7)-10(-6) g/ml) applied externally to the preparation or previously perfused through the frog vessels abolishes the propagated spikes but left unaffected the small potentials which, even under drug treatment, were normally modulated by the stimulus. The subthreshold potentials thus appear to be EPSPs generated at the cyto-neural junction between the hair cells and the endings of the ampullary nerve fibres.

Action Potentials↗
PubMed2003

Nature and expression of dihydropyridine-sensitive and -insensitive calcium currents in hair cells of frog semicircular canals.

Ca(2+) currents in hair cells of the frog crista ampullaris were studied using the whole-cell patch-clamp technique. Currents were recorded in situ from hair cells in peripheral, intermediate and central regions of the sensory epithelium. Two types of Ca(2+) currents were found: a partially inactivating current that was expressed by nearly all central cells and by about 65% of intermediate and peripheral cells, and a sustained current expressed by the remaining cell population. The mean Ca(2+) current amplitude was larger in intermediate cells than in central or peripheral cells. The two types of Ca(2+) currents were composed of two components: a large, nifedipine-sensitive (NS) current and a small, nifedipine-insensitive (NI) current. The latter was resistant to SNX-482, omega-conotoxin MVIIC and omega-agatoxin IVA and to omega-conotoxin GVIA, antagonists of R, P/Q and N-type Ca(2+) channels. The amplitude of NS and NI currents varied among peripheral cells, where the current density gradually increased from the beginning of the region toward its end. No significant variation of Ca(2+) current density was detected in hair cells of either intermediate or central regions. These results demonstrate the presence of regional and intraregional variations in the expression of L and non-L Ca(2+) channels in the frog crista ampullaris. Finally, immunocytochemical investigations revealed the presence of Ca(2+) channel subunits of the alpha(1D) type and the unexpected expression of alpha(1B)-subunits.

Animals↗
PubMed1987

Cation transport in the ampulla of the semicircular canal and in the endolymphatic sac.

We examined the effects of anoxia and ethacrynic acid on the endolymphatic potential and cation activity in the superior ampulla of the guinea pig, using double-barrelled ion-exchanger microelectrodes. In normal guinea pigs the ampullar endolymphatic potential was + 3.9 +/- 1.2 mV (n = 32), the Cl- activity 130 +/- 4.6 mM (n = 9), and the Na+ activity 18.4 +/- 4.4 mM (n = 20). After anoxia, the ampullar DC potential decreased rapidly and reversed its polarity within 5 min. It then decreased gradually for 60 min and increased afterwards to approximately zero. K+ activity decreased gradually after a latency of 10 min, whereas Na+ activity increased. During the gradual decrease of a negative ampullar endolymphatic potential, an increase in Na+ activity was observed. Thirty minutes after the intravenous injection of ethacrynic acid (100 mg/kg), the potential began to decrease, changed to a negative polarity, and approached a maximum negative level 100 min after the injection. The decrease in K+ activity corresponded to the reduction of potential whereas Na+ activity remained unchanged. The DC potential of the endolymphatic sac in normal guinea pigs was + 14.7 +/- 5.1 mV (n = 17). The Na+ concentration was 103.3 +/- 14.7 mM (n = 14) and the K+ concentration was 11.6 +/- 0.8 mM (n = 4). After anoxia, the DC potential decreased rapidly and approached 0 mV within 8 min. No negative potential could be observed. The Na+ concentration began to increase 2 min after anoxia and reached the extracellular Na+ concentration about 30 min later.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Morphometric studies of type I and type II hair cells in the gerbil's posterior semicircular canal crista.

The existence of separate subtypes of type I vestibular hair cells according to morphological criteria in situ was investigated. Gerbils were anesthetized and perfused with mixed aldehydes. The crista ampullaris of the posterior canal was dissected, fixed in osmium, dehydrated, and embedded in epon. Five-micron sections were cut orthogonal to the long axis of each crista. Measurements were made on camera lucida drawings of individual cells located in the apical, middle, and basal 1/3 of the crista. Measurements for each hair cell included the circumference, greatest width of the body, length, width of the apical surface (cuticular plate region, P), width at narrowest portion of the neck (NW), neck width to plate ratio (NPR), length at a point 2 times NW from the apical surface (L2N). Type I hair cells were subgrouped into three classes (long -1, intermediate -i, and short -s) based on a subjective determination of neck length. Statistical comparisons were made between type I (n = 612) and type II (n = 74) hair cells and the type I subtypes (l, i, s). Statistically significant differences were found between type I and II hair cells for NPR, width, and length, but not perimeter. Thus, as in pigeons, NPR distinguishes type I and type II hair cells in the gerbil crista. While type I hair cells are wider and longer than type IIs, the circumference is the same, due to the restricted neck in type I hair cells. The L2N statistic separates three subtypes of type I hair cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

Convergence of posterior semicircular canal and saccular inputs in single vestibular nuclei neurons in cats.

Convergence between posterior canal (PC) and saccular (SAC) inputs in single vestibular nuclei neurons was investigated in decerebrated cats. Postsynaptic potentials were recorded intracellularly after selective stimulation of the SAC and PC nerves. Stimulation of either the SAC or PC nerve orthodromically activated 143 vestibular nuclei neurons. Of these, 61 (43%) were antidromically activated by stimulation of the C1-C2 junction, 14 (10%) were antidromically activated by stimulation of the oculomotor or trochlear nucleus, and 14 (10%) were antidromically activated by stimulation of both the oculomotor or trochlear nucleus and the spinal cord. Fifty-four (38%) neurons were not activated by stimulation of either or both. We named these neurons vestibulospinal (VS), vestibulo-ocular (VO), vestibulooculo-spinal (VOS) and vestibular (V) neurons, respectively. Both PC and SAC inputs converged in 47 vestibular nuclei neurons (26 VS, 2 VO, 6 VOS and 13 V neurons). Of these, 19 received monosynaptic excitatory inputs from both nerves. This input pattern was frequently seen in VS neurons. Approximately half of the convergent VS neurons descended to the spinal cord through the lateral vestibulospinal tract. The remaining half and all the convergent VOS neurons descended to the spinal cord through the medial vestibulospinal tract. Most of the convergent neurons were located in the lateral nucleus or descending nucleus.

Animals↗
PubMed2000

Membrane properties of chick semicircular canal hair cells in situ during embryonic development.

The electrophysiological properties of developing vestibular hair cells have been investigated in a chick crista slice preparation, from embryonic day 10 (E10) to E21 (when hatching would occur). Patch-clamp whole-cell experiments showed that different types of ion channels are sequentially expressed during development. An inward Ca(2+) current and a slow outward rectifying K(+) current (I(K(V))) are acquired first, at or before E10, followed by a rapid transient K(+) current (I(K(A))) at E12, and by a small Ca-dependent K(+) current (I(KCa)) at E14. Hair cell maturation then proceeds with the expression of hyperpolarization-activated currents: a slow I(h) appears first, around E16, followed by the fast inward rectifier I(K1) around E19. From the time of its first appearance, I(K(A)) is preferentially expressed in peripheral (zone 1) hair cells, whereas inward rectifying currents are preferentially expressed in intermediate (zone 2) and central (zone 3) hair cells. Each conductance conferred distinctive properties on hair cell voltage response. Starting from E15, some hair cells, preferentially located at the intermediate region, showed the amphora shape typical of type I hair cells. From E17 (a time when the afferent calyx is completed) these cells expressed I(K, L), the signature current of mature type I hair cells. Close to hatching, hair cell complements and regional organization of ion currents appeared similar to those reported for the mature avian crista. By the progressive acquisition of different types of inward and outward rectifying currents, hair cell repolarization after both positive- and negative-current injections is greatly strengthened and speeded up.

Analysis of Variance↗
PubMed2003

Treatment of benign paroxysmal positional vertigo of posterior semicircular canal by "Quick Liberatory Rotation Manoeuvre".

Treatment of Benign Paroxysmal Positional Vertigo is based on Semont's Liberatory Manoeuvre and on so-called "Canalith Repositioning Manoeuvres", derived from the original Epley technique. Both manoeuvres are very effective and choice of which to use depends on the experience of the physician. Semont's manoeuvre requires a quick movement of the patient in mass in the frontal plane, from the involved, to the contralateral side, which sometimes causes symptoms such as nausea or vomiting. In this technique, a secondary liberatory nystagmus is often observed as sign of the success of the manoeuvre. Repositioning manoeuvres are less fastidious because of the slow movements, but we rarely observe an objective sign of success like the liberatory nystagmus. In the present randomised trial, 300 patients with posterior canalo/cupulolithias were divided into 3 treatment groups: 100 treated by Semont Technique; 100 by a Repositioning procedure (Parnes technique); 100 by a new manoeuvre called "Quick Liberatory Rotation". Results of treatment are also compared with the natural evolution of Benign Paroxysmal Positional Vertigo observed in 18 untreated patients. Quick Liberatory Rotation is similar in the sequence of the positions of the head in the horizontal plane, to repositioning procedures, but is more like the Semont manoeuvre in the speed of the movement (about 180 degrees in less than one second). Quick Liberatory Rotation is easy to perform, well tolerated and very effective (success rate: 98% in one-three cycles). In the present investigation, a secondary liberatory nystagmus was observed in 76.1%, with a sensitivity of 81.9% in detecting patients who had completely recovered and a specificity of 43.8% in detecting failures. Effectiveness, in short and medium period (1-15 months), is similar to Semont and Parnes techniques. Authors consider Quick Liberatory Rotation, at present, a possible first choice technique in the treatment of posterior canalolithiasis.

Adolescent↗
PubMed2001

Neural processing of gravito-inertial cues in humans. II. Influence of the semicircular canals during eccentric rotation.

All linear accelerometers, including the otolith organs, respond equivalently to gravity and linear acceleration. To investigate how the nervous system resolves this ambiguity, we measured perceived roll tilt and reflexive eye movements in humans in the dark using two different centrifugation motion paradigms (fixed radius and variable radius) combined with two different subject orientations (facing-motion and back-to-motion). In the fixed radius trials, the radius at which the subject was seated was held constant while the rotation speed was changed to yield changes in the centrifugal force. In variable radius trials, the rotation speed was held constant while the radius was varied to yield a centrifugal force that nearly duplicated that measured during the fixed radius condition. The total gravito-inertial force (GIF) measured by the otolith organs was nearly identical in the two paradigms; the primary difference was the presence (fixed radius) or absence (variable radius) of yaw rotational cues. We found that the yaw rotational cues had a large statistically significant effect on the time course of perceived tilt, demonstrating that yaw rotational cues contribute substantially to the neural processing of roll tilt. We also found that the orientation of the subject relative to the centripetal acceleration had a dramatic influence on the eye movements measured during fixed radius centrifugation. Specifically, the horizontal vestibuloocular reflex (VOR) measured in our human subjects was always greater when the subject faced the direction of motion than when the subjects had their backs toward the motion during fixed radius rotation. This difference was consistent with the presence of a horizontal translational VOR response induced by the centripetal acceleration. Most importantly, by comparing the perceptual tilt responses to the eye movement responses, we found that the translational VOR component decayed as the subjective tilt indication aligned with the tilt of the GIF. This was true for both the fixed radius and variable radius conditions even though the time course of the responses was significantly different for these two conditions. These findings are consistent with the hypothesis that the nervous system resolves the ambiguous measurements of GIF into neural estimates of gravity and linear acceleration. More generally, these findings are consistent with the hypothesis that the nervous system uses internal models to process and interpret sensory motor cues.

Acceleration↗
PubMed1989

Electrophysiological properties and morphology of hair cells isolated from the semicircular canal of the frog.

Hair cells isolated from the crista ampullaris of the frog (Rana pipiens) remained viable for up to 5 h and were studied using whole cell voltage- and current clamp recordings. Morphological characteristics of isolated crista hair cells were compared with hair cells studied in situ using light- and electron microscopy. While other labyrinthine hair cells such as mammalian inner and outer hair cells of the cochlea, saccular hair cells of the frog, and cochlear hair cells of the turtle typically have a cylindrical shape, the crista hair cells in the frog are predominantly bulbous, having a thin elongated trunk projecting from a spherical base just large enough to enclose the nucleus. This shape correlates well with the compressed packing configuration of hair cells of the crista ampullaris observed in situ in the histological material. The support cells often failed to separate adjacent hair cells, particularly the apical ends of the hair cells. Maximal cell density on the sensory epithelial ridge appears to be achieved by this arrangement. The mean resting membrane potential (Vz) of isolated crista hair cells was -44.8 mV. Cells with smooth surfaces and apparent opacity had the most negative Vz potentials. As the cells appeared to deteriorate, there was development of transparency and cell surface granulation. Such cells had more positive initial Vz values. Cells with Vz values more positive than -15 mV exhibited a distinct, contoured nucleus. Cells lacking these indicators of deterioration were characterized by input resistances of 1.9 +/- 0.31 G omega and membrane time constants of 13 +/- 2.5 ms. A large complex outwardly rectifying current was identified which was abolished by substituting Cs+ for K+ in the internal solution. The outward K+ current had two major components: a fast tetraethylammonium (TEA)-insensitive, voltage dependent I(A)-type current which showed voltage dependent inactivation; and a TEA sensitive current which had characteristics of a calcium dependent IK(Ca)-type current. Transient changes (20 ms duration) in membrane potential mimicking that which could be produced by the transduction current during cilial displacement potently modulated the I(A) current. Depolarizing current pulses of greater than 63800 pA were required to elicit membrane voltage oscillations. The resulting membrane potential offset of at least 40 mV is well beyond the magnitude of hair cell receptor potentials making it unlikely that these oscillations would play a role in enhancing frequency selectivity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1970

Characteristics of neural transmission from the semicircular canal to the vestibular nuclei of cats.

1. The characteristics of the dynamic response of specifically canal-dependent neural units in cat vestibular nuclei have been examined during sinusoidal rotation of the head in decerebrate cats over the narrow frequency range 0.-1.7 Hz.2. Unit action potential frequencies were averaged on line from extracellular steel micro-electrodes stereotaxically located in the vestibular nuclei through the intact cerebellum.3. Action potential frequency was approximately in phase with stimulus angular velocity, the mean phase for forty-six units being + 11. degrees S.E. of the mean +/- 2.2 degrees ). Correction for a form of dynamic asymmetry reduced this value almost to zero.4. The mean gain of thirty-nine single unit responses was 0.76 S.E. +/- 0.08) AP/sec per degrees /sec. The gain varied as the (-0.28) power of stimulus angular velocity, for the five cells appropriately tested.5. A method was evolved for computing the spontaneous condition of cells, in terms of an equivalent spontaneous firing frequency, f(sp) irrespective of whether they were spontaneously active or silent. This f(sp) value was normally distributed about a mean value of 11.2 AP/sec (range + 70 to - 40 AP/sec).6. Directionality was examined in 116 units, of which 62% were ipsilateral (e.g. cells on left side excited by left-going rotational velocity) and 38% contralateral. Ipsilateral units proved easier to isolate and retain than contralateral ones.7. No significant differences in mean phase or gain were found in the sub-sets of spontaneously active/inactive cells and ipsilateral/contralateral cells.8. It is inferred that the cell population examined was a functionally homogeneous one in which the neural signal was closely tied to the angular velocity of canal rotation for the narrow band of sinusoidal rotational stimuli here employed. It is suggested that this signal is probably retained essentially intact in the ensemble neural message fed forwards from this region.

Action Potentials↗
PubMed1992

The site of brainstem lesions causing semicircular canal paresis: an MRI study.

Ten patients with canal paresis of central origin and ten patients with peripheral canal paresis were studied using MRI of the brainstem to identify lesions within the central vestibular pathways. In the central group, the magnitude of the canal paresis was generally lower than in the peripheral group and removal of fixation had little effect on the nystagmic response. In the peripheral group, removal of fixation enhanced the nystagmus and lessened the discrepancy between the two ears. Statistical processing of the MRI showed that in the central group significant spatially coincident lesions occurred within the medial vestibular nucleus, lateral vestibular nucleus and proximal portion of the vestibular fascicle.

Adult↗