Differential effects of duration for ocular and cervical vestibular evoked myogenic potentials evoked by air- and bone-conducted stimuli

We investigated the changes in cervical (cVEMP) and ocular (oVEMP) vestibular evoked myogenic potentials in response to differing stimulus durations. cVEMPs (n = 12 subjects) and oVEMPs (n = 13 subjects) were recorded using air-conducted (AC: 500 Hz) and bone-conducted (BC: 500 Hz) tone burst stimuli with durations varying from 2 to 10 ms. BC stimulation was applied both frontally and to the mastoid. AC cVEMPs showed an increase in amplitude with stimuli up to 6-ms duration associated with a prolonged latency, as previously reported. In contrast, AC oVEMP amplitude decreased with increasing stimulus duration. BC stimuli showed no significant increase in amplitude with increasing stimulus duration for either reflex using either location of stimulation. BC cVEMPS following forehead stimulation showed a significant decrease as duration increased, and BC oVEMPs to mastoid stimulation were largest at 2 ms and decreased thereafter. We conclude that an increase in amplitude with increasing stimulus duration, using 500 Hz stimuli, only occurs for AC cVEMPs. There is no definite benefit in using longer stimuli than 2 ms for BC or oVEMP studies. Shorter stimuli also minimise subject exposure to sound and vibration.     

Ocular vestibular-evoked myogenic potentials (oVEMP) to skull taps in normal and dehiscent ears: mechanisms and markers of superior canal dehiscence

The site of stimulus delivery modulates the waveforms of cervical- and ocular vestibular-evoked myogenic potentials (cVEMP and oVEMP) to skull taps in healthy controls. We examine the influence of stimulus location on the oVEMP waveforms of 18 patients (24 ears) with superior canal dehiscence (SCD) and compare these with the results of 16 healthy control subjects (32 ears). oVEMPs were recorded in response to taps delivered with a triggered tendon-hammer and a hand-held minishaker at three midline locations; the hairline (Fz), vertex (Cz) and occiput (Oz). In controls, Fz stimulation evoked a consistent oVEMP waveform with a negative peak (n1) at 9.5 ± 0.5 ms. In SCD, stimulation at Fz produced large oVEMP waveforms with delayed n1 peaks (tendon-hammer = 13.2 ± 1.0 ms and minitap = 11.5 ± 1.1 ms). Vertex taps produced diverse low-amplitude waveforms in controls with n1 peaks at 15.5 ± 1.2 and 13.2 ± 1.3 ms for tendon-hammer taps and minitaps, respectively; in SCD, they produced large amplitude oVEMP waveforms with n1 peaks at 12.9 ± 0.8 ms (tendon-hammer) and 12.1 ± 0.5 ms (minitap). Occiput stimulation evoked oVEMPs with similar n1 latencies in both groups (tendon-hammer = 11.3 ± 1.3 and 10.7 ± 0.8; minitap = 10.3 ± 0.9 and 11.1 ± 0.4 for control and SCD ears, respectively). Compared to reflex amplitudes, n1 peak latencies to Fz taps provided clearer separation between SCD and control ears. The distinctly different effects of Fz and vertex taps on the oVEMP waveforms may represent an additional non-osseous mechanism of stimulus transmission in SCD. For skull taps at Fz, a prolonged n1 latency is an indicator of SCD.     

Evidence for the utricular origin of the vestibular short-latency-evoked potential (VsEP) to bone-conducted vibration in guinea pig

Previous studies have shown that the vestibular short-latency-evoked potential (VsEP) in response to the brief head acceleration stimulus is a compound action potential of neurons innervating the otolith organs. However, due to the lack of direct evidence, it is currently unclear whether the VsEP is primarily generated by the activity of utricular or saccular afferent neurons, or some mixture of the two. Here, we investigated the origin of the VsEP evoked by brief bone-conducted vibration pulses in guinea pigs, using selective destruction of the cochlea, semicircular canals (SCCs), saccule, or utricle, along with neural blockade with tetrodotoxin (TTX) application, and mechanical displacements of the surgically exposed utricular macula. To access each end organ, either a dorsal or a ventral surgical approach was used. TTX application abolished the VsEP, supporting the neurogenic origin of the response. Selective cochlear, SCCs, or saccular destruction had no significant effect on VsEP amplitude, whereas utricular destruction abolished the VsEP completely. Displacement of the utricular membrane changed the VsEP amplitude in a non-monotonic fashion. These results suggest that the VsEP evoked by BCV in guinea pigs represents almost entirely a utricular response. Furthermore, it suggests that displacements of the utricular macula may alter its response to bone-conduction stimuli.     

Correlation between acceleration magnitude and ocular vestibular-evoked myogenic potential

This study combined bone-conducted vibration (BCV) stimulation with triaxial accelerometry to correlate the acceleration magnitudes of BCV stimuli with ocular vestibular-evoked myogenic potential (oVEMP) test results. Fourteen healthy volunteers underwent oVEMP test using BCV stimuli with simultaneous monitoring the triaxial acceleration. All (100%) subjects exhibited clear oVEMPs in response to BCV stimuli from a vibrator. The lowest acceleration magnitudes for eliciting oVEMPs along the x-, y- and z-axes were 0.05±0.01 g, 0.16±0.08 g, and 0.04±0.01 g, respectively, exhibiting significantly higher acceleration magnitude along the y-axis than those along the x- and z-axes. In addition, significantly positive correlations were noted between the acceleration magnitude along each axis and the oVEMP amplitude. In conclusion, measuring the acceleration magnitude throughout oVEMP testing revealed a significant correlation between linear acceleration and oVEMP responses. Restated, increasing acceleration magnitude may have more synchronization of firing of vestibular afferents, resulting in more synchronized evoked potentials and greater oVEMP amplitude.     

Bone conducted vibration selectively activates irregular primary otolithic vestibular neurons in the guinea pig

The main objective of this study was to determine whether bone-conducted vibration (BCV) is equally effective in activating both semicircular canal and otolith afferents in the guinea pig or whether there is preferential activation of one of these classes of vestibular afferents. To answer this question a large number (346) of single primary vestibular neurons were recorded extracellularly in anesthetized guinea pigs and were identified by their location in the vestibular nerve and classed as regular or irregular on the basis of the variability of their spontaneous discharge. If a neuron responded to angular acceleration it was classed as a semicircular canal neuron, if it responded to maintained roll or pitch tilts it was classified as an otolith neuron. Each neuron was then tested by BCV stimuli—either clicks, continuous pure tones (200–1,500 Hz) or short tone bursts (500 Hz lasting 7 ms)—delivered by a B-71 clinical bone-conduction oscillator cemented to the guinea pig's skull. All stimulus intensities were referred to that animal's own auditory brainstem response (ABR) threshold to BCV clicks, and the maximum intensity used was within the animal's physiological range and was usually around 70 dB above BCV threshold. In addition two sensitive single axis linear accelerometers cemented to the skull gave absolute values of the stimulus acceleration in the rostro-caudal direction. The criterion for a neuron being classed as activated was an audible, stimulus-locked increase in firing rate (a 10% change was easily detectable) in response to the BCV stimulus. At the stimulus levels used in this study, semicircular canal neurons, both regular and irregular, were insensitive to BCV stimuli and very few responded: only nine of 189 semicircular canal neurons tested (4.7%) showed a detectable increase in firing in response to BCV stimuli up to the maximum 2 V peak-to-peak level we delivered to the B-71 oscillator (which produced a peak-to-peak skull acceleration of around 6–8 g and was usually around 60–70 dB above the animal's own ABR threshold for BCV clicks). Regular otolithic afferents likewise had a poor response; only 14 of 99 tested (14.1%) showed any increase in firing rate up to the maximum BCV stimulus level. However, most irregular otolithic afferents (82.8%) showed a clear increase in firing rate in response to BCV stimuli: of the 58 irregular otolith neurons tested, 48 were activated, with some being activated at very low intensities (only about 10 dB above the animal's ABR threshold to BCV clicks). Most of the activated otolith afferents were in the superior division of the vestibular nerve and were probably utricular afferents. That was confirmed by evidence using juxtacellular injection of neurobiotin near BCV activated neurons to trace their site of origin to the utricular macula. We conclude there is a very clear preference for irregular otolith afferents to be activated selectively by BCV stimuli at low stimulus levels and that BCV stimuli activate some utricular irregular afferent neurons. The BCV generates compressional and shear waves, which travel through the skull and constitute head accelerations, which are sufficient to stimulate the most sensitive otolithic receptor cells.     

Tuning of the ocular vestibular evoked myogenic potential (oVEMP) to air- and bone-conducted sound stimulation in superior canal dehiscence

Recent studies have demonstrated the frequency selectivity of air-conducted (AC) and bone-conducted (BC) stimuli in eliciting ocular vestibular evoked myogenic potentials (oVEMPs). In this study, frequency tuning of the oVEMP was assessed in patients with superior canal dehiscence (SCD) and compared with responses previously reported for healthy subjects. Six (five unilateral) SCD patients were stimulated using AC sound (50–1,200 Hz) and BC transmastoid vibration (50–1,000 Hz). Stimuli were delivered at two standardized intensities: one the same as previously used for healthy controls and the other at 10 dB above vestibular threshold (a similar relative intensity to that used in controls). For AC stimulation, SCD patients had larger oVEMP amplitudes across all frequencies tested for both stimulus intensities. Normalized tuning curves demonstrated greater high-frequency responses with the stronger stimulus. For BC stimulation, larger oVEMP amplitudes were produced at frequencies at and above 100 Hz using standard intensity stimuli. For the matched intensity above vestibular threshold, enhancement of the oVEMP response was present in SCD patients for 500–800 Hz only. We conclude that SCD causes greater facilitation for AC than BC stimuli. The high-frequency response is likely to originate from the superior (anterior) canal and is consistent with models of inner ear changes occurring in SCD.     

Posture-induced changes of ocular vestibular evoked myogenic potentials suggest a modulation by intracranial pressure

Ocular vestibular evoked myogenic potentials (oVEMPs) represent extraocular muscle activity in response to vestibular stimulation. We sought to investigate whether oVEMPs are modulated by increasing intracranial pressure (ICP). Air-conducted oVEMPs were elicited in 20 healthy subjects lying supine on a tilt table. In order to elevate the ICP, the table was stepwise tilted from the horizontal plane to a 30° declination, corresponding to a 0°, 10°, 20° and 30° head-down position. At each inclination angle, oVEMP recording was performed in two head positions: (1) the head in line with the body and (2) the head positioned horizontally with the body tilted. When tilting both the body and head, oVEMP amplitudes gradually declined from 4.59 μV at 0° to 2.24 μV at 30° head-down position, revealing a highly significant reduction in amplitudes for all tilt angles when compared to the baseline value (p < 0.001). In parallel, the response prevalence decreased and latencies prolonged. Similar effects were observed when the body was tilted but the head positioned horizontally, even though the decrease in oVEMP amplitudes was less pronounced. A gravitoinertial force effect upon the otolith organs could thereby be excluded as a possible confounder. Hence, oVEMPs were most likely modulated by increasing ICP. In the range of the horizontal plane to a 30° head-down tilt, there was a linear correlation between oVEMP amplitudes and the inclination angle. oVEMPs might in principle be suited for non-invasive ICP monitoring.     

Tuning of the ocular vestibular evoked myogenic potential (oVEMP) to AC sound shows two separate peaks

The ocular vestibular evoked myogenic potential (oVEMP) is a relatively new method used to assess otolith-ocular pathways in humans. When elicited using air-conducted (AC) sound stimulation, the oVEMP is thought to reflect mostly saccular activation. However, it has been recently suggested that utricular afferents may also contribute to the AC evoked oVEMP. While previous frequency tuning studies of the AC evoked oVEMP report predominately high frequency sensitivity (>400 Hz), few have included the lower frequencies (<200 Hz) at which it has been proposed the utricle is most sensitive. In this study, ten normal subjects were stimulated with AC sound delivered unilaterally using headphones over frequencies from 50 to 1,200 Hz at a near constant A-weighted intensity of 120 dB peak sound pressure level. For AC stimulation, the oVEMP demonstrated maximum amplitudes around 600 Hz, with a second, smaller peak occurring around 100 Hz. The AC evoked oVEMP tuning has two peaks, a dominant one consistent with excitation of the saccule and a smaller one consistent with excitation of the utricle.     

Direct Electrical Stimulation Using a Battery-Operated Device for Induction and Modulation of Colonic Contractions in Pigs

Direct electrical stimulation of the colon offers a promising approach for the induction of propulsive colonic contractions by using an implantable device. The objective of this study was to assess the feasibility to induce colonic contractions using a commercially available battery-operated stimulator (maximum pulse width of 1 ms and maximum amplitude of 10 V). Three pairs of pacing electrodes were inserted into the cecal seromuscular layer of anesthetized pigs. During a first set of in vivo experiments conducted on six animals, a pacing protocol leading to cecum contractions was determined: stimulation bursts with 1 ms pulse width, 10 V amplitude (7–15 mA), 120 Hz frequency, and 30-s burst duration, repeated every 2–5 min. In a second testing phase, an evaluation of the pacing protocol was performed in four animals (120 stimulation bursts in total). By using the battery-operated stimulator, contractions of the cecum and movement of contents could be induced in 92% of all stimulations. A cecal shortening of about 30% and an average intraluminal pressure increase of 10.0 ± 6.0 mmHg were observed.     

中耳用药对豚鼠平衡器影响的电镜观察

通过注入0.5%,1%,2%环丙沙星与庆大霉素溶液于豚鼠中耳(听泡)内,对内耳组织进行火棉胶切片及扫描电镜观察标本制作,借助光镜和扫描电镜观察平衡器的显微和超微结构的变化,并通过平衡功能的测试,比较环丙沙星与庆大霉素对平衡器的毒性作用,结果证明:环丙沙星对平衡器的毒性很低,功能与形态上都没有明显损伤.庆大霉素则使壶腹嵴毛细胞纤毛融合,缺失,壶胶帽消失,椭圆囊斑和球囊斑的毛细胞纤毛粘连,缺损,耳右变性,减少或消失.     

Design-based stereological study of the guinea-pig (Cavia porcellus) cerebellum

Guinea pigs have proved useful as experimental animal models in studying cerebellar anatomical and structural alterations in human neurological disease; however, they are also currently acquiring increasing veterinary interest as companion animals. The morphometric features of the normal cerebellum in guinea pigs have not been previously investigated using stereology. The objective of the present work was to establish normal volumetric and quantitative stereological parameters for cerebellar tissues in guinea pigs, by means of unbiased design-based stereology. Cerebellar total volume, gray and white matter volume fractions, molecular and granular layers volume fractions, cerebellar surface area, Purkinje cellular and nuclear volumes, and the Purkinje cell total count were stereologically estimated. For this purpose, cerebellar hemispheres from six adult male guinea pigs were employed. Isotropic, uniform random sections were obtained by applying the orientator method, and subsequently processed for light microscopy. The cerebellar total volume, the white and grey matter volume fractions, and the molecular and granular layer volumes were estimated using the Cavalieri's principle and the point counting system. The cerebellar surface area was estimated through the use of test lines; Purkinje cellular and nuclear volumes were analysed using the nucleator technique, whereas the Purkinje cell total count was obtained by means of the optical disector technique. The mean ± standard deviation total volume of a guinea-pig cerebellar hemisphere was 0.11 ± 0.01 cm³. The mean volumetric proportions occupied by the gray and white matters were, respectively, 78.0 ± 2.6% and 22.0 ± 2.6%, whereas their mean absolute volumes were found to be 0.21 ± 0.02 cm³ and 0.059 ± 0.006 cm³. The volumes of the molecular and granular layers were estimated at 112.4 ± 20.6 mm³ and 104.4 ± 7.3 mm³, whereas their mean thicknesses were calculated to be 0.184 ± 0.020 mm and 0.17 ± 0.02 mm. The molecular and granular layers accounted for 40.7 ± 3.9% and 37.4 ± 1.8% of total cerebellar volume respectively. The surface area of the cerebellum measured 611.4 ± 96.8 mm². Purkinje cells with a cellular volume of 3210.1 µm³ and with a nuclear volume of 470.9 µm³ had a higher incidence of occurrence. The mean total number of Purkinje cells for a cerebellar hemisphere was calculated to be 253,090 ± 34,754. The morphometric data emerging from the present study provide a set of reference data which might prove valuable as basic anatomical contribution for practical applications in veterinary neurology.     

Evidence of increased electro-mechanical delay in the left and right ventricle after prolonged exercise

We assessed the time delay from the onset of QRS (Q) to peak systolic (S′) and diastolic (E′) tissue velocities in the left (LV) and right ventricle (RV) before and after prolonged exercise. Nineteen well-trained runners (mean ± SD age, 41 ± 9 years) had tissue-Doppler echocardiography performed before and after an 89 km ultra-marathon race. Longitudinal tissue motion was analysed in LV basal and mid-wall segments and RV free wall. Electromechanical coupling was assessed by the delay between Q and S′ as well as E′ tissue velocities. Average data for all segments were adjusted for the R–R interval. Comparisons were made by paired t-tests. An increase in electro-mechanical delay (EMD) was reported post-exercise in systole (Q–S′ LV: 131 ± 20 vs. 175 ± 27 ms; RV: 171 ± 34 vs. 258 ± 35 ms; P < 0.05) and diastole (Q–E′ LV: 486 ± 51 vs. 647 ± 44 ms; RV: 500 ± 80 vs. 690 ± 75 ms; P < 0.05). Further, post-race peak tissue velocities in basal LV and RV wall segments were reduced (P < 0.05). Recovery from prolonged running was associated with an increased “EMD”, and reduced peak tissue velocities, in both ventricles.     

Different effects of head tilt on ocular vestibular-evoked myogenic potentials in response to bone-conducted vibration and air-conducted sound

The ocular vestibular-evoked myogenic potentials (oVEMPs) in response to air-conducted sound (ACS) and bone-conducted vibration (BCV) have recently been used to assess otolith-ocular pathways in humans. Although the oVEMPs to BCV are considered to reflect the function of the utricle and superior vestibular pathway, the pathway of the oVEMPs to ACS remains controversial. In this study, we compared the effect of different head positions in the roll plane on oVEMPs in response to BCV and ACS in 20 normal subjects. Head tilt in the roll plane significantly increased the asymmetry ratio of oVEMPs to BCV (p?<?0.01) but did not affect the asymmetry ratio of oVEMPs to ACS. Head tilt did not affect the latencies of oVEMPs to either BCV or ACS. Rotation of the body in the yaw plane while keeping the head straight ahead did not affect the asymmetry of oVEMPs to BCV (p?>?0.6). These results suggest that oVEMPs to BCV reflect the activity of a different population of vestibular afferents to those which are active during oVEMPs to ACS.     

Passive stretching effects on electromechanical delay and time course of recovery in human skeletal muscle: new insights from an electromyographic and mechanomyographic combined approach

Acute passive stretching has been shown to alter muscle-tendon unit (MTU) stiffness and to reduce peak tetanic force (pF). MTU mechanical properties and electro-mechanical delay (EMD) are closely related. Thus, EMD changes would be expected after stretching. The aim of the study was to assess the stretching-induced changes in both contractile and viscoelastic contributors to EMD. The time course of these changes will be also evaluated. Tetanic stimulations were delivered on the medial gastrocnemius muscle of 16 active males, before and after (every 15 min, for 2 h) passive stretching administration. During contractions, electromyographic (EMG), mechanomyographic (MMG) and force signals were recorded. The delays between EMG and force (Δt EMG-F, which corresponds to EMD), EMG and MMG (Δt EMG-MMG) and MMG and force (Δt MMG-F) signals were calculated, together with pF and EMG conduction velocity (CV). After stretching (i) pF decreased by 31% (P < 0.05) and remained depressed for the entire recovery period, while EMG CV did not change; (ii) Δt EMG-F, Δt EMG-MMG and Δt MMG-F increased significantly from 45.4 ± 3.0 ms, 2.2 ± 0.3 ms and 42.4 ± 3.1 ms to 52.7 ± 3.4 ms, 2.4 ± 0.3 ms and 50.3 ± 3.5 ms, respectively; (iii) Δt EMG-F and Δt MMG-F remained lengthened for the entire recovery period, while Δt EMG-MMG recovered to its pre-stretching condition within 15 min. These findings suggest that after stretching, the reduction in pF was accompanied by an elongation of the overall EMD. However, stretching had effects of short duration at the contractile level, but more persisting effects on MTU viscoelastic characteristics.     

An adaptive gyroscope-based algorithm for temporal gait analysis

Body-worn kinematic sensors have been widely proposed as the optimal solution for portable, low cost, ambulatory monitoring of gait. This study aims to evaluate an adaptive gyroscope-based algorithm for automated temporal gait analysis using body-worn wireless gyroscopes. Gyroscope data from nine healthy adult subjects performing four walks at four different speeds were then compared against data acquired simultaneously using two force plates and an optical motion capture system. Data from a poliomyelitis patient, exhibiting pathological gait walking with and without the aid of a crutch, were also compared to the force plate. Results show that the mean true error between the adaptive gyroscope algorithm and force plate was −4.5 ± 14.4 ms and 43.4 ± 6.0 ms for IC and TC points, respectively, in healthy subjects. Similarly, the mean true error when data from the polio patient were compared against the force plate was −75.61 ± 27.53 ms and 99.20 ± 46.00 ms for IC and TC points, respectively. A comparison of the present algorithm against temporal gait parameters derived from an optical motion analysis system showed good agreement for nine healthy subjects at four speeds. These results show that the algorithm reported here could constitute the basis of a robust, portable, low-cost system for ambulatory monitoring of gait.     

Heterogeneity of hair cells in the bullfrog sacculus

 Morphometric and electrophysiological features of hair cells in the sacculus of the bullfrog (Rana catesbeiana) were studied. Confocal microscopy observations of hair cells in situ revealed that three classes of hair cells can be distinguished by their somata shape and macular location. Two of these, termed central cylindrical (CCHCs) and central flask-shaped (CFHCs) hair cells, were found in the central part of the macula. The third class, termed peripheral elongated hair cells (PEHC), was only found around the perimeter of the sacculus. Using the whole-cell patch-clamp technique CCHCs and CFHCs were distinguished by the amplitude of their voltage-activated calcium currents (I _Ca). The mean amplitudes of steady-state I _Ca at –20 mV were –900 ± 500 pA (n = 18) for CCHCs and –160 ± 70 pA (n = 10) for CFHCs. The two hair-cell types also differed in the possession of a Cs⁺-resistant, apamin-sensitive, calcium-sensitive potassium current, found only the CFHCs. This study indicates that several populations of hair cells with distinct morphological features exist in the bullfrog sacculus, and that at least two of these differ in their complement of membrane conductances. Received: 18 February 1997 / Received after revision: 24 June 1997 / Accepted: 23 July 1997     

Rate‐dependent electrical,contractile and restitution properties of isolated left ventricular myocytes in guinea‐pig hypertrophy

Left ventricular hypertrophy predisposes to sudden cardiac death (SCD) and studies of human SCD suggest that the antecedent heart rate (HR) is usually <100 beats min^–1. This is surprising in view of the known association between adrenergic receptor stimulation and SCD which by itself would suggest that it is more likely to occur from high rather than low HR. We therefore hypothesized that there may be electrical or mechanical abnormalities present in myocytes isolated from animals with left ventricular hypertrophy that predispose to SCD at low stimulation frequencies but which may not be present at high HR. Mild left ventricular hypertrophy was induced in guinea‐pigs by infra‐renal aortic banding. Electrical and mechanical properties of isolated myocytes were studied at different stimulation frequencies between 0.1 and 3 Hz. Action potential duration (APD) is prolonged in hypertrophy at stimulation frequencies <1 Hz but not at faster rates. Contraction size, time‐to‐peak contraction (TTPC) and half‐relaxation time are greatly enhanced in hypertrophy at all frequencies between 0.1 and 3 Hz. Electrical (50.3 ± 5.2 ms in hypertrophy and 78.4 ± 12.1 ms in control, P < 0.03) and mechanical (205 ± 16 ms for hypertrophy and 266 ± 24 ms for control cells, P < 0.03) restitution time constants are quicker in hypertrophy. The finding of APD prolongation at low but not at high frequencies is consistent with the finding that SCD arises from low and not high HR. This data supports the role of abnormal repolarization in SCD.     

Gap junctions between the supporting cells in some acoustico-vestibular receptors

Summary Extensive gap junctions are found between the supporting cells in acoustico-vestibular receptors (saccular macula of the goldfish; ampullar crista, utricular macula and organ of Corti of the guinea pig). The fine structural details of these gap junctions were examined using lanthanum hydroxide staining and freeze-fracture replicas, as well as conventional thin sections. It was found in the lanthanum treated saccular macula of the goldfish that the gap junction globules consist of five or six subunits surrounding a central 2 nm hole. Similar subunits of the gap junction globule are also found in freeze-fracture replicas of the saccular macula of the goldfish and the ampullar crista of the guinea pig. Possible functions of the extensive gap junctions between supporting cells of these receptors are discussed.     

Zebrafish pax5 regulates development of the utricular macula and vestibular function.

The zebrafish otic vesicle initially forms with only two sensory epithelia, the utricular and saccular maculae, which primarily mediate vestibular and auditory function, respectively. Here, we test the role of pax5, which is preferentially expressed in the utricular macula. Morpholino knockdown of pax5 disrupts vestibular function but not hearing. Neurons of the statoacoustic ganglion (SAG) develop normally. Utricular hair cells appear to form normally but a variable number subsequently undergo apoptosis and are extruded from the otic vesicle. Dendrites of the SAG persist in the utricle but become disorganized after hair cell loss. Hair cells in the saccule develop and survive normally. Otic expression of pax5 requires pax2a and fgf3, mutations in which cause vestibular defects, albeit by distinct mechanisms. Thus, pax5 works in conjunction with fgf3 and pax2a to establish and/or maintain the utricular macula and is essential for vestibular function.