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H Sohmer

Publications and source records attributed to H Sohmer.

At least 19 recordsLinked to original sources
PubMed2000

Assessment of vestibular ototoxicity of ear drops by recording of vestibular evoked potentials to acceleration impulses.

INTRODUCTION: The cochlear ototoxicity of several ear drops is well documented in the literature, but very few studies exist on the vestibular ototoxicity of these topical drugs. GOAL OF STUDY: To develop an animal model for the assessment of the vestibular ototoxicity of ear drops. MATERIALS AND METHODS: Two animal groups, consisting of five fat sand rats (FSRs) each, underwent unilateral labyrinthectomy. Normal saline was topically applied into the middle ear cavity of rats in the first group for 7 days (control group). Rats in the second group were treated in the same way by topical gentamicin solution. Cochlear function was assessed by the recording of auditory evoked potential (ABPs) thresholds, and vestibular function was assessed by the recording of vestibular evoked potentials (VsEPs) to angular accelerations. RESULTS: In the control group, except for the amplitude of the first wave, there was no significant difference in the VsEPs recorded before and after topical application. In the gentamicin group, VsEPs could not be recorded after 7 days, and ABPs were recorded in one case only, with a threshold of 100 dB sound pressure level (SPL). CONCLUSION: VsEPs seem to be a reliable measure for evaluating the vestibular ototoxicity of topical ear drops.

Administration, Topical↗
PubMed2000

Bone conduction experiments in animals - evidence for a non-osseous mechanism.

Bone conducted stimuli are used to differentiate between conductive and sensori-neural hearing loss. It has been thought that the main route for the transfer of vibratory energy from the point of application of the bone vibrator on the skull to the inner ear is completely osseous. An additional mechanism may play a prominent role. In rats, a bone vibrator was applied to the skull and also directly on the brain, after removing bone (a craniotomy), exposing the brain. Auditory nerve-brainstem evoked response (ABR) could be elicited not only with the vibrator on bone, but also with the vibrator directly on the brain. Similar results were obtained in guinea-pigs and fat sand rats. Noise masked this ABR. Extensive removal of skull bone did not alter the ABR to bone-conducted stimuli delivered to the exposed brain. Experimental elimination of the ossicular chain inertial mechanism and of the occlusion effect did not greatly alter the bone conduction response. A reduction in the fluid volume of the cranial cavity induced threshold elevations of the bone conducted ABR but not of the air conducted ABR. These findings can be interpreted as evidence that the 'classical' bone conduction mechanisms should be modified to include a major pathway for cochlear excitation which is non-osseous: when a bone vibrator is applied to the skull, the bone vibrations may induce audio-frequency sound pressures in the skull contents (brain and cerebro-spinal fluid) which are then communicated by fluid channels to the fluids of the inner ear.

Animals↗
PubMed2000

Bone conduction experiments in humans - a fluid pathway from bone to ear.

Animal experiments in this laboratory have led to the suggestion that a major pathway in bone conduction stimulation to the inner ear is via the skull contents (brain and CSF). This hypothesis was now tested in humans. Auditory nerve brainstem evoked responses could be recorded in neonates to bone conduction stimulation over the fontanelle and audiometric responses were obtained in neurosurgical patients with the bone vibrator on the skin over a craniotomy. There were no differences in threshold between these responses and those obtained to bone conduction stimulation over skull bone in the same subjects. Audiometric thresholds in response to bone vibrator stimulation of the eye (a 'natural craniotomy') were no different from those to bone stimulation delivered to several sites on the head. Thus there is no need to vibrate bone in order to obtain 'bone conduction' responses. Bone vibrator thresholds to stimulation at the head region with thinnest bone (temporal) were better than those to stimulation at the forehead region which has much thicker bone, implying that the vibrations penetrate the skull at the site of the vibrator. In addition, the magnitude of vibration (acceleration) measured at various sites around the head in response to bone vibrator stimulation at a fixed point on the forehead generally decreased with distance from the point of vibration. Therefore it seems that the vibrations produced by a bone vibrator at a point on the head are also able to penetrate the skull, setting up audio-frequency pressures in the CSF which spread by fluid communications to the inner ear fluids, exciting the ear.

Adolescent↗
PubMed2000

Vestibular and cochlear ototoxicity of topical antiseptics assessed by evoked potentials.

OBJECTIVES/HYPOTHESIS: To evaluate and compare the effect of chlorhexidine gluconate, povidoneiodine, and alcohol-three antiseptics used before ear surgery-on the function of the vestibular and cochlear parts of the sand rat's inner ear. The assessment of damage is based on the recording of vestibular evoked potentials (VsEPs) and auditory brainstem response (ABR). STUDY DESIGN: Prospective controlled animal study. METHODS: Fat sand rats were randomly assigned to five different groups, each receiving topical application of a different agent: saline (control), gentamicin (ototoxic control), chlorhexidine, povidone-iodine, and alcohol. Right-side total labyrinthectomy was performed, and a polyethylene tube was inserted into the left (contralateral) middle ear. After baseline recordings were taken of VsEPs and ABR, each animal received five consecutive daily applications of the specific agent into the left middle ear. Three days after the fifth application, evoked potential recordings (VsEPs and ABRs) were repeated and compared with baseline measurements. RESULTS: Administration of saline affected neither VsEPs nor ABR. In contrast, as expected, neither of these responses could be recorded after gentamicin application. After application of chlorhexidine all waves disappeared in all sand rats. Alcohol caused the waves to disappear in some of the animals only. Povidone-iodine did not affect VsEP recordings and had only a small effect on ABR. CONCLUSIONS: Chlorhexidine and alcohol had a clear toxic effect on the vestibular and cochlear function of the inner ear of the sand rat, whereas povidone-iodine did not. Thus, taking into consideration that this is an animal study, it appears that povidone-iodine might be preferable to the other agents tested in disinfecting ears with a perforated tympanic membrane.

Administration, Topical↗
PubMed2000

Use of evoked potentials to objectively differentiate between selective vulnerability of cochlear and vestibular end organ function.

Auditory nerve brainstem evoked responses (ABR) have been used for several decades to investigate cochlear function. Recently techniques have been developed to elicit similar recordings from the vestibular end organs - short latency vestibular evoked potentials (VsEPs). Both ABR and VsEP reflect appropriate end organ function and may therefore be used to investigate the vulnerability of these end organs to various experimental insults, such as noise exposure and ototoxic drugs.

Animals↗
PubMed2000

Effect of high-dose cisplatin on auditory brainstem responses and otoacoustic emissions in laboratory animals.

OBJECTIVE: The role of transient evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE) as early indicators of cisplatin-induced ototoxicity in three different rodent species--the guinea pig. the albino rat, and the fat sand rat (Psammomys obesus)--was investigated. In addition, an attempt was made to determine which of the three rodent species is most susceptible to cisplatin-induced ototoxicity as measured by auditory brainstem responses (ABR), BACKGROUND: There have been numerous clinical and experimental reports on cisplatin-induced ototoxicity, but to the authors' best knowledge, there has been no comparative report on the short-term effects of cisplatin on OAE measured with commercially available equipment between different rodent species. METHODS: Cisplatin was systemically administered as a single high dose (12 mg/kg intraperitoneally) to all three species, and the ototoxic effects were measured before and 3 days after the injection of cisplatin in the same animals, using ABR, TEOAE, and DPOAE. RESULTS: The ABR thresholds were significantly elevated in the guinea pigs and the albino rats but not in the sand rats. Significant depression of TEOAE energy and DPOAE amplitude occurred only in the guinea pigs. The depression of the DPOAE was greater than that of the TEOAE. The guinea pigs showed the greatest degree of ototoxicity (depression of ABR and OAE). CONCLUSIONS: Among the three rodent species, the guinea pig has the potential to be used as a sensitive animal model in studies of cisplatin ototoxicity. The study also showed that the recordings of TEOAE and DPOAE, in addition to ABR, are sensitive techniques for the assessment of cisplatin-induced ototoxicity.

Animals↗
PubMed1999

Development of short latency vestibular evoked potentials in the neonatal rat.

The development of short latency vestibular evoked potentials (VsEPs) was investigated in the neonatal rat. Using the appropriate stimulus (linear or angular acceleration impulses) and head orientation, responses elicited in various vestibular end-organs (utricle: x-VsEP; saccule: z-VsEP; lateral semi-circular canal: a-VsEP) were measured in rat pups at various ages between post-natal days (PND) 5 and 30, and compared to those recorded from adult animals. It was found that the VsEPs initially appeared on PND 6 (x-VsEPs and z-VsEPs) or 7 (a-VsEPs), and that by PND 8 the three responses could be recorded in all animals. The first wave of the responses, generated in the primary sensory nerve and reflecting end-organ activity, reached adult latencies and amplitudes by PND 10, showing rapid maturity of the responses. Auditory responses, on the other hand, develop at a later stage (from PND 11). The possible mechanisms involved in this differential maturation between vestibular and auditory activity are discussed.

Acceleration↗
PubMed1999

Effect of white noise "masking" on vestibular evoked potentials recorded using different stimulus modalities.

Short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses (L-VsEPs) are initiated in the otolith organs (saccule and utricle). Some of the saccule afferents have been reported to respond not only to linear acceleration, but also to high intensity acoustic stimuli. If so, the L-VsEP recorded from the saccule (elicited with the stimulus orientated relative to the head so as to optimally activate the saccule, i.e. stimulus in the vertical plane, Z-VsEP) should be reduced during high intensity broad band noise (BBN) "masking". Conversely, the utricular afferents have been reported to be less auditory-sensitive. Therefore, an L-VsEP which is mainly utricular in origin (stimulus in the horizontal plane, X-VsEP) should be less affected by this noise "masking". This was investigated in rats by recording X-VsEPs and Z-VsEPs and angular VsEPs (A-VsEPs), originating in the lateral semi-circular canals, before, during and after exposure to short duration, high intensity (113 dB SPL) BBN. This intensity completely masked auditory nerve evoked responses. The Z-VsEP did appear to be slightly more affected by the noise "masking" than the X-VsEP, implying the presence of more auditory-sensitive elements in the saccule. The A-VsEP was also affected by the BBN. The overall effect was relatively small (on average, 10-25% depression of the first wave of the different VsEPs). The responses showed recovery 5 min later.

Animals↗
PubMed1999

Development of inner ear (cochlear and vestibular) function in the fetus-neonate.

The development of function in the various receptors in the inner ear was studied in the neonatal rat, which is altricious with respect to hearing, using short latency evoked potentials, both auditory (ABR) and vestibular (VsEP). It was found that VsEPs could be recorded from all the vestibular end-organs by post natal day (PND) 8, whilst ABR could only be recorded from all animals on PND 14, showing the earlier onset of vestibular function in the inner ear. These results are discussed with relation to onset of inner ear function in the human fetus.

Animals↗
PubMed1999

Origins of the short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses.

OBJECTIVE: To verify the vestibular origin of the short latency (t < 12.5 msec) vestibular evoked potentials (VsEPs) in response to linear acceleration impulses (L-VsEPs) and to differentiate between the contributions of the otolith organs and the semi-circular canals (SCCs) to their initiation. DESIGN AND METHODS: L-VsEPs (stimulus intensity, 3 g; rise time, 1.0 to 1.5 msec) were recorded in fat sand rats (Psammomys obesus) before and after unilateral labyrinthectomy, plugging of the SCCs in the remaining ear, and bilateral labyrinthectomy. Auditory nerve brainstem evoked responses (ABRs) and VsEPs to angular acceleration impulses (A-VsEPs) were also recorded. Wave amplitudes and latencies were statistically analyzed (MANOVA, repeated t-tests). RESULTS: In the intact animal, the linear VsEPs consisted of 5 to 6 waves, several mV in amplitude, with short latencies. The latency of the first wave was 2.0 msec. These waves were abolished after bilateral labyrinthectomy. Before and after plugging of the SCCs, linear acceleration VsEP wave latencies did not change, although amplitudes were slightly reduced. Similar results were obtained with respect to ABRs recorded from the same ear. Angular acceleration VsEPs were abolished after SCC plugging. CONCLUSIONS: These and other results confirm that the linear VsEPs are compound action potentials of the vestibular pathway, the first wave is the response of the vestibular nerve, and they are initiated mainly in the otolith organs.

Animals↗
PubMed1999

Surgical anatomy of the ear of the fat sand rat.

OBJECTIVE: This study was conducted to investigate and describe the anatomical details of the ear of the fat sand rat (Psammomys obesus). METHODS: Thirty ears (15 in dry skull and 15 in live animals) were dissected with the aid of an operating microscope and microsurgical techniques. Photographs were taken through an operating microscope. RESULTS: The temporal bone of the fat sand rat consists mainly of an unusually large bulla. Three distinct auditory ossicles were visualized and the manubrium of the malleus is relatively long in relation to the size of the ear. Most parts of the inner ear bulge into the bulla cavity and are easily accessible. The cochlea consists of 3.25 turns. The tympanic membrane, facial nerve, stapedial artery, and eustachian tube are described in detail. The large size of the bulla is probably related to the high sensitivity, particularly at low frequencies of the animals ear. CONCLUSION: The fat sand rat was found to be an excellent experimental animal for the investigation of middle and inner ear physiology.

Animals↗
PubMed1999

The effect of head orientation on the vestibular evoked potentials to linear acceleration impulses in rats.

OBJECTIVE: To investigate the influence of linear acceleration impulses delivered when the head is held in different static head orientations, on the first wave of the short latency vestibular evoked potential (VsEP). The first wave is the compound action potential of the primary vestibular neurons synchronously activated. BACKGROUND: It has been shown previously that the VsEP elicited in response to linear acceleration is initiated mainly in the otolith organs. These organs are responsive to both dynamic and static linear forces, including gravity. METHODS: VsEPs to linear acceleration stimuli (4g) were recorded when the rats head was oriented so that a) the plane of the utricular macula was aligned with the plane of the stimulus, b) in supine position and c) with the head pitched up and down in various angles with respect to gravity (stimulus-head spatial relation remained constant) as compared to a reference position. RESULTS: With the stimulus aligned with the plane of the utricular macula, the amplitude of the first wave of the L-VsEPs was significantly larger than in the reference position. In the supine position, the amplitude of the first wave was significantly larger and the latency was significantly shorter. The amplitude of the first VsEP wave tended to be larger in the "head up" orientations as compared to the "head down" orientations (not statistically significant). CONCLUSIONS: These results demonstrate the influence of head position and gravity on the VsEPs to linear acceleration impulses, which is in accordance with their otolithic origin.

Acceleration↗
PubMed1999

Differential effect of the loop diuretic furosemide on short latency auditory and vestibular-evoked potentials.

OBJECTIVE: This study aimed to investigate the differential effect of the loop diuretic furosemide on the auditory and vestibular (otolith) end organs in the same animals simultaneously. DESIGN AND METHODS: Auditory nerve-brain stem-evoked responses (ABR-generated in the cochlea) and short latency vestibular-evoked responses to linear acceleration impulses (L-VsEP-generated in the otolith organs) were recorded from albino Sabra rats both before and at minute intervals after intravenous injections of the loop diuretic furosemide. In some animals, an equal volume of saline was injected to control for the effect of the injection itself. In most animals, more than one injection of saline or furosemide was possible (furosemide, N = 17 injections in 10 rats; saline, N = 18 injections in 9 rats). Peak-to-peak amplitude and peak latency changes in the first wave in each recording (representing end-organ activity) as a function of postinjection time were compared between the two evoked potentials using analysis of variance and repeated t-tests. RESULTS: Saline injections caused only minor changes in the amplitude of the ABR and the L-VsEP. After administration of furosemide, the amplitude of the L-VsEP hardly changed. However, there was a noticeable decrease in the amplitude of the ABR. CONCLUSIONS: Although furosemide has a major depressant effect on cochlear function, vestibular end-organ activity is hardly altered.

Analysis of Variance↗
PubMed1997

Short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses in rats.

In this study, short latency (t < 12.7 ms) vestibular evoked potentials (VsEPs) in response to linear acceleration impulses were recorded in 37 rats. A new technique (based on a solenoid) was used for generating linear force impulses that were delivered to the animal's head. The impulse had a maximal peak acceleration of 12 g. During the impulse, the displacement was 50 microns (at 4 g) and the rise time was 1.0 ms. A stimulation rate of 2/s was usually used. The VsEPs (averaged responses to 128 stimulations, digital filter: 300-1500 Hz) were recorded with electrodes on pinna and vertex, and were composed of 4-6 clear waves with mean amplitudes (for a 4 g stimulus) of 1-5 microV. The VsEPs were resistant to white noise masking, and were significantly suppressed (P < 0.05) following bilateral application of a saturated KCl solution to the inner ear, showing that contributions of the auditory and somatosensory systems are negligible. The latency of the response decreased as a power law function of stimulus magnitude, and the amplitude of the first wave increased as a sigmoid function of stimulus magnitude. VsEP responses were still present at the lowest intensities attainable (0.06-0.4 g) and reached saturation at 9 g. The amplitude of the later components was reduced when stimulus rate was elevated to 20/s. These results suggest that VsEPs in response to linear accelerations are similar in their nature to VsEPs in response to angular acceleration impulses that were previously recorded. These VsEPs to linear accelerations are most likely initiated in the otolith organs.

Acceleration↗
PubMed1997

Contribution of the eighth nerve and cranial nerve nuclei to the short-latency vestibular evoked potentials in cats.

The object of this study was to assess the contributions of the vestibular nerve and various cranial nerve nuclei to the short-latency vestibular evoked potentials in cat. The following nuclei were investigated: vestibular nuclei and the third, sixth, and tenth cranial nerve nuclei. In unilateral labyrinthectomized cats, we performed suboccipital craniectomy and partial cerebellectomy to place bipolar electrodes into the neural structures under investigation. The surface-recorded vestibular evoked potentials (far field) were compared with the potentials recorded intracranially in response to the same acceleration impulses. The exact locations were later confirmed histologically. Reversible lesions also were induced by injection of lidocaine 2%. The results indicate that the first wave of the vestibular evoked potentials originates in the vestibular nerve, and the second wave is mainly generated in the superior and medial vestibular nuclei. The third, sixth, and tenth cranial nerve nuclei apparently contribute to the later waves of the vestibular evoked potentials, particularly waves 3 and 4.

Abducens Nerve↗
PubMed1997

Somatosensory functioning in children with attention deficit hyperactivity disorder.

In order to test the hypothesis that attention deficit hyperactivity disorder (ADHD) is related to deficits in somatosensory processing, 49 ADHD male children and 49 matched controls were tested on a wide range of tactile tasks, and somatosensory evoked potentials (SEP) were also recorded. In addition, parents' and teachers' ratings on the children's typical responses to tactile stimuli were obtained. The results show that the ADHD children were less skilled on suprathreshold, but not on threshold tasks than were the controls. Further, a larger percentage of ADHD children were 'tactile defensive'. Finally, the ADHD children showed larger-than-normal amplitudes of late, but not early components of the SEP. These data suggest that some aspects of somatosensory processing by ADHD children are deficient.

Attention Deficit Disorder with Hyperactivity↗
PubMed1997

Pathophysiological mechanisms of hearing loss.

An understanding of auditory transduction in the ear can contribute to a better comprehension of the pathophysiological mechanisms which give rise to hearing loss. The incoming sound sets up a mechanical traveling wave which begins at the base and progresses along the basilar membrane, reaching a point of maximal displacement. The region of maximal displacement is a function of stimulus frequency. The mechanical displacement, by directly opening ion channels in the stereocilia of the hair cells, induces changes in the electrical potential of the hair cells. This initial stage is called mechano-electrical transduction, and in the normal ear, is followed by a stage of electro-mechanical transduction based on the ability of the outer hair cells to respond to the electrical changes induced in them with a change in their length. This "electromotility" presumably provides mechanical feedback to the basilar membrane, augmenting its mechanical displacement. This is called the cochlear amplifier, providing the ear with improved sensitivity and frequency discrimination. Most forms of sensori-neural hearing losses (affecting the inner ear) are due to a lesion to some part of this cochlear amplifier (e.g. noise induced hearing loss, ototoxic drugs) and are therefore characterized by auditory threshold elevations and poorer frequency discrimination.

Acoustic Stimulation↗