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Biomedical subjects

T Murofushi

Publications and source records attributed to T Murofushi.

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

Auditory brainstem responses, electrocochleograms, and cochlear microphonics in the myelin deficient mutant hamster 'bt'.

Electrophysiological studies of the auditory pathway were performed on the mutant hamster 'bt' which is known to have myelin deficiencies in the central nervous system. Auditory brainstem responses (ABRs), electrocochleograms (EcochGs), and cochlear microphonics (CMs) were recorded. ABRs in 'bt' demonstrated markedly transformed waveforms with significantly prolonged latencies. EcochG in 'bt' showed significantly prolonged N1 latencies of the compound action potentials (CAPs) while 'bt' showed normal CMs. The myelin deficient mutant hamster 'bt' may have myelin deficiencies not only in the brainstem auditory pathway but also in the cochlear nerve.

Animals↗
PubMed1999

Tone burst-evoked myogenic potentials in human neck flexor and extensor.

Vestibular evoked myogenic potential (VEMP) has been proposed to be a manifestation of sacculocollic reflex. In a recent study using intracellular recording from neck flexor and extensor motoneurons, the neuronal connections and pathways underlying sacculocollic reflexes were determined in cats. The results showed that sacculocollic reflex displayed inhibitory connection to bilateral neck flexors and excitatory connection to bilateral neck extensors. A total of 16 normal young adults were tested with bilateral recordings of sternocleidomastoid (SCM) and splenius capitis (SC) muscles by acoustic stimulus of 500 Hz short tone burst. The results revealed that polarity of the wave I/II of VEMP on SC was the reverse of that on SCM. This implied that VEMP from ipsilateral SCM showed inhibitory neural activity; whereas VEMP from ipsilateral SC was an excitatory response. Using this non-invasive technique, the sacculocollic reflexes in human neck flexor and extensor were studied. The results in humans were consistent with the previous findings in cats.

Acoustic Stimulation↗
PubMed1999

The effect of click repetition rate on vestibular evoked myogenic potential.

Vestibular evoked myogenic potentials (VEMPs) generated by click stimulation and recorded on the sternocleidomastoid muscle have been used as a test of vestibular reflexes. Various parameters of the stimulus and recording setting have been studied. However, the influence of stimulation repetition rate of VEMPs and the most optimal stimulation rate for clinical use have not yet been defined. Each ear of 12 normal adults was tested at five different click stimulation rates (1 Hz, 5 Hz, 10 Hz, 15 Hz and 20 Hz) in random order. VEMP responses were evident in all 24 ears stimulated with 1 Hz, 5 Hz and 10 Hz. One ear was void of response at 15 Hz stimulation and nine ears at 20 Hz stimulation. The relative amplitude or the rank of amplitude in individual ears was higher at 1 Hz and 5 Hz stimulation, progressively decreasing as the stimulation rate increased. Comparisons of p13 and n23 latencies showed no difference among five stimulation rates, but variance was greatest at 20 Hz stimulation and smallest at 1 Hz. VEMPs generated at lower stimulation repetition rate seemed to be more marked and constant. However, with regard to examination time and patient compliance, a 5 Hz stimulus is advisable if both short examination time and higher signal/noise ratio are required.

Acoustic Stimulation↗
PubMed1998

Vestibular evoked myogenic potentials in patients with acoustic neuromas.

BACKGROUND: To diagnose acoustic neuromas (ANs), the auditory brainstem response test and the caloric test have been used in addition to magnetic resonance imaging. The auditory brainstem response and the caloric tests mainly reflect functions of the auditory pathway, ie, the cochlear nerve and the superior vestibular nerve, respectively. Because the vestibular evoked myogenic potential (VEMP) has been thought to originate in the inferior vestibular nerve, we hypothesized that the VEMP could provide different information from the auditory brainstem response and the caloric test and that it could be helpful in diagnosing ANs. In other words, we hypothesized that the VEMP could provide information concerning inferior vestibular nerve involvement in patients with ANs. OBJECTIVE: To find out if the VEMP could be useful in classifying ANs according to the involved nerves. DESIGN: We reviewed preoperative clinical tests, including VEMPs, in 21 patients (8 men, 13 women) with ANs confirmed surgically and histopathologically, comparing them with VEMPs in 8 normal subjects (5 men, 3 women). RESULTS: Whereas the first positive-negative peak of the VEMP, P13-N23, was ipsilaterally present on stimulation of the unaffected side in all patients with ANs and both sides in all normal subjects, it was absent on the affected side in 15 patients (71%) and significantly decreased in amplitude in 2 patients (9%). Thus, 17 (80%) of the 21 patients showed abnormal VEMPs. Three patients had abnormal VEMPs although they had normal caloric responses. Three patients had abnormal caloric responses although they had normal VEMPs. CONCLUSION: These results suggest that the VEMP could be useful for the diagnosis of AN, especially for classifying ANs according to the involved nerves.

Adult↗
PubMed1997

Vestibular abnormalities in charge association.

We report the vestibular abnormalities in 5 patients with the CHARGE association (Coloboma, Heart disease, Atresia of choanae, Retarded growth and development and/or central nervous system anomalies, Genital hypoplasia, and Ear anomalies). All patients had absent vestibular function as indicated by absent vestibulo-ocular reflexes and severe imbalance on simultaneous deprivation of proprioception and vision, as well as delayed motor development. All 6 semicircular canals were aplastic in each of the patients. While cochlear function was severely reduced in 6 of the 10 ears, it was absent only in 3 ears and was actually intact below 3 kHz in 1 ear. All 10 bony cochleas were present on computed tomography, and although 7 appeared abnormal, 3 appeared normal. This study confirms that absence of the bony semicircular canals in the presence of a bony cochlea is a characteristic finding in CHARGE association. It also demonstrates that these disproportionate structural abnormalities are reflected in the functional abnormalities: absent vestibular function with preservation of some cochlear function.

Adolescent↗
PubMed1997

Physiological and anatomical study of click-sensitive primary vestibular afferents in the guinea pig.

We studied the sensitivity of primary vestibular afferents in anaesthetised guinea pigs to clicks. These vestibular neurons were also tested by their response to pitch and roll tilts and yaw-axis angular acceleration. The click intensity was referred to the threshold for evoking the auditory brainstem responses. Recording sites in the vestibular nerve were confirmed histologically using iontophoretic injection of FCF green dye. To confirm the site of labyrinthine origin of the click-sensitive neurons, we used retrograde tracing with biocytin. In all, 647 out of 2354 neurons in the vestibular nerves of 51 guinea pigs were activated by clicks. Most were irregularly discharging primary neurons, but some were regularly discharging. We studied responses to vestibular stimuli in 188 click-sensitive neurons. Of these, 86% responded to pitch and/or roll tilt, but none responded to yaw angular acceleration. Conversely we also recorded vestibular neurons which did not respond to clicks. None of 300 neurons sensitive to yaw angular acceleration were responsive to 80-90 dB SL clicks (0 dB SL = threshold for auditory brainstem response to clicks). The latencies of click-evoked action potentials of neurons in the vestibular nerve were very short (mean +/- SD = 0.82 +/- 0.22 ms). Changing click polarity caused a heterogeneous pattern of latency change. Thresholds for evoking spikes in primary vestibular neurons were high (62.0 +/- 12.2 dB SL, range 30-90 dB, n = 371). Retrograde tracing of the origin of the click-sensitive afferents using extracellular biocytin showed that most neurons originated in the medial (striola area) of the saccular macula.

Acoustic Stimulation↗
PubMed1997

Intratympanic gentamicin in Ménière's disease: results of therapy.

To define better the benefits and risks of intratympanic gentamicin injection treatment of intractable vertigo or drop attacks due to Ménière's disease, we reviewed the charts of 18 patients whom we have now observed for > 1 year after having completed this mode of therapy. There were nine women and nine men aged 29-81 years; all had poor hearing in the affected ear. Of the 18 patients, 14 have had no further vertigo or drop attacks (11 patients after a single set of three to five injections, another three after a further set of one to five injections). The treatment could be effective even if it did not abolish caloric responses from the treated ear, even if it did not produce an acute vestibular deafferentation syndrome afterwards, and even after a failed vestibular nerve section. After treatment, five of the 18 patients developed oscillopsia and ataxia--symptoms and signs of (presumably permanent) chronic vestibular insufficiency; this proportion is not obviously lower than that after vestibular neurectomy or surgical labyrinthectomy. Of the 18 patients, 12 showed no change in the 1-kHz threshold and 13 showed no change in the 4-kHz threshold. When hearing did deteriorate, the threshold rose by more than 30 dB at 1 kHz in four patients and at 4 kHz in six patients. We conclude and confirm that intratympanic gentamicin injections are a convenient and, in most cases, effective and safe treatment for intractable vertigo or drop attacks due to Ménière's disease.

Adult↗
PubMed1996

Absent vestibular evoked myogenic potentials in vestibular neurolabyrinthitis. An indicator of inferior vestibular nerve involvement?

BACKGROUND: Benign paroxysmal positioning vertigo (BPPV) is generally thought to be caused by canalolithiasis in the posterior semicircular canal, an organ that is innervated by the inferior vestibular nerve. We hypothesized that absent vestibular evoked myogenic potentials (VEMPs) would indicate involvement of the inferior vestibular nerve and that posterior semicircular canal-type BPPV could not develop after vestibular neurolabyrinthitis (VNL) in patients with absent VEMPs. OBJECTIVE: To find out if VEMPs could be helpful in evaluating involvement of the inferior vestibular nerve in acute VNL. DESIGN: We reviewed the VEMP findings in 47 patients (34 men and 13 women) with acute VNL, 10 of whom had then developed posterior semicircular canal-type BPPV. RESULTS: While p13-n23, the first positive-negative peak of the VEMP, was ipsilaterally present on stimulation of the unaffected side in all patients, it was absent on the affected side in 16 patients (34%). The absence or presence of p13-n23 was independent of the results of caloric tests, pure tone audiometry, and auditory brain-stem responses. Typical posterior semicircular canal BPPV developed in 10 of the 47 patients after the acute attack of VNL, always on the same side as the neurolabyrinthitis. The p13-n23 potentials were preserved on stimulation of the affected ear in all 10 patients with BPPV. CONCLUSIONS: These results suggest that if VEMPs are absent from an ear that has suffered acute VNL, then posterior semicircular canal BPPV is unlikely to develop as a consequence of the VNL. The reason for this appears to be that the absence of VEMPs is due to involvement of the inferior vestibular nerve or involvement of the structures that it innervates.

Acoustic Stimulation↗
PubMed1996

Response of guinea pig vestibular nucleus neurons to clicks.

Responses of single neurons in the vestibular nuclei to clicks were studied by extracellular recording in anaesthetised guinea pigs. Eighty-four neurons in the ipsilateral vestibular nuclei were activated with an average latency of 1.75 +/- 0.30 ms, which is about 0.9 ms longer than the mean latency of activation of click-sensitive vestibular afferents to intense clicks. The threshold of clicks for evoking the response of these neurons was around 70 dB above the auditory brainstem response threshold. Earlier studies have indicated that click-sensitive vestibular afferents are tilt-sensitive and likely to originate from saccular receptors, and in the present study nine of the click-sensitive vestibular nucleus neurons were tilt-sensitive, suggesting that these central neurons receive monosynaptic input from the corresponding saccular afferents. Recording sites were marked by means of iontophoretic injection of FCF green dye; they were located in the lateral portion of the descending vestibular nucleus and the caudal and ventral regions of the lateral vestibular nucleus.

Acoustic Stimulation↗
PubMed1996

Pediatric brain stem gliomas with the predominant symptom of sleep apnea.

Two children complaining of sleep apnea presented with brain stem gliomas. In the early stage of their illness, neurological disorders were too subtle to be recognized as significant by the physicians or to be noted by the parents. Case 1 experienced an episode of unsteady gait and weakness in the bilateral arms, at the age of 5. When it recurred after 7 years of remission, the predominant symptom was sleep apnea. Case 2 exhibited nasality of speech as the earliest sign of this illness very early in his life, presumably 5 years before the diagnosis of brain stem glioma. A slight sleep apnea which developed afterwards did not draw attention of the physicians because no neurological signs other than paralyses of the bilateral soft palates were present. MRIs of the both cases revealed diffuse, infiltrating lesions in the pons, the medulla oblongata and the upper cervical spinal cord. Both cases shared some features: (1) diagnostic delay of several years from the first symptom; (2) the main lesion in the medulla oblongata, where important structures for respiratory control are identified; (3) infiltrative growth patterns in the MRI of the tumor, which might account for the uncommon clinical courses.

Blood Gas Analysis↗
PubMed1996

Lack of effect of vancomycin and gentamicin on auditory function in guinea pigs.

The dispositions of vancomycin (VCM) and gentamicin (GM) in plasma and perilymph after single and multiple administrations and the effects of multiple administrations of VCM or GM alone and the combination of both drugs on auditory function were studied in male guinea pigs. The pharmacokinetic parameters of VCM and GM obtained from plasma drug concentration-time data after single and multiple (22 days) intramuscular administrations of VCM (200 mg/kg of body weight) alone and GM (50 mg/kg) alone were not significantly different from those after combined administration of VCM (200 mg/kg) and GM (50 mg/kg). There was no change in the penetration ratio of VCM and GM into perilymph between administration of VCM or GM alone and the combination of both drugs. Furthermore, the hearing threshold of guinea pigs was not affected by VCM or GM alone or the combination of both drugs within the range of therapeutic VCM and GM levels in plasma in humans.

Animals↗
PubMed1995

Responses of guinea pig primary vestibular neurons to clicks.

Responses of single neurons in the vestibular nerve to high-intensity clicks were studied by extracellular recording in anaesthetised guinea pigs. One hundred and two neurons in the posterior division of the superior branch or in the inferior branch of the vestibular nerve were activated at short latency by intense clicks. The latency of activation was short (median 0.9 ms) and the threshold was high: the click intensity for evoking the response of these cells was around 60 dB above the auditory brainstem response threshold. Animals were tilted and rotated to identify physiologically the sensory region of the labyrinth from which the activated neurons originated. Seventeen neurons responded to static tilt as well as clicks. These results show that vestibular receptors, probably the otoliths, respond to clicks at intensities corresponding to those used in a new clinical test of the vestibulo-collic pathway.

Acoustic Stimulation↗
PubMed1995

Neuro-otological and neuropathological findings in two cases with Machado-Joseph disease.

We report chronological changes of neuro-otological findings and associated neuropathological findings in 2 patients. Concerning gaze limitation, upward gaze was primarily disturbed, followed by downward gaze and abduction. Adduction tended to be preserved although convergence was disturbed at the early stage. And, upward gaze limitation was followed by loss of oculocephalic responses (OCRs). Bell's phenomenon was preserved until the late stage of the disease. Caloric nystagmus was absent at the early stage. One patient showed dissociation between nystagmus and vestibulo-collic reflex in the caloric test at the early stage of the disease. Neuropathological examination revealed gliosis in the interstitial nucleus of Cajal and the MLF as well as neuronal loss and gliosis in the oculomotor nuclei. The vestibular nuclei also showed gliosis and atrophy of nerve cells.

Brain Stem↗
PubMed1994

Temporary latency shifts in auditory evoked potentials by injection of lidocaine in the rat.

Temporary latency shifts in auditory evoked potentials by intravenous injection of lidocaine were investigated in albino rats. Auditory brainstem responses (ABR) were recorded with 4000Hz short tone bursts. There was no significant difference of latencies in wave Pl of the ABR between drug-administered group (6 mg/kg body weight of lidocaine) and control group (0.6 ml/kg of 0.9% saline). As for waves P2. P3 and P4 of ABR, the latencies of the waves were significantly prolonged after the lidocaine injection (p < 0.05. U-test). The prolongation of latency of wave P4 was the most prominent in the fast waves and dependent on the dose of lidocaine. The latencies of the slow positive wave of the evoked potentials on the inferior colliculus (wave S) with clicks and the slow positive wave (wave P) and the negative wave following ABR (wave NA) with 4000Hz short tone bursts were also studied. The latencies of waves S. P and NA showed significant temporal prolongation (p < 0.05, U-test) after lidocaine injection. The present study revealed that a relatively small dose of lidocaine can cause temporary prolongation of latencies of auditory evoked potentials not only in the fast components but also in the slow components including wave NA which is a large slow negative wave following the ABR. The effects are considered to be caused by the action of lidocaine which reduces the excitabilities on the auditory nervous system.

Acoustic Stimulation↗
PubMed1994

Morphological changes in the tectorial and basilar membranes of aged rats.

Using both light and transmission electron microscopy presbycusic degeneration of the cochlea was observed in particular in the tectorial and basilar membranes, in naturally aged rats. These animals showed a descending auditory pattern as determined by auditory brainstem response. Ultrastructurally, the number of collagen fibers in the tectorial membrane was reduced and straight type A fibers were increased relative to branched, coiled type B fibers. The basilar membrane in the basal turn was also thickened by an increased homogeneous ground substance. These findings indicate that the specificity of vibration of the tectorial and basal membranes is very different in aged and young rats.

Aging↗
PubMed1994

Postcaloric nystagmus by positional change. 1. Study in normal subjects.

We investigated the postcaloric nystagmus related to positional change. Twenty-two healthy subjects were examined (experiment 1). A caloric test was carried out in the supine position. Following the cessation of the primary phase, the subject was reoriented to the upright position. An additional 10 subjects were also examined with other positional changes (experiment 2): following the cessation of the primary phase, the subject was reoriented to the lateral positions, irrigated-ear-up and irrigated-ear-down positions. As a control study, 6 subjects were examined without positional change (experiment 3). In 37 (84%) ears, postcaloric nystagmus was observed in the upright position. Furthermore, in 12 of 20 (60%) ears in the irrigated-ear-up position and in 13 of 20 (65%) ears in the irrigated-ear-down position, the horizontal component of postcaloric nystagmus was observed. Without positional change, no postcaloric nystagmus was observed. These findings indicate that caloric nystagmus is modified by an adaptive process and that postcaloric nystagmus as it relates to positional change might be attributed mainly to the vestibular adaptation.

Adolescent↗