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PubMed2001

Connections between the dorsal raphe nucleus and a hindbrain region consisting of the cochlear nucleus and neighboring structures.

Previous studies have shown that neurons in the raphe nuclei respond to acoustic stimuli. The present study investigated connections between the dorsal raphe nucleus (DRN) and a hindbrain region consisting of the cochlear nucleus (CN) and neighboring structures. A mixture of one or more tracers (cholera toxin B, biotinylated dextran amine (BDA), and 3H-leucine) was injected into the cat DRN. Retrograde-labeling results are presented whereby a new structure, to be called the juxta-acoustico-floccular fascicle (JAFF), is identified. The JAFF is surrounded by the CN, flocculus, lateral cerebellar nucleus, lateral vestibular nucleus, and restiform body. The JAFF is closely associated with the infracerebellar nucleus (ICN). Labeled neurons projecting to the DRN were concentrated in the JAFF, embedded among axons. Less numerous labeled neurons were in the ICN and CN. Anterograde-labeling results are presented showing fibers labeled with BDA or with BDA and 3H-leucine in the CN, cochlear nerve and vestibular nerve, indicating that the DRN projects to these structures. The ascending and descending connections between the DRN and the above hindbrain region may mediate a reflex that may alter the sensitivity of the auditory system in response to biologically salient (e.g. threatening or attractive) stimuli.

Animals↗
PubMed2000

Acoustic evoked response following transection of the eighth nerve in the rat.

OBJECT: The auditory brainstem response (ABR) is the most widely used means of intra-operative monitoring of the integrity of the auditory nerve and brainstem pathways during surgery in the cerebellopontine angle (CPA). Reliability of this and other electrophysiological techniques has been questioned because of persisting potentials in direct nerve recordings despite complete eighth nerve section. The study was designed to assess the extent to which an acoustic evoked response persists after the cochlear nerve is lesioned in the CPA of the adult rat. METHODS: The eighth nerve was exposed microsurgically via a lateral suboccipital approach without damage to surrounding structures. The auditory brainstem response to monaurally presented click stimuli was recorded using needle electrodes and a bandpass of 10 to 5000 Hz. FINDINGS: Complete sharp sectioning of the nerve in the CPA resulted in immediate disappearance of brainstem-generated potentials but persistence of a large primary, vertex-positive wave in all but one case. This response was also abolished in recordings three days later and after emptying the inner ear canal. Provided that the cochlea remained intact, two weeks later a single, vertex-positive potential in the latency range of wave Ia of the ABR reappeared, reaching its peak amplitude six weeks after sectioning of the nerve. CONCLUSIONS: The short-latency electrical potential recorded following damage of the eighth nerve in the cerebellopontine angle can be mistaken for an indication that nerve function is still preserved. The evoked injury potential is probably the major contributor to this potential that resembles wave I of the ABR. Monitoring of functional auditory integrity must neither be limited to early components of the ABR, nor to the electrocochleogram (EcoG) and the peripheral compound nerve action potential (CNAP), respectively.

Action Potentials↗
PubMed1995

Immunohistochemical localization of neurocalcin in the rat inner ear.

Localization in the rat inner ear of neurocalcin, a three EF-hand calcium-binding protein, was examined immunohistochemically. Neurocalcin-like immunoreactivity was restricted to neurons in neuroepithelial receptor organs, while hair cells and supporting cells showed no such immunoreactivity. In the organ of Corti, both afferent and efferent nerve terminals, which formed synapses on both inner and outer hair cells, showed distinct immunoreactions. Spiral ganglion neurons and cochlear nerves were immunopositive. In the cristae ampullaris, macula utriculi and macula sacculi, afferent nerve terminals forming nerve calices or terminal boutons were strongly immunopositive. Efferent nerve terminals making synapses either on nerve calices or on hair cells showed an intense immunoreactivity. Vestibular ganglion neurons were strongly immunopositive. In electron microscopy, immunoreaction products were diffuse in the cytoplasm of ganglion neurons and nerve terminals. Neurocalcin-like immunoreactivity occurred in association with microtubules, outer mitochondrial membranes, synaptic vesicles and synaptic membranes. It is thus likely that neurocalcin is involved in neural functions in each type of afferent and efferent transmission in the inner ear.

Animals↗
PubMed2004

Jugular foramen tumors: diagnosis and treatment.

OBJECT: Jugular foramen tumors are rare skull base lesions that present diagnostic and complex management problems. The purpose of this study was to evaluate a series of patients with jugular foramen tumors who were surgically treated in the past 16 years, and to analyze the surgical technique, complications, and outcomes. METHODS: The authors retrospectively studied 102 patients with jugular foramen tumors treated between January 1987 and May 2004. All patients underwent surgery with a multidisciplinary method combining neurosurgical and ear, nose, and throat techniques. Preoperative embolization was performed for paragangliomas and other highly vascularized lesions. To avoid postoperative cerebrospinal fluid (CSF) leakage and to improve cosmetic results, the surgical defect was reconstructed with specially developed vascularized flaps (temporalis fascia, cervical fascia, sternocleidomastoid muscle, and temporalis muscle). A saphenous graft bypass was used in two patients with tumor infiltrating the internal carotid artery (ICA). Facial nerve reconstruction was performed with grafts of the great auricular nerve or with 12th/seventh cranial nerve anastomosis. Residual malignant and invasive tumors were irradiated after partial removal. The most common tumor was paraganglioma (58 cases), followed by schwannomas (17 cases) and meningiomas (10 cases). Complete excision was possible in 45 patients (77.5%) with paragangliomas and in all patients with schwannomas. The most frequent and also the most dangerous surgical complication was lower cranial nerve deficit. This deficit occurred in 10 patients (10%), but it was transient in four cases. Postoperative facial and cochlear nerve paralysis occurred in eight patients (8%); spontaneous recovery occurred in three of them. In the remaining five patients the facial nerve was reconstructed using great auricular nerve grafts (three cases), sural nerve graft (one case), and hypoglossal/facial nerve anastomosis (one case). Four patients (4%) experienced postoperative CSF leakage, and four (4.2%) died after surgery. Two of them died of aspiration pneumonia complicated with septicemia. Of the remaining two, one died of pulmonary embolism and the other of cerebral hypoxia caused by a large cervical hematoma that led to tracheal deviation. CONCLUSIONS: Paragangliomas are the most common tumors of the jugular foramen region. Surgical management of jugular foramen tumors is complex and difficult. Radical removal of benign jugular foramen tumors is the treatment of choice, may be curative, and is achieved with low mortality and morbidity rates. Larger lesions can be radically excised in one surgical procedure by using a multidisciplinary approach. Reconstruction of the skull base with vascularized myofascial flaps reduces postoperative CSF leaks. Postoperative lower cranial nerves deficits are the most dangerous complication.

Adult↗
PubMed1985

Role of suppressive interactions in the cochlear microphonic response to wide-band clicks.

Cochlear microphonic responses (CM) were recorded from the guinea pig cochlea with conventional differential electrodes implanted in the first and second turns. The CM frequency functions were determined by calculating the Fast Fourier Transform of responses to wide-band clicks. These frequency functions appeared to be dependent upon the spectrum of the click. This effect was interpreted as resulting from suppressive interactions between the various components of the click. It is suggested that such CM interactions are related to corresponding effects reported previously concerning cochlear nerve responses.

Acoustic Stimulation↗
PubMedDate not supplied

Temporal relationship between the auditory brainstem response and focal responses of auditory nerve root and cochlear nucleus during development in the tammar wallaby (Macropus eugenii).

Thirty-two pouch-young tammar wallabies were used to discover the generators of the auditory brainstem response (ABR) during development by the use of simultaneous ABR and focal brainstem recordings. A click response from the auditory nerve root (ANR) in the wallaby was recorded from postnatal day (PND) 101, when no central auditory station was functional, and coincided with the ABR, a simple positive wave. The response of the cochlear nucleus (CN) was detected from PND 110, when the ABR had developed 1 positive and 1 negative peak. The dominant component of the focal ANR response, the N1 wave, coincided with the first half of the ABR P wave, and that of the focal CN response, the N1 wave, coincided with the later two thirds. In older animals, the ANR response coincided with the ABR's N1 wave, while the CN response coincided with the ABR's P2, N2 and P3 waves, with its contribution to the ABR P2 dominant. The protracted development of the marsupial auditory system which facilitated these correlations makes the tammar wallaby a particularly suitable model.

Animals↗
PubMed1972

Neural attenuation of responses to emitted sounds in echolocating rats.

Bats of the family Vespertilionidae enmit strong ultrasonic pulses for echolocation. If such sounds directly stimulate their ears, the detection of echoes from short distances would be impaired. The responses of lateral lemniscal neurons to emitted sounds were found to be much smaller than those to playback sounds, even when the response of the auditory nerve was the same to both types of sounds. Thus, responses to self-vocalized sounds were attenuated between the cochlear nerve and the inferior colliculus. The mean attenuation was 25 decibels. This neural attenuating mechanism is probably a part of the mechanisms for effective echo detection.

Animals↗
PubMedDate not supplied

Cryptococcal meningitis: implications for the otologist.

Cryptococcal meningitis can present to the otologist with hearing loss and vestibular dysfunction. A man with cryptococcal meningitis presenting with bilateral profound sensorineural hearing loss and vestibular dysfunction is described. The difficulty in arriving at the diagnosis and consequences of misdiagnosis are discussed. Histological and clinical studies suggest that the cochlear nerve is likely to be damaged in patients who have deafness associated with this disease. Retrocochlear damage may result in cochlear implantation having a poor outcome.

Acute Disease↗
PubMed1999

Magnetic resonance cisternography using the fast spin echo method for the evaluation of vestibular schwannoma.

Neuroimaging of vestibular schwannoma was performed with the fat-suppression spoiled gradient recalled acquisition in the steady state (SPGR) method and magnetic resonance (MR) cisternography, which is a fast spin echo method using a long echo train length, for the preoperative evaluation of the lateral extension of the tumor in the internal auditory canal, and the anatomical identification of the posterior semicircular canal and the nerves in the canal distal to the tumor. The SPGR method overestimated the lateral extension in eight cases, probably because of enhancement of the nerves adjacent to the tumor in the canal. The posterior semicircular canal could not be clearly identified, and the cranial nerves in the canal were shown only as a nerve bundle. In contrast, MR cisternography showed clear images of the lateral extension of the tumor and the facial and cochlear nerves adjacent to the tumor in the internal auditory canal. The anatomical location of the posterior semicircular canal was also clearly shown. These preoperative findings are very useful to plan the extent to which the internal auditory canal can be opened, and for intraoperative identification of the nerves in the canal. MR cisternography is less invasive since no contrast material or radiation is required, as with thin-slice high-resolution computed tomography (CT). MR cisternography should replace high-resolution CT for the preoperative neuroradiological evaluation of vestibular schwannoma.

Adult↗
PubMed2000

[Results and experiences with 55 cochlear implantations].

INTRODUCTION: The etiology of deafness in deaf people is defects in the cochlea hair cells. Cochlear implant treatment gives deaf born and patients with acquired deafness the possibility to reestablish or obtain hearing by electric stimulation of the cochlear nerve. In this paper the results of treatment of 35 adults and 20 children are reported. METHOD: The candidates for cochlear implant treatment are extensively investigated before the decision is made to operate. The operative treatment takes place under general anaesthesia and the operative technique is outlined. In the treatment of the deaf, different types of implants and stimulation strategies have been used. The effect of treatment is considered by hearing test and evaluation of speech. RESULTS: Nine of the adults obtained a hearing quality that made using a telephone possible. Almost all adults can by the combination of cochlear implant and lip reading perform a normal conversation. The results in the deaf born children are obtained slowly as the deaf born have to develop hearing and speech from zero. All the treated children have improved possibilities of communication. DISCUSSION: Cochlear implant treatment of deaf people now seems well established both internationally and nationally in Denmark. Cochlear implant equipment has improved considerably throughout the past years and that it today is possible to establish hearing in deaf born or patients with acquired deafness can be considered as one of the greatest developments in otology, maybe the greatest.

Adolescent↗
PubMed1997

Implication of NMDA type glutamate receptors in neural regeneration and neoformation of synapses after excitotoxic injury in the guinea pig cochlea.

In the adult mammalian cochlea, the ability of nerve fibres to regenerate has been observed following disruption of the organ of Corti by various means, or transsection of the cochlear nerve in the internal auditory meatus. Based upon the implication of glutamate as a neurotransmitter at synapses between sensory hair cells and terminal dendrites of the auditory nerve in the mammalian cochlea, we have developed, in a previous study, an in vivo model of neural regeneration and formation of synapses after the destruction of the afferent nerve endings by local application of the glutamate agonist alpha-amino-3-hydroxy-5-methyl-isoxazol-propionic acid (AMPA). In situ hybridization experiments performed during the re-innervation process revealed an overexpression of mRNA coding for NR1 subunit of N-methyl-D-aspartate (NMDA) receptors in the spiral ganglion neurons, suggesting that these receptors are implicated in neural regenerative processes. The present study has been designed to study the functional implication of NMDA receptors in the regrowth and synaptic repair of auditory dendrites in the guinea pig cochlea, by blocking the NMDA receptors during the period of normal functional recovery. In a first set of experiments, we recorded compound action potential after acute perilymphatic perfusion of cumulative doses (0.03-10mM) of DL 2-amino-5-phosphonovalerate (D-AP5), a NMDA antagonist, to determine the efficiency of the drug. In a second set of experiments, the auditory dendrites were destroyed by local application of the glutamate agonist AMPA. The blockage of NMDA by the antagonist D-AP5 applied with an osmotic micropump delayed the functional recovery and the regrowth of auditory dendrites. The findings of our study support the hypothesis that, in addition to acting as a fast transmitter, glutamate has a neurotrophic role via the activation of NMDA receptors.

2-Amino-5-phosphonovalerate↗
PubMed2004

Cavernous haemangioma of the internal auditory canal: a case report.

We report a patient with a cavernous haemangioma of the internal auditory canal (IAC). A 47-year-old man presented with a left profound hearing loss and a left facial palsy that had progressed over 5 years. With a preoperative diagnosis of acoustic or facial nerve neurinoma, the tumour was removed totally by a translabyrinthine approach. Intraoperatively, the tumour appeared red; it compressed the facial and cochlear nerves, and adhered to the vestibular nerve. The tumour was diagnosed as a cavernous haemangioma upon histologic and immunohistochemical examination. No recurrence of tumour occurred, but hearing loss and left facial palsy persisted. Although cavernous haemangiomas of the IAC is found in small size less than 10 mm, they often cause severe hearing loss and facial palsy. Our patient had no improvement of facial palsy, but many reports describe recovery of facial nerve function.

Ear Canal↗
PubMed1998

Hearing restoration in posterior fossa tumors.

OBJECTIVE: This study aimed to assess the results of hearing restoration with a cochlear or a brainstem implant in posterior fossa tumors. PATIENTS: Six patients were selected. Two patients with an acoustic neuroma in the only-hearing ear (cases 1 and 2), one patient with a posterior fossa meningioma (case 3), one patient with bilateral facial neuroma (case 4), and two patients with bilateral acoustic neuroma (cases 5 and 6) participated. INTERVENTION: In cases 1 and 2, the patients had a cochlear implant inserted on the only-hearing ear opposite the acoustic neuroma. In case 3, the patient presented with total deafness on the left side and a 10-mm meningioma on the right side. A cochlear implantation was performed after removal of the meningioma on the right side. In case 4, the patient was operated on on both sides with bilateral postoperative deafness. A cochlear implantation was performed on the better hearing ear. In cases 5 and 6, patients underwent an auditory brainstem implantation after the exeresis of the second tumor. RESULTS: Promontory test results were positive for patients 1, 2, 3, and 4. After implantation, patients 1, 2, 3, and 4 scored 98%, 13%, 70%, and 30%, respectively, in open-set sentence recognition tests, whereas patients 5 and 6 scored 0% and 20%, respectively. CONCLUSIONS: In case of nonfunctional cochlear nerve, in acoustic neuroma, either bilateral and in the only-hearing ear, promontory test should be performed. If positive results, a cochlear implantation should be performed, because successful results could be expected. Overall results of cochlear implantation on speech discrimination are better than those obtained with a brainstem implant.

Adolescent↗
PubMedDate not supplied

Four variations of the Mondini inner ear malformations as seen in microdissections.

Four variations and degrees of severity of the Mondini malformation were found in the temporal bones from two neonates, one with congenital heart disease and the other with trisomy D, and from one teenager with leukemia: 1) short cochlea and normal vestibular organs; 2) short cochlea and persistent horizontal canal anlage; 3) markedly shortened cochlea with no modiolus, wide internal auditory meatus, and persistent horizontal canal anlage; 4) same as variation 3, but with persistent anlagen in all semicircular canals. Variations 3 and 4 were from the case of trisomy D, in which the left cochlea had a normal hair cell population but few nerve fibers, and the intraganglionic spiral bundle was displaced from Rosenthal's canal to the osseous spiral lamina. The right ear had no cochlear nerve fibers; the organ of Corti was present, but hair cells were unusually small. In the case of trisomy D, both ears showed subtotal loss of vestibular nerve fibers. Although the rudimentary cristae of the right ear had numerous hair cells, the macular hair cells were fewer and malformed. No hydrops was present.

Adolescent↗
PubMed1996

[Acoustic neurinoma located exclusively in cerebellopontine angle cistern ("cisternal" acoustic neurinoma): a case report].

This is a case report of acoustic neurinoma which was located exclusively in the cerebellopontine angle (CPA) cistern and which did not extend into the internal auditory meatus ("cisternal" acoustic neurinoma). The 43-year-old female patient had signs of the left trigeminal nerve impairment including left face neuralgia. However, she did not have any neurootological symptom. No abnormal bony changes in the internal auditory meatus (IAM) were found by high-resolution bone-window CT. MRI showed a left CPA tumor of 25mm not extending into the IAM. The tumor was totally removed by the lateral suboccipital approach. It originated from the vestibular nerve medial to the porus acusticus and was located exclusively in the CPA cistern. No tumor extension into the IAM was confirmed. The cochlear nerve was involved in the tumor capsule and could not be preserved. The pathological diagnosis was that it was a neurilemmoma. Early diagnosis of "cisternal" acoustic neurinoma is difficult because it does not show neurootological symptoms in the early stage. The lateral suboccipital approach is appropriate for the removal of a "cisternal" acoustic neurinoma. However, in spite of the good preoperative hearing, the preservation of hearing is difficult because of the large tumor size.

Cerebellar Neoplasms↗
PubMed1995

Spontaneous activity and frequency selectivity of acoustically responsive vestibular afferents in the cat.

1. Recordings were made from single afferent fibers in the inferior vestibular nerve. Firing rates of a substantial portion of the afferents with irregular background activity increased in response to moderately intense tone bursts. 2. Spontaneous activity from acoustically responsive vestibular afferents was statistically analyzed and compared with data from a more widespread sampling of primary afferents in the cat's vestibulocochlear nerve. Acoustically responsive vestibular afferents had interspike interval histograms with modes > 10 ms, coefficients of variation > 0.15, and skews > 0.88. On the basis of spontaneous activity, these afferents were easily distinguishable from cochlear afferents and regular vestibular afferents, but no obvious features differentiated them from other irregular vestibular afferents. 3. The distributions of spike intervals in the spontaneous activity of acoustically responsive vestibular afferents were fitted by Erlang probability density functions describing the second-order interarrival times of a Poisson process initiated after a finite delay (refractory period). 4. Acoustically responsive vestibular afferents had broad, V-shaped tuning curves with best frequencies between 500 and 1,000 Hz, thresholds of > or = 90 dB SPL, and shapes comparable with the tuning-curve "tails" of cochlear afferents. In contrast to cochlear-nerve afferents, acoustically responsive vestibular afferents did not show a strong relationship between spontaneous rate and threshold. 5. We compare the acoustic frequency selectivity of vestibular and cochlear afferents in terms of their functional and evolutionary relationships. Our data and those of others indicate that acoustically responsive vestibular afferents are likely to provide an input to the acoustic activation of the sternocleidomastoid muscle in humans, and they may provide an input to other acoustic reflexes such as the middle-ear-muscle reflexes.

Acoustic Stimulation↗
PubMed1990

Salicylate, mefenamate, meclofenamate, and quinine on cochlear potentials.

The perilymphatic spaces of guinea pig cochleae were perfused with artificial perilymph, with and without drug, at a rate of 2.5 microliters/minute for 10 minutes. The compound action potential of the auditory nerve, cochlear microphonics, and the summating potential evoked by 10 kHz tone bursts of varying intensities were recorded from a wire inserted in the basal turn scala vestibuli. The endocochlear potential was recorded from the scala media. Sodium salicylate (1.25 to 10 mmol/L) reduced the magnitude of the compound action potential evoked by low-sound intensities without affecting the compound action potential evoked by high-sound intensities. Sodium salicylate also reduced cochlear microphonics and had no effect on summating potential. Cochlear perfusions of prostaglandin synthesis inhibitors, mefenamate (200 mumol/L), and meclofenamate (200 mumol/L), had no effect on the cochlear potentials. Quinine (10 to 100 mumol/L) reduced the compound action potential input-output function in a parallel fashion rather than selectively affecting the low-intensity compound action potential. Quinine (100 mumol/L) reduced cochlear microphonics and summating potential. Neither quinine (100 mumol/L) nor salicylate (5 mmol/L) affected endocochlear potential. These results suggest that salicylate-induced hearing loss is not caused by either antagonism of the hair cell transmitter or cyclooxygenase inhibition, nor is it caused by the same mechanism that causes quinine-induced hearing loss.

Acetates↗