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PubMed1979

Ultrastructural changes of the nerve elements following disruption of the organ of Corti. II. Nerve elements outside the organ of Corti.

Various stages of changes in the nerve fibers, spiral ganglion cells, and satellite cells from the guinea pig cochlea 3 to 137 days after perilymphatic perfusion with streptomycin solution (2 and 20%) were observed electron microscopically. Initially, the axoplasms of the cochlear nerve fibers became swollen or pyknotic. Then, the axons disappeared and myelin lamellae disrupted. The Schwann cells shrank and degenerated, though their basement membranes survived for a time. Regeneration of the cochlear nerve fibers began with extension of axonal sprouts into the tube of the basement membrane and surviving Schwann cells, which still contained myelin debris. Only one of the axonal sprouts matured for myelination. These regenerating cochlear nerve fibers were found in the osseous spiral lamina, modiolus and internal auditory meatus, but these fibers atrophied and disappeared afterward. Retrograde degeneration occurred in the olivo-cochlear bundle. Some of the efferent myelinated fibers also showed temporary regeneration.

Animals↗

PubMed2005

Cell transplantation to the auditory nerve and cochlear duct.

We have developed a technique to deliver cells to the inner ear without injuring the membranes that seal the endolymphatic and perilymphatic chambers. The integrity of these membranes is essential for normal hearing, and the technique should significantly reduce surgical trauma during cell transplantation. Embryonic stem cells transplanted at the internal auditory meatal portion of an atrophic auditory nerve migrated extensively along it. Four-five weeks after transplantation, the cells were found not only throughout the auditory nerve, but also in Rosenthal's canal and the scala media, the most distal portion of the auditory nervous system where the hair cells reside. Migration of the transplanted cells was more extensive following damage to the auditory nerve. In the undamaged nerve, migration was more limited, but the cells showed more signs of neuronal differentiation. This highlights an important balance between tissue damage and the potential for repair.

Animals↗

PubMed1981

Animal models of tinnitus.

There are few physiological data available on the origin and nature of tinnitus. It is not even known whether tinnitus associated with cochlear pathology is a manifestation of increased or decreased activity in the cochlear nerve. In previous investigations of cochlear pathology, the spontaneous neural activity has generally been found to be depressed. In the present experiments, an animal model has been established by the administration of sodium salicylate in doses producing blood concentrations that evoke tinnitus in humans. Under these conditions, changes occur in cochlear nerve-fibre thresholds and tuning, similar to those obtained in other types of cochlear pathology. However, under salicylate, the distribution of spontaneous discharge shifts significantly to higher rates than normal. These changes are accompanied in some, but not all, fibres by changes in the temporal patterns of discharge suggestive of excitation. In the second animal model studied, a normal guinea-pig that had a naturally occurring continuous tonal emission, analogous to that recently recorded in human "physiological" tinnitus, was investigated in detail. The emitted signal was recorded in the ear-canal acoustic pressure and in the round-window potential. Several lines of evidence point to the signal as being cochlear in origin, including: its resistance to muscular paralysis and section of the stapedius muscle; the effects of changes in middle-ear pressure; its reversible elimination by hypoxia; and its suppression by tones of higher frequency.

Acoustic Stimulation↗

PubMed2000

Cochlear fossa enhancement at MR evaluation of vestibular Schwannoma: correlation with success at hearing-preservation surgery.

PURPOSE: To describe a sign in magnetic resonance (MR) imaging that could reflect the state of the cochlear nerve before hearing-preservation surgery in small vestibular schwannomas. MATERIALS AND METHODS: Thirty-one patients with serviceable hearing underwent 1.5-T MR imaging before hearing-preservation surgery. The presence of cochlear fossa enhancement on T1-weighted spin-echo images obtained after the administration of contrast material was compared with the results of hearing-preservation surgery. RESULTS: Cochlear fossa enhancement was present in 13 patients, and all of them had total hearing loss after surgery. There was no cochlear fossa enhancement in 18 patients; 15 maintained serviceable hearing after surgery, and three had postoperative hearing loss with no serviceable hearing (sensitivity, 81%; specificity, 100%). CONCLUSION: Cochlear fossa enhancement on T1-weighted spin-echo images seems to be a reliable sign for analyzing the state of the cochlear nerve. The absence of cochlear fossa enhancement could become an additional criterion for selecting the surgical approach in vestibular schwannomas.

Adult↗

PubMed2005

An anatomical study of the vestibulocochlear anastomosis (anastomosis of Oort) in humans: preliminary results.

Von Oort first described the vestibulocochlear anastomosis in 1918, and there have been very few anatomical studies of it. It is located at the bottom of the internal auditory meatus and links the saccular nerve to the cochlear nerve. The aim of this study was to investigate the micro-anatomical characteristics of this anastomosis. We dissected 10 human temporal bones from five heads. We found the vestibulocochlear anastomosis in seven of the specimens, of which six were clearly visible. We were unable to uncover it in three specimens due to dissection problems. Its length was evaluated to be between 0.5 and 1 mm, with a diameter of 0.5 mm. The vestibulocochlear anastomosis could be the pathway for the nerve fibers of the cochlear efferent system, whose description remains incomplete. However, no anatomist, histologist or physiologist has demonstrated this function. From the results of this study, it seems likely that the vestibulocochlear anastomosis exists. Other studies are necessary to link it to the efferent system.

Aged↗

PubMed1986

Hearing preservation after acoustic neuroma surgery with intraoperative direct eighth cranial nerve monitoring: Part II. A classification of results.

Since the advent of brainstem auditory evoked response audiometry and computerized tomography, small acoustic neuromas are more frequently found. Often the patient has serviceable hearing, which we would like to preserve during complete tumor removal. Since 1978, sixteen patients with acoustic neuromas have been operated upon through the retrosigmoid suboccipital approach, with the goal of hearing preservation. In 1983, we began using intraoperative direct eighth nerve monitoring, which produced a rapid assessment of cochlear nerve function during the excision of small acoustic neuromas. The tumors varied in size from intracanalicular lesions to one lesion with a 3.0 cm protrusion medial to the porus acousticus. In eight of sixteen cases, intraoperative monitoring was used, and in four of the patients hearing was preserved. In eight cases, intraoperative monitoring was not used, and hearing was preserved in only two patients. The overall success rate--in total tumor removal with hearing preservation--was 37%. Hearing was preserved in six of eight patients who had tumors which measured less than 1.5 cm. In this group of cases, two of the patients had a Class I good hearing result (PTA 0 to 30 dB and 70 to 100% discrimination), one patient had Class III nonserviceable hearing, (PTA 65 to 75 dB and 25 to 45% discrimination), and three patients had Class IV poor hearing, (PTA 80 to 100 dB and 0 to 20% discrimination). We found that continuous monitoring of direct eighth-nerve-evoked action potentials were extremely valuable and rapidly indicated reversible cochlear nerve trauma.

Adult↗

PubMed1993

Maintenance of pharmacologically-immature glutamate receptors by aberrant synapses in the chick cochlear nucleus.

Surgical destruction of the otocyst in chick embryos prevents formation of the *** ear, abolishes normal cochlear input to the cochlear nucleus (nucleus magnocellularis, NM) and results in axons from the contralateral NM forming (in addition to their normal bilateral endings in nucleus laminaris, NL) a novel and functional aberrant projection to the deafferented NM. We studied the pharmacology of synaptic transmission at aberrant synapses in an in vitro preparation of the brainstem in chick embryos and hatchlings. Transmission at the aberrant synapses (as with cochlear nerve synapses in NM and NM synapses in NL) is blocked by the quinoxalinedione antagonists CNQX and NBQX, confirming the presence of excitatory amino acid receptors of the non-NMDA subtype. At cochlear nerve synapses in NM, the antagonist potency of NBQX normally decreases rapidly after embryonic day (E)18 (IC50 = 0.69 +/- 0.06 microM, mean +/- S.E.M.), reaching an asymptotic value by E21 (IC50 = 2.7 +/- 0.4 microM) that is maintained at least through posthatching day (P)14 (IC50 = 3.6 +/- 0.3 microM). In the case of the aberrant endings, the potency of NBQX remained (from E21 [IC50 = 0.6 +/- 0.1 microM] through at least P14[IC50 = 0.5 +/- 0.1 microM]) at levels that are statistically indistinguishable from the E18 value for normal cochlear nerve synapses.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMedDate not supplied

Cholinergic and noradrenergic nervous systems in the cynomolgus monkey cochlea.

The cholinergic and noradrenergic nervous systems in the cochleas of cynomolgus monkeys were examined by histochemical and immunohistochemical demonstration of acetylcholinesterase (AChE) and tyrosine hydroxylase (TH) and/or dopamine B-hydroxylase (DBH), respectively. AChE activity was demonstrated in the efferent fibers making synaptic contact with the perikarya and the cell processes of type II neurons. Type II neurons also demonstrated AChE activity on the cell surface and their neurites, suggesting that the AChE-positive fibers in the simian cochlear nerve trunk, previously believed to be of efferent origin, are the central processes of type II neurons. TH-like and DBH-like immunoreactivity of beaded unmyelinated fibers demonstrated similar distribution throughout the cochlear nerve trunk, Rosenthal's canal, and osseous spiral lamina. During their course, they came in contact with unmyelinated efferent fibers and neurites of type II neurons and abutted blood vessels. However, their distribution was not restricted to following blood vessels or cochlear nerve fibers. These observations indicate that the sympathetic nerve supply and olivocochlear efferent system in the cochleas of monkeys differ from those of smaller animals.

Acetylcholinesterase↗

PubMed2000

Microvascular decompression for cochlear symptoms.

OBJECT: The object of this study was to evaluate the efficacy of a new neurovascular decompression technique in relieving symptoms of cochlear nerve dysfunction. METHODS: Nineteen patients with slowly progressive hearing loss, low-frequency fluctuating hearing loss, and high-pitched tinnitus due to neurovascular compression (NVC) of the eighth cranial nerve in a triangular space between the seventh and eighth cranial nerves (the VII-VIII triangle) of the cerebellopontine angle (CPA) were treated using a new technique for microvascular decompression that was developed by anatomical study in 24 cadaver specimens of the CPA. In 12 of 19 patients the anterior inferior cerebellar artery (AICA) was observed to cause compression in the VII-VIII triangle and this vessel was easily mobilized medially for placement of a silicone sponge or Teflon cushion between the compressing artery and nerve. Postoperatively, hearing loss of 20 dB or more that was present in 11 of the 19 patients with NVC improved by more than 5 dB in seven (64%), including the patient with the most severe hearing loss. Of 18 patients presenting with tinnitus preoperatively, eight (44%) had no tinnitus and an additional nine (for a total of 94%) had good improvement in tinnitus after surgery and at long-term follow up. CONCLUSIONS: The microvascular decompression technique described is highly successful in treating symptoms due to direct or indirect compression of the cochlear nerve, with minimal risk of complications. Recordings of auditory brainstem responses confirmed the clinical diagnosis of NVC of the eighth cranial nerve and correlated with clinical results after microvascular decompression of the cochlear nerve.

Adult↗

PubMed1990

[Clinical and electrophysiological investigations of the influence of phenytoin natrium on tinnitus].

Anticonvulsant drugs like Carbamazepine and Phenytoin natrium (PHT) have been used for suppressing the tinnitus. In this paper, a clinical experience was reported, in that 100 patients with tinnitus were treated with intravenous administration of PHT, and the influence of PHT on auditory systems in the guinea pig investigated in detail electrophysiological examinations was also reported. The results are summarised as follows: 1. Clinical evaluation in the treatment of tinnitus (1) Of the 100 patients, more than 70% were well responded. (2) Pith match, loudness balance test correlated closely with the suppression of tinnitus. (3) Side effects were found in 5%, but there were all mild enough to be well tolerated. 2. Experimental evaluation in the guinea pig (1) In intravenous administration of PHT, latency and amplitude of each waveform peak in ABR were prolonged and decreased. As for the latency, waves III and IV were most prominently affected. The results may indicated that PHT works in the upper brain stem predominantly and effects also to the cochlear nucleus and cochlear nerve. (2) The amplitude of N1 in AP was depressed and its latency was slightly prolonged. These phenomena related closely with change of wave I in ABR. This may indicate that PHT can directly suppress the cochlear nerve. (3) Even at the dose that apparently influenced ABR and N1 in AP, no obvious change was observed on amplitudes in CM and EP, that may indicate PHT cannot affect on hair cells at this dose or it cannot proceed to the cochlea. (4) These changes were considered to be direct effect of PHT on auditory systems, since they were not correlated with change in the circulatory system. (5) In the perilymphatic perfusion of PHT, amplitudes in EP and CM were depressed slightly at the beginning of the perfusion. Changes in EP preceded those in CM. The results may indicate that PHT effects directly on the stria vascularis and secondarily on CM. (6) In this perfusion, no obvious change was found in AP. Nevertheless, the amplitude of N1 in AP increased over the initial level after the perfusion corresponding to the recovery of EP in some animals. The results may indicate that PHT cannot work directly on hair cells nor cochlear nerve and that the suppression of efferent inhibitory neurons can increase AP potentials. (7) PHT works on the large part of auditory pathway without cochlea, as a role of inhibitor. Considering antitinnitic effect of PHT, tinnitus bases on unusual excitement of the auditory pathway.

Adult↗

PubMed1991

Postnatal developmental changes in inner ear ornithine decarboxylase (ODC).

Ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine synthesis, is important in cellular growth, differentiation and development. Although ODC has been quantitated in cochlear tissues of the adult rat, it has not been assessed quantitatively in developing inner-ear tissues. The purpose of the present study was to quantitate ODC in cochlear tissues of the rat during the period of development of hearing. Cochlear ODC was significantly elevated throughout the period of cochlear maturation in that it increased rapidly during the first 10 days, peaked on day 10 and then declined thereafter. ODC in the lateral wall/organ of Corti tissues was significantly higher than in the cochlear nerve in developing, but not in adult rats. Further examination of separate cochlear tissues from 10-day old rats revealed that ODC activity was higher in the organ of Corti than in the lateral wall or cochlear nerve. Postnatal changes in ODC paralleled functional maturation of hearing and the hypersensitive period for aminoglycoside ototoxicity in the rat. Since aminoglycosides have been shown to inhibit ODC in vitro, aminoglycoside inhibition of polyamine synthesis may mediate the hypersensitivity of developing animals to the effects of these drugs.

Age Factors↗

PubMed1995

Detection of mRNA encoding guanylate cyclase A/atrial natriuretic peptide receptor in the rat cochlea by competitive polymerase chain reaction and in situ hybridization.

Expression of mRNA encoding guanylate cyclase A (GC-A)/atrial natriuretic peptide (ANP) receptor in the rat cochlea was examined by polymerase chain reaction (PCR) and in situ hybridization (ISH). After reverse-transcription, PCR amplification, subcloning, and sequencing, we found that GC-A mRNA with sequence identical to that previously cloned from the rat brain (Chinkers et al., 1989) was expressed in the rat spiral ligament as well as in the spiral ganglion. However, GC-A mRNA was not detected in the stria vascularis. Competitive PCR using internal standard DNAs indicated that the expression of GC-A in the cochlea occurred at a level approximately 16 times less than that measured in kidney cortex. ISH histochemistry using a 35S-labeled antisense riboprobe showed the highest level of expression of GC-A mRNA to be in oligodendrocytes of the cochlear nerve root. The results suggest that ANP may play a role in the cochlear nerve function.

Amino Acid Sequence↗

PubMed1997

Selective cochlear neurotomy in the cerebellopontine cistern using electrophysiological monitoring in a patient with intractable tinnitus. Case report.

Selective cochlear neurotomy for intractable tinnitus is quite difficult to perform because there is no way to approach the cochlear nerve without interfering with other neural structures. The authors successfully performed selective cochlear neurotomy in the cerebellopontine cistern in a patient with persistent intractable high-pitched tinnitus, but with normal hearing and vestibular functions, by monitoring cochlear nerve compound action potentials and auditory brainstem responses. The procedure is a very simple and safe technique for the treatment of intractable tinnitus. Although this destructive procedure is the last choice of treatment, it can be justified in patients who have poor hearing and severe tinnitus in spite of normal vestibular functions. The procedure may also be applied in some rare cases such as that of the present patient whose quality of life was markedly reduced because loud tinnitus prevented him from hearing anything with the affected ear even though his hearing and vestibular functions were normal.

Action Potentials↗

PubMed1987

Preservation of cochlear potentials in a deaf patient fifteen months after excision of an acoustic neuroma.

Intraoperative electrocochleographic monitoring has been used in an attempt to protect cochlear nerve function during acoustic neuroma excision. One patient is presented with an apparently intact cochlear nerve and waves N1 and N2 preserved at the end of surgery, but no hearing on subsequent testing. Fifteen months after operation, cochlear microphonics and the summating potential were still present, but N1 and N2 had disappeared. There had been no improvement in her hearing and there were no consistent brainstem auditory evoked potentials on the affected side. A possible explanation for these findings is given.

Adult↗

PubMedDate not supplied

Cochlear axon calibres are adjusted to characteristic frequencies.

This study explores factors determining axon calibres, using the normal cochlear nerve as a model. The topographic distribution of axon calibres in the cochlear nerve of the guinea pig was found to correspond to its known tonotopic organization. Axons derived from the cochlear apex which carry sounds of low pitch were located centrally in the nerve and were about half as thick as axons derived from the basal turns, which are located at the periphery and carry sounds of high pitch. Intermediate ranges were located in between. If one compares these measurements with physiological data one finds axon calibres matched to characteristic frequency ranges to a degree that should cause mismatching of conduction time.

Animals↗

PubMed1995

Localization of ornithine decarboxylase (ODC) in the cochlea of the immature rat.

Ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine synthesis, is important in cochlear development. Whereas tissue specific differences in cochlear ODC activity have been demonstrated, cellular localization of ODC protein in the inner ear of the immature rat has not. ODC was localized in inner ear structures using an ODC polyclonal antibody and the effects of cycloheximide on ODC immunoreactivity and enzymatic activity were determined. Tissues demonstrating elevated enzymatic activity contained cells with the strong immunoreactivity. ODC activity was highest in the organ of Corti and lateral wall followed by the cochlear nerve. Immunoreactivity was demonstrated throughout the cochlea with intense staining of the hair cells, pillar cells, Deiter's cells, inner sulcus cells, basilar membrane, stria vascularis, spiral ganglion cell bodies and cochlear nerve fibers. Cycloheximide rapidly diminished cochlear ODC activity and expression of ODC protein. The half-life of cochlear ODC was 30 min. Localization of cellular sites of ODC is important in understanding the role of the ODC-polyamine pathway in cochlear development and will be a valuable marker for tissue damage from ototoxic agents.

Animals↗

PubMed1990

[The histologic study of the inner ear in guinea pigs on anaphylatoxin].

Complement is known to relate to many inflammatory reactions. C4a, C3a and C5a, known as anaphylatoxins, are known to cause strong inflammatory reactions. In this study, the role of anaphylatoxins on the pathogenesis in the cochlea was examined. On hundred forty six male Harley guinea pigs, weighing about 350 grs, all susceptible to preyer's reflex, were used in this study. Anaphylatoxins were made from guinea pig serum treated with zymosan, and inoculated into the carotid artery of the guinea pigs. Parts of these animals were sacrificed and examined at ten minutes, one day, two days, three days, seven days, ten days and fifteen days after injection of anaphylatoxins. Pathological changes in inner ears were observed by light microscopy. After 10 minutes, inner ears were found morphologically normal. After one day, inner ears were found to be almost morphologically normal but the stria vascularis was observed with cystic formation. After two days, cystic formations in the stria vascularis were enlarged and Reissner's membranes were collapsed in some other animals. After three days, the stria vascularis in the various cochlear turns except in the basal turn, were extremely atrophied, some cochlear nerves showed degeneration and some cochlea showed endolymphatic hydrops. After seven days, ten days and fifteen days, the morphological changes showed atrophy in the stria vascularis similar to the results observed on the third days. Atrophy in the stria vascularis was improved gradually with time, but the degeneration of the cochlear nerve was not improved. Opinions have been divided on the cause of inner ear disease including Meniere's disease. Many authors have reported that infectious diseases, for example mumps, measles and cytomegalovirus infection, have caused human sensorineural hearing loss. These diseases have been reported to result in atrophy in the stria vascularis, degeneration of the cochlear nerve and some other pathological changes. In this study, it was clearly observed that the atrophy of the stria vascularis, the endolymphatic hydrops and other morphological changes were caused by introduction of anaphylatoxins. These results were similar to the pathological changes observed in inner ear diseases in human beings. Therefore, inflammatory substances, including anaphylatoxins, were closely related to the cause of inner ear diseases. The animal model used in this report is considered to be important for elucidating the pathogenesis of inner ear diseases.

Anaphylatoxins↗

PubMed1996

Iatrogenic impairment of hearing during surgery for acoustic neuroma.

Isolated or combined labyrinthine, neural, and vascular damage account for failure to preserve hearing during removal of acoustic neuromas. However, the specific mechanisms of auditory impairment remain unclear unless surgical maneuvers can be related to peri- and postoperative hearing on the basis of intraoperative monitoring of auditory function.Among the different auditory monitoring techniques, recording of cochlear nerve action potentials (CNAPs) from the intracranial portion of the nerve has proven particularly useful for identifying the mechanisms of iatrogenic auditory injury.The present investigation analyzes intra- and postoperative auditory impairment in relation to surgical steps in a group of 38 subjects with acoustic neuroma (size ranging from 5 to 24 mm) undergoing removal via a retrosigmoid approach.Coagulation close to the cochlear nerve, drilling of the internal auditory canal, and removal of the intrameatal portion of the acoustic neuroma have prove to be the most critical surgical steps in hearing preservation.Changes were correlated with intra- and extrameatal tumor size, the relationship between the internal auditory canal and vestibule, and internal auditory canal enlargement, anatomic involvement of the cochlear nerve, preoperative auditory level, and ABR and ENG test findings.Changes in CNAP morphology and latency are detailed, and mechanisms of injury are analyzed and discussed as a function of these variables.

Journal Article↗