Expression and distribution of μ opioid receptors in the inner ear of the rat

Opioid peptides have demonstrated modulatory effects on the vestibular afferent discharge and are putative vestibular efferent neuromodulators. The distribution of their receptors in the mammalian vestibular epithelia is not known. We used reverse transcriptase-polymerase chain reaction (RT-PCR), in situ hybridization, Western blots and immunohistochemistry to study the expression of mu opioid receptor (MOR) in the Scarpa's ganglia and cristae ampullares of rats. MOR transcript was only detected in the somata of the vestibular afferent neurons. MOR-like immunoreactivity was observed in the somata of vestibular afferents and in nerve terminals in the cristae ampullares epithelia both in the center and peripheral regions. Double labeling of cristae sections with the MOR1 antibody in combination with antibodies against calretinin (a marker for vestibular afferents terminating in calices) and peripherin (a marker for afferents terminating in boutons), respectively showed that MOR1 immunoreactivity was in calyx, dimorphic and bouton vestibular afferents. MOR immunoreactivity was not detected in vestibular efferent fibers identified with choline acetyltransferase immunohistochemistry. These results indicate that MOR may mediate effects of vestibular efferents on afferents.

Radiation hybrid mapping of 11 alpha and beta nicotinic acetylcholine receptor genes in Rattus norvegicus

Acetylcholine is the main neurotransmitter of the vestibular efferents and a wide variety of muscarinic and nicotinic acetylcholine receptors are expressed in the vestibular periphery. To date, 11 nicotinic subunits (alpha and beta) have been reported in mammals. Previously, our group [Brain Res. 778 (1997) 409] reported that these nicotinic acetylcholine receptor alpha and beta subunits were differentially expressed in the vestibular periphery of the rat. To begin an understanding of the molecular genetics of these vestibular efferents, this study examined the chromosomal locations of these nicotinic acetylcholine receptor genes in the rat (Rattus norvegicus). Using radiation hybrid mapping and a rat radiation hybrid map server (www.rgd.mcw.edu/RHMAP SERVER/), we determined the chromosomal position for each of these genes. The alpha2-7, alpha9, alpha10, and beta2-4 nicotinic subunits mapped to the following chromosomes: alpha2, chr. 15; alpha3, chr. 8; alpha4, chr. 3; alpha5, chr. 8; alpha6, chr. 16; alpha7, chr. 1; alpha9, chr. 14; alpha10, chr. 7; beta2, chr. 2; beta3, chr. 16; and beta4, chr. 8. With the location for each of these nicotinic subunits known, it is now possible to develop consomic and/or congenic strains of rats that can be used to study the functional genomics of each of these subunits.

Adjunctive use of endoscopy during posterior fossa surgery to treat cranial neuropathies

OBJECTIVE

The objective of this study was to determine the utility and safety of rigid endoscopy as an adjunct during posterior fossa surgery to treat cranial neuropathies.

METHODS

A suboccipital craniotomy was performed for 19 patients with non-neoplastic processes involving the Vth, VIIth, and/or VIIIth cranial nerves. Ten patients with trigeminal neuralgia (n = 8), hemifacial spasm (n = 1), or intractable tinnitus (n = 1) underwent primarily microvascular decompression procedures. One patient with geniculate neuralgia underwent nervus intermedius sectioning combined with microvascular decompression. Eight patients underwent unilateral vestibular nerve neurectomies for treatment of Meniere's disease. A 0- or 30-degree rigid endoscope was used in conjunction with the standard microscopic approach for all procedures.

RESULTS

All patients experienced resolution or significant improvement of their preoperative symptoms after posterior fossa surgery. The endoscope allowed improved definition of anatomic neurovascular relationships without the need for significant cerebellar or brainstem retraction. Cleavage planes between the cochlear and vestibular nerves entering the internal auditory canal and sites of vascular compression could not be microscopically observed for several patients; however, endoscopic identification was possible for all patients. There were no complications related to the use of the endoscope.

CONCLUSION

The rigid endoscope can be used safely during posterior fossa surgery to treat cranial neuropathies, and it allows improved observation of the cranial nerves, nerve cleavage planes, and vascular anatomic features without significant cerebellar or brainstem retraction.

Hearing Rehabilitation Using the BAHA Bone-Anchored Hearing Aid: Results in 40 Patients

OBJECTIVE

This study evaluates the U.S. experience with the first 40 patients who have undergone audiologic rehabilitation using the BAHA bone-anchored hearing aid.

STUDY DESIGN

This study is a multicenter, nonblinded, retrospective case series.

SETTING

Twelve tertiary referral medical centers in the United States.

PATIENTS

Eligibility for BAHA implantation included patients with a hearing loss and an inability to tolerate a conventional hearing aid, with bone-conduction pure tone average levels at 60 dB or less at 0.5, 1, 2, and 4 kHz.

INTERVENTION

Patients who met audiologic and clinical criteria were implanted with the Bone-Anchored Hearing Aid (BAHA, Entific Corp., Gothenburg, Sweden).

MAIN OUTCOME MEASURES

Preoperative air- and bone-conduction thresholds and air-bone gap; postoperative BAHA-aided thresholds; hearing improvement as a result of implantation; implantation complications; and patient satisfaction.

RESULTS

The most common indications for implantation included chronic otitis media or draining ears (18 patients) and external auditory canal stenosis or aural atresia (7 patients). Overall, each patient had an average improvement of 32+/-19 dB with the use of the BAHA. Closure of the air-bone gap to within 10 dB of the preoperative bone-conduction thresholds (postoperative BAHA-aided threshold vs. preoperative bone-conduction threshold) occurred in 32 patients (80%), whereas closure to within 5 dB occurred in 24 patients (60%). Twelve patients (30%) demonstrated 'overclosure' of the preoperative bone-conduction threshold of the better hearing ear. Complications were limited to local infection and inflammation at the implant site in three patients, and failure to osseointegrate in one patient. Patient response to the implant was uniformly satisfactory. Only one patient reported dissatisfaction with the device.

CONCLUSIONS

The BAHA bone-anchored hearing aid provides a reliable and predictable adjunct for auditory rehabilitation in appropriately selected patients, offering a means of dramatically improving hearing thresholds in patients with conductive or mixed hearing loss who are otherwise unable to benefit from traditional hearing aids.

Ligand-gated purinergic receptors are differentially expressed in the adult rat vestibular periphery

To further characterize the pattern of expression of the ligand-gated purinergic P2X receptors in the peripheral vestibular system, we conducted reverse transcription-polymerase chain reaction amplification of P2X1 and P2X2 messenger RNA extracted from adult rat vestibular ganglia (Scarpa's ganglia) and vestibular end organs. Transcripts encoding P2X1 were found in both Scarpa's ganglia and the end organs, but transcripts encoding P2X2 were found only in the vestibular end organs. These results support previous electrophysiological data, and they provide a more complete understanding of the specific role of purinergic (adenosine-5'-triphosphate) transmission in the vestibular periphery.

Adenylyl cyclase isoforms in the vestibular periphery of the rat

The expression of adenylyl cyclase (AC) isoforms in the adult rat vestibular periphery was investigated using reverse transcription polymerase chain reaction (RT-PCR). AC II, IV and V mRNAs were expressed in both Scarpa's ganglion and vestibular end organs. In addition, in the vestibular end organs, an AC mRNA not previously reported in the rat was identified. The cloned sequence (GenBank accession no. AF184150) represented 95 amino acids with 100% similarity to the human AC VII and 94% to the bovine AC VII. AC VII mRNA also was found in the cerebellum but was undetectable in heart, kidney, liver and Scarpa's ganglion.

Topographic distribution of nicotinic acetylcholine receptors in the cristae of a turtle

The neurochemical basis of cholinergic efferent modulation of afferent function in the vestibular periphery remains incompletely understood; however, there is cellular, biochemical and molecular biological evidence for both muscarinic and nicotinic acetylcholine (ACh) receptors (nAChRs) in this system. This study examined the topographic distribution of alpha-bungarotoxin (alpha-BTX) nAChRs in the cristae of a turtle species. Cristae were perfusion-fixed, cut at 20 micrometer on a cryostat and incubated with alpha-BTX or polyclonal antibodies raised against Torpedo nAChR. Light microscopy showed abundant specific labeling of nAChR in the central zone of each hemicrista on the calyx-bearing afferents surrounding type I hair cells and on the base of the type II hair cells. Within the peripheral zone, dense labeling of type II hair cells near the torus and sparse or no label was observed on type II hair cells near the planum. The alpha-BTX binding showed a similar pattern within the cristae. The similarity between the topographic distribution of alpha-BTX binding nAChR and of efferent inhibition of afferents supports the notion that the inhibitory effect of afferents is mediated by nAChR.

Partial cDNAs encoding G-protein alpha subunits in the rat vestibular periphery

To begin understanding what G-proteins are involved in signal transduction in the vestibular periphery, the expression of Galpha subunits in rat primary afferent neurons (Scarpa's ganglia) and end-organs was studied. Reverse transcription-polymerase chain reaction (RT-PCR) with degenerate primers corresponding to two conserved regions of the Galpha protein coding sequence produced partial cDNAs encoding two distinct forms of Galpha(s) subunit (Galpha(s2) and anove) Galpha(s2) subunit,GenBank accession number AF1841510); and two forms of Galpha(i2) subunits. A novel truncated form of Galpha(i2) (designated Galpha(i2(vest)),Gen Bank accession number AF189020) was detected in the vestibular periphery. Galpha(i2(vest)) was also expressed in rat cerebellum and heart. The possible role of the identified Galpha protein cDNAs in the function of the vestibular periphery is discussed.

Cochlear implantation for auditory rehabilitation in Camurati-Engelmann disease

Camurati-Engelmann disease (progressive hereditary diaphyseal dysplasia) is a rare sclerotic bone disease involving the diaphyses of the long bones, skull base, and clavicles. Progressive sclerosis of cranial nerve foramina has been implicated in cranial nerve deficits. including facial nerve palsy, vestibular disturbances, and hearing loss. Two patients with Camurati-Engelmann disease and concomitant sensorineural hearing loss are presented. Both patients were evaluated for cochlear implantation. One patient was successfully implanted after preoperative imaging revealed no involvement of the internal auditory canals. The porous nature of the affected bone, however. necessitated the inactivation of 1 electrode to prevent facial nerve stimulation. A second patient was rejected as a potential implant recipient due, in part, to narrow internal auditory canals and rapidly progressive disease. The otologic manifestations of Camurati-Engelmann disease are reviewed, and issues related to cochlear implantation in this rare disease are discussed.

Isolated primary unilateral stenosis of the internal auditory canal

Congenital primary stenosis of the internal auditory canal (IAC) may exist in isolation or along with a number of other osseous anomalies of the temporal bone. Most of the literature on IAC stenosis is concerned with its effect on the outcome of cochlear implantation (i.e. patients with profound bilateral hearing loss). In addition, some degree of canal asymmetry has been noted in patients with normal hearing, questioning the causal relationship of this finding to deafness. We describe two children with computed tomography (CT) documented severe primary unilateral narrowing of the IAC and an associated ipsilateral sensorineural hearing loss. Typical radiographic findings are described, and the relevant developmental pathology is discussed. The ipsilateral association of stenosis and hearing loss strengthens the link between narrowing of the IAC and deafness.

Adjunctive use of endoscopy during acoustic neuroma surgery

OBJECTIVE/HYPOTHESIS

In specific clinical situations, endoscopes offer better visualization than the microscope during acoustic neuroma (vestibular schwannoma) surgery and can therefore decrease the incidence of the postoperative complications of cerebrospinal fluid (CSF) leakage and recurrence of tumor. This study was undertaken to determine if the use of adjunctive endoscopy provides complementary information to the operating surgeon during surgery for acoustic neuromas.

METHOD

Seventy-eight patients with acoustic neuromas underwent tumor excision by two neurotologists (PAW., D.S.P.), together with their respective neurosurgical partners, via a retrosigmoid (suboccipital) approach (n = 68), translabyrinthine approach (n = 7), or middle cranial fossa approach (n = 3). Endoscopy with a rigid glass lens endoscope was used during tumor removal to examine posterior fossa neurovascular structures, and after tumor excision to inspect the internal auditory canal (IAC), inner ear, and middle ear, depending on the approach used. One of the authors (D.S.P.) has not used adjunctive endoscopy during resections via the translabyrinthine and middle cranial fossa approaches, and therefore, these cases were excluded from the data collection and analysis.

RESULTS

Complete tumor excision was achieved in 73 patients. Endoscopy allowed improved identification of tumor and adjacent neurovascular relationships in all cases. In addition, residual tumor at the fundus of the IAC (n = 11) and exposed air cells (n = 24) not seen with the microscope during retrosigmoid approaches were identified endoscopically. In one of the translabyrinthine cases, the endoscope allowed identification of open air cells not visualized with the microscope. None of the 78 patients developed CSF rhinorrhea. Incorporating the endoscope did not significantly increase operative time.

CONCLUSIONS

Endoscopy can be performed safely during surgery to remove acoustic neuromas. The adjunctive use of endoscopy may offer some advantages including improved visualization, more complete tumor removal, and a lowered risk of CSF leakage.

Endoscope-assisted surgery for acoustic neuromas (vestibular schwannomas): early experience using the rigid Hopkins telescope

OBJECTIVE

Endoscopes have been increasingly used during neurosurgical procedures. Previously, they have been shown to offer better visualization than the microscope in selected situations and frequently have allowed less invasive surgery. This study was undertaken to determine whether endoscopy is safe and effective during suboccipital surgery for vestibular schwannomas.

METHODS

Ten patients with vestibular schwannomas underwent suboccipital transmeatal craniotomies for tumor excision. Endoscopy with a rigid glass lens endoscope (Hopkins telescope) was used during tumor removal to examine posterior fossa neurovascular structures and after tumor excision to inspect the internal auditory canal.

RESULTS

Complete tumor excision was achieved in nine patients. Endoscopy allowed improved identification of tumor and adjacent neurovascular relationships in all cases without the need for significant retraction of the cerebellum or brain stem. In addition, residual tumor at the fundus of the internal auditory canal (n = 2) and exposed petrous air cells (n = 3) not seen with the microscope were identified endoscopically. Operative time was not significantly increased by incorporating the endoscope.

CONCLUSION

Posterior fossa endoscopy can be performed safely during surgery for tumor removal. Endoscope-assisted surgery for vestibular schwannomas may offer some advantages over standard microsurgery in selected cases. The advantages may include improved visualization, more complete tumor removal, and a lowered risk of cerebrospinal fluid leakage.

A critical appraisal of spontaneous perilymphatic fistulas of the inner ear

OBJECTIVE

This article provides an overview of relevant data supporting and refuting the existence of spontaneous perilymph fistula, as well as critically reviewing the literature pertaining to their evaluation and management.

DATA SOURCES

Sources used were relevant English language clinical and basic science publications.

STUDY SELECTION

A Medline search dating back to 1966 for articles concerning perilymphatic fistula, including both human and animal data, was performed. Articles were included if they contained relevant data or were significant reviews of the subject. A traditional bibliography search was then completed to acquire articles missed by the computerized search, including works published before 1966.

DATA EXTRACTION

The data from each publication were critically reviewed. Emphasis on understanding the clinical features of surgically created perilymph fistulas was used to more objectively assess the data regarding spontaneous perilymph fistulas.

DATA SYNTHESIS

The data were not amenable to formal meta-analysis or valid data summarization; however, when possible trends and contrasting data were emphasized.

CONCLUSIONS

Spontaneous perilymph fistulas are very rare occurrences and the majority are likely incited by a pressure-altering event. Current methodologies do not provide sufficient specificity and sensitivity to accurately diagnose perilymph fistulas. The results of endoscopic studies of the middle ear in the evaluation of perilymphatic fistula suggest a low incidence compared with the large number of fistulas reported in the literature. A high index of suspicion must be maintained, and appropriate preoperative counseling should reflect the current controversies. Questions must continue to be asked and further research pursued to help distinguish reality from myth.

Evaluation of surgical approaches to endoscopic auditory brainstem implantation

OBJECTIVES

This study investigates the use of endoscopy for the placement of an auditory brainstem implant by translabyrinthine, retrosigmoid (suboccipital), and middle cranial fossa approaches.

STUDY DESIGN

Cadaver dissection and endoscope-assisted placement of the auditory brainstem implant.

METHODS

Translabyrinthine, retrosigmoid, and middle cranial fossa dissections were performed bilaterally in five cadaveric heads. An auditory brainstem implant was placed within the lateral recess of the fourth ventricle under endoscopic visualization. The implantation was performed with all approaches and documented by digital image capture followed by production of dye-sublimation photographic prints.

RESULTS

The lateral recess was visualized with the endoscope in all three approaches to the brainstem. The 30 degrees endoscope provided the best visualization by translabyrinthine and retrosigmoid dissection and was essential for the middle cranial fossa approach. Refinement of implant position was readily achieved, as even the deepest portion of the recess could be seen with all three approaches.

CONCLUSIONS

This study finds that endoscopy provides superior visualization of the lateral recess of the fourth ventricle than the operating microscope with all approaches. The retrosigmoid approach is recommended, as it provides the best view of the implantation site and the easiest angle for placement of the prosthesis. The use of the endoscope may allow for a smaller craniotomy than with conventional microscopic techniques, depending on tumor size. The translabyrinthine approach provides a good view of the lateral recess but had no advantage over other approaches. The middle cranial fossa approach is only possible with angled endoscopes; however, it is technically the most difficult and places the facial nerve at greatest risk.

Endoscope-assisted vestibular neurectomy

OBJECTIVE/HYPOTHESIS

In some instances endoscopes offer better visualization than the microscope and frequently allow less invasive surgery. This study was undertaken to determine whether endoscopy is safe and effective during neurectomy of the vestibular nerve.

METHOD

Ten patients with intractable unilateral Meniere's disease underwent a retrosigmoid craniotomy for neurectomy of the vestibular nerve. Endoscopy with a Hopkins telescope was used during each procedure to study posterior fossa anatomic relationships and to assist the neurectomy. Preoperative and postoperative audiometric evaluation was performed in all patients undergoing vestibular neurectomy. Nine of these patients had preoperative electronystagmography, and four patients completed postoperative electronystagmography. The 1995 American Academy of Otolaryngology-Head and Neck Surgery's Committee on Hearing and Equilibrium guidelines for the diagnosis and evaluation of therapy in Meniere's disease were used.

RESULTS

Complete neurectomy was achieved in all 10 patients. Endoscopy allowed improved identification of the nervus intermedius and the facial, cochlear, and vestibular nerves and adjacent neurovascular relationships without the need for significant retraction of the cerebellum or brainstem. In addition, endoscopic identification of the cleavage plane between the cochlear and vestibular nerves medial to or within the internal auditory canal (n = 3) was not made with the 0-degree endoscope; however, identification was made with the 30- or 70-degree endoscope in all cases. In all patients with Meniere's disease, elimination of the recurrent episodes of vertigo (n = 10) or otolithic crisis of Tumarkin (n = 1) was achieved.

CONCLUSIONS

Posterior fossa endoscopy can be performed safely. Endoscope-assisted neurectomy of the vestibular nerve may offer some advantages over standard microsurgery including increased visualization, more complete neurectomy, minimal cerebellar retraction, and a lowered risk of cerebrospinal fluid leakage.

Evidence for three additional P2X2 purinoceptor isoforms produced by alternative splicing in the adult rat vestibular end-organs

P2X2 receptors are ligand-gated ion channels that are activated by extracellular ATP. To characterize the expression of P2X2 purinoceptor in the adult rat vestibular periphery, reverse transcription-polymerase chain reaction (RT-PCR) was used. No transcript for P2X2 receptor was found in the vestibular primary afferent neurons (Scarpa's ganglia); however, partial cDNAs encoding four splice variants of the P2X2 receptor were isolated from vestibular end-organs. In all four cDNAs, the deletions were of different lengths but started at the same position on the P2X2 gene (Val-370 codon) located toward the intracellular carboxyl terminus. One of these receptor isoforms was identical in sequence to the recently published P2X2(b) receptor (Simon et al., 1997, Mol. Pharmacol. 52, 237-248) (also known as P2X2-2, in the nomenclature of Brändle et al., 1997, FEBS Lett. 404, 294-298). The remaining three novel splice variants of the P2X2 receptor were designated P2X2(e), P2X2(f) and P2X2(g) (GenBank accession numbers AF028603, AF028604 and AF028605, respectively). The functional significance of these three splice variants remains to be determined. Pituitary and cerebellum were used as survey tissues and only the P2X2(b) receptor cDNA was found.

Molecular temporal bone pathology: III. Genotyping of the deltaF508 deletion in the DNA of patients with cystic fibrosis

Genomic DNA from a single celloidin-embedded archival temporal bone section was used to identify a specific genetic mutation. The polymerase chain reaction was used to amplify and detect the deltaF508 deletion, a common molecular genetic defect in cystic fibrosis. This mutation, present in more than 70% of white patients and carriers with cystic fibrosis, results in the deletion of codon 508, which specifies the amino acid phenylalanine of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. When this technique was applied to archival specimens from four patients with cystic fibrosis, all expressed the carrier state of this defective gene. These data demonstrate the feasibility of identifying genetic mutations in archival temporal bone specimens.

Molecular temporal bone pathology: IV. Analysis of DNA template length using mitochondrial PCR primers

The focus of this study was to identify, via molecular biology techniques, the length of the DNA templates present in individual archival celloidin-embedded human temporal bone sections. Earlier studies have suggested that the maximum template length present in these tissues is on the order of 471 base pair (bp). Polymerase chain reaction (PCR) amplification of 92 bp, 121 bp, 471 bp, and 609 bp regions of mitochondrial DNA (mtDNA), extracted from single archival celloidin-embedded human temporal bone sections, was used to assess the length of the template DNA extracted. These data are crucial to determine the limits of applying PCR technology to amplify specific genomic DNA targets located within the human inner ear. The results described should be of value to those investigators extracting DNA from archival individual human temporal bone sections for polymerase chain reaction assays of specific genetic alterations or infectious agents associated with temporal bone pathologies.

Molecules, Motion, and Man

The application of cell and molecular biology techniques to vestibular research is resulting in rapid changes in our understanding of the fundamental mechanisms of vestibular function. The clinical problems encountered in space travel together with the acute and chronic vestibular dysfunction affecting many of the patients otolaryngologists care for have driven this research at a rapid pace. A review of these methods and highlights of the major advances are discussed. (Otolaryngol Head Neck Surg 1998;118:S16-S24.)

Molecules, motion, and man

The application of cell and molecular biology techniques to vestibular research is resulting in rapid changes in our understanding of the fundamental mechanisms of vestibular function. The clinical problems encountered in space travel together with the acute and chronic vestibular dysfunction affecting many of the patients otolaryngologists care for have driven this research at a rapid pace. A review of these methods and highlights of the major advances are discussed.

Clinical and molecular pathology of aggressive Schneiderian papilloma involving the temporal bone

BACKGROUND

Inverting papilloma is a benign but locally aggressive sinonasal tumor that rarely involves the middle ear or temporal bone.

METHODS

A report of a case and the molecular pathology of the tumor is presented.

RESULTS

A 35-year-old woman with a history of recurrent inverting papilloma of the left paranasal sinuses was found to have evidence of extension through the eustachian tube and extensive involvement of the temporal bone. Surgical management resulted in the patient being disease-free at 14 months. Molecular pathology studies of the resected tumor suggest an association with human papillomavirus.

CONCLUSIONS

Direct extension of the sinonasal tumor through the eustachian tube may represent the pathologic mechanism involved in the development of inverting papilloma involving the middle ear and temporal bone.

Differential expression of alpha2-7, alpha9 and beta2-4 nicotinic acetylcholine receptor subunit mRNA in the vestibular end-organs and Scarpa's ganglia of the rat

To further characterize the pattern of expression of the nicotinic acetylcholine receptor (nAChR) subunits in the peripheral vestibular system, we conducted RT-PCR of all known mammalian nAChR alpha and beta subunits in mRNA extracted from adult rat vestibular primary afferent neurons (Scarpa's ganglia) and vestibular end-organs. Transcripts encoding the alpha2-7 and beta2-4 nAChR subunits were found in the vestibular ganglia, while alpha3, alpha5-7, alpha9 and beta2-4 nAChR subunits were expressed in the vestibular end-organs. These results support previous electrophysiological, immunocytochemical and molecular biological data, and also provide a more complete understanding of the role of nAChRs in the neurochemical transmission subserving the efferent-afferent interaction in the vestibular periphery.

Molecular and cellular pathology of Meniere's disease

The etiopathogenesis of Meniere's disease has remained controversial since the early 1900s. Many investigators have studied the molecular and cellular pathology of the inner ear in patients with this disorder. Three basic pathologic mechanisms have emerged; fibrosis of the endolymphatic sac and vestibular epithelia, altered glycoprotein metabolism, and immune-mediated inner ear disease. This article reviews the current understanding of these three basic pathologic processes.

Molecular characterization of muscarinic receptors in the human vestibular periphery. Implications for pharmacotherapy

HYPOTHESIS

Muscarinic acetylcholine receptor subtypes are expressed in the human vestibular periphery to receive efferent innervation on the type II vestibular hair cells and primary afferent dendrites.

BACKGROUND

Previous immunohistochemical and electrophysiologic studies have shown that acetylcholine (ACh) is likely the primary neurotransmitter of the efferent vestibular periphery. The structural distribution of nicotinic receptors (nAChR) and muscarinic receptors (mAChR) are not well established in the human vestibular periphery.

METHODS

Reverse transcription polymerase chain reaction (RT-PCR) was used to study the expression of all five mAChR subtypes in Scarpa's ganglia and the vestibular end-organs of the rat and human.

RESULTS

The authors found m1 through m5 expression in rats, and m1, m2, and m5 expression in humans.

CONCLUSIONS

These studies show evidence that both muscarinic acetylcholine receptors are present in the human vestibular periphery in addition to the nicotinic receptors reported previously. The pharmacologic implications of these data are discussed.

Molecular temporal bone pathology: I. Historical foundation

The application of molecular biology techniques to temporal bone research is resulting in rapid changes in our understanding of the fundamental mechanisms of auditory, facial nerve, and vestibular function. The use of the polymerase chain reaction, cDNA libraries, and in situ hybridization histochemistry, the determination of genetic defects, and the manipulation of transgenic animals are the molecular biology tools that are available to approach these research problems. Knowledge of the molecular pathology that results in the otologic and neuro-otologic dysfunction many of our patients experience is currently in its infancy. A review of the historical foundation of temporal bone pathology and the evolution of the application of cell and molecular biology methods to archival celloidin-embedded human temporal bone material is presented.

Molecular temporal bone pathology: II. Ramsay Hunt syndrome (herpes zoster oticus)

In 1907 J. Ramsay Hunt suggested that herpes zoster oticus resulted from a geniculate ganglionitis; however, many contemporary authors believe that this disorder represents a neuritis or polycranial neuropathy. Herpes varicella-zoster viral (VZV) DNA was identified, using the polymerase chain reaction, in archival celloidin-embedded temporal bone sections from two patients who clinically had Ramsay Hunt syndrome (herpes zoster oticus). The presence of VZV was confirmed by sequencing the PCR products. These experiments demonstrated that VZV genomic DNA was present in the geniculate ganglion of the side with facial paralysis and cutaneous recrudescence in both patients and in the clinically unaffected side in patient 1. In addition, patient 2 had a sudden hearing loss and was found to have VZV genomic DNA in sections from the affected side containing the spiral ganglion, Scarpa's ganglion, organ of Corti, and macula of the saccule. No VZV genomic DNA was identified in temporal bone sections from five patients with Bell's palsy and ten patients without evidence of otologic disease. In this study, the histopathology of these two cases yielded complementary information regarding the role of VZV in herpes zoster oticus. These data suggest that in patients with Ramsay Hunt syndrome, latent VZV is located in the geniculate ganglia and may be present in the auditory and vestibular primary afferent ganglia in some patients.

Distribution of calcitonin gene-related peptide immunoreactivity in vestibular efferent neurons of the chinchilla

The distribution of calcitonin gene-related peptide immunoreactivity (CGRPi) within efferent vestibular neurons in the chinchilla was investigated using fluorescent retrograde labeling combined with immunohistochemistry. Efferent vestibular neurons were found bilaterally in clusters: dorsolateral (group E1) and medial (group E2) to the genu of CN VII, as well as ventromedial to the descending CN VII fibers in the parvicellular reticular formation (PCR). The percentage of retrogradely labeled cells containing CGRPi was 77.1 +/- 5.7 for group E1 neurons, 90.3 +/- 3.8 in the E2 region. Among the PCR efferents more then half of the neurons (61.4 +/- 19.9%) expressed CGRP peptide or message. The wide distribution of CGRP among vestibular efferent neurons suggests that CGRP plays an important role in vestibular efferent function. In addition, the differential distribution among the groups of vestibular efferent neurons suggests that efferent modulation of vestibular function is different between the E cell group efferent neurons and the PCR efferent neurons.

Distribution of choline acetyltransferase mRNA in the efferent vestibular neurons of the chinchilla

The distribution of choline acetyltransferase messenger RNA (mRNA) among efferent vestibular neurons in the chinchilla was investigated. mRNA coding for choline acetyltransferase, the enzyme that synthesizes acetylcholine, was used as a marker for the cholinergic system. In order to retrogradely label the efferent vestibular neurons, Fluoro-gold was injected through the oval window into the inner ear of anesthetized young male chinchillas (6 to 12 months old). The animals were anesthetized and perfused through the heart 2 days post injection with 4% paraformaldehyde in phosphate buffer. Retrogradely labeled efferent vestibular neurons were mapped in brainstem sections prior to processing for in situ hybridization histochemistry using radiolabeled ribonucleic acid probes complementary to the 3' end of the choline acetyltransferase mRNA. At the levels of the ascending facial nerve and the genu of the facial nerve, we found that approximately 90% of the Fluoro-gold labeled cells in group E1 contained choline acetyltransferase mRNA. All of the group E2 cells that were labeled with Fluoro-gold were found to be cholinergic (contain choline acetyltransferase mRNA). Finally, 60% of the Fluoro-gold-labeled cells in the caudal pontine reticular nucleus contained choline acetyltransferase mRNA.

Vestibular Neuritis: Clinical-Pathologic Correlation

Postmortem examination of the brain and temporal bones of a patient with well-documented vestibular neuritis showed selective neuronal loss in Scarpa's ganglia on the side with absent caloric response. There was loss of hair cells and an “epithelialization” of the utricular macule and semicircular canal cristae on the deafferented side, and synaptic density in the vestibular nuclei on the deafferented side was decreased compared with that on the normal side. All findings were consistent with an isolated viral infection of Scarpa's ganglia. This is the first description of the effects of chronic deafferentation on the vestibular sensory epithelia and the vestibular nuclei in a human being.

Muscarinic acetylcholine receptor subtype mRNAs in the human and rat vestibular periphery

The expression of the five muscarinic acetylcholine receptor (mAChR) subtypes (m1-m5) in the vestibular end-organs and in the primary afferent vestibular ganglia of the human and rat was studied using RT-PCR from the two tissue populations from both species. In the human, although all five mAChR subtypes were expressed in brain, only the m1, m2, and m5 mAChR subtypes were amplified from both the vestibular ganglia and the vestibular end-organs, while in the rat, all five mAChR subtypes were expressed. These data suggest that the efferent cholinergic axo-dendritic and axo-somatic synapses have a muscarinic component and that there are pharmacologic implications for patients with vestibular dysfunction.

Distribution of efferent cholinergic terminals and alpha-bungarotoxin binding to putative nicotinic acetylcholine receptors in the human vestibular end-organs

Although acetylcholine (ACh) has been identified as the primary neurotransmitter of the efferent vestibular system in most animals studied, no direct evidence exists that ACh is the efferent neurotransmitter of the human vestibular system. Choline acetyltransferase immunohistochemistry (ChATi), acetylcholinesterase (AChE) histochemistry, and alpha-bungarotoxin binding were used in human vestibular end-organs to address this question. ChATi and AChE activity was found in numerous bouton-type terminals contacting the basal area of type II vestibular hair cells and the afferent chalices surrounding type I hair cells; alpha-bungarotoxin binding suggested the presence of nicotinic acetylcholine receptors on type II vestibular hair cells and on the afferent chalices surrounding type I hair cells. This study provides evidence that the human efferent vestibular axons and terminals are cholinergic and that the receptors receiving this innervation may be nicotinic.

Characterization of lymphocyte subpopulations in Warthin's tumor

Cell suspensions from six Warthin's tumors (WTs) were characterized with fluorescence-labeled cell cytometry. WT lymphocyte subsets were identified with monoclonal antibodies directed against lymphocyte-associated cell antigens including T lymphocyte subsets, B lymphocytes, and natural killer (NK) cells. Results showed that T cell proportions were 58% and B cell proportions were 39%. The T cell helper:cytotoxic-suppressor ratio was 5.7:1 and the B to T cell ratio was 0.8:1. NK cells represented 1.3% of cells. When compared to peripheral blood lymphocytes (PBLs) in the same patients, statistically significant differences were noted between PBLs and WT lymphocytes in the percentage of B lymphocytes (P < .01), T cytotoxic-suppressor lymphocytes (P < .02), NK cells (P < .01), and in the ratios of B to T lymphocytes (P < .01) and T helper to T cytotoxic-suppressor lymphocytes (P < .03). Comparing these data to retrospective data on lymphocyte distribution in normal and reactive lymph nodes, the epithelial component does not appear to exert a local effect on the lymphoid component of WT.

Expression of alpha 4 and beta 2 nicotinic acetylcholine receptor subunit mRNA and localization of alpha-bungarotoxin binding proteins in the rat vestibular periphery

In situ hybridization histochemistry was used to map the distribution of alpha 2, alpha 3, alpha 4, and beta 2 nAChR subunit mRNAs throughout the peripheral vestibular system of the rat. The alpha 4 and beta 2 nAChR subunit genes were co-expressed by populations of primary afferent neurons within Scarpa's ganglion, while there was no expression of the alpha 2, alpha 3, alpha 4, or beta 2 nAChR subunit genes by type I or type II vestibular hair cells. alpha-bungarotoxin binding to nAChRs in the vestibular end-organs was primarily limited to the afferent chalices surrounding type I hair cells and the basal aspect of type II hair cells. These data suggest that nAChRs composed of alpha 4 and beta 2 subunits are localized on afferent chalices innervating the type I vestibular hair cells and that the direct cholinergic efferent innervation of the type II vestibular hair cells utilizes nAChR composed of other subunits.

Histopathologic findings in Menière's disease

The etiopathogenesis of Menière's disease has remained controversial since the early 1900s. Many investigators have studied the histopathology of the inner ear in patients with this disorder. Three basic pathologic mechanisms have emerged: fibrosis of the endolymphatic sac and vestibular epithelia, altered glycoprotein metabolism, and inner ear viral infection. This article reviews the current understanding of these three basic pathologic processes.

Characterization of DNA extracted from archival celloidin-embedded human temporal bone sections

The focus of the present investigation was to study, via molecular biology techniques, the character of the DNA present in individual archival celloidin-embedded human temporal bone sections. Polymerase chain reaction (PCR) amplification of 92 base pair (bp), 121 bp, and 471 bp regions of mitochondrial DNA (mtDNA) extracted from a single archival celloidin-embedded human temporal bone section was used to assess the length of the template DNA extracted. The effects of digestion time and sample motion during the extraction method on DNA concentration was also studied. These data are crucial to determine the limits of applying PCR technology to amplify specific genomic DNA targets located within the human inner ear. Further development of these methods will allow additional molecular temporal bone pathologic studies to be completed and, more specifically, hypotheses regarding the molecular etiopathogenesis of many auditory, vestibular, and facial nerve disorders, such as autoimmune hearing loss, congenital hearing losses, Meniere's disease, otosclerosis, or Bell's palsy could be tested. The results described should be of great value to those investigators extracting DNA from archival individual human temporal bone sections for PCR assays of specific genetic alterations or infectious agents associated with temporal bone pathologies.

Choline acetyltransferase immunoreactivity in the human vestibular end-organs

Acetylcholine (ACh) is believed to play a major role in the efferent vestibular system in several animal models, however no information regarding the role of ACh in the human efferent vestibular system has been published. Post-embedding immunohistochemistry in a hydrophilic resin was used to investigate the choline acetyltransferase immunoreactivity (ChATi) and acetylcholinesterase (AChE) histochemistry in human vestibular end-organs. ChATi and AChE activity was found in numerous bouton-type terminals at the basal area of the vestibular hair cells. These terminals were found to contact type II vestibular hair cells and the afferent chalices surrounding type I hair cells. This study provides the first evidence that the human efferent vestibular axons and terminals are cholinergic.

Subcellular innervation patterns of the calcitonin gene-related peptidergic efferent terminals in the chinchilla vestibular periphery

We examined the ultrastructural distribution of calcitonin gene-related peptide immunoreactivity in the peripheral vestibular system of the chinchilla to study the innervation patterns of this efferent neuropeptide. Immunoelectron microscopic localization of calcitonin gene-related peptide immunoreactive terminals in the maculae and cristae revealed an extensive innervation pattern on the afferent vestibular pathway. Calcitonin gene-related peptide immuno-reactive terminals made synaptic contacts with the unmyelinated portions of the primary afferent vestibular dendrites innervating both type I and type II hair cells. Abundant synaptic contact between calcitonin gene-related peptide immunoreactive terminals and the chalices surrounding type I hair cells was observed. Direct contact between calcitonin gene-related peptide immunoreactive terminals and type II hair cells was observed. In addition, vesiculated efferent terminals without calcitonin gene-related peptide immunoreactivity were seen synapsing on the chalices of type II hair cells and on the surrounding type I hair cells. The primary afferent somata in the vestibular ganglion of Scarpa did not contain calcitonin gene-related peptide immunoreactivity. Unmyelinated calcitonin gene-related peptide immunoreactive axons passed among the primary afferent fibers in Scarpa's ganglion, and these fibers continued through the subepithelial regions of the vestibular end-organs. The calcitonin gene-related peptide immunoreactive axons ramified to produce numerous calcitonin gene-related peptide immunoreactive terminals throughout the neurosensory epithelium of the maculae and cristae. These data suggest that calcitonin gene-related peptide-mediated modulation of the afferent vestibular system is functionally important.

Malignant hyperthermia in the otology patient: the UCLA experience

Malignant hyperthermia is a seemingly rare genetic myopathy. Hypermetabolic crisis accompanied by a rise in body temperature to as high as 44 degrees C is its hallmark. Malignant hyperthermia is usually triggered by potent inhalational anesthetics and/or depolarizing muscle relaxants. Because of the extraordinary risk of death in patients who are at risk, otologists may be reluctant to operate on these patients. Seven such patients were referred to the Section of Otology, Neurotology, and Skull Base Surgery and the UCLA Malignant Hyperthermia Center Following first episodes of malignant hyperthermia or with a strong family history of malignant hyperthermia for anesthetic and surgical management. They were anesthetized with nitrous oxide, barbiturates, opiates, tranquilizers, and nondepolarizing muscle relaxants. The patients were not treated prophylactically with dantrolene. Cardiac monitoring, end-tidal PC02, and rectal temperatures were followed. All seven patients had a vastus lateralis muscle biopsy performed and subsequent caffeine/halothane contracture studies completed. The contracture study was positive in six of the seven patients studied. No anesthetic or surgical complications were encountered. This study demonstrates that patients at risk of developing malignant hyperthermia crisis can have otologic surgical procedures performed safely while undergoing appropriately selected general anesthesia.

Cloning and sequencing of genomic DNA extracted from archival human temporal bone sections

Cloning techniques allow the engineering and production of highly purified DNA. Further advances in molecular biology have provided the means to identify DNA sequences in a rapid fashion. Sequencing methods can identify mutations, deletions, polymorphisms, or confirm a known genetic sequence. The use of these techniques in clinical medicine has made it possible to accurately diagnose infectious diseases and determine the molecular etiology of many genetic disorders and malignancies. In this study, DNA extracted from archival, celloidin-embedded temporal bone sections has been cloned and sequenced using these techniques. We amplified, cloned, and sequenced varicella-zoster viral DNA extracted from archival temporal bone sections from patients who had herpes zoster oticus. The application of cloning and sequencing techniques to DNA extracted from archival temporal bones provides the methodology to study temporal bone pathology at the molecular level.

Distribution of calcitonin gene-related peptide mRNA and immunoreactivity in the rat central and peripheral vestibular system

The distribution of calcitonin gene-related peptide (CGRP) mRNA and immunoreactivity (CGRPi) was examined in sections of brainstem and decalcified temporal bones to study the peptidergic innervation patterns in both the central and peripheral vestibular system. In the brainstem, neuron somata associated with the vestibular system and containing CGRP mRNA and CGRPi were found in both the dorsolateral and medial regions of the group E vestibular efferents as well as scattered throughout the caudal pontine reticular nucleus (CPR). The only labelled neuron somata containing CGRP mRNA and CGRPi in the temporal bone were found in the gustatory geniculate ganglion. Coarse CGRPi axons were traced ventrally from the dorsolateral and medial group E somata and dorsally from the CPR somata. CGRPi axons from the medial group E and CPR crossed the facial nerve ventral to the facial genu before entering the eighth nerve root. Immunoreactive axons projected from medial group E cells, beneath the ependyma of the fourth ventricle, to the contralateral brainstem. Unmyelinated CGRPi fibers passed among the primary afferent fibers in Scarpa's ganglion and continued through the subepithelial regions of the vestibular end-organs. Within the neurosensory epithelia of the maculae and cristae, the CGRPi axons ramified to produce numerous CGRPi terminals. An efferent neuromodulatory role of CGRP in the vestibular system is inferred from the wide distribution of CGRP mRNA and immunoreactivity found within efferent vestibular neurons.

Polymerase chain reaction amplification of DNA from archival celloidin-embedded human temporal bone sections

A method was developed for fast and efficient isolation of DNA from formalin-fixed, decalcified, celloidin-embedded human temporal bone sections for subsequent use in polymerase chain reaction (PCR) DNA amplification. The method relies on the use of an enzymatic digestion with proteinase K to release and solubilize the patient's DNA from an individual 20- to 25-microns temporal bone section. The method described should be of great value to those investigators extracting DNA from archival individual human temporal bone sections for polymerase chain reaction assays of specific genetic alterations associated with temporal bone pathologies. The molecular characterization of viral infections, oncogenes, or other etiological agents of disease using PCR could provide important information regarding the etiopathogenesis of many auditory, vestibular, and facial nerve disorders, such as autoimmune hearing loss, congenital hearing losses, Meniere's disease, otosclerosis, or Bell's palsy.

Early diagnosis of otologic Wegener's granulomatosis using the serologic marker C-ANCA

Wegener's granulomatosis is a systemic vasculitis that may involve any organ system. Otologic manifestations are common, and can be the presenting complaint. In the past, diagnosis often necessitated the development of characteristic pulmonary or renal disease. The identification of a new serologic marker, cytoplasmic pattern antineutrophil cytoplasmic autoantibody (C-ANCA), allows for the early diagnosis of Wegener's granulomatosis and gives the patient the best chance for remission with cytotoxic therapy. We report two patients with Wegener's granulomatosis who presented with refractory otitis media, one of whom subsequently developed facial nerve paralysis, in which an early diagnosis was facilitated by the use of the C-ANCA test. Otologic manifestations of Wegener's granulomatosis and the basis of the C-ANCA test are discussed.

Management of large scalp defects with local pedicle flaps

Recent reports have emphasized free-flap reconstruction for large defects of the scalp and calvarium following resection of tumors, infection, or trauma. In most cases, however, a carefully planned local transposition or rotation flap may be equally effective, and the technical difficulties and donor-site problems associated with microsurgical tissue transfer are then avoided. We present 10 patients whose full-thickness scalp defects covered an average area of 241 cm2, or 27 percent, of the skull surface. Although this series included defects as large as 450 cm2, or 50 percent, of the skull surface area, each was easily managed with a local pedicle flap transfer. Four patients were reconstructed with parietal scalp transfer, four with an occipital scalp flap, and two with temporal scalp transfer. The technique and results are discussed.

Ultrastructural organization of calcitonin gene-related peptide immunoreactive efferent axons and terminals in the vestibular periphery

The ultrastructural distribution of calcitonin gene-related peptide immunoreactivity (CGRPi) was examined in sections of decalcified temporal bones in order to study the complex peptidergic innervation patterns of this efferent neuromodulator in the peripheral vestibular system of the rat. A new method of preembedding immunoelectron microscopy was developed to accomplish this study. Unmyelinated CGRPi axons, measuring 1 to 3 microns in diameter, passed among the primary afferent fibers in Scarpa's ganglion, and these fibers continued through the subepithelial regions of the vestibular end-organs. Within the neurosensory epithelia of the maculae and cristae, the CGRPi axons ramified to produce numerous CGRPi terminals. Immunoelectron microscopic localization of CGRPi terminals in the maculae and cristae revealed an extensive innervation pattern on the afferent vestibular pathway. Calcitonin gene-related peptide immunoreactive terminals made synaptic contacts with the unmyelinated portions of the primary afferent vestibular fibers innervating both type I and type II hair cells. Abundant synaptic contact between CGRPi terminals and the chalices surrounding type I hair cells was observed. Rare direct contact between CGRPi terminals and type I or type II hair cells was observed. In addition, vesiculated efferent terminals without CGRPi were seen contacting type II hair cells. These data suggest that the efferent vestibular system has a much more complex innervation pattern on the afferent vestibular pathway than previously believed.

In situ hybridization for the localization of gene products in the auditory system

In this article, an overview of the technique and examples of our data demonstrate that our protocols produce excellent, reliable in situ hybridization of mRNAs and immunohistochemical localization of mRNA translation products in the temporal bone and brain stem. This in situ hybridization protocol has been used to localize eight different mRNAs, including four types of nicotinic acetylcholine receptor subunit mRNAs, actin mRNA, CGRP mRNA, and two mRNAs coding for gap junction proteins, in both paraffin-embedded and sectioned (6 microns) and cryostat sectioned (15 microns) temporal bones (unpublished data). In conclusion, in situ hybridization of mRNAs with single-stranded RNA probes allows screening of brain stem and temporal bone sections for the expression of specific genes, with cellular resolution, and this protocol gives reliable results for all mRNAs studied. Of great potential significance is the ability to assess variations in gene expression by in situ hybridization of specific mRNAs. It is expected that such variations accompany changes in the physiologic state of an organism, such as developmental, pathologic or experimentally induced, and that these variations in gene expression are important in understanding basic auditory processes at the cellular level.

Differential diagnosis of virus-like particles in the human inner ear

The entire endolymphatic duct and sac as well as the vestibular epithelia were obtained from four patients with Meniere's disease during translabyrinthine (TL) eighth nerve section and from 12 patients undergoing TL resection of acoustic schwannomas. After these specimens were processed for routine transmission electron microscopy (TEM), they were studied for morphologic evidence of viral infection. Although no virus particles were identified, numerous regularly occurring cell components and artifacts were found to morphologically mimic viruses. An atlas of these structures is presented.