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.