Tsuyoshi Kitanishi

Vasopressin and oxytocin receptor mRNAs are expressed in the rat inner ear.

THE cause of endolymphatic hydrops, a characteristic finding in Menières disease, is not known. To study the possible involvement of the neurohormones vasopressin and oxytocin in this condition, we investigated whether transcripts of the genes encoding the arginine vasopressin (AVP) and oxytocin receptors are expressed in the rat inner ear. Utilizing the reverse transcription-polymerase chain reaction (RT-PCR) method, primers specific for each receptor showed a single message band of the expected size in the rat inner ear. When the PCR products were cloned, the sequences were identical to those of the real-type (V2) AVP receptor and oxytocin receptor transcripts. The finding of vasopressin and oxytocin receptor mRNAs in the inner ear suggests that these neurohypophyseal hormones may have roles in the regulation of inner ear fluid. In particular, the presence of vasopressin receptor mRNA in the inner ear supports the hypothesis of a relationship between high plasma vasopressin levels and endolymphatic hydrops.

Regulation of inner ear fluid in the rat by vasopressin.

The anti-diuretic hormone vasopressin has been shown to be important in regulating inner ear fluid. The diuretic hormone, CNP, and its receptor, ANP-B receptor, may also function in the regulation of inner ear fluid. To determine whether vasopressin directly affects the fluid level, we infused this hormone to rat and assay of V2-AVP receptor mRNA by semiquantitative RT-PCR demonstrated a significantly lower level of this transcript in vasopressin-infused animals than in saline-infused animals. The levels of CNP and ANP-B receptors mRNA, however, were the same in both groups of rats. Results suggest that high plasma levels of vasopressin may be a principal causal factor of endolymphatic hydrops in Menieres disease, perhaps by down-regulating the number of vasopressin receptors.

RT-PCR analysis of mRNA expression of natriuretic peptide family and their receptors in rat inner ear

To assess the possible physiological role of the atrial natriuretic peptide (ANP) family, we investigated the expression of mRNA of ANP, brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and their receptors in rat inner ear using the reverse transcription-polymerase chain reaction method. ANP and CNP message bands were detected in the inner ear, but the BNP message band was not. Amplification products of the expected sizes of ANP-A, ANP-B and ANP-C receptors were detected in the inner ear. These results suggest that natriuretic peptide family may influence the function of the inner ear through the ANP-A, ANP-B, and ANP-C receptors.

Detection of C-type natriuretic peptide(CNP) and atrial natriuretic peptide(ANP-B) receptor mRNAs in rat inner ear

C-TYPE natriuretic peptide (CNP) is the third member of the natriuretic peptide family which plays an important role in body fluid homeostasis. To determine a possible role of CNP in regulation of an inner ear fluid, we investigated the expression of CNP and atrial natriuretic peptide B receptor (ANP-B receptor) mRNAs in rat inner ear using a reverse transcription polymerase chain reaction (RT-PCR) method. Amplification products with sizes expected for CNP and ANP-B were detected in the inner ear. After cloning and analysis, the sequences for PCR products were identical to those of CNP or ANP-B receptor in the brain. These results indicate that both CNP and ANP-B receptor are expressed in the inner ear of the rat and suggest that CNP may play a role in inner ear function (such as regulation of inner ear fluid) in an autocrine and/or paracrine manner.

Clinical Findings in Meniere's Disease with Bilateral Fluctuant Hearing Loss

Our department conducted an examination of the clinical characteristics of Menières disease with bilateral fluctuant hearing loss, using data obtained in a survey involving sixteen institutes associated with the Vestibular Disorder Research Committee, Japan. A total of 480 cases were surveyed, of which 204 showed normal hearing in the second ear, and were thus classified as unilateral Menières disease, or Menières disease with unilateral involvement; 135 cases showed fluctuating cochlear symptoms in the second ear, and were therefore classified as Menières disease with bilateral fluctuant hearing loss or bilateral involvement. Our results show that patients with bilateral involvement experience increased disruption of daily life activities, and respond poorly to therapy with diuretics or steroids. Hospitalization is often considered for these patients. For these reasons it is especially important that bilaterality be diagnosed as early as possible, and that intensive treatment be carried out. ENT specialists must recognize the seriousness of bilateral involvement, and take particular precautions against its occurrence.

Immunohistochemical Detection of Vasoactive Intestinal Polypeptide (VIP) and the VIP Receptor in the Rat Inner Ear

Vasoactive intestinal polypeptide (VIP) is a 28 amino acid peptide that was originally isolated from porcine duodenum. The presence of VIP has been demonstrated in the central nervous system and peripheral tissues. However, there have been few reports on VIP as a neurotransmitter, especially in the inner ear. To investigate the function of VIP in the rat inner ear, we examined the expression of VIP and the VIP receptor by immunohistochemistry. Using the anti-VIP and VIP receptor antibodies, scattered fibres in the cochlear nerve trunk demonstrating VIP-like immunoreactivity were found, and the spiral ganglion cells demonstrated ring-shaped VIP-like immunoreactivity. Immunoreactivity for the VIP receptor was predominantly found in the spiral ganglion cells. Our results suggest that VIP may play an important role as a possible neurotransmitter not only in the local control of cochlear blood flow, but also in the auditory system.

Autoantibodies against inner ear proteins in patients with delayed endolymphatic hydrops and unilateral juvenile deafness.

Conclusions. Patients with the contralateral type of delayed endolymphatic hydrops (DEH) may undergo an autoimmune attack against the other inner ear. As patients with unilateral juvenile deafness show no progression, despite lengthy observation, the autoantibody against the 68-kDa protein may be unrelated to the pathogenesis of DEH. Objective. The contralateral type of DEH is believed to have an autoimmune etiology, and sometimes develops from unilateral juvenile deafness. The purpose of this study was to determine whether autoantibodies are pathogenetically important in DEH. Material and methods. Sera from 9 patients with DEH, 18 patients with profound unilateral juvenile hearing loss and 15 control volunteer without inner ear diseases were investigated by means of Western blot assay against rat inner ear proteins. Results. Among 8 patients with the contralateral type of DEH, 6 (75%) showed at least 1 reactive band on Western blotting. The protein that reacted most frequently had a molecular weight of 28 kDa, which was consistent with our previous results. Among 18 patients with unilateral juvenile deafness, 5 (28%) showed reactive bands, exclusively at 68 kDa.

Presence of mRNA for vasoactive intestinal polypeptide (VIP) and its receptor in the rat inner ear

Although mechanisms regulating inner ear fluid have not been yet elucidated, control of blood flow has been thought to be of great importance. Vasoactive intestinal polypeptide (VIP) was the first neuropeptide demonstrated in cerebrovascular nerves. To study the possible role of VIP in regulation of inner ear fluid, we investigated the presence of mRNA for VIP and VIP receptor in the rat inner ear using a reverse transcription-polymerase chain reaction (RT-PCR) method. A single band of the size expected for VIP and its receptor was detected in mRNA from the rat inner ear by using primers specific for VIP and the receptor. The nucleotide sequences of the subcloned RT-PCR products were identical to those of rat VIP and the rat lung VIP receptor. These results indicate that both VIP and VIP receptor are expressed in the inner ear of the rat and suggest that VIP may be implicated in regulation of fluid in the inner ear.

Distinct Localization of Peripheral and Central Types of Choline Acetyltransferase in the Rat Cochlea

We previously discovered a splice variant of choline acetyltransferase (ChAT) mRNA, and designated the variant protein pChAT because of its preferential expression in peripheral neuronal structures. In this study, we examined the immunohistochemical localization of pChAT in rat cochlea and compared the distribution pattern to those of common ChAT (cChAT) and acetylcholinesterase. Some neuronal cell bodies and fibers in the spiral ganglia showed immunoreactivity for pChAT, predominantly the small spiral ganglion cells, indicating outer hair cell type II neurons. In contrast, cChAT- and acetylcholinesterase-positive structures were localized to fibers and not apparent in ganglion cells. After ablation of the cochlear nuclei, many pChAT-positive cochlear nerve fibers became clearly visible, whereas fibers immunopositive for cChAT and acetylcholine esterase disappeared. These results suggested that pChAT and cChAT are localized in different systems of the rat cochlea; pChAT in the afferent and cChAT in the efferent structures.

A Case of Inflammatory Pseudotumor of the Orbit

An inflammatory pseudotumor is one of the major neoplasm arising in the orbit. We reported a case of inflammatory pseudotumor of the orbit that was successfully treated. A 73-old-male was referred to our department with a complaint of swelling of the left eye lid. CT findings showed a tumor of the left orbit extending into the ethmoid sinus. Incisional biopsy was performed through the left maxillary sinus. Histologic examination demonstrated a non-specific inflammatory lesion with fibrous tissues and inflammatory cells. The pathologic diagnosis was benign pseudotumor. The patient was given steroid therapy (for 5 weeks) and radiotherapy (2 Gy•~10 days) which resulted in complete response at discharge. Steroid therapy was continued for 6 months after discharge. There has not been any recurrence of the tumor during more than 2 years follow up. Clinical manifestations, histopathologic findings and treatment of this lesion are discussed.