Effect of lidocaine on salicylate-induced tinnitus in guinea pigs: A focus on the auditory cortex.

This study aimed to investigate the effects of the intravenous administration of lidocaine in the auditory cortex after the systemic administration of salicylate. Healthy male albino Hartley guinea pigs were divided into two groups. The control group received only lidocaine, whereas the experimental group received lidocaine after checking for the effects of salicylate. Extracellular recordings of spikes in the primary auditory cortex and dorsocaudal areas in healthy albino Hartley guinea pigs were continuously documented (pre- and post-lidocaine, pre- and post-salicylate, and post-salicylate after adding lidocaine to post-salicylate). We recorded 160 single units in the primary auditory cortex from five guinea pigs and 155 single units in the dorsocaudal area from another five guinea pigs to confirm the effects of lidocaine on untreated animals. No significant change was detected in either the threshold or Q10dB value after lidocaine administration in the primary auditory cortex and dorsocaudal areas. Spontaneous firing activity significantly decreased after lidocaine administration in the primary auditory cortex and dorsocaudal areas. Next, we recorded 160 single units in the primary auditory cortex from five guinea pigs and 137 single units in the dorsocaudal area from another five guinea pigs to determine the effects of lidocaine on salicylate-treated animals. The threshold was significantly elevated after salicylate administration; however, no additional change was detected after adding lidocaine to the primary auditory cortex and dorsocaudal areas. Regarding the Q10dB value, lidocaine negated the significant changes induced by salicylate in the primary auditory cortex and dorsocaudal areas. Moreover, lidocaine negated the significant changes in spontaneous firing activities induced by salicylate in the primary auditory cortex and dorsocaudal areas. In conclusion, changes in the Q10dB value and spontaneous firing activities induced by salicylate administration are abolished by lidocaine administration, suggesting that these changes are related to the presence of tinnitus.

The effect of systemic administration of salicylate on the auditory cortex of guinea pigs.

OBJECTIVE: To investigate the effect of systemic administration of salicylate as a tinnitus inducing drug in the auditory cortex of guinea pigs. METHODS: Extracellular recording of spikes of the primary auditory cortex and dorsocaudal areas in healthy male albino Hartley guinea pigs was continuously performed (pre- and post-salicylate). RESULTS: We recorded 160 single units in the primary auditory cortex from five guinea pigs and 156 single units in the dorsocaudal area from another five guinea pigs. The threshold was significantly elevated after the administration of salicylate in both the primary auditory cortex and dorsocaudal areas. The Q10dB value was significantly increased in the primary auditory cortex, whereas it has significantly decreased in the dorsocaudal area. Spontaneous firing activity was significantly decreased in the primary auditory cortex, whereas it has significantly increased in the dorsocaudal area. CONCLUSION: Salicylate induces significant changes in single units of both stimulated and spontaneous activity in the auditory cortex of guinea pigs. The spontaneous activity changed differently depending on its cortical areas, which may be due to the neural elements that generate tinnitus.

Ear involvement in patients with rheumatoid arthritis.

OBJECTIVE: This study evaluates the degree of hearing impairment in patients with rheumatoid arthritis (RA) and examines the correlation between hearing impairment and the clinical data or chemical mediators. BACKGROUND: Both sensorineural hearing loss (SNHL) and conductive hearing loss (CHL) have been reported in patients with RA, but the results of most studies are not in agreement, and the pathophysiology of hearing impairment in RA is not well known. METHODS: Hearing in patients with RA and controls was examined using pure-tone audiometry and tympanometry. Also, the amounts of pro-inflammatory cytokines and matrix metalloproteinases in addition to antibodies against type II collagen in plasma of the patients with RA were determined using enzyme-linked immunosorbent assay. RESULTS: The frequency of SNHL in the patients with RA was higher than in normal controls (36.1% versus 13.9%), and bone conduction at 2,000 Hz differed significantly between the patients with RA and the controls (p < 0.01). Moreover, the presence of SNHL was related to ESR (p < 0.05), plasma interleukin-6 (p < 0.05), and plasma matrix metalloproteinase-3 (p < 0.001). On the other hand, CHL was not observed, whereas As-type tympanograms increased in the patients with RA (p < 0.01). Abnormal tympanograms were not related to any clinical findings or any chemical mediators tested. CONCLUSION: We demonstrated that there is increased SNHL in patients with RA, which may result from systemic inflammation and tissue injury, and increased latent-type CHL caused by stiffness of the middle ear system whose mechanisms are not yet clear.

Effects of nimodipine on quinine ototoxicity.

The compound action potential (CAP) in response to a click train stimulus was recorded at the round window of guinea pigs. Administration of quinine hydrochloride (200 mg/kg) significantly elevated the CAP thresholds by 5 to 25 dB (p < .05), and the CAP waveform elicited by the click train stimulus was abnormal. The amplitude of the CAP elicited by the second click was bigger than that elicited by the first click. These changes may be caused by an abnormally broadened N1 response to the first click in the click train. In contrast, CAP waveforms elicited by the second and subsequent clicks appeared normal. After administration of nimodipine (2 mg/kg), the CAP thresholds and waveforms elicited by the click train stimulus were unchanged. Simultaneous administration of both quinine (200 mg/kg) and nimodipine (2 mg/kg) resulted in the same electrophysiological changes as those induced by quinine alone. These results suggest that nimodipine prevents neither the deterioration in the CAP nor the abnormal properties in the response to a click train stimulus.

Changes in CAP adaptation in experimentally induced endolymphatic hydrops.

OBJECTIVE: To determine the effect of experimentally induced endolymphatic hydrops (ELHs) on compound action potential (CAP) adaptation. METHODS: The CAP was recorded 1 month after surgical treatment to produce ELH. The CAP threshold in response to click stimuli showed no significant differences between the hydropic and control groups. The CAP was elicited from the retroauricular-exposed round window using a silver ball electrode. Click trains consisting of 10 clicks with an interclick interval (Deltat) of either 4 or 8 ms were delivered through a loudspeaker placed in front of the animals' ears. The patterns of adaptation to these click trains were evaluated as functions of Deltat and intensity level. RESULTS: An abnormal pattern of CAP adaptation was observed in hydropic ears. CONCLUSIONS: These findings suggest that early ELH influences CAP adaptation.

Zinc deficiency and tinnitus.

OBJECTIVE: To determine if there is a correlation between serum zinc levels and audiometric performance in tinnitus patients. METHODS: Seventy-three patients participated in this study. Patient's age was restricted to 20-59 years. All patients were examined at the otolaryngology outpatient clinic of the St. Marianna University Toyoko Hospital. The control group consisted of 38 age- and sex-matched healthy volunteers. A blood sample was taken to measure serum zinc levels. Hypozincemia was set at a level of the mean minus one S.D. in the control group. An average hearing sensitivity was calculated as the mean value of hearing thresholds at five frequencies: 250, 500, 1000, 2000, and 4000 Hz. Normal hearing was indicated when the hearing threshold at each of these frequencies was within 20 dB of normal thresholds. RESULTS: There was no significant difference in serum zinc levels between patients with tinnitus and controls. However, patients with tinnitus who had normal hearing had significantly lower serum zinc levels compared to controls. In contrast, no significant difference in serum zinc levels was found between patients with tinnitus who had hearing loss, and controls. A significant correlation between average hearing sensitivity and serum zinc level was observed. CONCLUSIONS: These findings suggest that zinc is involved in the generation of tinnitus, especially in patients whose hearing is relatively normal.

Effect of fexofenadine hydrochloride on cedar pollinosis.

OBJECTIVE: To investigate the therapeutic efficacy of fexofenadine hydrochloride (Allegra(R) tablets), an antihistaminic launched in 2001, in patients with cedar pollinosis by dividing them into two groups for comparison, i.e. the early-treatment group in which treatment was started before the initial day of the pollen scattering, and the therapeutic-treatment group in which treatment was started after the initial day of the pollen scattering. METHODS: Early-treatment group: patients who visited the hospital before the initial day of cedar pollen scattering were orally given one tablet of the drug twice daily. Therapeutic-treatment group: patients who visited the hospital after the initial day of cedar pollen scattering were orally given one tablet of the drug twice daily. The total number of cases in which the efficacy evaluation was possible was 37 cases (19 cases of the early-treatment group and 18 cases of the therapeutic-treatment group) after application of exclusion criteria. RESULTS: The useful rate of moderately effective or better against sneeze was 90% in the early-treatment group, and 78% in the therapeutic-treatment group, and there was a significant difference between both groups. The degree of satisfaction in the early-treatment group was 3.8 points, and 4.2 points in the therapeutic-treatment group, and the therapeutic-treatment group showed a higher score, but there was no significant difference between both groups. As adverse reaction, there was only one case of mild dizziness (2.7%), and no other adverse reactions such as sleepiness were observed. CONCLUSIONS: It was suggested that fexofenadine hydrochloride administered in patients with cedar pollinosis from before substantial pollen scattering might control their symptoms to mild ones, and might control worsening of their symptoms after the substantial pollen scattering, and, therefore, the drug was considered to be useful in early therapy.

Neurotological findings in a patient with narrow internal auditory canal: a case report.

We report neurotological findings in a patient with unilateral narrow internal auditory canal, as confirmed by computed tomography. The patient presented no auditory brainstem response on the affected side. Vestibular tests including vestibular-evoked myogenic potentials (VEMP) and caloric test revealed normal function of both inferior and superior vestibular neural pathways.

A case of carcinoid tumor of the middle ear.

We report here a case of a carcinoid tumor observed in the middle ear (ME), which was initially diagnosed as ME adenoma. The patient was a 64-year-old woman who was first seen in our hospital in March 2001 for a 7-month hearing loss. On otoscopic examination, a whitish mass could be observed through the intact tympanic membrane. High-resolution computed tomography demonstrated a tumor-like lesion in the ME with no evidence of bone destruction. A myringotomy and biopsy were performed and an initial diagnosis of ME adenoma was made. Light microscopy showed fragments of cellular tissue in which both glandular (adenomatous) and trabecular (carcinoid) growth patterns could be identified, but neuroendocrine differentiation was not detected by immunohistochemistry (negative staining for chromogranin A and synaptophysin). On the basis of this diagnosis, the patient underwent a tympanomastoidectomy in June 2001, in which the presumed ME adenoma was completely excised and the diagnosis was modified to ME carcinoid tumor. Immunohistochemical examinations at that time showed positive staining of the tumor cells for chromogranin A and synaptophysin. This case suggests the difficulties in distinguishing ME carcinoid tumors from ME adenomas. The patient is without recurrence of her disease to date.

Acoustic tensor tympani response and vestibular-evoked myogenic potential.

OBJECTIVE: To investigate the acoustic response properties and the vestibular-evoked myogenic potential (VEMP) in various lesions. STUDY DESIGN: Retrospective study of the clinical records of patients. METHODS: Neurotological tests including acoustic response and VEMP were performed and analyzed in 62 patients with facial palsy, otosclerosis, ossicular chain interruption, sensorineural hearing loss, or acoustic tumor. RESULTS: Inverted acoustic responses were observed in 25 of 38 (65.8%) patients with facial palsy, in 5 of 6 (83.3%) patients with acoustic tumor, and in all patients with otosclerosis, ossicular chain interruption, or sensorineural hearing loss. These inverted responses were obtained only when ipsilateral stimulation was used. The thresholds of the inverted responses were statistically significantly higher than those of the normal response. CONCLUSIONS: The vibration of the eardrum is thought to stimulate the ipsilateral trigeminal nerve, leading to contraction of the tensor tympani muscle. The stapedius response had an inhibitory effect on the inverted response. Vibration of the stapes footplate (which requires a normal middle ear conduction system) is necessary to induce the VEMP, whereas the functioning of the facial and cochlear nerves is independent of the VEMP response.

Effects of nimodipine on salicylate ototoxicity.

The purpose of this study was to examine the effects of nimodipine on salicylate ototoxicity in guinea pigs. The compound action potential (CAP) was recorded at the round window, and the cochlear blood flow (CBF) was measured simultaneously from the lateral wall of the basal turn of the cochlea by laser Doppler flowmetry. After administration of salicylate (100 mg/kg), the CAP thresholds were significantly elevated, by 5 to 20 dB (p < .05), and the CBF was significantly decreased (p < .05). After administration of nimodipine (2 mg/kg), the CAP thresholds were unchanged, but the CBF had increased significantly (p < .05), while systemic blood pressure had decreased significantly (p < .05). Simultaneous administration of both salicylate (100 mg/kg) and nimodipine (2 mg/kg) resulted in significant elevation of the CAP thresholds (p < .05), while the CBF did not decrease. These results suggest that nimodipine prevents the decrease in CBF induced by salicylate, but that nimodipine does not prevent the deterioration in the CAP.

Quinine affects the response properties of compound action potentials elicited by periodic click trains.

The effects of systemically applied quinine on the compound action potential (CAP) were investigated in 5 guinea pigs. A dose of 200 mg/kg body weight of quinine hydrochloride was administered intramuscularly, and CAPs were recorded at the round window before and after administration. The CAP thresholds of the animals were elevated by 5 to 25 dB approximately 30 minutes after administration, and thresholds recovered in some animals during the experimental session. The CAP waveform elicited by the click train stimulus was abnormal after administration of quinine. The amplitude of the CAPs elicited by the second click was larger than that of those elicited by the first click. These changes may be induced by an abnormally broadened N1 response to the first click in the click train following quinine administration. In contrast, the CAP waveforms elicited by the second click and by the following clicks in the click train appeared normal.