Eiichi Arakawa

The Effect of Transient Anoxia Upon the Cochlear Potentials

To contribute to the analysis of the electrocochleographical findings in humans, the reversibility of the cochlear potentials (the AP, CM, and SP) after transient anoxia was examined using 24 albino guinea pigs. The durations of anoxia ranged from 5 to 120 min, and the AP, CM and SP were examined one hour after restoration of the blood supply. The mildest form of cochlear damage after transient anoxia was the disappearance of the L-part of the AP and the severest was the complete abolition of these potentials. The severity of the damage closely correlated with the duration of anoxia. The AP was poorer in reversibility than the CM and the SP. These results were analysed and discussed in the light of literature on clinical and basic studies.

Effect of kainic acid upon N1 latency.

Although the N1 latency of whole nerve action potential is one of the important pieces of information obtained from ECochG, there are some conflicting opinions as to whether or not it is prolonged in scnsorineural hearing loss. Kainic acid (KA) is known to destroy neurons selectively through an action at glutamatergic synapses. Therefore, a model of “neural deafness” was made by perfusing the scala tympani with KA solution. The effect of KA upon cochlear microphonics was minimal. Although the N1 amplitude was markedly suppressed by KA, the N1 latency was neither prolonged nor shortened. The result obtained in the present study strongly suggests that the N1 latency is not prolonged in “neural deafness.”

Gas Analysis of the Middle Ear Cavity in Normal and Pathological Conditions

The gas of the tympanic bulla was measured using 18 normal and 14 tube-obstructed guinea pigs. The concentrations of CO2 and O2 were 4.8 +/- 1.0% and 7.2 +/- 1.8% in normal animals, and 4.3 +/- 1.6% and 8.1 +/- 2.0% in tube-obstructed animals, respectively. The bulla was opened to room air and then closed again. The recovery process of each gas was examined. In normal animals, CO2 and O2 were exponentially changed toward the pre-open value with time. The time constants of this recovery process were 15 min and 97 min in CO2 and O2, respectively. In tube-obstructed animals, however, this quick recovery of CO2 was significantly delayed (time constant, 50 to 80 min), although there was no effect upon the recovery of O2. This delayed recovery of CO2 is likely to be due to the edema of the mucous membrane.

Time-Related Changes in Cochlear Potentials in Guinea Pigs with Experimentally Induced Endolymphatic Hydrops

In order to examine the changes in cochlear function occurring in hydropic ears over time, endolymphatic hydrops was provoked by obliterating the endolymphatic sac in 62 albino guinea pigs. Cochlear potentials (EP, CM, SP and AP) were recorded in the 1st, 2nd, 4th and 12th postoperative weeks, respectively. A significant reduction in the level of EP was already observed in the 2nd week and the potential was further suppressed by the 4th week. There was no significant difference between the levels of the 4th and 12th weeks. The amplitudes of CM and AP decreased progressively as time elapsed after the surgery. In sharp contrast to the other potentials, the abnormality in SP was most frequently observed in the 1st week. These results are discussed in the light of the available literature.

Saccular and Cochlear Endolymphatic Potentials in Experimentally Induced Endolymphatic Hydrops of Guinea Pigs

Saccular and cochlear endolymphatic potentials (SEP and CEP) were recorded in 33 normal animals. We confirmed that SEP is not produced in the saccule per se, but is a potential leak from the cochlea. CEP was reduced to one-tenth of the original value when it reached the saccule. Endolymphatic hydrops was provoked in 32 animals, and CEP and SEP were successfully recorded in 29 and 20 cases, respectively. The measurements were performed in the 2nd, 4th and 12th postoperative week. Both CEP and SEP decreased in magnitude as time elapsed after the surgery. This reduction is attributed to the strial dysfunction. In advanced hydrops, CEP transmission to the saccule is greatly inhibited. It is concluded that the saccular dysfunction can occur in the hydropic ear.

Generation Mechanism of the Negative Endocochlear Potential during Early Stage of Anoxia

To investigate the generation mechanism of the -EP in anoxic cochlea, the perilymphatic space was perfused with solution of various K+ concentrations in 38 guinea pigs when the -EP was maximally reduced by anoxia. Although the perfusion of scala tympani and vestibuli with Ringer-Locke solution or that of scala vestibuli with 154 mM K+ solution did not have any effect upon the -EP, the potential was elevated to 0 mV when the scala tympani was perfused with 154 mM K+ solution. Furthermore, the elevation of the potential was less remarkable when the K+ concentration in perfusate was reduced. The level of the potential during perfusion was closely related to K+ concentration in perfusates. The present results strongly suggest that the -EP is the result of the K+ diffusion potential and this diffusion mechanism is performed through the organ of Corti.

ABR Audiometry in the Diagnosis of Cerebellopontine Angle Tumors

Auditory brain-stem responses (ABR) examination with simultaneous lobe-vertex (L-V) and membrane-vertex cm-v) recording was performed in 34 ears with cerebellopontine angle tumors. The detectability of wave I was better in M-V recording than in L-V recording, whereas L-V recording exhibited better detectability of wave V. ABR waveforms were classified into three groups, and the relations between the waveforms and the size of tumor or the degree of hearing loss were analyzed. Positive finding in ABR were obtained in 25 out of 34 ears in the present study. It was stressed that this dual recording in ABR was extremely useful in the diagnosis of cerebellopontine angle tumors.

Cochlear Potentials of Guinea Pigs with Experimentally Induced Renal Failure

In order to investigate the relationship between renal failure and hearing loss, the authors made a guinea pig model with experimentally induced renal failure and examined cochlear potentials (N1, CM and EP). When renal damage was greater, the amplitudes of N1 and CM were decreased and the latency of N1 was prolonged, but EP was within normal range. The sensory cells of the cochlea were considered responsible for the hearing loss in the guinea pig model. No pathological alterations of the cochlea were revealed by a light microscopy. It is suggested that the etiology of the hearing loss was due mainly to metabolic disturbances such as uremic toxins, electrolyte imbalance or endocrine abnormalities.

Electrophysiological Aspects of Surgically-Induced Endolymphatic Hydrops

Endolymphatic hydrops, a characteristic finding in Meniere’s disease can be induced in guinea pigs by surgical obliteration of the endolymphatic duct and sac. Since the reports by Harada [1], Naito [2], and Kimura [3], this hydropic animal has frequently been used as an animal model of Meniere’s disease. The purpose of the present paper is to summarize the results of our 10-year study on these animals [4–9] and to review the recently published articles by other investigators. In the present study, endolymphatic hydrops was induced in 136 albino guinea pigs by obliterating the endolymphatic duct and sac. The presence of the hydrops was histologically confirmed in a majority of the cases (Fig. 5.1). The endolymphatic potential (EP) was recorded through the round window and the recording electrode for other cochlear potentials was placed at the round window. The sound stimuli were clicks generated by a 90 μs rectangular pulse and tone bursts of 0.5–16 kHz with a 1 ms rise-fall time and a 10 ms duration. Similar methods were used in the majority of the reports reviewed in the present paper. Therefore, the methods or the conditions of the experiments used elsewhere will be described only when they differ from ours.

Static and dynamic differences in perilymphatic potassium between scala tympani (ST) and scala vestibuli (SV)

Cochlear perilymph has been regarded as a single, homogeneous fluid, although K is usually found in lower concentration in ST (3–4 mM) than SV (6–7 mM). Since perforation of the cochlea (to aspirate a sample or insert an ion selective electrode) releases cochlear pressure, allowing cerebrospinal fluid (CSF) (3 mM K) to enter, it has not been established whether the K difference is genuine or artifactual by contamination with CSF. In guinea pigs (GP) stringent precautions were used to prevent perilymph leakage and release of cochlear pressure during insertion of the ion selective electrodes. We found that K in ST is significantly lower than in SV, demonstrating for the first time a systematic physiological difference between the scalae. We have also found marked differences between the clearance of K in ST and SV following high K perfusion (20 mM) of guinea pigs (GP) with the cochlear aqueduct occluded. In general, the rate of K clearance from SV is 2–3 times slower than the clearance from ST. These data d...