내이 정원창에 투여한 KCI이 cochlear microphonic에 미치는 영향에 대한 실험적 연구
Changes in the cochlear microphonic following application of KCI to the round window
Since 1930, Wever and Bray reported their study of electrical responses of the inner ear, many investigators have examined the phenomena. Four different responses have been demonstrated, viz., Cochlear Microphonic (CM) of Adrian (1931), Action Potential (AP) of Derbyshire and Davis(1935), Summating Potential (SP) of Davis, et al. (1950), and Endocochlear DC Potential (EP) of Bekesy (1951-b).
In order to study effects of chemicals on the inner ear mechanism for hearing, various substances have been introduced into the cochlea by means of injection through the round window, application to the round window membrane, and perfusion methods. The chemicals used included topics] anesthetics (cocaine, procaine and pontocaine), eleotrotytes (NaCl, KCI and CaCl^^2 ), and antibiotics (streptomycin, chloramphenicol, neomycin, polymixin B and colimycin).
The purpose of the present study was to investigate the pathway of KCI flow from the round window membrane to the hair cell and the effects of the chemical on the cochlear microphonic.
Colored guinea pigs, weighing 250∼300g., were anesthetized intraperitoneally with pentobarbital sodium (20 mg/kg of body weight), fixed in a head holder, tracheostomized, curarized, and connected to a primp respirator.
The bulla was exposed by a submandibular approach, and an observation window made with a dental drill. Under an operating stereomicroscope and with use of a hand drill, holes of 100 micron diameter were made into the scala vestibuli and the scala tympani of the basal and third turns. Special care was taken to avoid injury of the endosteum.
The active electrodes, four glass-coated steel wires 100 micron in diameter, were fixed in the holes. The inactive electrode, a copper plate, was inserted into the mouth.
The acoustic signal consisted of continually alternating pure tones of 300 and 3,000 Hz. Intensity was adjusted to produce 200 to 300 microvolt cochlear miorophonic. The cochlear microphonic was continuou니y monitored with a dual-beam oscilloscope and oscillograph.
KCI was applied to the round window membrane as either a solution (160 mEq/l) or in crystal form (30, 67, and 90 gamma).
In order to obtain relatively uncontaminated recordings ocher possible influences on the cochlear microphonics, e, q., anoxia, tissue injury, tissue fluid accumulation and body temperature were also studied and controlled insofar as possible.
RESULTS AND CONCLUSIONS
1. Application of 160 mEq/l KCI solution produced a sudden decrease in the CM of 20∼30 micro-volt which was probably due to the mass effect of the solution. This was followed by a slow decrease, partial recovery, a second slow decrease and finally full recovery.
2. Application of KCI crystals generated a response consisting of an initial augmentation, than a rapid decrease, followed by a slower recovery and final fadeout of the cochlear microphonic. With increase in crystal size, the duration of the cycle was shortened. However, differences in CM output among the various doses was minimal.
Augmentation may be due to localized decrease of the perilymphatic pressure of the scala tympani of the basal turn. The decrease and recovery phase may indicate reversible damage of the hair cells. The last phase, fadeout, is possibly the result of irreversible cell damage by KCI.
3. Applications of KCI which produced distinct changes in the cochlear microphonic at the basal turn, brought about only negligible or minimal changes in the third turn. This indicated that the more probable route of KCI flow from the round window to the hair cells is via the scala tympani and the basilar membrane
rather than via Reissner's membrane.
4. For low frequencies, cochlear microphonic at the basal turn were quite distinctive from those the differential electrode method is preferable to the round window monoelectrode technique for the study of localized specificity of inner ear function.