Kohtaroh Yamamura

Effects of Acute Lead Acetate Exposure on Adult Guinea Pigs: Electrophysiological Study of the Inner Ear

The effects on humans of lead acetate exposure may involve the cranial nerves, since vertigo and sensory neuronal deafness have been reported in lead workers; however, there exist only a few reports concerning the dose effects of lead acetate both on the cochlea and the eighth cranial nerve. The effects of lead acetate on the cochlea and the eighth nerve were investigated systematically using cochlear microphonics (CM), whole-nerve action potential (AP), and endocochlear potential (EP) in guinea pigs (male albino Hartley). Guinea pigs were injected with 2 ml of a 1% solution of lead acetate (20 mg) once a week for 1-5 weeks. The threshold of whole-nerve AP (N1) was elevated by injection of lead acetate, even 40 mg, and whole-nerve AP (N1) output voltage decreased after injection of 100 mg of lead acetate. On the other hand, no change was observed in CM after lead acetate injection (100 mg) or in EP after lead acetate exposure (40 mg). The blood concentrations of lead acetate were as follows (mean): control, 4.5 micrograms/dl; Expt 1, 80 micrograms/dl; Expt 2, 126 micrograms/dl; Expt 3, 142 micrograms/dl. We conclude that dysfunction of the eighth nerve is induced by high-dose lead exposure, but that lead exposure does not induce electrophysiological dysfunction of the organ of Corti and the stria vascularis.

An experimental study of the effects of lead acetate on hearing Cochlear microphonics and action potential of the guinea pig

Guinea pigs were poisoned with repeated i.p. injections of 1% lead acetate. After 5 weeks, the animals were examined electrophysiologically by using cochlear microphonics (CM) and action potential (AP). The thresholds of maximum voltage of N1 in the AP of the animals injected with a total of 100 mg lead acetate were elevated about 15 dB and increased N1 latency was also observed. However, no significant changes in those of CM were found. The results suggest that lead acetate not only induces damage to the peripheral nerves, but also to the cranial nerves.

Effect of 4 kHz tone exposure on the guinea pig inner ear: relation in the change of cochlear microphonics, action potential, electrochemical potential and K+ ion concentration induced by noise exposure.

Using 110 male albino guinea pigs, and applying electrophysiological methods, we investigated the effects of 4 kHz tone at moderate sound pressure level on the inner ear at different exposure times (6, 12, 24 and 48 h). Longer than 12 h exposure to 4 kHz tone had a considerable effect on the hearing, inducing a decrease in the maximum output voltage of cochlear microphonics and an increase in the K+ concentration in the endolymph.

Effects of lead acetate on guinea pig—Cochear microphonics, action potential, and motor nerve conduction velocity

Segmental demyelination and axonal degeneration of motor nerves induced by lead exposure is well known in man, and animals. The effect of lead acetate exposure to man may involve the cranial nerves, since vertigo and sensory neuronal deafness have been reported among lead workers. However, there are few reports concerning the dose-effects of lead acetate both to the peripheral nerve and the cranial VII nerve with measurement of blood lead concentration. The authors investigated the effects of lead acetate to the cochlea and the VIII nerve using CM (cochlear microphonics) and AP (action potential) of the guinea pigs. The effects of lead acetate to the sciatic nerve were measured by MCV of the sciatic nerve with measurement of blood lead concentration.

Effect of lead on electrophoretic mobility of rat erythrocytes.

Lead often affects the erythrocyte membrane. The relationship between the changes in erythrocyte membrane and the anemia caused by lead is still unclear. Initially, the effect of lead injected intraperitoneally on the electrophoretic mobility of rat erythrocytes was investigated in order to study the relationship between them. As indices of lead exposure, hemoglobin (Hb) levels, hematocrits (Ht), delta-aminolevulinic acid dehydratase (ALA-D) activities and blood lead (blood Pb) levels in the injected rats were also examined. Exposure to lead significantly decreased the mobility of rat erythrocytes. The changes in mobility seemed to be less sensitive than those in ALA-D activity, however, the decreases in mobility were simultaneous with or prior to those in Hb level and Ht. The decreases in mobility were evident to some extent below a blood Pb level of 100 micrograms/100 ml and generally present at a level of 100 micrograms/100 ml and over. In the rats exposed to lead a significant negative correlation was found between the mobilities and the logarithms of blood Pb level.

The effect of 6 kHz tone exposure on inner ear function of the guinea pig: relation to changes in cochlear microphonics, action potential, endocochlear potential and chemical potentials of K+-ions and Na+-ions, using a double-barrel glass electrode

Using 97 male albino guinea pigs and applying electrophysiological methods, the effects of a 6 kHz tone were investigated at a moderate sound pressure level to the inner ear during a 24-h exposure time. Following exposure to the 6 kHz tone at 90 dB, cochleas showed decreased maximum output voltage of cochlear microphonics (CM) and action potential (AP). In the endolymph, K+ ion and Na+ ion concentrations remained unchanged during 40 min anoxia and 90 dB tone exposure. At 80 dB sound exposure decreases in maximum output voltage of CM and AP and decreases in the absolute value of EP could not be detected. Endolymph K+-ion Na+-ion concentrations were also unchanged. These findings indicate that diffusion potentials are induced at the same time as decreases of maximum output voltage in CM induced by exposure to sound at 90 dB.

Effects of trichloroethylene exposure on hearing

SummaryFour groups of guinea pigs with normal Preyers reflex were exposed to trichloroethylene (TCE). Each group consisted of nine to 10 naive male albino Hartley guinea pigs of 9 weeks of age with a body weight of approximately 400 g.To test the suggestion that TCE causes damage to the cochlear system, a study was conducted involving four experiments.The results were as follows: No significant difference was observed between the intensity functions of the CM (4 kHz) and AP (7 kHz) potentials of the control groups and those of the TCE-exposed groups by analysis of variance. It was considered that there was no difference in the cochlear reaction to high frequency sound between guinea pig and man. It therefore might be suggested that acute exposure to TCE of a high concentration does not always induce dysfunction of the organ of Corti and the 8th nerve in man.

Experimental Study on the Effects of Gentamicin Injection on the Guinea-pig: Electrophysiological Studies

The inner ear distortion induced by gentamicin (GM), a type of aminoglycoside antibiotic, was examined in guinea-pigs. Previous studies which investigated the function of the eighth cranial nerve and organ of Corti using cochlear microphonics (CM) and compound action potential (CAP) reported ototoxicity following experimental exposure to GM. In this report, the effects of GM on the cochlea and the eighth cranial nerve were investigated systematically by measuring CM, CAP, summating potentials induced by 90 dB (SPL) tone burst, endocochlear potential (EP) and K+ ion concentration of the endolymph. Guinea-pigs were treated with a daily intramuscular injection of GM (60 mg in 1.5 cc) at a dose of 60 mg/kg during different treatment periods. The maximum output voltage of AP was decreased by injection of GM (60 mg/kg x 24). A decrease in the CM maximum output voltage and the elevation of CM pseudothreshold were typically seen after GM injection at a test frequency of 8 kHz and a decrease in CAP was also observed. Changes in EP during 3 min anoxia were observed, in particular a decrease in the absolute value of the negative potential. The endolymph K+ ion concentration remained unchanged. These findings indicate that the diffusion potentials decreased at the same time as reduction of maximum output voltage in CM induced by GM injection.

Motor Nerve Conduction Velocity (MCV) and Lead Content in Sciatic Nerve of Lead-Exposed Rats

There have been many pathological and electrophysiological studies of peripheral nerves in inorganic lead intoxication. Peripheral nerve conduction velocity (NCV) has been used as an objective measure of the effects of lead on the peripheral nerve function and has been examined with blood lead content. There have been few reports on the changes in NCV related to lead content in the peripheral nerve tissue under lead poisoning. In the present study, the authors have examined motor nerve conduction velocity (MCV) of the tail by a non-invasive method and lead content of the peripheral nerve in lead-exposed rats. Furthermore, they have attempted to assess the relationship between these two parameters.

An Electrophysiological Study of the Effects of Acute Methylmercury Chloride Exposure on the Function of the Guinea Pig Cochlea

The inner ear function of methylmercury chloride (MMC)-exposed guinea-pigs was examined in this study. Previous studies which investigated the function of the eighth cranial nerve and Corti-organ using cochlear microphonics (CM), compound action potential (CAP) and measurement of endocochlear potential (EP) reported ototoxicity following experimental exposure to MMC. In this report, the effect of MMC on the cochlea and the eighth cranial nerve were investigated systematically by measuring CM, action potential (AP), EP and K+ ion concentration of the endolymph. Guinea-pigs were injected with 5 mg/kg MMC (using 0.2% solution) twice a week for 1-3 weeks. The maximum output voltage of AP was decreased by injection of MMC (5 mg/kg x 6). A decrease in the CM maximum output voltage and the elevation of CM pseudothreshold was seen after MMC injection. Changes in EP during 3 min anoxia were observed, especially a decrease in the absolute value of the negative potential. The endolymph K+ ion concentration remained unchanged. These findings indicate that the diffusion potentials decreased and at the same time was reduced the maximum output voltage in CM induced by MMC injection (5 mg/kg x 6) in this experiment.