Nobuya Yagi

Prenatal maturation of endocochlear potential and electrolyte composition of inner ear fluids in guinea pigs

SummaryThe maturation of the endocochlear potential (EP) and the inner ear fluid ionic composition were studied in fetal and neonate guinea pigs. The concentration of sodium and potassium in endolymph and perilymph approximated adult values more than 2 weeks before birth. Endolymph had acquired its specific ionic composition before the onset of cochlear microphonics (52–55 gestation days, results of other authors). Positive EP was recorded starting on day 62 of gestation. The EP rose fast to reach near adult level at birth. It is speculated that the negative EP recorded after the onset of cochlear microphonics was an artifact, probably a result of fetal hypoxia. The significance of the negative EP recorded before the onset of the cochlear microphonics is discussed in relation to the source of the anoxic negative EP in the adult animal.

Viscosity of effusion in the middle ear and eustachian tube in patients with otitis media with effusion.

The viscosity of middle ear effusion (MEE) in the tympanic cavity and in the bony portion of the eustachian tube (ET) was compared in 11 specimens (10 patients) with otitis media with effusion (OME). Twenty microliters of effusion from the bony portion of the ET was sampled through myringotomy on the anterosuperior quadrant of the tympanic membrane with a micro-syringe with a curved needle. MEE in the hypotympanum was also sampled by separately puncturing the posteroinferior quadrant of the tympanic membrane. Using the microviscometer developed by one of the authors, the relative viscosity of these effusions were measured, and their natural logarithmic values were compared between the two sites mentioned above in each patient by obtaining their ratios (ET/ME). Effusion was found to have a significantly higher viscosity in the bony portion of the ET than in the hypotympanum (paired t-test: t = 3.859, p less than 0.01). In two patients with OME (serous mastoiditis) due to radiation to the temporal region, the ratios of the viscosity were comparatively small. On the other hand, excluding these two patients with serous mastoiditis mentioned above, the ratios were highest in two patients with a history of more than 60 days of hearing loss. These results were considered to be a clue to the possibility that viscous effusion aggravates ET function as a result of OME.

Stapedial electromyograms recorded by electrocochleography.

The stapedial reflex (SR) can be obtained by the impedance method only when the middle ear is intact. In order to examine the function of the stapedius muscle in diseased ears, the recording of the stapedial electromyogram by an electrocochleographic (ECoG) method was considered. The SR was recorded simultaneously by the impedance method in ten normal subjects for comparison. The outputs of ECoC were averaged by a signal processor up to 200 times under a longer sweep time, and a large biphasic wave with a latency of about 11 ms was obtained on the ECoC records. The amplitude increase of the biphasic wave caused by raising the intensity of the acoustic stimulation paralleled that of the SR. This means that the biphasic wave obtained by ECoC with a latency of about 11 ms originated from the stapedius muscle.

The Effect of Injection of High K+ Solution into Scala Media

Thirty guinea pig ears were studied to investigate the effect of endolymphatic hydrops on the cochlea. High K(+) solution was injected into the scala media, and cochlear microphonics (CM) and endocochlear potential (EP) were observed before, during and after the injection. The CM amplitude decreased rapidly after injection, ending in a depressed plateau value. By contrast, EP remained almost unchanged. By changing the composition of the solution it was suggested that the effect of the injection was mechanical one, rather than biochemical. In three ears, spontaneous recovery of CM was observed during a relatively long interval after the injection. The meaning of these findings for the hearing loss in Menieres disease is discussed.

Effect of Glycerol on the Ep Decrease Caused by Furosemide

A change in endocochlear potential (EP) following furosemide injection was observed in regard to prior glycerol administration in two groups of guinea pigs. In one group, various doses of furosemide (20, 30, 40, 50 mg/kg) were injected, while in the other, glycerol (50 v/v %, 1 ml/kg) was injected prior to the furosemide (20, 30, 40 mg/kg) injection. In the glycerol-furosemide group, the decrease in EP was 40% greater than in the furosemide group. Therefore, glycerol was thought to potentiate the EP lowering action of furosemide. Such an effect of glycerol was assumed to be resulted by facilitating the access of furosemide to the site of action in the stria vascularis.

Effects of glycerol on sodium and potassium concentrations in guinea pig perilymph

ZusammenfassungBlutserum, Liquor cerebrospinalis und Perilymphe von Scala vestibuli und Scala tympani wurden von 85 normalen Meerschweinchen vor und nach i.v. Glycerolapplikation entnommen und die Na- und K-Konzentration bestimmt. Dabei wurde nach Glycerolgabe ein deutlicher Anstieg der Na-Konzentration in der Perilymphe der Scala tympani und im Liquor festgestellt, während die Perilymphe der Scala vestibuli keine Veränderungen zeigte. Die Zunahme der Na-Konzentration wird auf die Dehydration durch das Glycerol zurückgeführt, wobei die unterschiedliche Reaktion beider Perilymphen noch weiterer Untersuchungen bedarf. Die erhobenen Befunde könnten zur Aufklärung der Glycerolwirkung auf das Hören beim endolymphatischen Hydrops von Bedeutung sein.SummarySerum, cerebrospinal fluid (CSF), scala vestibuli perilymph, and scala tympani perilymph were collected from 85 normal guinea pigs both before and after i.v. administration of glycerol (1 ml/kg), and the sodium and potassium concentrations were assessed using a microflame photometer. Marked increases in sodium concentrations were observed in scala tympani perilymph and CSF, while there was a slight decrease in the serum and there was no significant change in scala vestibuli perilymph. These increases in sodium concentrations are considered to occur in the dehydration process in the body fluids mentioned above. On the other hand, increase in the potassium concentrations was found only in scala vestibuli perilymph and thus cannot be explained by simple dehydration process. This potassium elevation in scala vestibuli perilymph should be understood by further experiment on endolymph. It became evident that scala vestibuli perilymph differs from scala tympani perilymph and CSF in the dynamics of electrolytes after glycerol administration. In this regard, the nature of the scala vestibuli as fluid space should be studied in future. The above findings obtained in the present study may imply the significance in elucidating the glycerol effect on hearing of endolymphatic hydrops case.

Eustachian tube patency detected by a photoelectric method

A method was developed to observe tubal orifice movement by fiberscope and detect patency of the eustachian tube by a photoelectric device (phototubometry). A highly sensitive photodiode in the external ear canal detected tube opening as increased luminosity in the tympanic cavity from a light source placed at the pharyngeal portion of the eustachian tube. The phototubometric record was superimposed on a TV screen to compare the opening in the pharyngeal portion of the eustachian tube to the tube opening during swallowing. The phototubometric records of 21 normal subjects examined by phototubometry showed the close relationship with the opened tubal lumen at the tensor veli palatini muscle (TVP) attached portion. This method is useful for examining tubalpatency and observing changes in the pharyngeal portion of the eustachian tube.

A new microviscometer for determining the viscosity of middle ear effusion

A new microviscometer has been developed based on the capillary viscometer method. The device uses a glass sensor tube for aspirating 15-microliter samples. The relative viscosity of the samples was estimated from the negative pressure required for aspiration of the fluid. These pressures ranged widely from 1 centipoise (cp) to 10,000 cp. Measurement of the viscosity of middle ear effusions in 119 samples from 110 otitis media with effusion patients using this device revealed a close relation between their values and their gross appearance (serous less than seromucoid less than mucoid). The microviscometer is useful to determine the relative viscosity of a very small amount of fluid such as middle ear effusion.

Effect of Glycerol on Furosemide-caused EP Decrease in Guinea Pig Neonates

Furosemide, a loop diuretic, reduces the endocochlear potential in guinea pigs. In our previous experiment using adult guinea pigs, glycerol was thought to open the blood-cochlea barrier and to help furosemide to reach its site of action in the stria vascularis. The present study was designed to determine whether or not the same potentiation by glycerol occurs in neonate guinea pigs. In one group, furosemide (10-30 mg/kg) was administered, while in another group, 50 v/v% glycerol (1 ml/kg) was administered 15 minutes prior to the injection of furosemide. Furosemide reduced the EP significantly more in neonates than in adults. This effect was not potentiated in the glycerol-pretreated group. From these findings, it seemed conceivable that the neonate blood-cochlea barrier still remains immature in some functions.

RESPONSE OF SINGLE PURKINJE NEURONS IN THE FLOCCULUS OF ALBINO RABBITS TO CALORIC STIMULATION

The response of Purkinje neurons of the flocculus to caloric stimulation was investigated in the Urethane-chlorarose anesthetized rabbit. Twenty-five of 37 flocculus neurons which responded to ipsilateral caloric stimulation showed an increase in firing response, while 12 neurons showed a decrease. Fifteen of 28 flocculus neurons which responded to contralateral caloric stimulation showed an increase, while the firing of 13 neurons was decreased. Forty-one percent of flocculus neurons responded to ipsilateral caloric stimulation, and 41% responded to caloric stimulation of both sides. Eighteen percent of flocculus neurons responded only to contralateral stimulation. The ipsilateral flocculus may thus be responsible for the major control of the primary vestibular signal flow in the cerebellum.