Hair Cell Activity Research Articles

Diode pump cochlear audition theory.

A model of the cochlea is developed whereby the motion of the basilar membrane due to sound pressure in the scala media creates, through the pivotal motion of the pillars of Corti, modulated pressure on the fluid in the inner sulcus. This modulated pressure causes fluid to flow through the tectorial gap at selected longitudinal positions along the basilar membrane causing excitation or inhibition of the hair cell activity depending upon the direction of fluid flow. Specific functional relationships are developed for a two component model composed of a resonant and a nonresonant region. Relevant experimental data show good agreement with the predictions of the model.

An analysis of microphonic potentials of the sacculus of goldfish.

1. A study was made to clarify the nature of the intramacular microphonic potentials of the sacculus of goldfish in comparison with the more common, negative microphonic potential which can be recorded from the saccular lumen. The intramacular microphonic potential was evoked as mostly positive deflections and at the same frequency as sound, while negative microphonic potential was evoked at twice the frequency of the sound.2. A comparison was made of different types of microphonic potentials obtained from various depths of the macula. Effects of pressure changes applied to the fish's abdomen were also studied.3. Studies on input-output function disclosed that the intramacular microphonic potential was sinusoidal in shape for a weak sound, but it deviated from sinusoidal when sound intensity increased, for its negative deflections were clipped. It was found that the negative microphonic potential could be recorded only for such a relatively strong sound.4. From these results, it was concluded that the intramacular microphonic potential represents the activity of hair cells of a homogeneous group. The operational characteristics of hair cell activity were drawn based on results of input-output studies.5. The recording conditions of intramacular microphonic potentials are discussed in relation to the functional differentiation of the saccular macula whose dorsal and ventral halves are concerned only with the reception of compression and rarefaction phases of sound, respectively.

Functional Significance of the Efferent Control Mechanisms

The question of the functional significance of the efferent innervation of the vestibular system is one of the most urgent ones. Ever since the ultrastructural evidence of efferent synapses on the hair cell became available, this matter has been pondered upon by many people. A first guess would be that the efference acts as a setting mechanism of the basic hair cell activity. Results obtained with d.c. polarization which showed that it is possible to shift the working point of a hair cell up and down its S-shaped characteristic make it encouraging to think that hyperpolarization of the hair cell membrane via the efferent synapse could achieve this very effect at any rate unidirectionally by inhibition. This possibility is still to be taken seriously. Two recent findings show convincingly that the basic activity of the hair cells can be affected by efference. In one case, the activity of the hair cells in the lateral line organ of Xenopus is inhibited whenever the ventral horn cells of the spinal cord are activated for swimming movements. In the other, the same happens in a goldfish immobilized by MS 222 when the animal is subjected to an optokinetic stimulus to which paralysis prevents it from responding by an appropriate motor response.

Active ion transport from the scala vestibuli into the scala media. Participation therein of Reissner's membrane and its blockade.

The effect of G-strophantin and 2.4-dinitrophenol introduced into the scala vestibuli of 24 guinea pigs was studied by measuring endocochlea and microphonic potentials (EP and MP) which indicate ion transport and the activity of hair cells. MP were evoked by tones of 500, 1000 and 2000 c/sec. and an intensity of 60 dB. MP were always found to change together with EP but in dependence on changes of EP. Inhibition of ion transport with G-strophantin introduced into the scala vestibuli decreased EP to nearly zero while 2.4-dinitrophenol even caused EP to show negative values which in part represent the diffusion potential of a certain ionic difference between the cochlear duct and the surroundings. It is concluded that not only the stria vascularis, but also Reissner's membrane, participate in active ion transport between the cochlear duct and its surroundings. The active ion transport is a source of EP.

Efferent inhibition in the cochlea related to hair-cell dc activity: study of postsynaptic activity of the crossed olivocochlear fibres in the cat.

Intracochlear dc potentials were evoked by stimulating the crossed olivocochlear fibres and were recorded with microelectrodes in 28 cats. From the organ of Corti to the scala media, the dc potentials changed from positive to negative and became larger by a factor of 4–10, reaching −3 mV relative to a reference electrode outside the cochlea. It is concluded that the dc potentials represented postsynaptic activity, generated by crossed olivocochlear fibres impinging on outer hair cells, and that auditory-nerve fibres are presynaptically inhibited by such activity. New and previous findings on the action of the crossed olivocochlear fibres are discussed in relation to present concepts of summating potentials. The findings that centrifugally and acoustically evoked dc activity interact are taken to indicate that sound-evoked dc activity in hair cells might regulate activity in auditory nerve fibres. New and previous findings on the uncrossed olivocochlear fibres are discussed. The tentative hypothesis is proposed that these fibres inhibit by their action on the afferent terminals underneath the inner hair cells, and perhaps in no other way.

Vulnerability of the organ of Corti in poisoning.

The direct effects of some toxic drugs (kanamycin, dihydrostreptomycin, chloramphenicol, and quinine) upon the organ of Corti have been observed in the guinea pigs. The drug was injected into the middle ear cavity and subsequently reached the organ of Corti through the round window membrane. After several days, the inner ear was taken out and stained with the reagents for succinic dehydrogenase or DPN diaphorase, which were introduced into the tympanic scala through the round window. The following results were obtained:1. Loss of the enzymes was more apparent in the cells witli higher metabolic activities, such as the outer hair cells or the nerve endings.2. Patterns of damage to the organ of Corti seemed to be almost identical. But a smaller difference between antibiotic poisoning and quinine poisoning was found.Generally, it seemed to be possible that higher metabolic activities of the outer hair cells are responsible for weakness of the cells in pathologic processes in the ear.Die unmittelbaren Wirkung...

Children's Socks

One prominent manifestation of mechanical activity in hair cells is spontaneous otoacoustic emission, the unprovoked emanation of sound by an internal ear. Because active hair bundle motility probably constitutes the active process of nonmammalian hair cells, we investigated the ability of hair bundles in the bullfrog9s sacculus to produce oscillations that might underlie spontaneous otoacoustic emissions. When maintained in the normal ionic milieu of the ear, many bundles oscillated spontaneously through distances as great as 80 nm at frequencies of 5–50 Hz. Whole-cell recording disclosed that the positive phase of movement was associated with the opening of transduction channels. Gentamicin, which blocks transduction channels, reversibly arrested oscillation; drugs that affect the cAMP phosphorylation pathway and might influence the activity of myosin altered the rate of oscillation. Increasing the Ca ²⁺ concentration rendered oscillations faster and smaller until they were suppressed; lowering the Ca ²⁺ concentration moderately with chelators had the opposite effect. When a bundle was offset with a stimulus fiber, oscillations were transiently suppressed but gradually resumed. Loading a bundle by partial displacement clamping, which simulated the presence of the accessory structures to which a bundle is ordinarily attached, increased the frequency and diminished the magnitude of oscillation. These observations accord with a model in which oscillations arise from the interplay of the hair bundle9s negative stiffness with the activity of adaptation motors and with Ca ²⁺-dependent relaxation of gating springs.