Biomedical subjects

A R Cody

Publications and source records attributed to A R Cody.

21 records · Page 2Linked to original sources

PubMedDate not supplied

Outer hair cells in the mammalian cochlea and noise-induced hearing loss.

Hair cells in the mammalian cochlea transduce mechanical stimuli into electrical signals leading to excitation of auditory nerve fibres. Because of their important role in hearing, these cells are a possible site for the loss of cochlear sensitivity that follows acoustic overstimulation. We have recorded from inner and outer hair cells (IHC, OHC) in the guinea pig cochlea during and after exposure to intense tones. Our results show functional changes in the hair cells that may explain the origin of noise-induced hearing loss. Both populations of hair cells show a reduction in amplitude and an increase in the symmetry of their acoustically evoked receptor potentials. In addition, the OHCs also suffer a sustained depolarization of the membrane potential. Significantly, the membrane and receptor potentials of the OHCs recover in parallel with cochlear sensitivity as measured by the IHC receptor potential amplitude and the auditory nerve threshold. Current theories of acoustic transduction suggest that the mechanical input to IHCs may be regulated by the OHCs. Consequently, the modified function of OHCs after acoustic overstimulation may determine the extent of the hearing loss following loud sound.

Acoustic Stimulation↗

PubMedDate not supplied

Mechanosensitivity of mammalian auditory hair cells in vitro.

Intracellular responses recorded in vitro from the cochleas of anaesthetized mammals have shown that the mechanoreceptive inner and outer hair cells are sharply tuned, accounting for many of the properties of the afferent fibres in the auditory nerve. However, in vivo it has not been possible to measure directly the excitatory mechanical input to these cells (the displacement of their mechanosensitive stereocilia) and thus to determine the relationship between the receptor potentials and displacement of their stereocilia. As a means of circumventing this technical difficulty, we have developed an organ culture of the mouse cochlea and here we describe the receptor potentials generated by the hair cells in response to direct displacement of their stereocilia.

Animals↗

PubMedDate not supplied

Electrophysiological and morphological changes in the guinea pig cochlea following mechanical trauma to the organ of Corti.

Small discrete lesions were produced in the organ of Corti of the guinea pig cochlea using fine probes to produce direct mechanical insult. The electrophysiological state of the cochlea was assessed using N1 electrocochleography and loss of receptor cells determined by scanning electron microscopy. Principal findings were: 1) Excellent agreement between the location of hair cell losses and the frequency of maximum sensitivity change in the N1 audiogram; 2) The spatial extent of the mechanically induced lesion appears to be more important than the total number of hair cells lost, in determining the magnitude of N1 sensitivity loss; 3) Hair cell losses extending over only 72 micrometers could be detected as significant changes in N1 sensitivity. These results further emphasize the accuracy and usefulness of the N1 electrocochleogram for assessing the functional status of the cochlea; 4) Lesions involving only outer hair cell loss also produced marked elevations of N1 threshold.

Action Potentials↗