Audiology & neuro-otology
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Audiology & neuro-otology · Sep 1998
Comparative StudyDegeneration of spiral ganglion cells in the chinchilla after inner hair cell loss induced by carboplatin.
The anticancer drug carboplatin has been used to generate inner hair cell (IHC) lesions in the cochlea of chinchillas. This has provided a valuable model for the study of the relative roles of IHCs and outer hair cells (OHCs). In the present study, we examined the pathological and temporal relationships between the degeneration of the cochlear IHCs and type I spiral ganglion cells (SGCs). ⋯ On the other hand, the SGC population progressively decreased from 2 to 12 weeks after treatment, to about half of the control density values. A positive correlation existed between the density of SGC and the number of surviving IHCs. These results indicate that selective damage to IHCs causes a distinct loss of SGCs.
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Audiology & neuro-otology · Mar 1998
ReviewLearning-induced physiological memory in adult primary auditory cortex: receptive fields plasticity, model, and mechanisms.
It is well established that the functional organization of adult sensory cortices, including the auditory cortex, can be modified by deafferentation, sensory deprivation, or selective sensory stimulation. This paper reviews evidence establishing that the adult primary auditory cortex develops physiological plasticity during learning. Determination of frequency receptive fields before and at various times following aversive classical conditioning and instrumental avoidance learning in the guinea pig reveals increased neuronal responses to the pure tone frequency used as a conditioned stimulus (CS). ⋯ This prediction has been confirmed. Additional tests of the model are described. RF plasticity is thought to translate the acquired significance of sound into an increased frequency representation of behaviorally important stimuli.
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Audiology & neuro-otology · Jan 1997
The molecular biology of hair cell regeneration in the avian cochlea.
The sensory cells of the ear, the hair cells, are damaged by loud noise or certain types of drugs. In the bird cochlea, new hair cells are produced to replace those that are lost. Regeneration also occurs in the vestibular epithelia of birds, fish, and mammals but does not occur in the mammalian cochlea. ⋯ However, the small size of this organ has made it difficult to use traditional molecular biology methods to address these problems. Recently, many molecular techniques have been adapted for use with small amounts of tissue. Northern blot analysis, the ribonuclease protection assay, semiquantitative PCR and differential display of mRNA are all techniques that are being used to greatly improve our understanding of hair cell regeneration and may eventually provide the information necessary to induce regeneration in hearing-impaired humans.
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Neck afferents not only assist the coordination of eye, head, and body, but they also affect spatial orientation and control of posture. This implies that stimulation of, or lesions in, these structures can produce cervical vertigo. ⋯ Neurological, vestibular, and psychosomatic disorders must first be excluded before the dizziness and unsteadiness in cervical pain syndromes can be attributed to a cervical origin. To date, however, the syndrome remains only a theoretical possibility awaiting a reliable clinical test to demonstrate its independent existence.
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Audiology & neuro-otology · Mar 1996
Incomplete recovery of chicken distortion product otoacoustic emissions following acoustic overstimulation.
Distortion product otoacoustic emissions (DPOAEs) were measured in chickens before and after exposure to a 525-Hz pure tone (120 dB SPL, 48 h). The exposure caused extensive hair cell loss and destroyed the tectorial membrane along the abneural edge of the basilar papilla in the low-to-mid-frequency region of the cochlea. ⋯ By 28 days of recovery, the previously damaged region of the basilar papilla had been repopulated by hair cells and the lower honeycomb layer of the tectorial membrane had regenerated, but not the upper fibrous layer. The upper fibrous layer of the tectorial membrane was still missing after 16 weeks of recovery and the region of damage corresponded closely to the frequency regions where the DPOAEs were depressed.