M. Ulfendahl et al., CHANGES IN THE MECHANICAL TUNING CHARACTERISTICS OF THE HEARING ORGANFOLLOWING ACOUSTIC OVERSTIMULATION, European journal of neuroscience, 5(6), 1993, pp. 713-723
An in vitro preparation of the guinea-pig temporal bone was used to st
udy the effects of acoustic overstimulation on the mechanical tuning c
haracteristics of the inner ear. Using laser heterodyne interferometry
, the vibratory responses of selected sensory and supporting cells wit
hin the hearing organ were measured in response to acoustic signals ap
plied to the ear to obtain mechanical tuning curves before and after a
pplying acoustic overstimulation. Following overstimulation the freque
ncy at which the maximal vibration response occurred moved towards low
er frequencies, the vibration amplitude generally increased and the sh
ape of the mechanical tuning curves became considerably flatter. These
effects were seen within minutes of overstimulation. The micromechani
cal changes were accompanied by distinct morphological changes mainly
affecting the first row of outer hair cells, which were swollen and sh
ortened. Hensen bodies and swelling of the subsurface cisternae were o
bserved in the affected cells. Apart from this, most of the shortened
cells looked structurally intact, had undamaged sensory hair bundles a
nd made synaptic contacts to both afferent and efferent nerve fibres.
The results demonstrate that the outer hair cells play a key role in d
etermining the tuning of the hearing organ.