Cochlear potentials and their modulation by low-frequency sound in early endolymphatic hydrops.
Seventeen guinea pigs were unilaterally operated to produce endolymphatic hydrops. After 2 wk (9 animals) or 4 wk (8 animals), extracochlear electrophysiological responses to tone bursts of several frequencies were recorded in both the operated and non-operated ears. In addition, modulation by low-frequency (29 Hz sinusoidal bias) sound of the responses to 8 kHz tonebursts was measured. After the electrophysiological measurements, the animals were killed and examined histologically. Four weeks after the operation, cochlear microphonics in response to a 500 Hz tone burst and to the 29 Hz bias were significantly smaller in the operated ears. The summating potential showed a tendency to be larger in the operated ears. The compound action potential input-output curves for 2 kHz probes showed a small threshold shift accompanied by steep slopes, reminiscent of recruitment. Modulation of summating potentials by the low-frequency bias was smaller on the operated side. In most cochleae an endolymphatic hydrops was observed. Three cochleae showed a collapse of Reissner's membrane.
Klis
J F
JF
Department of Otorhinolaryngology, University Hospital Utrecht, The Netherlands.
Smoorenburg
G F
GF
D000161:Acoustic Stimulation; D000818:Animals; D003055:Cochlear Microphonic Potentials; D004487:Edema / Q000473:pathology / Q000503:physiopathology*; D004710:Endolymph / Q000502:physiology*; D005072:Evoked Potentials, Auditory; D006168:Guinea Pigs; D007759:Labyrinth Diseases / Q000473:pathology / Q000503:physiopathology*; D007761:Labyrinthine Fluids / Q000502:physiology*