Role of the efferent medial olivocochlear system in contralateral masking and binaural interactions: an electrophysiological study in guinea pigs.

Contralateral broadband noise (BBN) elevates ipsilateral auditory thresholds (central masking) and reduces the amplitude of ipsilateral brainstem auditory evoked potentials (BAEPs). Binaural interactions are complex psychophysical phenomena, but binaural interaction components are easily extracted from BAEPs to monaural versus binaural click stimulation. However, contralateral, or binaural, acoustical stimulation is known to activate simultaneously the crossed and uncrossed medial olivocochlear (MOC) efferent systems and decrease activity in both cochleas.

Changes in electrovestibular brainstem responses after aminoglycoside intoxication in guinea pigs.

Objective: To verify the usefulness of short-latency vestibular responses evoked by a combination of round window electrical stimulation and sinusoidal rotation (electrovestibular brainstem responses; EVBRs) as a new monitoring tool of the vestibular function in animal experiments.

Methods: EVBRs were obtained before, during, and after treatment with aminoglycosides, along with compound action potential (CAP) audiograms. The changes in EVBRs were compared with morphological changes observed by scanning electron microscopy.

Effects of contralateral acoustical stimulation on three measures of cochlear function in the guinea pig.

The magnitudes of suppression of the click-evoked compound action potential of the auditory nerve (CAP), transient click-evoked otoacoustic emissions (TEOAEs) and ensemble background activity of the auditory nerve (EBA), elicited by contralateral acoustical stimulation, were compared in awake or lightly sedated guinea pigs. The contralateral ear was stimulated either by continuous broad-band noise or by low-pass or high-pass noise (intensity 41-62 dB SPL) with cut-off frequencies of 2, 8 and 12 kHz. The maximal suppression of TEOAEs was achieved by contralateral noise containing mainly low frequencies, whereas for suppression of the CAP it was necessary for middle frequencies to be present in the contralateral noise (less than 8 kHz).

Rate influences on tone burst summating potential amplitude in electrocochleography: clinical(a) and experimental(b) data.

Electrocochleographic recordings of action and summating potentials are widely used in the electrophysiological assessment of endolymphatic hydrops (ELH). Increased amplitudes of the summating potential (SP) in response to tone burst stimuli are indicative of positive ELH. This study reports the effect of repetition rate of tone burst stimulation on the SP amplitude.

Acute and chronic effects of aminoglycosides on cochlear hair cells.

The first detectable effect on the auditory system after a single high-dose injection of an aminoglycosidic antibiotic (AA) like gentamicin (GM) is the reversible blockade of medial efferent function, probably via blockade of calcium channels at the base of the outer hair cells (OHC). The kinetics of this effect are compatible with that of the molecule in perilymph. In the course of chronic treatment with lower doses, however, ototoxicity develops only after several days of treatment.