Abstract
The effects of electrical stimulation of the inferior colliculus (IC) on the activation of olivocochlear nerve fibers were investigated in guinea pigs in which the 2 f 1− f 2 distortion product otoacoustic emissions (DPOAE) were recorded. Animals were anesthetized with ketamine (33 mg/kg) and xylazine (6.6 mg/kg). Bipolar electrical stimulation of the IC by a train of pulses with currents less than the threshold for evoking muscle twitches resulted in a small depression of the DPOAE amplitude by 0.1–2 dB. The maximal effect was observed when the stimulating electrodes were located in the rostro-medial or ventral parts of the IC. The suppression of electrically evoked DPOAE was similar to the DPOAE suppression produced by acoustical stimulation of the contralateral ear by a broad-band noise. Suppression of DPOAE amplitude in response to both acoustical and electrical stimulation was abolished 1–2 h after a single intramuscular injection of gentamicin (210–250 mg/kg). The results indicate that electrical stimulation of the IC can activate the efferent system and produce DPOAE changes by similar mechanisms as does acoustical stimulation of the contralateral ear.
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