Cochlear Microphonic and Action Potential Thresholds during Acute Salicylism

Abstract

Guinea pigs were prepared with indwelling rigid depth electrodes located in the auditory nerve or flexible electrodes placed on the round window membrane. Absolute thresholds (VDL) were traced by the experimenter over 3-min periods by controlling stimulus intensity with a motor driven recording attenuator so that electrophysiological responses displayed on an oscilloscope were kept just detectable from the baseline. Threshold traces were obtained from restrained, waking animals under control conditions and at 2, 4, and 24 h following single injections of 300 mg/kg of sodium salicylate solution. Stimuli were continuous or pulsed trains of 1, 100, 250, or 1000 clicks/sec. Cochlear microphonic threshold traces showed little or no shift, while action potential thresholds were elevated 5–9 dB 2–4 h after injection. No differences between pulsed- and steady-stimulus conditions were demonstrable during salicylism for either CM or AP responses. Envelopes of traces (width in decibels showed no systematic differences between types of response or experimental conditions.