The relation between the endocochlear potential and spontaneous activity in auditory nerve fibres of the cat.

The relation between the endocochlear potential and spontaneous discharge rate in auditory nerve fibres was determined following intravenous injections of furosemide in anaesthetized cats. Following furosemide administration, both the endocochlear potential and the spontaneous discharge rates of auditory nerve fibres decreased synchronously. The logarithm of the spontaneous discharge rate was proportional to the endocochlear potential. The slope of the logarithmic relation increased as a function of the characteristic frequency of the fibre. The slope of the logarithmic relation is steeper for fibres with 'medium' spontaneous discharge rates (0.5-12 spikes/s) than for fibres with 'high' spontaneous discharge rates (greater than 18 spikes/s). Among high spontaneous rate fibres, the slope does not appear to vary systematically with the spontaneous rate of the fibre. The decrease in spontaneous discharge rate in auditory nerve fibres is interpreted as follows: (1) the injection of furosemide causes a decrease in the endocochlear potential, (2) a decrease in the endocochlear potential produces a linearly related hyperpolarization of the membrane potential of the hair cell by altering the standing current which flows through the transducer membrane, and (3) the logarithm of the rate of release of transmitter quanta decreases with the hyperpolarization of the membrane potential of the hair cell, which decreases the rate of occurrence of action potentials at the hair cell afferent junction.