Suppression of auditory nerve activity in the guinea pig cochlea by 1-(p-bromobenzoyl)-piperazine-2,3-dicarboxylic acid.

1-(p-Bromobenzoyl)-piperazine-2,3-dicarboxylic acid (pBB-PzDA; 0.03-5 mM), an excitatory amino acid antagonist, was perfused through the guinea pig cochlea while monitoring various cochlear potentials. pBB-PzDA (1-5 mM) reversibly suppressed the amplitude of the compound action potential of the auditory nerve (CAP) and increased the latency of N1 (the first negative wave of the CAP) at all sound intensities. pBB-PzDA had no detectable effect on N1 latency at CAP threshold or presynaptic potentials such as the cochlear microphonics and the summating potential. At the single-cell level pBB-PzDA (5 mM) reversibly suppressed the firing of single auditory nerve ganglion cells. pBB-PzDA appeared to have the same potency in the cochlea as kynurenic acid. We conclude that the mechanism of action of pBB-PzDA is consistent with an antagonism of the hair-cell transmitter at the afferent auditory nerve.