THE ACTION OF SUBSTANCE-P METHYL-ESTER ON COCHLEAR POTENTIALS IN THE GUINEA-PIG

The action of the substance P agonist, substance P methyl ester (SPME) on cochlear potentials was examined in the guinea pig. Previous studi es have shown that SPME is a selective agonist for neurokinin 1(NK1) r eceptor. Perfusion with SPME at a concentration of more than 10(-6)M p roduced an increase in the amplitudes of the compound action potential and negative summating potential in a dose-dependent manner. N1 laten cy showed a tendency to be shortened, but this change was not signific ant. Amplitudes of the cochlear microphonics and endocochlear potentia l remained unchanged. Substance P fragment 7-11, an inactive analogue, produced no changes in the cochlear potentials. In contrast, the subs tance P antagonist [D-Pro2,D-Trp7,9]-SP blocked the action of SPME on the cochlear potentials. These results suggest that substance P may mo dulate neurotransmission through NK1 receptors in the cochlea.