Intense sound increases the level of an unidentified amine found in perilymph

The hypothesis tested was that intense sound increases the levels of a substance such as glutamate, a putative neurotransmitter and neurotoxic substance, in the perilymph compartment of the cochlea. Artificial perilymph was perfused through the perilymphatic compartment of the guinea pig cochlea and the effluent collected during successive 10-min periods. The effects of perfusing an artificial perilymph containing normal levels of Na+ (NARP) were compared to the effects of perfusing an artificial perilymph containing very low concentrations of Na+ (VLNa). The effluent was collected during ambient noise and during increasing intensities of broad-band noise (10 min at 106, 112, 118 and 124 dB SPL). Levels of amines in the effluent were measured by HPLC utilizing precolumn o-phthalaldehyde (OPA) derivatization and fluorescence detection. VLNa increased the levels of glutamate and several other amines in effluent from the cochlea compared to levels obtained in NARP. Compared with its level during ambient room noise, the concentration of an unidentified amine labeled Unk 2.5 increased during intense noise (124 dB SPL). Intense noise induced no detectable changes in the concentrations of glutamate and fifteen other amines. The chemical identity and role of Unk 2.5 remain to be determined.