EFFECT OF SODIUM-NITROPRUSSIDE ON COMPOUND ACTION-POTENTIAL THRESHOLDS IN THE GERBIL COCHLEA

The presence of active nitric oxide synthase (NOS) in the spiral gangl ion cells of the cochlea suggests that the neuromodulator nitric oxide (NO) may play a role in hearing. This study investigated the effects of sodium nitroprusside (SNP), an NO donor, upon cochlear function med iated through its activation of guanylate cyclase. In gerbils, cochlea r compound action potential (CAP) thresholds were recorded after cochl ear perfusions of control and test solutions in four experimental grou ps. Perfusions were performed using the following: artificial perilymp h solution (APS); the NO donor SNP; the guanylate cyclase inhibitor me thylene blue (MB); and sodium dodecyl sulfate (SDS), which facilitates MB entrance into cells. SNP caused significant elevations of CAP thre sholds from baseline (25 dB SPL +/- 1.54 dB to 64.3 dB SPL +/- 2.54 dB ). SNP with MB also resulted in significant CAP threshold elevations ( 29.4 dB SPL +/- 4.27 dB to 38.1 dB SPL +/- 4.0 dB); however, these ele vations were significantly lower than those seen in SNP perfusions wit hout MB. Drilling perfusion holes and perfusion of APS, APS/SDS, and M B/SDS/APS solutions did not significantly affect CAP thresholds. These results suggest that the NO donor nitroprusside does affect cochlear neuromodulation and effects this mediation in part through NO activati on of guanylate cyclase.