OBJECTIVETo investigate the suppressive effect and its frequency selection of dopamine on the cochlear auditory afferent nerve activity. To offer an important step in understanding the modulation of dopamine in the inner cell synaptic complex.

METHODSForty guinea pigs were randomly divided into four groups and the whole intracochlear perfusions were performed: (1) perfused with artificial perilymph solutions; (2) perfused with artificial perilymph solutions containing 10 mmol/L dopamine; (3) perfused with artificial perilymph solutions containing 30 mmol/L dopamine; (4) perfused with artificial perilymph solutions containing 50 mmol/L dopamine. Compound action potential (CAP) evoked by different frequencies (250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, 8000 Hz, 16 000 Hz) and cochlear microphonics (CM) evoked by 4000 Hz tone burst were recorded from the round window of guinea pigs before perfusion and 1 hours, 2 hours after perfusions.

RESULTSThere was no significant difference in CAP threshold before and after perfusion in the artificial perilymph solutions group (P > 0.05). An increase of CAP threshold of most detecting frequencies were observed in the three dopamine-perfused groups (P < 0.05). The inhibition effect intended with the increasing of the concentration of dopamine in the perfusion solution. There was significant difference in CAP threshold shift between different frequencies, especially in the group perfused with 30 mmol/L dopamine. The maximal threshold shift was found at 4000 Hz and 8000 Hz. No significant changes of CM amplitude and non-linearity of input-output function were observed before and after perfusion with artificial perilymph solutions and dopamine.

CONCLUSIONSDopamine can inhibit the cochlear auditory afferent nerve, but there is no obvious influence on outer hair cell produced by dopamine. The inhibition effect has frequency selection, the suppression on high frequencies is more stronger than low frequencies.