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Conclusion: Our study demonstrates that the regulation of D2 receptors may be frequency specific. The reduction in cochlear microphonics (CM) and distortion product otoacoustic emission (DPOAE) amplitudes after perfusion with a D2 antagonist suggests that this receptor plays a role in the regulation of cochlear hair cell activation. Objectives: Dopaminergic terminals are subject to negative feedback from dopamine D2 receptors. In the present study we investigated whether the regulation of dopamine D2 receptor is frequency specific and evaluated changes in CM in guinea pig cochlea. Methods: A total of 30 male guinea pigs were randomly assigned to 3 groups and perfused with artificial perilymph (AP), AP containing ethanol (0.1%), or a D2 antagonist (L741626) for 2 h. In each group, compound action potentials (CAPs) evoked by a 1, 2, 4, 8, 16 or 24 kHz tone pip, CM evoked by 4 kHz tone bursts, and DPOAEs were measured before and 2 h after perilymphatic perfusion. Results: Perfusion with the D2 antagonist resulted in increased CAP thresholds compared with the other two groups at high frequencies (4, 8, 16, 24 kHz, p < 0.05); however, no significant increase was observed at low frequencies (1, 2 kHz, p > 0.05). There was a significant reduction in DPOAEs and CM amplitudes after the 2 h perfusion with the D2 antagonist. A CM input/output (I/O) function curve plotted with the stimulating level as input and the CM relative amplitude as output indicated obvious nonlinearity after the 2 h perfusion in all three groups. [ABSTRACT FROM AUTHOR]

Conclusions: The majority of the patients with unilateral auditory neuropathy spectrum disorder (UANSD) were pediatric and mostly showed a great degree of hearing loss when diagnosed. Abnormal auditory brainstem response (ABR) and preserved otoacoustic emissions (OAEs) and/or cochlear microphonics (CM) were important features to differentiate it from common sensorineural deafness and central nerve hearing loss. Objective: To identify the clinical characteristics of patients with UANSD. Methods: This was a retrospective study involving 14 patients diagnosed as having UANSD between 2004 and 2010 in the Chinese PLA Hospital. Results: In all, 50% of the cases were males (1:1 sex ratio) and the average age of onset was 4.1 years. Of the 14 affected ears with UANSD in these cases, 6 were left-sided, while 8 were right-sided. Of the 14 contralateral ears, 4 presented with sensorineural hearing loss, while the other 10 showed normal hearing. The degree of hearing loss in the 14 affected ears varied, including moderate in 1, moderately severe in 4, severe in 5, and profound in 4. ABRs were absent in the 14 affected ears, while the OAEs, and/or CM were present. [ABSTRACT FROM AUTHOR]