Postnatal maturation of contralateral DPOAE suppression in a precocious animal model (chinchilla) of the human neonate

Abstract

Conclusion: In the neonatal chinchilla, the degree of contralateral distortion product otoacoustic emission (DPOAE) suppression and the latency and time constants of suppression are immature for 40–60 days. This suggests that olivocochlear efferent innervation of outer hair cells is not fully mature at birth in this animal model, and this may also be the case for human neonates. Objectives: To track postnatal changes in the dynamics of the olivocochlear efferent system in an animal model with cochlear development at birth similar to that in humans. Methods: Real-time measurements of contralateral DPOAE suppression were made in 79 ears of anaesthetized chinchillas, ranging in age from 1 day to 70 days. An adult control group (13 ears) was also tested. DPOAE (2f1-f2; f2 = 4.4 kHz; f2/f1 = 1.22) input/output functions were measured. Dynamics of contralateral broadband noise suppression were measured, including latency and suppression time constants. Results: DPOAE amplitude input/output functions are immature until 20–30 days postnatally. The maturation period for contralateral suppression amplitude is about 30 days. Latency of onset suppression was 40 ms at birth reducing to adult values (23 ms) at 40 days. The DPOAE suppression time constant was about 350 ms at birth and mature (230 ms) at 60 days.

Keywords::

• Otoacoustic emissions
• outer hair cell
• superior olivary complex
• olivo-cochlear efferents
• OHC inhibition
• cochlear maturation
• DPOAE suppression dynamics
• neonatal cochlea

Acknowledgments

This work was supported with funding from the Canadian Institutes of Health Research (CIHR). The technical assistance of Jaina Negandhi is much appreciated.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.