Prior Acoustic Trauma Alters Type II Afferent Activity in the Mouse Cochlea

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Cellular Biology

Background:

• Auditory stimuli are transmitted via type I and type II cochlear afferents.
• Type I afferents process sound frequency, intensity, and timing.
• The function of type II afferents is largely unknown, but they may detect damaging sound levels.

Purpose of the Study:

• To investigate the role of type II cochlear afferents in response to acoustic trauma.
• To explore the hypothesis that type II afferents sense loud, potentially damaging sounds.

Main Methods:

• Calcium imaging using GCaMP6f expression driven by marker genes (Th, Drd2, Tac1) in mice.
• Focal damage induced via photoablation in the organ of Corti.
• Assessment of type II afferent activity before and after acoustic trauma.

Main Results:

• Mature type II afferents responded to acute damage less frequently but for longer durations than prehearing neurons.
• Acoustic trauma induced delayed bursts of activity in type II afferents and surrounding cells minutes after initial damage.
• Calcium imaging successfully reported type II afferent responses to damage in mature and noise-exposed animals.

Conclusions:

• Type II cochlear afferents are activated by focal damage and exhibit prolonged responses.
• Acoustic trauma can lead to novel, delayed hyperactivity patterns in the cochlea.
• Calcium imaging is a viable method for studying type II afferent function in response to injury.