Event Date and Time
1103 Bioscience Research Building

Inhibition of Medial Olivocochlear Neurons

Olivocochlear neurons are the final stage of descending control of the mammalian auditory system. Through their inhibition of cochlear outer hair cells (OHC), the medial olivocochlear (MOC) neurons have been implicated in diverse roles in hearing including cochlear gain control, protection against noise trauma, and detection of salient sounds. MOC neurons have cell bodies in the ventral brainstem where they are activated by a sound reflex circuit from the cochlea, but anatomical evidence suggests that MOC neurons have diverse additional inputs. However, activity of these additional inputs, and whether they inhibit or modulate MOC neurons, has not been demonstrated. We use whole-cell patch-clamp recordings in mouse brain slices, imaging techniques, and computational modeling to investigate inhibitory synaptic inputs to MOC neurons. Glycinergic and GABAergic inhibitory inputs to the MOC originate in the medial nucleus of the trapezoid body (MNTB). This suggests that sound input to the same ear can drive both inhibitory inputs from the MNTB as well as excitatory inputs from the cochlear nucleus onto MOC neurons. Inhibitory inputs depress at rates of stimulation relevant for acoustic stimuli, suggesting decreased inhibitory inputs and increased MOC action potential rates with ongoing sound. The presence of sound-driven inhibition suggests that MOC activity is not a simple reflex, and that MOC function, and thus synaptic output in the cochlea, is the result of interplay between both excitatory and inhibitory synaptic responses.

Dr. Catherine Weisz is an Investigator and Acting Chief of the Section on Neuronal Circuitry at NIDCD/NIH.

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Dr. Catherine Weisz