Electrophysiological and Immunohistochemical Analysis of Inhibitory Input to Neurons in the Medial Olivocochlear Circuit

Authors

• MJ Fischl
• L Torres Cadenas
• I Dame
• CJC Weisz

Abstract

Medial olivocochlear neurons (MOCs) reside in the auditory brainstem and are part of an efferent feedback circuit that receives sound information and projects back to the cochlea. While the function of MOC feedback to the cochlea is well studied, the physiology of MOCs and their presynaptic inputs is poorly understood. Our lab has recently observed that MOCs receive inhibitory input. However, the specific nature, source and function of these inputs are unclear. Here, we sought to support this observation using immunohistochemical analysis of synapses onto MOC neurons and further explore the electrophysiological features of these inputs. For immunohistochemical analysis we used antibodies associated with both inhibitory and excitatory synaptic transmission. We observed presynaptic localization of both GABA- and glycinergic markers in addition to the known glutamatergic input. We also found GABAa receptors localized to MOCs, indicating the capacity for GABA reception. We employed whole-cell patch clamp recording of MOCs paired with focal glutamate uncaging to determine the source of inhibitory input. Uncaging glutamate in the medial nucleus of the trapezoid body (MNTB) resulted in a significant increase in the frequency of postsynaptic currents in the patched MOC cell from 7.6 ± 3.5Hz in control conditions to 17.1 ± 13.4Hz during the stimulus (n=15, p

Scientific Focus Area: Neuroscience

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