227 | Optogenetic activation of inner hair cells in the mammalian cochlea

Neural excitability, synaptic transmission and neuron-glia interactions

Author: Walen Gribaudo | Email: walen.gribaudo@gmail.com

Walen Gribaudo , Juan Goutman


Inner hair cells (IHCs) in the mammalian cochlea are considered the true phonoreceptors as they are responsible for both the detection of environmental sounds and the signaling of acoustic information to the brain. IHCs present synapses with spiral ganglion neurons (SGNs) that are characterized by the presence of a specialized presynaptic organelle called ribbon. Due to the critical role that these synapses play, multiple studies have concentrated in investigating the physiological basis of its function. However, due to the fragility of the tissue and small size of these cells, purely electrophysiological approaches have been challenging. Here, we investigated the possibility of expressing the light-activated conductance, channelrhodopsin2 (ChR2), in IHCs to circumvent the need for a patch-clamp electrode controlling these cells. Mice carrying a floxed ChR2 cassette were crossed with others expressing Cre under the control of the vesicular glutamate transporter type 3 promotor. The specific expression of ChR2, fused to YFP, was visualized in IHCs, whereas the photo-currents were elicited by illumination with a 470 nm LED at various intensities and recorded by the patch-clamp technique. The relationship between the amplitude of these light responses and the LED power was drawn, finding a maximum photo-current of 520 ± 77 pA with a narrow dynamic range, since minimal to maximal activation was achieved within ~12.5 % of the total LED potency.