Optical Stimulation of the Auditory Pathway by Blue-Shifted Photoswitchable Glutamate Receptor Agonists
1) Antoine Huet (PI; University of Göttingen), coworker:
2) Tobias Moser (PI; University of Göttingen), coworker:
The focus of our work within the SPP 1926 “Next Generation Optogenetics” is to investigate the potential of photoswitchable glutamate receptor agonist to stimulate auditory neurons of the rodent cochlea. This research performed as part of the efforts at the Göttingen Institute for Auditory Neuroscience to develop an optical cochlear implant (i.e. implanted neuroprosthesis which stimulate auditory neurons to restore a sense of hearing to sever to profound deaf people).
A first photoswitch suitable for in-vivo investigation was generated by our collaborator Pau Gorostiza’s team at the Institute for Bioengineering of Catalonia, and administration to the cochlea enabled photostimulation of auditory neurons with a performance similar or better when compared to state of the art optogenetic stimulation.
Our project aims to characterize the photopharmacological response of the auditory neurons at the single and population levels, to investigate to potential of the approach in rodent models of deafness and to perform a proof of concept of chronic photopharmacological stimulation by combining chronic drug delivery and optical cochlear implants with behavioral experiments.
Light stimulation of spiral ganglion neurons (SGNs) in the ear provides a future alternative to electrical stimulation used in cochlear implants. Optogenetic manipulation of neuronal activity is based on the expression of light-sensitive proteins, which requires gene therapy. An alternative to optogenetics is offered by photopharmacology which operates on endogenous receptors and does not require genetic manipulation. Among the “photoswitches”, the Targeted Covalent Photoswitches (TCP) developed by Pau Gorostiza, mainly reacts with the ionotropic kainate receptor GluK1. It was previously shown in vitro on hippocampal neurons that TCP9, the best first-generation compound, activates native GluK1 receptor upon ultraviolet light (380 nm) and a deactivates the receptor upon visible light (500 nm). We performed a preliminary study of a new generation of blueTCP1 and blueTCP2 in vivo by applying the compound to the gerbil cochlea via the round window. Electrocochleography via a round window niche electrode showed a preservation of acoustically-evoked cochlear microphonic and a compound action potential (CAP) amplitude, suggesting a normal cochlear physiology in the presence of TCPs and an absence of acute toxicity. Upon light stimulation using an optical fiber (lambda = 473 nm), we observed optically evoked CAPs (oCAPs). oCAPs could be evoked by light pulse radiant flux as low than 3 mW, oCAP amplitudes were maximum in response to 80 micro s light pulse and were sizable up to a repetition rate of 1 kHz. This performance makes these compounds interesting tools for optical SGN stimulation. The project aims to establish and characterize in vivo photopharmacological stimulation of SGNs using the blueTCP1 and blueTCP2 in the context of developing the optical cochlear implant. Two main aspects will be addressed: i) physiological characterization of SGN responses to blueTCP/light stimulation to identify the most suitable of the two compounds.; ii) testing the translational potential of blueTCP for optical hearing restoration in a deafness model fitted with a chronic drug delivery system coupled to an optical cochlear implant.