@article {Martinez-MonederoENEURO.0078-16.2016, author = {Rodrigo Martinez-Monedero and Chang Liu and Catherine Weisz and Pankhuri Vyas and Paul Albert Fuchs and Elisabeth Glowatzki}, title = {GluA2-containing AMPA receptors distinguish ribbon-associated from ribbon-less afferent contacts on rat cochlear hair cells}, elocation-id = {ENEURO.0078-16.2016}, year = {2016}, doi = {10.1523/ENEURO.0078-16.2016}, publisher = {Society for Neuroscience}, abstract = {Mechanosensory hair cells release glutamate at ribbon synapses to excite postsynaptic afferent neurons, via AMPA-type ionotropic glutamate receptors (GluAs). However, type II afferent neurons contacting outer hair cells in the mammalian cochlea were thought to differ in this respect, failing to show GluA immunolabeling and with many {\textquoteleft}ribbonless{\textquoteright} afferent contacts. Here it is shown that antibodies to the AMPA subunit GluA2 labeled afferent contacts below inner and outer hair cells in the rat cochlea, and that synaptic currents in type II afferents had AMPAR-specific pharmacology. Only half the postsynaptic densities of type II afferents that labelled for PSD95, Shank or Homer were associated with GluA2 immunopuncta or presynaptic ribbons, the {\textquoteleft}empty slots{\textquoteright} corresponding to {\textquoteleft}ribbonless{\textquoteright} contacts described previously. These results extend the universality of AMPA-ergic transmission by hair cells, and support the existence of silent afferent contacts.Significance Statement: Transmission from cochlear hair cells to afferent neurons is mediated by ionotropic glutamate receptors. Inner hair cells efficiently drive acoustic coding in type I afferents that express GluA2-containing AMPA receptors. Type II cochlear afferents differ from type I afferents not only in number, caliber, myelination and excitability, but also in the utility of their terminal contacts with hair cells. Outer hair cell to type II afferent transmission is far less effective, but also employs GluA2-containing receptors. Only half the type II afferent boutons that immuno-labeled for postsynaptic density proteins had GluA2 receptors. And, only GluA2-containing contacts were associated with presynaptic ribbons, the hair cell{\textquoteright}s transmitter release active zones.}, URL = {https://www.eneuro.org/content/early/2016/05/09/ENEURO.0078-16.2016}, eprint = {https://www.eneuro.org/content/early/2016/05/09/ENEURO.0078-16.2016.full.pdf}, journal = {eNeuro} }