title: Localization of kainate receptors in inner and outer hair cell synapses.
abstract: Glutamate plays a role in hair cell afferent transmission, but the receptors that mediate neurotransmission between outer hair cells (OHCs) and type II ganglion neurons are not well defined. A previous study using in situ hybridization showed that several kainate-type glutamate receptor (KAR) subunits are expressed in cochlear ganglion neurons. To determine whether KARs are expressed in hair cell synapses, we performed X-gal staining on mice expressing lacZ driven by the GluK5 promoter, and immunolabeling of glutamate receptors in whole-mount mammalian cochleae. X-gal staining revealed GluK5 expression in both type I and type II ganglion neurons and OHCs in adults. OHCs showed X-gal reactivity throughout maturation from postnatal day 4 (P4) to 1.5 months. Immunoreactivity for GluK5 in IHC afferent synapses appeared to be postsynaptic, similar to GluA2 (GluR2; AMPA-type glutamate receptor (AMPAR) subunit), while GluK2 may be on both sides of the synapses. In OHC afferent synapses, immunoreactivity for GluK2 and GluK5 was found, although GluK2 was only in those synapses bearing ribbons. GluA2 was not detected in adult OHC afferent synapses. Interestingly, GluK1, GluK2 and GluK5 were also detected in OHC efferent synapses, forming several active zones in each synaptic area. At P8, GluA2 and all KAR subunits except GluK4 were detected in OHC afferent synapses in the apical turn, and GluA2, GluK1, GluK3 decreased dramatically in the basal turn. These results indicate that AMPARs and KARs (GluK2/GluK5) are localized to IHC afferent synapses, while only KARs (GluK2/GluK5) are localized to OHC afferent synapses in adults. Glutamate spillover near OHCs may act on KARs in OHC efferent terminals to modulate transmission of acoustic information and OHC electromotility.
authors.affiliation: Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA; Department of Otolaryngology, Tokyo Medical and Dental University, Bunkyo-ku, 113-8519 Tokyo, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Fujikawa
authors.affiliation: Advanced Imaging Core, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA. Electronic address: petralia@nidcd.nih.gov.
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Petralia
authors.affiliation: Mouse Auditory Testing Core Facility, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Tracy S
authors.initials: TS
authors.lastname: Fitzgerald
authors.affiliation: Advanced Imaging Core, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Ya-Xian
authors.initials: YX
authors.lastname: Wang
authors.affiliation: Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Bryan
authors.initials: B
authors.lastname: Millis
authors.affiliation: Cellular Biology Division, National Cancer Institute, Rio de Janeiro CEP 20230-050, Brazil.
authors.forename: José Andrés
authors.initials: JA
authors.lastname: Morgado-Díaz
authors.affiliation: Department of Otolaryngology, Tokyo Medical and Dental University, Bunkyo-ku, 113-8519 Tokyo, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Kitamura
authors.affiliation: Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Bechara
authors.initials: B
authors.lastname: Kachar
mesh_terms: D000818:Animals; D003051:Cochlea / Q000378:metabolism; D006199:Hair Cells, Auditory, Inner / Q000166:cytology*; D018072:Hair Cells, Auditory, Outer / Q000166:cytology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D009474:Neurons / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018092:Kainic Acid Receptors / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism / Q000502:physiology*; D013701:Temporal Bone / Q000473:pathology; D000097806:GluK2 Kainate Receptor; D000097808:GluK3 Kainate Receptor
chemical_list: D018092:Kainic Acid Receptors; D000097806:GluK2 Kainate Receptor; D000097808:GluK3 Kainate Receptor