title: Synaptic plasticity in the medial superior olive of hearing, deaf, and cochlear-implanted cats.
abstract: The medial superior olive (MSO) is a key auditory brainstem structure that receives binaural inputs and is implicated in processing interaural time disparities used for sound localization. The deaf white cat, a proven model of congenital deafness, was used to examine how deafness and cochlear implantation affected the synaptic organization at this binaural center in the ascending auditory pathway. The patterns of axosomatic and axodendritic organization were determined for principal neurons from the MSO of hearing, deaf, and deaf cats with cochlear implants. The nature of the synapses was evaluated through electron microscopy, ultrastructure analysis of the synaptic vesicles, and immunohistochemistry. The results show that the proportion of inhibitory axosomatic terminals was significantly smaller in deaf animals when compared with hearing animals. However, after a period of electrical stimulation via cochlear implants the proportion of inhibitory inputs resembled that of hearing animals. Additionally, the excitatory axodendritic boutons of hearing cats were found to be significantly larger than those of deaf cats. Boutons of stimulated cats were significantly larger than the boutons in deaf cats, although not as large as in the hearing cats, indicating a partial recovery of excitatory inputs to MSO dendrites after stimulation. These results exemplify dynamic plasticity in the auditory brainstem and reveal that electrical stimulation through cochlear implants has a restorative effect on synaptic organization in the MSO.
authors.affiliation: Department of Biomedical Engineering, Center for Hearing and Balance, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Natasha N
authors.initials: NN
authors.lastname: Tirko
authors.forename: David K
authors.initials: DK
authors.lastname: Ryugo
mesh_terms: D000818:Animals; D001306:Auditory Pathways / Q000473:pathology / Q000648:ultrastructure; D002415:Cats; D019929:Cochlear Implantation / Q000379:methods*; D003638:Deafness / Q000473:pathology* / Q000628:therapy*; D004195:Disease Models, Animal; D004558:Electric Stimulation / Q000379:methods; D055032:Electron Microscope Tomography; D050487:Glycine Plasma Membrane Transport Proteins / Q000378:metabolism; D009473:Neuronal Plasticity / Q000502:physiology*; D009847:Olivary Nucleus / Q000473:pathology* / Q000503:physiopathology; D013569:Synapses / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D013572:Synaptic Vesicles / Q000648:ultrastructure; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism
chemical_list: D050487:Glycine Plasma Membrane Transport Proteins; D050598:Vesicular Glutamate Transport Protein 1