Synaptic plasticity in the medial superior olive of hearing, deaf, and cochlear-implanted cats

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 implan...

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Bibliographic Details
Published in:Journal of comparative neurology (1911) 2012-07, Vol.520 (10), p.2202-2217
Main Authors: Tirko, Natasha N., Ryugo, David K.
Format: Article
Language:English
Subjects:
Animals
Auditory Pathways - pathology
Auditory Pathways - ultrastructure
Cats
cochlear implant stimulation
Cochlear Implantation - methods
congenital deafness
Deafness - pathology
Deafness - therapy
Disease Models, Animal
Electric Stimulation - methods
Electron Microscope Tomography
Glycine Plasma Membrane Transport Proteins - metabolism
Neuronal Plasticity - physiology
Olivary Nucleus - pathology
Olivary Nucleus - physiopathology
Synapses - metabolism
Synapses - pathology
Synapses - ultrastructure
synaptic excitation and inhibition
synaptic vesicles
Synaptic Vesicles - ultrastructure
Vesicular Glutamate Transport Protein 1 - metabolism
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Summary: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. J. Comp. Neurol. 520:2202–2217, 2012. © 2012 Wiley Periodicals, Inc.
ISSN:0021-9967
1096-9861
DOI:10.1002/cne.23038