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

• Published in: Journal of comparative neurology (1911) Vol. 520; no. 10; pp. 2202 - 2217
• Main Authors: Tirko, Natasha N., Ryugo, David K.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.07.2012; Wiley Subscription Services, Inc
• 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
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23038

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.