title: Acute cochlear nucleus compression alters tuning properties of inferior colliculus neurons.
abstract: Auditory brainstem implants (ABI) have been used in neurofibromatosis type 2 (NF2) patients in an attempt to restore hearing sensation, with limited clinical success. Factors associated with poor clinical outcomes for NF2 ABI patients include larger tumour size, longer duration of hearing loss, and brainstem distortion and/or deformation caused by tumours that compress the brainstem. The present study investigated changes in tuning properties of inferior colliculus (IC) neurons following compression of the contralateral cochlear nucleus (CN). The left CN in adult rats (n = 8) was exposed and a 32-channel acute recording probe inserted along the tonotopic gradient of the right IC. In 4 animals, an ethylene vinyl acetate bead was applied to the exposed CN. Three recordings were made corresponding to T(1) = 0 min (before compression), T(2) = 45 min (during compression) and T(3) = 225 min (following bead removal/recovery). Recordings consisted of a response area protocol using pure tones of various frequencies and intensities (1-44 kHz; 10-70 dB SPL) to determine the characteristic frequency for each probe site. Compression of the CN led to sharpened tuning curves, decreased spike rate, and increased threshold and characteristic frequency in the IC. Reversal of compression enabled these variables, excluding threshold, to recover to baseline. NF2 patients may have poorer ABI performance due to damage to the physical structure of the CN, resulting in alterations to the tonotopic organisation of the auditory pathway which may complicate ABI implantation and activation.
authors.affiliation: School of Psychological Science, La Trobe University, Bundoora, Vic., Australia.
authors.forename: Katherine N
authors.initials: KN
authors.lastname: Crea
authors.forename: Mohit N
authors.initials: MN
authors.lastname: Shivdasani
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Argent
authors.forename: Stefan J
authors.initials: SJ
authors.lastname: Mauger
authors.forename: Graeme D
authors.initials: GD
authors.lastname: Rathbone
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: O'Leary
authors.forename: Antonio G
authors.initials: AG
authors.lastname: Paolini
mesh_terms: D000161:Acoustic Stimulation; D000704:Analysis of Variance; D000818:Animals; D038262:Auditory Brain Stem Implants; D001306:Auditory Pathways / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology; D001309:Auditory Threshold / Q000502:physiology*; D017626:Cochlear Nucleus / Q000502:physiology*; D004567:Electrodes, Implanted; D004594:Electrophysiology; D007245:Inferior Colliculi / Q000502:physiology*; D008297:Male; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013194:Staining and Labeling; D013997:Time Factors