title: Ventral cochlear nucleus responses to contralateral sound are mediated by commissural and olivocochlear pathways.
abstract: In the normal guinea pig, contralateral sound inhibits more than a third of ventral cochlear nucleus (VCN) neurons but excites <4% of these neurons. However, unilateral conductive hearing loss (CHL) and cochlear ablation (CA) result in a major enhancement of contralateral excitation. The response properties of the contralateral excitation produced by CHL and CA are similar, suggesting similar pathways are involved for both types of hearing loss. Here we used the neurotoxin melittin to test the hypothesis that this "compensatory" contralateral excitation is mediated either by direct glutamatergic CN-commissural projections or by cholinergic neurons of the olivocochlear bundle (OCB) that send collaterals to the VCN. Unit responses were recorded from the left VCN of anesthetized, unilaterally deafened guinea pigs (CHL via ossicular disruption, or CA via mechanical destruction). Neural responses were obtained with 16-channel electrodes to enable simultaneous data collection from a large number of single- and multiunits in response to ipsi- and contralateral tone burst and noise stimuli. Lesions of each pathway had differential effects on the contralateral excitation. We conclude that contralateral excitation has a fast and a slow component. The fast excitation is likely mediated by glutamatergic neurons located in medial regions of VCN that send their commissural axons to the other CN via the dorsal/intermediate acoustic striae. The slow component is likely mediated by the OCB collateral projections to the CN. Commissural neurons that leave the CN via the trapezoid body are an additional source of fast, contralateral excitation.
authors.affiliation: Kresge Hearing Research Institute, Department of Otolaryngology, University of Michigan, Ann Arbor, Michigan 48109-5616, USA.
authors.forename: Sanford C
authors.initials: SC
authors.lastname: Bledsoe
authors.forename: Seth
authors.initials: S
authors.lastname: Koehler
authors.forename: Debara L
authors.initials: DL
authors.lastname: Tucci
authors.forename: Jianxun
authors.initials: J
authors.lastname: Zhou
authors.forename: Colleen
authors.initials: C
authors.lastname: Le Prell
authors.forename: Susan E
authors.initials: SE
authors.lastname: Shore
mesh_terms: D000161:Acoustic Stimulation; D000200:Action Potentials; D000818:Animals; D001306:Auditory Pathways / Q000187:drug effects / Q000293:injuries / Q000502:physiology*; D001933:Brain Stem / Q000187:drug effects / Q000293:injuries / Q000502:physiology*; D002794:Choline / Q000378:metabolism; D003051:Cochlea / Q000293:injuries; D017626:Cochlear Nucleus / Q000502:physiology*; D003638:Deafness / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism; D006168:Guinea Pigs; D006319:Hearing Loss, Sensorineural / Q000503:physiopathology; D008307:Malleus / Q000293:injuries; D008555:Melitten / Q000633:toxicity; D008839:Microelectrodes; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009498:Neurotoxins / Q000633:toxicity; D018058:Tympanic Membrane Perforation
chemical_list: D009498:Neurotoxins; D008555:Melitten; D018698:Glutamic Acid; D002794:Choline