title: The Corticofugal Effects of Auditory Cortex Microstimulation on Auditory Nerve and Superior Olivary Complex Responses Are Mediated via Alpha-9 Nicotinic Receptor Subunit.
abstract: The auditory efferent system is a complex network of descending pathways, which mainly originate in the primary auditory cortex and are directed to several auditory subcortical nuclei. These descending pathways are connected to olivocochlear neurons, which in turn make synapses with auditory nerve neurons and outer hair cells (OHC) of the cochlea. The olivocochlear function can be studied using contralateral acoustic stimulation, which suppresses auditory nerve and cochlear responses. In the present work, we tested the proposal that the corticofugal effects that modulate the strength of the olivocochlear reflex on auditory nerve responses are produced through cholinergic synapses between medial olivocochlear (MOC) neurons and OHCs via alpha-9/10 nicotinic receptors.
  
  
  
  We used wild type (WT) and alpha-9 nicotinic receptor knock-out (KO) mice, which lack cholinergic transmission between MOC neurons and OHC, to record auditory cortex evoked potentials and to evaluate the consequences of auditory cortex electrical microstimulation in the effects produced by contralateral acoustic stimulation on auditory brainstem responses (ABR).
  
  
  
  Auditory cortex evoked potentials at 15 kHz were similar in WT and KO mice. We found that auditory cortex microstimulation produces an enhancement of contralateral noise suppression of ABR waves I and III in WT mice but not in KO mice. On the other hand, corticofugal modulations of wave V amplitudes were significant in both genotypes.
  
  
  
  These findings show that the corticofugal modulation of contralateral acoustic suppressions of auditory nerve (ABR wave I) and superior olivary complex (ABR wave III) responses are mediated through MOC synapses.
authors.affiliation: Programa de Fisiología y Biofísica, ICBM, Facultad de Medicina, Universidad de Chile, Santiago, Chile.|Departamento de Tecnología Médica, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
authors.forename: Cristian
authors.initials: C
authors.lastname: Aedo
authors.affiliation: Programa de Fisiología y Biofísica, ICBM, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Terreros
authors.affiliation: Programa de Fisiología y Biofísica, ICBM, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
authors.forename: Alex
authors.initials: A
authors.lastname: León
authors.affiliation: Programa de Fisiología y Biofísica, ICBM, Facultad de Medicina, Universidad de Chile, Santiago, Chile.|Departamento de Otorrinolaringología, Hospital Clínico de la Universidad de Chile, Santiago, Chile.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Delano
mesh_terms: D000818:Animals; D001303:Auditory Cortex / Q000378:metabolism / Q000502:physiology; D003056:Cochlear Nerve / Q000378:metabolism / Q000502:physiology*; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D008297:Male; D051379:Mice; D011978:Receptors, Nicotinic / Q000235:genetics* / Q000378:metabolism; D065832:Superior Olivary Complex / Q000378:metabolism / Q000502:physiology*
chemical_list: C402445:Chrna9 protein, mouse; D011978:Receptors, Nicotinic