Research Article

Journal of the Association for Research in Otolaryngology

, Volume 15, Issue 1, pp 73-86

First online:

Input–Output Functions of Vestibular Afferent Responses to Air-Conducted Clicks in Rats

  • Hong ZhuAffiliated withDepartment of Otolaryngology and Communicative Sciences, University of Mississippi Medical CenterDepartment of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center Email author 
  • , Xuehui TangAffiliated withDepartment of Otolaryngology and Communicative Sciences, University of Mississippi Medical Center
  • , Wei WeiAffiliated withDepartment of Otolaryngology and Communicative Sciences, University of Mississippi Medical Center
  • , Adel MakladAffiliated withDepartment of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center
  • , William MustainAffiliated withDepartment of Otolaryngology and Communicative Sciences, University of Mississippi Medical Center
  • , Richard RabbittAffiliated withDepartment of Bioengineering, University of UtahMarine Biological Laboratory
  • , Steve HighsteinAffiliated withMarine Biological Laboratory
  • , Jerome AllisonAffiliated withDepartment of Otolaryngology and Communicative Sciences, University of Mississippi Medical CenterDepartment of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center
  • , Wu ZhouAffiliated withDepartment of Otolaryngology and Communicative Sciences, University of Mississippi Medical CenterDepartment of Neurobiology and Anatomical Sciences, University of Mississippi Medical CenterDepartment of Neurology, University of Mississippi Medical Center

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Abstract

Sound-evoked vestibular myogenic potentials recorded from the sternocleidomastoid muscles (the cervical vestibular-evoked myogenic potential or cVEMP) and the extraocular muscles (the ocular VEMP or oVEMP) have proven useful in clinical assessment of vestibular function. VEMPs are commonly interpreted as a test of saccular function, based on neurophysiological evidence showing activation of saccular afferents by intense acoustic click stimuli. However, recent neurophysiological studies suggest that the clicks used in clinical VEMP tests activate vestibular end organs other than the saccule. To provide the neural basis for interpreting clinical VEMP testing results, the present study examined the extent to which air-conducted clicks differentially activate the various vestibular end organs at several intensities and durations in Sprague–Dawley rats. Single unit recordings were made from 562 vestibular afferents that innervated the otoliths [inferior branch otolith (IO) and superior branch otolith (SO)], the anterior canal (AC), the horizontal canal (HC), and the posterior canal (PC). Clicks higher than 60 dB SL (re-auditory brainstem response threshold) activated both semicircular canal and otolith organ afferents. Clicks at or below 60 dB SL, however, activated only otolith organ afferents. Longer duration clicks evoked larger responses in AC, HC, and SO afferents, but not in IO afferents. Intra-axonal recording and labeling confirmed that sound sensitive vestibular afferents innervated the horizontal and anterior canal cristae as well as the saccular and utricular maculae. Interestingly, all sound sensitive afferents are calyx-bearing fibers. These results demonstrate stimulus-dependent acoustic activation of both semicircular canals and otolith organs, and suggest that sound activation of vestibular end organs other than the saccule should not be ruled out when designing and interpreting clinical VEMP tests.

Keywords

vestibular sound VEMP single unit recording rat saccule semicircular canal