title: Analysis of small hair bundles in the utricles of mature guinea pigs.
abstract: OBJECTIVE
  This study aimed to determine whether hair cells with immature hair bundles exist in the normal utricular maculae of mature guinea pigs.
  
  
  BACKGROUND
  A low rate of hair cell "turnover" occurs in the vestibular organs of normal adult birds. Small immature-appearing hair cells have been identified in the utricles of juvenile guinea pigs, but their existence in the vestibular system of mature mammals has not been confirmed.
  
  
  METHODS
  Nine utricles from 14- to 16-week-old guinea pigs were processed for scanning electron microscopy. A systematic search for small hair bundles was made. These bundles were classified as either "newborn-like" or "intermediate" depending on specific characteristics of the apical cell surface, the stereocilia, and the kinocilium.
  
  
  RESULTS
  A mean of 7 newborn-like and 41 intermediate hair bundles per utricle were identified. The average hair cell count for the guinea pig utricular macula was 7,200; thus, these small hair bundles comprise 0.7% of the total.
  
  
  CONCLUSIONS
  The small hair bundles are interpreted as developing vestibular hair cells, produced to replace hair cells lost to normal processes. This is thought to represent a biologic phenomenon that is in some ways similar, but in other ways distinct, from hair cell regeneration after trauma.
authors.affiliation: University of Virginia Medical Center, Department of Otolaryngology-Head and Neck Surgery, Charlottesville 22908, USA.
authors.forename: P R
authors.initials: PR
authors.lastname: Lambert
authors.forename: R
authors.initials: R
authors.lastname: Gu
authors.forename: J T
authors.initials: JT
authors.lastname: Corwin
mesh_terms: D000818:Animals; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000648:ultrastructure*; D008854:Microscopy, Electron; D012444:Saccule and Utricle