Olivocochlear innervation of inner and outer hair cells during postnatal maturation: an immunocytochemical study

Brain Res Dev Brain Res. 1996 Sep 2;95(2):213-26. doi: 10.1016/0165-3806(96)00084-3.


Changes in the expression of several neurochemical markers associated with either axonal growth (GAP-43), synaptic vesicles (synaptophysin), or the cholinergic population of lateral olivocochlear (OC) efferents were investigated in the postnatal cochlea of hamsters. Growth-associated protein was expressed in the neonatal cochlea but not in the adult; immunoreactivity was found below inner hair cells (IHCs) from postnatal day (P) 2 through P14 and below outer hair cells (OHCs) from P5 to P14. In contrast, synaptophysin was expressed in both the neonate and adult cochlea; immunoreactivity was found below IHCs around P4 and below OHCs at P5. Both GAP-43 and synaptophysin immunoreactivities occurred first below IHCs in basal regions of the cochlea. Efferent fibers containing calcitonin gene-related peptide (CGRP) immunoreactivity were identified as early as P4 within the cochlear nerve but were not observed underneath IHCs until P7. Similar to GAP-43 and synaptophysin immunoreactivity, CGRP expression followed a basal to apical gradient; however, expression below OHCs appeared restricted to apical regions. These data raise the possibility that efferents expressing growth proteins and efferents expressing synaptic vesicle proteins co-exist during the first postnatal week. Furthermore, it is hypothesized that CGRP-containing lateral OC neurons form part of a later, secondary innervation to the cochlea.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcitonin Gene-Related Peptide / analysis
  • Cochlea / anatomy & histology*
  • Cochlea / growth & development
  • Cricetinae
  • Efferent Pathways / anatomy & histology
  • Efferent Pathways / growth & development
  • Hair Cells, Auditory, Inner / chemistry
  • Hair Cells, Auditory, Inner / ultrastructure*
  • Hair Cells, Auditory, Outer / chemistry
  • Hair Cells, Auditory, Outer / ultrastructure*
  • Immunohistochemistry
  • Mesocricetus
  • Microscopy, Electron
  • Nerve Tissue Proteins / analysis
  • Neurons, Efferent / chemistry
  • Neurons, Efferent / ultrastructure*
  • Olivary Nucleus / anatomy & histology*
  • Olivary Nucleus / growth & development
  • Synaptic Vesicles / chemistry


  • Nerve Tissue Proteins
  • Calcitonin Gene-Related Peptide