Olivocochlear innervation of inner and outer hair cells during postnatal maturation: an immunocytochemical study.
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.
Simmons
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Department of Physiological Science, UCLA 90095-1527, USA. simmons@biology.ucla.edu
Moulding
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HD
Zee
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D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis; D003051:Cochlea / Q000033:anatomy & histology* / Q000254:growth & development; D006224:Cricetinae; D004525:Efferent Pathways / Q000033:anatomy & histology / Q000254:growth & development; D006199:Hair Cells, Auditory, Inner / Q000737:chemistry / Q000648:ultrastructure*; D018072:Hair Cells, Auditory, Outer / Q000737:chemistry / Q000648:ultrastructure*; D007150:Immunohistochemistry; D008647:Mesocricetus; D008854:Microscopy, Electron; D009419:Nerve Tissue Proteins / Q000032:analysis; D009476:Neurons, Efferent / Q000737:chemistry / Q000648:ultrastructure*; D009847:Olivary Nucleus / Q000033:anatomy & histology* / Q000254:growth & development; D013572:Synaptic Vesicles / Q000737:chemistry
D009419:Nerve Tissue Proteins; D015740:Calcitonin Gene-Related Peptide