The proposed research addresses specific questions about the development of the auditory periphery and the establishment of the topographic organization of cochlear spiral ganglion projections to the cochlear nuclei (CN). Cytochemical labeling techniques (NB and DiI) for neuronal tract tracing combined with physiological recording and extensive light and electron microscopic analyses will be employed. Initial studies have revealed that projections from basal sectors of the spiral ganglion to the anteroventral subdivision (AVCN) undergo substantial remodeling during post natal development, but the descending collaterals of these same neurons projecting to the dorsal (DCN) and posteroventral (PVCN) subnuclei form nearly adult-like, refined projections at birth. Objectives of further experiments include: 1) To determine in detail the timing and sequence of topographic refinement during development of the highly ordered projections to each subdivision of the CN; specifically to characterize remodeling of projections to DCN and PVCN by studying earlier ages. 2) To examine projections from the apical cochlea to determine of maturation of CN projections parallels the basal-to-apical maturation of the organ of corti. 3) To determine whether CN projections develop normally or if significant reorganization occurs as a consequence of lesions of the spiral ganglion created during early development. 3) To determine whether anatomical remodeling of CN projections underlies the apparent loss of frequency selectivity induced by electrical stimulation with a cochlear implant. 4) To determine whether development of CN projections is activity dependent by examining the effects of inhibition of nitrous oxide synthesis and of blockade of auditory nerve activity. 5) To characterize specific ultrastructural features of postnatal development of the cat cochlea at specific frequency locations. The proposed experiments will increase our understanding of the anatomical framework for information processing mechanisms in the developing peripheral auditory system and will address important questions regarding critical periods and plasticity. Studies in deafened animals have practical implications regarding efficacy and optimization of cochlear implants in children.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC000160-20
Application #
6379188
Study Section
Hearing Research Study Section (HAR)
Program Officer
Freeman, Nancy
Project Start
1980-07-01
Project End
2002-06-30
Budget Start
2001-07-01
Budget End
2002-06-30
Support Year
20
Fiscal Year
2001
Total Cost
$214,503
Indirect Cost
Name
University of California San Francisco
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
073133571
City
San Francisco
State
CA
Country
United States
Zip Code
94143
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Leake, Patricia A; Stakhovskaya, Olga; Hradek, Gary T et al. (2008) Factors influencing neurotrophic effects of electrical stimulation in the deafened developing auditory system. Hear Res 242:86-99
Leake, Patricia A; Hradek, Gary T; Bonham, Ben H et al. (2008) Topography of auditory nerve projections to the cochlear nucleus in cats after neonatal deafness and electrical stimulation by a cochlear implant. J Assoc Res Otolaryngol 9:349-72
Jones, Timothy A; Leake, Patricia A; Snyder, Russell L et al. (2007) Spontaneous discharge patterns in cochlear spiral ganglion cells before the onset of hearing in cats. J Neurophysiol 98:1898-908
Leake, Patricia A; Hradek, Gary T; Chair, Leila et al. (2006) Neonatal deafness results in degraded topographic specificity of auditory nerve projections to the cochlear nucleus in cats. J Comp Neurol 497:13-31
Leake, Patricia A; Snyder, Russell L; Hradek, Gary T (2002) Postnatal refinement of auditory nerve projections to the cochlear nucleus in cats. J Comp Neurol 448:6-27
Sato, M; Leake, P A; Hradek, G T (1999) Postnatal development of the organ of Corti in cats: a light microscopic morphometric study. Hear Res 127:1-13
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