The efferent innervation to the cochlea arises from neurons in the brainstem which project to the peripheral auditory receptor, the organ of Corti, where they make synaptic contacts with either cochlear nerve fibers beneath the inner hair cells or with outer hair cells directly. These connections comprise a complex feedback mechanism that can suppress or enhance acoustic reception, depending of the specific efferent subsystem involved. Recent studies in the rat and guinea pig indicate that olivocochlear neurons that contact cochlear nerve fibers beneath the inner hair cells, known as lateral olivocochlear neurons (LOC) are two types, those that terminate in discrete, dense arbors and those that travel long distances making contacts in passing and giving off terminal branches en route. In this project it is proposed to examine the differences in structure and organization between the two kinds of LOC, Shell and Intristic neurons. Relying principally on axonal tracing methods involving DiI, a lipophilic dye that can be used with fixed material, 1) the tonotopic organization of the efferent innervation of the cochlea provided by intrinsic and Shell neurons will be determined in the rat, 2) the prevalence of branching of efferent axons belonging to Intrinsic and Shell neurons will be determined in the rat, since profuse branching could well amplify the impact of a relatively small number of neurons, 3) the specific structures that are contacted by Shell axons in the rat will be determined using the electron microscope, and finally, 4) in order to assess the biological generality of dual LOC systems, attempts will be made to identify Shell and Intrinsic axons in several species in which preliminary evidence suggests dual LOC efferents may exist, including the mouse, gerbil, chinchilla and cat. The studies in the mouse and cat are expected to provide important normative data on the efferent innervation in species being used in Projects II and III, respectively.

Project Start
2001-02-01
Project End
2002-01-31
Budget Start
Budget End
Support Year
17
Fiscal Year
2001
Total Cost
Indirect Cost
Name
Father Flanagan's Boys'Home
Department
Type
DUNS #
City
Boys Town
State
NE
Country
United States
Zip Code
68010
Yang, Tian; Jia, Zhonglin; Bryant-Pike, Whitney et al. (2014) Analysis of PRICKLE1 in human cleft palate and mouse development demonstrates rare and common variants involved in human malformations. Mol Genet Genomic Med 2:138-51
Fritzsch, Bernd; Tessarollo, Lino; Coppola, Enzo et al. (2004) Neurotrophins in the ear: their roles in sensory neuron survival and fiber guidance. Prog Brain Res 146:265-78
Cohn, Edward; Bhattacharya, Gautam; Pearsall, Nicole et al. (2004) Immunohistochemistry and reverse transcriptase-polymerase chain reaction as methods for diagnostic determination of usher syndrome type IIa. Laryngoscope 114:1310-4
Maklad, Adel; Fritzsch, Bernd (2003) Development of vestibular afferent projections into the hindbrain and their central targets. Brain Res Bull 60:497-510
Fritzsch, Bernd (2003) Development of inner ear afferent connections: forming primary neurons and connecting them to the developing sensory epithelia. Brain Res Bull 60:423-33
Maklad, Adel; Fritzsch, Bernd (2003) Partial segregation of posterior crista and saccular fibers to the nodulus and uvula of the cerebellum in mice, and its development. Brain Res Dev Brain Res 140:223-36
Xiang, Mengqing; Maklad, Adel; Pirvola, Ulla et al. (2003) Brn3c null mutant mice show long-term, incomplete retention of some afferent inner ear innervation. BMC Neurosci 4:2
Maklad, Adel; Fritzsch, Bernd (2002) The developmental segregation of posterior crista and saccular vestibular fibers in mice: a carbocyanine tracer study using confocal microscopy. Brain Res Dev Brain Res 135:1-17
Fritzsch, B; Beisel, K W; Jones, K et al. (2002) Development and evolution of inner ear sensory epithelia and their innervation. J Neurobiol 53:143-56
Judice, Tiffany N; Nelson, Nathan C; Beisel, Chase L et al. (2002) Cochlear whole mount in situ hybridization: identification of longitudinal and radial gradients. Brain Res Brain Res Protoc 9:65-76

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