We have developed techniques whereby single auditory-nerve fibers can be filled with horseradish peroxidase (HRP) after their response properties have been determined by recording discharge patterns intracellularly. After histological processing, each labelled fiber can be traced to its endings inthe cochlea where detailed observations can be made of the nature of the neuron, its synaptic connections, and the condition of the sensory cell(s) that are innervated by that fiber. Because the HRP reaction rpoduct is electron dense, the morphological analysis can be performed at both the light and electron-microscopic levels. The studies proposed here should provide us with definitive data on some basic questions concerning the relation between structure and function in the peripheral auditory system. A definitive map relating cochlear locus and characteristic frequency will be established for the cat. It should also be possible to determine the anatomical basis for the functional classification of auditory nerve fibers according to threshold and spontaneous discharge rate. The new labelling techniques will also be applied to the study of noise induced cochlear pathology. Specific physiological abnormalities at the single unit level can then be associated with the morphological condition of the relevant hair cells and nerve fibers. We propose to study the pathological changes associated with a wide range of functional losses, from the slight to the profound, and to investigate these correlations at a number of post-exposure survival times, from the chronic to the acute. From these studies we expect to increase greatly our understanding of the cellular bases for sensorineural hearing disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS018339-04
Application #
3398389
Study Section
Communication Sciences and Disorders (CMS)
Project Start
1982-04-01
Project End
1987-03-31
Budget Start
1985-04-01
Budget End
1986-03-31
Support Year
4
Fiscal Year
1985
Total Cost
Indirect Cost
Name
Massachusetts Eye and Ear Infirmary
Department
Type
DUNS #
073825945
City
Boston
State
MA
Country
United States
Zip Code
Liberman, M C; Dodds, L W; Pierce, S (1990) Afferent and efferent innervation of the cat cochlea: quantitative analysis with light and electron microscopy. J Comp Neurol 301:443-60
Liberman, M C (1990) Effects of chronic cochlear de-efferentation on auditory-nerve response. Hear Res 49:209-23
Liberman, M C (1990) Quantitative assessment of inner ear pathology following ototoxic drugs or acoustic trauma. Toxicol Pathol 18:138-48
Warren 3rd, E H; Liberman, M C (1989) Effects of contralateral sound on auditory-nerve responses. I. Contributions of cochlear efferents. Hear Res 37:89-104
Liberman, M C (1989) Rapid assessment of sound-evoked olivocochlear feedback: suppression of compound action potentials by contralateral sound. Hear Res 38:47-56
Warren 3rd, E H; Liberman, M C (1989) Effects of contralateral sound on auditory-nerve responses. II. Dependence on stimulus variables. Hear Res 37:105-21
Brown, M C; Liberman, M C; Benson, T E et al. (1988) Brainstem branches from olivocochlear axons in cats and rodents. J Comp Neurol 278:591-603
Simmons, D D; Liberman, M C (1988) Afferent innervation of outer hair cells in adult cats: II. Electron microscopic analysis of fibers labeled with horseradish peroxidase. J Comp Neurol 270:145-54
Simmons, D D; Liberman, M C (1988) Afferent innervation of outer hair cells in adult cats: I. Light microscopic analysis of fibers labeled with horseradish peroxidase. J Comp Neurol 270:132-44
Liberman, M C (1988) Physiology of cochlear efferent and afferent neurons: direct comparisons in the same animal. Hear Res 34:179-91

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