Recent evidence suggesting that mammalian hair cells are capable of regeneration after noise-induced trauma or exposure to ototoxic drugs lends hope to the possibility of restoring hearing to humans with certain types of sensorineural deafness. The most extensively studied system in terms of regeneration has been the inner ear of the chick. Investigators have focused on the anatomical and functional recovery of auditory nerve fibers that innervate the hair cells of the inner ear; the role that cochlear efferent fibers may play in recovery, however, has not been addressed. In order to understand how cochlear efferent fibers contribute to the recovery of the damaged cochlea, we propose a study of the efferent innervation of the cochlea in the normal chick. Indeed, the contribution that cochlear efferent fibers make to the normal physiology of the inner ear remains to be elucidated. Such information may lead to the improved design of cochlear prostheses by increasing their ability to integrate incoming auditory information with the brain's feedback control via cochlear efferent fibers. A first step toward better understanding the role that cochlear efferents might play in hair cell regeneration and normal functioning of the chick's inner ear is their neurochemical identification. This proposal will determine the distribution of immunocytochemically-distinct cochlear efferent cell bodies in the brainstem as well as the distribution of their terminals in the cochlea. Neurochemically-identified efferent terminals will be examined from normal cochleas and from those exposed to ototoxic drugs. Although the locations of cochlear efferent neurons in the chick brainstem are known, the inputs to these neurons are not. Identifying what controls the activity of cochlear efferent neurons might provide some indication of the functional role that cochlear efferents play in the normal physiology of the cochlea. The superior olive (SO) is a likely source of inputs to cochlear efferent neurons. Although the avian SO receives information on both the timing and intensity of auditory signals, it is not known if these two types of information remain in separate channels within the SO or whether cochlear efferent neurons receive both time-and intensity-coded information from the SO. We will study the types of cells in the SO that project to cochlear efferent neurons and relate them to inputs to the SO from time- and intensity-coded pathways.
| Stack, K E; Code, R A (2000) Calretinin expression in the chick cochlear nucleus after deafferentation. Brain Res 873:135-9 |
| Code, R A; McDaniel, A E (1998) Development of dynorphin-like immunoreactive auditory nerve terminals in the chick. Brain Res Dev Brain Res 106:165-72 |
| Code, R A; Westbrook, E W; Ryals, B M (1998) Effects of columella removal on inner ear morphology in the chick. Hear Res 126:113-22 |
| Parks, T N; Code, R A; Taylor, D A et al. (1997) Calretinin expression in the chick brainstem auditory nuclei develops and is maintained independently of cochlear nerve input. J Comp Neurol 383:112-21 |
| Code, R A (1996) Chick auditory terminals contain dynorphin-like immunoreactivity. Neuroreport 7:2917-20 |
