Afferent and efferent innervation of the chicken basilar papilla was studied during development. Observations from the 10-day embryonic stage (E 10) and the 8-day post-hatch (P 8), were focussed on some characteristic features of the synaptogenesis. The presynaptic specializations (synaptic bodies: SB) appear early (E 10) in hair cells, opposite afferent dendrites. They are found at all developmental stages in tall hair cells (THC), whereas they become rare in short hair cells (SHC). The maturation of afferent endings, especially those connected to THC, is characterized around the E 15 stage, by an over abundant sprouting and branching. The development of the efferent system indicates two stages. Starting at E 14, some small efferent synapses are seen at the base of the THC and SHC. From E 18, the large synapses extend to the base of SHC. These results are discussed in the light of homologies with the mammalian inner and outer cochlear hair cells.
Cochlear degeneration in white cats was investigated by light- and electron-microscopic examinations. A great variety of histological damage was encountered both in completely and partially deaf animals. These variable features are discussed mainly with regard to the rate of degeneration and the site of the first damage. Atypical findings, such as primary degeneration of spiral ganglion neurons, are presented. The possibility for some damaged cochleas to work without hair cells is described. These results clearly demonstrate that hereditary degeneration in the cochlea of white cats is not a unique and regular process.
Eleven white kittens were investigated from 2 days after birth up to an age of 4 months. After their hearing ability or deafness had been tested electrophysiologically, electron microscopic work was done at the level of the cochlea. Previous histological data indicated that the hereditary process of degeneration begins at the epithelial and sensory elements of the cochlea, and that the neural degeneration is only a secondary and very slow process. Results presented here indicate that, a t least in some white cats, this assumption needs to be modified. Early failure in the myelination of the lamina Jpirulis fibres was noticed in most of the white kittens. Furthermore, two kittens (7 and 16 days old) presented a complete degeneration of the spiral ganglion neurons, and signs of anterograde degeneration of their fibres going to the organ of Corti. These primary neural defects indicate that hereditary hearing defects may directly affect both epithelio-sensory and neural structures.
Acta Otolaryngol83Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 12/22/14 For personal use only. Actn Otolaryngol83 Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 12/22/14 For personal use only. Actu OtolaryngolS3 Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 12/22/14 For personal use only.DISCUSSION Ch. Chouard-P. Montandon-H. Spoendlin-A. H. Morgon Acta Otolaryngol83 Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 12/22/14 For personal use only.
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