Innervation of the chicken basilar papilla during its development.

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.