Tonotopic Gradients of Eph Family Proteins in the Chick Nucleus Laminaris during Synaptogenesis

ABSTRACT: Topographically precise projections are established early in neural development. One such topographically organized network is the auditory brain-stem. In the chick, the auditory nerve transmits auditory information from the cochlea to nucleus magnocellularis (NM). NM in turn innervates nucleus laminaris (NL) bi-laterally. These projections preserve the tonotopy estab-lished at the level of the cochlea. We have begun to examine the expression of Eph family proteins during the formation of these connections. Optical density measurements were used to describe gradients of Eph proteins along the tono-topic axis of NL in the neuropil, the somata, and the NM axons innervating NL at embryonic day 10, when synaptic connections from NM to NL are established. At E10–11, NL dorsal neuropil expresses EphA4 at a higher concen