IMMUNOHISTOCHEMICAL ANALYSIS OF THE NEUROTROPHINS BDNF AND NT-3 AND THEIR RECEPTORS TRK-B, TRK-C, AND P75 IN THE DEVELOPING CHICK RETINA

?The neurotrophins are trophic and mitogenic factors critical for the development of specific classes of neurons in the central and peripher al nervous systems. In the retina, BDNF and NT-3 have been shown to pr omote the survival of differentiated ganglion cells (Rodriguez-Tebar e t al., 1989; De La Rosa et al., 1994). NT-3 has also been demonstrated to support the survival of amacrine cells and facilitates the differe ntiation of retinal neurons in culture (De La Rosa et al., 1994). Here , we examine immunohistochemically the expression of BDNF and NT-3 pro teins, their cognate receptors, trk B and trk C, respectively, and the p75 neurotrophin receptor in the developing chick retina. At E8, the earliest stage of retinal development examined, all of these proteins exhibit diffuse expression throughout the width of the retina, with th e strongest reactivity in the innermost layers. A gradual restriction in expression to ganglion cells and amacrine cells, the staining of wh ich is most prominent at E15, is followed by a downregulation of expre ssion with the strongest immunoreactivity persisting in the ganglion c ell layer. Overlapping patterns of expression throughout embryonic dev elopment indicate a colocalization of the neurotrophins and their rece ptors, although NT-3 and p75 alone are present in the inner plexiform layer and only p75 is observed in the outer plexiform layer. Although some of the immunoreactivity for BDNF NT-3, and their receptors in ret ina may reflect trophic mechanisms operating in association with the o ptic tectum and isthmo-optic nucleus, the colocalization of ligands an d receptors in retina strengthens the assertion that these neurotrophi ns function locally during development.