Nerve growth factor receptor TrkA is expressed by horizontal and amacrine cells during chicken retinal development

Nerve growth factor is known to stimulate neurite outgrowth and support neuronal survival during embryonic development. We have studied the expression of the nerve growth factor receptor, TrkA, at both mRNA and protein levels during the course of chicken retinal development. Furthermore, we have compared the expression of trkA mRNA with that of the 75-kD low-affinity neurotrophin receptor (p75NTR). RNase protection assay identified peak-levels of trkA mRNA in the late embryonic retina. Using in situ hybridization and immunohistochemistry, we found cells expressing TrkA in both the internal and the external part of the inner nuclear layer, corresponding to amacrine and horizontal cells, respectively. The TrkA-expressing amacrine cell has a unistratified dendritic arborization in the second sublamina of the inner plexiform layer, and may represent the stellate amacrine cell described by Cajal. The horizontal cells, possessing arciform dendrite processes in the outer plexiform layer, showed strong TrkA immunoreactivity in both dendrites and cell bodies. During the course of retinal development, the TrkA-expressing amacrine cells decreased in number, whereas the TrkA-expressing horizontal cells persisted. Because nerve growth factor was expressed where the horizontal cells, but not where the amacrine cells were located, these findings raise the question of whether nerve growth factor could locally support the survival of TrkA-expressing interneurons during retinal development.