Developing rat retinal ganglion cells express the functional NGF receptor p140trkA

The expression and cellular localization of NGF receptors in the developing rat retina were investigated immunocytochemically and biochemically. In in vitro preparations of retinal neurons from neonatal rats the functional NGF receptor p140trkA was immunocytochemically detected on retrogradely labeled retinal ganglion cells (RGCs). In transverse retinal sections p140trk-immunopositive cells were localized exclusively at the level of the RGC layer. Affinity labeling with 125I-NGF, chemical cross-linking, and immunoprecipitation with anti-NGF antibodies revealed the presence of three complexes which migrate on SDS-PAGE at approximately 90, 95, and 150 kDa. The bands at 90 and 95 kDa correspond to the so-called low affinity NGF receptor p75NGFR. Western blotting experiments using anti-TRK antibodies revealed that the slowest migrating band (150 kDa), which is not immunoprecipitated by monoclonal antibodies to p75NGFR, corresponds to p140trkA. The presence of the functional NGF receptor on RGCs provides the molecular explanation for the reported sensitivity of these cells to the biological action of NGF.