THE DEVELOPMENT OF NEUROTROPHIN RECEPTOR TRK IMMUNOREACTIVITY IN THE RETINA OF THE ZEBRAFISH (BRACHYDANIO-RERIO)

The purpose of this study was to examine the cellular distribution of the Trk family of neurotrophin receptors in the retina and optic nerve of the zebrafish (Brachydanio rerio) during embryonic development. Se mithin sections from zebrafish retinae were examined immunohistochemic ally for the presence of Trk polypeptides using commercially available antisera that cross-react with the fish. Cross-reactivity was confirm ed by Western blot. Trk polypeptides were detected at about 1 day of a ge on the surfaces of retinal neuroblasts and faint Trk immunoreactivi ty was observed in the primordial optic nerve at 1.5 days. By 2 days t he optic nerve was clearly positive for Trk and at 2.5 days Trk immuno reactivity was found in the outer plexiform, inner nuclear, inner plex iform and ganglion cell layers, as well as in the optic nerve. At 3 da ys and 4 days the location of Trk immunoreactivity was unchanged but b y 4 days it had diminished in intensity. In the adult zebrafish retina Trk immunoreactivity was found in the same locations as in the embryo nic fish, as well as in a population of cells in the middle of the inn er nuclear layer and in photoreceptors. We conclude that Trk neurotrop hin receptors are present in the zebrafish eye during development and that their persistence in the adult may support the continuous neural reorganization that accompanies the growth of the eye in the fish.