The teleost kidney expresses Trk neurotrophin receptor-like proteins

Neurotrophins are involved in the development and maintenance of some neuronal populations, acting through tyrosine protein kinase (Trk) receptors, TrkA, TrkB and TrkC. In addition, recent studies have demonstrated the occurrence of Trk receptors in a wide variety of adult and embryonic non-neuronal tissues in vertebrates, including kidney. Nevertheless no data are available on Trk proteins distribution in teleost kidney. The present study, by using an immunoperoxidase technique, analyses Trk receptor protein distribution in the kidney of three species of freshwater and saltwater teleost. TrkA-like immunoreactivity was the only one detected in all examined species, while TrkB-like immunoreactivity was completely absent and TrkC-like immunoreactivity was detected only in goldfish. The TrkA immunoreactive cells were mainly localised in the collecting duct system, as this system was the only one to also display TrkC. Such data could provide new clues to Trk in fish and aid assessment of the role of Trk protein receptors during vertebrate evolution.