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The present study investigates the occurrence of Trk-like neurotrophin receptor proteins in the lizard and frog kidney. In lizard rare TrkB-like immunoreactive cells in intermediate and distal tubules were found. TrkC-like immunoreactive cells were numerous in collecting tubules and became less numerous in collecting ducts. No TrkC-like immunoreactivity was detected in the ureteric duct. In the frog, we observed numerous TrkC-like immunoreactive cells in collecting tubules and ducts while they were scattered among negative epithelial cells in the wolffian duct. TrkB- and TrkA-like immunoreactivity was never found. Western blot analysis demonstrated that the frog and lizard kidney contains TrkC-like protein; TrkB-like protein was present only in the lizard kidney. These results demonstrate for the first time the occurrence of Trk-like proteins in the kidney of amphibians and reptiles, and aid in the assessment of the role of Trk receptor-like proteins in the kidney physiology of vertebrates. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]