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KEY WORDS neurotrophins; fish; juxtaglomerular cells; immunohistochemistryABSTRACT By means of immunochemistry and immunohistochemistry, we investigated in thekidney of freshwater and marine teleostean species for the presence and localization of three neuro-trophins: nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin(NT)-3. In both species studied, NGF-like and NT-3-like immunoreactivity were present in the kid-ney with different distribution patterns, while BDNF-like immunoreactivity was never detected. Ingoldfish, NGF-like and NT-3-like immunoreactivity were identified extensively in cells along partof the arterial branches adjacent to the afferent arterioles. In scorpion fish, NGF-like and NT-3-likeimmunoreactive cells were observed both on afferent arterioles and on adjacent secondarybranches derived from renal arteries. No immunoreactivity was detected in other renal structures.A staining pattern of immunoreactivity similar to that obtained for NGF and NT-3 was detectedutilizing S100 antibody as a juxtaglomerular (JG) cell marker. Double immunolabellings NGF/S100 and NT-3/S100 evidenced the coexistence of neurotrophin-like proteins and S100-like proteinin the same immunoreactive cells, thus identifying them as juxtaglomerular cells. Western blotanalysis revealed the presence of molecules immunoreactive to NGF and NT-3, whose molecularweights were very similar to those of the corresponding mammalian neurotrophins. These findingsextend the presence and distribution of NGF-like and NT-3-like IR in the kidney to teleost species,suggesting a probable participation of these proteins in the renal functions of freshwater andmarine teleosts. Microsc. Res. Tech. 66:17–24, 2005.

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. TrkClike 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.

The immunolocalization of S100-like protein was investigated in the kidney of saltwater fishes (Dicentrarchus labrax; Coris julis; Serranus cabrilla; Scorpaena porcus), amphibia (Rana aesculenta), reptiles (Lacerta viridis), and aves (Gallus domesticus; Strutio camelus). S100-like immunoreactivity was detected in the juxtaglomerular cells of all saltwater fishes studied. No immunoreactivity was observed in other tracts of the nephron or in the interstitial tissue. In frog kidney, S100-like immunoreactive cells were localized in the proximal tubule, singly distributed or placed side by side in clusters of two or three cells. S100-like immunoreactive cells were distributed in the distal and in the collecting tubules in lizard, chicken, and ostrich kidney. In the distal tubule of lizard kidney, S100-like immunoreactive cells were numerous and uniformly distributed. In lizard collecting tubules, S100-like immunoreactive cells showed less intense immunoreactivity than in the distal tubule, except for a cluster of cells at the junction with the initial collecting duct. In chicken and ostrich kidney, S100-like immunoreactive cells of the distal tubules were closely packed together. In the collecting tubules, S100-like immunoreactive cells were alternate to negative cells. These results indicate the high conservation degree of S100 proteins through phylogenesis and suggest a functional role for these proteins in the vertebrate kidney.

By immunohistochemistry VIP-like immunoreactive cells were observed in the second segment of some renal proximal tubules of Carassius auratus. Immunoreactivity displayed a granular appearance all over the cells. VIP-like immunoreactive cells showed a shape of an overturned flask whose globe-like part looks like the tubular lumen. No immunoreactive material was observed in other tracts of the nephron and in the interstitial cells. The presence of VIP-like immunoreactive cells is discussed in relation to their possible function.