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Olfactory crypt neurons have been observed in several bony fishes and chondrichtyans. Although their morphology is uniform in all fish, very few is known about their antigenic properties, usually studied in zebrafish, but quite overlooked in other species. We tested in Poecilia reticulata (guppy) the two antibodies recognized to mark zebrafish crypt cells: while anti-S100 showed an immunohistochemical pattern comparable to what reported in zebrafish, anti-TrkA gave no signal. Western blot analysis revealed that S100-antiserum bound an antigen of expected weight, probably belonging to the S100 family. On the contrary, anti-TrkA detected more bands, but the protein/s might be too much diffused and/or diluted in the tissue to be detected with immunohistochemistry. Because of the high level of conservation in the Trk family proteins of the kinase domain, on which anti-TrkA was produced, we also tested anti-TrkB to exclude cross reactivity. Immunohistochemistry and Western blot confirmed that anti-TrkB displayed high specificity to its target and a different staining pattern compared to anti-TrkA, but, as anti-TrkA, it did not label crypt neurons. Finally, we documented that calretinin, a known marker of zebrafish ciliated and microvillous olfactory cells, in the guppy is expressed also by a subpopulation of S100-positive crypt neurons. These results reveal differences in antigen expression between zebrafish and guppy crypt cells. Together with the already known species-specific projections to the olfactory bulb and a heterogeneous panel of odorants, our findings support the possibility that crypt cells are functionally less uniform as supposed. [ABSTRACT FROM AUTHOR]

The olfactory and vomeronasal systems of vertebrates are characterised by neurogenesis occurring throughout life. The regenerative ability of olfactory receptor neurons relies on specific glial cells, the olfactory and vomeronasal axon-surrounding cells. Numerous studies have examined mammalian olfactory ensheathing cells which are considered potential candidates for spinal cord injury repair using cell-based therapy. With regard to non-mammalian vertebrates, limited information is available on these glial cells in fish, and there is no information on them in terrestrial anamniotes, the amphibians. In the present research, we studied the immunocytochemical characteristics of axon-surrounding cells in Ambystoma mexicanum. Urodeles have relatively simple olfactory and vomeronasal systems, and represent a good model for studying ensheathing cells in extant representatives of basal tetrapods. Sections from the decalcified heads of A. mexicanum were immunocytochemically processed for the detection of proteins used in research on mammalian olfactory-ensheathing cells. S100, GFAP and NCAM were clearly observed. p75NTR, Gal-1 and PSA-NCAM showed weak staining. No vimentin immunopositivity was observed. The corresponding areas of the olfactory and vomeronasal pathways displayed the same staining characteristics, with the exception of Gal-1, p75NTR and PSA-NCAM in the mucosae. The degree of marker expression was not uniform throughout the sensory pathways. In contrast to fish, both olfactory and vomeronasal nerves displayed uniform staining intensity. This study showed that some markers for mammalian and fish-ensheathing glia are also applicable in urodeles. The olfactory systems of vertebrates show similarities, and also clear dissimilarities. Further investigations are required to ascertain the functional significance of these regional and interspecific differences. [ABSTRACT FROM AUTHOR]

In the olfactory system of vertebrates, neurogenesis occurs throughout life. The regenerating activities of the olfactory receptor neurons are connected to particular glial cells in the olfactory pathway: the olfactory ensheathing cells. A considerable number of studies are available in literature regarding mammalian olfactory ensheathing cells; this is due to their potential role in cell-based therapy for spinal cord injury repair. But very little is known about these cells in non-mammalian vertebrates. In this study we examined the immunocytochemical characteristics of the olfactory ensheathing cells in fish, which provide a good model for the study of glial cells in the olfactory pathway of non-mammalian vertebrates. Paraffin sections from decalcified heads of Poecilia reticulata (microsmatic fish) and Carassius auratus (macrosmatic fish) were processed to immunocytochemically detect ensheathing cell markers used in research on mammals: GFAP, S100, NCAM, PSA-NCAM, vimentin, p75NTR and galectin-1. GFAP, S100 and NCAM were clearly detected in both fish, though the intracranial tract of the primary olfactory pathway of Carassius appears more S100 stained than the extracranial tract. P75NTR staining is more evident in Poecilia, PSA-NCAM positivity in Carassius. A slight vimentin immunostaining was detected only in Carassius. No galectin-1 staining appeared in the olfactory pathways of either fish. This study shows that some markers for mammalian olfactory ensheathing cells also stain the olfactory pathway in fish. Immunocytochemical staining differs in the two fish under examination, even along the various tracts of the olfactory pathway in the same species. [ABSTRACT FROM AUTHOR]