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Chronic renal disease is known to alter olfactory function, but the specific changes induced in olfactory organs during this process remain unclear. Of the uraemic toxins generated during renal disease, high levels of urea are known to induce hyposmic conditions. In this study, the effects of environmental exposure to elevated concentrations of urea (7, 13.5 and 20 g L-1) on the sensory mucosa of zebrafish in acute toxicity and chronic toxicity tests were described. It was observed that lamellae maintained structural integrity and epithelial thickness was slightly reduced, but only following exposure to the highest concentrations of urea. Panneuronal labelling with anti-Hu revealed a negative correlation with levels of urea, leading to investigation of whether distinct neuronal subtypes were equally sensitive. Using densitometric analysis of immunolabelled tissues, numbers of Gα olf-, TRPC2- and TrkA-expressing cells were compared, representing ciliated, microvillous and crypt neurons, respectively. The three neuronal subpopulations responded differently to increasing levels of urea. In particular, crypt cells were more severely affected than the other cell types, and Gα olf-immunoreactivity was found to increase when fish were exposed to low doses of urea. It can be concluded that exposure to moderate levels of urea leads to sensory toxicity directly affecting olfactory organs, in accordance with the functional olfactometric measurements previously reported in the literature. [ABSTRACT FROM AUTHOR]

Continuous lifelong neurogenesis is typical of the vertebrate olfactory system. The regenerative ability of olfactory receptor neurons is dependent on the glial cell type specific to the olfactory pathway, designated 'olfactory ensheathing cells'. Several studies to date have focused on mammalian olfactory ensheathing cells, owing to their potential roles in cell-based therapy for spinal cord injury repair. However, limited information is available regarding this glial cell type in non-mammalian vertebrates, particularly anamniotes. In the current immunocytochemical study, we analysed the features of olfactory ensheathing cells in the zebrafish, Danio rerio. Fish provide a good model for studying glial cells associated with the olfactory pathway of non-mammalian vertebrates. In particular, zebrafish has numerous valuable features that enable its use as a prime model organism for genetic, neurobiological and developmental studies, as well as toxicology and genomics research. Paraffin sections from decalcified heads of zebrafish were processed immunocytochemically to detect proteins used in the research on mammalian olfactory ensheathing cells, including glial fibrillary acid protein ( GFAP), S100, neural cell adhesion molecule ( NCAM), polysialylated NCAM ( PSA- NCAM), vimentin (VIM), p75 NTR and galactin (Gal)-1. Notably, GFAP, S100, NCAM and Gal-1 were clearly observed, whereas no vimentin staining was detected. Weak immunostaining for PSA- NCAM and p75 NTR was evident. Moreover the degree of marker expression was not uniform in various tracts of the zebrafish olfactory pathway. The immunostaining patterns of the zebrafish olfactory system are distinct from those of other fish to some extent, suggesting interspecific differences. We also showed that the olfactory pathway of zebrafish expresses markers of mammalian olfactory ensheathing cells. The olfactory systems of vertebrates have similarities but there are also marked variations between them. The issue of whether regional and interspecific differences in immunostaining patterns of olfactory pathway markers have functional significance requires further investigation. [ABSTRACT FROM AUTHOR]

A study of the peripheral olfactory organ, with special attention to the olfactory epithelium, has been carried out in the guppy ( Poecilia reticulata). Guppy is well known to have a vision-based sexual behavior. The olfactory chamber caudally opens directly in an accessory nasal sac, which is bent medially and gives rise to two recesses that can be considered secondary accessory nasal sacs, antero-medial and postero-medial, respectively. The sensory epithelium, which lines only the medial wall of the nasal cavity, is basically flat rising in a very low lamella only in the posterior part. The olfactory receptors are not evenly distributed in the olfactory mucosa, but aggregate in shallow folds separated by epithelial cells with evident microridges. Ciliated olfactory sensory neurons and microvillous olfactory sensory neurons are clearly identified by transmission electron microscopy (TEM). Scarce crypt olfactory neurons are found throughout the sensory folds. The nasal sacs indicates the capacity to regulate the flow of odorant molecules over the sensory epithelium, possibly through a pump-like mechanism associated with gill ventilation. The organization of the olfactory organ in guppy is simple and reminds what is found in early posthatching stages of fish which at the adult state have a well developed olfactory organ. This simple organization supports the idea that the guppy rely on olfaction less than other fish species provided with more extended olfactory receptorial surface. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

AbstractFranceschini, V. Lazzari, M. and Ciani, F. 2000. Cell surface glycoconjugates in the olfactory system of lungfish Protopterus annectens Owen. — Acta Zoologica (Stockholm) 81: 131–137 Lectin binding was performed on the olfactory system of lungfish Protopterus annectens to identify specific glycoconjugates on the cell surface of olfactory receptor cells. The lectin histochemical patterns and the Western blot analysis indicate that the receptor cells of the olfactory mucosa are characterized by high density of α-N-acetyl-d-galactosamine residues on the saccharidic chains of the surface glycoproteins. Other lectins display a regional pattern between the regions of the olfactory bulbs. This different histochemical lectin pattern might be due to a different regional segregation of the olfactory projections. On the other hand it could allow the identification of an area corresponding to the accessory olfactory bulb of terrestrial vertebrates in the ventrolateral region of Protopterus olfactory bulb. The presence in the dipnoan olfactory system of a vomeronasal organ homologous to the organ in amphibians is discussed. Moreover, the selective lectin binding on the surface of primary olfactory neurones suggests that specific cell surface glycoproteins may have a role in the axonal growth due to the continuous cycle of proliferation and the death of olfactory receptor cells. [ABSTRACT FROM AUTHOR]