Effects of urea on olfaction in zebrafish (Danio rerio)

Introduction Urea treatment in Danio rerio affects the expression or degradation of the G protein alpha subunit olfactory type (Gαolf), involved in olfactory transduction, causing an increased presence of this protein in the olfactory cilia (Ferrando et al, 2014; Bettini et al 2015). The effects of uremia on human olfactory functions have been evaluated in some clinical studies (Landis et al 2011). We here attempt to determine a specific action of urea, among all the uremic toxins, on the olfactory capability of a vertebrate.The OAT on CTRL showed a sudden burst of swimming. The U5m fishes showed a reaction to the stimuli similar to the CTRL. The U20m did not show an appreciable response to the stimuli. The unresponsiveness lasted during the 5 days of treatment. A recovery of 15 min. in clean water did not restore the responsiveness, while 1h was enough to show an appreciable response to the stimuli, still not equal to the CTRL. Although HIC is not quantitative, it was possible to observe that the Gαolf immunoreactivity (ir) was similar in the CTRL and in the U20m fishes, while it was more intense in the U5d and the U5dR1h adults.Urea altered the response to the OAT of D. rerio with a quite rapid and reversible effect. This effect is probably independent from a mere interference of urea on the receptor-ligand binding (Ferrando et al 2014). The Gαolf ir level after 5 days was higher than control and 5-20 min. This suggests that two different mechanisms would be involved in effect of urea on olfaction capability in the long and short term. Since in the rat striatum the activation of Gαolf cause its degradation (Hervé et al 2001) we speculate that in our experimental setting the Gαolf ir increase could depend by the lack of Gαolf activation after the receptor binding with odorant molecules or by an alteration of further post signal transduction cascade.