Methyltestosterone-induced changes in olfaction and androgen receptor expression in the olfactory organs of zebrafish (Danio rerio)

Belanger, Rachelle, Stephanie Conant, Haley Ross, Gita Sabhapathy, Eric Spicuzza, and Norm Stacey

Steroid-induced central neural effects that influence olfactory sensitivity, sex partner preferences, and chemoinvestigative behaviours are well known in vertebrates. However, with the data currently available, it is difficult to speculate on which specific component(s) of the neural pathway that processes olfactory signals are targeted for differentiation by steroid hormones in the developing nervous system. We used juveniles of a cyprinid fish, the zebrafish (Danio rerio) to investigate the effects of 17α-methyltestosterone (MT; 10-8 M) or ethanol vehicle (control) on both electro-olfactogram (EOG) recording and behavioural assays in order to determine if androgens enhance pheromone detection and male sex behaviours. MT treatment increased both the magnitudes and sensitivities of EOG response to F2 prostaglandins, which function as female sex pheromones in cyprinid fishes. Further, MT-treated juvenile zebrafish performed more courtship behaviors (nuzzling and quivering) with a PGF2α –treated stimulus fish than did control juveniles, showing that MT induced a functional response to pheromonal prostaglandin. Lastly, to assess the olfactory targets of androgens, thus linking androgen treatment with changes in olfaction, we examined androgen receptor expression in the olfactory bulb and olfactory epithelium using RNA extraction, quantification and reverse transcriptase PCR. Overall, the results of these experiments indicate that androgen treatment induces increases in olfactory responsiveness to pheromonal prostaglandins and may also lead to increases in androgen receptor expression in the olfactory bulb and epithelium.