Abstract
Fish use olfaction to gain a variety of information. To know what they receive and how they receive is important for understanding the species. However, studies on fish olfactory or pheromone receptors are still few and most of them are based on the neural response from a cultured cell. Here, we established a method to detect a biological-derived neural response from the olfactory epithelium of East African cichlid, the most diversified fish lineage, by c-fos in situ hybridization. We tested the response of microvillous neurons, which are expected to be dominated by V2R-expressing neurons, against several odorants. We showed microvillous neurons respond to amino acids the most whereas they do not respond to conjugated steroids. We next tested the response of V2R receptors. Although some subfamilies of V2R responded to amino acids, other did not respond which contrasts with the traditional hypothesis. Especially, one V2R subfamily responded to arginine. Not all the copies in this subfamily responded to arginine, which indicates the ligand differentiation in the cichlid-specifically expanded subfamily. Finally, we tested the response of putative pheromone receptor V1R to male urine. For this experiment, we established a new method to collect urine from cichlid. We showed two V1R receptors responded to male urine. Moreover, we showed that V1R2 receptor responded to 4-hydroxyphenyl acetate and lithocholic acid. This study is expected to provide a basis for the study on the olfaction of East African cichlids.
Competing Interest Statement
The authors have declared no competing interest.
