Neural Activation in the Olfactory Epithelium of East African Cichlid in Response to Odorant Exposure

Abstract

AbstractFish use olfaction to gain various information. To know what they receive and how they receive is vital for understanding the diversity of fish. However, studies on fish olfactory or pheromone receptors are still insufficient, and most of them are on a model organism. Here, we established an experimental system to detect a biological-derived neural response from the olfactory epithelium of East African cichlid, the most diversified fish lineage, by in situ hybridizations of c-fos. We first tested the response of microvillous neurons, which are expected to be dominated by V2R-expressing neurons, to several odorants. We showed that microvillous neurons responded to amino acids and food extraction, suggesting that fish receive amino acids via V2R receptors as food-related odorants. We next tested the response of each of the four subfamilies of V2R receptors, showing that two of four subfamilies responded to proteinogenic amino acids. Notably, individual paralogs in subfamily 14, which responded to arginine, had variability in receptivity to arginine, indicating the ligand differentiation in the cichlid-specifically expanded subfamily. Finally, we established a noninvasive method to collect urine and tested the response of putative pheromone receptor V1R to male urine, and we showed two V1R receptors responded to male urine. Furthermore, we showed V1R2 receptor responded to 4-hydroxyphenyl acetate and lithocholic acid. This study provides an experimental basis for the study of olfaction in East African cichlids related to its ecology and speciation.