Extreme olfactory sensitivity of mature and gonadally-regressed goldfish to a potent steroidal pheromone, 17?,20?-dihydroxy-4-pregnen-3-one

Abstract

1. Electrical responses (electro-olfactogram; EOG) were obtained from the olfactory epithelium of goldfish exposed to a variety of sex steroids thought to function as pheromones, severall-amino acids, and a bile acid. Responses of male and female goldfish with both mature and regressed gonads were compared. 2. 17α,20β-dihydroxy-4-pregnen-3-one (17,20P) and progesterone were potent odorants. 17,20P had a detection threshold of 10−13M and at a concentration of 10−8M evoked an EOG response two to three times that of 10−5Ml-serine. Progesterone was less stimulatory than 17,20P. This finding corroborates recent endocrinological and behavioral studies (Stacey and Sorensen 1986; Dulka et al. 1987) which indicate that 17,20P is a potent pheromone in mature male goldfish. 3. Preliminary cross-adaptation experiments suggest that 17,20P is detected by receptor site(s) differing from those which detect bile acids andl-amino acids. 4. The goldfish olfactory epithelium did not respond to etiocholanolone glucuronide, 17β-estradiol glucuronide, testosterone glucuronide and 17β-estradiol, which have also been hypothesized to function as pheromones in fish. 5. The olfactory thresholds of goldfish tol-amino acids and taurocholic acid were similar to other species of fish: approximately 10−13M forl-serine and 10−9M forl-cysteine and taurocholic acid. 6. The olfactory sensitivities of mature male, mature female and gonadally-regressed fish were similar to all compounds tested suggesting that differences in olfactory receptor function are not responsible for the fact that only mature males exhibit behavioral and endocrine responses to pheromonal 17,20P.