Possible hormonal interaction for eliciting courtship behavior in the male newt, Cynops pyrrhogaster.

Reproductive behavior in amphibians, as in other vertebrate animals, is under the control of multiple hormonal substances. Prolactin (PRL), arginine vasotocin (AVT), androgen, and 7α-hydroxypregnenolone (7α-OH PREG), four such substances with hormonal activity, are known to be involved in the expression of the tail vibration behavior which is the initial step of courtship performed by the male newt, Cynops pyrrhogaster. As current information on the interaction(s) between these hormones in terms of eliciting tail vibration behavior is limited, we have investigated whether the decline of expression of tail vibration behavior due to suppression of the activity of any one of these hormones can be restored by supplying any one of the other three hormones exogenously. Expression of the behavior was determined in terms of incidence (% of test animals exhibiting the behavior) and frequency (number of times that the behavior was repeated during the test period). Neither PRL nor androgen restored the decline in the incidence and frequency of the tail vibration behavior caused by the suppression of the activity of any one of other three hormones. AVT completely restored both the anti-PRL antibody-induced and flutamide (an androgen receptor antagonist)-induced, but not ketoconazole (an inhibitor of the steroidogenic CYP enzymes)-induced decline in the incidence and frequency of the tail vibration behavior. The neurosteroid, 7α-OH PREG, failed to restore flutamide-induced decline in the incidence and frequency of the behavior. However, it was able to restore both anti-PRL antibody-induced and AVT receptor antagonist-induced decline in the incidence, but not in the frequency of the behavior. In another experiment designed to see the activity of hormones enhancing the frequency of the tail vibration behavior, AVT was revealed to be more potent than 7α-OH PREG. The role of each hormonal substance in determining the expression of the tail vibration behavior was discussed based on the results.