Testosterone binding sites in the brain, plasma sex hormones and reproductive behaviour in males of the toad Bufo bufo

Abstract

The central action of steroid hormones of the regulation of reproductive behaviour has been recognized in Amphibia, as in, other Vertebrates. Central and peripheral endocrine aspects of reproductive behaviour were studied in the toad Bufo bufo during the breeding aspects of reproductive behaviour were studied in the toad Bufo bufo during the breeding (DHT) and estradiol (E) levels. In the first experiment the effect of early and late entrance into the breeding pond and the difference between animals entering and leaving was established: DHT and E plasma levels, as well as T binding capacity in the brain were lower in animals leaving the pond at the end of the breeding season; animals entering early in the season showed higher levels of E than those entering late. In the second experiment the hormonal effect of amplexus and spawning was established: single males showed lower plasma DHT, higher plasma E and higher T binding values in the brain than males paired with a female. Males in amplexus with a non-spawning female showed higher plasma E levels than those with a spawning female. These results show that it is possible to relate the different reproductive success to different T binding in the brain. The effect of amplexus on potential responsiveness to steroid hormones at the central level and on peripheral hormone concentrations suggests the presence of a regulatory mechanism which is more active when both amplexus and spawning occur. On the other hand, the data concerning animals entering and leaving the pond indicate that the hormonal variations are not due solely to the end of sexual behaviour since the difference is already significant between groups entering early and late in the breeding season.