Multidisciplinary Research on Reproductive Biology in Japanese Toads

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Biological aspects of reproduction in the Japanese toad (Bufo japonicus) were examined by use of multidisciplinary research techniques.Development and maturation of reproductive organs. Patterns of development and maturation of gonads were examined by morphological techniques.Endocrine approaches. Adenohypophysial hormones, e.g., prolactin (PRL), follicle stimulating hormone (FSH) and luteinizing hormone (LH), were purified to establish radio immunoassay methods for them. Seasonal variations of various hormones including PRL, FSH and LH measured by RIAs corresponded reproductive activity. In addition, nucleotide sequences of mRNAs for vasotocin and mesotocin were determined by a recombinant DNA technique.Ethology. Comparisons of ethograms of toad reproductive behavior showed that the toad gradually terminates hibernation and initiates migration to a particular breeding pond. The toad may detect the location of the pond by a memory concerning olfactory cues. Hibernation is not necessitated for maturation of gonads and initiation of reproductive behavior.Neuroethology. A triggering center for male reproductive behavior was localized in the preoptic nucleus, especially in its anterior part (APON). Mate calling was evoked by an electrical stimulation of the APON. Activities of APON neurons may be motivated by LHRH and TRH, hypothalamic neurohormones.Developmental chemistry. Jerry coats surrounding eggs are a reservoir for Ca ions required for fertilization.