Studies on development, structure and function of pituitary gland in amphibians

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1.Ontogenic study of pituitary glandAs a tool for tracing the cells that migrate with pituitary primordium but remain in the foregut region, transgenic toads (Xenopus laevis) that express GFP were prepared.2.Central action of prolactinAn adenohypophyseal hormone prolactin is involved in eliciting courtship behavior in the newt, genus Cynops, acting centrally. As a step to elucidate the mechanism of the prolactin action, distribution of prolactin receptors in the newt (Cynops pyrrhogaster) brain was studied by immunohistochemistry and in situ hybridization. Immunohistochemically detectable prolactin receptors as well as prolactin receptor mRNAs were observed in several region of hypothalamic nuclei, and most notably in the choroid plexus. Involvement of choroid plexus in transporting prolactin molecules into the brain was suggested.3.Regulation of pituitary function by hypothalamic neuropeptidesNewly developed radioimmunoassay for amphibian TSH made it possible to detect TSH-releasing factors in the amphibian brain. As a result, CRF was revealed to be the most potent substance to stimulate the release of TSH from the bullfrog pituitary. Using CRF antagonists and agonists, CRF receptor type 2 was demonstrated to mediate the action of CRF to release TSH.