A new research technique with the computerized radioluminographic imaging-plate system for receptors of neurotransmitters

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The quantitative receptor autoradiographic method with three experimental techniques, 1) in vitro radioligand-binding technique for functional sites of receptors, 2) quantitative radioimmunohistochemical technique for sites of receptor proteins maturation, and 3) in situ hybridization technique for production sites of receptors, have been developed to determine the precise location and kinetic properties of receptors for neurotransmitters. Based on the method, we investigated the neuroanatomical distribution of endothelin (ET) receptors. ET_A mRNA was of very few amount, but a significant expression was detected in the choroid plexus, circumventricular organ, oral linear nucleus and parabigeminal nucleus. There was a massive amount of ET_B mRNA expression, as seen in brain areas such as the pontine nucleus, interpeduncular nuclei, superior colliculus and cerebellum. A unique localization of ET_A binding sites was observed in the area postrema, solitary tract nucleus and vagal nucleus. ET_A mRNA was discretely localized in the area postrema, with rich ET-3 mRNA.ET_B binding sites were widely distributed throughout the brain stem, with rich ET_B mRNA.A cell-cluster with ET_B mRNA expression was noted in the commissural nucleus. Purkinje cell layr of the cerebellum had rich ET_B binding sites and ET-3 and ET_B mRNAs were observed in Bergmann glia, an astrocyte in the layr. The quantitative receptor autoradiographic method should enable investigators to elucidate the roles of receptors for neurotransmitters.