DISTRIBUTION OF BRADYKININ B-2 RECEPTORS IN SHEEP BRAIN AND SPINAL-CORD VISUALIZED BY IN-VITRO AUTORADIOGRAPHY

Bradykinin Bz receptors were localized in the sheep brain and spinal c ord by quantitative in vitro autoradiography using a radiolabelled and specific bradykinin Bz receptor antagonist analogue, propionyl-D-Arg( O)-[Hyp(3).Thi(5),D-Tic(7),Oic(8)] (HPP-HOE140). This radioligand disp lays high affinity and specificity for bradykinin Bz receptors. The re spective Ki values of 0.32, 1.37 and 156 nM were obtained for bradykin in, HOE140 and D-Arg[Hyp(3),D-Phe(7),Leu(8)]bradykinin competing for r adioligand binding to lamina Il of sheep spinal cord sections. Using t his radioligand, we have demonstrated the distribution of bradykinin B a receptors in many brain regions which have not been previously repor ted. The highest density of bradykinin B-2 receptors occur in the pleo glial periaqueductal gray, oculomotor and trochlear nuclei and the cir cumventricular organs. Moderate densities of receptors occur in the su bstantia nigra, particularly the reticular part, the posterior thalami c and subthalamic nuclei, zona incerta, the red and pontine nuclei, so me of the pretectal nuclei and in discrete layers of the superior coll iculus. In the hindbrain, moderate levels of bradykinin Pa receptor bi nding occur in the nucleus of the solitary tract, and in spinal trigem inal, inferior olivary, cuneate and vestibular nuclei. Laminae II, X a nd dorsal root ganglia display the most striking binding densities in the spinal cord, while the remainder of the dorsal and ventral horn di splay a low and diffuse density of binding. Bradykinin Bz receptors ar e extensively distributed throughout the sheep brain and spinal cord, not only to sensory areas but also to areas involved in motor activity . (C) 1997 Wiley-Liss, Inc.