[3H]Neurokinin B and 125I-Bolton Hunter Eledoisin Label Identical Tachykinin Binding Sites in the Rat Brain |
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Authors: | L. Bergstrom,Y. Torrens,M. Saffroy,J. C. Beaujouan,S. Lavielle,G. Chassaing,J. L. Morgat&dagger ,J. Glowinski,A. Marquet |
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Affiliation: | Chaire de Neuropharmacologie, INSERM U. 114, Collège de France;CEA Saclay, Gif/Yvette, France;Laboratoire de Chimie Organique Biologique, ERA 823, UniversitéP. et M. Curie, Paris;CEA Saclay, Gif/Yvette, France;Service de Biochimie, Département de Biologie, CEA Saclay, Gif/Yvette, France |
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Abstract: | [3H]Neurokinin B ([3H]NKB) of high specific activity (75 Ci/mmol) was synthesized for study of its binding to crude synaptosomes from the rat cerebral cortex. The specific binding of [3H]NKB (75% of total binding) was temperature dependent, saturable, and reversible. Scatchard analyses and Hill plots showed the existence of a single population of noninteracting binding sites (KD = 4.3 nM; Bmax = 123 fmol/mg of protein). Competition studies indicated the following rank order of potencies among tachykinins: NKB greater than eledoisin (E) greater than kassinin greater than physalaemin greater than neurokinin A (NKA) greater than substance P (SP), a result suggesting that NKB might be the endogenous ligand for [3H]NKB binding sites. It is of interest that 127I-Bolton Hunter (BH) NKA (127I-BHNKA) was much more potent than NKA in inhibiting the specific binding of [3H]NKB, which raises certain questions concerning the use of 125I-BHNKA as a ligand for NKA binding sites in the brain. These results, as well as those obtained with different SP analogues, show a close similarity to those obtained previously with 125I-BHE binding to cortical synaptosomes. This suggested that the two ligands labeled identical binding sites. In addition, using either [3H]NKB or 125I-BHE as ligands, similar displacement curves were obtained with increasing concentrations of NKB and 127I-BHE. The similarity of the [3H]NKB and 125I-BHE binding sites was further confirmed by comparison of their localization on rat brain sections by autoradiography. The distribution of binding sites for [3H]NKB and 125I-BHE was identical throughout the brain, and the highest density of binding sites for the two ligands was found in layers IV and V of the cerebral cortex, the paraventricular nucleus of the hypothalamus (magnocellular part), and the ventral tegmental area. |
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Keywords: | Tachykinin binding sites [3H]Neurokinin B Autoradiography Bolton-Hunter derivatization |
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