TY - JOUR
T1 - Application of [125I]iodocyanopindolol to measure 5-hydroxytryptamine(1B) receptors in the brain of the rat
AU - Offord, S. J.
AU - Ordway, G. A.
AU - Frazer, A.
N1 - Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 1988
Y1 - 1988
N2 - In this study, [125I]iodocyanopindolol ([125I]ICYP), in the presence of isoproterenol, was used to label 5-hydroxytryptamine(1B) (5-HT(1B)) receptors in homogenates of the cortex, substantia nigra and caudate-putamen of the rat. The determination of the appropriate concentrations of isoproterenol required to block optimally beta adrenoceptors whereas producing minimal occupancy of 5-HT(1B) receptors was achieved by generating isotherms for isoproterenol at multiple concentrations of [125I]ICYP. When different concentrations of isoproterenol were used with increasing concentrations of [125I]ICYP, a linear Scatchard transformation of the saturation curve was achieved, even with ligand concentrations about 6-fold greater than the K(D) for [125I]ICYP. Competition for [125I]ICYP (100 pM) labeled binding sites by 15 serotonin agonists or antagonists was adequately described by a single site model, and the affinity of these drugs for the site labeled by [125I]ICYP was similar to that determined previously when using indirect methods to label 5-HT(1B) receptors. Serotonin itself showed high affinity for this binding site as did two antagonists, metergoline and methiothepin. By contrast, drugs thought to be selective for the 5-HT(1A) receptor (e.g., 8-hydroxy-2-(di-n-propylamino)tetralin, buspirone and spiperone) showed very weak affinity for the binding site labeled with [125I]ICYP. The effect of nucleotide regulation of [125I]ICYP binding at 5-HT(1B) receptors also was evaluated. It was determined that GTP had little effect on the binding of [125I]ICYP, reducing total binding by only 15% and shifting the displacement curve of 5-HT by a factor of less than two. The regulation of 5-HT(1B) receptors, labeled by [125I]ICYP, also was evaluated. Intraventricular injections of 5,7- dihydroxytryptamine increased significantly the number of 5-HT(1B) receptors in the caudate-putamen; this treatment had no effect on 5-HT(1B) binding sites either in the cortex or substantia nigra. The regulatable binding site for [125I]ICYP in the caudate-putamen had a pharmacological profile very similar to that of the 5-HT(1B) binding site in the cortex. [125I]ICYP appears to be a useful ligand to measure 5-HT(1B) receptors in the brain of the rat. The localized increase in 5-HT(1B) receptors in the caudate-putamen after destruction of central serotonergic neurons might indicate that the majority of 5-HT(1B) receptors in this area of brain are not located on serotonergic nerve terminals.
AB - In this study, [125I]iodocyanopindolol ([125I]ICYP), in the presence of isoproterenol, was used to label 5-hydroxytryptamine(1B) (5-HT(1B)) receptors in homogenates of the cortex, substantia nigra and caudate-putamen of the rat. The determination of the appropriate concentrations of isoproterenol required to block optimally beta adrenoceptors whereas producing minimal occupancy of 5-HT(1B) receptors was achieved by generating isotherms for isoproterenol at multiple concentrations of [125I]ICYP. When different concentrations of isoproterenol were used with increasing concentrations of [125I]ICYP, a linear Scatchard transformation of the saturation curve was achieved, even with ligand concentrations about 6-fold greater than the K(D) for [125I]ICYP. Competition for [125I]ICYP (100 pM) labeled binding sites by 15 serotonin agonists or antagonists was adequately described by a single site model, and the affinity of these drugs for the site labeled by [125I]ICYP was similar to that determined previously when using indirect methods to label 5-HT(1B) receptors. Serotonin itself showed high affinity for this binding site as did two antagonists, metergoline and methiothepin. By contrast, drugs thought to be selective for the 5-HT(1A) receptor (e.g., 8-hydroxy-2-(di-n-propylamino)tetralin, buspirone and spiperone) showed very weak affinity for the binding site labeled with [125I]ICYP. The effect of nucleotide regulation of [125I]ICYP binding at 5-HT(1B) receptors also was evaluated. It was determined that GTP had little effect on the binding of [125I]ICYP, reducing total binding by only 15% and shifting the displacement curve of 5-HT by a factor of less than two. The regulation of 5-HT(1B) receptors, labeled by [125I]ICYP, also was evaluated. Intraventricular injections of 5,7- dihydroxytryptamine increased significantly the number of 5-HT(1B) receptors in the caudate-putamen; this treatment had no effect on 5-HT(1B) binding sites either in the cortex or substantia nigra. The regulatable binding site for [125I]ICYP in the caudate-putamen had a pharmacological profile very similar to that of the 5-HT(1B) binding site in the cortex. [125I]ICYP appears to be a useful ligand to measure 5-HT(1B) receptors in the brain of the rat. The localized increase in 5-HT(1B) receptors in the caudate-putamen after destruction of central serotonergic neurons might indicate that the majority of 5-HT(1B) receptors in this area of brain are not located on serotonergic nerve terminals.
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M3 - Article
C2 - 3335996
AN - SCOPUS:0023818721
VL - 244
SP - 144
EP - 153
JO - Journal of Pharmacology and Experimental Therapeutics
JF - Journal of Pharmacology and Experimental Therapeutics
SN - 0022-3565
IS - 1
ER -