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Fillion G, Fillion MP, Jacob J, Rousselle J C. 
“5-HT and LSD high affinity binding sites to brain synaptosomal membranes”. 
Brit.J.Pharmacol.. 1976;58(3):425P-26P.
Abstract
Serotonin (5-HT) and LSD binding were studied, using purified synaptosomal membranes isolated from different regions of bovine brain by a density gradient centrifugation technique or in some experiments a lysed Pi fraction isolated either from bovine or from rat brains. Membranes were incubated at various temperatures (generally 22 or for different purposes 0) in TrisHCl buffer 50 mM pH 7.4 using tritiated ligands 3H -5-HT, 17 Ci/ mM. 3H-LSD 22 Ci/mM). Separation of bound and free radioactivity was performed using an ultrafiltration technique under vacuum. The filter was rinsed with Tris-HCI buffer 0 and the radioactivity trapped onto the filter was counted by liquid scintillation. LSD Binding corresponded to a saturable reversible high affinity site with a corresponding dissociation constant similar to that of 5-HT (KD = 2 x 10-q M) and a second, saturable and reversible site of less affinity with a corresponding ED close to 2 to 3 x 10-5 M. Various plotting systems of the binding curve indicated for the second site a positive cooperativity, the Hill coefficient being 3.7. Dissociation rates were quite high for both ligands, however. it was much higher for 5-HT than for LSD; both were temperature-dependent with a respective QO close to 2.5 and 3. Regional distributions of binding capacities for LSD and 5-HT weIe very similar. They were not homogenous within the brain but varied according to the studied region, e.g. in decreasing order: striatum, hippocampus, cortex, raphe, cerebellum. Specific lesions of the tryptaminergic system by stereotaxic injections of 5 6-dibydroxytryptamine within raphe and anterior ventricles did not significantly modify binding of either ligand. Bromlysergamide and cyproheptadine were more efficient in displacing LSD than 5-HT (respective ID -50s: 3 x 10-8 and 6 x 10-7 M for LSD; 1.5 x 10-6 and 6 x 10-6 for 5-HT).
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