(R)-(-)-[77Br]4-bromo-2,5-dimethoxyamphetamine labels a novel 5-hydroxytryptamine binding site in brain membranes.
(R)-(-)-[77Br]4-Bromo-2,5-dimethoxyamphetamine [(R)-(-)-[77Br] DOB] was synthesized to a high specific activity (1875 +/- 50 Ci/mmol) and used to label membrane-associated recognition sites in rat brain. (R)-(-)-[77Br]DOB displayed high affinity (KD = 0.60 +/- 0.08 nM) for a relatively low density of binding sites (Bmax = 1.2 +/- 0.08 pmol/g of tissue) in rat cortical membranes as compared with [3H]ketanserin (KD = 0.65 +/- 0.1 nM; Bmax = 6.2 +/- 0.6 pmol/g of tissue). Guanine, but not adenine, nucleotides were found to inhibit specific (R)-(-)-[77Br]DOB binding. GTP (10(-4) M) did not eliminate specific (R)-(-)-[77Br]DOB binding but caused a competitive inhibition of the radioligand. Drug competition studies of 5-hydroxytryptamine (5-HT) and related agents indicate that both putative agonists and antagonists display nanomolar potency for these sites. A significant correlation (p less than 0.01) exists between drug potencies for (R)-(-)-[77Br]DOB-labeled sites and both 5-HT2 (r = 0.64) and 5-HT1C (r = 0.68) binding sites. However, the sites do not appear to be identical. Moreover, a significant correlation exists between drug potencies for (R)-(-)-[77Br]DOB-labeled sites and human hallucinogenic drug potencies (r = 0.89; p less than 0.01). We conclude that (R)-(-)-[77Br]DOB labels a unique 5-HT recognition site in rat brain that does not coincide with previously described 5-HT binding site subtypes. The (R)-(-)-[77Br]DOB site does not appear to be a high affinity "state" of the 5-HT2 receptor but may label a subset of heterogeneous 5-HT2 recognition sites.
Peroutka
S J
SJ
Department of Neurology, Stanford University, California 94305.
Hamik
A
A
Harrington
M A
MA
Hoffman
A J
AJ
Mathis
C A
CA
Pierce
P A
PA
Wang
S S
SS
D004290:DOM 2,5-Dimethoxy-4-Methylamphetamine / Q000031:analogs & derivatives / Q000378:metabolism*; D000662:Amphetamines / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D001931:Brain Mapping; D004305:Dose-Response Relationship, Drug; D006213:Hallucinogens; D066298:In Vitro Techniques; D007700:Kinetics; D011685:Purine Nucleotides / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D011985:Receptors, Serotonin / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*; D013329:Structure-Activity Relationship
D000662:Amphetamines; D006213:Hallucinogens; D011685:Purine Nucleotides; D011985:Receptors, Serotonin; D004290:DOM 2,5-Dimethoxy-4-Methylamphetamine; C003943:2,5-dimethoxy-4-bromoamphetamine; D012701:Serotonin