Radioligand binding analysis of knockout mice reveals 5-hydroxytryptamine(7) receptor distribution and uncovers 8-hydroxy-2-(di-n-propylamino)tetralin interaction with alpha(2) adrenergic receptors.
In the present autoradiographic study, we took advantage of 5-hydroxytryptamine(7) (5-HT(7)) receptor knockout mice to analyze the brain distribution of 5-HT(7) receptor binding sites using [(3)H]5-carboxamidotryptamine (5-CT; a 5-HT(1A/1B/1D/5/7) receptor ligand) and [(3)H]8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; a 5-HT(1A/7) receptor ligand). Low to moderate densities of [(3)H]5-CT (2 nM) binding sites insensitive to pindolol (10 microM, for 5-HT(1A/1B) receptor blockade) and GR-127935 (1 microM; for 5-HT(1D) receptor blockade) were observed in wild-type mice (mainly in thalamus and hypothalamus) but not in 5-HT(7) receptor knockout mice. Surprisingly, moderate to high densities of [(3)H]8-OH-DPAT (10 nM) binding sites insensitive to pindolol (10 microM) remained in 5-HT(7) receptor knockout mouse brain. These non-5-HT(1A), non-5-HT(7) binding sites were found to be adrenergic alpha(2A) receptor binding sites. In alpha(2A) receptor knockout mice low to moderate densities of [(3)H]8-OH-DPAT binding sites insensitive to pindolol but sensitive to the selective 5-HT(7) receptor antagonist SB-269970 (300 nM) were observed mainly in thalamus and hypothalamus. Therefore, in addition to 5-HT(1A) and 5-HT(7) binding sites, [(3)H]8-OH-DPAT also binds to alpha(2A) receptor binding sites in wild-type mouse brain. [(3)H]8-OH-DPAT (in the presence of pindolol and 1 microM RX-821002 for alpha(2) receptor blockade) and [(3)H]5-CT (in the presence of pindolol and GR-127935) bind to a similar receptor binding population corresponding to 5-HT(7) binding sites. Detailed anatomical mapping of 5-HT(7) receptor binding sites in wild-type mouse brain was then performed using both radioligands in the presence of suitable pharmacological agents for non-5-HT(7) receptor binding sites blockade. The mapping revealed binding sites consistent with the mRNA distribution with the highest densities found in anterior thalamic nuclei.
Bonaventure
P
P
Johnson and Johnson Pharmaceutical Research and Development, L.L.C., San Diego, CA 92121, USA.
Nepomuceno
D
D
Hein
L
L
Sutcliffe
J G
JG
Lovenberg
T
T
Hedlund
P B
PB
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009994:Osmolar Concentration; D011869:Radioligand Assay; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000378:metabolism*; D012701:Serotonin / Q000031:analogs & derivatives* / Q000378:metabolism; D017366:Serotonin Receptor Agonists / Q000378:metabolism*; D014018:Tissue Distribution
C547769:Adra2a protein, mouse; C547775:Adra2c protein, mouse; D018341:Receptors, Adrenergic, alpha-2; D011985:Receptors, Serotonin; D017366:Serotonin Receptor Agonists; C104425:serotonin 7 receptor; D012701:Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C047087:5-carboxamidotryptamine