51. [3H]Alnespirone: a novel specific radioligand of 5-HT1A receptors in the rat brain
- Author
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V, Fabre, C, Boni, E, Mocaër, M, Lesourd, M, Hamon, and A M, Laporte
- Subjects
Male ,8-Hydroxy-2-(di-n-propylamino)tetralin ,Temperature ,Brain ,Hydrogen-Ion Concentration ,Ligands ,Rats ,Serotonin Receptor Agonists ,Rats, Sprague-Dawley ,Anti-Anxiety Agents ,Chlorides ,Manganese Compounds ,Ethylmaleimide ,Receptors, Serotonin ,Animals ,Autoradiography ,Spiro Compounds ,Guanosine Triphosphate ,Receptors, Serotonin, 5-HT1 - Abstract
Determination of the optimal assay conditions for the specific binding of a tritiated derivative of the novel potential anxiolytic drug alnespirone (S-20499, (+)-4-[N-(5-methoxy-chroman-3-yl)-N-propylamino]butyl-8-azaspiro-( 4,5)-decane-7,9-dione) allowed the demonstration that this radioligand bound with a high affinity (Kd = 0.36 nM) to a homogeneous class of sites in rat hippocampal membranes. The pharmacological properties of [3H]alnespirone specific binding sites matched exactly (r = 0.95) those of 5-HT1A receptors identified with [3H]8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) as radioligand. Furthermore, membrane binding experiments and autoradiographic labeling of tissue sections showed that the regional distribution of [3H]alnespirone specific binding sites in the rat brain and spinal cord superimposed over that of 5-HT1A receptors specifically labeled by [3H]8-OH-DPAT. However, the differential sensitivity of [3H]alnespirone and [3H]8-OH-DPAT specific binding to various physicochemical effectors (temperature, pH, Mn2+, N-ethyl-maleimide) supports the idea that these two agonist radioligands did not recognize 5-HT1A receptors exactly in the same way. These differences probably account for the reported inability of alnespirone, in contrast to 8-OH-DPAT, to induce some 5-HT1A receptor-mediated behavioural effects in rats.
- Published
- 1998