%0 Journal Article %A M Rinaldi-Carmona %A C Congy %A J Simiand %A F Oury-Donat %A P Soubrie %A J C Breliere %A G Le Fur %T Repeated administration of SR 46349B, a selective 5-hydroxytryptamine2 antagonist, up-regulates 5-hydroxytryptamine2 receptors in mouse brain. %D 1993 %J Molecular Pharmacology %P 84-89 %V 43 %N 1 %X Adaptive changes in 5-hydroxytryptamine (5-HT)2 receptors were investigated in mice after repeated administration of SR 46349B, a potent, selective, and competitive 5-HT2 receptor antagonist (Kl = 0.72 +/- 0.05 nM). Repeated administration (twice per day for 3 days and once on the morning of the fourth day) of SR 46349B (5 or 10 mg/kg, orally) caused 24 hr later a marked increase in 5-HT2 receptor number (+41% and +75%, respectively), measured ex vivo in brain cortical membranes with [3H] ketanserin, without affecting its affinity constant. Further, administration of the 5-HT2 agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane produced, in SR 46349B (10 mg/kg, orally)-treated mice, a significant stimulation of the 5-HT2 receptor-linked phosphoinositide turnover in vivo in the brain. In addition, subacute administration of SR 46349B (5 or 10 mg/kg, orally) caused a significant increase of the head-twitch response to L-5-hydroxytryptophan. This enhanced response was blocked by an acute administration of ritanserin (1 mg/kg). These results show that repeated administration of SR 46349B produced a parallel enhancement in 5-HT2 receptor number, in 5-HT2 receptor-linked signal transduction, and in 5-HT2 receptor-mediated behavioral responses in mice. These findings suggest for the first time that an up-regulation of 5-HT2 receptors can occur after repeated treatment with a selective 5-HT2 antagonist. %U https://molpharm.aspetjournals.org/content/molpharm/43/1/84.full.pdf