Regulation of 5-HT2 receptors in rat cortex. Studies with a putative selective agonist and an antagonist.
The phenylisopropylamine derivative 1-(2,5-dimethoxy-4-iodo-phenyl)-2-aminopropane (DOI) has been suggested recently as a selective serotonin2 (5-HT2) receptor agonist. Because of the potential importance of such a tool for investigations of 5-HT2 receptor regulation, receptor binding studies were performed in rats after acute and chronic treatment with DOI, the selective 5-HT2 antagonist ketanserin, or vehicle. Single injections of 5 or 10 mg/kg DOI reduced the Bmax of cortical sites labeled with [3H]1-(2,5-dimethoxy-4-bromo-phenyl)-2-aminopropane and [3H]ketanserin (9-32 or 32-46%, respectively). Chronic daily treatment with DOI (3-9 mg/kg) further down-regulated 5-HT2 sites in cortex identified with either [3H]ketanserin (-60%) or with [3H]DOB (-75%), without altering Kd values or affecting 5-HT1 sites. In vitro addition to the [3H]ketanserin or [3H]DOB binding assay of 10 nM to 1 microM DOI resulted in competitive inhibition, suggesting that down-regulation found in vivo was not secondary to residual drug. Chronic treatment with ketanserin (10 mg/kg) also down-regulated both [3H]ketanserin (-38%) and [3H]DOB (-58%) sites in cortex without charges in 5-HT1 sites. In naive cortex, competition experiments revealed a Ki (nM) for ( +/- )-DOI of 1.7 +/- 0.02 at sites labeled by [3H]DOB, and a KH and KL of 4.8 +/- 1.5 and 53 +/- 2 nM at sites labeled by [3H]ketanserin. These data indicate that in chronic treatment, DOI, like ketanserin, is highly selective for 5-HT2 vs 5-HT1 sites at behaviorally useful doses. However, a representative putative 5-HT2 selective agonist and antagonist have similar effects on 5-HT2 receptors labeled by agonist or antagonist radioligands.
Pranzatelli
M R
MR
Department of Neurology, George Washington University, Washington, DC 20010.
D000662:Amphetamines / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D002540:Cerebral Cortex / Q000378:metabolism*; D007650:Ketanserin / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology*; D014316:Tritium
D000662:Amphetamines; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D014316:Tritium; D007650:Ketanserin; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine