Abstract

This study pharmacologically characterizes a novel behavioral response as a potential in vivo model of serotonin (5-HT)1A receptor-mediated activity. In rats restrained in horizontal cylinders, the selective 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino) tetralin HBr (8-OH-DPAT), dose-dependently (0.04-10.0 mg/kg s.c.) elicited spontaneous tail-flicks (STFs). This action was mimicked by other ligands possessing high affinity and high efficacy at 5-HT1A sites: RU 24969 [(5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole], lisuride, (+)-lysergic acid diethylamide and 5-methoxy-N,N-dimethyltryptamine hydrogen oxalate. The response could not be elicited by CGS 12066B [7-trifluormethyl-4-(4-methyl-l-piperazonyl)-pyrrolol- [1-2-a] quinoxaline dimaleate], mCPP 1-(3-chlorophenyl)-piperazine-2-HCl, TFMPPm-trifluromethylphenylpiperazine HCl, MK 212 [6-chloro-2-(l-piperzinyl)pyrazine], quipazine and DOI (+-)-2,5-dimethoxy-4-iodophenyl-2-aminopropane HCl, which act in vivo as agonists at 5-HT1B, 5-HT1C and/or 5-HT2 receptors, or by the 5-HT3 agonist, 2-methyl-5-HT. p-chloroamphetamine, which releases endogenous 5-HT, also evoked STFs; in contrast, d-amphetamine, a preferential releaser of catecholamines, was inactive, as were agonists and antagonists at alpha-1, alpha-2, beta-1, beta-2, dopamine D1 and D2 sites. 8-OH-DPAT-elicited STFs were blocked by the 5-HT1/2 antagonist, methiothepin, but not by the 5-HT1C/5-HT2 antagonists, mianserin, ritanserin and ICI 169,369 [2-(2-dimethylaminoetheylthio)-3-phenylquinoline] nor by the 5-HT3 antagonists, GR 38032F [(1,2,3,9-tetrahydro-9-methyl-3-[(2-methyl-1H-imidazol-l-yl)methyl]-4H- carbazol-4-one HCl], ICS 205,930 [(3 alpha-tropanyl)-1H-indol-3-carboxylic acid ester] and MDL 72222 [(1 alpha H, 3 alpha, 5 alpha H)-tripan-3-yl-3,5- dichlorobenzoate]. beta-Blockers with 5-HT1A affinity i.e., (-)-alprenolol, (+/-)-isamoltane and, stereoselectivity, (-)-but not (+)-pindolol, blocked the action of 8-OH-DPAT. Spiperone and spiroxatrine, D2 antagonists with high 5-HT1A affinity, also inhibited 8-OH-DPAT-induced STFs. Selective beta-blockers and D2 antagonists with low 5-HT1A affinity were inactive. 5-HT1A partial agonists, the pyrimidinylpiperazines, buspirone, gepirone and ipsapirone, the halogenated phenylpiperazine, LY 165,163 [1-(2-(4-aminophenyl) ethyl-4-(3-trifluoromethylphenyl)-piperazine], and the benzodioxane, MDL 72832 [8-(4-(1,4-benzodioxan-2-yl-methylamino)-butyl-8-azaspiro-(4 ,5)-decane- 7,9-dione] did not elicit STFs and antagonized the effect of 8-OH-DPAT.(ABSTRACT TRUNCATED AT 400 WORDS)