1 In the hippocampus, axon collaterals of CA1 pyramidal cells project locally onto neighbouring CA1 pyramidal cells and interneurones, forming a local excitatory network which, in disinhibited conditions, feeds polysynaptic epscs (poly-epscs). 5-hydroxytryptamine (5-HT) has been shown to inhibit poly-epscs through activation of a presynaptic receptor. The aim of the present work was the pharmacological characterization of the 5-HT receptor involved in this 5-HT action. 2 Poly-epscs, evoked by electrical stimulation of the stratum radiatum and recorded in whole-cell voltage-clamp from CA1 pyramidal neurones, were studied in mini-slices of the CA1 region under pharmacological block of GABA A , GABA B , and 5-HT 1A receptors. 3 The 5-HT 1B receptor selective agonist 1,4-dihydro-3-(1,2,3,6-tetrahydro-4-pyridinyl)-5H-pyrrolo[3,2-b]pyridin-5-one dihydrochloride (CP 93129) inhibited poly-epscs (EC 50 =55 nM), an eect mimicked by the 5-HT 1B ligands 5-carboxamidotryptamine (5-CT; EC 50 =14 nM) and methylergometrine (EC 50 =78 nM), but not by 1-(3-chlorophenyl)piperazine dihydrochloride (mCPP; 10 mM) or 7-tri¯uoromethyl-4(4-methyl-1-piperazinyl)-pyrrolo[1,2-a]quinoxaline dimaleate (CGS 12066B; 10 mM). 4 The eects of CP 93129 and 5-CT were blocked by the selective 5-HT 1B receptor antagonist 3-[3-(dimethylamino)propyl]-4-hydroxy-N-[4-(4-pyridinyl)phenyl]benzamide dihydrochloride (GR 55562; K B &100 nM) and by cyanopindolol (K B =6 nM); methiothepin (10 mM) and dihydroergotamine (1 mM). For both GR 55562 and methiothepin, application times of at least two hours were required in order to achieve their full antagonistic eects. 5 Our results demonstrate that 5-HT 1B receptors are responsible for the presynaptic inhibition of neurotransmission at CA1/CA1 local excitatory synapses exerted by 5-HT.

The pharmacological properties of cyclohexanecarboxylic acid, {2-[4-(2-bromo-5-methoxybenzyl)piperazin-1-yl]ethyl}-(2-trifluoromethoxyphenyl)amide (Rec 27/0224), and cyclohexanecarboxylic acid, (2-methoxy-phenyl)-{2-[4-(2-methoxyphenyl)-piperazin-1-yl]ethyl}amide (Rec 27/0074), were characterized using radioligand displacement and guanosine 5Ј-O-(3- -{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-2-pyridinylcyclo-hexanecarboxamide (WAY-100635).Impairment of 5-hydroxytryptamine (5-HT) neurotransmission is involved in major neuropsychiatric pathological states (e.g., depression, anxiety, schizophrenia, and Parkinson's disease). Considerable effort has been consistently made to understand the functioning of the 5-HT system and to develop new selective drugs for 5-HT receptor subtypes.The 5-HT 1A receptor has been extensively studied because of the early discovery of a selective agonist (Gozlan et al., 1983) and receptor cloning (Kobilka et al., 1987;Albert et al., 1990). 5-HT 1A receptors are G protein-coupled receptors (GPCR) expressed throughout the central nervous system (Pompeiano et al., 1992). Stimulation of 5-HT 1A receptors activates Gi/o proteins, leading to at least two different cellular responses: inhibition of adenylate cyclase and opening Article, publication date, and citation information can be found at