G-PROTEIN ACTIVATION AT 5-HT1A RECEPTORS BY THE 5-HT(1F) LIGAND LY334370 IN GUINEA-PIG BRAIN SECTIONS AND RECOMBINANT CELL-LINES

1 G-protein activation by the 5-ht(1F) receptor agonist benzoyl)amino- 3-(1-methylpiperidin-4-yl)-1H-indole fumarate (LY334370) was investiga ted by use of autoradiography of receptor-activated G-proteins in guin ea-pig brain sections and [S-35]-GTP gamma S binding responses in cell lines stably expressing human 5-HT1A (h 5-HT1A) receptors. 2 LY334370 (10 mu M) caused little or no stimulation of [S-35]-GTP gamma S bindi ng in guinea-pig brain regions enriched in 5-ht(1F) binding sites (e.g ., claustrum, caudate/putamen and thalamic nuclei), as identified by l abelling with 10 nM [H-3]-sumatriptan plus 10 nM 5-carboxamidotryptami ne (5-CT). 3 Application of LY334370 (10 mu M) to guinea-pig brain sec tions resulted in an increase of [S-35]-GTP gamma S binding in hippoca mpus (123+/-17%), lateral septum (58+/-14%) dorsal raphe (57+/-10%), e ntorhinal (37+/-11%) and cingulate cortex (28+/-10%). This distributio n fits with the G-protein activation mediated by 5-HT1A receptors as f ound with lisuride (10 mu M), and labelling of 5-HT1A receptors by 140 pM [I-125]-4-(2'-methoxy-phenyl)-1-[2'-(n-2 ''-pyridinyl)-p-iodobenza mido]-ethyl-piperazine (p-MPPI). 4 The LY334370-mediated [S-35]-GTP ga mma S response was antagonized by the selective, silent 5-HT1A recepto r antagonist zinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide (WAY10 0635, 1 mu M) in each of the brain structures investigated. The distri bution pattern of the [S-35]-GTP gamma S binding response and the anta gonist profile suggest that the LY334370-induced response in guinea-pi g brain is mediated by 5-HT1A receptors. 5 The maximal LY334370-induce d [S-35]-GTP gamma S binding response (83 to 94%) in membranes of reco mbinant C6-glial/h 5-HT1A and HeLa/h 5-HT1A cells was close to that of 5-HT, suggesting LY334370 to exert high intrinsic activity at h 5-HT1 A receptors. 6 In conclusion, in guinea-pig brain sections and recombi nant cell lines the 5-ht(1F) receptor agonist LY334370 causes G-protei n activation that is mediated by 5-HT1A receptors. Caution should be t aken when employing this ligand as a putative selective 5-ht(1F) agoni st.