G-protein activation by the 5-ht1F receptor agonist 5-(4-fluorobenzoyl)amino-3-(1-methylpiperidin-4-yl)-1H-indole fumarate (LY334370) was investigated by use of autoradiography of receptor-activated G-proteins in guinea-pig brain sections and [35S]-GTPgammaS binding responses in cell lines stably expressing human 5-HT1A (h 5-HT1A) receptors. 2. LY334370 (10 microM) caused little or no stimulation of [35S]-GTPgammaS binding in guinea-pig brain regions enriched in 5-ht1F binding sites (e.g., claustrum, caudate/putamen and thalamic nuclei), as identified by labelling with 10 nM [3H]-sumatriptan plus 10 nM 5-carboxamidotryptamine (5-CT). 3. Application of LY334370 (10 microM) to guinea-pig brain sections resulted in an increase of [35S]-GTPgammaS binding in hippocampus (123+/-17%), lateral septum (58+/-14%), dorsal raphe (57+/-10%), entorhinal (37+/-11%) and cingulate cortex (28+/-10%). This distribution fits with the G-protein activation mediated by 5-HT1A receptors as found with lisuride (10 microM), and labelling of 5-HT1A receptors by 140 pM [125I]-4-(2'-methoxy-phenyl)- -[2'-(n-2"-pyridinyl)-p-iodobenzamido]-ethyl-piperazine (p-MPPI). 4. The LY334370-mediated [35S]-GTPgammaS response was antagonized by the selective, silent 5-HT1A receptor antagonist N-[2-[4-(2-methoxyphenyl)1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohex anecarboxa-mide (WAY100635, 1 microM) in each of the brain structures investigated. The distribution pattern of the [35S]-GTPgammaS binding response and the antagonist profile suggest that the LY334370-induced response in guinea-pig brain is mediated by 5-HT1A receptors. 5. The maximal LY334370-induced [35S]-GTPgammaS binding response (83 to 94%) in membranes of recombinant 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-HT1A receptors. 6. In conclusion, in guinea-pig brain sections and recombinant cell lines the 5-ht1F receptor agonist LY334370 causes G-protein activation that is mediated by 5-HT1A receptors. Caution should be taken when employing this ligand as a putative selective 5-ht1F agonist.
