BACKGROUND AND PURPOSEActivation of post-synaptic 5-HT(1A) receptors may provide enhanced therapy against depression. We describe the signal transduction profile of F15599, a novel 5-HT(1A) receptor agonist.EXPERIMENTAL APPROACHF15599 was compared with a chemical congener, F13714, and with (+)8-OH-DPAT in models of signal transduction in vitro and ex vivo.KEY RESULTSF15599 was highly selective for 5-HT(1A) receptors in binding experiments and in [(35)S]-GTPgammaS autoradiography of rat brain, where F15599 increased labelling in regions expressing 5-HT(1A) receptors. In cell lines expressing h5-HT(1A) receptors, F15599 more potently stimulated extracellular signal-regulated kinase (ERK1/2) phosphorylation, compared with G-protein activation, internalization of h5-HT(1A) receptors or inhibition of cAMP accumulation. F13714, (+)8-OH-DPAT and 5-HT displayed a different rank order of potency for these responses. F15599 stimulated [(35)S]-GTPgammaS binding more potently in frontal cortex than raphe. F15599, unlike 5-HT, more potently and efficaciously stimulated G(alphai) than G(alphao) activation. In rat prefrontal cortex (a region expressing post-synaptic 5-HT(1A) receptors), F15599 potently activated ERK1/2 phosphorylation and strongly induced c-fos mRNA expression. In contrast, in raphe regions (expressing pre-synaptic 5-HT(1A) receptors) F15599 only weakly or did not induce c-fos mRNA expression. Finally, despite its more modest affinity in vitro, F15599 bound to 5-HT(1A) receptors in vivo almost as potently as F13714.CONCLUSIONS AND IMPLICATIONSF15599 showed a distinctive activation profiles for 5-HT(1A) receptor-mediated signalling pathways, unlike those of reference agonists and consistent with functional selectivity at 5-HT(1A) receptors. In rat, F15599 potently activated signalling in prefrontal cortex, a feature likely to underlie its beneficial effects in models of depression and cognition.