Preferential in vivo action of F15599, a novel 5-HT1A receptor agonist, at postsynaptic 5-HT1A receptors

Background and purpose: F15599, a novel 5-hydroxytryptamine (5-HT)(1A) receptor agonist with 1000-fold selectivity for 5-HT compared with other monoamine receptors, shows antidepressant and procognitive activity at very low doses in animal models. We examined the in vivo activity of F15599 at somatodendritic autoreceptors and postsynaptic 5-HT1A heteroreceptors. Experimental approach: In vivo single unit and local field potential recordings and microdialysis in the rat. Key results: F15599 increased the discharge rate of pyramidal neurones in medial prefrontal cortex (mPFC) from 0.2 mu g center dot kg-1 i.v and reduced that of dorsal raphe 5-hydroxytryptaminergic neurones at doses > 10-fold higher (minimal effective dose 8.2 mu g center dot kg-1 i.v.). Both effects were reversed by the 5-HT1A antagonist (+/-)WAY100635. F15599 did not alter low frequency oscillations (similar to 1 Hz) in mPFC. In microdialysis studies, F15599 increased dopamine output in mPFC (an effect dependent on the activation of postsynaptic 5-HT1A receptors) with an ED50 of 30 mu g center dot kg-1 i.p., whereas it reduced hippocampal 5-HT release (an effect dependent exclusively on 5-HT1A autoreceptor activation) with an ED50 of 240 mu g center dot kg-1 i.p. Likewise, application of F15599 by reverse dialysis in mPFC increased dopamine output in a concentration-dependent manner. All neurochemical responses to F15599 were prevented by administration of (+/-)WAY100635. Conclusions and implications: These results indicate that systemic administration of F15599 preferentially activates postsynaptic 5-HT1A receptors in PFC rather than somatodendritic 5-HT1A autoreceptors. This regional selectivity distinguishes F15599 from previously developed 5-HT1A receptor agonists, which preferentially activate somatodendritic 5-HT1A autoreceptors, suggesting that F15599 may be particularly useful in the treatment of depression and of cognitive deficits in schizophrenia.