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Background and purpose: Activation of post-synaptic 5-HT1A receptors may provide enhanced therapy against depression. We describe the signal transduction profile of F15599, a novel 5-HT1A receptor agonist. Experimental approach: F15599 was compared with a chemical congener, F13714, and with (+)8-OH-DPAT in models of signal transduction in vitro and ex vivo. Key results: F15599 was highly selective for 5-HT1A receptors in binding experiments and in [35S]-GTPγS autoradiography of rat brain, where F15599 increased labelling in regions expressing 5-HT1A receptors. In cell lines expressing h5-HT1A receptors, F15599 more potently stimulated extracellular signal-regulated kinase (ERK1/2) phosphorylation, compared with G-protein activation, internalization of h5-HT1A 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 [35S]-GTPγS binding more potently in frontal cortex than raphe. F15599, unlike 5-HT, more potently and efficaciously stimulated Gαi than Gαo activation. In rat prefrontal cortex (a region expressing post-synaptic 5-HT1A receptors), F15599 potently activated ERK1/2 phosphorylation and strongly induced c-fos mRNA expression. In contrast, in raphe regions (expressing pre-synaptic 5-HT1A receptors) F15599 only weakly or did not induce c-fos mRNA expression. Finally, despite its more modest affinity in vitro, F15599 bound to 5-HT1A receptors in vivo almost as potently as F13714. Conclusions and implications: F15599 showed a distinctive activation profiles for 5-HT1A receptor-mediated signalling pathways, unlike those of reference agonists and consistent with functional selectivity at 5-HT1A receptors. In rat, F15599 potently activated signalling in prefrontal cortex, a feature likely to underlie its beneficial effects in models of depression and cognition.

Background and purpose: Combining 5-HT1A receptor activation with dopamine D2/D3 receptor blockade should improve negative symptoms and cognitive deficits in schizophrenia. We describe the in vitro profile of F15063 (N-[(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)ethyl]-3-(cyclopent-1-enyl)-benzylamine). Experimental approach: F15063 was characterised in tests of binding affinity and in cellular models of signal transduction at monoamine receptors. Key results: Affinities (receptor and pKi values) of F15063 were: rD2 9.38; hD2L 9.44; hD2S 9.25; hD3 8.95; hD4 8.81; h5-HT1A 8.37. F15063 had little affinity (40-fold lower than D2) at other targets. F15063 antagonised dopamine-activated G-protein activation at hD2, rD2 and hD3 receptors with potency (pKb values 9.19, 8.29 and 8.74 in [35S]GTPγS binding experiments) similar to haloperidol. F15063 did not exhibit any hD2 receptor agonism, even in tests of ERK1/2 phosphorylation and G-protein activation in cells with high receptor expression. In contrast, like (±)8-OH-DPAT, F15063 efficaciously activated h5-HT1A (Emax 70%, pEC50 7.57) and r5-HT1A receptors (52%, 7.95) in tests of [35S]GTPγS binding, cAMP accumulation (90%, 7.12) and ERK1/2 phosphorylation (93%, 7.13). F15063 acted as a partial agonist for [35S]GTPγS binding at hD4 (29%, 8.15) and h5-HT1D receptors (35%, 7.68). In [35S]GTPγS autoradiography, F15063 activated G-proteins in hippocampus, cortex and septum (regions enriched in 5-HT1A receptors), but antagonised quinelorane-induced activation of D2/D3 receptors in striatum. Conclusions and implications: F15063 antagonised dopamine D2/D3 receptors, a property underlying its antipsychotic-like activity, whereas activation of 5-HT1A and D4 receptors mediated its actions in models of negative symptoms and cognitive deficits of schizophrenia (see companion papers). British Journal of Pharmacology (2007) 151, 237–252. doi:10.1038/sj.bjp.0707158

Ataxia-telangiectasia (A-T) is a genetic disease, associated with progressive motor impairment and a lack of functional ATM protein. It has been reported that immunoreactive tyrosine hydroxylase and dopamine transporter are reduced in an Atm-/- mouse model of A-T. These observations led to a hypothesis that A-T is associated with loss of nigrostriatal dopamine and prompted the launch of clinical trials to evaluate a therapeutic utility of the anti-parkinsonian drug, l-DOPA. To test for dopamine depletion more directly, we measured regional levels of monoamines and their metabolites in the Atm-/- mouse brain. We also measured levels of NAD+, a cofactor for dopamine biosynthesis and substrate of the DNA damage surveillance enzyme, poly(ADP-ribose) polymerase (PARP). Constitutive activation of PARP has been posited to cause NAD+ depletion. We observed no reduction in monoamine transmitters and no depletion of NAD+, or other high energy phosphate donors in the adult Atm-/- cerebellum, striatum, or ventral mesencephalon. However, our studies did reveal a progressive sensorimotor impairment in Atm-/- mice that may serve as a relevant proxy for progressive neurological impairment in the human disease. Our results call into question the involvement of dopamine in A-T and the therapeutic strategy of enhancing dopaminergic function with l-DOPA.

Poly(ADP-ribose) polymerase (PARP) is a DNA binding protein that uses nicotinamide adenine dinucleotide (NAD+) as a substrate. Evidence from in vitro studies on nonneuronal cells in culture have shown that when fully activated by free radical-induced DNA damage, PARP depletes cellular NAD+ and consequently adenosine triphosphate (ATP) levels within a matter of minutes, and that this depletion is associated with a cell death that can be prevented by PARP inhibitors. The present in vivo study utilized the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse, a model of central nigrostriatal dopamine neurotoxicity that recapitulates certain features of Parkinson's disease (PD), and one in which we have previously shown PARP inhibitors to be protective, to examine whether MPTP acutely caused region- and time-dependent changes in levels of NAD+ and ATP in the brain in vivo and whether such effects were modified by treatments with neuroprotective doses of the PARP inhibitor benzamide. The results confirm that MPTP reduces striatal ATP levels, as previously reported by Chan et al., show that MPTP causes a regionally-selective (striatal and midbrain) loss of NAD+, and indicate that the PARP inhibitor benzamide can prevent these losses without interfering with MPTP-induced striatal dopamine release. These findings suggest an involvement of PARP in the control of brain energy metabolism during neurotoxic insult, provide further evidence in support of the participation of PARP in MPTP-induced neurotoxicity in vivo and suggest that PARP inhibitors might be beneficial in the treatment of PD.

A search for novel, selective agonists with high intrinsic activity at the 5-HT1A subtype of serotonin (5-HT) receptors was undertaken. Mechanistic and thermodynamic considerations led to the design of 6-substituted-2-pyridinylmethylamine as a potential 5-HT1A pharmacophore. Various adducts derived from the 6-substituted-2-pyridinylmethylamine moiety were tested for their affinity at 5-HT1A, α1-adrenergic, and D2-dopaminergic receptors. Compounds with high affinity for 5-HT1A receptors (pKi ≥ 8) were examined for agonist properties by measuring their ability to inhibit forskolin-stimulated cAMP production in HA7 cells (i.e., HeLa cells permanently transfected with the h5-HT1A receptor gene and expressing the h5-HT1A receptor protein). Several compounds of the type aryl{4-[(6-substituted-pyridin-2-ylmethylamino)methyl]piperidin-1-yl}methanone had nanomolar affinity for 5-HT1A binding sites and were more than 500-fold selective with respect to α1 and D2 sites. Importantly, their 5-HT1A agonist properties we...