Newman-Tancredi A, Martel JC, Assié MB, Buritova J, Lauressergues E, Cosi C, Heusler P, BruinsSlot L, Colpaert F, Vacher B, Cussac D.
Br J Pharmacol. 2009 Jan;156(2):338-53. Epub 2009 Jan 12.

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Levitt ES, Hunnicutt BJ, Knopp SJ, Williams JT, Bissonnette JM.
J Appl Physiol (1985). 2013 Dec;115(11):1626-33. Epub 2013 Oct 3.

Rett syndrome is a neurological disorder caused by loss of function mutations in the gene that encodes the DNA binding protein methyl-CpG-binding protein 2 (Mecp2). A prominent feature of the syndrome is disturbances in respiration characterized by frequent apnea and an irregular interbreath cycle. 8-Hydroxy-2-dipropylaminotetralin has been shown to positively modulate these disturbances (Abdala AP, Dutschmann M, Bissonnette JM, Paton JF, Proc Natl Acad Sci USA 107: 18208-18213, 2010), but the mode of action is not understood. Here we show that the selective 5-HT1A biased agonist 3-chloro-4-fluorophenyl-(4-fluoro-4-{[(5-methylpyrimidin-2-ylmethyl)-amino]-methyl}-piperidin-1-yl)-methanone (F15599) decreases apnea and corrects irregularity in both heterozygous Mecp2-deficient female and in Mecp2 null male mice. In whole cell voltage-clamp recordings from dorsal raphe neurons, F15599 potently induced an outward current, which was blocked by barium, reversed at the potassium equilibrium potential, and was antagonized by the 5-HT1a antagonist WAY100135. This is consistent with somatodendritic 5-HT1A receptor-mediated activation of G protein-coupled inwardly rectifying potassium channels (GIRK). In contrast, F15599 did not activate 5-HT1B/D receptors that mediate inhibition of glutamate release from terminals in the nucleus accumbens by a presynaptic mechanism. Thus F15599 activated somatodendritic 5-HT1A autoreceptors, but not axonal 5-HT1B/D receptors. In unanesthetized Mecp2-deficient heterozygous female mice, F15599 reduced apnea in a dose-dependent manner with maximal effect of 74.5 ± 6.9% at 0.1 mg/kg and improved breath irrregularity. Similarly, in Mecp2 null male mice, apnea was reduced by 62 ± 6.6% at 0.25 mg/kg, and breathing became regular. The results indicate respiration is improved with a 5-HT1A agonist that activates GIRK channels without affecting neurotransmitter release.

Lladó-Pelfort L, Assié MB, Newman-Tancredi A, Artigas F, Celada P.
Br J Pharmacol. 2010 Aug;160(8):1929-40.

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Bardin L, Assié MB, Pélissou M, Royer-Urios I, Newman-Tancredi A, Ribet JP, Sautel F, Koek W, Colpaert FC.
J Pharmacol Exp Ther. 2005 Mar;312(3):1034-42. Epub 2004 Nov 4.

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The aim of the present study was to establish the relationship between the plasma and brain concentration-time profiles of F 13640 [(3-chloro-4-fluoro-phenyl)-[4-fluoro-4-{[(5-methyl-pyridin-2-ylmethyl)-amino]-methyl}piperidin-1-yl]methanone, fumaric acid salt] after acute administration and both its hyper- and hypoanalgesic effects in rats. The maximal plasma concentration (Cmax) of F 13640 after i.p. administration of 0.63 mg/kg was obtained at 15 min and decreased to half its maximal value after about 1 h. The amount of F13640 collected by means of in vivo microdialysis in hippocampal dialysates could be measured reliably after 0.63 and 2.5 mg/kg, reached its maximum at about 1 h, and fell to half of its maximal value at about 3 h. 5-Hydroxytryptamine 1A (5-HT1A) receptor occupancy was estimated by ex vivo binding in rat brain sections. F 13640 inhibited [3H]8-hydroxy-2-[di-n-propylamino] tetralin binding ex vivo in rat hippocampus, entorhinal cortex, and frontal cortex (ED50, 0.34 mg/kg i.p.). Maximal inhibition was reached at approximately 30 min after 0.63 mg/kg F 13640 and fell to half of its value after about 4 to 8 h. After injection (15 min) in the paw pressure test, F 13640 (0.63 mg/kg i.p.) induced an initial hyperalgesia that was followed 4 h later by a paradoxical analgesia that lasted until 8 h. In contrast, in the formalin test, F 13640 inhibited pain behaviors until 4 h after drug administration. F 13640 also produced elements of the 5-HT syndrome that lasted up to 4 h after administration. These results demonstrate that F 13640 induces hyperalgesia and/or analgesia with a time course that parallels the occupancy of 5-HT1A receptors and the presence of the compound in blood and brain.