Floxed heterozygous F1 animals were discriminated from wild type by PCR using couples primers specific for targeted (GW224/GW475) and wild-type alleles (GW264, 5-CGACTGGTCAAGAGAAGTCC-3/GW265, 5-AGGAGAACCATCTTCAAGGC-3) and by Southern blot on XbaI-digested genomic DNA using an XbaI/HindIII probe specific for the 5-targeted region (Fig. genetic deletion of TA1R did not affect increases in DA levels evoked by para-chloroamphetamine (PCA), which was inactive at hTA1sites. The TA1R agonisto-phenyl-3-iodotyramine (o-PIT) blunted the DA-releasing actions of PCA bothin vivo(dialysis) andin vitro(synaptosomes) in WT but notTA1-KOanimals. MDMA-elicited increases in dialysis levels of serotonin (5-HT) were similarly greater inTA1-KOversus WT mice, and 5-HT-releasing actions of PCA were bluntedin vivoandin vitrobyo-PIT in WT mice only. In conclusion, TA1Rs exert an inhibitory influence on both dopaminergic and serotonergic transmission, and MDMA auto-inhibits its neurochemical and functional actions by recruitment of TA1R. These observations have important implications for the effects of MDMA in humans. == Introduction == The monoamine releaser and reuptake suppressor, ecstasy [3,4-methylenedioxymetamphetamine (MDMA)], facilitates prosocial behaviors in animals and humans (Bedi et al., 2009;Johansen and Krebs, 2009), actions related to enhanced release MT-DADMe-ImmA of oxytocin in centers controlling social behavior, like amygdala and septum (McGregor et al., 2008). However, greater attention has been devoted to the psychostimulant properties of MDMA and its widespread recreational use (Vollenweider et al., 1999,2002). In addition, MDMA can trigger a serotonergic syndrome and disrupt thermoregulatory mechanisms, neurotoxic effects especially prominent in young adults under conditions of dehydration (Schifano, 2004;Baumann et al., 2007;Karlsen et al., 2008). It is thus important to elucidate the precise mechanisms of action of MDMA. MDMA displaces neuronal serotonin (5-HT) via reversal of vesicular and plasma membrane transporters (Rudnick and Wall, 1992;Mlinar and Corradetti, 2003). Further, it prevents 5-HT reuptake (Iravani et al., 2000) and inhibits the activity of the catabolytic enzyme monoamine oxidase A (Leonardi and Azmitia, 1994). Concomitant elevations in dopamine (DA) and noradrenaline (NA) levels occur either via a comparable pattern of direct actions upon catecholaminergic pathways (Gough et al., 2002;Baumann et al., 2005,2008) and/or MT-DADMe-ImmA events downstream of serotonergic transmission, such as activation of 5-HT2Areceptors (Gobert MT-DADMe-ImmA et al., 2000). Moreover, at high concentrations, MDMA binds to 5-HT2A, histamine H1, and muscarinic M1/M2receptors, though their putative functions in its functional actions remain poorly characterized (Green et al., 2003). A potentially novel dimension to the neurobiology of MDMA was unveiled by the suggestion that it recognizes Gs-coupled TA1receptors [TA1Rs (sometimes called TAAR1s)] (Bunzow MT-DADMe-ImmA et al., 2001;Lindemann and Hoener, 2005;Maguire et al., 2009). While most subtypes of trace amine (TA) receptor are preferentially expressed in olfactory epithelium (Liberles and Buck, 2006), TA1Rs are mainly distributed in limbic structures and regions made up of monoaminergic perykarias (Borowsky et al., 2001;Wolinsky et al., 2007;Lindemann et al., 2008). The TAs, tyramine, tryptamine, and -phenethylamine are implicated in psychiatric and neurological disorders associated with monoaminergic dysfunction (Branchek and Blackburn, 2003;Berry, 2004;Burchett and Hicks, 2006;Sotnikova et al., 2008), yet it remains unproven that they take action via TA1Rsin vivo. Conversely, the thyroxine derivatives 3-iodothyronamine (T1AM) ando-phenyl-3-iodotyramine (o-PIT) behave as agonists at TA1Rs, and their hypothermic actions are blunted in TA1knock-out (TA1-KO) mice (Scanlan et al., 2004;Hart et al., 2006;Doyle et al., 2007) (M.J. Millan, unpublished observations). Similarly of pertinence to MDMA, TA1Rs inhibit the electrical and synthetic activity of nigrostriatal dopaminergic neurons (Geracitano et al., 2004;Lindemann et al., 2008;Bradaia et al., 2009;Ledonne et al., 2010). Moreover, functional interactions have been reported between colocalized TA1R and DA transporters (Xie and Miller, 2008;Xie et al., 2008). Interestingly, T1AM ando-PIT BMP2 suppress locomotor activity in mice (Scanlan et al., 2004), actions opposite to those of MDMA (Baumann et al., 2008). Collectively, these observations raise the intriguing possibility that TA1R may modulate the actions of MDMA. Though EPPTB (N-(3-ethoxy-phenyl)-4-pyrrolidin-1-yl-3-trifluoromethyl-benzamide) was described as a selective TA1R antagonist (Bradaia et al., 2009;Stalder et al., 2011), it is not centrally active.