Previous studies indicate that agonists of the group II metabotropic glutamate receptors (mGluRs), mGluR2 and mGluR3, may provide a novel approach for the treatment of anxiety disorders and schizophrenia. However, the relative contributions of the mGluR2 and mGluR3 subtypes to the effects of the group II mGluR agonists remain unclear. In the present study, we describe an alternate synthesis and further pharmacological characterization of a recently reported positive allosteric modulator of mGluR2 termed biphenyl-indanone A (BINA). In recombinant systems, BINA produced a robust and selective potentiation of the response of mGluR2 to glutamate with no effect on the glutamate response of other mGluR subtypes. In hippocampal brain slices, BINA (1 M) significantly potentiated the mGluR2/3 agonist-induced inhibition of excitatory synaptic transmission at the medial perforant path-dentate gyrus synapse. BINA was also efficacious in several models predictive of antipsychotic-and anxiolytic-like activity in mice. The behavioral effects of BINA were blocked by the mGluR2/3 antagonist (2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495), suggesting that the in vivo effects of BINA are mediated by increased activation of mGluR2. Collectively, these results indicate that BINA is a selective mGluR2 positive allosteric modulator and provide further support for the growing evidence that selective allosteric potentiators of mGluR2 mimic many of the in vivo actions of mGluR2/3 agonists that may predict therapeutic utility of these compounds.Metabotropic glutamate receptors (mGluRs) are classified into three major groups based on sequence homologies, coupling to second messenger systems, and selectivities for various agonists (Conn and Pin, 1997). Group II mGluR subtypes, mGluR2 and mGluR3, couple to G i/o and associated effector pathways, such as the inhibition of adenylyl cyclase and the regulation of ion channels. Group II mGluRs reduce transmission at glutamatergic synapses in multiple brain regions, where excessive glutamatergic neurotransmission has been implicated in the underlying pathophysiology of anxiety disorders and schizophrenia (Walker and Davis, 2002;Moghaddam and Jackson, 2003). Based on these findings, it has been postulated that selective agonists of group II mGluRs may provide anxiolytic and/or antipsychotic effects through a reduction in glutamatergic neurotransmission within these brain regions.

Recent studies suggest that agonists of group II metabotropic glutamate (mGlu) receptors (mGlu2/3) have potential utility as novel therapeutic agents for treatment of psychiatric disorders such as anxiety and schizophrenia. Agonists of mGlu2/3 receptors block amphetamine-and phencyclidine (PCP)-induced hyperlocomotor activity in rodents, two actions that may predict potential antipsychotic activity of these compounds. We now report that LY487379 [N-(4-(2-methoxyphenoxy)phenyl)-N-(2,2,2-trifluoroethylsulfonyl)pyrid-3-ylmethylamine], a recently described selective allosteric potentiator of mGlu2 receptor, has behavioral effects similar to mGlu2/3 receptor agonists. LY487379 and LY379268 [(Ϫ)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate], an ortho-steric mGlu2/3 receptor agonist, induced similar dosedependent reductions in PCP-and amphetamine-induced hyperlocomotor activity in C57BL6/J mice at doses that did not significantly alter spontaneous locomotor activity. These effects were blocked by the mGlu2/3 receptor antagonist LY341495 [(2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid]. LY487379 had a short duration of action compared with LY379268. Furthermore, unlike the mGlu2/3 agonist, LY487379 reversed amphetamine-induced disruption of prepulse inhibition of the acoustic startle reflex. When LY379268 was given chronically, it failed to block amphetamine-and PCP-induced hyperlocomotor activity. The finding that the effects of an orthosteric mGlu2/3 receptor agonist in these models can be mimicked by a selective allosteric potentiator of mGlu2 suggests that these effects are mediated by the mGlu2 receptor subtype. Furthermore, these data raise the possibility that a selective allosteric potentiator of mGlu2 receptor could have utility as a novel approach for the treatment of schizophrenia.

Evidence has accumulated supporting a role for 5-hydroxytryptamine (5-HT) 7 receptors in circadian rhythms, sleep, and mood disorders, presumably as a consequence of the modulation of 5-HT-mediated neuronal activity. We hypothesized that a selective 5-HT 7 receptor antagonist,should increase activity of 5-HT neurons and potentiate the effect of selective serotonin reuptake inhibitors (citalopram). In rats, administration of 3 mg/kg s.c. citalopram alone increased the extracellular concentration of 5-HT. This effect of citalopram on extracellular 5-HT concentration was significantly enhanced by an ineffective dose of SB-269970. Combining this dose of SB-269970 with a low dose of citalopram also resulted in a significant increase in extracellular concentration of 5-HT, suggesting a potentiation of neurochemical effects. In mice, citalopram and SB-269970 dose-dependently decreased immobility time in the tail suspension test. The dose-effect curve of citalopram was shifted leftward by coadministration of an effective dose of SB-269970. Furthermore, combining ineffective doses of citalopram and SB-269970 also resulted in a significant decrease of immobility time in the tail suspension test, suggesting potentiation of antidepressant-like effects. In rats, SB-269970 potentiated the increase of rapid eye movement (REM) latency and the REM sleep decrease induced by citalopram. SB-269970 also reversed the increase in sleep fragmentation induced by citalopram. Rat plasma and brain concentrations of citalopram were not affected by coadministration of SB-269970, arguing for a pharmacodynamic rather than a pharmacokinetic mechanism. Overall, these results indicate that selective blockade of 5-HT 7 receptors may enhance the antidepressant efficacy of citalopram and may provide a novel therapy to alleviate sleep disturbances associated with depression.

Insulin affects brain reward pathways and there is converging evidence that this occurs through insulin regulation of the dopamine (DA) transporter (DAT). In rats made hypoinsulinemic by fasting, synaptosomal DA uptake is reduced. Interestingly, [3 H]DA uptake is increased in hypoinsulinemic rats with a history of amphetamine self-administration. The possibility that amphetamine and insulin act in concert to regulate DAT activity prompted this study. Here we show that [ 3 H]DA uptake, measured in vitro and clearance of exogenously applied DA in vivo, is significantly reduced in rats made hypoinsulinemic by a single injection of streptozotocin. Strikingly, amphetamine (1.78 mg/kg, given every other day for 8 days) restored DA clearance in streptozotocin-treated rats but was without effect on DA clearance in saline-treated rats. Basal locomotor activity of streptozotocin-treated rats was lower compared to control rats; however, in streptozotocintreated rats, hyperlocomotion induced by amphetamine increased over successive amphetamine injections. In salinetreated rats the locomotor stimulant effect of amphetamine remained stable across the four amphetamine injections. These results provide exciting new evidence that actions of amphetamine on DA neurotransmission are insulin-dependent and further suggest that exposure to amphetamine may cause long-lasting changes in DAT function.

Collectively, these results indicate, for the first time, that blockade of orexin-2 receptors is effective in reducing the reinforcing effects of ethanol.