The Group II Metabotropic Glutamate Receptor Agonist (−)-2-Oxa-4-aminobicyclo[3.1.0.]hexane-4,6-dicarboxylate (LY379268) and Clozapine Reverse Phencyclidine-Induced Behaviors in Monoamine-Depleted Rats

Abstract
Recent studies have indicated that the selective group II metabotropic glutamate (mGlu) receptor agonist (−)-2-oxa-4-aminobicyclo[3.1.0.]hexane-4,6-dicarboxylate (LY379268) shares common biochemical and pharmacological effects with the atypical antipsychotic clozapine. The present study aimed to further investigate these similarities (or differences) in monoamine-depleted animals by using the phencyclidine (PCP) model. Animals were pretreated 24 h before PCP administration with (i.p.) vehicle, α-methyl-dl-p-tyrosine methyl ester (α-MPT; 400 mg/kg), ordl-p-chlorophenyl-alanine methyl ester (PCPA; 300 mg/kg) injections. α-MPT and PCPA pretreatment significantly and selectively reduced catecholamine (dopamine and norepinepherine) or 5-hydroxytryptamine (5-HT, serotonin) and 5-hydroxyindoleacetic acid levels, respectively, in whole brain tissue. Both LY379268 and clozapine (s.c.) blocked PCP-evoked ambulatory activity and fine movements in control, α-MPT-, and PCPA-treated animals. In contrast, the typical antipsychotic haloperidol (s.c.) attenuated PCP behaviors in control and PCPA-pretreated animals, but was without effect in subjects pretreated with α-MPT. The α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid/kainate-selective antagonist (3S,4aR,6R,8aR)-6-[2-(1(2)OH-tetrazole-6-yl)ethyl]decahydroisoquinoline-3-carboxylic acid (LY293558) attenuated locomotor activity in α-MPT-treated animals only, whereas the 5-HT2A/2C-selective antagonist ketanserin was effective at reducing ambulations and fine movements in control and α-MPT-treated animals. Taken together, these data indicate an important role for glutamatergic and serotonergic mechanisms for PCP-evoked behaviors in catecholamine-depleted animals and suggest that like clozapine, LY379268 is more effective than typical antipsychotics in these models. This study further supports the potential use of group II mGlu agonists as novel therapeutic agents in the treatment of schizophrenia.