pentobarbital and a guide cannula (22G) was implanted using the following stereotaxic coordinates: From bregma: 0.9 anterior/posterior (AP), 1.5 medial/lateral (ML), 3.5 dorsal/ventral (DV). the rat forced swim test are completely blocked by the mTOR inhibitor, rapamycin. The results indicate that the antidepressant actions ofLY341495are mediated by activation of mTOR and suggest that this and other mGluR2/3antagonists could produce rapid antidepressant effects in depressed patients. Keywords:Depression, synapse, glutamate, ketamine, behavior == Introduction == Depression is a debilitating psychiatric disorder that affects ~17% of the population (Kessler et al., 2003). All currently approved antidepressant treatments work through various mechanisms to modulate monoaminergic neurotransmitter systems and can take several weeks to months to produce a therapeutic response. Recently, efforts have focused on novel classes of drugs that work by modulating glutamatergic neurotransmission. Ketamine, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, has received the most attention. Ketamine produces rapid (within 2 hrs) and sustained (~1 week) antidepressant effects in depressed patients refractory to typical antidepressant treatment (Berman et al., 2000;Zarate et al., 2006). While the mechanisms underlying these surprisingly fast and robust effects remain somewhat unclear, we have found that ketamine treatment produces rapid activation of the mammalian target of rapamycin (mTOR) pathway and subsequent sustained increases in synaptic proteins and increased excitatory spine synapses in the prefrontal cortex (PFC) (Li et al., 2010;Li et al., 2011). mTOR is a serine/threonine protein kinase that integrates signals from growth factors, such as brain-derived neurotrophic factor (BDNF) (Takei et al., 2001), as well and energy and nutrient levels to regulate protein synthesis (reviewed inSengupta et al., 2010). Activation of mTOR signaling leads to induction of NS6180 mRNA translation and new protein synthesis via phosphorylation of downstream substrates including p70S6 kinase and eukaryotic initiation factor 4E binding protein 1 (4E-BP1). We found that the phosphorylation of both of these proteins, as well as mTOR, is rapidly increased by ketamine (Li et al., 2010). In addition, ketamine-induction of mTOR signaling is followed by Rabbit Polyclonal to SREBP-1 (phospho-Ser439) a sustained increase in levels of the synaptic proteins PSD-95, GluR1 and Synapsin I (Li et al., 2010). While ketamine produces robust antidepressant effects, the deleterious side effects and abuse potential limit its widespread use for treatment of depression, as well as suicide (DiazGranados et al., 2010;Larkin and Beautrais, 2011). Therefore, there remains a clear unmet medical need for drugs that can produce ketamine-like antidepressant effects with a safer side effect profile and decreased abuse liability. In the present study, we sought to evaluate alternative ways to modulate the glutamatergic system that would result in ketamine-like effects. mGluR2/3receptors are metabotropic glutamate receptors distributed in regions of the brain implicated in depression, including cortical and limbic regions (Ohishi et al., 1994;Ohishi et al., 1993a). mGluR2receptors are primarily located in the preterminal portion of neurons (Shigemoto et al., 1997) acting as autoreceptors or heteroceptors whereas mGluR3receptors are located post-synaptically and on glia (Ohishi et al., 1993b;Tanabe et al., 1993). Both subtypes are Gi-coupled receptors that negatively regulate adenylyl cyclase and decrease glutamatergic and monoaminergic neurotransmission. Antagonism of these receptors increases extracellular glutamate in limbic structures, NS6180 including the PFC (Hascup et al., 2010;Xi et al., 2002). Since ketamine has also been shown to increase glutamatergic outflow (Moghaddam et al., 1997) and the behavioral and biochemical effects of ketamine are dependent on -amino-3-hydroxy-5-methyl-4-isoxazolepropionic NS6180 acid (AMPA) receptor activation (Li et al., 2010;Maeng et al., 2008), we hypothesized that mGluR2/3blockade would have the potential to produce ketamine-like biochemical and behavioral effects. In fact, evidence demonstrates that the antidepressant effects of mGluR2/3antagonists are also blocked by AMPA receptor blockade (Karasawa et al., 2005). In the present study we demonstrate that the selective mGluR2/3antagonist,LY341495(Kingston et al., 1998) produces the same biochemical effects as ketamine and that the behavioral effects of this drug are dependent on mTOR signaling. == Materials and Methods == == Animals, Drug Administration and Surgical Procedures == Adult male Sprague Dawley rats (Charles River Laboratories) weighing ~150250 g were pair housed in a 12 hr light:dark cycle withad libitumaccess to food and water. All procedures were done in accordance with the NIH guidelines for the care and use of laboratory animals and the Yale University Institutional Animal NS6180 Care and Use Committee (IACUC). Rats received a single injection ofLY341495(3.