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1.  Reduced Metabotropic Glutamate Receptor 5 Density in Major Depression Determined by [11C]ABP688 Positron Emission Tomography and Postmortem Study 
The American journal of psychiatry  2011;168(7):727-734.
Objective
Clinical and preclinical evidence suggest a hyperactive glutamatergic system in clinical depression. Recently, the metabotropic glutamate receptor 5 (mGluR5) has been proposed as an attractive target for discovery of novel therapeutic approaches against depression. The goal of this study was to compare mGluR5 binding (PET study) and mGluR5 protein expression (postmortem study) between subjects with major depressive disorder and healthy controls.
Method
Images of mGluR5 receptor binding were acquired using PET and [11C]ABP688 that binds to an allosteric site with high specificity in 11 unmedicated subjects with major depression and 11 matched healthy controls; the amount of mGluR5 protein was investigated using Western blot method in brain samples of 15 depressed subjects and 15 matched controls (postmortem study).
Results
The PET study revealed decreased regional mGluR5 binding in the prefrontal cortex, the cingulate cortex, the insula, the thalamus and the hippocampus of the depressed individuals (uncorrected p<0.001). Severity of depression correlated negatively with mGluR5 binding in the hippocampus (cluster-level corrected p=0.029). The postmortem study showed reduced mGluR5 protein expression in the prefrontal cortex (Brodmann's area 10) in depression (p<0.014), while prefrontal mGluR1 protein expression was unchanged.
Conclusions
The reductions in mGluR5 binding found in the depressed sample are compatible with reduced protein expression in postmortem tissue. Thus, both studies suggest that basal or compensatory changes in excitatory neurotransmission play roles in the pathophysiology of major depression.
doi:10.1176/appi.ajp.2011.09111607
PMCID: PMC3129412  PMID: 21498461
2.  Chronic corticosterone administration down-regulates metabotropic glutamate receptor 5 protein expression in the rat hippocampus 
Neuroscience  2010;169(4):1567-1574.
Several lines of evidence suggest a dysfunctional glutamate system in major depressive disorder (MDD). Recently, we reported reduced levels of metabotropic glutamate receptor subtype 5 (mGluR5) in postmortem brains in MDD, however the neurobiological mechanisms that induce these abnormalities are unclear. In the present study, we examined the effect of chronic corticosterone (CORT) administration on the expression of mGluR5 protein and mRNA in the rat frontal cortex and hippocampus. Rats were injected with CORT (40 mg/kg, s.c.) or vehicle once daily for 21 days. The expression of mGluR5 protein and mRNA was assessed by Western blotting and quantitative real-time PCR. In addition, mGluR1 protein was measured in the same animals. The results revealed that while there was a significant reduction (− 27 %, p=0.0006) in mGluR5 protein expression in the hippocampus from CORT treated rats, mRNA levels were unchanged. Also unchanged were mGluR5 mRNA and protein levels in the frontal cortex and mGluR1 protein levels in both brain regions. Our findings provide the first evidence that chronic CORT exposure regulates the expression of mGluR5 and are in line with previous postmortem and imaging studies showing reduced mGluR5 in MDD. Our findings suggest that elevated levels of glucocorticoids may contribute to impairments in glutamate neurotransmission in MDD.
doi:10.1016/j.neuroscience.2010.06.023
PMCID: PMC2918667  PMID: 20600666
hippocampus; frontal cortex; metabotropic glutamate receptor 5; metabotropic glutamate receptor 1; corticosterone; rat
3.  Elevated Level of Metabotropic Glutamate Receptor 2/3 in the Prefrontal Cortex in Major Depression 
Clinical, postmortem and preclinical research strongly implicates dysregulation of glutamatergic neurotransmission in major depressive disorder (MDD). Recently, metabotropic glutamate receptors (mGluRs) have been proposed as attractive targets for discovery of novel therapeutic approaches against depression. The aim of this study was to examine mGluR2/3 protein levels in the prefrontal cortex (PFC) from depressed subjects. In addition, to test whether antidepressants influence mGluR2/3 expression we also studied levels of mGluR2/3 in fluoxetine treated monkeys. Postmortem human prefrontal samples containing Brodmann’s area 10 (BA 10) were obtained from 11 depressed and 11 psychiatrically healthy controls. Male rhesus monkeys were treated chronically with fluoxetine (dose escalated to 3mg/kg, p.o; n=7) or placebo (n=6) for 39 weeks. The mGluR2/3 immunoreactivity was investigated using Western blot method. There was a robust (+67%) increase in the expression of the mGlu2/3 protein in the PFC of depressed subjects relative to healthy controls. The expression of mGlu2/3 was unchanged in the PFC of monkeys treated with fluoxetine. Our findings provide the first evidence that mGluR2/3 is elevated in the PFC in MDD. This observation is consistent with reports showing that mGluR2/3 antagonists exhibit antidepressant-like activity in animal models and demonstrates that these receptors are promising targets for the discovery of novel antidepressants.
doi:10.1016/j.pnpbp.2009.11.018
PMCID: PMC2826512  PMID: 19945495
prefrontal cortex; metabotropic glutamate receptor; major depression; postmortem; fluoxetine; rhesus monkey
4.  Reduced Level of Glutamic Acid Decarboxylase-67 kDa in the Prefrontal Cortex in Major Depression 
Accumulating evidence suggests dysfunction of the gamma-aminobutyric acid (GABA) system in major depressive disorder (MDD). Neuroimaging studies consistently report reductions of cortical GABA in depressed patients. Our post-mortem analyses demonstrate a reduction in the density and size of GABAergic interneurons in the dorsolateral prefrontal cortex (PFC) in MDD. The goal of this study was to test whether the level of glutamic acid decarboxylase (GAD), the GABA synthesizing enzyme, will also be reduced in the same cortical region in MDD. Levels of GAD-65 and GAD-67 proteins were investigated by Western blotting in samples from the dorsolateral PFC (BA9) in 13 medication-free subjects with MDD, and 13 psychiatrically healthy controls. The overall amount of GAD-67 was significantly reduced (−34 %) in depressed subjects as compared to matched controls. Since recent neuroimaging studies demonstrate that antidepressants modulate GABA levels, additional experiments were performed to examine the levels of GAD in 8 depressed subjects treated with antidepressant medications. Levels of GAD-67 were unchanged in these depressed subjects as compared to their respective controls (n=8). The overall amounts of GAD-65 were similar in depressed subjects compared to matched controls, regardless of antidepressant medication. Reduced levels of GAD-67, which is localized to somata of GABA neurons, further support our observation of a decreased density of GABAergic neurons in the PFC in depression. It is likely that a decrease in GAD-67 accounts for the reduction in GABA levels revealed by neuroimaging studies. Moreover, our data support previous neuroimaging observations that antidepressant medication normalizes GABA deficits in depression.
doi:10.1017/S1461145709990587
PMCID: PMC2857696  PMID: 20236554
Post-mortem; GAD; GABA; antidepressants; major depressive disorder; dorsolateral prefrontal cortex
5.  Reduced levels of NR2A and NR2B subunits of NMDA receptor and PSD-95 in the prefrontal cortex in major depression 
Recent neuroimaging and postmortem studies have demonstrated abnormalities in glutamatergic transmission in major depression. Glutamate NMDA (N-methyl-D-aspartate) receptors are one of the major mediators of excitatory neurotransmission in the central nervous system. At synaptic sites, NMDA receptors are linked with postsynaptic density protein-95 (PSD-95) that plays a key role in mediating trafficking, clustering, and downstream signaling events, following receptor activation. In this study, we examined the expression of NMDA receptor subunits NR1, NR2A, and NR2B as well as PSD-95 in the anterior prefrontal cortex (PFC) using Western blot method. Cortical samples were obtained from age, gender and postmortem interval matched depressed and psychiatrically healthy controls. The results revealed that there was a reduced expression of the NMDA receptor subunits NR2A (−54%) and NR2B (−48%), and PSD-95 protein level (−40%) in the PFC of depressed subjects relative to controls, with no change in the NR1 subunit. The alterations in NMDA receptor subunits, especially the NR2A and NR2B, as well as PSD-95 suggest an abnormality in the NMDA receptor signaling in the PFC in major depression. Our findings in conjunction with recent clinical, cellular, and neuroimaging studies further implicate the involvement of glutamate neurotransmission in the pathophysiology of depression. This study provides additional evidence that NMDA receptor complex is a target for discovery of novel antidepressants.
doi:10.1016/j.pnpbp.2008.10.005
PMCID: PMC2655629  PMID: 18992785
major depressive disorder; glutamate receptors; postmortem; postsynaptic density protein; anterior prefrontal cortex

Results 1-5 (5)