Chronic L-dopa treatment of Parkinson's disease (PD) often leads to debilitating involuntary movements, termed L-dopa-induced dyskinesia (LID), mediated by dopamine (DA) receptors. RGS9 -2 is a GTPase accelerating protein that inhibits DA D2 receptor-activated G proteins. Herein, we assess the functional role of RGS9 -2 on LID. In monkeys, Western blot analysis of striatal extracts shows that RGS9 -2 levels are not altered by MPTP-induced DA denervation and/or chronic L-dopa administration. In MPTP monkeys with LID, striatal RGS9 -2 overexpression -achieved by viral vector injection into the striatum -diminishes the involuntary movement intensity without lessening the anti-parkinsonian effects of the D1/D2 receptor agonist L-dopa. In contrasts, in these animals, striatal RGS9 -2 overexpression diminishes both the involuntary movement intensity and the anti-parkinsonian effects of the D2/D3 receptor agonist ropinirole. In unilaterally 6-OHDA-lesioned rats with LID, we show that the time course of viral vector-mediated striatal RGS9 -2 overexpression parallels the time course of improvement of L-dopa-induced involuntary movements. We also find that unilateral 6-OHDA-lesioned RGS9 Ϫ/Ϫ mice are more susceptible to L-dopa-induced involuntary movements than unilateral 6-OHDA-lesioned RGS9 ϩ/ϩ mice, albeit the rotational behavior -taken as an index of the anti-parkinsonian response -is similar between the two groups of mice. Together, these findings suggest that RGS9 -2 plays a pivotal role in LID pathophysiology. However, the findings also suggest that increasing RGS9 -2 expression and/or function in PD patients may only be a suitable therapeutic strategy to control involuntary movements induced by nonselective DA agonist such as L-dopa.

The present study explored a possible role for RGS (regulators of G protein signalling) proteins in the long term actions of morphine in the locus coeruleus (LC), a brainstem region implicated in opiate physical dependence and withdrawal. Morphine influences LC neurons through activation of micro -opioid receptors, which, being Gi/o-linked, would be expected to be modulated by RGS proteins. We focused on several RGS subtypes that are known to be expressed in this brain region. Levels of mRNAs encoding RGS2, -3, -4, -5, -7, -8 and -11 are unchanged following chronic morphine, but RGS2 and -4 mRNA levels are increased 2-3-fold 6 h following precipitation of opiate withdrawal. The increases in RGS2 and -4 mRNA peak after 6 h of withdrawal and return to control levels by 24 h. Immunoblot analysis of RGS4 revealed a striking divergence between mRNA and protein responses in LC: protein levels are elevated twofold following chronic morphine and decrease to control values by 6 h of withdrawal. In contrast, levels of RGS7 and -11 proteins, the only other subtypes for which antibodies are available, were not altered by these treatments. Intracellular application of wild-type RGS4, but not a GTPase accelerating-deficient mutant of RGS4, into LC neurons diminished electrophysiological responses to morphine. The observed subtype- and time-specific regulation of RGS4 protein and mRNA, and the diminished morphine-induced currents in the presence of elevated RGS4 protein levels, indicate that morphine induction of RGS4 could contribute to aspects of opiate tolerance and dependence displayed by LC neurons.

Objective-Preclinical and clinical data implicate the group II metabotropic glutamate receptors (mGluR2 and mGluR3) in the pathophysiology of schizophrenia. Moreover, a recent phase II clinical trial has demonstrated the antipsychotic efficacy of a mGluR2/3 agonist. The current study was designed to distinguish the expression of mGluR2 and mGluR3 receptor protein in schizophrenia and to quantify glutamate carboxypeptidase II (GCPII) in order to explore a role for the metabotropic receptors in schizophrenia therapeutics. GCPII is an enzyme that metabolizes Nacetylaspartylglutamate (NAAG), the only known specific endogenous agonist of mGluR3 in the mammalian brain.Method-The normal expression levels of mGluR2, mGluR3 and GCPII were determined in 10 regions of the human post mortem brain using specific antibodies. Differences in expression levels of each protein were then examined in the dorsolateral prefrontal (DLPFC), temporal (TC) and motor cortex (MC) in 15 matched cases of schizophrenia and normal controls. Chronic antipsychotic treatment in rodents was conducted to examine the potential effect of antipsychotic drugs on expression of the 3 proteins.Results-We found a significant increase in GCPII protein and a reduction in mGluR3 protein in the DLPFC in schizophrenia with mGluR2 protein levels unchanged. Chronic antipsychotic treatment in rodents did not influence GCPII or mGluR3 levels.Conclusions-Increased GCPII expression and low mGluR3 expression in the DLPFC suggest that NAAG-mediated signaling is impaired in this brain region in schizophrenia. Further, these data implicate the mGluR3 receptor in the antipsychotic action of mGluR2/3 agonists.

RGS9-2 is a striatum-enriched protein that negatively modulates dopamine and opioid receptor signaling. We examined the role of RGS9-2 in modulating complex behavior. Genetic deletion of RGS9-2 does not lead to global impairments, but results in selective abnormalities in certain behavioral domains. RGS9 knockout (KO) mice have decreased motor coordination on the accelerating rotarod and deficits in working memory as measured in the delayed-match to place version of the water maze. In contrast, RGS9 KO mice exhibit normal locomotor activity, anxietylike behavior, cue and contextual fear conditioning, startle threshold, and pre-pulse inhibition. These studies are the first to describe a role for RGS9-2 in motor coordination and working memory and implicate RGS9-2 as a potential therapeutic target for motor and cognitive dysfunction. KeywordsRGS9; motor coordination; working memory; delayed-match to place water maze; dopamine; striatum IntroductionThe regulators of G protein signaling (RGS) family of proteins negatively modulate heterotrimeric G protein signaling by stimulating the GTPase activity of G protein α subunits (Berman and Gilman, 1998) and can function as effector molecules in certain signaling networks (De Vries et al., 2000). RGS proteins also regulate cellular excitability via their indirect modulation of G-protein-coupled inwardly rectifying K+ channels (GIRK) and voltage-dependent calcium channels (Berman et al., 1996;Chuang et al., 1998;Doupnik et al., 1997;Hollinger and Hepler, 2002;Sondek and Siderovski, 2001;Zhou et al., 2000).The greater than 25 mammalian RGS proteins identified to date are defined by their 120 amino acid RGS domain and can be organized into subfamilies based on structural features and relative specificity for different G-protein subunits (Traynor and Neubig, 2005). Numerous RGS genes are expressed in brain with highly region-specific expression patterns (Dohlman and Thorner, 1997). The biological role of specific RGS proteins is currently an area of active research.

G protein-coupled receptor (GPCR) signaling cascades may be key substrates for the antidepressant effects of chronic electroconvulsive seizures (ECS). To better understand changes in these signaling pathways, alterations in levels of mRNA's encoding regulators of G protein signaling (RGS) protein subtypes-2, -4, -7, -8 and -10 were evaluated in rat brain using northern blotting and in situ hybridization. In prefrontal cortex, RGS2 mRNA levels were increased severalfold 2 h following an acute ECS. Increases in RGS8 mRNA were of lesser magnitude (30%), and no changes were evident for the other RGS subtypes. At 24 h following a chronic ECS regimen, RGS4, -7, and -10 mRNA levels were reduced by 20-30%; only RGS10 was significantly reduced 24 h after acute ECS. Levels of RGS2 mRNA were unchanged 24 h following either acute or chronic ECS. In hippocampus, RGS2 mRNA levels were markedly increased 2 h following acute ECS. More modest increases were seen for RGS4 mRNA expression, whereas levels of the other RGS subtypes were unaltered. At 24 h following chronic ECS, RGS7, -8 and -10 mRNA levels were decreased in the granule cell layer, and RGS7 and -8 mRNA levels were decreased in the pyramidal cell layers. Only RGS8 and -10 mRNA levels were significantly reduced in hippocampus 24 h following an acute ECS. Paralleling neocortex, RGS2 mRNA content was unchanged in hippocampus 24 h following either acute or chronic ECS. In ventromedial hypothalamus, RGS4 mRNA content was increased 24 h following chronic ECS, whereas RGS7 mRNA levels were only increased 24 h following an acute ECS. The increased RGS4 mRNA levels in hypothalamus were significant by 2 h following an acute ECS. These studies demonstrate subtype-, time-, and region-specific regulation of RGS proteins by ECS, adaptations that may contribute to the antidepressant effects of this treatment.