On the G-protein-coupled receptor heteromers and their allosteric receptor-receptor interactions in the central nervous system: focus on their role in pain modulation

The modulatory role of allosteric receptor-receptor interactions in the pain pathways of the Central Nervous System and the peripheral nociceptors has become of increasing interest. As integrators of nociceptive and antinociceptive wiring and volume transmission signals, with a major role for the opioid receptor heteromers, they likely have an important role in the pain circuits and may be involved in acupuncture. The delta opioid receptor (DOR) exerts an antagonistic allosteric influence on the mu opioid receptor (MOR) function in a MOR-DOR heteromer. This heteromer contributes to morphine-induced tolerance and dependence, since it becomes abundant and develops a reduced G-protein-coupling with reduced signaling mainly operating via beta-arrestin 2 upon chronic morphine treatment. A DOR antagonist causes a return of the Gi/o binding and coupling to the heteromer and the biological actions of morphine. The gender- and ovarian steroid-dependent recruitment of spinal cord MOR/kappa opioid receptor (KOR) heterodimers enhances antinociceptive functions and if impaired could contribute to chronic pain states in women. MOR1D heterodimerizes with gastrin-releasing peptide receptor (GRPR) in the spinal cord, mediating morphine induced itch. Other mechanism for the antinociceptive actions of acupuncture along meridians may be that it enhances the cross-desensitization of the TRPA1 (chemical nociceptor)-TRPV1 (capsaicin receptor) heteromeric channel complexes within the nociceptor terminals located along these meridians. Selective ionotropic cannabinoids may also produce cross-desensitization of the TRPA1-TRPV1 heteromeric nociceptor channels by being negative allosteric modulators of these channels leading to antinociception and antihyperalgesia

Cultura y Trabajo (no. 78/79 nov 2009 )

Editorial No podemos seguir el camino hacia el abismo General A cien años del sindicalismo antioqueño Cien años y la Sociedad de Artesanos ahí El petróleo y la protesta obrera Entrevista a Pablo Gentili, de CLACSO. En América Latina está surgiendo una nueva derecha Informe Nacional de Trabajo Decente, 2008 La Internacional Comunista y su impacto en los inicios del comunismo colombiano La negociación del salario mínimo La prensa obrera. De las primeras décadas del siglo XX en Colombi

Role of the 5-HT1A receptors in the effect of Galanin(1-15) on Fluoxetine-mediated action in the forced swimming test

Galanin N-terminal fragment (1-15) [GAL(1-15)] modulates the antidepressant effects induced by the 5-HT1A receptor (5-HT1AR) agonist in the forced swimming test (FST) and the binding characteristics and mRNA levels of 5-HT1AR in the dorsal hippocampus and dorsal raphe (DR). Recently, we observed that GAL(1-15) enhanced the antidepressant-like effects induced by Fluoxetine (FLX) in the FST. In this work, we have studied whether the effects of GAL(1–15) on FLX action were mediated via 5-HT1AR, analyzing the effect of the 5-HT1AR antagonist WAY100635 in this effect and if the binding characteristics and mRNA levels of 5-HT1AR in the DR and dorsal hippocampus are modified by GAL(1-15)+FLX. Groups of rats (n=6-8) received three injections of sc FLX(10mg/kg) and 15 minutes before the FST a single icv injection of GAL(1-15) (1nmol) and 5HT1AR antagonist WAY100635(6nmol) icv alone or in combination. We also analyzed the effects of GAL(1-15)+FLX in the binding characteristics of the 5-HT1AR agonist [H3]-8-OH-DPAT and 5-HT1A mRNA levels in the DR, CA1 and Dentate Gyrus (DG). WAY100635 significantly blocked the reduction in immobility time (p<0.05), and the increase in swimming time (p<0.01) induced by GAL(1-15)+FLX in the FST. GAL(1-15)+FLX produced a significant increase in the 5HT1AR mRNA levels in CA1 (p<0.05) and DG (p<0.05). This effect was not observed in the DR. Moreover, GAL(1-15)+FLX produced a significant decrease in the Kd value (p<0.01) and in the Bmax value (p<0.05) of [3H]-8-OH-DPAT in the DG. These effects were not observed in the CA1 or in the DR. These results indicate that 5HT1AR participates in the GAL(1-15)/FLX interactions in the FST and the mechanism underlying affected the binding characteristics and the mRNA levels of 5-HT1AR specifically in the dorsal hippocampus. The heteroreceptor 5-HT1AR-GALR1-GALR2 located in the dorsal hippocampus may be the target for GAL(1-15). This work was supported by SAF2016-79008-P; PSI2013-44901-P.SAF2016-79008-P; PSI2013-44901-P. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Galanin and neuropeptide y Y1 receptor agonist coinjection increases newborn cells proliferation on hippocampal dentate gyrus in rats

The hippocampus is a region in which neurogenesis persists throughout the lifespan in a wide variety of species including humans. Within the dentate gyrus of the hippocampus, the subgranular zone (SGZ) is maintained as a stem cell niche. We have previously shown that Galanin (GAL) interacts with Neuropeptide Y Y1 receptors (NPYY1R) in several regions of the central nervous system associated with mood and motivation. To examine the acute effects of GALR2/NPYY1R interactions on newborn cells proliferation we analyzed the effects of the intracerebroventricular (icv) of single injections with GAL and NPYY1 agonists or coadministered. Male Sprague-Dawley rats (n = 6-8 per group) were randomly assigned to the groups. Each group received i.c.v. injections of artificial Cerebro Spinal Fluid (aCSF), GAL or NPYY1R agonist [Leu31,Pro34]NPY alone or in combination. Intraperitoneal (ip) injections of exogenous cell DNA marker 5-bromo- 2-deoxyuridine (BrdU) 50mg/Kg were made at 2 and 4 hours after icv injections and 24 hours later rats were anesthetized, transcardially perfused and the brains collected for immunostaining to evaluate cell proliferation. Coadministration of GAL and NPYY1R agonist increased BrdU-labeled cells located in the SGZ (P<0,001) compared with aCSF, GAL and the NPYY1R-mediated hippocampal cell proliferation, These results will contribute to a better knowledge of the potential role of GAL and NPY family in mediating neurogenic actions and may give the basis for the therapeutic potential of targeting the GAL and NPY system in depressive disorders. Study supported by Proyecto Puente-Universidad de Málaga. Acknowledgements to Grupo Vithas.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Proyecto Puente-Universidad de Málaga

Galanin (1-15) enhances the behavioral effects of fluoxetine in the forced swimming test: a new therapeutic strategy against depression

The selective serotonergic (5- HT) reuptake inhibitors, including Fluoxetine (FLX), are the most commonly used for treatment of major depression. However, the understanding of the mechanism of action of FLX beyond its effect of elevating 5-HT is limited. The interaction between 5-HT system and neuropeptides signaling could be a key aspect. The neuropeptide Galanin(1-15) [GAL(1-15)], induced a strong depression-like and anxiogenic-like effects in the forced swimming test (FST), the tail suspension test, the open field and the light/dark test. The GALR1-GALR2 heteroreceptor complexes in the dorsal hippocampus and in the dorsal raphe were involved in these effects. We have analyzed the effect of GAL(1–15) on FLX-mediated responses in the FST. We tested the involvement of GALR in the GAL(1–15) effect with the selective GALR2 antagonist M871 and using siRNA GALR2 or GALR1 knockdown rats. Groups of rats received three injections of sc FLX(2.5mg/Kg) or FLX(10mg/Kg) and a single icv injection of a threshold dose of GAL(1-15)(1nmol) 15 minutes before the FST. In a second set of experiments, we determined the involvement of GALR1 and GALR2 in the effect of GAL(1-15) on FLX-mediated action. Groups of rats received three injections of sc FLX(10mg/kg), a single icv injection of GAL(1-15) (1nmol) and the GALR2 antagonist M871 (3nmol) icv alone or in combination. Also, in siRNA GALR1 or GALR2 knockdown rats we coadministered FLX(10mg/Kg) and GAL(1-15)(1nmol). The coadministration of sc FLX(2.5mg/Kg) and icv injection of GAL(1-15)(1nmol) induced antidepressant-like effects with a significant decrease in the immobility (p<0.05). Moreover, an increase in the swimming time (p <0.05) was also observed. The strong enhancement by GAL(1-15) of the antidepressant-like effects mediated by FLX was validated using the effective dose of FLX 10mg/kg. Icv GAL(1-15) significantly decreased the immobility time induced by the effective dose of FLX(10mg/kg) by 50% in the FST (p<0.05). Moreover, an increase of the swimming time by about 40% versus FLX(10mg/kg) group was also observed (p<0.01). The GALR2 antagonist M871 3nmol significantly blocked the GAL(1–15)-induced reduction of the immobility time (p<0.05), and increase in the swimming time (p<0.01) found after coadministration of icv injection of GAL(1-15) and sc FLX(10mg/kg) in the FST. The coadministration of sc FLX(10mg/kg) and icv injection of GAL(1-15) in siRNA GALR1 or GALR2 knockdown animals did not produce a further reduction of the immobility time and a further increase in the swimming time compared to FLX alone. In the current study we describe for the first time that GAL(1-15) enhances the antidepressant-like effects induced by FLX in the FST. Indications were also obtained for the involvement of a GALR1/GALR2 heteroreceptor complex in the GAL (1-15)-mediated actions based on the use of the specific GALR2 antagonist M871 and icv injections of GALR1 siRNA or GALR2 siRNA producing a reduction of GALR1 or GALR2, respectively. The results open up the possibility to use GAL(1-15) as for a combination therapy with FLX as a novel strategy for treatment of depression. This work was supported by grants awarded by Spanish Ministry of Economy (SAF2016-79008-P),Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Understanding the role of adenosine A2AR heteroreceptor complexes in neurodegeneration and neuroinflammation

Adenosine is a nucleoside mainly formed by degradation of ATP, located intracellularly or extracellularly, and acts as a neuromodulator. It operates as a volume transmission signal through diffusion and flow in the extracellular space to modulate the activity of both glial cells and neurons. The effects of adenosine are mediated via four adenosine receptor subtypes: A1R, A2AR, A2BR, A3R. The A2AR has a wide-spread distribution but it is especially enriched in the ventral and dorsal striatum where it is mainly located in the striato-pallidal GABA neurons at a synaptic and extrasynaptic location. A number of A2AR heteroreceptor complexes exist in the striatum. The existence of A2AR-D2R heteroreceptor complexes with antagonistic A2AR-D2R interactions in the striato-pallidal GABA neurons is well-known with A2AR activation inhibiting Gi/o mediated signaling of D2Rs. A2AR-mGluR5 heteroreceptor complexes were also found in with synergistic receptor-receptor interactions enhancing the inhibition of the D2R protomer signaling. They are located mainly in extrasynaptic regions of the striato-pallidal GABA neurons. Results recently demonstrated the existence of brain A2AR-A2BR heteroreceptor complexes, in which A2BR protomer constitutively inhibited the function of the A2AR protomer. These adenosine A2AR heteroreceptor complexes may modulate alpha-synuclein aggregation and toxicity through postulated bidirectional direct interactions leading to marked increases in A2AR signaling both in nerve cells and microglia. It is of high interest that formation of A2AR-A2ABR heteroreceptor complexes provides a brake on A2AR recognition and signaling opening up a novel strategy for treatment of A2AR mediated neurodegeneration. KEYWORDS: G protein-coupled receptor; Parkinson's diseases; adenosine A2A receptor; adenosine receptor; heteroreceptor complexes; neurodegeneration; neuroinflammation; oligomerizatio

The G protein-coupled receptor heterodimer network (GPCR-HetNet) and its hub components

G protein-coupled receptors (GPCRs) oligomerization has emerged as a vital characteristic of receptor structure. Substantial experimental evidence supports the existence of GPCR-GPCR interactions in a coordinated and cooperative manner. However, despite the current development of experimental techniques for large-scale detection of GPCR heteromers, in order to understand their connectivity it is necessary to develop novel tools to study the global heteroreceptor networks. To provide insight into the overall topology of the GPCR heteromers and identify key players, a collective interaction network was constructed. Experimental interaction data for each of the individual human GPCR protomers was obtained manually from the STRING and SCOPUS databases. The interaction data were used to build and analyze the network using Cytoscape software. The network was treated as undirected throughout the study. It is comprised of 156 nodes, 260 edges and has a scale-free topology. Connectivity analysis reveals a significant dominance of intrafamily versus interfamily connections. Most of the receptors within the network are linked to each other by a small number of edges. DRD2, OPRM, ADRB2, AA2AR, AA1R, OPRK, OPRD and GHSR are identified as hubs. In a network representation 10 modules/clusters also appear as a highly interconnected group of nodes. Information on this GPCR network can improve our understanding of molecular integration. GPCR-HetNet has been implemented in Java and is freely available at http://www.iiia.csic.es/similar to ismel/GPCR-Nets/index.html

acute cocaine treatment enhances the antagonistic allosteric adenosine a2a dopamine d2 receptor receptor interactions in rat dorsal striatum without increasing significantly extracellular dopamine levels

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Combined treatment with Sigma1R and A2AR agonists fails to inhibit cocaine self-administration despite causing strong antagonistic accumbal A2AR-D2R complex interactions: the potential role of astrocytes

Previous studies have indicated that acute treatment with the monoamine stabilizer OSU-6162 (5 mg/kg), which has a high affinity for Sigma1R, significantly increased the density of accumbal shell D2R-Sigma1R and A2AR-D2R heteroreceptor complexes following cocaine self-administration. Ex vivo studies using the A2AR agonist CGS21680 also suggested the existence of enhanced antagonistic accumbal A2AR-D2R allosteric interactions after treatment with OSU-6162 during cocaine self-administration. However, a 3-day treatment with OSU-6162 (5 mg/kg) failed to alter the behavioral effects of cocaine self-administration. To test these results and the relevance of OSU-6162 (2.5 mg/kg) and/or A2AR (0.05 mg/kg) agonist interactions, we administered low doses of receptor agonists during cocaine self-administration and assessed their neurochemical and behavioral effects. No effects were observed on cocaine self-administration; however, marked and highly significant increases using the proximity ligation assay (PLA) were induced by the co-treatment on the density of the A2AR-D2R heterocomplexes in the nucleus accumbens shell. Significant decreases in the affinity of the D2R high- and low-affinity agonist binding sites were also observed. Thus, in low doses, the highly significant neurochemical effects observed upon cotreatment with an A2AR agonist and a Sigma1R ligand on the A2AR-D2R heterocomplexes and their enhancement of allosteric inhibition of D2R high-affinity binding are not linked to the modulation of cocaine self-administration. The explanation may be related to an increased release of ATP and adenosine from astrocytes in the nucleus accumbens shell in cocaine self-administration. This can lead to increased activation of the A1R protomer in a putative A1R-A2AR-D2R complex that modulates glutamate release in the presynaptic glutamate synapse. We hypothesized that the integration of changes in presynaptic glutamate release and postjunctional heteroreceptor complex signaling, where D2R plays a key role, result in no changes in the firing of the GABA anti-reward neurons, resulting in no reduction in cocaine self-administration in the present experiments