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Endogenous Agonist (endogenous + agonist)
Selected AbstractsThe uptake by cells of 2-arachidonoylglycerol, an endogenous agonist of cannabinoid receptorsFEBS JOURNAL, Issue 7 2001Tiziana Bisogno It is not yet clear if the endocannabinoid 2-arachidonoylglycerol (2-AG) is transported into cells through the same membrane transporter mediating the uptake of the other endogenous cannabinoid, anandamide (N -arachidonoylethanolamine, AEA), and whether this process (a) is regulated by cells and (b) limits 2-AG pharmacological actions. We have studied simultaneously the facilitated transport of [14C]AEA and [3H]2-AG into rat C6 glioma cells and found uptake mechanisms with different efficacies but similar affinities for the two compounds (Km 11.0 ± 2.0 and 15.3 ± 3.1 µm, Bmax 1.70 ± 0.30 and 0.24 ± 0.04 nmol·min,1·mg protein,1, respectively). Despite these similar Km values, 2-AG inhibits [14C]AEA uptake by cells at concentrations (Ki = 30.1 ± 3.9 µm) significantly higher than those required to either 2-AG or AEA to inhibit [3H]2-AG uptake (Ki = 18.9 ± 1.8 and 20.5 ± 3.2 µm, respectively). Furthermore: (a) if C6 cells are incubated simultaneously with identical concentrations of [14C]AEA and [3H]2-AG, only the uptake of the latter compound is significantly decreased as compared to that observed with [3H]2-AG alone; (b) the uptake of [14C]AEA and [3H]2-AG by cells is inhibited with the same potency by AM404 (Ki = 7.5 ± 0.7 and 10.2 ± 1.7 µm, respectively) and linvanil (Ki = 9.5 ± 0.7 and 6.4 ± 1.2 µm, respectively), two inhibitors of the AEA membrane transporter; (c) nitric oxide (NO) donors enhance the uptake of both [14C]AEA and [3H]2-AG, thus suggesting that 2-AG action can be regulated through NO release; (d) AEA and 2-AG induce a weak release of NO that can be blocked by a CB1 cannabinoid receptor antagonist, and significantly enhanced in the presence of AM404 and linvanil, thus suggesting that transport into C6 cells limits the action of both endocannabinoids. [source] Identification of soluble CD14 as an endogenous agonist for Toll-like receptor 2 on human astrocytes by genome-scale functional screening of glial cell derived proteinsGLIA, Issue 5 2007Malika Bsibsi Abstract Human astrocytes express a limited repertoire of Toll-like receptor (TLR) family members including TLR1-4, which are expressed on the cell surface. Also, TLR3 but not TLR4 activation on astrocytes induces expression of several factors involved in neuroprotection and down-regulation of inflammation rather than in the onset of traditional pro-inflammatory reactions. The notion that astrocyte TLR may thus play a role not only in host defense but also in tissue repair responses prompted us to examine the possibility that endogenous TLR agonists could be expressed in the human central nervous system to regulate the apparently dual astrocyte functions during trauma or inflammation. As a potential source of endogenous agonists, a cDNA library derived from several human brain tumor cell lines was used. Gene pools of this library were transfected into COS-7 cells and the expression products were screened for their ability to induce TLR activation in human primary astrocytes. The screening resulted in the identification of soluble CD14. By using a panel of TLR-transfected HEK293 cells, we found that signaling by soluble CD14 was TLR2 dependent. Moreover, the CD14-triggered TLR2-mediated response in astrocytes lead to the production of CXCL8, IL-6, and IL12p40, whereas typical TLR-induced pro-inflammatory cytokines, like TNF-, and IL-1,, were not produced at detectable levels. In conclusion, our data indicate that apart from its well-known ability to act as a co-receptor for TLR-dependent signaling by peptidoglycans or LPS, soluble CD14 can also act as a direct agonist for TLR2. © 2007 Wiley-Liss, Inc. [source] Glycine Receptors in the Nucleus Accumbens Involved in the Ethanol Intake-Reducing Effect of AcamprosateALCOHOLISM, Issue 1 2010PeiPei Chau Background:, We have previously demonstrated that strychnine-sensitive glycine receptors (GlyRs) in the nucleus accumbens (nAc) and nicotinic acetylcholine receptors (nAChRs) in the ventral tegmental area are involved in mediating ethanol (EtOH)-induced elevation of dopamine in the rat mesolimbic dopamine system. This neuronal circuitry was also demonstrated to mediate dopamine elevation in the nAc after both taurine, an endogenous agonist of GlyRs, and acamprosate, a synthetic derivate of homotaurine. The aim of this study was to investigate whether the EtOH intake-reducing effect of acamprosate involves accumbal GlyRs. Methods:, For this purpose, we used a voluntary EtOH consumption model where EtOH medium- and high-preferring rats were implanted with guide cannulae in the nAc. The animals received daily injections of acamprosate or 0.9% NaCl before accessing a bottle of 6% EtOH and a bottle of water. After 2 days, a microinjection of strychnine or vehicle preceded the daily systemic injection and bottle-access period. Results:, Acamprosate, but not saline, decreased EtOH intake. Pretreatment with Ringer in the nAc did not influence EtOH intake in saline or acamprosate-treated animals. Pretreatment with strychnine had no effect on EtOH intake in saline-treated animals, whereas it completely reversed the EtOH intake-reducing effect of acamprosate. Conclusions:, Based on current and previous results, we suggest that acamprosate primarily interacts with accumbal GlyRs and secondarily with ventral tegmental nAChRs, in a similar manner to that previously observed with EtOH and taurine. The interaction between acamprosate and GlyRs does not only influence dopamine output in the nAc but also EtOH consumption, giving further support for our hypothesis that GlyRs are of importance in EtOH reinforcement. [source] Nociceptin system does not affect MAC of volatile anaestheticsACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 6 2005S. Himukashi Background:, Nociceptin is the endogenous agonist of the opioid receptor-like (ORL) 1 receptor (NOP), and both nociceptin and NOP are widely expressed in the brain and spinal cord, which are target organs of general anaesthetics. As nociceptin has been reported to be involved in modulating pain mechanisms and stress responses, it is possible that the activity of the nociceptin system affects the anaesthetic potency of general anaesthetics. To address this possibility, we investigated the minimum alveolar concentrations (MACs) of various volatile anaesthetics in nociceptin receptor knockout mice (NOP,/,) and wild-type mice (NOP+/+). Methods:, We used male NOP,/, mice and NOP+/+ mice. MACs for halothane, isoflurane and sevoflurane were determined by the tail-clamp method. Results:, MACs for halothane, isoflurane and sevoflurane in NOP,/, mice were 1.60 (SD 0.06), 1.68 (0.08) and 3.36 (0.07)%, respectively. In NOP+/+ mice, MACs for halothane, isoflurane and sevoflurane were 1.59 (SD 0.07), 1.72 (0.07) and 3.38 (0.09)%, respectively. Conclusion:, MACs in NOP,/, mice did not significantly differ from those in NOP+/+ mice for halothane, isoflurane and sevoflurane. This result suggests that the nociceptin system does not affect the anaesthetic potency of volatile anaesthetics. [source] Oleamide is a selective endogenous agonist of rat and human CB1 cannabinoid receptorsBRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2004James D Leggett The ability of the endogenous fatty acid amide, cis -oleamide (ODA), to bind to and activate cannabinoid CB1 and CB2 receptors was investigated. ODA competitively inhibited binding of the nonselective cannabinoid agonist [3H]CP55,940 and the selective CB1 antagonist [3H]SR141716A to rat whole-brain membranes with Ki values of 1.14 ,M (0.52,2.53 ,M, Hill slope=0.80, n=6) and 2.63 ,M (0.62,11.20 ,M, Hill slope=0.92, n=4), respectively. AEA inhibited [3H]CP55,940 binding in rat whole-brain membranes with a Ki of 428 nM (346,510 nM, Hill slope=,1.33, n=3). ODA competitively inhibited [3H]CP55,940 binding in human CB1 (hCB1) cell membranes with a Ki value of 8.13 ,M (4.97,13.32 ,M, n=2). In human CB2 transfected (hCB2) HEK-293T cell membranes, 100 ,M ODA produced only a partial (42.5±7%) inhibition of [3H]CP55,940 binding. ODA stimulated [35S]GTP,S binding in a concentration-dependent manner (EC50=1.64 ,M (0.29,9.32 ,M), R2=0.99, n=4,9), with maximal stimulation of 188±9% of basal at 100 ,M. AEA stimulated [35S]GTP,S binding with an EC50 of 10.43 ,M (4.45,24.42 ,M, R2=1.00, n=3, 195±4% of basal at 300 ,M). Trans -oleamide (trans- ODA) failed to significantly stimulate [35S]GTP,S binding at concentrations up to 100 ,M. ODA (10 ,M)-stimulated [35S]GTP,S binding was reversed by the selective CB1 antagonist SR141716A (IC50=2.11 nM (0.32,13.77 nM), R2=1.00, n=6). The anatomical distribution of ODA-stimulated [35S]GTP,S binding in rat brain sections was indistinguishable from that of HU210. Increases of similar magnitude were observed due to both agonists in the striatum, cortex, hippocampus and cerebellum. ODA (10 ,M) significantly inhibited forskolin-stimulated cyclic AMP (cAMP) accumulation in mouse neuroblastoma N1E 115 cells (P=0.02, n=11). ODA-mediated inhibition was completely reversed by 1 ,M SR141716A (P<0.001, n=11) and was also reversed by pretreatment with 300 ng ml,1 pertussis toxin (P<0.001, n=6). These data demonstrate that ODA is a full cannabinoid CB1 receptor agonist. Therefore, in addition to allosteric modulation of other receptors and possible entourage effects due to fatty acid amide hydrolase inhibition, the effects of ODA may be mediated directly via the CB1 receptor. British Journal of Pharmacology (2004) 141, 253,262. doi:10.1038/sj.bjp.0705607 [source] Identification of soluble CD14 as an endogenous agonist for Toll-like receptor 2 on human astrocytes by genome-scale functional screening of glial cell derived proteinsGLIA, Issue 5 2007Malika Bsibsi Abstract Human astrocytes express a limited repertoire of Toll-like receptor (TLR) family members including TLR1-4, which are expressed on the cell surface. Also, TLR3 but not TLR4 activation on astrocytes induces expression of several factors involved in neuroprotection and down-regulation of inflammation rather than in the onset of traditional pro-inflammatory reactions. The notion that astrocyte TLR may thus play a role not only in host defense but also in tissue repair responses prompted us to examine the possibility that endogenous TLR agonists could be expressed in the human central nervous system to regulate the apparently dual astrocyte functions during trauma or inflammation. As a potential source of endogenous agonists, a cDNA library derived from several human brain tumor cell lines was used. Gene pools of this library were transfected into COS-7 cells and the expression products were screened for their ability to induce TLR activation in human primary astrocytes. The screening resulted in the identification of soluble CD14. By using a panel of TLR-transfected HEK293 cells, we found that signaling by soluble CD14 was TLR2 dependent. Moreover, the CD14-triggered TLR2-mediated response in astrocytes lead to the production of CXCL8, IL-6, and IL12p40, whereas typical TLR-induced pro-inflammatory cytokines, like TNF-, and IL-1,, were not produced at detectable levels. In conclusion, our data indicate that apart from its well-known ability to act as a co-receptor for TLR-dependent signaling by peptidoglycans or LPS, soluble CD14 can also act as a direct agonist for TLR2. © 2007 Wiley-Liss, Inc. [source] Cannabinoid,vanilloid receptor interactions in pain signalingJOURNAL OF NEUROCHEMISTRY, Issue 2003V. Di Marzo Agents that activate cannabinoid CB1 receptors for marijuana's active principal, THC, or vanilloid VR1 receptors for red chilli peppers' pungent ingredient, capsaicin, modulate pain perception. Stimulation of presynaptic CB1 leads to inhibition of glutamate release in the spinal cord, whereas VR1 stimulation causes release of substance P and CGRP from DRG neurons. VR1 undergoes rapid desensitization by its agonists, which makes VR1-expressing neurons insensitive to subsequent stimulation and results in analgesia. Thus, both CB1 and VR1, which are coexpressed in several spinal and DRG neurons, are targets for analgesic drug development. CB1 and VR1 also share endogenous agonists, namely anandamide, NADA and some of their analogs, and may be regarded as metabotropic and ionotropic receptors for the same family of mediators, with opposing roles in pain perception. The development of ,hybrid' CB1/VR1 agonists as potent analgesics and the functional relationships between CB1 and VR1 in sensory neurons will be discussed. [source] Opioids in the Hypothalamic Paraventricular Nucleus Stimulate Ethanol IntakeALCOHOLISM, Issue 2 2010Jessica R. Barson Background:, Specialized hypothalamic systems that increase food intake might also increase ethanol intake. To test this possibility, morphine and receptor-specific opioid agonists were microinjected in the paraventricular nucleus (PVN) of rats that had learned to drink ethanol. To cross-validate the results, naloxone methiodide (m-naloxone), an opioid antagonist, was microinjected with the expectation that it would have the opposite effect of morphine and the specific opioid agonists. Methods:, Sprague,Dawley rats were trained, without sugar, to drink 4 or 7% ethanol and were then implanted with chronic brain cannulas aimed at the PVN. After recovery, those drinking 7% ethanol, with food and water available, were injected with 2 doses each of morphine or m-naloxone. To test for receptor specificity, 2 doses each of the ,-receptor agonist [d -Ala2,N -Me-Phe4,Gly5 -ol]-Enkephalin (DAMGO), ,-receptor agonist d -Ala-Gly-Phe-Met-NH2 (DALA), or ,-receptor agonist U-50,488H were injected. DAMGO was also tested in rats drinking 4% ethanol without food or water available. As an anatomical control for drug reflux, injections were made 2 mm dorsal to the PVN. Results:, A main result was a significant increase in ethanol intake induced by PVN injection of morphine. The opposite effect was produced by m-naloxone. The effects of morphine and m-naloxone were exclusively on intake of ethanol, even though food and water were freely available. In the analysis with specific receptor agonists, PVN injection of the ,-agonist DALA significantly increased 7% ethanol intake without affecting food or water intake. This is in contrast to the ,-agonist U-50,488H, which decreased ethanol intake, and the ,-agonist DAMGO, which had no effect on ethanol intake in the presence or absence of food and water. In the anatomical control location 2 mm dorsal to the PVN, no drug caused any significant changes in ethanol, food, or water intake, providing evidence that the active site was close to the cannula tip. Conclusions:, The ,-opioid receptor agonist in the PVN increased ethanol intake in strong preference over food and water, while the ,-opioid agonist suppressed ethanol intake. Prior studies show that learning to drink ethanol stimulates PVN expression and production of the peptides enkephalin and dynorphin, which are endogenous agonists for the ,- and ,-receptors, respectively. These results suggest that enkephalin via the ,-opioid system can function locally within a positive feedback circuit to cause ethanol intake to escalate and ultimately contribute to the abuse of ethanol. This is in contrast to dynorphin via the ,-opioid system, which may act to counter this escalation. Naltrexone therapy for alcoholism may act, in part, by blocking the enkephalin-triggered positive feedback cycle. [source] G protein-independent neuromodulatory action of adenosine on metabotropic glutamate signalling in mouse cerebellar Purkinje cellsTHE JOURNAL OF PHYSIOLOGY, Issue 2 2007Toshihide Tabata Adenosine receptors (ARs) are G protein-coupled receptors (GPCRs) mediating the neuromodulatory actions of adenosine that influence emotional, cognitive, motor, and other functions in the central nervous system (CNS). Previous studies show complex formation between ARs and metabotropic glutamate receptors (mGluRs) in heterologous systems and close colocalization of ARs and mGluRs in several central neurons. Here we explored the possibility of intimate functional interplay between Gi/o protein-coupled A1 -subtype AR (A1R) and type-1 mGluR (mGluR1) naturally occurring in cerebellar Purkinje cells. Using a perforated-patch voltage-clamp technique, we found that both synthetic and endogenous agonists for A1R induced continuous depression of a mGluR1-coupled inward current. A1R agonists also depressed mGluR1-coupled intracellular Ca2+ mobilization monitored by fluorometry. A1R indeed mediated this depression because genetic depletion of A1R abolished it. Surprisingly, A1R agonist-induced depression persisted after blockade of Gi/o protein. The depression appeared to involve neither the cAMP-protein kinase A cascade downstream of the alpha subunits of Gi/o and Gs proteins, nor cytoplasmic Ca2+ that is suggested to be regulated by the beta-gamma subunit complex of Gi/o protein. Moreover, A1R did not appear to affect Gq protein which mediates the mGluR1-coupled responses. These findings suggest that A1R modulates mGluR1 signalling without the aid of the major G proteins. In this respect, the A1R-mediated depression of mGluR1 signalling shown here is clearly distinguished from the A1R-mediated neuronal responses described so far. These findings demonstrate a novel neuromodulatory action of adenosine in central neurons. [source] | |||||||||||||