1
|
Abstract
A substantial fraction of the human population suffers from chronic pain states, which often cannot be sufficiently treated with existing drugs. This calls for alternative targets and strategies for the development of novel analgesics. There is substantial evidence that the G protein-coupled GABAB receptor is involved in the processing of pain signals and thus has long been considered a valuable target for the generation of analgesics to treat chronic pain. In this review, the contribution of GABAB receptors to the generation and modulation of pain signals, their involvement in chronic pain states as well as their target suitability for the development of novel analgesics is discussed.
Collapse
Affiliation(s)
- Dietmar Benke
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland.
| |
Collapse
|
2
|
Ryu SW, Kim YO, Kim HB, Oh SB, Choi JI, Yoon MH. Antinociceptive effect of intrathecal P7C3 via GABA in a rat model of inflammatory pain. Eur J Pharmacol 2021; 899:174029. [PMID: 33727053 DOI: 10.1016/j.ejphar.2021.174029] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 03/09/2021] [Accepted: 03/11/2021] [Indexed: 02/06/2023]
Abstract
The recently identified molecule P7C3 has been highlighted in the field of pain research. We examined the effect of intrathecal P7C3 in tissue injury pain evoked by formalin injection and determined the role of the GABA system in the activity of P7C3 at the spinal level. Male Sprague-Dawley rats with intrathecal catheters implanted for experimental drug delivery were studied. The effects of intrathecal P7C3 and nicotinamide phosphoribosyltransferase (NAMPT) administered 10 min before the formalin injection were examined. Animals were pretreated with bicuculline, a GABA-A receptor antagonist; saclofen, a GABA-B receptor antagonist; L-allylglycine, a glutamic acid decarboxylase (GAD) blocker; and CHS 828, an NAMPT inhibitor; to observe involvement in the effects of P7C3. The effects of P7C3 alone and the mixture of P7C3 with GABA receptor antagonists on KCl-induced calcium transients were examined in rat dorsal root ganglion (DRG) neurons. The expression of GAD and the concentration of GABA in the spinal cord were evaluated. Intrathecal P7C3 and NAMPT produced an antinociceptive effect in the formalin test. Intrathecal bicuculline, saclofen, L-allylglycine, and CHS 828 reversed the antinociception of P7C3 in both phases. P7C3 decreased the KCl-induced calcium transients in DRG neurons. Both bicuculline and saclofen reversed the blocking effect of P7C3. The levels of GAD expression and GABA concentration decreased after formalin injection and were increased by P7C3. These results suggest that P7C3 increases GAD activity and then increases the GABA concentration in the spinal cord, which in turn may act on GABA receptors causing the antinociceptive effect against pain evoked by formalin injection.
Collapse
Affiliation(s)
- Sang Wan Ryu
- Department of Anesthesiology and Pain Medicine, Chonnam National University, Medical School, Gwangju, Republic of Korea
| | - Yeo Ok Kim
- Department of Anesthesiology and Pain Medicine, Chonnam National University, Medical School, Gwangju, Republic of Korea
| | - Han-Byul Kim
- Department of Neurobiology and Physiology, School of Dentistry Seoul National University, Seoul, Republic of Korea; Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea
| | - Seog Bae Oh
- Department of Neurobiology and Physiology, School of Dentistry Seoul National University, Seoul, Republic of Korea; Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea
| | - Jeong Il Choi
- Department of Anesthesiology and Pain Medicine, Chonnam National University, Medical School, Gwangju, Republic of Korea; The Brain Korea 21 Project, Center for Biomedical Human Resources at Chonnam National University, Gwangju, Republic of Korea
| | - Myung Ha Yoon
- Department of Anesthesiology and Pain Medicine, Chonnam National University, Medical School, Gwangju, Republic of Korea; The Brain Korea 21 Project, Center for Biomedical Human Resources at Chonnam National University, Gwangju, Republic of Korea.
| |
Collapse
|
3
|
Chartier M, Tannous S, Benturquia N, Labat L, Reis R, Risède P, Chevillard L, Mégarbane B. Baclofen-Induced Neuro-Respiratory Toxicity in the Rat: Contribution of Tolerance and Characterization of Withdrawal Syndrome. Toxicol Sci 2019; 164:153-165. [PMID: 29945230 DOI: 10.1093/toxsci/kfy073] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Baclofen, a γ-amino-butyric acid type-B receptor agonist with exponentially increased use at high-dose to facilitate abstinence in chronic alcoholics, is responsible for increasing poisonings. Tolerance and withdrawal syndromes have been reported during prolonged treatment but their contribution to the variability of baclofen-induced neurotoxicity in overdose is unknown. We studied baclofen-induced effects on rat sedation, temperature, and ventilation and modeled baclofen pharmacokinetics and effect/concentration relationships aiming to investigate the consequences of repeated baclofen pretreatment and to characterize withdrawal syndrome. Baclofen-induced dose-dependent sedation (p <0.01), hypothermia (p <.001) and respiratory depression (p <.01) were altered in repeatedly baclofen-pretreated rats (p <.05). Repeatedly baclofen-pretreated rats did not exhibit respiratory depression following baclofen overdose due to limitations on baclofen-induced increase in inspiratory (p <.01) and expiratory times (p <.01). Only slight hypoxemia without respiratory acidosis was observed. Baclofen discontinuation resulted in hyperlocomotion and non-anxiogenic withdrawal symptoms. Regarding pharmacokinetics, repeated baclofen pretreatment increased the peak concentration (p <.05) and absorption constant rate (p <.05) and reduced the distribution volume (p <.0001) and elimination half-life (p <.05). Analysis of the effect/concentration relationships indicated that plasma baclofen concentration decreases more rapidly than all studied neuro-respiratory effects, in tolerant and non-tolerant rats. Taken together, our findings supported the role of brain distribution in baclofen-induced neurotoxicity expression and its probable involvement in tolerance-related attenuation in addition to physiological adaptations of ventilation. In conclusion, repeated pretreatment attenuates baclofen-attributed neurotoxicity in overdose and results in post-discontinuation withdrawal syndrome. Our findings suggest both pharmacodynamic and pharmacokinetic mechanisms whose relative contributions to the variability of baclofen-induced neurotoxicity in overdose remain to be established.
Collapse
Affiliation(s)
- Magali Chartier
- Inserm, UMRS-1144, Paris-Descartes University, 75006 Paris, France
| | - Salma Tannous
- Inserm, UMRS-1144, Paris-Descartes University, 75006 Paris, France
| | - Nadia Benturquia
- Inserm, UMRS-1144, Paris-Descartes University, 75006 Paris, France
| | - Laurence Labat
- Inserm, UMRS-1144, Paris-Descartes University, 75006 Paris, France.,Pharmacokinetics and Pharmacochemistry Unit, Cochin Hospital, 75010 Paris, France.,Laboratory of Toxicology, Lariboisière Hospital, 75010 Paris, France
| | - Rafael Reis
- Pharmacokinetics and Pharmacochemistry Unit, Cochin Hospital, 75010 Paris, France
| | - Patricia Risède
- Inserm, UMRS-1144, Paris-Descartes University, 75006 Paris, France
| | - Lucie Chevillard
- Inserm, UMRS-1144, Paris-Descartes University, 75006 Paris, France
| | - Bruno Mégarbane
- Inserm, UMRS-1144, Paris-Descartes University, 75006 Paris, France.,Department of Medical and Toxicological Critical Care, Lariboisière Hospital, 75010 Paris, France
| |
Collapse
|
4
|
Kasten CR, Boehm SL. Identifying the role of pre-and postsynaptic GABA(B) receptors in behavior. Neurosci Biobehav Rev 2015; 57:70-87. [PMID: 26283074 DOI: 10.1016/j.neubiorev.2015.08.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2015] [Revised: 06/18/2015] [Accepted: 08/09/2015] [Indexed: 12/15/2022]
Abstract
Although many reviews exist characterizing the molecular differences of GABAB receptor isoforms, there is no current review of the in vivo effects of these isoforms. The current review focuses on whether the GABAB1a and GABAB1b isoforms contribute differentially to behaviors in isoform knockout mice. The roles of these receptors have primarily been characterized in cognitive, anxiety, and depressive phenotypes. Currently, the field supports a role of GABAB1a in memory maintenance and protection against an anhedonic phenotype, whereas GABAB1b appears to be involved in memory formation and a susceptibility to developing an anhedonic phenotype. Although GABAB receptors have been strongly implicated in drug abuse phenotypes, no isoform-specific work has been done in this field. Future directions include developing site-specific isoform knockdown to identify the role of different brain regions in behavior, as well as identifying how these isoforms are involved in development of behavioral phenotypes.
Collapse
Affiliation(s)
- Chelsea R Kasten
- Department of Psychology, Indianapolis University Purdue University-Indianapolis, 402N Blackford St LD 124, Indianapolis, IN 46202, United States.
| | - Stephen L Boehm
- Department of Psychology, Indianapolis University Purdue University-Indianapolis, 402N Blackford St LD 124, Indianapolis, IN 46202, United States; Indiana Alcohol Research Center, 545 Barnhill Drive EH 317, Indianapolis, IN, United States.
| |
Collapse
|
5
|
Keegan BMT, Beveridge TJR, Pezor JJ, Xiao R, Sexton T, Childers SR, Howlett AC. Chronic baclofen desensitizes GABA(B)-mediated G-protein activation and stimulates phosphorylation of kinases in mesocorticolimbic rat brain. Neuropharmacology 2015; 95:492-502. [PMID: 25724082 PMCID: PMC4537290 DOI: 10.1016/j.neuropharm.2015.02.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Revised: 12/30/2014] [Accepted: 02/11/2015] [Indexed: 01/19/2023]
Abstract
The GABAB receptor is a therapeutic target for CNS and neuropathic disorders; however, few preclinical studies have explored effects of chronic stimulation. This study evaluated acute and chronic baclofen treatments on GABAB-activated G-proteins and signaling protein phosphorylation as indicators of GABAB signaling capacity. Brain sections from rats acutely administered baclofen (5 mg/kg, i.p.) showed no significant differences from controls in GABAB-stimulated GTPγS binding in any brain region, but displayed significantly greater phosphorylation/activation of focal adhesion kinase (pFAK(Tyr397)) in mesocorticolimbic regions (caudate putamen, cortex, hippocampus, thalamus) and elevated phosphorylated/activated glycogen synthase kinase 3-β (pGSK3β(Tyr216)) in the prefrontal cortex, cerebral cortex, caudate putamen, nucleus accumbens, thalamus, septum, and globus pallidus. In rats administered chronic baclofen (5 mg/kg, t.i.d. for five days), GABAB-stimulated GTPγS binding was significantly diminished in the prefrontal cortex, septum, amygdala, and parabrachial nucleus compared to controls. This effect was specific to GABAB receptors: there was no effect of chronic baclofen treatment on adenosine A1-stimulated GTPγS binding in any region. Chronically-treated rats also exhibited increases in pFAK(Tyr397) and pGSK3β(Tyr216) compared to controls, and displayed wide-spread elevations in phosphorylated dopamine- and cAMP-regulated phosphoprotein-32 (pDARPP-32(Thr34)) compared to acutely-treated or control rats. We postulate that those neuroadaptive effects of GABAB stimulation mediated by G-proteins and their sequelae correlate with tolerance to several of baclofen's effects, whereas sustained signaling via kinase cascades points to cross-talk between GABAB receptors and alternative mechanisms that are resistant to desensitization. Both desensitized and sustained signaling pathways should be considered in the development of pharmacotherapies targeting the GABA system.
Collapse
Affiliation(s)
- Bradley M T Keegan
- Center for the Neurobiology of Addiction Treatment, Winston-Salem, NC 27157, USA; Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA
| | - Thomas J R Beveridge
- Center for the Neurobiology of Addiction Treatment, Winston-Salem, NC 27157, USA; Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA
| | - Jeffrey J Pezor
- Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA; Department of Chemistry, Wake Forest University, Winston-Salem, NC 27157, USA
| | - Ruoyu Xiao
- Center for the Neurobiology of Addiction Treatment, Winston-Salem, NC 27157, USA; Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA
| | - Tammy Sexton
- Center for the Neurobiology of Addiction Treatment, Winston-Salem, NC 27157, USA; Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA
| | - Steven R Childers
- Center for the Neurobiology of Addiction Treatment, Winston-Salem, NC 27157, USA; Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA
| | - Allyn C Howlett
- Center for the Neurobiology of Addiction Treatment, Winston-Salem, NC 27157, USA; Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA.
| |
Collapse
|
6
|
Grönbladh A, Johansson J, Nyberg F, Hallberg M. Administration of growth hormone and nandrolone decanoate alters mRNA expression of the GABAB receptor subunits as well as of the GH receptor, IGF-1, and IGF-2 in rat brain. Growth Horm IGF Res 2014; 24:60-66. [PMID: 24480470 DOI: 10.1016/j.ghir.2014.01.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Revised: 12/10/2013] [Accepted: 01/08/2014] [Indexed: 01/15/2023]
Abstract
OBJECTIVE The illicit use of anabolic androgenic steroids (AAS), especially among young adults, is of major concern. Among AAS users it is common to combine the AAS nandrolone decanoate (ND), with intake of growth hormone (GH) and a connection between gonadal steroids and the GH system has been suggested. Both AAS and GH affect functions in the brain, for example those associated with the hypothalamus and pituitary, and several GH actions are mediated by growth factors such as insulin-like growth factor 1 (IGF-1) and insulin-like growth factor 2 (IGF-2). The GABAergic system is implicated in actions induced by AAS and previous studies have provided evidence for a link between GH and GABAB receptors in the brain. Our aim was to examine the impact of AAS administration and a subsequent administration of GH, on the expression of GABAB receptors and important GH mediators in rat brain. DESIGN The aim was to investigate the CNS effects of a high-dose ND, and to study if a low, but physiological relevant, dose of GH could reverse the ND-induced effects. In the present study, male rats were administered a high dose of ND every third day during three weeks, and subsequently the rats were given recombinant human GH (rhGH) during ten days. Quantitative PCR (qPCR) was used to analyze gene expression in hypothalamus, anterior pituitary, caudate putamen, nucleus accumbens, and amygdala. RESULTS In the pituitary gland, the expression of GABAB receptor subunits was affected differently by the steroid treatment; the GABAB1 mRNA expression was decreased whereas a distinct elevation of the GABAB2 expression was found. Administration of ND also caused a decrease of GHR, IGF-1, and IGF-2 mRNA expression in the pituitary while the corresponding expression in the hypothalamus, caudate putamen, nucleus accumbens, and amygdala was unaffected. The rhGH administration did not alter the GABAB2 expression but increased the GABAB1 gene expression in the hypothalamus as compared to the AAS treated group. CONCLUSIONS These results provide new insights on the impact of ND and GH on the brain and highlight the interaction of these hormones with systems influencing GABAB receptor expression. The physiological significance of the observed effects of these hormones is discussed.
Collapse
Affiliation(s)
- Alfhild Grönbladh
- Department of Pharmaceutical Biosciences, Division of Biological Research on Drug Dependence, Uppsala University, P.O. Box 591, SE-751 24 Uppsala, Sweden.
| | - Jenny Johansson
- Department of Pharmaceutical Biosciences, Division of Biological Research on Drug Dependence, Uppsala University, P.O. Box 591, SE-751 24 Uppsala, Sweden
| | - Fred Nyberg
- Department of Pharmaceutical Biosciences, Division of Biological Research on Drug Dependence, Uppsala University, P.O. Box 591, SE-751 24 Uppsala, Sweden
| | - Mathias Hallberg
- Department of Pharmaceutical Biosciences, Division of Biological Research on Drug Dependence, Uppsala University, P.O. Box 591, SE-751 24 Uppsala, Sweden
| |
Collapse
|
7
|
McCarson KE, Enna SJ. GABA pharmacology: the search for analgesics. Neurochem Res 2014; 39:1948-63. [PMID: 24532294 DOI: 10.1007/s11064-014-1254-x] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 01/28/2014] [Accepted: 01/31/2014] [Indexed: 12/28/2022]
Abstract
Decades of research have been devoted to defining the role of GABAergic transmission in nociceptive processing. Much of this work was performed using rigid, orthosteric GABA analogs created by Povl Krogsgaard-Larsen and his associates. A relationship between GABA and pain is suggested by the anatomical distribution of GABA receptors and the ability of some GABA agonists to alter nociceptive responsiveness. Outlined in this report are data supporting this proposition, with particular emphasis on the anatomical localization and function of GABA-containing neurons and the molecular and pharmacological properties of GABAA and GABAB receptor subtypes. Reference is made to changes in overall GABAergic tone, GABA receptor expression and activity as a function of the duration and intensity of a painful stimulus or exposure to GABAergic agents. Evidence is presented that the plasticity of this receptor system may be responsible for the variability in the antinociceptive effectiveness of compounds that influence GABA transmission. These findings demonstrate that at least some types of persistent pain are associated with a regionally selective decline in GABAergic tone, highlighting the need for agents that enhance GABA activity in the affected regions without compromising GABA function over the long-term. As subtype selective positive allosteric modulators may accomplish these goals, such compounds might represent a new class of analgesic drugs.
Collapse
Affiliation(s)
- Kenneth E McCarson
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Boulevard, Mail Stop 1018, Kansas City, KS, 66160, USA
| | | |
Collapse
|
8
|
Bonaventura MM, Crivello M, Ferreira ML, Repetto M, Cymeryng C, Libertun C, Lux-Lantos VA. Effects of GABAB receptor agonists and antagonists on glycemia regulation in mice. Eur J Pharmacol 2011; 677:188-96. [PMID: 22210053 DOI: 10.1016/j.ejphar.2011.12.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2011] [Revised: 12/02/2011] [Accepted: 12/09/2011] [Indexed: 11/30/2022]
Abstract
γ-Aminobutyric acid (GABA) inhibits insulin secretion through GABA(B) receptors in pancreatic β-cells. We investigated whether GABA(B) receptors participated in the regulation of glucose homeostasis in vivo. BALB/c mice acutely pre-injected with the GABA(B) receptor agonist baclofen (7.5mg/kg, i.p.) presented glucose intolerance and diminished insulin secretion during a glucose tolerance test (GTT, 2g/kg body weight, i.p.). The GABA(B) receptor antagonist 2-hydroxysaclofen (15 mg/kg, i.p.) improved the GTT and reversed the baclofen effect. Also a slight increase in insulin secretion was observed with 2-hydroxysaclofen. In incubated islets 1.10(-5)M baclofen inhibited 20mM glucose-induced insulin secretion and this effect was reversed by coincubation with 1.10(-5)M 2-hydroxysaclofen. In chronically-treated animals (18 days) both the receptor agonist (5mg/kg/day i.p.) and the receptor antagonist (10mg/kg/day i.p.) induced impaired GTTs; the receptor antagonist, but not the agonist, also induced a decrease in insulin secretion. No alterations in insulin tolerance tests, body weight and food intake were observed with the treatments. In addition glucagon, insulin-like growth factor I, prolactin, corticosterone and growth hormone, other hormones involved in glucose metabolism regulation, were not affected by chronic baclofen or 2-hydroxysaclofen. In islets obtained from chronically injected animals with baclofen, 2-hydroxysaclofen or saline (as above), GABA(B2) mRNA expression was not altered. Results demonstrate that GABA(B) receptors are involved in the regulation of glucose homeostasis in vivo. Treatment with receptor agonists or antagonists, given acutely or chronically, altered glucose homeostasis and insulin secretion alerting to the need to evaluate glucose metabolism during the clinical use of these drugs.
Collapse
Affiliation(s)
- María M Bonaventura
- Instituto de Biología y Medicina Experimental-CONICET, Buenos Aires, Argentina
| | | | | | | | | | | | | |
Collapse
|
9
|
Pacey LKK, Tharmalingam S, Hampson DR. Subchronic administration and combination metabotropic glutamate and GABAB receptor drug therapy in fragile X syndrome. J Pharmacol Exp Ther 2011; 338:897-905. [PMID: 21636656 DOI: 10.1124/jpet.111.183327] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The most common cause of inherited mental retardation, fragile X syndrome, results from a triplet repeat expansion in the FMR1 gene and loss of the mRNA binding protein, fragile X mental retardation protein (FMRP). In the absence of FMRP, signaling through group I metabotropic glutamate receptors (mGluRs) is enhanced. We previously proposed a mechanism whereby the audiogenic seizures exhibited by FMR1 null mice result from an imbalance in excitatory mGluR and inhibitory GABA(B) receptor (GABA(B)R) signaling (Mol Pharmacol 76:18-24, 2009). Here, we tested the mGluR5-positive allosteric modulator 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB), the mGluR5 inverse agonist 2-methyl-6-(phenylethynyl)pyridine (MPEP), and GABA(B) receptor agonists, alone and in combination on receptor protein expression and audiogenic seizures in FMR1 mice. Single doses of MPEP (30 mg/kg), the GABA(B)R orthosteric agonist R-baclofen (1 mg/kg), or the GABA(B)R-positive allosteric modulator N,N'-dicyclopentyl-2-(methylthio)-5-nitro-4,6-pyrimidine diamine (GS-39783) (30 mg/kg), reduced the incidence of seizures. However, when administered subchronically (daily injections for 6 days), MPEP retained its anticonvulsant activity, whereas R-baclofen and GS-39783 did not. When administered at lower doses that had no effect when given alone, a single injection of MPEP plus R-baclofen also reduced seizures, but the effect was lost after subchronic administration. We were surprised to find that subchronic treatment with R-baclofen also induced tolerance to a single high dose of MPEP. These data demonstrate that tolerance develops rapidly to the antiseizure properties of R-baclofen alone and R-baclofen coadministered with MPEP, but not with MPEP alone. Our findings suggest that cross-talk between the G-protein signaling pathways of these receptors affects drug efficacy after repeated treatment.
Collapse
Affiliation(s)
- Laura K K Pacey
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada
| | | | | |
Collapse
|
10
|
Ghose S, Winter MK, McCarson KE, Tamminga CA, Enna SJ. The GABAβ receptor as a target for antidepressant drug action. Br J Pharmacol 2011; 162:1-17. [PMID: 20735410 PMCID: PMC3012402 DOI: 10.1111/j.1476-5381.2010.01004.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2010] [Revised: 08/06/2010] [Accepted: 08/11/2010] [Indexed: 11/29/2022] Open
Abstract
Preclinical and clinical data suggest that a modification in GABA(B) receptor expression and function may contribute to the symptoms of major depression and the response to antidepressants. This includes laboratory animal experiments demonstrating that antidepressants modify brain GABA(B) receptor expression and function and that GABA(B) receptor antagonists display antidepressant potential in animal models of this condition. Clinical and post-mortem studies reveal changes in GABAergic transmission associated with depression as well as depression-related changes in GABA(B) subunit expression that are localized to the cortical depression network. Detailed in this review are the preclinical and clinical data implicating a role for the GABA(B) receptor system in mediating symptoms of this disorder and its possible involvement in the response to antidepressants. Particular emphasis is placed on clinical and post-mortem studies, including previously unpublished work demonstrating regionally-selective modifications in GABA(B) receptor subunit expression in brain samples obtained from depressed subjects. Together with the earlier preclinical studies, these new data point to a role for the GABA(B) system in major depression and support the antidepressant potential of GABA(B) receptor antagonists.
Collapse
Affiliation(s)
- Subroto Ghose
- Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | | | | | | | | |
Collapse
|
11
|
Mamelak M. Narcolepsy and depression and the neurobiology of gammahydroxybutyrate. Prog Neurobiol 2009; 89:193-219. [PMID: 19654034 DOI: 10.1016/j.pneurobio.2009.07.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Revised: 05/24/2009] [Accepted: 07/28/2009] [Indexed: 12/23/2022]
Abstract
A voluminous literature describes the relationship between disturbed sleep and depression. The breakdown of sleep is one of the cardinal features of depression and often also heralds its onset. Frequent arousals, periods of wakefulness and a short sleep onset REM latency are typical polysomnographic features of depression. The short latency to REM sleep has been attributed to the combination of a monoaminergic deficiency and cholinergic supersensitivity and these irregularities have been proposed to form the biological basis of the disorder. A similar imbalance between monoaminergic and cholinergic neurotransmission has been found in narcolepsy, a condition in which frequent awakenings, periods of wakefulness and short sleep onset REM latencies are also characteristic findings during sleep. In many cases of narcolepsy, this imbalance appears to result from a deficiency of hypocretin but once established, whether in depression or narcolepsy, this disequilibrium sets the stage for the dissociation or premature appearance of REM sleep and for the dissociation of the motor inhibitory component of REM sleep or cataplexy. In the presence of this monoaminergic/cholinergic imbalance, gammahydroxybutyrate (GHB) may acutely further reduce the latency of REM sleep and induce cataplexy, in both patients with narcolepsy or depression. On the other hand, the repeated nocturnal application of GHB in patients with narcolepsy improves the continuity of sleep, prolongs the latency to REM sleep and prevents cataplexy. Evidence to date suggests that GHB may restore the normal balance between monoaminergic and cholinergic neurotransmission. As such, the repeated use of GHB at night and the stabilization of sleep over time makes GHB an effective treatment for narcolepsy and a potentially effective treatment for depression.
Collapse
Affiliation(s)
- Mortimer Mamelak
- Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada.
| |
Collapse
|
12
|
Abstract
Hyperalgesia and allodynia are frequent symptoms of disease and may be useful adaptations to protect vulnerable tissues. Both may, however, also emerge as diseases in their own right. Considerable progress has been made in developing clinically relevant animal models for identifying the most significant underlying mechanisms. This review deals with experimental models that are currently used to measure (sect. II) or to induce (sect. III) hyperalgesia and allodynia in animals. Induction and expression of hyperalgesia and allodynia are context sensitive. This is discussed in section IV. Neuronal and nonneuronal cell populations have been identified that are indispensable for the induction and/or the expression of hyperalgesia and allodynia as summarized in section V. This review focuses on highly topical spinal mechanisms of hyperalgesia and allodynia including intrinsic and synaptic plasticity, the modulation of inhibitory control (sect. VI), and neuroimmune interactions (sect. VII). The scientific use of language improves also in the field of pain research. Refined definitions of some technical terms including the new definitions of hyperalgesia and allodynia by the International Association for the Study of Pain are illustrated and annotated in section I.
Collapse
Affiliation(s)
- Jürgen Sandkühler
- Department of Neurophysiology, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| |
Collapse
|
13
|
Abstract
The GABA(B) receptors belong to the family of class C metabotropic receptors. They are inhibitory receptors forming obligatory heterodimers. Their analgesic role in the dorsal horn of the spinal cord is well established since more than 25 years ago. However, Baclofen, the reference agonist of the GABA(B) receptor, proved to have little efficiency in clinics in neuropathic patients. It seems therefore useful to decipher GABA(B) functions in the nociceptive circuitry, and their regulation in conditions of chronic pain. In the present review, we will focus first on the distribution of the GABA(B) subtypes. Then, we will consider their pre- and post-synaptic functions in the dorsal horn of naïve rats. Finally, we will document the mechanisms that may lead to receptor impairment in neuropathic conditions.
Collapse
Affiliation(s)
- Marc Landry
- Université Bordeaux 2, INSERM U862, 146 rue Léo Saignat, 33077 Bordeaux Cedex, France.
| | | |
Collapse
|
14
|
Abstract
Radioligand binding using [(3)H]NCS-382, an antagonist of the GHB receptor, revealed specific binding sites in the rat cerebrocortical and hippocampal membranes. Scatchard analysis of saturation isotherms revealed two different populations of binding sites. NCS-382 was about 10 times more potent than GHB in inhibiting [(3)H]NCS-382 binding. A variety of ligands for other receptors did not affect [(3)H]NCS-382 binding. Quantitative autoradiographic analysis of [(3)H]NCS-382 binding revealed similar characteristics. Thus [(3)H]NCS-382, being more potent and selective, offers advantage over [(3)H]GHB as a radioligand. Unlike GHB, several analogues of GHB such as UMB68 (a tertiary alcohol analogue of GHB), UMB86 (4-hydroxy-4-napthylbutanoic acid, sodium salt), UMB72 [4-(3-phenylpropyloxy)butyric acid, sodium salt], UMB73 (4-benzyloxybutyric acid, sodium salt), UMB66 (3-chloropropanoic acid), gamma-hydroxyvaleric acid (that is, GHV, a 4-methyl-substituted analogue of GHB), 3-HPA (3-hydroxyphenylacetic acid), and ethers of 3-hydroxyphenylacetic acid (UMB108, UMB109, and UMB119) displaced [(3)H]NCS-382 without affecting [(3)H]GABA binding to GABA(B) receptor. Thus these compounds offer an advantage over GHB as an experimental tool. Our study, aimed at exploring the potential involvement of the GHB receptor in the pharmacology of ethanol, indicated that ethanol does not affect [(3)H]NCS-382 binding in the rat brain, thereby suggesting that ethanol does not interact directly with the GHB receptor. Our study, aimed at exploring the involvement of the GHB receptor in the pathology of succinate semialdehyde dehydrogenase deficiency, which is known to cause elevation of GHB levels, revealed no change in the affinity, receptor density or displacement potency as determined by using [(3)H]NCS-382 as a radioligand in Aldh5a1(-/-) vs. Aldh5a1(+/+) mouse brain.
Collapse
Affiliation(s)
- Maharaj K Ticku
- Department of Pharmacology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA
| | | |
Collapse
|
15
|
Cinar R, Freund TF, Katona I, Mackie K, Szucs M. Reciprocal inhibition of G-protein signaling is induced by CB(1) cannabinoid and GABA(B) receptor interactions in rat hippocampal membranes. Neurochem Int 2008; 52:1402-9. [PMID: 18407377 DOI: 10.1016/j.neuint.2008.02.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2008] [Accepted: 02/21/2008] [Indexed: 11/27/2022]
Abstract
Cannabinoid CB(1) and the metabotropic GABA(B) receptors have been shown to display similar pharmacological effects and co-localization in certain brain regions. Previous studies have reported a functional link between the two systems. As a first step to investigate the underlying molecular mechanism, here we show cross-inhibition of G-protein signaling between GABA(B) and CB(1) receptors in rat hippocampal membranes. The CB(1) agonist R-Win55,212-2 displayed high potency and efficacy in stimulating guanosine-5'-O-(3-[(35)S]thio)triphosphate, [(35)S]GTPgammaS binding. Its effect was completely blocked by the specific CB(1) antagonist AM251 suggesting that the signaling was via CB(1) receptors. The GABA(B) agonists baclofen and SKF97541 also elevated [(35)S]GTPgammaS binding by about 60%, with potency values in the micromolar range. Phaclofen behaved as a low potency antagonist with an ED(50) approximately 1mM. However, phaclofen at low doses (1 and 10nM) slightly but significantly attenuated maximal stimulation of [(35)S]GTPgammaS binding by the CB(1) agonist R-Win55,212-2. The observation that higher concentrations of phaclofen had no such effect rule out the possibility of its direct action on CB(1) receptors. The pharmacologically inactive stereoisomer S-Win55,212-3 had no effect either alone or in combination with phaclofen establishing that the interaction is stereospecific in hippocampus. The specific CB(1) antagonist AM251 at a low dose (1 nM) also inhibited the efficacy of G-protein signaling of the GABA(B) receptor agonist SKF97541. Cross-talk of the two receptor systems was not detected in either spinal cord or cerebral cortex membranes. It is speculated that the interaction might occur via an allosteric interaction between a subset of GABA(B) and CB(1) receptors in rat hippocampal membranes. Although the exact molecular mechanism of the reciprocal inhibition between CB(1) and GABA(B) receptors will have to be explored by future studies it is intriguing that the cross-talk might be involved in balance tuning the endocannabinoid and GABAergic signaling in hippocampus.
Collapse
Affiliation(s)
- Resat Cinar
- Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, Szeged, Hungary
| | | | | | | | | |
Collapse
|
16
|
Hefferan MP, Fuchigami T, Marsala M. Development of baclofen tolerance in a rat model of chronic spasticity and rigidity. Neurosci Lett 2006; 403:195-200. [PMID: 16716507 DOI: 10.1016/j.neulet.2006.04.048] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2006] [Revised: 04/18/2006] [Accepted: 04/27/2006] [Indexed: 11/17/2022]
Abstract
Systemic or spinal treatment with baclofen has been associated with the development of tolerance in patients with chronic spasticity. In the present study, we used a rat model of spinal ischemia-induced spasticity to characterize the development of baclofen tolerance after chronic intrathecal (i.t.) baclofen infusion. Following the induction of spinal ischemia and the development of behavioral spasticity, animals were implanted with i.t. catheters connected to osmotic pumps to continuously infuse baclofen (1.0 microg/0.5 microl/h). Hindleg peripheral muscle resistance (PMR) was measured periodically after initiation of chronic infusion and after bolus i.t. baclofen injection (1.0 microg). Peripheral muscle resistance was significantly decreased at the onset of baclofen infusion, however, after 5-7 days of infusion a progressive return of spasticity was noted, where baseline PMR values returned to preinfusion levels. At the same time, the efficacy of bolus i.t. baclofen treatment also decreased, where after 5 days of baclofen infusion 1.0 microg (i.t.) baclofen only reduced PMR by 10% (compared to 40-50% preinfusion). Baclofen efficacy progressively returned once continuous infusion was stopped. These data demonstrate that transient spinal ischemia leads to the development of spasticity which is sensitive to spinal baclofen. Chronic i.t. infusion leads to a progressive development of tolerance. This model offers potential to study tolerance mechanisms after spinal injury, and aid in drug discovery for use in baclofen-tolerant patients.
Collapse
Affiliation(s)
- Michael P Hefferan
- Anesthesiology Research Laboratory, Department of Anesthesiology, University of California, San Diego, 9500 Gilman Drive, La Jolla, 92093-0818, USA.
| | | | | |
Collapse
|
17
|
Mehta AK, Gould GG, Gupta M, Carter LP, Gibson KM, Ticku MK. Succinate semialdehyde dehydrogenase deficiency does not down-regulate gamma-hydroxybutyric acid binding sites in the mouse brain. Mol Genet Metab 2006; 88:86-9. [PMID: 16406647 DOI: 10.1016/j.ymgme.2005.11.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2005] [Revised: 11/21/2005] [Accepted: 11/22/2005] [Indexed: 11/26/2022]
Abstract
We investigated whether succinate semialdehyde dehydrogenase deficiency alters gamma-hydroxybutyric acid (GHB) receptor characteristics due to elevation of GHB levels in the mouse brain. The membrane homogenate binding and quantitative autoradiography using [3H]NCS-382 revealed no significant changes in the affinity (Kd), receptor density (Bmax), or displacement potency (IC50) in various brain regions of Aldh5a1-/- vs. Aldh5a1+/+ mice.
Collapse
Affiliation(s)
- Ashok K Mehta
- Department of Pharmacology, MC 7764, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA
| | | | | | | | | | | |
Collapse
|
18
|
Bettler B, Tiao JYH. Molecular diversity, trafficking and subcellular localization of GABAB receptors. Pharmacol Ther 2006; 110:533-43. [PMID: 16644017 DOI: 10.1016/j.pharmthera.2006.03.006] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2006] [Accepted: 03/23/2006] [Indexed: 12/14/2022]
Abstract
GABAB receptors are the G-protein coupled receptors for the main inhibitory neurotransmitter in the brain, gamma-aminobutyric acid (GABA). While native studies predicted pharmacologically distinct GABAB receptor subtypes, molecular studies failed to identify the expected receptor varieties. Mouse genetic experiments therefore addressed whether the cloned receptors can account for the classical electrophysiological, biochemical and behavioral GABAB responses or whether additional receptors exist. Among G-protein coupled receptors, GABAB receptors are unique in that they require 2 distinct subunits for functioning. This atypical receptor structure triggered a large body of work that investigated the regulation of receptor assembly and trafficking. With the availability of molecular tools, substantial progress was also made in the analysis of the receptor protein distribution in neuronal compartments. Here, we review recent studies that shed light on the molecular diversity, the subcellular distribution and the cell surface dynamics of GABAB receptors.
Collapse
Affiliation(s)
- Bernhard Bettler
- Institute of Physiology, Department of Clinical-Biological Sciences, Pharmazentrum, Klingelbergstrasse 50-70, University of Basel, CH-4056 Basel, Switzerland.
| | | |
Collapse
|
19
|
Abstract
A great deal of effort has been expended in attempting to define the role of GABA in mediating the transmission and perception of pain. Pursuit of this question has been stimulated by the fact that GABAergic neurons are widely distributed throughout the central nervous system, including regions of the spinal cord dorsal horn known to be important for transmitting pain impulses to the brain. In addition, GABA neurons and receptors are found in supraspinal sites known to coordinate the perception and response to painful stimuli and this neurotransmitter system has been shown to regulate control of sensory information processing in the spinal cord. The discovery that GABA receptor agonists display antinociceptive properties in a variety of animal models of pain has provided an impetus for developing such agents for this purpose. It has been shown that GABA receptor agonists, as well as inhibitors of GABA uptake or metabolism, are clinically effective in treating this symptom. However, even with an enhanced understanding of the relationship between GABAergic transmission and pain, it has proven difficult to exploit these findings in designing novel analgesics that can be employed for the routine management of pain. Work in this area has revealed a host of reasons why GABAergic drugs have, to date, been of limited utility in the management of pain. Chief among these are the side effects associated with such agents, in particular sedation. These limitations are likely due to the simultaneous activation of GABA receptors throughout the neuraxis, most of which are not involved in the transmission or perception of pain. This makes it difficult to fully exploit the antinociceptive properties of GABAergic drugs before untoward effects intervene. The discovery of molecularly and pharmacologically distinct GABAA receptors may open the way to developing subtype selective agents that target those receptors most intimately involved in the transmission and perception of pain. The more limited repertoire of GABAB receptor subunits makes it more difficult to develop subtype selective agents for this site. Nonetheless, a GABAB agonist, CGP 35024, has been identified that induces antinociceptive responses at doses well below those that cause sedation (Patel et al., 2001). It has also been reported that, unlike baclofen, tolerance to antinociceptive responses is not observed with CGP 44532, a more potent GABAB receptor agonist (Enna et al., 1998). While the reasons for these differences in responses to members of the same class remain unknown, these findings suggest it may be possible to design a GABAB agonist with a superior clinical profile than existing agents. Besides the challenges associated with identifying subtype selective GABAA and GABAB receptor agonists, the development of GABA analgesics has been hindered by the fact that the responsiveness of these receptor systems appear to vary with the type and duration of pain being treated and the mode of drug administration. Further studies are necessary to more precisely define the types of pain most amenable to treatment with GABAergic drugs. Inasmuch as the antinociceptive responses to these agents in laboratory animals are mediated, at least in part, through activation or inhibition of other neurotransmitter and neuromodulator systems, it is conceivable that GABA agonists will be most efficacious as analgesics when administered in combination with other agents. The results of anatomical, biochemical, molecular, and pharmacological studies support the notion that generalized activation of GABA receptor systems dampens the response to painful stimuli. The data leave little doubt that, under certain circumstances, stimulation of neuroanatomically discreet GABA receptor sites could be of benefit in the management of pain. Continued research in this area is warranted given the limited choices, and clinical difficulties, associated with conventional analgesics.
Collapse
Affiliation(s)
- S J Enna
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
| | | |
Collapse
|
20
|
McCarson KE, Duric V, Reisman SA, Winter M, Enna SJ. GABA(B) receptor function and subunit expression in the rat spinal cord as indicators of stress and the antinociceptive response to antidepressants. Brain Res 2005; 1068:109-17. [PMID: 16368079 DOI: 10.1016/j.brainres.2005.11.015] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Revised: 11/02/2005] [Accepted: 11/06/2005] [Indexed: 02/05/2023]
Abstract
Experiments were undertaken to examine whether once daily i.p. administration of either of two antidepressants used for the treatment of neuropathic pain, amitriptyline (10 mg/kg) and fluoxetine (5 mg/kg), to rats for 7 days modifies GABA(B) receptor function and subunit expression in the lumbar spinal cord. The results indicate that, as previously reported for desipramine, both amitriptyline and fluoxetine increase the pain threshold to a thermal stimulus, the expression of GABA(B(1)) subunits, and baclofen-stimulated [35S]GTPgammaS binding, a measure of GABA(B) receptor function. The effects of antidepressant administration on GABA(B(1b)) and GABA(B(2)) subunit expression in spinal cord are more variable than for GABA(B(1a)). It was also discovered that repeated daily exposure to a thermal stimulus or immobilization stress increases GABA(B(1a)) expression in the lumbar spinal cord, with no commensurate change in thermal pain threshold or GABA(B) receptor sensitivity. These results support a relationship between GABA(B) receptors and the action of antidepressants. The findings demonstrate that drug-induced increases in GABA(B) receptor function can occur independently of any change in GABA(B) receptor subunit expression and are consistent with the notion that GABA(B) receptor subunits have multiple functions, only one of which is dimerization to form GABA(B) receptors. The data also suggest that GABA(B) subunit gene expression may serve as a preclinical marker of antidepressant efficacy and of drug- or stress-induced modifications in central nervous system activity.
Collapse
Affiliation(s)
- Kenneth E McCarson
- Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA
| | | | | | | | | |
Collapse
|
21
|
McCarson KE, Ralya A, Reisman SA, Enna SJ. Amitriptyline prevents thermal hyperalgesia and modifications in rat spinal cord GABAB receptor expression and function in an animal model of neuropathic pain. Biochem Pharmacol 2005; 71:196-202. [PMID: 16293232 DOI: 10.1016/j.bcp.2005.10.026] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2005] [Revised: 10/10/2005] [Accepted: 10/13/2005] [Indexed: 11/18/2022]
Abstract
Using an animal model of neuropathic pain, behavioral and biochemical experiments were performed to assess the effects of this condition on pain threshold and GABA(B) receptor sensitivity and subunit gene expression in the rat lumbar spinal cord. The results indicate that partial sciatic nerve ligation decreases thermal and mechanical pain withdrawal latencies, and increases baclofen-stimulated [35S]GTPgammaS binding and GABA(B) receptor subunit gene expression in the rat lumbar spinal cord, suggesting that neuropathic pain may be due, in part, to a deficiency in GABAergic transmission. The experiments also demonstrate that daily administration (10 mg/kg, i.p.) of amitriptyline, a tricyclic antidepressant used for the treatment of neuropathic pain, for 1 week after surgery prevents the decline in thermal pain threshold, the increase in GABA(B2) gene expression, and development of increased GABA(B) receptor function in spinal cord resulting from nerve damage. These findings indicate that the efficacy of amitriptyline as a treatment for neuropathic pain may be related to an ability to maintain spinal cord GABA(B) receptor activity.
Collapse
Affiliation(s)
- Kenneth E McCarson
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Boulevard, Mail Stop 1018, Kansas City, KS 66160, USA
| | | | | | | |
Collapse
|
22
|
Shi X, Li X, Clark JD. Formalin injection causes a coordinated spinal cord CO/NO-cGMP signaling system response. Mol Pain 2005; 1:33. [PMID: 16297238 PMCID: PMC1310513 DOI: 10.1186/1744-8069-1-33] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2005] [Accepted: 11/18/2005] [Indexed: 12/02/2022] Open
Abstract
Background The CO/NO-cGMP signalling system participates in the regulation of many physiological processes. The roles this system plays in spinal cord nociceptive signalling are particularly important. While individual components have been examined in isolation, little study has been dedicated to understanding the regulation and functioning of the system as a whole. Results In these studies we examined the time course of expression of 13 genes coding for components of this system including isoforms of the heme oxygenase (HO), nitric oxide synthase (NOS), soluble guanylate cyclase (sGC), cGMP dependent protein kinase (PKG) and phosphodiesterase (PDE) enzyme systems. Of the 13 genes studied, 11 had spinal cord mRNA levels elevated at one or more time points up to 48 hours after hindpaw formalin injection. Of the 11 with elevated mRNA, 8 had elevated protein levels 48 hours after formalin injection when mechanical allodynia was maximal. No component had an increased protein level which did not have an increased mRNA level at one or more time points. Injection of morphine 10 mg/kg prior to formalin completely abolished the acute nociceptive behaviours, but did not alter the degree of sensitivity which developed in the formalin treated hind paws during the subsequent 48 hours. Morphine treatment did, however, eliminate formalin induced increases in enzyme protein levels. Conclusion Our results indicate that the expression of the components of the CO/NO-cGMP signalling system seems to be coordinated in such a way that a generalized multi-level enhancement rather than a tightly limited step specific response occurs with noxious stimulation. Furthermore, the analgesic morphine administered prior to noxious stimulation can prevent long-term changes in gene expression though not necessarily nociceptive sensitisation.
Collapse
Affiliation(s)
- Xiaoyou Shi
- Stanford University Department of Anesthesiology, Stanford, CA, USA
| | - Xiangqi Li
- Stanford University Department of Anesthesiology, Stanford, CA, USA
| | - J David Clark
- Stanford University Department of Anesthesiology, Stanford, CA, USA
- Veterans Affairs Palo Alto Healthcare System, Palo Alto, CA, USA
| |
Collapse
|
23
|
Pibiri F, Carboni G, Carai MAM, Gessa GL, Castelli MP. Up-regulation of GABA(B) receptors by chronic administration of the GABA(B) receptor antagonist SCH 50,911. Eur J Pharmacol 2005; 515:94-8. [PMID: 15893746 DOI: 10.1016/j.ejphar.2005.03.040] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2004] [Revised: 03/15/2005] [Accepted: 03/30/2005] [Indexed: 11/19/2022]
Abstract
Chronic treatment of mice with the specific gamma-aminobutyric acid(B) (GABA(B)) receptor antagonist (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50,911) increased both the number of GABA(B) receptors in the whole brain (measured as [3H]CGP 54626 [S-(R,R)]-3-[[1-(3,4-dichlorophenyl)amino]-2-hydroxypropyl](cyclohexylmethyl)phosphinic acid hydrochloride binding) and the ability of baclofen to activate GABA(B) receptor coupled G-protein (measured as % reduction of the EC50 of baclofen to activate [35S]GTP(gamma)S binding). The results indicate that persistent blockade of GABA(B) receptors leads to their compensatory up-regulation and suggest that GABA(B) receptors are tonically activated by endogenous GABA.
Collapse
Affiliation(s)
- Fabio Pibiri
- B.B. Brodie Department of Neuroscience, University of Cagliari, Cittadella Universitaria di Monserrato, 09042 Monserrato (CA), Italy
| | | | | | | | | |
Collapse
|
24
|
Purisai MG, Sands SA, Davis TD, Price JL, Chronwall BM. GABAB receptor subunit mRNAs are differentially regulated in pituitary melanotropes during development and detection of functioning receptors coincides with completion of innervation. Int J Dev Neurosci 2005; 23:315-26. [PMID: 15927755 DOI: 10.1016/j.ijdevneu.2005.01.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2004] [Revised: 01/26/2005] [Accepted: 01/26/2005] [Indexed: 11/30/2022] Open
Abstract
This study examines the developmental expression of GABAB receptor subunits (GABAB(1a), GABAB(1b), GABAB(2)) in the pituitary intermediate lobe using in situ hybridization, reverse transcriptase-polymerase chain reaction, immunohistochemistry, and Western blots. Receptor functionality was studied by baclofen-stimulated GTPgammaS binding. In the adult rat pituitary all three transcripts were detected in melanotropes, but not in glia, of the intermediate lobe. No transcripts of any subunit were detected in the neural lobe. Transcripts of GABAB(1a) and GABAB(1b), but not of GABAB(2), were detected in specific subpopulations of cells in the anterior lobe. All three transcripts were detected in melanotropes on gestational day 18 using in situ hybridization. Reverse transcriptase-polymerase chain reactions comparing postnatal day 2 and adult transcript levels in the neurointermediate lobe support in situ hybridization data that GABAB(1a) mRNA levels do not change, GABAB(1b) levels increase, and GABAB(2) levels decrease as the rat matures. Thus, GABAB receptor subunit transcripts are differentially regulated in melanotropes during development. In the adult rat both GABAB(1) and GABAB(2) proteins were detected in the neurointermediate lobe using Western blotting and in melanotropes by immunohistochemistry. Developmentally, GABAB(1) protein was not detected until postnatal day 7, but was clearly expressed by postnatal day 15 while GABAB(2) protein could not be detected until postnatal day 15. Functional receptors were found in the intermediate lobe at postnatal day 15 and in the adult. The demonstration of transcripts for GABAB(1a), GABAB(1b) and GABAB(2) subunits at gestational day 18 contrasted with the failure to detect any protein before postnatal day 7, suggesting that the regulation of GABAB subunit isoforms occurs differentially at both the transcriptional and translational level as development progresses. The disparity in the regulation of the receptor subunits may suggest that GABAB(1) could have other functions besides being part of the GABAB receptor heterodimer.
Collapse
Affiliation(s)
- Maya Gadhvi Purisai
- Division of Cell Biology and Biophysics and Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, 5100 Rockhill Road, Kansas City, MO 64110-2499, USA
| | | | | | | | | |
Collapse
|
25
|
Sands SA, Reisman SA, Enna SJ. Effect of antidepressants on GABA(B) receptor function and subunit expression in rat hippocampus. Biochem Pharmacol 2005; 68:1489-95. [PMID: 15451391 DOI: 10.1016/j.bcp.2004.07.027] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Laboratory and clinical studies suggest that depression is associated with changes in the hippocampus and that this brain region is a major target for antidepressant drugs. Given the data suggesting that GABA(B) receptor antagonists display antidepressant properties, the present study was undertaken to assess the effect of antidepressant administration on GABA(B) receptors in the rat hippocampus to determine whether changes in this regional receptor system may play a role in the response to these agents. Rats were administered (i.p.) the monoamine oxidase inhibitors tranylcypromine (10mg/kg) or phenelzine (10mg/kg), the tricyclic antidepressant desipramine (15 mg/kg), or fluoxetine (5mg/kg), a selective serotonin re-uptake inhibitor, once daily for seven consecutive days. Two hours following the last drug treatment the hippocampal tissue was prepared for defining the distribution and quantity of GABA(B) receptor subunits using in situ hybridization and for assessing GABA(B) receptor function by quantifying baclofen-stimulated [(35)S]-GTPgammaS binding. All of these antidepressants selectively increased the expression of the GABA(B(1a)) subunit in hippocampus, having no consistent effect on the expression of GABA(B(1b)) or GABA(B(2)). Moreover, except for fluoxetine, these treatments increased GABA(B) receptor function in this brain region. The results indicate that an enhancement in the production of hippocampal GABA(B(1a)) subunits may be a component of the response to antidepressants, supporting a possible role for this receptor in the symptoms of depression and the treatment of this condition.
Collapse
Affiliation(s)
- Scott A Sands
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical School, 3901 Rainbow Boulevard, Mail Stop 1018, Kansas City, KS 66160-7417, USA
| | | | | |
Collapse
|
26
|
Enna SJ, Bowery NG. GABA(B) receptor alterations as indicators of physiological and pharmacological function. Biochem Pharmacol 2005; 68:1541-8. [PMID: 15451397 DOI: 10.1016/j.bcp.2004.06.037] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2004] [Accepted: 06/21/2004] [Indexed: 11/15/2022]
Abstract
Given the widespread distribution of GABA(B) receptors throughout the central nervous system, and within certain peripheral organs, it is likely their selective pharmacological manipulation could be of benefit in the treatment of a variety of disorders. Studies aimed at defining the clinical potential of GABA(B) receptor agonists and antagonists have included gene deletion experiments, examination of changes in receptor binding, subunit expression and function in diseased tissue, as well as after the chronic administration of drugs. The results indicate that a functional GABA(B) receptor requires the combination of GABA(B(1)) and GABA(B(2)) subunits, that receptor function does not always correlate with subunit expression and receptor binding, and that GABA(B) receptor modifications may be associated with the clinical response to antidepressants, mood stabilizers, and GABA(B) receptor agonists and antagonists. Moreover, changes in GABA(B) binding or expression suggest this receptor may be involved in mediating symptoms associated with chronic pain, epilepsy and schizophrenia. This, together with results from other types of studies, indicates the potential therapeutic value of developing drugs capable of selectively activating, inhibiting, or modulating GABA(B) receptor function.
Collapse
Affiliation(s)
- S J Enna
- Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical School, 3901 Rainbow Boulevard, Mail Stop 1018, Kansas City, Kansas 66160-0227, USA.
| | | |
Collapse
|
27
|
Escher T, Mittleman G. Effects of ethanol and GABAB drugs on working memory in C57BL/6J and DBA/2J mice. Psychopharmacology (Berl) 2004; 176:166-74. [PMID: 15064920 DOI: 10.1007/s00213-004-1875-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2004] [Accepted: 03/08/2004] [Indexed: 11/30/2022]
Abstract
RATIONALE It has been suggested that GABA(B) receptors may be part of a neural substrate mediating some of the effects of ethanol. OBJECTIVE The purpose of this experiment was to investigate, in mice, the effects of ethanol on working memory in a delayed matching-to position (DMTP) task, and additionally to determine if these effects were modulated by GABA(B) receptors. METHODS Female C57BL/6J and DBA/2J mice were trained in the DMTP task, and after asymptotic levels of performance accuracy were achieved, injections (IP) of ethanol, baclofen, or phaclofen were administered. Baclofen or phaclofen were then co-administered with ethanol. Each test was repeated twice. RESULTS Ethanol caused deficits in working memory at 2.0 g/kg and higher. The highest dose (2.5 g/kg) produced additional non-specific effects, indicative of sedation. Baclofen increased performance accuracy (2.5 mg/kg), while decreasing the total number of trials completed. When combined with ethanol (1.5 g/kg), baclofen increased memory deficits at the highest dose (7.5 mg/kg). Phaclofen increased performance accuracy at 10 and 30 mg/kg but had no effect on the total number of trials completed. When combined with ethanol (2.5 g/kg), phaclofen did not significantly alter ethanol-induced deficits in performance. CONCLUSIONS Analyses of performance accuracy, total trials completed and variables indexing bias and motor impairment indicated that GABA(B) drugs modulate working memory in a behaviorally specific manner. Overall, these receptors may be part of a neural substrate that modulates some of the effects of ethanol.
Collapse
Affiliation(s)
- T Escher
- Department of Psychology, University of Memphis, Memphis, TN 38152, USA
| | | |
Collapse
|
28
|
Sands SA, McCarson KE, Enna SJ. Relationship between the antinociceptive response to desipramine and changes in GABAB receptor function and subunit expression in the dorsal horn of the rat spinal cord. Biochem Pharmacol 2004; 67:743-9. [PMID: 14757174 DOI: 10.1016/j.bcp.2003.10.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Although tricyclic antidepressants are among the drugs of choice for the treatment of neuropathic pain, their mechanism of action in this regard remains unknown. Because previous reports suggest these agents may influence gamma-aminobutyric acid (GABA) neurotransmission, and GABAB receptors are known to participate in the transmission of pain impulses, the present experiments were undertaken to examine whether the administration of desipramine alters GABAB receptor subunit expression and function in the dorsal horn of the rat spinal cord. For the study, rats were injected (i.p.) once daily with desipramine (15 mg/kg) for 7 consecutive days, during which their thermal withdrawal threshold was monitored, and after which GABAB receptor function, and the levels of GABAB receptor subunit mRNA, were quantified in the spinal cord dorsal horn. The results indicate that 4-7 days of continuous administration of desipramine are necessary to observe a significant increase in the thermal pain threshold. Moreover, it was found that 7 days of treatment with desipramine enhances GABAB receptor function, as measured by baclofen-stimulated [35S]GTPgammaS binding, and increases mRNA expression for the GABAB(1a) and GABAB(2), but not GABAB(1b), subunits. These findings suggest the antinociceptive effect of desipramine is accompanied by a change in spinal cord GABAB receptor sensitivity that could be an important component in the analgesic response to this agent.
Collapse
Affiliation(s)
- Scott A Sands
- Department Pharmacology, Toxicology and Therapeutics, Kansas University School of Medicine, 3901 Rainbow Blvd., Mail Code 1018, Kansas City, KS 66160, USA
| | | | | |
Collapse
|
29
|
Fairfax BP, Pitcher JA, Scott MGH, Calver AR, Pangalos MN, Moss SJ, Couve A. Phosphorylation and chronic agonist treatment atypically modulate GABAB receptor cell surface stability. J Biol Chem 2004; 279:12565-73. [PMID: 14707142 DOI: 10.1074/jbc.m311389200] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
GABA(B) receptors are heterodimeric G protein-coupled receptors that mediate slow synaptic inhibition in the central nervous system. The dynamic control of the cell surface stability of GABA(B) receptors is likely to be of fundamental importance in the modulation of receptor signaling. Presently, however, this process is poorly understood. Here we demonstrate that GABA(B) receptors are remarkably stable at the plasma membrane showing little basal endocytosis in cultured cortical and hippocampal neurons. In addition, we show that exposure to baclofen, a well characterized GABA(B) receptor agonist, fails to enhance GABA(B) receptor endocytosis. Lack of receptor internalization in neurons correlates with an absence of agonist-induced phosphorylation and lack of arrestin recruitment in heterologous systems. We also demonstrate that chronic exposure to baclofen selectively promotes endocytosis-independent GABA(B) receptor degradation. The effect of baclofen can be attenuated by activation of cAMP-dependent protein kinase or co-stimulation of beta-adrenergic receptors. Furthermore, we show that increased degradation rates are correlated with reduced receptor phosphorylation at serine 892 in GABA(B)R2. Our results support a model in which GABA(B)R2 phosphorylation specifically stabilizes surface GABA(B) receptors in neurons. We propose that signaling pathways that regulate cAMP levels in neurons may have profound effects on the tonic synaptic inhibition by modulating the availability of GABA(B) receptors.
Collapse
Affiliation(s)
- Benjamin P Fairfax
- Medical Research Council Laboratory of Molecular Cell Biology and Department of Pharmacology, University College London, London WC1E 6BT, United Kingdom
| | | | | | | | | | | | | |
Collapse
|
30
|
Abstract
Arginine plays an important role in many physiologic and biologic processes beyond its role as a protein-incorporated amino acid. Dietary supplementation of arginine can enhance wound healing, regulate endocrine activity and potentiate immune activity. Under normal unstressed conditions the arginine requirement of adult humans is fulfilled by endogenous sources, however this is compromised during times of stress, especially in critical illness. These finding have led to use of arginine supplementation as part of an immune-enhancing dietary regimen to help combat the immune suppression seen in such patients. Though the results from studies examining the use of this type of immunonutrition in critically ill patients are far from definitive, they are promising that this mode of therapy may be of some advantage. A better understanding of the in vivo biology of arginine and its metabolism is necessary to truly define a benefit from arginine supplementation.
Collapse
Affiliation(s)
- D Efron
- Department of Surgery, Sinai Hospital of Baltimore, MD 21215, USA
| | | |
Collapse
|