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Bizzozzero-Hiriart M, Di Giorgio NP, Libertun C, Lux-Lantos V. GABAergic input through GABA B receptors is necessary during a perinatal window to shape gene expression of factors critical to reproduction such as Kiss1. Am J Physiol Endocrinol Metab 2020; 318:E901-E919. [PMID: 32286880 DOI: 10.1152/ajpendo.00547.2019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Lack of GABAB receptors in GABAB1 knockout mice decreases neonatal ARC kisspeptin 1 (Kiss1) expression in the arcuate nucleus of the hypothalamus (ARC) in females, which show impaired reproduction as adults. Our aim was to selectively impair GABAB signaling during a short postnatal period to evaluate its impact on the reproductive system. Neonatal male and female mice were injected with the GABAB antagonist CGP 55845 (CGP, 1 mg/kg body wt sc) or saline from postnatal day 2 (PND2) to PND6, three times per day (8 AM, 1 PM, and 6 PM). One group was killed on PND6 for collection of blood samples (hormones by radioimmunoassay), brains for gene expression in the anteroventral periventricular nucleus-periventricular nucleus continuum (AVPV/PeN), and ARC micropunches [quantitative PCR (qPCR)] and gonads for qPCR, hormone contents, and histology. A second group of mice was injected with CGP (1 mg/kg body wt sc) or saline from PND2 to PND6, three times per day (8 AM, 1 PM, and 6 PM), and left to grow to adulthood. We measured body weight during development and parameters of sexual differentiation, puberty onset, and estrous cycles. Adult mice were killed, and trunk blood (hormones), brains for qPCR, and gonads for qPCR and hormone contents were obtained. Our most important findings on PND6 include the CGP-induced decrease in ARC Kiss1 and increase in neurokinin B (Tac2) in both sexes; the decrease in AVPV/PeN tyrosine hydroxylase (Th) only in females; the increase in gonad estradiol content in both sexes; and the increase in primordial follicles and decrease in primary and secondary follicles. Neonatally CGP-treated adults showed decreased ARC Kiss1 and ARC gonadotropin-releasing hormone (Gnrh1) and increased ARC glutamic acid decarboxylase 67 (Gad1) only in males; increased ARC GABAB receptor subunit 1 (Gabbr1) in both sexes; and decreased AVPV/PeN Th only in females. We demonstrate that ARC Kiss1 expression is chronically downregulated in males and that the normal sex difference in AVPV/PeN Th expression is abolished. In conclusion, neonatal GABAergic input through GABAB receptors shapes gene expression of factors critical to reproduction.
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MESH Headings
- Animals
- Animals, Newborn
- Arcuate Nucleus of Hypothalamus/drug effects
- Arcuate Nucleus of Hypothalamus/metabolism
- Estradiol/metabolism
- Female
- Follicle Stimulating Hormone/metabolism
- GABA-B Receptor Antagonists/pharmacology
- Gene Expression Regulation, Developmental/drug effects
- Gene Expression Regulation, Developmental/physiology
- Glutamate Decarboxylase/genetics
- Glutamate Decarboxylase/metabolism
- Gonadotropin-Releasing Hormone/genetics
- Gonadotropin-Releasing Hormone/metabolism
- Hypothalamus, Anterior/drug effects
- Hypothalamus, Anterior/metabolism
- Kisspeptins/genetics
- Kisspeptins/metabolism
- Luteinizing Hormone/metabolism
- Male
- Mice
- Ovary/drug effects
- Ovary/metabolism
- Phosphinic Acids/pharmacology
- Propanolamines/pharmacology
- Protein Precursors/genetics
- Protein Precursors/metabolism
- Puberty/drug effects
- Puberty/genetics
- Receptors, Estrogen/genetics
- Receptors, Estrogen/metabolism
- Receptors, GABA-B/genetics
- Receptors, GABA-B/metabolism
- Receptors, Progesterone/genetics
- Receptors, Progesterone/metabolism
- Reproduction/drug effects
- Reproduction/genetics
- Reverse Transcriptase Polymerase Chain Reaction
- Sex Differentiation/drug effects
- Sex Differentiation/genetics
- Tachykinins/genetics
- Tachykinins/metabolism
- Testis/drug effects
- Testis/metabolism
- Testosterone/metabolism
- Tyrosine 3-Monooxygenase/genetics
- Tyrosine 3-Monooxygenase/metabolism
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Affiliation(s)
- Marianne Bizzozzero-Hiriart
- Laboratorio de Neuroendocrinología, Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Noelia P Di Giorgio
- Laboratorio de Neuroendocrinología, Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Carlos Libertun
- Laboratorio de Neuroendocrinología, Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
- Departamento de Fisiología, Facultad de Medicina, Universidad de Buenos Aires, Argentina
| | - Victoria Lux-Lantos
- Laboratorio de Neuroendocrinología, Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
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Salio C, Merighi A, Bardoni R. GABA B receptors-mediated tonic inhibition of glutamate release from Aβ fibers in rat laminae III/IV of the spinal cord dorsal horn. Mol Pain 2018; 13:1744806917710041. [PMID: 28565998 PMCID: PMC5456036 DOI: 10.1177/1744806917710041] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Presynaptic GABAB receptors (GABABRs) are highly expressed in dorsal root ganglion neurons and spinal cord dorsal horn. GABABRs located in superficial dorsal horn play an important antinociceptive role, by acting at both pre- and postsynaptic sites. GABABRs expressed in deep dorsal horn could be involved in the processing of touch sensation and possibly in the generation of tactile allodynia in chronic pain. The objective of this study was to characterize the morphological and functional properties of GABABRs expressed on Aβ fibers projecting to lamina III/IV and to understand their role in modulating excitatory synaptic transmission. We performed high-resolution electron microscopic analysis, showing that GABAB2 subunit is expressed on 71.9% of terminals in rat lamina III-IV. These terminals were engaged in axodendritic synapses and, for the 46%, also expressed glutamate immunoreactivity. Monosynaptic excitatory postsynaptic currents, evoked by Aβ fiber stimulation and recorded from lamina III/IV neurons in spinal cord slices, were strongly depressed by application of baclofen (0.1-2.5 µM), acting as a presynaptic modulator. Application of the GABABR antagonist CGP 55845 caused, in a subpopulation of neurons, the potentiation of the first of two excitatory postsynaptic currents recorded with the paired-pulse protocol, showing that GABABRs are endogenously activated. A decrease in the paired-pulse ratio accompanied the effect of CGP 55845, implying the involvement of presynaptic GABABRs. CGP 55845 facilitated only the first excitatory postsynaptic current also during a train of four consecutive stimuli applied to Aβ fibers. These results suggest that GABABRs tonically inhibit glutamate release from Aβ fibers at a subset of synapses in deep dorsal horn. This modulation specifically affects only the early phase of synaptic excitation in lamina III-IV neurons.
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Affiliation(s)
- Chiara Salio
- 1 Department of Veterinary Sciences, University of Turin, Grugliasco, Italy
| | - Adalberto Merighi
- 1 Department of Veterinary Sciences, University of Turin, Grugliasco, Italy
| | - Rita Bardoni
- 2 Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy
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3
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Fukuhara K, Katafuchi T, Yoshimura M. Effects of baclofen on mechanical noxious and innocuous transmission in the spinal dorsal horn of the adult rat: in vivo patch-clamp analysis. Eur J Neurosci 2013; 38:3398-407. [PMID: 23961926 DOI: 10.1111/ejn.12345] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2013] [Revised: 06/30/2013] [Accepted: 07/25/2013] [Indexed: 12/20/2022]
Abstract
The effects of a GABAB agonist, baclofen, on mechanical noxious and innocuous synaptic transmission in the substantia gelatinosa (SG) were investigated in adult rats with the in vivo patch-clamp technique. Under current-clamp conditions, perfusion with baclofen (10 μm) on the surface of the spinal cord caused hyperpolarisation of SG neurons and a decrease in the number of action potentials elicited by pinch and touch stimuli applied to the receptive field of the ipsilateral hindlimb. The suppression of action potentials was preserved under blockade of postsynaptic G-proteins, although baclofen-induced hyperpolarisation was completely blocked. These findings suggest presynaptic effects of baclofen on the induced action potentials. Under voltage-clamp conditions, application of baclofen reduced the frequency, but not the amplitude, of miniature excitatory postsynaptic currents (mEPSCs), whereas the GABAB receptor antagonist CGP55845 increased the frequency of mEPSCs without affecting the amplitude. Furthermore, application of a GABA uptake inhibitor, nipecotic acid, decreased the frequency of mEPSCs; this effect was blocked by CGP55845, but not by the GABAA antagonist bicuculline. Both the frequency and the amplitude of the pinch-evoked barrage of excitatory postsynaptic currents (EPSCs) were suppressed by baclofen in a dose-dependent manner. The frequency and amplitude of touch-evoked EPSCs was also suppressed by baclofen, but the suppression was significantly smaller than that of pinch-evoked EPSCs. We conclude that mechanical noxious transmission is presynaptically blocked through GABAB receptors in the SG, and is more effectively suppressed than innocuous transmission, which may account for a part of the mechanism of the efficient analgesic effects of baclofen.
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Affiliation(s)
- Kaori Fukuhara
- Department of Integrative Physiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, 812-8582, Japan
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4
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Liu T, Fujita T, Kumamoto E. Acetylcholine and norepinephrine mediate GABAergic but not glycinergic transmission enhancement by melittin in adult rat substantia gelatinosa neurons. J Neurophysiol 2011; 106:233-46. [DOI: 10.1152/jn.00838.2010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
GABAergic and glycinergic inhibitory synaptic transmissions in substantia gelatinosa (SG; lamina II of Rexed) neurons of the spinal dorsal horn play an important role in regulating nociceptive transmission from the periphery. It has not yet been well known whether each of the inhibitory transmissions plays a distinct role in the regulation. We report an involvement of neurotransmitters in GABAergic but not glycinergic transmission enhancement produced by the PLA2 activator melittin, where the whole-cell patch-clamp technique is applied to the SG neurons of adult rat spinal cord slices. Glycinergic but not GABAergic spontaneous inhibitory postsynaptic current (sIPSC) was increased in frequency and amplitude by melittin in the presence of nicotinic, muscarinic acetylcholine, and α1-adrenergic receptor antagonists (mecamylamine, atropine, and WB-4101, respectively). GABAergic transmission enhancement produced by melittin was unaffected by the 5-hydroxytryptamine 3 receptor and P2X receptor antagonists (ICS-205,930 and pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid, respectively). Nicotinic and muscarinic acetylcholine receptor agonists [(−)-nicotine and carbamoylcholine, respectively] and norepinephrine, as well as melittin, increased GABAergic sIPSC frequency and amplitude. A repeated application of (−)-nicotine, carbamoylcholine, and norepinephrine, but not melittin, at an interval of 30 min produced a similar transmission enhancement. These results indicate that melittin produces the release of acetylcholine and norepinephrine, which activate (nicotinic and muscarinic) acetylcholine and α1-adrenergic receptors, respectively, resulting in GABAergic but not glycinergic transmission enhancement in SG neurons. The desensitization of a system leading to the acetylcholine and norepinephrine release is slow in recovery. This distinction in modulation between GABAergic and glycinergic transmissions may play a role in regulating nociceptive transmission.
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Affiliation(s)
- Tao Liu
- Department of Physiology, Saga Medical School, Saga, Japan; and
- Department of Pediatrics, Medical College of Nanchang University, Nanchang, China
| | - Tsugumi Fujita
- Department of Physiology, Saga Medical School, Saga, Japan; and
| | - Eiichi Kumamoto
- Department of Physiology, Saga Medical School, Saga, Japan; and
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5
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Lee M, Schwab C, McGeer PL. Astrocytes are GABAergic cells that modulate microglial activity. Glia 2011; 59:152-65. [PMID: 21046567 DOI: 10.1002/glia.21087] [Citation(s) in RCA: 228] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
GABA is assumed to function in brain only as an inhibitory neurotransmitter. Here we report a much broader CNS role. We show that human astrocytes are GABAergic cells, and that human microglia are GABAceptive cells. We show that in adult human brain tissue, astrocytes immunostain for the GABA synthesizing enzyme GAD 67, the GABA metabolizing enzyme GABA-T and the GABA(A) and GABA(B) receptors. The intensity of staining is comparable or greater to that observed for known inhibitory neurons. We show that cultured human astrocytes strongly express the mRNA and protein for GAD 67, as well as GABA-T, and the GABA(A) and GABA(B) receptors. We further show that cultured human microglia express the mRNA and protein for GABA-T, in addition to the GABA(A) and GABA(B) receptors characterizing them as GABAceptive cells. We demonstrate that GABA suppresses the reactive response of both astrocytes and microglia to the inflammatory stimulants lipopolysaccharide (LPS) and interferon-γ by inhibiting induction of inflammatory pathways mediated by NFκB and P38 MAP kinase. This results in a reduced release of the inflammatory cytokines TNFα and IL-6 and an attenuation of conditioned medium neurotoxicity toward neuroblastoma SH-SY5Y cells. These inhibitory reactions are partially mimicked by the GABA(A) receptor agonist muscimol and the GABA(B) receptor agonist baclofen, indicating that GABA can stimulate both types of receptors in astrocytes as well as microglia. We conclude that the antiinflammatory actions of GABA offer new therapeutic opportunities since agonists should enhance the effectiveness of other antiinflammatory agents that operate through non-GABA pathways.
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Affiliation(s)
- Moonhee Lee
- Kinsmen Laboratory of Neurological Research, University of British Columbia, Vancouver, BC, Canada
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6
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Lasarge CL, Bañuelos C, Mayse JD, Bizon JL. Blockade of GABA(B) receptors completely reverses age-related learning impairment. Neuroscience 2009; 164:941-7. [PMID: 19723562 PMCID: PMC2874897 DOI: 10.1016/j.neuroscience.2009.08.055] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Revised: 08/21/2009] [Accepted: 08/22/2009] [Indexed: 11/16/2022]
Abstract
Impaired cognitive functions are well-described in the aging process. GABA(B) antagonists can facilitate learning and memory in young subjects, but these agents have not been well-characterized in aging. Here we show a complete reversal of olfactory discrimination learning deficits in cognitively-impaired aged Fischer 344 rats using the GABA(B) antagonist CGP55845, such that drug treatment restored performance to that on par with young and cognitively-unimpaired aged subjects. There was no evidence that this improved learning was due to enhanced olfactory detection abilities produced by the drug. These results highlight the potential of targeting GABA(B) receptors to ameliorate age-related cognitive deficits and demonstrate the utility of olfactory discrimination learning as a preclinical model for testing novel therapies to improve cognitive functions in aging.
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Affiliation(s)
- C L Lasarge
- Department of Psychology and Faculty of Neuroscience, Texas A&M University, College Station, TX 77843-4235, USA
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7
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Zarrindast MR, Ghadimi M, Ramezani-Tehrani B, Sahebgharani M. EFFECT OF GABA RECEPTOR AGONISTS OR ANTAGONISTS ON MORPHINE-INDUCED STRAUB TAIL IN MICE. Int J Neurosci 2009; 116:963-73. [PMID: 16861161 DOI: 10.1080/00207450600550428] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The effects of GABA receptor agents on Straub tail induced by morphine were investigated in mice. Subcutaneous injection of different doses of morphine (10-60 mg/kg) induced a dose-dependent Straub tail in mice. Maximum response was obtained with 40 mg/kg of the drug, 30 min after the drug administration. The morphine response was decreased by subcutaneous injection of naloxone (0.5-2 mg/kg). Intraperitoneal administration of different doses of baclofen (2-8 mg/kg) reduced Straub tail induced by morphine (40 mg/kg). The response of baclofen was decreased by Intraperitoneal injection of CGP35348 (150 mg/kg). CGP35348 by itself did not elicit any response. Different Intraperitoneally doses of muscimol (1-4 mg/kg) bicuculline (1-3 mg/kg), or picrotoxin (1-3 mg/kg) also reduced morphine effect. The effect of muscimol was not altered by bicuculline pretreatment. It is concluded that both GABAA and GABAB receptor activation reduced Straub tail induced by morphine.
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Affiliation(s)
- M R Zarrindast
- Department of Pharmacology, Medical School, Tehran University of Medical Sciences, Iran.
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8
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The glycine transporter GlyT2 controls the dynamics of synaptic vesicle refilling in inhibitory spinal cord neurons. J Neurosci 2008; 28:9755-68. [PMID: 18815261 DOI: 10.1523/jneurosci.0509-08.2008] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
At inhibitory synapses, glycine and GABA are accumulated into synaptic vesicles by the same vesicular transporter VGAT/VIAAT (vesicular GABA transporter/vesicular inhibitory amino acid transporter), enabling a continuum of glycine, GABA, and mixed phenotypes. Many fundamental aspects of the presynaptic contribution to the inhibitory phenotypes remain unclear. The neuronal transporter GlyT2 is one of the critical presynaptic factors, because glycinergic transmission is impaired in knock-out GlyT2(-/-) mice and mutations in the human GlyT2 gene slc6a5 are sufficient to cause hyperekplexia. Here, we establish that GlyT2-mediated uptake is directly coupled to the accumulation of glycine into recycling synaptic vesicles using cultured spinal cord neurons derived from GlyT2-enhanced green fluorescent protein transgenic mice. Membrane expression of GlyT2 was confirmed by recording glycine-evoked transporter current. We show that GlyT2 inhibition induces a switch from a predominantly glycine to a predominantly GABA phenotype. This effect was mediated by a reduction of glycinergic quantal size after cytosolic depletion of glycine and was entirely reversed by glycine resupply, illustrating that the filling of empty synaptic vesicles is tightly coupled to GlyT2-mediated uptake. Interestingly, high-frequency trains of stimuli elicit two phases of vesicle release with distinct kinetic requirements for glycine refilling. Thus, our results demonstrate the central role played by GlyT2 in determining inhibitory phenotype and therefore in the physiology and pathology of inhibitory circuits.
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9
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Li DP, Yang Q, Pan HM, Pan HL. Plasticity of pre- and postsynaptic GABAB receptor function in the paraventricular nucleus in spontaneously hypertensive rats. Am J Physiol Heart Circ Physiol 2008; 295:H807-15. [PMID: 18567709 DOI: 10.1152/ajpheart.00259.2008] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
GABA(B) receptor function is upregulated in the paraventricular nucleus (PVN) of the hypothalamus in spontaneously hypertensive rats (SHR), but it is unclear whether this upregulation occurs pre- or postsynaptically. We therefore determined pre- and postsynaptic GABA(B) receptor function in retrogradely labeled spinally projecting PVN neurons using whole cell patch-clamp recording in brain slices in SHR and Wistar-Kyoto (WKY) rats. Bath application of the GABA(B) receptor agonist baclofen significantly decreased the spontaneous firing activity of labeled PVN neurons in both SHR and WKY rats. However, the magnitude of reduction in the firing rate was significantly greater in SHR than in WKY rats. Furthermore, baclofen produced larger membrane hyperpolarization and outward currents in labeled PVN neurons in SHR than in WKY rats. The baclofen-induced current was abolished by either including G protein inhibitor GDPbetaS in the pipette solution or bath application of the GABA(B) receptor antagonist in both SHR and WKY rats. Blocking N-methyl-d-aspartic acid receptors had no significant effect on baclofen-elicited outward currents in SHR. In addition, baclofen caused significantly greater inhibition of glutamatergic excitatory postsynaptic currents (EPSCs) in labeled PVN neurons in brain slices from SHR than WKY rats. By contrast, baclofen produced significantly less inhibition of GABAergic inhibitory postsynaptic currents (IPSCs) in labeled PVN neurons in SHR than in WKY rats. Although microinjection of the GABA(B) antagonist into the PVN increases sympathetic vasomotor tone in SHR, the GABA(B) antagonist did not affect EPSCs and IPSCs of the PVN neurons in vitro. These findings suggest that postsynaptic GABA(B) receptor function is upregulated in PVN presympathetic neurons in SHR. Whereas presynaptic GABA(B) receptor control of glutamatergic synaptic inputs is enhanced, presynaptic GABA(B) receptor control of GABAergic inputs in the PVN is attenuated in SHR. Changes in both pre- and postsynaptic GABA(B) receptors in the PVN may contribute to the control of sympathetic outflow in hypertension.
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Affiliation(s)
- De-Pei Li
- Dept. of Critical Care, Unit 110, The Univ. of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA.
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5-HT2C and GABAB receptors influence handling-induced convulsion severity in chromosome 4 congenic and DBA/2J background strain mice. Brain Res 2008; 1198:124-31. [PMID: 18262506 DOI: 10.1016/j.brainres.2008.01.024] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2007] [Revised: 12/21/2007] [Accepted: 01/05/2008] [Indexed: 11/21/2022]
Abstract
Progress towards elucidating the underlying genetic variation for susceptibility to complex central nervous system (CNS) hyperexcitability states has just begun. Genetic mapping analyses suggest that a gene(s) on mid-chromosome 4 has pleiotropic effects on multiple CNS hyperexcitability states in mice, including alcohol and barbiturate withdrawal and convulsions elicited by chemical and audiogenic stimuli. We recently identified Mpdz within this chromosomal region as a gene that influences alcohol and barbiturate withdrawal convulsions. Mpdz encodes the multi-PDZ domain protein (MPDZ). Currently, there is limited information available about the mechanism by which MPDZ influences drug withdrawal and/or other CNS hyperexcitability states, but may involve its interaction with 5-HT2C and/or GABAB receptors. One of the most useful tools we have developed thus far is a congenic strain that possesses a segment of chromosome 4 from the C57BL/6J (donor) mouse strain superimposed on a genetic background that is >99% from the DBA/2J strain. The introduced segment spans the Mpdz gene. Here, we demonstrate that handling-induced convulsions are less severe in congenic vs. background strain mice in response to either a 5-HT2C receptor antagonist (SB242084) or a GABAB receptor agonist (baclofen), but not a GABAA receptor channel blocker (pentylenetetrazol). These data suggest that allelic variation in Mpdz, or a linked gene, influences SB242084- and baclofen-enhanced convulsions. Our results are consistent with the hypothesis that Mpdz's effects on CNS hyperexcitability, including alcohol and barbiturate withdrawal, involve MPDZ interaction with 5-HT2C and/or GABAB receptors. However, additional genes reside within the congenic interval and may also influence CNS hyperexcitability.
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Mannoury la Cour C, Herbelles C, Pasteau V, de Nanteuil G, Millan MJ. Influence of positive allosteric modulators on GABA(B) receptor coupling in rat brain: a scintillation proximity assay characterisation of G protein subtypes. J Neurochem 2007; 105:308-23. [PMID: 18021295 DOI: 10.1111/j.1471-4159.2007.05131.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Little is known concerning coupling of cerebral GABA(B) receptors to G protein subtypes, and the influence of positive allosteric modulators (PAMs) has not been evaluated. These questions were addressed by an antibody-capture/scintillation proximity assay strategy. GABA concentration-dependently enhanced the magnitude of [(35)S]GTPgammaS binding to Galphao and, less markedly, Galphai(1/3) in cortex, whereas Gq and Gs/olf were unaffected. (R)-baclofen and SKF97581 likewise activated Galphao and Galphai(1/3), expressing their actions more potently than GABA. Similar findings were acquired in hippocampus and cerebellum, and the GABA(B) antagonist, CGP55845A, abolished agonist-induced activation of Galphao and Galphai(1/3) in all structures. The PAMs, GS39783, CGP7930 and CGP13501, inactive alone, enhanced efficacy and potency of agonist-induced [(35)S]GTPgammaS binding to Galphao in all regions, actions abolished by CGP55845A. In contrast, they did not modify efficacies at Galphai(1/3). Similarly, in human embryonic kidney cells expressing GABA(B(1a+2)) or GABA(B(1b+2)) receptors, allosteric modulators did not detectably enhance efficacy of GABA at Galphai(1/3), though they increased its potency. To summarise, GABA(B) receptors coupled both to Galphao and to Galphai, but not Gq and Gs/olf, in rat brain. PAMs more markedly enhanced efficacy of coupling to Go versus Gi(1/3). It will be of interest to confirm these observations employing complementary techniques and to evaluate their potential therapeutic significance.
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12
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Li DP, Pan HL. Plasticity of GABAergic control of hypothalamic presympathetic neurons in hypertension. Am J Physiol Heart Circ Physiol 2005; 290:H1110-9. [PMID: 16243912 DOI: 10.1152/ajpheart.00788.2005] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Increased sympathetic outflow contributes to the pathogenesis of hypertension. However, the mechanisms of increased sympathetic drive in hypertension remain unclear. We examined the tonic GABAergic inhibition in control of the excitability of paraventricular (PVN) presympathetic neurons in spontaneously hypertensive rats (SHR) and normotensive controls, including Sprague-Dawley (SD) and Wistar-Kyoto (WKY) rats. Whole cell patch-clamp recordings were performed on retrogradely labeled PVN neurons projecting to the rostral ventrolateral medulla (RVLM) in brain slices. The basal firing rate of PVN neurons was significantly decreased in 13-wk-old SD and WKY rats but increased in 13-wk-old SHR, compared with their respective 6-wk-old controls. The GABA(A) antagonist bicuculline consistently increased the firing of PVN neurons in normotensive controls. Surprisingly, bicuculline either decreased the firing or had no effect in 59.3% of labeled cells in 13-wk-old SHR. In contrast, the GABA(B) antagonist CGP-55845 had no effect on the firing of PVN neurons in normotensive controls but significantly increased the firing of 75% of cells studied in 13-wk-old SHR. Furthermore, the evoked GABA(A) current decreased significantly in labeled PVN neurons of 13-wk-old SHR compared with that in normotensive controls. Both the frequency and amplitude of GABAergic spontaneously inhibitory postsynaptic currents were also reduced in 13-wk-old SHR. This study demonstrates an unexpected functional change in GABA(A) and GABA(B) receptors in regulation of the firing activity of PVN-RVLM neurons in SHR. This change in GABA(A) receptor function and GABAergic inputs to PVN output neurons may contribute to increased sympathetic outflow in hypertension.
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Affiliation(s)
- De-Pei Li
- Department of Anesthesiology H187, Pennsylvania State University College of Medicine, 500 University Dr., Hershey, Pennsylvania 17033, USA
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13
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Abstract
The study of pain development has come into its own. Reaping the rewards of years of developmental and molecular biology, it has now become possible to translate fundamental knowledge of signalling pathways and synaptic physiology into a better understanding of infant pain. Research has cast new light on the physiological and pharmacological processes that shape the newborn pain response, which will help us to understand early pain behaviour and to design better treatments. Furthermore, it has shown how developing pain circuitry depends on non-noxious sensory activity in the healthy newborn, and how early injury can permanently alter pain processing.
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Affiliation(s)
- Maria Fitzgerald
- Department of Anatomy and Developmental Biology, Wellcome Pain Consortium; University College London, Gower Street, London, WC1E 6BT, UK.
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14
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Brooks JW, Thompson SWN, Rice ASC, Malcangio M. (S)-AMPA inhibits electrically evoked calcitonin gene-related peptide (CGRP) release from the rat dorsal horn: reversal by cannabinoid receptor antagonist SR141716A. Neurosci Lett 2004; 372:85-8. [PMID: 15531093 DOI: 10.1016/j.neulet.2004.09.014] [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: 07/27/2004] [Revised: 09/03/2004] [Accepted: 09/08/2004] [Indexed: 12/27/2022]
Abstract
Previous studies in the hippocampus and cerebellum demonstrate that depolarisation of postsynaptic neurones stimulates the rapid synthesis and release of an endocannabinoid that retrogradely interacts with pre-synaptic CB(1) to modulate neurotransmitter release. This study evaluated whether depolarisation of second order neurones in the dorsal horn of the spinal cord by the AMPA receptor agonist, (S)-AMPA, would modulate sensory neurotransmission via release of endocannabinoids. Using an isolated rat dorsal horn with dorsal root attached in vitro preparation the release of calcitonin gene-related peptide (CGRP) after electrical stimulation of the dorsal roots was measured. Superfusion of either WIN55,212-2 (1 microM) or (S)-AMPA (1 microM) significantly attenuated CGRP release in a CB(1)-dependent manner (SR141716A, 5 microM). This provides indirect pharmacological evidence for an AMPA-evoked release of endogenous cannabinoids inhibiting peptide release from primary afferent neurons. This study confirms that CGRP release from the dorsal horn is modulated via CB(1) activation. Furthermore a depolarising stimulus also modulates CGRP release, potentially via the release of endogenous cannabinoids.
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Affiliation(s)
- J W Brooks
- Pain Research Group, Department of Anaesthetics, Faculty of Medicine, Imperial College, London SW109NH, UK
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Baccei ML, Fitzgerald M. Development of GABAergic and glycinergic transmission in the neonatal rat dorsal horn. J Neurosci 2004; 24:4749-57. [PMID: 15152035 PMCID: PMC6729459 DOI: 10.1523/jneurosci.5211-03.2004] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Cutaneous spinal sensory transmission appears to lack inhibitory control in the newborn spinal cord, but the properties of GABAergic and glycinergic synapses in the neonatal dorsal horn have not been characterized. Whole-cell patch-clamp recordings from rat superficial dorsal horn neurons in spinal cord slices at postnatal day 0 (P0) to P2, P6-P7, and P13-P14 revealed an age-dependent increase in the frequency of spontaneous IPSCs, which were abolished by the GABA(A) receptor (GABA(A)R) antagonist bicuculline between P0 and P7 but not at P14. GABA(A)R-mediated miniature IPSCs (mIPSCs), but not glycinergic mIPSCs, were present at birth, and GABA mIPSCs remained more frequent than glycine mIPSCs at all ages. Sciatic nerve stimulation resulted in IPSCs with both GABAergic and glycinergic components, although a larger contribution arose from GABA(A) receptors at all ages. In gramicidin perforated patch-clamp recordings, exogenous GABA applications produced depolarization in 40% of neurons at P0-P2, but the reversal potential of GABA-evoked currents (E(GABA)) was consistently more negative than action potential threshold at this age. By P6-P7, GABA evoked only membrane hyperpolarization. The GABA(B)R agonist baclofen elicited an outward current in all neurons with peak amplitudes observed by P6-P7 and abolished sciatic nerve-evoked monosynaptic glutamatergic EPSCs in all groups. The results show considerable postnatal development of inhibitory processing in the dorsal horn with GABAergic mechanisms initially dominant over glycinergic events. GABA(A)R-mediated depolarizations during the first postnatal week are likely to be important for the maturation of spinal networks but do not provide a major excitatory drive to the newborn dorsal horn.
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Affiliation(s)
- Mark L Baccei
- Department of Anatomy and Developmental Biology, University College London, London WC1E 6BT, United Kingdom.
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Bandrowski AE, Huguenard JR, Prince DA. Baseline glutamate levels affect group I and II mGluRs in layer V pyramidal neurons of rat sensorimotor cortex. J Neurophysiol 2003; 89:1308-16. [PMID: 12626613 PMCID: PMC3005275 DOI: 10.1152/jn.00644.2002] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Possible functional roles for glutamate that is detectable at low concentrations in the extracellular space of intact brain and brain slices have not been explored. To determine whether this endogenous glutamate acts on metabotropic glutamate receptors (mGluRs), we obtained whole cell recordings from layer V pyramidal neurons of rat sensorimotor cortical slices. Blockade of mGluRs with (+)-alpha-amino-4-carboxy-alpha-methyl-benzeacetic acid (MCPG, a general mGluR antagonist) increased the mean amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), an effect attributable to a selective increase in the occurrence of large amplitude sEPSCs. 2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-yl)propanoic acid (LY341495, a group II antagonist) increased, but R(-)-1-amino-2,3-dihydro-1H-indene-1,5-dicarboxylic acid (AIDA) and (RS)-hexyl-HIBO (group I antagonists) decreased sEPSC amplitude, and (R,S)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG, a group III antagonist) did not change it. The change in sEPSCs elicited by MCPG, AIDA, and LY341495 was absent in tetrodotoxin, suggesting that it was action potential-dependent. The increase in sEPSCs persisted in GABA receptor antagonists, indicating that it was not due to effects on inhibitory interneurons. AIDA and (S)-3,5-dihydroxyphenylglycine (DHPG, a group I agonist) elicited positive and negative shifts in holding current, respectively. LY341495 and (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV, a group II agonist) elicited negative and positive shifts in holding current, respectively. The AIDA and LY341495 elicited currents persisted in TTX. Finally, in current clamp, LY341495 depolarized cells by approximately 2 mV and increased the number of action potentials to a given depolarizing current pulse. Thus ambient levels of glutamate tonically activate mGluRs and regulate cortical excitability.
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Affiliation(s)
- A E Bandrowski
- Department of Neurology, Stanford University Medical Center, Stanford, California 94305, USA
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Kombian SB, Hirasawa M, Matowe WC, Pittman QJ. GABA(B) receptors modulate short-term potentiation of spontaneous excitatory postsynaptic currents in the rat supraoptic nucleus in vitro. Neuropharmacology 2001; 41:554-64. [PMID: 11587710 DOI: 10.1016/s0028-3908(01)00098-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
High-frequency stimulation of afferents to the supraoptic nucleus (SON) results in a robust increase in the frequency and amplitude of pharmacologically isolated, tetrodotoxin-resistant, miniature excitatory postsynaptic currents (mEPSCs) lasting for 5-20 min. This increase in mEPSC frequency, termed short-term potentiation (STP), is tightly coupled to increases in action potential firing in magnocellular neurons (MCNs) suggesting a functional role for STP. gamma-Aminobutyric acid (GABA), acting selectively on GABA(B) receptors, has been shown to modulate action potential-dependent EPSCs, as well as mEPSCs in this nucleus. In this study, we examined the role of GABA in STP. Using in vitro hypothalamic slices containing the SON and the nystatin perforated-patch recording technique to record from MCNs, we tested the hypothesis that GABA modulates STP. Baclofen, a GABA(B) receptor agonist, caused a reversible decrease in the frequency of mEPSCs as well as a reduction in the magnitude and duration of STP. GABA(B) receptor antagonists blocked the baclofen-induced decrease in mEPSC frequency and reduction in STP. In addition, the antagonists by themselves increased basal mEPSC frequency while prolonging the duration of STP in most cells. By contrast, picrotoxin, a GABA(A) chloride channel blocker, had no effect on STP.These findings indicate that GABA is tonically present in the SON and its action at the GABA(B) receptor may determine the magnitude and duration of STP.
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Affiliation(s)
- S B Kombian
- Faculty of Pharmacy, Kuwait University, PO Box 24923, 13110, Safat, Kuwait.
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Storer RJ, Akerman S, Goadsby PJ. GABA receptors modulate trigeminovascular nociceptive neurotransmission in the trigeminocervical complex. Br J Pharmacol 2001; 134:896-904. [PMID: 11606331 PMCID: PMC1573015 DOI: 10.1038/sj.bjp.0704325] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2001] [Revised: 07/31/2001] [Accepted: 08/03/2001] [Indexed: 11/09/2022] Open
Abstract
1. GABA (gamma-aminobutyric acid) receptors involved in craniovascular nociceptive pathways were characterised by in vivo microiontophoresis of GABA receptor agonists and antagonists onto neurones in the trigeminocervical complex of the cat. 2. Extracellular recordings were made from neurones in the trigeminocervical complex activated by supramaximal electrical stimulation of superior sagittal sinus, which were subsequently stimulated with L-glutamate. 3. Cell firing evoked by microiontophoretic application of L-glutamate (n=30) was reversibly inhibited by GABA in every cell tested (n=19), the GABA(A) agonist muscimol (n=10) in all cells tested, or both where tested, but not by iontophoresis of either sodium or chloride ions at comparable ejection currents. Inhibited cells received wide dynamic range (WDR) or nociceptive specific input from cutaneous receptive fields on the face or forepaws. 4. The inhibition of trigeminal neurones by GABA or muscimol could be antagonized by the GABA(A) antagonist N-methylbicuculline, 1(S),9(R) in all but two cells tested (n=16), but not by the GABA(B) antagonist 2-hydroxysaclofen (n=11). 5. R(-)-baclofen, a GABA(B) agonist, inhibited the firing of three out of seven cells activated by L-glutamate. Where tested, this inhibition could be antagonized by 2-hydroxysaclofen. These baclofen-inhibited cells were characterized as having low threshold mechanoreceptor/WDR input. 6. GABA thus appears to modulate nociceptive input to the trigeminocervical complex mainly through GABA(A) receptors. GABA(A) receptors may therefore provide a target for the development of new therapeutic agents for primary headache disorders.
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Affiliation(s)
- R James Storer
- Headache Group, Institute of Neurology, The National Hospital for Neurology and Neurosurgery, Queen Square, London
| | - Simon Akerman
- Headache Group, Institute of Neurology, The National Hospital for Neurology and Neurosurgery, Queen Square, London
| | - Peter J Goadsby
- Headache Group, Institute of Neurology, The National Hospital for Neurology and Neurosurgery, Queen Square, London
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Ataka T, Kumamoto E, Shimoji K, Yoshimura M. Baclofen inhibits more effectively C-afferent than Adelta-afferent glutamatergic transmission in substantia gelatinosa neurons of adult rat spinal cord slices. Pain 2000; 86:273-282. [PMID: 10812257 DOI: 10.1016/s0304-3959(00)00255-4] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Although intrathecal administration of baclofen, a selective GABA(B)-receptor agonist, is known to have an antinociceptive effect on various pain models, the role of presynaptic GABA(B) receptors in antinociception is not well characterized. In the present study, the action of baclofen on primary afferent-evoked glutamatergic excitatory transmission was examined in substantia gelatinosa (SG) neurons of an adult rat spinal cord slice with an attached dorsal root, prepared from the lumbar segment, by use of the blind whole-cell patch-clamp technique. Under the condition where a postsynaptic action of baclofen was inhibited, baclofen (1 microM) reduced the amplitudes of excitatory postsynaptic currents (EPSCs; V(H)=-70 mV) which were monosynaptically evoked by stimulating primary-afferent C- and/or Adelta-fibers and which were remarkably depressed by CNQX (10 microM). The identification of the C-fiber or Adelta-fiber EPSC was based on antidromic action potentials recorded from neurons of isolated dorsal root ganglia. The C-fiber EPSC was depressed in peak amplitude by baclofen (1 microM) to a larger extent than the Adelta-fiber EPSC (20 and 45% of control, respectively). Each of the baclofen actions was suppressed by a selective GABA(B)-receptor antagonist, CGP 35348 (50 microM). Baclofen (1 microM) did not affect a response of SG neurons to bath-applied AMPA (10 microM). These results indicate that baclofen inhibits the release of L-glutamate from Adelta and C primary-afferent terminals in the SG through the activation of GABA(B) receptor; this action is more effective to C-fiber than Adelta-fiber transmission. Considering that the SG is the main part of termination of Adelta- and C-fibers transmitting nociceptive information, the present finding would account for at least a part of the inhibitory action of baclofen on pain transmission.
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Affiliation(s)
- Toyofumi Ataka
- Department of Physiology, Saga Medical School, 5-1-1 Nabeshima, Saga 849-8501, Japan Department of Anesthesiology, Niigata University School of Medicine, 1-757 Asahimachidori, Niigata 951-8510, Japan
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20
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Iyadomi M, Iyadomi I, Kumamoto E, Tomokuni K, Yoshimura M. Presynaptic inhibition by baclofen of miniature EPSCs and IPSCs in substantia gelatinosa neurons of the adult rat spinal dorsal horn. Pain 2000; 85:385-393. [PMID: 10781911 DOI: 10.1016/s0304-3959(99)00285-7] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Intrathecal administration of baclofen, a GABA(B)-receptor agonist, affects pain behavior induced by formalin in a biphasic manner; baclofen at low doses enhances pain while producing antinociception at high doses. This may be due to the fact that baclofen modulates each of excitatory and inhibitory transmission in the dorsal horn of the spinal cord with a distinct sensitivity, resulting in a biphasic action on pain transmission. To address this issue, we examined the actions of baclofen on miniature excitatory (glutamatergic) and inhibitory (GABAergic) postsynaptic currents (mEPSCs and mIPSCs, respectively) in substantia gelatinosa (SG) neurons of adult rat spinal cord slices by using the whole-cell voltage-clamp technique. Baclofen reduced the frequency of both mEPSC and mIPSC without a change in their amplitudes. These actions were dose-dependent in a concentration range of 0.1-100 microM; the effective concentrations for the half-inhibition of mEPSC and mIPSC frequency were 4.44+/-0. 60 microM (n=7) and 4.31+/-0.77 microM (n=6), respectively. These results indicate that each of glutamatergic and GABAergic nerve terminals in the SG is endowed with the GABA(B) receptor, the activation of which depresses the release of neurotransmitter from the terminal; this provides a cellular basis for the modulation of pain by baclofen. It is suggested from a similar affinity for baclofen of the GABA(B) receptors on both terminals that the baclofen-induced biphasic action on pain behaviors cannot be accounted for by only its presynaptic actions in the SG and that other actions such as an inhibitory action of baclofen on postsynaptic neurons also have to be taken into consideration.
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Affiliation(s)
- Minako Iyadomi
- Department of Physiology, Saga Medical School, 5-1-1 Nabeshima, Saga 849-8501, Japan Department of Community Health Science, Saga Medical School, 5-1-1 Nabeshima, Saga 849-8501, Japan Department of Anesthesiology, Saga Medical School, 5-1-1 Nabeshima, Saga 849-8501, Japan
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21
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Bussières N, El Manira A. GABA(B) receptor activation inhibits N- and P/Q-type calcium channels in cultured lamprey sensory neurons. Brain Res 1999; 847:175-85. [PMID: 10575086 DOI: 10.1016/s0006-8993(99)02002-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In lamprey, sensory transmission from mechanosensory receptors (dorsal cells) to central neurons is presynaptically inhibited by GABA(B) receptor activation. The mechanisms underlying this effect were investigated using isolated dorsal cells, where voltage-dependent calcium currents were recorded in the whole-cell configuration. Activation of GABA(B) receptors by baclofen decreased the peak amplitude of high voltage-activated (HVA) calcium currents and slowed the activation phase. The role of G-proteins in mediating the effects of baclofen was examined. Intracellular dialysis of GTPgammaS occluded the effects of baclofen. Intracellular dialysis of GDPbetaS and preincubation in pertussis toxin both attenuated the effect of baclofen. Specific calcium channel blockers were used to study the types of HVA calcium channels involved in the GABA(B)-mediated modulation. The baclofen-induced inhibition was not affected by the L-type calcium channel antagonist nimodipine, but was partially blocked by the N-type blocker omega-conotoxin GVIA, and completely occluded by omega-conotoxin MVIIC, a blocker of both N- and P/Q-type channels. The pharmacology of dorsal cell GABA(B) receptors was studied using two agonists, baclofen and CGP 27492, and four antagonists, CGP 35348, CGP 55845, phaclofen and saclofen. The inhibition induced by either of the two agonists was blocked by CGP 55845, phaclofen and saclofen. The antagonist CGP 35348 completely blocked the inhibition of HVA calcium current induced by the agonist CGP 27492, but had no effect on baclofen-induced GABA(B) receptor activation. This study thus demonstrates that GABA(B) receptor activation in lamprey mechanosensory neurons inhibits N- and P/Q-type calcium channels in a voltage- and G-protein-dependent manner.
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Affiliation(s)
- N Bussières
- The Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, S-171 77, Stockholm, Sweden
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22
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Vigot R, Batini C. Purkinje cell inhibitory responses to 3-APPA (3-aminopropylphosphinic acid) in RAT cerebellar slices. Neurosci Res 1999; 34:141-7. [PMID: 10515256 DOI: 10.1016/s0168-0102(99)00044-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
3-APPA is considered to be a GABA(B) agonist more potent than baclofen. We report here the results obtained by applying this agonist to Purkinje cells (PCs) recorded in current clamp mode on cerebellar slices. The responses were compared to those obtained with other GABA agonists and antagonists. The drugs were delivered either in the perfusion solution or by pressure to the molecular layer near the recorded cell. When applied to the PCs either in the bathing medium or by pressure, 3-APPA evoked a potent inhibitory response which was however different from that obtained with baclofen. The response was complex and similar to that evoked by application of GABA, the endogenous neurotransmitter. In fact it showed: (1) very sensitive dose-response not affected by TTX in the bath; (2) an equilibrium potential compatible with Cl-channel conductance; (3) a massive reduction with the competitive GABA(A) antagonist bicuculline; (4) a small reduction, if any, with the potent competitive GABA(B) antagonist CGP55845A; (5) persistence of the responses under 4-AP (4-aminopyridine), the potassium channel blocker, and inhibition of the 4-AP-induced calcium bursts of spikes. The conclusion was reached that the inhibitory response of PCs to 3-APPA is induced, like GABA inhibition, by binding to both GABA(A) and GABA(B) postsynaptic receptors.
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Affiliation(s)
- R Vigot
- Laboratoire de Physiologie de la Motricité, CNRS UMR 9923, Université Pierre et Marie Curie, CHU Pitié-Salpêtrière, Paris, France
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Grudt TJ, Henderson G. Glycine and GABAA receptor-mediated synaptic transmission in rat substantia gelatinosa: inhibition by mu-opioid and GABAB agonists. J Physiol 1998; 507 ( Pt 2):473-83. [PMID: 9518706 PMCID: PMC2230795 DOI: 10.1111/j.1469-7793.1998.473bt.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/1997] [Accepted: 11/10/1997] [Indexed: 11/28/2022] Open
Abstract
1. Bicuculline-sensitive and strychnine-sensitive inhibitory postsynaptic currents (IPSCs) could be evoked in neurones of the rat substantia gelatinosa of the spinal trigeminal nucleus pars caudalis. 2. Spontaneous tetrodotoxin (TTX)-insensitive-mediated miniature IPSCs (mIPSCs) blocked by strychnine or bicuculline were also present in many neurones. The decay of the glycine receptor-mediated mIPSCs was fitted by a single exponential, whereas the decay of the GABAA receptor-mediated mIPSCs could in some instances be fitted by a single exponential, but in other instances required two exponentials. 3. An increase in baseline current noise developed during the course of the recording. This noise was abolished by strychnine (1 microM) but was insensitive to bicuculline (10 microM), TTX (0.5 microM), [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO, 1 microM) or baclofen (30 microM). The single-channel conductance underlying the noise was estimated to be 21 pS. 4. The mu-opioid agonist DAMGO (1-10 microM) reduced the amplitude of the evoked glycine receptor-mediated IPSC and the evoked GABAA receptor-mediated IPSC. The mu-opioid antagonist D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP, 1 microM) reversed the DAMGO inhibition. 5. The GABAB agonist baclofen (30 microM) reduced the amplitude of the evoked glycine receptor-mediated IPSC and the GABAA receptor-mediated IPSC. The inhibition was reversed by the selective GABAB antagonist 3-N[1-(S)-(3,4-dichlorophenyl)ethyl]amino- 2-(S)-hydroxypropyl-P-benzyl-phosphinic acid (CGP 55845A, 1 microM). 6. Both DAMGO and baclofen reduced the frequency of glycine and GABAA receptor-mediated mIPSCs without affecting average amplitude, and increased the percentage of failures of the evoked glycine and GABAA receptor-mediated IPSCs, suggesting a presynaptic site of action.
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Affiliation(s)
- T J Grudt
- Department of Pharmacology, School of Medical Sciences, Bristol, UK
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Cao CQ, Tse HW, Jane DE, Evans RH, Headley PM. Metabotropic glutamate receptor antagonists, like GABA(B) antagonists, potentiate dorsal root-evoked excitatory synaptic transmission at neonatal rat spinal motoneurons in vitro. Neuroscience 1997; 78:243-50. [PMID: 9135104 DOI: 10.1016/s0306-4522(96)00579-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Recordings of whole-cell synaptic current responses elicited by electrical stimulation of dorsal roots were made from motoneurons, identified by antidromic invasion, in isolated spinal cord preparations from five- to eight-day-old Wistar rats. Supramaximal electrical stimulation of the dorsal root evoked complex excitatory postsynaptic currents with mean latencies (+/- S.E.M.) of 6.1 +/- 0.26 ms, peak amplitude of -650 +/- 47 pA and duration of 4.30 +/- 0.46 s (n=34). All phases of excitatory postsynaptic currents were potentiated to approximately 20% above control levels in the presence of the metabotropic glutamate receptor antagonists S-2-amino-2-methyl-4-phosphonobutanoate (MAP4; 200 microM; n=15) and 2S, 1'S,2'S-2-methyl-2-(carboxycyclopropyl)glycine (MCCG; 200 microM; n=9). A similar level of potentiation was produced by the GABA(B) receptor antagonist 3-N[1-(S)-(3,4-dichlorophenyl)ethyl]amino-2-(S)-hydroxypropyl-P-benzyl-p hosphinic acid (CGP55845; 200 nM; n=5). MAP4 (200 microM) produced a six-fold rightward shift in the concentration-effect plot for the depressant action of the metabotropic glutamate receptor agonist S-2-amino-4-phosphonobutanoate (L-AP4), whereas CGP55845 produced no significant change in the potency of L-AP4. MAP4 did not antagonize the depressant actions of baclofen (n=8), 1S,3S-1-aminocyclopentane-1,3-dicarboxylate (n=4) or 2-S,1'S,2'S-2-(carboxycyclopropyl)glycine (n=4). The metabotropic glutamate receptor antagonists produced no change in the holding current of any of the neurons, indicating that they had no significant postsynaptic excitatory actions. These results are the first to indicate a possible physiological role for metabotropic glutamate receptors in the spinal cord. Like GABA(B) receptors, they control glutamatergic synaptic transmission in the segmental spinal pathway to motoneurons. This is likely to be a presynaptic control mechanism.
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Affiliation(s)
- C Q Cao
- Department of Pharmacology, School of Medical Sciences, Bristol, U.K
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25
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GABAB receptor antagonists:New tools and potential new drugs. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s0165-7208(96)80021-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/05/2023]
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Abstract
GABAB receptors are a distinct subclass of receptors for the major inhibitory transmitter 4-aminobutanoic acid (GABA) that mediate depression of synaptic transmission and contribute to the inhibition controlling neuronal excitability. The development of specific agonists and antagonists for these receptors has led to a better understanding of their physiology and pharmacology, highlighting their diverse coupling to different intracellular effectors through Gi/G(o) proteins. This review emphasises our current knowledge of the neurophysiology and neurochemistry of GABAB receptors, including their heterogeneity, as well as the therapeutic potential of drugs acting at these sites.
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Affiliation(s)
- D I Kerr
- Department of Anaesthesia and Intensive Care, University of Adelaide, Australia
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