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Cathenaut L, Schlichter R, Hugel S. Short-term plasticity in the spinal nociceptive system. Pain 2023; 164:2411-2424. [PMID: 37578501 DOI: 10.1097/j.pain.0000000000002999] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Accepted: 06/08/2023] [Indexed: 08/15/2023]
Abstract
ABSTRACT Somatosensory information is delivered to neuronal networks of the dorsal horn (DH) of the spinal cord by the axons of primary afferent neurons that encode the intensity of peripheral sensory stimuli under the form of a code based on the frequency of action potential firing. The efficient processing of these messages within the DH involves frequency-tuned synapses, a phenomenon linked to their ability to display activity-dependent forms of short-term plasticity (STP). By affecting differently excitatory and inhibitory synaptic transmissions, these STP properties allow a powerful gain control in DH neuronal networks that may be critical for the integration of nociceptive messages before they are forwarded to the brain, where they may be ultimately interpreted as pain. Moreover, these STPs can be finely modulated by endogenous signaling molecules, such as neurosteroids, adenosine, or GABA. The STP properties of DH inhibitory synapses might also, at least in part, participate in the pain-relieving effect of nonpharmacological analgesic procedures, such as transcutaneous electrical nerve stimulation, electroacupuncture, or spinal cord stimulation. The properties of target-specific STP at inhibitory DH synapses and their possible contribution to electrical stimulation-induced reduction of hyperalgesic and allodynic states in chronic pain will be reviewed and discussed.
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Affiliation(s)
- Lou Cathenaut
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, Strasbourg, France
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2
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A Historical Review of Brain Drug Delivery. Pharmaceutics 2022; 14:pharmaceutics14061283. [PMID: 35745855 PMCID: PMC9229021 DOI: 10.3390/pharmaceutics14061283] [Citation(s) in RCA: 49] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 06/01/2022] [Accepted: 06/07/2022] [Indexed: 12/13/2022] Open
Abstract
The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.
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3
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Pardridge WM. Blood-brain barrier delivery for lysosomal storage disorders with IgG-lysosomal enzyme fusion proteins. Adv Drug Deliv Rev 2022; 184:114234. [PMID: 35307484 DOI: 10.1016/j.addr.2022.114234] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 02/25/2022] [Accepted: 03/14/2022] [Indexed: 12/12/2022]
Abstract
The majority of lysosomal storage diseases affect the brain. Treatment of the brain with intravenous enzyme replacement therapy is not successful, because the recombinant lysosomal enzymes do not cross the blood-brain barrier (BBB). Biologic drugs, including lysosomal enzymes, can be re-engineered for BBB delivery as IgG-enzyme fusion proteins. The IgG domain of the fusion protein is a monoclonal antibody directed against an endogenous receptor-mediated transporter at the BBB, such as the insulin receptor or the transferrin receptor. This receptor transports the IgG across the BBB, in parallel with the endogenous receptor ligand, and the IgG acts as a molecular Trojan horse to ferry into brain the lysosomal enzyme genetically fused to the IgG. The IgG-enzyme fusion protein is bi-functional and retains both high affinity binding for the BBB receptor, and high lysosomal enzyme activity. IgG-lysosomal enzymes are presently in clinical trials for treatment of the brain in Mucopolysaccharidosis.
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4
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Zhao M, Shao C, Dong J, Chen Q, Ma R, Jiang P, Zhang WN, Yang K. GABA B receptors constrain glutamate presynaptic release and postsynaptic actions in substantia gelatinosa of rat spinal cord. Brain Struct Funct 2022; 227:1893-1905. [PMID: 35318502 DOI: 10.1007/s00429-022-02481-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2021] [Accepted: 03/06/2022] [Indexed: 11/25/2022]
Abstract
The substantia gelatinosa (SG, lamina II of spinal cord gray matter) is pivotal for modulating nociceptive information from the peripheral to the central nervous system. γ-Aminobutyric acid type B receptors (GABABRs), the metabotropic GABA receptor subtype, are widely expressed in pre- and postsynaptic structures of the SG. Activation of GABABRs by exogenous agonists induces both pre- and postsynaptic inhibition. However, the actions of endogenous GABA via presynaptic GABABRs on glutamatergic synapses, and the postsynaptic GABABRs interaction with glutamate, remain elusive. In the present study, first, using in vitro whole-cell recordings and taking minimal stimulation strategies, we found that in rat spinal cord glutamatergic synapses, blockade of presynaptic GABABRs switched "silent" synapses into active ones and increased the probability of glutamate release onto SG neurons; increasing ambient GABA concentration mimicked GABABRs activation on glutamatergic terminals. Next, using holographic photostimulation to uncage glutamate on postsynaptic SG neurons, we found that postsynaptic GABABRs modified glutamate-induced postsynaptic potentials. Taken together, our data identify that endogenous GABA heterosynaptically constrains glutamate release via persistently activating presynaptic GABABRs; and postsynaptically, GABABRs modulate glutamate responses. The results give new clues for endogenous GABA in modulating the nociception circuit of the spinal dorsal horn and shed fresh light on the postsynaptic interaction of glutamate and GABA.
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Affiliation(s)
- Mingwei Zhao
- Department of Anatomy, School of Medicine, Jiangsu University, Zhenjiang, 212013, Jiangsu, China
| | - Caifeng Shao
- Department of Anatomy, School of Medicine, Jiangsu University, Zhenjiang, 212013, Jiangsu, China
| | - Jiaxue Dong
- Department of Anatomy, School of Medicine, Jiangsu University, Zhenjiang, 212013, Jiangsu, China
| | - Qian Chen
- Department of Anatomy, School of Medicine, Jiangsu University, Zhenjiang, 212013, Jiangsu, China
| | - Rui Ma
- Department of Anatomy, School of Medicine, Jiangsu University, Zhenjiang, 212013, Jiangsu, China
| | - Ping Jiang
- Department of Anatomy, School of Medicine, Jiangsu University, Zhenjiang, 212013, Jiangsu, China
| | - Wei-Ning Zhang
- Department of Pathophysiology, School of Medicine, Jiangsu University, Zhenjiang, 212013, Jiangsu, China
| | - Kun Yang
- Department of Anatomy, School of Medicine, Jiangsu University, Zhenjiang, 212013, Jiangsu, China. .,Department of Neurology, University of Maryland School of Medicine, Baltimore, MD, 21201, USA.
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5
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Inhibitory interneurons with differential plasticities at their connections tune excitatory/inhibitory balance in the spinal nociceptive system. Pain 2021; 163:e675-e688. [PMID: 34490851 DOI: 10.1097/j.pain.0000000000002460] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Accepted: 08/18/2021] [Indexed: 11/25/2022]
Abstract
ABSTRACT Networks of the dorsal-horn of the spinal-cord process nociceptive information from the periphery. In these networks, the excitation/inhibition balance is critical to shape this nociceptive information and to gate it to the brain where it is interpreted as pain. Our aim was to define whether short-term plasticity of inhibitory connections could tune this inhibition/excitation balance by differentially controlling excitatory and inhibitory microcircuits. To this end, we used spinal-cord slices from adult mice expressing enhanced green fluorescent protein (eGFP) under the GAD65 promoter and recorded from both eGFP+ (putative inhibitory) and eGFP- (putative excitatory) neurons of lamina II while stimulating single presynaptic GABAergic interneurons at various frequencies. Our results indicate that GABAergic neurons of lamina II simultaneously contact eGFP- and eGFP+ neurons, but these connections display very different frequency-dependent short-term plasticities. Connections onto eGFP- interneurons displayed limited frequency-dependent changes, and strong time-dependent summation of inhibitory synaptic currents that was however subjected to a tonic activity-dependent inhibition involving A1 adenosine receptors. In contrast, GABAergic connections onto eGFP+ interneurons expressed pronounced frequency-dependent depression, thus favoring disinhibition at these synapses by a mechanism involving the activation of GABAB autoreceptors at low frequency. Interestingly, the balance favors inhibition at frequencies associated with intense pain whether it favors excitation at frequencies associated with low pain. Therefore, these target- and frequency-specific plasticities allow to tune the balance between inhibition and disinhibition while processing frequency-coded information from primary afferents. These short-term plasticities and their modulation by A1 and GABAB receptors might represent an interesting target in pain-alleviating strategies.
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6
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Presynaptic Inhibition of Pain and Touch in the Spinal Cord: From Receptors to Circuits. Int J Mol Sci 2021; 22:ijms22010414. [PMID: 33401784 PMCID: PMC7795800 DOI: 10.3390/ijms22010414] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Revised: 12/28/2020] [Accepted: 12/30/2020] [Indexed: 02/07/2023] Open
Abstract
Sensory primary afferent fibers, conveying touch, pain, itch, and proprioception, synapse onto spinal cord dorsal horn neurons. Primary afferent central terminals express a wide variety of receptors that modulate glutamate and peptide release. Regulation of the amount and timing of neurotransmitter release critically affects the integration of postsynaptic responses and the coding of sensory information. The role of GABA (γ-aminobutyric acid) receptors expressed on afferent central terminals is particularly important in sensory processing, both in physiological conditions and in sensitized states induced by chronic pain. During the last decade, techniques of opto- and chemogenetic stimulation and neuronal selective labeling have provided interesting insights on this topic. This review focused on the recent advances about the modulatory effects of presynaptic GABAergic receptors in spinal cord dorsal horn and the neural circuits involved in these mechanisms.
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Papon MA, Le Feuvre Y, Barreda-Gómez G, Favereaux A, Farrugia F, Bouali-Benazzouz R, Nagy F, Rodríguez-Puertas R, Landry M. Spinal Inhibition of GABAB Receptors by the Extracellular Matrix Protein Fibulin-2 in Neuropathic Rats. Front Cell Neurosci 2020; 14:214. [PMID: 32765223 PMCID: PMC7378325 DOI: 10.3389/fncel.2020.00214] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Accepted: 06/17/2020] [Indexed: 12/23/2022] Open
Abstract
In the central nervous system, the inhibitory GABAB receptor is the archetype of heterodimeric G protein-coupled receptors (GPCRs). Receptor interaction with partner proteins has emerged as a novel mechanism to alter GPCR signaling in pathophysiological conditions. We propose here that GABAB activity is inhibited through the specific binding of fibulin-2, an extracellular matrix protein, to the B1a subunit in a rat model of neuropathic pain. We demonstrate that fibulin-2 hampers GABAB activation, presumably through decreasing agonist-induced conformational changes. Fibulin-2 regulates the GABAB-mediated presynaptic inhibition of neurotransmitter release and weakens the GABAB-mediated inhibitory effect in neuronal cell culture. In the dorsal spinal cord of neuropathic rats, fibulin-2 is overexpressed and colocalized with B1a. Fibulin-2 may thus interact with presynaptic GABAB receptors, including those on nociceptive afferents. By applying anti-fibulin-2 siRNA in vivo, we enhanced the antinociceptive effect of intrathecal baclofen in neuropathic rats, thus demonstrating that fibulin-2 limits the action of GABAB agonists in vivo. Taken together, our data provide an example of an endogenous regulation of GABAB receptor by extracellular matrix proteins and demonstrate its functional impact on pathophysiological processes of pain sensitization.
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Affiliation(s)
- Marie-Amélie Papon
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | - Yves Le Feuvre
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | | | - Alexandre Favereaux
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | - Fanny Farrugia
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | - Rabia Bouali-Benazzouz
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | - Frédéric Nagy
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | | | - Marc Landry
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
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Nasirinezhad F, Hosseini M, Karami Z, Janzadeh A, Yousefifard M. Comparative Efficacy of GABAA and GABAB Receptor Agonists in Pain Alleviation in a Spinal Cord Injury Model of Neuropathic Pain. NEUROPHYSIOLOGY+ 2020. [DOI: 10.1007/s11062-020-09826-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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9
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Molecular mechanisms of the antispasticity effects of baclofen on spinal ventral horn neurons. Neuroreport 2019; 30:19-25. [DOI: 10.1097/wnr.0000000000001155] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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10
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In vivo electrophysiological analysis of mechanisms of monoaminergic pain inhibitory systems. Pain 2018; 158 Suppl 1:S85-S91. [PMID: 28240646 DOI: 10.1097/j.pain.0000000000000844] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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11
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Brewer CL, Baccei ML. Enhanced Postsynaptic GABA B Receptor Signaling in Adult Spinal Projection Neurons after Neonatal Injury. Neuroscience 2018; 384:329-339. [PMID: 29885525 PMCID: PMC6053268 DOI: 10.1016/j.neuroscience.2018.05.046] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 04/28/2018] [Accepted: 05/30/2018] [Indexed: 12/19/2022]
Abstract
Clinical and basic science research have revealed persistent effects of early-life injury on nociceptive processing and resulting pain sensitivity. While recent work has identified clear deficits in fast GABAA- and glycine receptor-mediated inhibition in the adult spinal dorsal horn after neonatal tissue damage, the effects of early injury on slow, metabotropic inhibition within spinal pain circuits are poorly understood. Here we provide evidence that neonatal surgical incision significantly enhances postsynaptic GABAB receptor signaling within the mature superficial dorsal horn (SDH) in a cell type-dependent manner. In vitro patch-clamp recordings were obtained from identified lamina I projection neurons and GABAergic interneurons in the SDH of adult female mice following hindpaw incision at postnatal day (P)3. Early tissue damage increased the density of the outward current evoked by baclofen, a selective GABAB receptor agonist, in projection neurons but not inhibitory interneurons. This could reflect enhanced postsynaptic expression of downstream G protein-coupled inward-rectifying potassium channels (GIRKs), as the response to the GIRK agonist ML297 was greater in projection neurons from neonatally incised mice compared to naive littermate controls. Meanwhile, presynaptic GABAB receptor-mediated reduction of spontaneous neurotransmitter release onto both neuronal populations was unaffected by early-life injury. Collectively, our findings suggest that ascending nociceptive transmission to the adult brain is under stronger control by spinal metabotropic inhibition in the aftermath of neonatal tissue damage.
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Affiliation(s)
- Chelsie L Brewer
- Neuroscience Graduate Program, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Pain Research Center, Department of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267, USA
| | - Mark L Baccei
- Neuroscience Graduate Program, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Pain Research Center, Department of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267, USA.
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12
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Merighi A. The histology, physiology, neurochemistry and circuitry of the substantia gelatinosa Rolandi (lamina II) in mammalian spinal cord. Prog Neurobiol 2018; 169:91-134. [PMID: 29981393 DOI: 10.1016/j.pneurobio.2018.06.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 06/07/2018] [Accepted: 06/30/2018] [Indexed: 02/06/2023]
Abstract
The substantia gelatinosa Rolandi (SGR) was first described about two centuries ago. In the following decades an enormous amount of information has permitted us to understand - at least in part - its role in the initial processing of pain and itch. Here, I will first provide a comprehensive picture of the histology, physiology, and neurochemistry of the normal SGR. Then, I will analytically discuss the SGR circuits that have been directly demonstrated or deductively envisaged in the course of the intensive research on this area of the spinal cord, with particular emphasis on the pathways connecting the primary afferent fibers and the intrinsic neurons. The perspective existence of neurochemically-defined sets of primary afferent neurons giving rise to these circuits will be also discussed, with the proposition that a cross-talk between different subsets of peptidergic fibers may be the structural and functional substrate of additional gating mechanisms in SGR. Finally, I highlight the role played by slow acting high molecular weight modulators in these gating mechanisms.
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Affiliation(s)
- Adalberto Merighi
- Department of Veterinary Sciences, University of Turin, Largo Paolo Braccini 2, I-10095 Grugliasco (TO), Italy.
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13
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Top-down descending facilitation of spinal sensory excitatory transmission from the anterior cingulate cortex. Nat Commun 2018; 9:1886. [PMID: 29760484 PMCID: PMC5951839 DOI: 10.1038/s41467-018-04309-2] [Citation(s) in RCA: 136] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Accepted: 04/20/2018] [Indexed: 12/28/2022] Open
Abstract
Spinal sensory transmission is under descending biphasic modulation, and descending facilitation is believed to contribute to chronic pain. Descending modulation from the brainstem rostral ventromedial medulla (RVM) has been the most studied, whereas little is known about direct corticospinal modulation. Here, we found that stimulation in the anterior cingulate cortex (ACC) potentiated spinal excitatory synaptic transmission and this modulation is independent of the RVM. Peripheral nerve injury enhanced the spinal synaptic transmission and occluded the ACC-spinal cord facilitation. Inhibition of ACC reduced the enhanced spinal synaptic transmission caused by nerve injury. Finally, using optogenetics, we showed that selective activation of ACC-spinal cord projecting neurons caused behavioral pain sensitization, while inhibiting the projection induced analgesic effects. Our results provide strong evidence that ACC stimulation facilitates spinal sensory excitatory transmission by a RVM-independent manner, and that such top-down facilitation may contribute to the process of chronic neuropathic pain. It is known that descending facilitation of spinal responses may contribute to chronic pain, however many studies have focussed on brainstem mechanisms. Here the authors show that stimulation of the anterior cingulate cortex increases excitatory transmission in the dorsal horn, and that this may be via a direct pathway independent of the brainstem.
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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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15
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Functional Synaptic Integration of Forebrain GABAergic Precursors into the Adult Spinal Cord. J Neurosci 2017; 36:11634-11645. [PMID: 27852772 DOI: 10.1523/jneurosci.2301-16.2016] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Revised: 08/26/2016] [Accepted: 08/31/2016] [Indexed: 01/17/2023] Open
Abstract
Spinal cord transplants of embryonic cortical GABAergic progenitor cells derived from the medial ganglionic eminence (MGE) can reverse mechanical hypersensitivity in the mouse models of peripheral nerve injury- and paclitaxel-induced neuropathic pain. Here, we used electrophysiology, immunohistochemistry, and electron microscopy to examine the extent to which MGE cells integrate into host circuitry and recapitulate endogenous inhibitory circuits. Whether the transplants were performed before or after nerve injury, the MGE cells developed into mature neurons and exhibited firing patterns characteristic of subpopulations of cortical and spinal cord inhibitory interneurons. Conversely, the transplanted cells preserved cortical morphological and neurochemical properties. We also observed a robust anatomical and functional synaptic integration of the transplanted cells into host circuitry in both injured and uninjured animals. The MGE cells were activated by primary afferents, including TRPV1-expressing nociceptors, and formed GABAergic, bicuculline-sensitive, synapses onto host neurons. Unexpectedly, MGE cells transplanted before injury prevented the development of mechanical hypersensitivity. Together, our findings provide direct confirmation of an extensive, functional synaptic integration of MGE cells into host spinal cord circuits. This integration underlies normalization of the dorsal horn inhibitory tone after injury and may be responsible for the prophylactic effect of preinjury transplants. SIGNIFICANCE STATEMENT Spinal cord transplants of embryonic cortical GABAergic interneuron progenitors from the medial ganglionic eminence (MGE), can overcome the mechanical hypersensitivity produced in different neuropathic pain models in adult mice. Here, we examined the properties of transplanted MGE cells and the extent to which they integrate into spinal cord circuitry. Using electrophysiology, immunohistochemistry, and electron microscopy, we demonstrate that MGE cells, whether transplanted before or after nerve injury, develop into inhibitory neurons, are activated by nociceptive primary afferents, and form GABA-A-mediated inhibitory synapses with the host. Unexpectedly, cells transplanted into naive spinal cord prevented the development of nerve-injury-induced mechanical hypersensitivity. These results illustrate the remarkable plasticity of adult spinal cord and the potential of cell-based therapies against neuropathic pain.
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16
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Zemoura K, Ralvenius WT, Malherbe P, Benke D. The positive allosteric GABAB receptor modulator rac-BHFF enhances baclofen-mediated analgesia in neuropathic mice. Neuropharmacology 2016; 108:172-8. [PMID: 27108932 DOI: 10.1016/j.neuropharm.2016.04.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Revised: 04/01/2016] [Accepted: 04/20/2016] [Indexed: 10/21/2022]
Abstract
Neuropathic pain is associated with impaired inhibitory control of spinal dorsal horn neurons, which are involved in processing pain signals. The metabotropic GABAB receptor is an important component of the inhibitory system and is highly expressed in primary nociceptors and intrinsic dorsal horn neurons to control their excitability. Activation of GABAB receptors with the orthosteric agonist baclofen effectively reliefs neuropathic pain but is associated with severe side effects that prevent its widespread application. The recently developed positive allosteric GABAB receptor modulators lack most of these side effects and are therefore promising drugs for the treatment of pain. Here we tested the high affinity positive allosteric modulator rac-BHFF for its ability to relief neuropathic pain induced by chronic constriction of the sciatic nerve in mice. rac-BHFF significantly increased the paw withdrawal threshold to mechanical stimulation in healthy mice, indicating an endogenous GABABergic tone regulating the sensitivity to mechanical stimuli. Surprisingly, rac-BHFF displayed no analgesic activity in neuropathic mice although GABAB receptor expression was not affected in the dorsal horn as shown by quantitative receptor autoradiography. However, activation of spinal GABAB receptors by intrathecal injection of baclofen reduced hyperalgesia and its analgesic effect was considerably potentiated by co-application of rac-BHFF. These results indicate that under conditions of neuropathic pain the GABAergic tone is too low to provide a basis for allosteric modulation of GABAB receptors. However, allosteric modulators would be well suited as an add-on to reduce the dose of baclofen required to achieve analgesia.
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Affiliation(s)
- Khaled Zemoura
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - William T Ralvenius
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Pari Malherbe
- Discovery Neuroscience, F. Hoffmann-La Roche AG, pRED, Pharma Research & Early Development, Grenzacherstrasse 124, CH4070 Basel, Switzerland
| | - Dietmar Benke
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Neuroscience Center Zurich (ZNZ), Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Drug Discovery Network Zurich (DDNZ), Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
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18
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Salte K, Lea G, Franek M, Vaculin S. Baclofen reversed thermal place preference in rats with chronic constriction injury. Physiol Res 2015; 65:349-55. [PMID: 26447518 DOI: 10.33549/physiolres.933008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Chronic constriction injury to the sciatic nerve was used as an animal model of neuropathic pain. Instead of frequently used reflex-based tests we used an operant thermal place preference test to evaluate signs of neuropathic pain and the effect of baclofen administration in rats with neuropathy. Chronic constriction injury was induced by four loose ligations of the sciatic nerve. Thermal place preference (45 °C vs. 22 °C and 45 °C vs. 11 °C) was measured after the ligation and after the administration of baclofen in sham and experimental rats. Rats with the chronic constriction injury spent significantly less time on the colder plate compared to sham operated animals at the combination 45 °C vs. 11 °C. After administration of baclofen (10 mg/kg s.c.), the aversion to the colder plate in rats with chronic constriction injury disappeared. At the combination 45 °C vs. 22 °C, no difference in time spent on colder and/or warmer plate was found between sham and experimental animals. These findings show the importance of cold allodynia evaluation in rats with chronic constriction injury and the effectiveness of baclofen in this neuropathic pain model.
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Affiliation(s)
- K Salte
- Department of Normal, Pathological and Clinical Physiology, Third Faculty of Medicine, Charles University in Prague, Prague, Czech Republic.
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Abstract
Distinct subsets of sensory nerve fibres are involved in mediating mechanical and thermal pain hypersensitivity. They may also differentially respond to analgesics. Heat-sensitive C-fibres, for example, are thought to respond to μ-opioid receptor (MOR) activation while mechanoreceptive fibres are supposedly sensitive to δ-opioid receptor (DOR) or GABAB receptor (GABABR) activation. The suggested differential distribution of inhibitory neurotransmitter receptors on different subsets of sensory fibres is, however, heavily debated. In this study, we quantitatively compared the degree of presynaptic inhibition exerted by opioids and the GABABR agonist baclofen on (1) vesicular glutamate transporter subtype 3-positive (VGluT3) non-nociceptive primary afferent fibres and (2) putative nociceptive C-fibres. To investigate VGluT3 sensory fibres, we evoked excitatory postsynaptic currents with blue light at the level of the dorsal root ganglion (DRG) in spinal cord slices of mice, expressing channelrhodopsin-2. Putative nociceptive C-fibres were explored in VGluT3-knockout mice through electrical stimulation. The MOR agonist DAMGO strongly inhibited both VGluT3 and VGluT3 C-fibres innervating lamina I neurons but generally had less influence on fibres innervating lamina II neurons. The DOR agonist SNC80 did not have any pronounced effect on synaptic transmission in any fibre type tested. Baclofen, in striking contrast, powerfully inhibited all fibre populations investigated. In summary, we report optogenetic stimulation of DRG neurons in spinal slices as a capable approach for the subtype-selective investigation of primary afferent nerve fibres. Overall, pharmacological accessibility of different subtypes of sensory fibres considerably overlaps, indicating that MOR, DOR, and GABABR expressions are not substantially segregated between heat and mechanosensitive fibres.
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Yadav R, Yan X, Maixner DW, Gao M, Weng HR. Blocking the GABA transporter GAT-1 ameliorates spinal GABAergic disinhibition and neuropathic pain induced by paclitaxel. J Neurochem 2015; 133:857-69. [PMID: 25827582 DOI: 10.1111/jnc.13103] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Revised: 03/02/2015] [Accepted: 03/05/2015] [Indexed: 11/24/2022]
Abstract
Paclitaxel is a chemotherapeutic agent widely used for treating carcinomas. Patients receiving paclitaxel often develop neuropathic pain and have a reduced quality of life which hinders the use of this life-saving drug. In this study, we determined the role of GABA transporters in the genesis of paclitaxel-induced neuropathic pain using behavioral tests, electrophysiology, and biochemical techniques. We found that tonic GABA receptor activities in the spinal dorsal horn were reduced in rats with neuropathic pain induced by paclitaxel. In normal controls, tonic GABA receptor activities were mainly controlled by the GABA transporter GAT-1 but not GAT-3. In the spinal dorsal horn, GAT-1 was expressed at presynaptic terminals and astrocytes while GAT-3 was only expressed in astrocytes. In rats with paclitaxel-induced neuropathic pain, the protein expression of GAT-1 was increased while GAT-3 was decreased. This was concurrently associated with an increase in global GABA uptake. The paclitaxel-induced attenuation of GABAergic tonic inhibition was ameliorated by blocking GAT-1 but not GAT-3 transporters. Paclitaxel-induced neuropathic pain was significantly attenuated by the intrathecal injection of a GAT-1 inhibitor. These findings suggest that targeting GAT-1 transporters for reversing disinhibition in the spinal dorsal horn may be a useful approach for treating paclitaxel-induced neuropathic pain. Patients receiving paclitaxel for cancer therapy often develop neuropathic pain and have a reduced quality of life. In this study, we demonstrated that animals treated with paclitaxel develop neuropathic pain, have enhancements of GABA transporter-1 protein expression and global GABA uptake, as well as suppression of GABAergic tonic inhibition in the spinal dorsal horn. Pharmacological inhibition of GABA transporter-1 ameliorates the paclitaxel-induced suppression of GABAergic tonic inhibition and neuropathic pain. Thus, targeting GAT-1 transporters for reversing GABAergic disinhibition in the spinal dorsal horn could be a useful approach for treating paclitaxel-induced neuropathic pain.
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Affiliation(s)
- Ruchi Yadav
- Department of Pharmaceutical and Biomedical Sciences, The University of Georgia College of Pharmacy, Athens, Georgia, USA
| | - Xisheng Yan
- Department of Pharmaceutical and Biomedical Sciences, The University of Georgia College of Pharmacy, Athens, Georgia, USA.,Department of Cardiovascular Medicine, the Third Hospital of Wuhan, Wuhan, Hubei Province, China
| | - Dylan W Maixner
- Department of Pharmaceutical and Biomedical Sciences, The University of Georgia College of Pharmacy, Athens, Georgia, USA
| | - Mei Gao
- Department of Pharmaceutical and Biomedical Sciences, The University of Georgia College of Pharmacy, Athens, Georgia, USA
| | - Han-Rong Weng
- Department of Pharmaceutical and Biomedical Sciences, The University of Georgia College of Pharmacy, Athens, Georgia, USA
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Qu CL, Huo FQ, Huang FS, Tang JS. Activation of mu-opioid receptors in the ventrolateral orbital cortex inhibits the GABAergic miniature inhibitory postsynaptic currents in rats. Neurosci Lett 2015; 592:64-9. [DOI: 10.1016/j.neulet.2015.02.045] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Revised: 02/09/2015] [Accepted: 02/18/2015] [Indexed: 01/09/2023]
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