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Canto-Bustos M, Loeza-Alcocer E, Cuellar CA, Osuna P, Elias-Viñas D, Granados-Soto V, Manjarrez E, Felix R, Delgado-Lezama R. Tonically Active α 5GABA A Receptors Reduce Motoneuron Excitability and Decrease the Monosynaptic Reflex. Front Cell Neurosci 2017; 11:283. [PMID: 28970784 PMCID: PMC5609539 DOI: 10.3389/fncel.2017.00283] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Accepted: 08/31/2017] [Indexed: 11/19/2022] Open
Abstract
Motoneurons, the final common path of the Central Nervous System (CNS), are under a complex control of its excitability in order to precisely translate the interneuronal pattern of activity into skeletal muscle contraction and relaxation. To fulfill this relevant function, motoneurons are provided with a vast repertoire of receptors and channels, including the extrasynaptic GABAA receptors which have been poorly investigated. Here, we confirmed that extrasynaptic α5 subunit-containing GABAA receptors localize with choline acetyltransferase (ChAT) positive cells, suggesting that these receptors are expressed in turtle motoneurons as previously reported in rodents. In these cells, α5GABAA receptors are activated by ambient GABA, producing a tonic shunt that reduces motoneurons’ membrane resistance and affects their action potential firing properties. In addition, α5GABAA receptors shunted the synaptic excitatory inputs depressing the monosynaptic reflex (MSR) induced by activation of primary afferents. Therefore, our results suggest that α5GABAA receptors may play a relevant physiological role in motor control.
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Affiliation(s)
- Martha Canto-Bustos
- Department of Neuroscience, Center for the Neural Basis of Cognition, University of PittsburghPittsburgh, PA, United States
| | - Emanuel Loeza-Alcocer
- Department of Neurobiology, University of Pittsburgh School of MedicinePittsburgh, PA, United States
| | - Carlos A Cuellar
- Laboratory of Neuronal Engineering, Mayo Clinic MinnesotaRochester, MN, United States
| | - Paulina Osuna
- Departamento de Fisiología, Biofísica y Neurociencias, CinvestavMexico City, Mexico
| | | | | | - Elías Manjarrez
- Instituto de Fisiología, Benemérita Universidad Autónoma de PueblaPuebla, Mexico
| | - Ricardo Felix
- Departamento de Biología Celular, CinvestavMexico City, Mexico
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Marchenko V, Ghali MGZ, Rogers RF. The role of spinal GABAergic circuits in the control of phrenic nerve motor output. Am J Physiol Regul Integr Comp Physiol 2015; 308:R916-26. [PMID: 25833937 DOI: 10.1152/ajpregu.00244.2014] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Accepted: 03/26/2015] [Indexed: 01/20/2023]
Abstract
While supraspinal mechanisms underlying respiratory pattern formation are well characterized, the contribution of spinal circuitry to the same remains poorly understood. In this study, we tested the hypothesis that intraspinal GABAergic circuits are involved in shaping phrenic motor output. To this end, we performed bilateral phrenic nerve recordings in anesthetized adult rats and observed neurogram changes in response to knocking down expression of both isoforms (65 and 67 kDa) of glutamate decarboxylase (GAD65/67) using microinjections of anti-GAD65/67 short-interference RNA (siRNA) in the phrenic nucleus. The number of GAD65/67-positive cells was drastically reduced on the side of siRNA microinjections, especially in the lateral aspects of Rexed's laminae VII and IX in the ventral horn of cervical segment C4, but not contralateral to microinjections. We hypothesize that intraspinal GABAergic control of phrenic output is primarily phasic, but also plays an important role in tonic regulation of phrenic discharge. Also, we identified respiration-modulated GABAergic interneurons (both inspiratory and expiratory) located slightly dorsal to the phrenic nucleus. Our data provide the first direct evidence for the existence of intraspinal GABAergic circuits contributing to the formation of phrenic output. The physiological role of local intraspinal inhibition, independent of descending direct bulbospinal control, is discussed.
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Affiliation(s)
- Vitaliy Marchenko
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Michael G Z Ghali
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Robert F Rogers
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania
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Andres C, Aguilar J, González-Ramírez R, Elias-Viñas D, Felix R, Delgado-Lezama R. Extrasynaptic α6 subunit-containing GABAA receptors modulate excitability in turtle spinal motoneurons. PLoS One 2014; 9:e115378. [PMID: 25531288 PMCID: PMC4274054 DOI: 10.1371/journal.pone.0115378] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 11/22/2014] [Indexed: 11/22/2022] Open
Abstract
Motoneurons are furnished with a vast repertoire of ionotropic and metabotropic receptors as well as ion channels responsible for maintaining the resting membrane potential and involved in the regulation of the mechanisms underlying its membrane excitability and firing properties. Among them, the GABAA receptors, which respond to GABA binding by allowing the flow of Cl− ions across the membrane, mediate two distinct forms of inhibition in the mature nervous system, phasic and tonic, upon activation of synaptic or extrasynaptic receptors, respectively. In a previous work we showed that furosemide facilitates the monosynaptic reflex without affecting the dorsal root potential. Our data also revealed a tonic inhibition mediated by GABAA receptors activated in motoneurons by ambient GABA. These data suggested that the high affinity GABAA extrasynaptic receptors may have an important role in motor control, though the molecular nature of these receptors was not determined. By combining electrophysiological, immunofluorescence and molecular biology techniques with pharmacological tools here we show that GABAA receptors containing the α6 subunit are expressed in adult turtle spinal motoneurons and can function as extrasynaptic receptors responsible for tonic inhibition. These results expand our understanding of the role of GABAA receptors in motoneuron tonic inhibition.
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Affiliation(s)
- Carmen Andres
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional (Cinvestav-IPN), México DF, México
| | - Justo Aguilar
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional (Cinvestav-IPN), México DF, México
| | - Ricardo González-Ramírez
- Departamento de Biología Molecular e Histocompatibilidad, Hospital General “Dr. Manuel Gea González,” México DF, México
| | | | - Ricardo Felix
- Departamento de Biología Celular, Cinvestav-IPN, México DF, México
| | - Rodolfo Delgado-Lezama
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional (Cinvestav-IPN), México DF, México
- * E-mail:
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The sedative but not the memory-blocking properties of ethanol are modulated by α5-subunit-containing γ-aminobutyric acid type A receptors. Behav Brain Res 2011; 217:379-85. [DOI: 10.1016/j.bbr.2010.11.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2010] [Revised: 10/29/2010] [Accepted: 11/01/2010] [Indexed: 12/26/2022]
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Khristy W, Ali NJ, Bravo AB, de Leon R, Roy RR, Zhong H, London NJL, Edgerton VR, Tillakaratne NJK. Changes in GABA(A) receptor subunit gamma 2 in extensor and flexor motoneurons and astrocytes after spinal cord transection and motor training. Brain Res 2009; 1273:9-17. [PMID: 19358834 DOI: 10.1016/j.brainres.2009.03.060] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2008] [Revised: 03/26/2009] [Accepted: 03/29/2009] [Indexed: 01/01/2023]
Abstract
GABA signaling plays an important role in the spinal cord response to injury and subsequent motor training. Since benzodiazepines are commonly used to treat muscle spasticity in spinal cord injured subjects and the gamma2 subunit of the GABA(A) receptor is necessary for benzodiazepine binding, this subunit may be an important factor modulating sensorimotor function after an injury. Changes in gamma2 levels in muscle-specific motoneurons and surrounding astrocytes were determined approximately 3 months after a complete mid-thoracic spinal cord transection at P5 in non-trained and in step-trained spinal rats. Soleus (ankle extensor) and tibialis anterior (TA, ankle flexor) motor pools were identified using retrograde labeling via intramuscular injections of Fast Blue or Fluoro Gold, respectively. Lumbar spinal cord sections showed gamma2 immunostaining in both soleus and TA motoneurons and astrocytes. gamma2 immunoreactivity on the soma of soleus and TA motoneurons in spinal rats was differentially modulated. Compared to intact rats, spinal rats had higher levels of gamma2 in TA, and lower levels in soleus motoneurons. Step training restored GABA(A) gamma2 levels towards control values in motoneuronal pools of both muscles. In contrast, the gamma2 levels were elevated in surrounding astrocytes of both motor pools in spinal rats, and step training had no further effect. Thus, motor training had a specific effect on those neurons that were directly involved with the motor task. Since the gamma2 subunit is involved with GABA(A) receptor trafficking and synaptic clustering, it appears that this subunit could be an important component of the activity-dependent response of the spinal cord after a spinal injury.
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Affiliation(s)
- Windyanne Khristy
- Department of Physiological Science, University of California at Los Angeles, Los Angeles, CA 90095, USA
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del Río JC, Araujo F, Ramos B, Ruano D, Vitorica J. Prevalence between different alpha subunits performing the benzodiazepine binding sites in native heterologous GABA(A) receptors containing the alpha2 subunit. J Neurochem 2001; 79:183-91. [PMID: 11595770 DOI: 10.1046/j.1471-4159.2001.00551.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The presence of two heterologous alpha subunits and a single benzodiazepine binding site in the GABA(A) receptor implicates the existence of pharmacologically active and inactive alpha subunits. This fact raises the question of whether a particular alpha subtype could predominate performing the benzodiazepine binding site. The hippocampal formation expresses high levels of alpha subunits with different benzodiazepine binding properties (alpha1, alpha2 and alpha5). Thus, we first demonstrated the existence of alpha2-alpha1 (36.3 +/- 5.2% of the alpha2 population) and alpha2-alpha5 (20.2 +/- 2.1%) heterologous receptors. A similar alpha2-alpha1 association was observed in cortex. This association allows the direct comparison of the pharmacological properties of heterologous native GABA(A) receptors containing a common (alpha2) and a different (alpha1 or alpha5) alpha subunit. The alpha2 subunit pharmacologically prevailed over the alpha1 subunit in both cortex and hippocampus (there was an absence of high-affinity binding sites for Cl218,872, zolpidem and [3H]zolpidem). This prevalence was directly probed by zolpidem displacement experiments in alpha2-alpha1 double immunopurified receptors (K(i) = 295 +/- 56 nM and 200 +/- 8 nM in hippocampus and cortex, respectively). On the contrary, the alpha5 subunit pharmacologically prevailed over the alpha2 subunit (low- and high-affinity binding sites for zolpidem and [3H]L-655,708, respectively). This prevalence was probed in alpha2-alpha5 double immunopurified receptors. Zolpidem displayed a single low-affinity binding site (K(i) = 1.73 +/- 0.54 microM). These results demonstrated the existence of a differential dominance between the different alpha subunits performing the benzodiazepine binding sites in the native GABA(A) receptors.
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Affiliation(s)
- J C del Río
- Department of Bioquimica, Bromatologia y Toxicologia, Facultad de Farmacia, Universidad de Sevilla, Seville, Spain
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