1
|
Grau JW, Hudson KE, Johnston DT, Partipilo SR. Updating perspectives on spinal cord function: motor coordination, timing, relational processing, and memory below the brain. Front Syst Neurosci 2024; 18:1184597. [PMID: 38444825 PMCID: PMC10912355 DOI: 10.3389/fnsys.2024.1184597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2023] [Accepted: 01/29/2024] [Indexed: 03/07/2024] Open
Abstract
Those studying neural systems within the brain have historically assumed that lower-level processes in the spinal cord act in a mechanical manner, to relay afferent signals and execute motor commands. From this view, abstracting temporal and environmental relations is the province of the brain. Here we review work conducted over the last 50 years that challenges this perspective, demonstrating that mechanisms within the spinal cord can organize coordinated behavior (stepping), induce a lasting change in how pain (nociceptive) signals are processed, abstract stimulus-stimulus (Pavlovian) and response-outcome (instrumental) relations, and infer whether stimuli occur in a random or regular manner. The mechanisms that underlie these processes depend upon signal pathways (e.g., NMDA receptor mediated plasticity) analogous to those implicated in brain-dependent learning and memory. New data show that spinal cord injury (SCI) can enable plasticity within the spinal cord by reducing the inhibitory effect of GABA. It is suggested that the signals relayed to the brain may contain information about environmental relations and that spinal cord systems can coordinate action in response to descending signals from the brain. We further suggest that the study of stimulus processing, learning, memory, and cognitive-like processing in the spinal cord can inform our views of brain function, providing an attractive model system. Most importantly, the work has revealed new avenues of treatment for those that have suffered a SCI.
Collapse
Affiliation(s)
- James W. Grau
- Lab of Dr. James Grau, Department of Psychological and Brain Sciences, Cellular and Behavioral Neuroscience, Texas A&M University, College Station, TX, United States
| | | | | | | |
Collapse
|
2
|
Liao YH, Chen MX, Chen SC, Luo KX, Wang B, Ao LJ, Liu Y. Low-Intensity Focused Ultrasound Alleviates Spasticity and Increases Expression of the Neuronal K-Cl Cotransporter in the L4–L5 Sections of Rats Following Spinal Cord Injury. Front Cell Neurosci 2022; 16:882127. [PMID: 35634464 PMCID: PMC9133482 DOI: 10.3389/fncel.2022.882127] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 04/19/2022] [Indexed: 11/13/2022] Open
Abstract
Low-intensity focused ultrasound (LIFU) has been shown to provide effective activation of the spinal cord neurocircuits. The aim of this study was to investigate the effects of LIFU in order to alleviate spasticity following spinal cord injury (SCI) by activating the spinal neurocircuits and increasing the expression of the neuronal K-Cl cotransporter KCC2. Adult male Sprague Dawley (SD) rats (220–300 g) were randomly divided into a sham control group, a LIFU− group, and a LIFU+ group. The mechanical threshold hold (g) was used to evaluate the behavioral characteristics of spasm. Electromyography (EMG) was used to assess activation of the spinal cord neurocircuits and muscle spontaneous contraction. Spasticity was assessed by frequency-dependent depression (FDD). The expression of KCC2 of the lumbar spinal cord was determined via western blot (WB) and immunofluorescence (IF) staining. The spinal cord neurocircuits were activated by LIFU simulation, which significantly reduced the mechanical threshold (g), FDD, and EMG recordings (s) after 4 weeks of treatment. WB and IF staining both demonstrated that the expression of KCC2 was reduced in the LIFU− group (P < 0.05). After 4 weeks of LIFU stimulation, expression of KCC2 had significantly increased (P < 0.05) in the LIFU+ group compared with the LIFU− group. Thus, we hypothesized that LIFU treatment can alleviate spasticity effectively and upregulate the expression of KCC2 in the L4–L5 section of SCI rats.
Collapse
Affiliation(s)
- Ye-Hui Liao
- School of Rehabilitation, Kunming Medical University, Kunming, China
- Department of Orthopaedics, Affiliated Hospital of Southwest Medical University, Luzhou, China
| | - Mo-Xian Chen
- School of Rehabilitation, Kunming Medical University, Kunming, China
| | - Shao-Chun Chen
- School of Rehabilitation, Kunming Medical University, Kunming, China
| | - Kai-Xuan Luo
- School of Rehabilitation, Kunming Medical University, Kunming, China
| | - Bing Wang
- School of Rehabilitation, Kunming Medical University, Kunming, China
| | - Li-Juan Ao
- School of Rehabilitation, Kunming Medical University, Kunming, China
- *Correspondence: Li-Juan Ao
| | - Yao Liu
- School of Rehabilitation, Kunming Medical University, Kunming, China
- Yao Liu
| |
Collapse
|
3
|
GABAergic Mechanisms Can Redress the Tilted Balance between Excitation and Inhibition in Damaged Spinal Networks. Mol Neurobiol 2021; 58:3769-3786. [PMID: 33826070 PMCID: PMC8279998 DOI: 10.1007/s12035-021-02370-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Accepted: 03/22/2021] [Indexed: 12/19/2022]
Abstract
Correct operation of neuronal networks depends on the interplay between synaptic excitation and inhibition processes leading to a dynamic state termed balanced network. In the spinal cord, balanced network activity is fundamental for the expression of locomotor patterns necessary for rhythmic activation of limb extensor and flexor muscles. After spinal cord lesion, paralysis ensues often followed by spasticity. These conditions imply that, below the damaged site, the state of balanced networks has been disrupted and that restoration might be attempted by modulating the excitability of sublesional spinal neurons. Because of the widespread expression of inhibitory GABAergic neurons in the spinal cord, their role in the early and late phases of spinal cord injury deserves full attention. Thus, an early surge in extracellular GABA might be involved in the onset of spinal shock while a relative deficit of GABAergic mechanisms may be a contributor to spasticity. We discuss the role of GABA A receptors at synaptic and extrasynaptic level to modulate network excitability and to offer a pharmacological target for symptom control. In particular, it is proposed that activation of GABA A receptors with synthetic GABA agonists may downregulate motoneuron hyperexcitability (due to enhanced persistent ionic currents) and, therefore, diminish spasticity. This approach might constitute a complementary strategy to regulate network excitability after injury so that reconstruction of damaged spinal networks with new materials or cell transplants might proceed more successfully.
Collapse
|
4
|
Bilchak JN, Yeakle K, Caron G, Malloy D, Côté MP. Enhancing KCC2 activity decreases hyperreflexia and spasticity after chronic spinal cord injury. Exp Neurol 2021; 338:113605. [PMID: 33453210 PMCID: PMC7904648 DOI: 10.1016/j.expneurol.2021.113605] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 12/21/2020] [Accepted: 01/09/2021] [Indexed: 02/03/2023]
Abstract
After spinal cord injury (SCI), the majority of individuals develop spasticity, a debilitating condition involving involuntary movements, co-contraction of antagonistic muscles, and hyperreflexia. By acting on GABAergic and Ca2+-dependent signaling, current anti-spastic medications lead to serious side effects, including a drastic decrease in motoneuronal excitability which impairs motor function and rehabilitation efforts. Exercise, in contrast, decreases spastic symptoms without decreasing motoneuron excitability. These functional improvements coincide with an increase in expression of the chloride co-transporter KCC2 in lumbar motoneurons. Thus, we hypothesized that spastic symptoms can be alleviated directly through restoration of chloride homeostasis and endogenous inhibition by increasing KCC2 activity. Here, we used the recently developed KCC2 enhancer, CLP257, to evaluate the effects of acutely increasing KCC2 extrusion capability on spastic symptoms after chronic SCI. Sprague Dawley rats received a spinal cord transection at T12 and were either bike-trained or remained sedentary for 5 weeks. Increasing KCC2 activity in the lumbar enlargement improved the rate-dependent depression of the H-reflex and reduced both phasic and tonic EMG responses to muscle stretch in sedentary animals after chronic SCI. Furthermore, the improvements due to this pharmacological treatment mirror those of exercise. Together, our results suggest that pharmacologically increasing KCC2 activity is a promising approach to decrease spastic symptoms in individuals with SCI. By acting to directly restore endogenous inhibition, this strategy has potential to avoid severe side effects and improve the quality of life of affected individuals.
Collapse
Affiliation(s)
- Jadwiga N Bilchak
- Marion Murray Spinal Cord Injury Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, United States of America
| | - Kyle Yeakle
- Marion Murray Spinal Cord Injury Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, United States of America
| | - Guillaume Caron
- Marion Murray Spinal Cord Injury Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, United States of America
| | - Dillon Malloy
- Marion Murray Spinal Cord Injury Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, United States of America
| | - Marie-Pascale Côté
- Marion Murray Spinal Cord Injury Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, United States of America.
| |
Collapse
|
5
|
Borrus DS, Grover CJ, Conradi Smith GD, Del Negro CA. Role of Synaptic Inhibition in the Coupling of the Respiratory Rhythms that Underlie Eupnea and Sigh Behaviors. eNeuro 2020; 7:ENEURO.0302-19.2020. [PMID: 32393585 PMCID: PMC7363481 DOI: 10.1523/eneuro.0302-19.2020] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 04/14/2020] [Accepted: 05/01/2020] [Indexed: 11/21/2022] Open
Abstract
The preBötzinger complex (preBötC) gives rise to two types of breathing behavior under normal physiological conditions: eupnea and sighing. Here, we examine the neural mechanisms that couple their underlying rhythms. We measured breathing in awake intact adult mice and recorded inspiratory rhythms from the preBötC in neonatal mouse brainstem slice preparations. We show previously undocumented variability in the temporal relationship between sigh breaths or bursts and their preceding eupneic breaths or inspiratory bursts. Investigating the synaptic mechanisms for this variability in vitro, we further show that pharmacological blockade of chloride-mediated synaptic inhibition strengthens inspiratory-to-sigh temporal coupling. These findings contrast with previous literature, which suggested glycinergic inhibition linked sigh bursts to their preceding inspiratory bursts with minimal time intervals. Furthermore, we verify that pharmacological disinhibition did not alter the duration of the prolonged interval that follows a sigh burst before resumption of the inspiratory rhythm. These results demonstrate that synaptic inhibition does not enhance coupling between sighs and preceding inspiratory events or contribute to post-sigh apneas. Instead, we conclude that excitatory synaptic mechanisms coordinate inspiratory (eupnea) and sigh rhythms.
Collapse
Affiliation(s)
- Daniel S Borrus
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, VA 23185
| | - Cameron J Grover
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, VA 23185
| | - Gregory D Conradi Smith
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, VA 23185
| | - Christopher A Del Negro
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, VA 23185
| |
Collapse
|
6
|
Mitchell L, MacFarlane PM. Mechanistic actions of oxygen and methylxanthines on respiratory neural control and for the treatment of neonatal apnea. Respir Physiol Neurobiol 2020; 273:103318. [PMID: 31626973 PMCID: PMC6986994 DOI: 10.1016/j.resp.2019.103318] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Revised: 10/07/2019] [Accepted: 10/08/2019] [Indexed: 12/14/2022]
Abstract
Apnea remains one of the most concerning and prevalent respiratory disorders spanning all ages from infants (particularly those born preterm) to adults. Although the pathophysiological consequences of apnea are fairly well described, the neural mechanisms underlying the etiology of the different types of apnea (central, obstructive, and mixed) still remain incompletely understood. From a developmental perspective, however, research into the respiratory neural control system of immature animals has shed light on both central and peripheral neural pathways underlying apnea of prematurity (AOP), a highly prevalent respiratory disorder of preterm infants. Animal studies have also been fundamental in furthering our understanding of how clinical interventions (e.g. pharmacological and mechanical) exert their beneficial effects in the clinical treatment of apnea. Although current clinical interventions such as supplemental O2 and positive pressure respiratory support are critically important for the infant in respiratory distress, they are not fully effective and can also come with unfortunate, unintended (and long-term) side-effects. In this review, we have chosen AOP as one of the most common clinical scenarios involving apnea to highlight the mechanistic basis behind how some of the interventions could be both beneficial and also deleterious to the respiratory neural control system. We have included a section on infants with critical congenital heart diseases (CCHD), in whom apnea can be a clinical concern due to treatment with prostaglandin, and who may benefit from some of the treatments used for AOP.
Collapse
Affiliation(s)
- Lisa Mitchell
- Department of Pediatrics, Case Western Reserve University, Rainbow Babies & Children's Hospital, Cleveland, OH 44106, USA
| | - Peter M MacFarlane
- Department of Pediatrics, Case Western Reserve University, Rainbow Babies & Children's Hospital, Cleveland, OH 44106, USA.
| |
Collapse
|
7
|
Akhter ET, Griffith RW, English AW, Alvarez FJ. Removal of the Potassium Chloride Co-Transporter from the Somatodendritic Membrane of Axotomized Motoneurons Is Independent of BDNF/TrkB Signaling But Is Controlled by Neuromuscular Innervation. eNeuro 2019; 6:ENEURO.0172-19.2019. [PMID: 31541001 PMCID: PMC6795555 DOI: 10.1523/eneuro.0172-19.2019] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Revised: 08/21/2019] [Accepted: 09/15/2019] [Indexed: 01/09/2023] Open
Abstract
The potassium-chloride cotransporter (KCC2) maintains the low intracellular chloride found in mature central neurons and controls the strength and direction of GABA/glycine synapses. We found that following axotomy as a consequence of peripheral nerve injuries (PNIs), KCC2 protein is lost throughout the somatodendritic membrane of axotomized spinal cord motoneurons after downregulation of kcc2 mRNA expression. This large loss likely depolarizes the reversal potential of GABA/glycine synapses, resulting in GABAergic-driven spontaneous activity in spinal motoneurons similar to previous reports in brainstem motoneurons. We hypothesized that the mechanism inducing KCC2 downregulation in spinal motoneurons following peripheral axotomy might be mediated by microglia or motoneuron release of BDNF and TrkB activation as has been reported on spinal cord dorsal horn neurons after nerve injury, motoneurons after spinal cord injury (SCI), and in many other central neurons throughout development or a variety of pathologies. To test this hypothesis, we used genetic approaches to interfere with microglia activation or delete bdnf from specifically microglia or motoneurons, as well as pharmacology (ANA-12) and pharmacogenetics (F616A mice) to block TrkB activation. We show that KCC2 dysregulation in axotomized motoneurons is independent of microglia, BDNF, and TrkB. KCC2 is instead dependent on neuromuscular innervation; KCC2 levels are restored only when motoneurons reinnervate muscle. Thus, downregulation of KCC2 occurs specifically while injured motoneurons are regenerating and might be controlled by target-derived signals. GABAergic and glycinergic synapses might therefore depolarize motoneurons disconnected from their targets and contribute to augment motoneuron activity known to promote motor axon regeneration.
Collapse
Affiliation(s)
- Erica Tracey Akhter
- Departments of Physiology, Emory University, Atlanta, GA 30322
- Cell Biology, Emory University, Atlanta, GA 30322
| | | | | | | |
Collapse
|
8
|
Mechanisms underlying a critical period of respiratory development in the rat. Respir Physiol Neurobiol 2019; 264:40-50. [PMID: 30999061 DOI: 10.1016/j.resp.2019.04.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 04/05/2019] [Accepted: 04/10/2019] [Indexed: 01/13/2023]
Abstract
Twenty-five years ago, Filiano and Kinney (1994) proposed that a critical period of postnatal development constitutes one of the three risk factors for sudden infant death syndrome (SIDS). The underlying mechanism was poorly understood. In the last 17 years, much has been uncovered on this period in the rat. Against several expected trends of development, abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory system at P12-13. This results in a transient synaptic imbalance with suppressed excitation and enhanced inhibition, and the response to acute hypoxia is the weakest at this time, both at the cellular and system's levels. The basis for the synaptic imbalance is likely to be contributed by a reduced expression of brain-derived neurotrophic factor (BDNF) and its TrkB receptors in multiple brain stem respiratory-related nuclei during the critical period. Exogenous BDNF or a TrkB agonist partially reverses the synaptic imbalance, whereas a TrkB antagonist accentuates the imbalance. A transient down-regulation of pituitary adenylate cyclase-activating polypeptide (PACAP) at P12 in respiratory-related nuclei also contributes to the vulnerability of this period. Carotid body denervation during this time or perinatal hyperoxia merely delays and sometimes prolongs, but not eliminate the critical period. The rationale for the necessity of the critical period in postnatal development is discussed.
Collapse
|
9
|
Allen LL, Seven YB, Baker TL, Mitchell GS. Cervical spinal contusion alters Na +-K +-2Cl- and K +-Cl- cation-chloride cotransporter expression in phrenic motor neurons. Respir Physiol Neurobiol 2019; 261:15-23. [PMID: 30590202 PMCID: PMC6939623 DOI: 10.1016/j.resp.2018.12.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2018] [Revised: 12/21/2018] [Accepted: 12/23/2018] [Indexed: 12/11/2022]
Abstract
Spinal chloride-dependent synaptic inhibition is critical in regulating breathing and requires neuronal chloride gradients established by cation-chloride cotransporters Na+-K+-2Cl- (NKCC1) and K+-Cl- (KCC2). Spinal transection disrupts NKCC1/KCC2 balance, diminishing chloride gradients in neurons below injury, contributing to spasticity and chronic pain. It is not known if similar disruptions in NKCC1/KCC2 balance occur in respiratory motor neurons after incomplete cervical contusion (C2SC). We hypothesized that C2SC disrupts NKCC1/KCC2 balance in phrenic motor neurons. NKCC1 and KCC2 immunoreactivity was assessed in CtB-positive phrenic motor neurons. Five weeks post-C2SC: 1) neither membrane-bound nor cytosolic NKCC1 expression were significantly changed, although the membrane/cytosolic ratio increased, consistent with net chloride influx; and 2) both membrane and cytosolic KCC2 expression increased, although the membrane/cytosolic ratio decreased, consistent with net chloride efflux. Thus, contrary to our original hypothesis, complex shifts in NKCC1/KCC2 balance occur post-C2SC. The functional significance of these changes remains unclear.
Collapse
Affiliation(s)
- Latoya L Allen
- Department of Physical Therapy, University of Florida, Gainesville, FL 32611 USA; Department of Neuroscience, University of Florida, Gainesville, FL 32610 USA; Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL 32611 USA
| | - Yasin B Seven
- Department of Physical Therapy, University of Florida, Gainesville, FL 32611 USA; Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL 32611 USA
| | - Tracy L Baker
- Department of Comparative Biosciences, University of Wisconsin-Madison, Madison, WI 53706 USA
| | - Gordon S Mitchell
- Department of Physical Therapy, University of Florida, Gainesville, FL 32611 USA; Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL 32611 USA.
| |
Collapse
|
10
|
Huang YJ, Lee KH, Murphy L, Garraway SM, Grau JW. Acute spinal cord injury (SCI) transforms how GABA affects nociceptive sensitization. Exp Neurol 2016; 285:82-95. [PMID: 27639636 PMCID: PMC5926208 DOI: 10.1016/j.expneurol.2016.09.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Revised: 09/09/2016] [Accepted: 09/12/2016] [Indexed: 10/21/2022]
Abstract
Noxious input can sensitize pain (nociceptive) circuits within the spinal cord, inducing a lasting increase in spinal cord neural excitability (central sensitization) that is thought to contribute to chronic pain. The development of spinally-mediated central sensitization is regulated by descending fibers and GABAergic interneurons. The current study provides evidence that spinal cord injury (SCI) transforms how GABA affects nociceptive transmission within the spinal cord, recapitulating an earlier developmental state wherein GABA has an excitatory effect. In spinally transected rats, noxious electrical stimulation and inflammation induce enhanced mechanical reactivity (EMR), a behavioral index of nociceptive sensitization. Pretreatment with the GABAA receptor antagonist bicuculline blocked these effects. Peripheral application of an irritant (capsaicin) also induced EMR. Both the induction and maintenance of this effect were blocked by bicuculline. Cellular indices of central sensitization [c-fos expression and ERK phosphorylation (pERK)] were also attenuated. In intact (sham operated) rats, bicuculline had the opposite effect. Pretreatment with a GABA agonist (muscimol) attenuated nociceptive sensitization in intact, but not spinally injured, rats. The effect of SCI on GABA function was linked to a reduction in the Cl- transporter, KCC2, leading to a reduction in intracellular Cl- that would attenuate GABA-mediated inhibition. Pharmacologically blocking the KCC2 channel (with i.t. DIOA) in intact rats mimicked the effect of SCI. Conversely, a pharmacological treatment (bumetanide) that should increase intracellular Cl- levels blocked the effect of SCI. The results suggest that GABAergic neurons drive, rather than inhibit, the development of nociceptive sensitization after spinal injury.
Collapse
Affiliation(s)
- Yung-Jen Huang
- Behavioral and Cellular Neuroscience, Department of Psychology, Texas A&M University, College Station, TX 77843, USA.
| | - Kuan H Lee
- Center for Pain Research, Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Lauren Murphy
- Behavioral and Cellular Neuroscience, Department of Psychology, Texas A&M University, College Station, TX 77843, USA
| | - Sandra M Garraway
- Department of Physiology, Emory University School of Medicine, Atlanta, GA 30307, USA
| | - James W Grau
- Behavioral and Cellular Neuroscience, Department of Psychology, Texas A&M University, College Station, TX 77843, USA
| |
Collapse
|
11
|
Doyon N, Vinay L, Prescott SA, De Koninck Y. Chloride Regulation: A Dynamic Equilibrium Crucial for Synaptic Inhibition. Neuron 2016; 89:1157-1172. [PMID: 26985723 DOI: 10.1016/j.neuron.2016.02.030] [Citation(s) in RCA: 156] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2015] [Revised: 12/24/2015] [Accepted: 02/18/2016] [Indexed: 01/02/2023]
Abstract
Fast synaptic inhibition relies on tight regulation of intracellular Cl(-). Chloride dysregulation is implicated in several neurological and psychiatric disorders. Beyond mere disinhibition, the consequences of Cl(-) dysregulation are multifaceted and best understood in terms of a dynamical system involving complex interactions between multiple processes operating on many spatiotemporal scales. This dynamical perspective helps explain many unintuitive manifestations of Cl(-) dysregulation. Here we discuss how taking into account dynamical regulation of intracellular Cl(-) is important for understanding how synaptic inhibition fails, how to best detect that failure, why Cl(-) regulation is energetically so expensive, and the overall consequences for therapeutics.
Collapse
Affiliation(s)
- Nicolas Doyon
- Institut Universitaire en Santé Mentale de Québec, Québec, QC G1J 2G3, Canada; Department of Mathematics and Statistics, Université Laval, Québec, QC G1V 0A6, Canada
| | - Laurent Vinay
- Team P3M, Institut de Neurosciences de la Timone, UMR 7289, CNRS and Aix Marseille Université, F-13385 Marseille, France
| | - Steven A Prescott
- Program in Neurosciences and Mental Health, Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Yves De Koninck
- Institut Universitaire en Santé Mentale de Québec, Québec, QC G1J 2G3, Canada; Department of Psychiatry and Neuroscience, Université Laval, Québec, QC, G1V 0A6, Canada.
| |
Collapse
|
12
|
Doyon N, Prescott SA, De Koninck Y. Mild KCC2 Hypofunction Causes Inconspicuous Chloride Dysregulation that Degrades Neural Coding. Front Cell Neurosci 2016; 9:516. [PMID: 26858607 PMCID: PMC4731508 DOI: 10.3389/fncel.2015.00516] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Accepted: 12/23/2015] [Indexed: 11/17/2022] Open
Abstract
Disinhibition caused by Cl− dysregulation is implicated in several neurological disorders. This form of disinhibition, which stems primarily from impaired Cl− extrusion through the co-transporter KCC2, is typically identified by a depolarizing shift in GABA reversal potential (EGABA). Here we show, using computer simulations, that intracellular [Cl−] exhibits exaggerated fluctuations during transient Cl− loads and recovers more slowly to baseline when KCC2 level is even modestly reduced. Using information theory and signal detection theory, we show that increased Cl− lability and settling time degrade neural coding. Importantly, these deleterious effects manifest after less KCC2 reduction than needed to produce the gross changes in EGABA required for detection by most experiments, which assess KCC2 function under weak Cl− load conditions. By demonstrating the existence and functional consequences of “occult” Cl− dysregulation, these results suggest that modest KCC2 hypofunction plays a greater role in neurological disorders than previously believed.
Collapse
Affiliation(s)
- Nicolas Doyon
- Institut Universitaire en Santé Mentale de QuébecQuébec, QC, Canada; Department of Mathematics and Statistics, Université LavalQuébec, QC, Canada
| | - Steven A Prescott
- Program in Neurosciences and Mental Health, Hospital for Sick ChildrenToronto, ON, Canada; Department of Physiology, University of TorontoToronto, ON, Canada
| | - Yves De Koninck
- Institut Universitaire en Santé Mentale de QuébecQuébec, QC, Canada; Department of Psychiatry and Neuroscience, Université LavalQuébec, QC, Canada
| |
Collapse
|
13
|
Wang H, Liu S, Wang H, Wang G, Zhu A. The effect of propofol postconditioning on the expression of K(+)-Cl(-)-co-transporter 2 in GABAergic inhibitory interneurons of acute ischemia/reperfusion injury rats. Brain Res 2015; 1597:210-9. [PMID: 25463027 DOI: 10.1016/j.brainres.2014.11.036] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Revised: 11/01/2014] [Accepted: 11/16/2014] [Indexed: 12/20/2022]
Abstract
It has been shown in our previous study that propofol postconditioning enhanced the activity of phosphatidylinositol-3-kinase (PI3K) and prevented the internalization of GluR2 subunit of α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, thus provided neuroprotection in cerebral ischemia/reperfusion (I/R) injury. Regarding inhibitory system in CNS, K(+)-Cl(-)-co-transporter 2 (KCC2), a Cl(-) extruder, plays a critical role in gamma-aminobutyric acid (GABA) inhibitory effect in mature central neurons. However, the effect of propofol postconditioning on the expression of KCC2 in GABAergic interneurons is unclear. Therefore, in this article we describe the role of KCC2 in GABAergic interneurons in the ipsilateral hippocampal CA1 region of adult rats and the effects of propofol postconditioning on this region. Herein we demonstrate that propofol postconditioning (20mg/kg/h, 2h) improved rats' neurobehavioral abilities, increased the number of survival neurons, and up-regulated neuronal KCC2 expression in glutamic acid decarboxylase 67 (GAD67) expressing GABAergic interneurons in hippocampal CA1 region at 24h after I/R. In contrast, when rats were injected with the KCC2 antagonist, [(dihydroindenyl)oxy] alkanoic acid (DIOA), the neuroprotective effects induced by propofol postconditioning were reversed. Our study indicated that propofol postconditioning increased the expression of KCC2 in inhibitory GABAergic interneurons, thus providing acute neuroprotection to rats who had undergone cerebral I/R injury.
Collapse
Affiliation(s)
- Hongbai Wang
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin Research Institute of Anesthesiology, Tianjin, People׳s Republic of China
| | - Shuying Liu
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin Research Institute of Anesthesiology, Tianjin, People׳s Republic of China
| | - Haiyun Wang
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin Research Institute of Anesthesiology, Tianjin, People׳s Republic of China.
| | - Guolin Wang
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin Research Institute of Anesthesiology, Tianjin, People׳s Republic of China
| | - Ai Zhu
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin Research Institute of Anesthesiology, Tianjin, People׳s Republic of China
| |
Collapse
|
14
|
Lindsly C, Gonzalez-Islas C, Wenner P. Activity blockade and GABAA receptor blockade produce synaptic scaling through chloride accumulation in embryonic spinal motoneurons and interneurons. PLoS One 2014; 9:e94559. [PMID: 24733046 PMCID: PMC3986094 DOI: 10.1371/journal.pone.0094559] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Accepted: 03/18/2014] [Indexed: 12/03/2022] Open
Abstract
Synaptic scaling represents a process whereby the distribution of a cell's synaptic strengths are altered by a multiplicative scaling factor. Scaling is thought to be a compensatory response that homeostatically controls spiking activity levels in the cell or network. Previously, we observed GABAergic synaptic scaling in embryonic spinal motoneurons following in vivo blockade of either spiking activity or GABAA receptors (GABAARs). We had determined that activity blockade triggered upward GABAergic scaling through chloride accumulation, thus increasing the driving force for these currents. To determine whether chloride accumulation also underlies GABAergic scaling following GABAAR blockade we have developed a new technique. We expressed a genetically encoded chloride-indicator, Clomeleon, in the embryonic chick spinal cord, which provides a non-invasive fast measure of intracellular chloride. Using this technique we now show that chloride accumulation underlies GABAergic scaling following blockade of either spiking activity or the GABAAR. The finding that GABAAR blockade and activity blockade trigger scaling via a common mechanism supports our hypothesis that activity blockade reduces GABAAR activation, which triggers synaptic scaling. In addition, Clomeleon imaging demonstrated the time course and widespread nature of GABAergic scaling through chloride accumulation, as it was also observed in spinal interneurons. This suggests that homeostatic scaling via chloride accumulation is a common feature in many neuronal classes within the embryonic spinal cord and opens the possibility that this process may occur throughout the nervous system at early stages of development.
Collapse
Affiliation(s)
- Casie Lindsly
- Physiology Department, Emory University, School of Medicine, Atlanta, Georgia, United States of America
| | - Carlos Gonzalez-Islas
- Physiology Department, Emory University, School of Medicine, Atlanta, Georgia, United States of America
| | - Peter Wenner
- Physiology Department, Emory University, School of Medicine, Atlanta, Georgia, United States of America
- * E-mail:
| |
Collapse
|
15
|
Liu Q, Wong-Riley MTT. Postnatal development of Na(+)-K(+)-2Cl(-) co-transporter 1 and K(+)-Cl(-) co-transporter 2 immunoreactivity in multiple brain stem respiratory nuclei of the rat. Neuroscience 2012; 210:1-20. [PMID: 22441038 PMCID: PMC3358512 DOI: 10.1016/j.neuroscience.2012.03.018] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Revised: 03/06/2012] [Accepted: 03/07/2012] [Indexed: 12/22/2022]
Abstract
Previously, we reported that in rats, GABA(A) and glycine receptor immunoreactivity increased markedly in multiple brain stem respiratory nuclei around postnatal days (P) 12-13, a critical period when abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory network and when the system is under greater inhibition than excitation. Since Na(+)-K(+)-2Cl(-) co-transporter 1 (NKCC1) and K(+)-Cl(-) co-transporter 2 (KCC2) play pivotal roles in determining the responses of GABA(A) and glycine receptors, we hypothesized that NKCC1 and KCC2 undergo significant changes during the critical period. An in-depth immunohistochemical and single neuron optical densitometric study of neurons in seven respiratory-related nuclei (the pre-Bötzinger complex [PBC], nucleus ambiguus [Amb], hypoglossal nucleus [XII], ventrolateral subnucleus of solitary tract nucleus [NTS(VL)], retrotrapezoid nucleus/parafacial respiratory group [retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG)], dorsal motor nucleus of the vagus nerve [dorsal motor nucleus of the vagus nerve (DMNX)], and inferior olivary nucleus [IO]) and a non-respiratory cuneate nucleus (CN, an internal control) was undertaken in P0-P21 rats. Our data revealed that (1) NKCC1 immunoreactivity exhibited a developmental decrease from P0 to P21 in all eight nuclei examined, being relatively high during the first 1½ postnatal weeks and decreased thereafter. The decrease was abrupt and statistically significant at P12 in the PBC, Amb, and XII; (2) KCC2 immunoreactivity in these eight nuclei showed a developmental increase from P0 to P21; and (3) the significant reduction in NKCC1 and the greater dominance of KCC2 around P12 in multiple respiratory nuclei of the brain stem may form the basis of an enhanced inhibition in the respiratory network during the critical period before the system stabilizes to a more mature state.
Collapse
Affiliation(s)
- Q Liu
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, Wisconsin 53226, USA
| | | |
Collapse
|
16
|
Cutaneous inputs from the back abolish locomotor-like activity and reduce spastic-like activity in the adult cat following complete spinal cord injury. Exp Neurol 2012; 235:588-98. [PMID: 22487200 DOI: 10.1016/j.expneurol.2012.03.013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2012] [Revised: 03/11/2012] [Accepted: 03/25/2012] [Indexed: 11/20/2022]
Abstract
Spasticity is a condition that can include increased muscle tone, clonus, spasms, and hyperreflexia. In this study, we report the effect of manually stimulating the dorsal lumbosacral skin on spontaneous locomotor-like activity and on a variety of reflex responses in 5 decerebrate chronic spinal cats treated with clonidine. Cats were spinalized 1 month before the terminal experiment. Stretch reflexes were evoked by stretching the left triceps surae muscles. Crossed reflexes were elicited by electrically stimulating the right tibial or superficial peroneal nerves. Wind-up of reflex responses was evoked by electrically stimulating the left tibial or superficial peroneal nerves. We found that pinching the skin of the back abolished spontaneous locomotor-like activity. We also found that back pinch abolished the rhythmic activity observed during reflex testing without eliminating the reflex responses. Some of the rhythmic episodes of activity observed during reflex testing were consistent with clonus with an oscillation frequency greater than 3 Hz. Pinching the skin of the back effectively abolished rhythmic activity occurring spontaneously or evoked during reflex testing, irrespective of oscillation frequency. The results are consistent with the hypothesis that locomotion and clonus are produced by common central pattern-generators. Stimulating the skin of the back could prove helpful in managing undesired rhythmic activity in spinal cord-injured humans.
Collapse
|