1
|
Danaf J, da Silveira Scarpellini C, Montandon G. βγ G-proteins, but not regulators of G-protein signaling 4, modulate opioid-induced respiratory rate depression. Front Physiol 2023; 14:1043581. [PMID: 37089428 PMCID: PMC10117644 DOI: 10.3389/fphys.2023.1043581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Accepted: 03/24/2023] [Indexed: 04/09/2023] Open
Abstract
Opioid medications are the mainstay of pain management but present substantial side-effects such as respiratory depression which can be lethal with overdose. Most opioid drugs, such as fentanyl, act on opioid receptors such as the G-protein-coupled µ-opioid receptors (MOR). G-protein-coupled receptors activate pertussis toxin-sensitive G-proteins to inhibit neuronal activity. Binding of opioid ligands to MOR and subsequent activation G proteins βγ is modulated by regulator of G-protein signaling (RGS). The roles of G-proteins βγ and RGS in MOR-mediated inhibition of the respiratory network are not known. Using rodent models to pharmacologically modulate G-protein signaling, we aim to determine the roles of βγ G-proteins and RGS4. We showed that inhibition of βγ G-proteins using gallein perfused in the brainstem circuits regulating respiratory depression by opioid drugs results in complete reversal of respiratory depression. Blocking of RGS4 using CCG55014 did not change the respiratory depression induced by MOR activation despite co-expression of RGS4 and MORs in the brainstem. Our results suggest that neuronal inhibition by opioid drugs is mediated by G-proteins, but not by RGS4, which supports the concept that βγ G-proteins could be molecular targets to develop opioid overdose antidotes without the risks of re-narcotization often found with highly potent opioid drugs. On the other hand, RGS4 mediates opioid analgesia, but not respiratory depression, and RGS4 may be molecular targets to develop pain therapies without respiratory liability.
Collapse
Affiliation(s)
- Jamil Danaf
- St. Michael’s Hospital, Unity Health Toronto, Toronto, ON, Canada
| | | | - Gaspard Montandon
- St. Michael’s Hospital, Unity Health Toronto, Toronto, ON, Canada
- Department of Medicine, University of Toronto, Toronto, ON, Canada
- *Correspondence: Gaspard Montandon,
| |
Collapse
|
2
|
Burgraff NJ, Phillips RS, Severs LJ, Bush NE, Baertsch NA, Ramirez JM. Inspiratory rhythm generation is stabilized by Ih. J Neurophysiol 2022; 128:181-196. [PMID: 35675444 PMCID: PMC9291429 DOI: 10.1152/jn.00150.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Cellular and network properties must be capable of generating rhythmic activity that is both flexible and stable. This is particularly important for breathing, a rhythmic behavior that dynamically adapts to environmental, behavioral, and metabolic changes from the first to the last breath. The pre-Bötzinger complex (preBötC), located within the ventral medulla, is responsible for producing rhythmic inspiration. Its cellular properties must be tunable, flexible as well as stabilizing. Here, we explore the role of the hyperpolarization-activated, nonselective cation current (Ih) for stabilizing PreBötC activity during opioid exposure and reduced excitatory synaptic transmission. Introducing Ih into an in silico preBötC network predicts that loss of this depolarizing current should significantly slow the inspiratory rhythm. By contrast, in vitro and in vivo experiments revealed that the loss of Ih minimally affected breathing frequency, but destabilized rhythmogenesis through the generation of incompletely synchronized bursts (burstlets). Associated with the loss of Ih was an increased susceptibility of breathing to opioid-induced respiratory depression or weakened excitatory synaptic interactions, a paradoxical depolarization at the cellular level, and the suppression of tonic spiking. Tonic spiking activity is generated by nonrhythmic excitatory and inhibitory preBötC neurons, of which a large percentage express Ih. Together, our results suggest that Ih is important for maintaining tonic spiking, stabilizing inspiratory rhythmogenesis, and protecting breathing against perturbations or changes in network state.NEW & NOTEWORTHY The Ih current plays multiple roles within the preBötC. This current is important for promoting intrinsic tonic spiking activity in excitatory and inhibitory neurons and for preserving rhythmic function during conditions that dampen network excitability, such as in the context of opioid-induced respiratory depression. We therefore propose that the Ih current expands the dynamic range of rhythmogenesis, buffers the preBötC against network perturbations, and stabilizes rhythmogenesis by preventing the generation of unsynchronized bursts.
Collapse
Affiliation(s)
- Nicholas J. Burgraff
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington
| | - Ryan S. Phillips
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington
| | - Liza J. Severs
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington
| | - Nicholas E. Bush
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington
| | - Nathan A. Baertsch
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington,2Department of Pediatrics, University of Washington, Seattle, Washington
| | - Jan-Marino Ramirez
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington,2Department of Pediatrics, University of Washington, Seattle, Washington,3Department of Neurological Surgery, University of Washington, Seattle, Washington
| |
Collapse
|
3
|
de Sousa Abreu RP, Bondarenko E, Feldman JL. Phase- and state-dependent modulation of breathing pattern by preBötzinger complex somatostatin expressing neurons. J Physiol 2022; 600:143-165. [PMID: 34783033 PMCID: PMC9261878 DOI: 10.1113/jp282002] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 11/12/2021] [Indexed: 01/03/2023] Open
Abstract
As neuronal subtypes are increasingly categorized, delineating their functional role is paramount. The preBötzinger complex (preBötC) subpopulation expressing the neuropeptide somatostatin (SST) is classified as mostly excitatory, inspiratory-modulated and not rhythmogenic. We further characterized their phenotypic identity: 87% were glutamatergic and the balance were glycinergic and/or GABAergic. We then used optogenetics to investigate their modulatory role in both anaesthetized and freely moving mice. In anaesthetized mice, short photostimulation (100 ms) of preBötC SST+ neurons modulated breathing-related variables in a combinatory phase- and state-dependent manner; changes in inspiratory duration, inspiratory peak amplitude (Amp), and phase were different at higher (≥2.5 Hz) vs. lower (<2.5 Hz) breathing frequency (f). Moreover, we observed a biphasic effect of photostimulation during expiration that is probabilistic, that is photostimulation given at the same phase in consecutive cycles can evoke opposite responses (lengthening vs. shortening of the phase). These unexpected probabilistic state- and phase-dependent responses to photostimulation exposed properties of the preBötC that were not predicted and cannot be readily accounted for in current models of preBötC pattern generation. In freely moving mice, prolonged photostimulation decreased f in normoxia, hypoxia or hypercapnia, and increased Amp and produced a phase advance, which was similar to the results in anaesthetized mice when f ≥ 2.5 Hz. We conclude that preBötC SST+ neurons are a key mediator of the extraordinary and essential lability of breathing pattern. KEY POINTS: PreBötzinger complex (preBötC) SST+ neurons, which modulate respiratory pattern but are not rhythmogenic, were transfected with channelrhodopsin to investigate phase- and state-dependent modulation of breathing pattern in anaesthetized and freely behaving mice in normoxia, hypoxia and hypercapnia. In anaesthetized mice, photostimulation during inspiration increased inspiratory duration and amplitude regardless of baseline f, yet the effects were more robust at higher f. In anaesthetized mice with low f (<2.5 Hz), photostimulation during expiration evoked either phase advance or phase delay, whereas in anaesthetized mice with high f (≥2.5 Hz) and in freely behaving mice in normoxia, hypoxia or hypercapnia, photostimulation always evoked phase advance. Phase- and state-dependency is a function of overall breathing network excitability. The f-dependent probabilistic modulation of breathing pattern by preBötC SST+ neurons was unexpected, requiring reconsideration of current models of preBötC function, which neither predict nor can readily account for such responses.
Collapse
|
4
|
Cinelli E, Bongianni F, Pantaleo T, Mutolo D. Activation of μ-opioid receptors differentially affects the preBötzinger Complex and neighbouring regions of the respiratory network in the adult rabbit. Respir Physiol Neurobiol 2020; 280:103482. [DOI: 10.1016/j.resp.2020.103482] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Revised: 06/05/2020] [Accepted: 06/12/2020] [Indexed: 11/25/2022]
|
5
|
Montandon G, Horner RL. Electrocortical changes associating sedation and respiratory depression by the opioid analgesic fentanyl. Sci Rep 2019; 9:14122. [PMID: 31575947 PMCID: PMC6773755 DOI: 10.1038/s41598-019-50613-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2019] [Accepted: 09/12/2019] [Indexed: 01/05/2023] Open
Abstract
Opioid drugs are the mainstay of pain management but present the side-effect of respiratory depression that can be lethal with overdose. In addition to their respiratory effect, opioids also induce a profound sedative state and produce electrocortical features characteristic of a state of reduced brain arousal, similar to anaesthesia or sleep. In such states, respiratory activity depends more on the integrity of the brainstem respiratory network than it does during wakefulness. Accordingly, we propose that sedation by fentanyl induces specific electrocortical changes consistent with reduced brain arousal, and that the magnitude of respiratory depression is associated with distinct electrocortical changes. To these aims, we determined the effects of systemic injections of fentanyl (dosage 100 µg ·kg) versus control on electrocortical and respiratory activities of freely-behaving rats. We found that fentanyl induced electrocortical changes that differed from those observed in sleep or wakefulness. Fentanyl increased δ (1-3 Hz) frequency power (P < 0.001), but reduced α (7.5-13.5 Hz) and β2 (20-30 Hz) powers (P = 0.012 and P < 0.001, respectively), when compared to wakefulness. Interestingly, respiratory rate depression by fentanyl was significantly correlated with increased θ power (R = 0.61, P < 0.001), therefore showing a clear association between electrocortical activity and the magnitude of respiratory rate depression. Overall, we provide new evidence linking specific electrocortical changes to the severity of respiratory depression by opioids, which highlights the importance of considering the cortical and subcortical effects of opioids in addition to their impacts on breathing when evaluating opioid-induced respiratory depression.
Collapse
Affiliation(s)
- Gaspard Montandon
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Canada.
- Keenan Research Centre for Biomedical Sciences, Unity Health Toronto - St. Michael's Hospital, Toronto, Canada.
| | - Richard L Horner
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Canada
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Canada
| |
Collapse
|
6
|
Pickett KL, Stein PS, Vincen-Brown MA, Pilarski JQ. Maturation of Breathing-Related Inhibitory Neurotransmission in the Medulla Oblongata of the Embryonic and Perinatal Zebra Finch (Taeniopygia guttata). Dev Neurobiol 2018; 78:1081-1096. [PMID: 30160056 PMCID: PMC6596416 DOI: 10.1002/dneu.22632] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 07/07/2018] [Accepted: 07/08/2018] [Indexed: 11/05/2022]
Abstract
The medullary portion of the embryonic zebra finch hindbrain was isolated and superfused with physiologically relevant artificial cerebral spinal fluid. This in vitro preparation produced uninterrupted rhythmic episodes of neural activity via cranial nerve IX (glossopharyngeal) from embryonic day 4 (E4) through hatching on E14. Cranial nerve IX carries motor activity to the glottis during the inspiratory phase of breathing, and we focused on the role of synaptic inhibition during the embryonic and perinatal maturation of this branchiomotor outflow. We show that spontaneous neural activity (SNA) is first observed on E4 and temporally transforms as the embryo ages. To start, SNA is dependent on the excitatory actions of GABAA and glycine. As the embryo continues to develop, GABAergic and glycinergic neurotransmission take on a modulatory role, albeit an excitatory one, through E10. After that, data show that GABAergic and glycinergic neurotransmission switches to a phenotype consistent with inhibition, coincident with the onset of functional breathing. We also report that the inhibitory action of GABAergic and glycinergic receptor gating is not necessary for the spontaneous generation of branchiomotor motor rhythms in these birds near hatching. This is the first report focusing on the development of central breathing-related inhibitory neurotransmission in birds during the entire period of embryogenesis.
Collapse
Affiliation(s)
- Kaci L. Pickett
- Department of Biological Sciences, Idaho State University, Pocatello, ID. 83209-8007
| | - Paxton S. Stein
- Department of Biological Sciences, Idaho State University, Pocatello, ID. 83209-8007
| | | | - Jason Q. Pilarski
- Department of Biological Sciences, Idaho State University, Pocatello, ID. 83209-8007
- Department of Dental Sciences, Idaho State University, Pocatello, ID. 83209-8007
| |
Collapse
|
7
|
David F, Çarçak N, Furdan S, Onat F, Gould T, Mészáros Á, Di Giovanni G, Hernández VM, Chan CS, Lőrincz ML, Crunelli V. Suppression of Hyperpolarization-Activated Cyclic Nucleotide-Gated Channel Function in Thalamocortical Neurons Prevents Genetically Determined and Pharmacologically Induced Absence Seizures. J Neurosci 2018; 38:6615-6627. [PMID: 29925625 PMCID: PMC6067077 DOI: 10.1523/jneurosci.0896-17.2018] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Revised: 04/13/2018] [Accepted: 05/05/2018] [Indexed: 12/31/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and the Ih current they generate contribute to the pathophysiological mechanisms of absence seizures (ASs), but their precise role in neocortical and thalamic neuronal populations, the main components of the network underlying AS generation, remains controversial. In diverse genetic AS models, Ih amplitude is smaller in neocortical neurons and either larger or unchanged in thalamocortical (TC) neurons compared with nonepileptic strains. A lower expression of neocortical HCN subtype 1 channels is present in genetic AS-prone rats, and HCN subtype 2 knock-out mice exhibit ASs. Furthermore, whereas many studies have characterized Ih contribution to "absence-like" paroxysmal activity in vitro, no data are available on the specific role of cortical and thalamic HCN channels in behavioral seizures. Here, we show that the pharmacological block of HCN channels with the antagonist ZD7288 applied via reverse microdialysis in the ventrobasal thalamus (VB) of freely moving male Genetic Absence Epilepsy Rats from Strasbourg decreases TC neuron firing and abolishes spontaneous ASs. A similar effect is observed on γ-hydroxybutyric acid-elicited ASs in normal male Wistar rats. Moreover, thalamic knockdown of HCN channels via virally delivered shRNA into the VB of male Stargazer mice, another genetic AS model, decreases spontaneous ASs and Ih-dependent electrophysiological properties of VB TC neurons. These findings provide the first evidence that block of TC neuron HCN channels prevents ASs and suggest that any potential anti-absence therapy that targets HCN channels should carefully consider the opposite role for cortical and thalamic Ih in the modulation of absence seizures.SIGNIFICANCE STATEMENT Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels play critical roles in the fine-tuning of cellular and network excitability and have been suggested to be a key element of the pathophysiological mechanism underlying absence seizures. However, the precise contribution of HCN channels in neocortical and thalamic neuronal populations to these nonconvulsive seizures is still controversial. In the present study, pharmacological block and genetic suppression of HCN channels in thalamocortical neurons in the ventrobasal thalamic nucleus leads to a marked reduction in absence seizures in one pharmacological and two genetic rodent models of absence seizures. These results provide the first evidence that block of TC neuron HCN channels prevents absence seizures.
Collapse
Affiliation(s)
- François David
- Neuroscience Division, School of Biosciences, Cardiff University, Cardiff CF10 3AX, United Kingdom,
- Lyon Neuroscience Research Center, CNRS UMR 5292-INSERM U1028-Université Claude Bernard, 69008 Lyon, France
| | - Nihan Çarçak
- Neuroscience Division, School of Biosciences, Cardiff University, Cardiff CF10 3AX, United Kingdom
- Department of Pharmacology, Faculty of Pharmacy, Istanbul University, Istanbul, Turkey
| | - Szabina Furdan
- Department of Physiology, Anatomy, and Neuroscience, University of Szeged, Szeged 6726, Hungary
| | - Filiz Onat
- Department of Pharmacology and Clinical 34452 Pharmacology, Marmara University School of Medicine, Istanbul 81326, Turkey
| | - Timothy Gould
- Neuroscience Division, School of Biosciences, Cardiff University, Cardiff CF10 3AX, United Kingdom
| | - Ádám Mészáros
- Department of Physiology, Anatomy, and Neuroscience, University of Szeged, Szeged 6726, Hungary
| | - Giuseppe Di Giovanni
- Department of Physiology and Biochemistry, University of Malta, Msida MSD 2080, Malta, and
| | - Vivian M Hernández
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Robert H Lurie Medical Research Center, Chicago, Illinois 60611
| | - C Savio Chan
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Robert H Lurie Medical Research Center, Chicago, Illinois 60611
| | - Magor L Lőrincz
- Department of Physiology, Anatomy, and Neuroscience, University of Szeged, Szeged 6726, Hungary
| | - Vincenzo Crunelli
- Neuroscience Division, School of Biosciences, Cardiff University, Cardiff CF10 3AX, United Kingdom,
- Department of Physiology and Biochemistry, University of Malta, Msida MSD 2080, Malta, and
| |
Collapse
|
8
|
δ-Subunit Containing GABA A Receptors Modulate Respiratory Networks. Sci Rep 2017; 7:18105. [PMID: 29273726 PMCID: PMC5741762 DOI: 10.1038/s41598-017-17379-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Accepted: 11/13/2017] [Indexed: 12/20/2022] Open
Abstract
Persistent and stable respiratory activity across behavioral states is key to homeostasis. Extrasynaptic δ-subunit containing GABAA receptors (δGABAARs) mediate tonic inhibition and regulate network activity. However, the influence of δGABAARs on respiratory rhythm and motor outputs is unknown. We manipulated extra-synaptic GABAA receptor function in the preBötzinger Complex (preBötC), a site central to the generation of inspiratory motor activity in mammals. Activation of preBötC δGABAARs in anesthetized rats and wild-type mice decreased breathing rate. In δGABAAR knockout (Gabrd -/-) mice, however, δGABAARs activation had no effect on breathing rate. We then found that during active wakefulness associated with behaviors and movements, diaphragm activation was higher in the Gabrd -/- compared to wild-type mice, but not in other states. These findings identify that δGABAARs modulate the respiratory network, which is critical to understand how δGABAARs change breathing in pathological conditions affecting extra-synaptic GABAA receptor function such as exposure to anesthetics and neurosteroids.
Collapse
|
9
|
Contribution of the respiratory network to rhythm and motor output revealed by modulation of GIRK channels, somatostatin and neurokinin-1 receptors. Sci Rep 2016; 6:32707. [PMID: 27599866 PMCID: PMC5013327 DOI: 10.1038/srep32707] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Accepted: 07/28/2016] [Indexed: 01/07/2023] Open
Abstract
Breathing is generated by a respiratory network in the brainstem. At its core, a population of neurons expressing neurokinin-1 receptors (NK1R) and the peptide somatostatin (SST) form the preBötzinger Complex (preBötC), a site essential for the generation of breathing. PreBötC interneurons generate rhythm and follower neurons shape motor outputs by activating upper airway respiratory muscles. Since NK1R-expressing preBötC neurons are preferentially inhibited by μ-opioid receptors via activation of GIRK channels, NK1R stimulation may also involve GIRK channels. Hence, we identify the contribution of GIRK channels to rhythm, motor output and respiratory modulation by NK1Rs and SST. In adult rats, GIRK channels were identified in NK1R-expressing preBötC cells. Their activation decreased breathing rate and genioglossus muscle activity, an important upper airway muscle. NK1R activation increased rhythmic breathing and genioglossus muscle activity in wild-type mice, but not in mice lacking GIRK2 subunits (GIRK2−/−). Conversely, SST decreased rhythmic breathing via SST2 receptors, reduced genioglossus muscle activity likely through SST4 receptors, but did not involve GIRK channels. In summary, NK1R stimulation of rhythm and motor output involved GIRK channels, whereas SST inhibited rhythm and motor output via two SST receptor subtypes, therefore revealing separate circuits mediating rhythm and motor output.
Collapse
|
10
|
G-protein-gated Inwardly Rectifying Potassium Channels Modulate Respiratory Depression by Opioids. Anesthesiology 2016; 124:641-50. [PMID: 26675532 DOI: 10.1097/aln.0000000000000984] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Drugs acting on μ-opioid receptors (MORs) are widely used as analgesics but present side effects including life-threatening respiratory depression. MORs are G-protein-coupled receptors inhibiting neuronal activity through calcium channels, adenylyl cyclase, and/or G-protein-gated inwardly rectifying potassium (GIRK) channels. The pathways underlying MOR-dependent inhibition of rhythmic breathing are unknown. METHODS By using a combination of genetic, pharmacological, and physiological tools in rodents in vivo, the authors aimed to identify the role of GIRK channels in MOR-mediated inhibition of respiratory circuits. RESULTS GIRK channels were expressed in the ventrolateral medulla, a neuronal population regulating rhythmic breathing, and GIRK channel activation with flupirtine reduced respiratory rate in rats (percentage of baseline rate in mean ± SD: 79.4 ± 7.4%, n = 7), wild-type mice (82.6 ± 3.8%, n = 3), but not in mice lacking the GIRK2 subunit, an integral subunit of neuronal GIRK channels (GIRK2, 101.0 ± 1.9%, n = 3). Application of the MOR agonist [D-Ala, N-MePhe, Gly-ol]-enkephalin (DAMGO) to the ventrolateral medulla depressed respiratory rate, an effect partially reversed by the GIRK channel blocker Tertiapin-Q (baseline: 42.1 ± 7.4 breath/min, DAMGO: 26.1 ± 13.4 breath/min, Tertiapin-Q + DAMGO: 33.9 ± 9.8 breath/min, n = 4). Importantly, DAMGO applied to the ventrolateral medulla failed to reduce rhythmic breathing in GIRK2 mice (percentage of baseline rate: 103.2 ± 12.1%, n = 4), whereas it considerably reduced rate in wild-type mice (62.5 ± 17.7% of baseline, n = 4). Respiratory rate depression by systemic injection of the opioid analgesic fentanyl was markedly reduced in GIRK2 (percentage of baseline: 12.8 ± 15.8%, n = 5) compared with wild-type mice (72.9 ± 27.3%). CONCLUSIONS Overall, these results identify that GIRK channels contribute to respiratory inhibition by MOR, an essential step toward understanding respiratory depression by opioids.
Collapse
|
11
|
Hajek MA, Buchanan GF. Influence of vigilance state on physiological consequences of seizures and seizure-induced death in mice. J Neurophysiol 2016; 115:2286-93. [PMID: 26888097 DOI: 10.1152/jn.00011.2016] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 02/13/2016] [Indexed: 12/31/2022] Open
Abstract
Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy. SUDEP occurs more commonly during nighttime sleep. The details of why SUDEP occurs at night are not well understood. Understanding why SUDEP occurs at night during sleep might help to better understand why SUDEP occurs at all and hasten development of preventive strategies. Here we aimed to understand circumstances causing seizures that occur during sleep to result in death. Groups of 12 adult male mice were instrumented for EEG, EMG, and EKG recording and subjected to seizure induction via maximal electroshock (MES) during wakefulness, nonrapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep. Seizure inductions were performed with concomitant EEG, EMG, and EKG recording and breathing assessment via whole body plethysmography. Seizures induced via MES during sleep were associated with more profound respiratory suppression and were more likely to result in death. Despite REM sleep being a time when seizures do not typically occur spontaneously, when seizures were forced to occur during REM sleep, they were invariably fatal in this model. An examination of baseline breathing revealed that mice that died following a seizure had increased baseline respiratory rate variability compared with those that did not die. These data demonstrate that sleep, especially REM sleep, can be a dangerous time for a seizure to occur. These data also demonstrate that there may be baseline respiratory abnormalities that can predict which individuals have higher risk for seizure-induced death.
Collapse
Affiliation(s)
- Michael A Hajek
- Department of Neurology, Yale School of Medicine, New Haven, Connecticut
| | - Gordon F Buchanan
- Department of Neurology, Yale School of Medicine, New Haven, Connecticut; Veterans Affairs Medical Center, West Haven, Connecticut; and Department of Neurology, University of Iowa Carver College of Medicine, Iowa City, Iowa
| |
Collapse
|
12
|
Giles WR, Carmeliet EE. Editorial commentary: This sodium current may be late, but it is important. Trends Cardiovasc Med 2016; 26:123-5. [DOI: 10.1016/j.tcm.2015.06.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Accepted: 06/06/2015] [Indexed: 12/18/2022]
|
13
|
Feldman JL, Kam K. Facing the challenge of mammalian neural microcircuits: taking a few breaths may help. J Physiol 2015; 593:3-23. [PMID: 25556783 DOI: 10.1113/jphysiol.2014.277632] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Accepted: 11/01/2014] [Indexed: 12/27/2022] Open
Abstract
Breathing in mammals is a seemingly straightforward behaviour controlled by the brain. A brainstem nucleus called the preBötzinger Complex sits at the core of the neural circuit generating respiratory rhythm. Despite the discovery of this microcircuit almost 25 years ago, the mechanisms controlling breathing remain elusive. Given the apparent simplicity and well-defined nature of regulatory breathing behaviour, the identification of much of the circuitry, and the ability to study breathing in vitro as well as in vivo, many neuroscientists and physiologists are surprised that respiratory rhythm generation is still not well understood. Our view is that conventional rhythmogenic mechanisms involving pacemakers, inhibition or bursting are problematic and that simplifying assumptions commonly made for many vertebrate neural circuits ignore consequential detail. We propose that novel emergent mechanisms govern the generation of respiratory rhythm. That a mammalian function as basic as rhythm generation arises from complex and dynamic molecular, synaptic and neuronal interactions within a diverse neural microcircuit highlights the challenges in understanding neural control of mammalian behaviours, many (considerably) more elaborate than breathing. We suggest that the neural circuit controlling breathing is inimitably tractable and may inspire general strategies for elucidating other neural microcircuits.
Collapse
Affiliation(s)
- Jack L Feldman
- Systems Neurobiology Laboratory, Department of Neurobiology, David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, CA, USA
| | | |
Collapse
|
14
|
Montandon G, Horner R. CrossTalk proposal: The preBotzinger complex is essential for the respiratory depression following systemic administration of opioid analgesics. J Physiol 2015; 592:1159-62. [PMID: 24634011 DOI: 10.1113/jphysiol.2013.261974] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
|