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Herman MA, Gillis RA, Vicini S, Dretchen KL, Sahibzada N. Tonic GABAA receptor conductance in medial subnucleus of the tractus solitarius neurons is inhibited by activation of μ-opioid receptors. J Neurophysiol 2011; 107:1022-31. [PMID: 22114164 DOI: 10.1152/jn.00853.2011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Our laboratory previously reported that gastric activity is controlled by a robust GABA(A) receptor-mediated inhibition in the medial nucleus of the tractus solitarius (mNTS) (Herman et al. 2009), and that μ-opioid receptor activation inhibits gastric tone by suppression of this GABA signaling (Herman et al. 2010). These data raised two questions: 1) whether any of this inhibition was due to tonic GABA(A) receptor-mediated conductance in the mNTS; and 2) whether μ-opioid receptor activation suppressed both tonic and phasic GABA signaling. In whole cell recordings from rat mNTS neurons, application of three GABA(A) receptor antagonists (gabazine, bicuculline, and picrotoxin) produced a persistent reduction in holding current and decrease in population variance or root mean square (RMS) noise, suggesting a blockade of tonic GABA signaling. Application of gabazine at a lower concentration abolished phasic currents, but had no effect on tonic currents or RMS noise. Application of the δ-subunit preferring agonist gaboxadol (THIP) produced a dose-dependent persistent increase in holding current and RMS noise. Pretreatment with tetrodotoxin prevented the action of gabazine, but had no effect on the THIP-induced current. Membrane excitability was unaffected by the selective blockade of phasic inhibition, but was increased by blockade of both phasic and tonic currents. In contrast, activation of tonic currents decreased membrane excitability. Application of the μ-opioid receptor agonist DAMGO produced a persistent reduction in holding current that was not observed following pretreatment with a GABA(A) receptor antagonist and was not evident in mice lacking the δ-subunit. These data suggest that mNTS neurons possess a robust tonic inhibition that is mediated by GABA(A) receptors containing the δ-subunit, that determines membrane excitability, and that is partially regulated by μ-opioid receptors.
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Affiliation(s)
- Melissa A Herman
- Interdisciplinary Program in Neuroscience, Georgetown University, Washington, District of Columbia, USA
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Dufour A, Tell F, Baude A. Perinatal development of inhibitory synapses in the nucleus tractus solitarii of the rat. Eur J Neurosci 2010; 32:538-49. [PMID: 20718854 DOI: 10.1111/j.1460-9568.2010.07309.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The nucleus tractus solitarii (NTS) plays a key role in the central control of the autonomic nervous system. In adult rats, both GABA and glycine are used as inhibitory neurotransmitter in the NTS. Using a quantitative morphological approach, we have investigated the perinatal development of inhibitory synapses in the NTS. The density of both inhibitory axon terminals and synapses increased from embryonic day 20 until the end of the second postnatal week (postnatal day 14). Before birth, only GABAergic axon terminals developed and their number increased during the first postnatal week. Mixed GABA/glycine axon terminals appeared at birth and their number increased during the first postnatal week. This suggests the development of a mixed GABA/glycine inhibition in parallel to pure GABA inhibition. However, whereas GABAergic axon terminals were distributed throughout the NTS, mixed GABA/glycine axon terminals were strictly located in the lateral part of the NTS. Established at birth, this specific topography remained in the adult rat. From birth, GABA(A) receptors, glycine receptors and gephyrin were clustered in inhibitory synapses throughout the NTS, revealing a neurotransmitter-receptor mismatch within the medial part of the NTS. Together these results suggest that NTS inhibitory networks develop and mature until postnatal day 14. Developmental changes in NTS synaptic inhibition may play an important role in shaping neural network activity during a time of maturation of autonomic functions. The first two postnatal weeks could represent a critical period where the impact of the environment influences the physiological phenotypes of adult rats.
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Affiliation(s)
- Amandine Dufour
- Centre National de Recherche Scientifique, CRN2M, Unité Mixte de Recherche 6231, Université Paul Cézanne, Université de Méditerranée, IFR Jean Roche, Faculté de Médecine, CS80011, Boulevard Pierre Dramard, 13344, Marseille Cx15, France
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Jin YH, Zhang Z, Mendelowitz D, Andresen MC. Presynaptic actions of propofol enhance inhibitory synaptic transmission in isolated solitary tract nucleus neurons. Brain Res 2009; 1286:75-83. [PMID: 19559683 DOI: 10.1016/j.brainres.2009.06.058] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2009] [Revised: 06/17/2009] [Accepted: 06/18/2009] [Indexed: 10/20/2022]
Abstract
General anesthetics variably enhance inhibitory synaptic transmission that relies on (-aminobutyric acid (GABA) and GABAA receptor function with distinct differences across brain regions. Activation of "extra-synaptic" GABAA receptors produces a tonic current considered the most sensitive target for general anesthetics, particularly in forebrain neurons. To evaluate the contribution of poor drug access to neurons in slices, we tested the intravenous anesthetic propofol in mechanically isolated neurons from the solitary tract nucleus (NTS). Setting chloride concentrations to ECl=-29 mV made GABA currents inward at holding potentials of -60 mV. Propofol triggered pronounced but slowly-developing tonic currents that reversed with 5 min washing. Effective concentrations in isolated cells were lower than in slices and propofol enhanced phasic IPSCs more potently than tonic currents (1 microM increased phasic decay-time constant vs. >3 microM tonic currents). Propofol increased IPSC frequency (>3 microM), a presynaptic action. Bicuculline blocked all propofol actions. Gabazine blocked only phasic IPSCs. IPSCs persisted in TTX and/or cadmium but these agents prevented propofol-induced increases in IPSC frequency. Furosemide (>1 mM) reversibly blocked propofol-evoked IPSC frequency changes without altering waveforms. We conclude that presynaptic actions of propofol depend on a depolarizing chloride gradient across presynaptic inhibitory terminals. Our results in isolated neurons indicate that propofol pharmacokinetics intrinsically trigger the tonic currents slowly and the time course is not related to slow permeation or delivery. Unlike forebrain, phasic NTS GABAA receptors are more sensitive to propofol than tonic receptors but that presynaptic GABAA receptor mechanisms regulate GABA release.
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Affiliation(s)
- Young-Ho Jin
- Department of Physiology, Kyung Hee University, Seoul 130-701, Republic of Korea
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Slavíková B, Krištofíková Z, Chodounská H, Buděšínský M, Durán FJ, Veleiro AS, Burton G, Kasal A. Allopregnanolone (3α-Hydroxy-5α-pregnan-20-one) Derivatives with a Polar Chain in Position 16α: Synthesis and Activity. J Med Chem 2009; 52:2119-25. [DOI: 10.1021/jm801454a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Barbora Slavíková
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Zdena Krištofíková
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Hana Chodounská
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Miloš Buděšínský
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Fernando J. Durán
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Adriana S. Veleiro
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Gerardo Burton
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
| | - Alexander Kasal
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, CZ16610 Prague 6, Czech Republic, Prague Psychiatric Centre, Ústavní 91, CZ18103 Prague, Czech Republic, and Departamento de Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
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Grabauskas G. Time course of GABA in the synaptic clefts of inhibitory synapses in the rostral nucleus of the solitary tract. Neurosci Lett 2005; 373:10-5. [PMID: 15555768 DOI: 10.1016/j.neulet.2004.09.051] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2004] [Revised: 09/22/2004] [Accepted: 09/23/2004] [Indexed: 11/26/2022]
Abstract
Concentration and time course of neurotransmitter in the synaptic cleft determines the amplitude and the duration of the resulting postsynaptic current. However, technical limitations involved in monitoring the time course of neurotransmitter concentration in the extra-cellular space have prevented direct evaluation of factors that influence neurotransmitter level in the cleft. Tetanic stimulation results in saturation of postsynaptic GABA(A) receptors in the rostral nucleus of the solitary tract (rNST) and GABA diffusion defines the decay time course of the inhibitory potentials or currents (IPSP/Cs). By applying a GABA concentration-response curve to these data it is possible to calculate the GABA concentration transient in the clefts of rNST inhibitory synapses. The analysis indicates that tetanic stimulation produces a GABA concentration that exceeds the concentration of neurotransmitter required to activate all postsynaptic GABA(A) receptors, resulting in short-term modification of the IPSP/Cs decay time. Moreover, the results also demonstrate that the rate of diffusion of GABA from the synaptic cleft is defined by two exponentials. A mathematical model of this process has been developed that supports these conclusions.
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Affiliation(s)
- Gintautas Grabauskas
- Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, MI 48109, USA.
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Tolstykh G, Belugin S, Mifflin S. Responses to GABA(A) receptor activation are altered in NTS neurons isolated from chronic hypoxic rats. Brain Res 2004; 1006:107-13. [PMID: 15047029 DOI: 10.1016/j.brainres.2004.01.060] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/29/2004] [Indexed: 11/25/2022]
Abstract
The inhibitory amino acid GABA is released within the nucleus of the solitary tract (NTS) during hypoxia and modulates the respiratory response to hypoxia. To determine if responses of NTS neurons to activation of GABA(A) receptors are altered following exposure to chronic hypoxia, GABA(A) receptor-evoked whole cell currents were measured in enzymatically dispersed NTS neurons from normoxic and chronic hypoxic rats. Chronic hypoxic rats were exposed to 10% O(2) for 9-12 days. Membrane capacitance was the same in neurons from normoxic (6.9+/-0.5 pF, n=16) and hypoxic (6.3+/-0.5 pF, n=15) rats. The EC(50) for peak GABA-evoked current density was significantly greater in neurons from hypoxic (21.7+/-2.2 microM) compared to normoxic rats (12.2+/-0.9 microM) (p<0.001). Peak and 5-s adapted GABA currents evoked by 1, 3 and 10 microM were greater in neurons from normoxic compared to hypoxic rats (p<0.05) whereas peak and 5-s adapted responses to 30 and 100 microM GABA were not different comparing normoxic to hypoxic rats. Desensitization of GABA(A)-evoked currents was observed at concentrations greater than 3 microM and, measured as the ratio of the current 5 s after the onset of 100 microM GABA application to the peak GABA current, was the same in neurons from normoxic (0.37+/-0.03) and hypoxic rats (0.33+/-0.04). Reduced sensitivity to GABA(A) receptor-evoked inhibition in chronic hypoxia could influence chemoreceptor afferent integration by NTS neurons.
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Affiliation(s)
- Gleb Tolstykh
- The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229-3900, USA
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