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Koniuszewski F, Vogel FD, Dajić I, Seidel T, Kunze M, Willeit M, Ernst M. Navigating the complex landscape of benzodiazepine- and Z-drug diversity: insights from comprehensive FDA adverse event reporting system analysis and beyond. Front Psychiatry 2023; 14:1188101. [PMID: 37457785 PMCID: PMC10345211 DOI: 10.3389/fpsyt.2023.1188101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Accepted: 06/05/2023] [Indexed: 07/18/2023] Open
Abstract
Introduction Medications which target benzodiazepine (BZD) binding sites of GABAA receptors (GABAARs) have been in widespread use since the nineteen-sixties. They carry labels as anxiolytics, hypnotics or antiepileptics. All benzodiazepines and several nonbenzodiazepine Z-drugs share high affinity binding sites on certain subtypes of GABAA receptors, from which they can be displaced by the clinically used antagonist flumazenil. Additional binding sites exist and overlap in part with sites used by some general anaesthetics and barbiturates. Despite substantial preclinical efforts, it remains unclear which receptor subtypes and ligand features mediate individual drug effects. There is a paucity of literature comparing clinically observed adverse effect liabilities across substances in methodologically coherent ways. Methods In order to examine heterogeneity in clinical outcome, we screened the publicly available U.S. FDA adverse event reporting system (FAERS) database for reports of individual compounds and analyzed them for each sex individually with the use of disproportionality analysis. The complementary use of physico-chemical descriptors provides a molecular basis for the analysis of clinical observations of wanted and unwanted drug effects. Results and Discussion We found a multifaceted FAERS picture, and suggest that more thorough clinical and pharmacoepidemiologic investigations of the heterogenous side effect profiles for benzodiazepines and Z-drugs are needed. This may lead to more differentiated safety profiles and prescription practice for particular compounds, which in turn could potentially ease side effect burden in everyday clinical practice considerably. From both preclinical literature and pharmacovigilance data, there is converging evidence that this very large class of psychoactive molecules displays a broad range of distinctive unwanted effect profiles - too broad to be explained by the four canonical, so-called "diazepam-sensitive high-affinity interaction sites". The substance-specific signatures of compound effects may partly be mediated by phenomena such as occupancy of additional binding sites, and/or synergistic interactions with endogenous substances like steroids and endocannabinoids. These in turn drive the wanted and unwanted effects and sex differences of individual compounds.
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Affiliation(s)
- Filip Koniuszewski
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Florian D. Vogel
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Irena Dajić
- Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria
| | - Thomas Seidel
- Department of Pharmaceutical Sciences, University of Vienna, Vienna, Austria
| | - Markus Kunze
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Matthäus Willeit
- Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria
| | - Margot Ernst
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
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Liu J, Lin D, Yau A, Cottrell JE, Kass IS. Early-life propofol exposure does not affect later-life GABAergic inhibition, seizure induction, or social behavior. IBRO Neurosci Rep 2023; 14:483-493. [PMID: 37252630 PMCID: PMC10220478 DOI: 10.1016/j.ibneur.2023.05.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Accepted: 05/13/2023] [Indexed: 05/31/2023] Open
Abstract
The early developing brain is especially vulnerable to anesthesia, which can result in long lasting functional changes. We examined the effects of early-life propofol on adult excitatory-inhibitory balance and behavior. Postnatal day 7 male mice were exposed to propofol (250 mg/kg i.p.) and anesthesia was maintained for 2 h; control mice were given the same volume of isotonic saline and treated identically. The behavior and electrophysiology experiments were conducted when the mice were adults. We found that a 2-h neonatal propofol exposure did not significantly reduce paired pulse inhibition, alter the effect of muscimol (3 µM) to inhibit field excitatory postsynaptic potentials or alter the effect of bicuculline (100 µM) to increase the population spike in the CA1 region of hippocampal slices from adult mice. Neonatal propofol did not alter the evoked seizure response to pentylenetetrazol in adult mice. Neonatal propofol did not affect anxiety, as measured in the open field apparatus, depression-like behavior, as measured by the forced swim test, or social interactions with novel mice, in either the three-chamber or reciprocal social tests. These results were different from those with neonatal sevoflurane which demonstrated reduced adult GABAergic inhibition, increased seizure susceptibility and reduced social interaction. Even though sevoflurane and propofol both prominently enhance GABA inhibition, they have unique properties that alter the long-term effects of early-life exposure. These results indicate that clinical studies grouping several general anesthetic agents in a single group should be interpreted with great caution when examining long-term effects.
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Affiliation(s)
- Jinyang Liu
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
| | - Daisy Lin
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
- Department of Physiology and Pharmacology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
| | - Alice Yau
- State University of New York Downstate Health Sciences University College of Medicine, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
| | - James E. Cottrell
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
| | - Ira S. Kass
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
- Department of Physiology and Pharmacology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
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Lin D, Liu J, Florveus A, Ganesan V, Cottrell JE, Kass IS. Exposure to Sevoflurane, But Not Ketamine, During Early-life Brain Development has Long-Lasting Effects on GABA A Receptor Mediated Inhibitory Neurotransmission. Neuroscience 2021; 472:116-127. [PMID: 34384844 DOI: 10.1016/j.neuroscience.2021.08.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Revised: 07/30/2021] [Accepted: 08/02/2021] [Indexed: 11/19/2022]
Abstract
Understanding the different mechanisms associated with different anesthetic targeted receptors is critical towards identifying accurate long-term outcome measures as a result of early-life anesthetic exposure. We examined changes in GABAA receptor mediated neurotransmission by a predominately GABAA receptor targeted anesthetic, sevoflurane or a predominately NMDA receptor targeted anesthetic, ketamine. Postnatal day 7 male mice were exposed to sevoflurane or ketamine and examined as adults for changes in inhibitory neurotransmission and its associated change in induced seizure activity. Paired pulse stimulation experiment showed that early-life sevoflurane treated mice had significantly less hippocampal CA1 inhibition later in life. There was significantly increased CA1 excitatory output in the sevoflurane treated group compared to the no sevoflurane treated group after the GABA agonist muscimol. Similar to our previously established data for early-life sevoflurane, here we established early-life ketamine administration resulted in neurodevelopmental behavioral changes later in life. However, muscimol did not produce a significant difference on the excitatory CA1 output between early-life ketamine group and saline group. While sevoflurane treated mice showed significantly higher induced seizure intensities and shorter latency periods to reach seizure intensity stage 5 (Racine score) compared with no sevoflurane treated mice, this phenomenon was not observed in the ketamine vs. saline treated groups. Early-life sevoflurane, but not ketamine, exposure reduced GABAergic inhibition and enhanced seizure activity later in life. The results indicate that early-life exposure to different anesthetics lead to distinct long-term effects and their unique pathways require mechanistic studies to understand induced long-lasting changes in the brain.
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Affiliation(s)
- Daisy Lin
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA; Department of Physiology and Pharmacology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
| | - Jinyang Liu
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
| | - Alizna Florveus
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
| | - Vanathi Ganesan
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
| | - James E Cottrell
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
| | - Ira S Kass
- Department of Anesthesiology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA; Department of Physiology and Pharmacology, State University of New York Downstate Health Sciences University, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA.
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Noma K, Akaike H, Kurauchi Y, Katsuki H, Oyama Y, Akaike N. Effects of triphenyltin on glycinergic transmission on rat spinal neurons. ENVIRONMENTAL RESEARCH 2018; 163:186-193. [PMID: 29453030 DOI: 10.1016/j.envres.2018.02.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Revised: 01/31/2018] [Accepted: 02/06/2018] [Indexed: 06/08/2023]
Abstract
Glycine is a fast inhibitory transmitter like γ-aminobutyric acid in the mammalian spinal cord and brainstem, and it is involved in motor reflex, nociception, and neuronal development. Triphenyltin (TPT) is an organometallic compound causing environmental hazard to many wild creatures. Our previous findings show that TPT ultimately induces a drain and/or exhaustion of glutamate in excitatory presynaptic nerve terminals, resulted in blockage of neurotransmission as well as methylmercury. Therefore, we have investigated the neurotoxic mechanism how TPT modulates inhibitory glycinergic transmission in the synaptic bouton preparation of rat isolated spinal neurons using a patch clamp technique. TPT at environmentally relevant concentrations (3-300 nM) significantly increased the number of frequency of glycinergic spontaneous and miniature inhibitory postsynaptic currents (sIPSC and mIPSC) without affecting the current amplitude and decay time. The TPT effects were also observed in external Ca2+-free solution containing tetrodotoxin (TTX) but removed in Ca2+-free solution with both TTX and BAPTA-AM (Ca2+ chelator). On the other hand, the amplitude of glycinergic evoked inhibitory postsynaptic currents (eIPSCs) increased with decreasing failure rate (Rf) and paired pulse ratio (PPR) in the presence of 300 nM TPT. At a high concentration (1 µM), TPT completely blocked eIPSCs after a transient facilitation. Overall, these results suggest that TPT directly acts transmitter-releasing machinery in glycinergic nerve terminals. Effects of TPT on the nerve terminals releasing fast transmitters were greater in the order of glycinergic > glutamatergic > GABAergic ones. Thus, TPT is supposed to cause a strong synaptic modulations on glycinergic neurotransmission in wild creatures.
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Affiliation(s)
- Kazuki Noma
- Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-Honmachi, Chuo-ku, Kumamoto 862-0973, Japan
| | - Hironari Akaike
- Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-Honmachi, Chuo-ku, Kumamoto 862-0973, Japan
| | - Yuki Kurauchi
- Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-Honmachi, Chuo-ku, Kumamoto 862-0973, Japan
| | - Hiroshi Katsuki
- Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-Honmachi, Chuo-ku, Kumamoto 862-0973, Japan
| | - Yasuo Oyama
- Laboratory of Bioassessment, Faculty of Bioscience and Bioindustry, Tokushima University, Minami-Josanjima 2-1, Tokushima 770-8501, Japan
| | - Norio Akaike
- Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-Honmachi, Chuo-ku, Kumamoto 862-0973, Japan; Research Division for Clinical Pharmacology, Medical Corporation, Juryo Group, Kumamoto Kinoh Hospital, 6-8-1 Yamamuro, Kita-ku, Kumamoto 860-8518, Japan; Research Division of Neurophysiology, Kitamoto Hospital, 3-7-6 Kawarasone, Koshigaya, Saitama 343-0821, Japan
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Betelli C, MacDermott AB, Bardoni R. Transient, activity dependent inhibition of transmitter release from low threshold afferents mediated by GABAA receptors in spinal cord lamina III/IV. Mol Pain 2015; 11:64. [PMID: 26463733 PMCID: PMC4605127 DOI: 10.1186/s12990-015-0067-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Accepted: 10/06/2015] [Indexed: 12/20/2022] Open
Abstract
Background Presynaptic GABAA receptors (GABAARs) located on central terminals of low threshold afferent fibers are thought to be involved in the processing of touch and possibly in the generation of tactile allodynia in chronic pain. These GABAARs mediate primary afferent depolarization (PAD) and modulate transmitter release. The objective of this study was to expand our understanding of the presynaptic inhibitory action of GABA released onto primary afferent central terminals following afferent stimulation. Results We recorded evoked postsynaptic excitatory responses (eEPSCs and eEPSPs) from lamina III/IV neurons in spinal cord slices from juvenile rats (P17–P23, either sex), while stimulating dorsal roots. We investigated time and activity dependent changes in glutamate release from low threshold A fibers and the impact of these changes on excitatory drive. Blockade of GABAARs by gabazine potentiated the second eEPSC during a train of four afferent stimuli in a large subset of synapses. This resulted in a corresponding increase of action potential firing after the second stimulus. The potentiating effect of gabazine was due to inhibition of endogenously activated presynaptic GABAARs, because it was not prevented by the blockade of postsynaptic GABAARs through intracellular perfusion of CsF. Exogenous activation of presynaptic GABAARs by muscimol depressed evoked glutamate release at all synapses and increased paired pulse ratio (PPR). Conclusions These observations suggest that afferent driven release of GABA onto low threshold afferent terminals is most effective following the first action potential in a train and serves to suppress the initial strong excitatory drive onto dorsal horn circuitry.
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Affiliation(s)
- Chiara Betelli
- Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Via Campi, 287, 41125, Modena, Italy.
| | - Amy B MacDermott
- Departments of Physiology and Cellular Biophysics, Neuroscience, Columbia University, 630 W. 168th Street, New York, NY, 10032, USA.
| | - Rita Bardoni
- Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Via Campi, 287, 41125, Modena, Italy.
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Wakita M, Kotani N, Yamaga T, Akaike N. Nitrous oxide directly inhibits action potential-dependent neurotransmission from single presynaptic boutons adhering to rat hippocampal CA3 neurons. Brain Res Bull 2015; 118:34-45. [PMID: 26343381 DOI: 10.1016/j.brainresbull.2015.09.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Revised: 08/26/2015] [Accepted: 09/01/2015] [Indexed: 11/16/2022]
Abstract
We evaluated the effects of N2O on synaptic transmission using a preparation of mechanically dissociated rat hippocampal CA3 neurons that allowed assays of single bouton responses evoked from native functional nerve endings. We studied the effects of N2O on GABAA, glutamate, AMPA and NMDA receptor-mediated currents (IGABA, IGlu, IAMPA and INMDA) elicited by exogenous application of GABA, glutamate, (S)-AMPA, and NMDA and spontaneous, miniature, and evoked GABAergic inhibitory and glutamatergic excitatory postsynaptic current (sIPSC, mIPSC, eIPSC, sEPSC, mEPSC and eEPSC) in mechanically dissociated CA3 neurons. eIPSC and eEPSC were evoked by focal electrical stimulation of a single bouton. Administration of 70% N2O altered neither IGABA nor the frequency and amplitude of both sIPSCs and mIPSCs. In contrast, N2O decreased the amplitude of eIPSCs, while increasing failure rates (Rf) and paired-pulse ratios (PPR) in a concentration-dependent manner. On the other hand, N2O decreased IGlu, IAMPA and INMDA. Again N2O did not change the frequency and amplitude of either sEPSCs of mEPSCs. N2O also decreased amplitudes of eEPSCs with increased Rf and PPR. The decay phases of all synaptic responses were unchanged. The present results indicated that N2O inhibits the activation of AMPA/KA and NMDA receptors and also that N2O preferentially depress the action potential-dependent GABA and glutamate releases but had little effects on spontaneous and miniature releases.
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Affiliation(s)
- Masahito Wakita
- Research Division for Clinical Pharmacology, Medical Corporation, Jyuryo Group, Kumamoto Kinoh Hospital, 6-8-1 Yamamuro, Kitaku, Kumamoto 860-8518, Japan; Research Division for Life Science, Kumamoto Health Science University, 325 Izumi-machi, Kitaku, Kumamoto 861-5598, Japan
| | - Naoki Kotani
- Research Division of Neurophysiology, Kitamoto Hospital, 3-7-6 Kawarasone, Koshigaya, Saitama 343-0821, Japan
| | - Toshitaka Yamaga
- Research Division for Life Science, Kumamoto Health Science University, 325 Izumi-machi, Kitaku, Kumamoto 861-5598, Japan
| | - Norio Akaike
- Research Division for Clinical Pharmacology, Medical Corporation, Jyuryo Group, Kumamoto Kinoh Hospital, 6-8-1 Yamamuro, Kitaku, Kumamoto 860-8518, Japan; Research Division for Life Science, Kumamoto Health Science University, 325 Izumi-machi, Kitaku, Kumamoto 861-5598, Japan; Research Division of Neurophysiology, Kitamoto Hospital, 3-7-6 Kawarasone, Koshigaya, Saitama 343-0821, Japan.
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Wakita M, Kotani N, Kogure K, Akaike N. Inhibition of excitatory synaptic transmission in hippocampal neurons by levetiracetam involves Zn²⁺-dependent GABA type A receptor-mediated presynaptic modulation. J Pharmacol Exp Ther 2013; 348:246-59. [PMID: 24259680 DOI: 10.1124/jpet.113.208751] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Levetiracetam (LEV) is an antiepileptic drug with a unique but as yet not fully resolved mechanism of action. Therefore, by use of a simplified rat-isolated nerve-bouton preparation, we have investigated how LEV modulates glutamatergic transmission from mossy fiber terminals to hippocampal CA3 neurons. Action potential-evoked excitatory postsynaptic currents (eEPSCs) were recorded using a conventional whole-cell patch-clamp recording configuration in voltage-clamp mode. The antiepileptic drug phenytoin decreased glutamatergic eEPSCs in a concentration-dependent fashion by inhibiting voltage-dependent Na⁺ and Ca²⁺ channel currents. In contrast, LEV had no effect on eEPSCs or voltage-dependent Na⁺ or Ca²⁺ channel currents. Activation of presynaptic GABA type A (GABA(A)) receptors by muscimol induced presynaptic inhibition of eEPSCs, resulting from depolarization block. Low concentrations of Zn²⁺, which had no effect on eEPSCs, voltage-dependent Na⁺ or Ca²⁺ channel currents, or glutamate receptor-mediated whole cell currents, reduced the muscimol-induced presynaptic inhibition. LEV applied in the continuous presence of 1 µM muscimol and 1 µM Zn²⁺ reversed this Zn²⁺ modulation on eEPSCs. The antagonizing effect of LEV on Zn²⁺-induced presynaptic GABA(A) receptor inhibition was also observed with the Zn²⁺ chelators Ca-EDTA and RhodZin-3. Our results clearly show that LEV removes the Zn²⁺-induced suppression of GABA(A)-mediated presynaptic inhibition, resulting in a presynaptic decrease in glutamate-mediated excitatory transmission. Our results provide a novel mechanism by which LEV may inhibit neuronal activity.
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Affiliation(s)
- Masahito Wakita
- Research Division for Clinical Pharmacology, Medical Corporation, Jyuryokai, Kumamoto Kinoh Hospital, Kumamoto, Japan (M.W., N.A.); Research Division for Life Science, Kumamoto Health Science University, Kumamoto, Japan (M.W., N.A.); Research Division of Neurophysiology, Kitamoto Hospital, Koshigaya, Japan (N.K., N.A); and Kogure Medical Clinic, Chouseikai Medical Corporation, Fukaya City, Saitama, Japan (K.K.)
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Wakita M, Kotani N, Nonaka K, Shin MC, Akaike N. Effects of propofol on GABAergic and glutamatergic transmission in isolated hippocampal single nerve-synapse preparations. Eur J Pharmacol 2013; 718:63-73. [DOI: 10.1016/j.ejphar.2013.09.018] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 08/26/2013] [Accepted: 09/04/2013] [Indexed: 01/12/2023]
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Piracetam induces plasma membrane depolarization in rat brain synaptosomes. Neurosci Lett 2013; 553:206-10. [DOI: 10.1016/j.neulet.2013.08.045] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Revised: 08/02/2013] [Accepted: 08/20/2013] [Indexed: 11/17/2022]
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Iwata S, Wakita M, Shin MC, Fukuda A, Akaike N. Modulation of allopregnanolone on excitatory transmitters release from single glutamatergic terminal. Brain Res Bull 2013; 93:39-46. [DOI: 10.1016/j.brainresbull.2012.11.002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Revised: 11/02/2012] [Accepted: 11/05/2012] [Indexed: 10/27/2022]
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Shin MC, Wakita M, Iwata S, Nonaka K, Kotani N, Akaike N. Comparative effects of pentobarbital on spontaneous and evoked transmitter release from inhibitory and excitatory nerve terminals in rat CA3 neurons. Brain Res Bull 2012; 90:10-8. [PMID: 23026118 DOI: 10.1016/j.brainresbull.2012.09.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Revised: 09/14/2012] [Accepted: 09/19/2012] [Indexed: 10/27/2022]
Abstract
Pentobarbital (PB) modulates GABA(A) receptor-mediated postsynaptic responses through various mechanisms, and can directly activate the channel at higher doses. These channels exist both pre- and postsynaptically, and on the soma outside the synapse. PB also inhibits voltage-dependent Na⁺ and Ca²⁺ channels to decrease excitatory synaptic transmission. Just how these different sites of action combine to contribute to the overall effects of PB on inhibitory and excitatory synaptic transmission is less clear. To compare these pre- and postsynaptic actions of PB, we used a 'synaptic bouton' preparation of isolated rat hippocampal CA3 pyramidal neurons where we could measure in single neurons the effects of PB on spontaneous and single bouton evoked GABAergic inhibitory and glutamatergic excitatory postsynaptic currents (sIPSCs, sEPSCs, eIPSCs and eEPSCs), respectively. Low (sedative) concentrations (3-10 μM) of PB increased the frequency and amplitude of sIPSCs and sEPSCs, and also presynaptically increased the amplitude of both eIPSCs and eEPSCs. There was no change in current kinetics at this low concentration. At higher concentrations (30-300 μM), PB decreased the frequency, and increased the amplitude of sIPSCs, and presynaptically decreased the amplitude of eIPSCs. The current decay phase of sIPSCs and eIPSCs was increased. An increase in both frequency and amplitude was seen for sEPSCs, while the eIPSCs was also decreased by a bicuculline-sensitive presynaptic effect. The results confirm the multiple sites of action of PB on inhibitory and excitatory transmission and demonstrate that the most sensitive site of action is on transmitter release, via effects on presynaptic GABA(A) receptors. At low concentrations, however, both glutamate and GABA release is similarly enhanced, making the final effects on neuronal excitability difficult to predict and dependent on the particular systems involved and/or on subtle differences in susceptibility amongst individuals. At higher concentrations, release of both transmitters is decreased, while the postsynaptic effects to increase IPSPs and decrease EPSCs would be expected to both results in reduced neuronal excitability.
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Affiliation(s)
- Min-Chul Shin
- Research Division for Life Sciences, Kumamoto Health Science University, Kumamoto 861-5598, Japan
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Effects of halothane on GABAergic and glutamatergic transmission in isolated hippocampal nerve-synapse preparations. Brain Res 2012; 1473:9-18. [DOI: 10.1016/j.brainres.2012.07.035] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Revised: 07/17/2012] [Accepted: 07/18/2012] [Indexed: 01/31/2023]
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The effects of volatile anesthetics on synaptic and extrasynaptic GABA-induced neurotransmission. Brain Res Bull 2012; 93:69-79. [PMID: 22925739 DOI: 10.1016/j.brainresbull.2012.08.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Revised: 07/17/2012] [Accepted: 08/01/2012] [Indexed: 02/02/2023]
Abstract
Examination of volatile anesthetic actions at single synapses provides more direct information by reducing interference by surrounding tissue and extrasynaptic modulation. We examined how volatile anesthetics modulate GABA release by measuring spontaneous or miniature GABA-induced inhibitory postsynaptic currents (mIPSCs, sIPSCs) or by measuring action potential-evoked IPSCs (eIPSCs) at individual synapses. Halothane increased both the amplitude and frequency of sIPSCs. Isoflurane and enflurane increased mIPSC frequency while sevoflurane had no effect. These anesthetics did not alter mIPSC amplitudes. Halothane increased the amplitude of eIPSCs, with a decrease in failure rate (Rf) and paired-pulse ratio. In contrast, isoflurane and enflurane decreased the eIPSC amplitude and increased Rf, while sevoflurane decreased the eIPSC amplitude without affecting Rf. Volatile anesthetics did not change kinetics except for sevoflurane, suggesting that presynaptic mechanisms dominate changes in neurotransmission. Each anesthetic showed somewhat different GABA-induced response and these results suggest that GABA-induced synaptic transmission cannot have a uniformly common site of action as suggested for volatile anesthetics. In contrast, all volatile anesthetics concentration-dependently enhanced the GABA-induced extrasynaptic currents. Extrasynaptic receptors containing α4 and α5 subunits are reported to have high sensitivities to volatile anesthetics. Also, inhibition of GABA uptake by volatile anesthetics results in higher extracellular GABA concentration, which may lead to prolonged activation of extrasynaptic GABAA receptors. The extrasynaptic GABA-induced receptors may be major site of volatile anesthetic-induced neurotransmission. This article is part of a Special Issue entitled 'Extrasynaptic ionotropic receptors'.
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