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Kovács Z, Rauch E, D’Agostino DP, Ari C. Putative Role of Adenosine A1 Receptors in Exogenous Ketone Supplements-Evoked Anti-Epileptic Effect. Int J Mol Sci 2024; 25:9869. [PMID: 39337356 PMCID: PMC11432942 DOI: 10.3390/ijms25189869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2024] [Revised: 09/02/2024] [Accepted: 09/10/2024] [Indexed: 09/30/2024] Open
Abstract
Approximately 30% of patients with epilepsy are drug-refractory. There is an urgent need to elucidate the exact pathophysiology of different types of epilepsies and the mechanisms of action of both antiseizure medication and metabolic therapies to treat patients more effectively and safely. For example, it has been demonstrated that exogenous ketone supplement (EKS)-generated therapeutic ketosis, as a metabolic therapy, may decrease epileptic activity in both animal models and humans, but its exact mechanism of action is unknown. However, it was demonstrated that therapeutic ketosis, among others, can increase adenosine level, which may enhance activity of A1 adenosine receptors (A1Rs) in the brain. It has also been demonstrated previously that adenosine has anti-epileptic effect through A1Rs in different models of epilepsies. Thus, it is possible that (i) therapeutic ketosis generated by the administration of EKSs may exert its anti-epileptic effect through, among other mechanisms, increased adenosine level and A1R activity and that (ii) the enhanced activity of A1Rs may be a necessary anti-epileptic mechanism evoked by EKS administration-generated ketosis. Moreover, EKSs can evoke and maintain ketosis without severe side effects. These results also suggest that the therapeutic application of EKS-generated ketosis may be a promising opportunity to treat different types of epilepsies. In this literature review, we specifically focus on the putative role of A1Rs in the anti-epileptic effect of EKS-induced ketosis.
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Affiliation(s)
- Zsolt Kovács
- Department of Biology, BDTTC, ELTE Eötvös Loránd University, Károlyi Gáspár tér 4., 9700 Szombathely, Hungary or (Z.K.); (E.R.)
| | - Enikő Rauch
- Department of Biology, BDTTC, ELTE Eötvös Loránd University, Károlyi Gáspár tér 4., 9700 Szombathely, Hungary or (Z.K.); (E.R.)
- Institute of Biology, University of Pécs, Ifjúság Str. 6, 7624 Pécs, Hungary
| | - Dominic P. D’Agostino
- Ketone Technologies LLC., Tampa, FL 33612, USA;
- Department of Molecular Pharmacology and Physiology, Laboratory of Metabolic Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA
- Institute for Human and Machine Cognition, Ocala, FL 34471, USA
| | - Csilla Ari
- Ketone Technologies LLC., Tampa, FL 33612, USA;
- Department of Psychology, Behavioral Neuroscience Research Laboratory, University of South Florida, Tampa, FL 33620, USA
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Tsentsevitsky AN, Gafurova CR, Petrov AM. KATP channels as ROS-dependent modulator of neurotransmitter release at the neuromuscular junctions. Life Sci 2022; 310:121120. [DOI: 10.1016/j.lfs.2022.121120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 10/12/2022] [Accepted: 10/20/2022] [Indexed: 11/09/2022]
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Brunner B, Ari C, D’Agostino DP, Kovács Z. Adenosine Receptors Modulate the Exogenous Ketogenic Supplement-Evoked Alleviating Effect on Lipopolysaccharide-Generated Increase in Absence Epileptic Activity in WAG/Rij Rats. Nutrients 2021; 13:nu13114082. [PMID: 34836344 PMCID: PMC8623289 DOI: 10.3390/nu13114082] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 11/04/2021] [Accepted: 11/11/2021] [Indexed: 01/23/2023] Open
Abstract
It has been previously demonstrated that KEKS food containing exogenous ketogenic supplement ketone salt (KS) and ketone ester (KE) decreased the lipopolysaccharide (LPS)-generated increase in SWD (spike-wave discharge) number in Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats, likely through ketosis. KEKS-supplemented food-generated ketosis may increase adenosine levels, and may thus modulate both neuroinflammatory processes and epileptic activity through adenosine receptors (such as A1Rs and A2ARs). To determine whether these adenosine receptors are able to modify the KEKS food-generated alleviating effect on LPS-evoked increases in SWD number, an antagonist of A1R DPCPX (1,3-dipropyl-8-cyclopentylxanthine; 0.2 mg/kg) with LPS (50 µg/kg) and an antagonist of A2AR SCH58261 (7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine; 0.5 mg/kg) with LPS were co-injected intraperitoneally (i.p.) on the ninth day of KEKS food administration, and their influence not only on the SWD number, but also on blood glucose, R-beta-hydroxybutyrate (R-βHB) levels, and body weight were measured. We showed that inhibition of A1Rs abolished the alleviating effect of KEKS food on LPS-generated increases in the SWD number, whereas blocking A2ARs did not significantly modify the KEKS food-generated beneficial effect. Our results suggest that the neuromodulatory benefits of KEKS-supplemented food on absence epileptic activity are mediated primarily through A1R, not A2AR.
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Affiliation(s)
- Brigitta Brunner
- Faculty of Sciences, Institute of Biology, University of Pécs, Ifjúság Str. 6, 7624 Pécs, Hungary;
- Savaria University Centre, Department of Biology, ELTE Eötvös Loránd University, Károlyi Gáspár tér 4, 9700 Szombathely, Hungary;
| | - Csilla Ari
- Ketone Technologies LLC, Tampa, FL 33612, USA;
- Behavioral Neuroscience Research Laboratory, Department of Psychology, University of South Florida, Tampa, FL 33620, USA
- Correspondence: ; Tel.: +1-(813)-2409925
| | - Dominic P. D’Agostino
- Ketone Technologies LLC, Tampa, FL 33612, USA;
- Laboratory of Metabolic Medicine, Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA
- Institute for Human and Machine Cognition, Ocala, FL 34471, USA
| | - Zsolt Kovács
- Savaria University Centre, Department of Biology, ELTE Eötvös Loránd University, Károlyi Gáspár tér 4, 9700 Szombathely, Hungary;
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Spanoghe J, Larsen LE, Craey E, Manzella S, Van Dycke A, Boon P, Raedt R. The Signaling Pathways Involved in the Anticonvulsive Effects of the Adenosine A 1 Receptor. Int J Mol Sci 2020; 22:ijms22010320. [PMID: 33396826 PMCID: PMC7794785 DOI: 10.3390/ijms22010320] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2020] [Revised: 12/22/2020] [Accepted: 12/27/2020] [Indexed: 12/20/2022] Open
Abstract
Adenosine acts as an endogenous anticonvulsant and seizure terminator in the brain. Many of its anticonvulsive effects are mediated through the activation of the adenosine A1 receptor, a G protein-coupled receptor with a wide array of targets. Activating A1 receptors is an effective approach to suppress seizures. This review gives an overview of the neuronal targets of the adenosine A1 receptor focusing in particular on signaling pathways resulting in neuronal inhibition. These include direct interactions of G protein subunits, the adenyl cyclase pathway and the phospholipase C pathway, which all mediate neuronal hyperpolarization and suppression of synaptic transmission. Additionally, the contribution of the guanyl cyclase and mitogen-activated protein kinase cascades to the seizure-suppressing effects of A1 receptor activation are discussed. This review ends with the cautionary note that chronic activation of the A1 receptor might have detrimental effects, which will need to be avoided when pursuing A1 receptor-based epilepsy therapies.
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Affiliation(s)
- Jeroen Spanoghe
- 4Brain, Department of Head and Skin, Ghent University, 9000 Ghent, Belgium; (J.S.); (L.E.L.); (E.C.); (S.M.); (P.B.)
| | - Lars E. Larsen
- 4Brain, Department of Head and Skin, Ghent University, 9000 Ghent, Belgium; (J.S.); (L.E.L.); (E.C.); (S.M.); (P.B.)
| | - Erine Craey
- 4Brain, Department of Head and Skin, Ghent University, 9000 Ghent, Belgium; (J.S.); (L.E.L.); (E.C.); (S.M.); (P.B.)
| | - Simona Manzella
- 4Brain, Department of Head and Skin, Ghent University, 9000 Ghent, Belgium; (J.S.); (L.E.L.); (E.C.); (S.M.); (P.B.)
| | - Annelies Van Dycke
- Department of Neurology, General Hospital Sint-Jan Bruges, 8000 Bruges, Belgium;
| | - Paul Boon
- 4Brain, Department of Head and Skin, Ghent University, 9000 Ghent, Belgium; (J.S.); (L.E.L.); (E.C.); (S.M.); (P.B.)
| | - Robrecht Raedt
- 4Brain, Department of Head and Skin, Ghent University, 9000 Ghent, Belgium; (J.S.); (L.E.L.); (E.C.); (S.M.); (P.B.)
- Correspondence:
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5
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Abstract
It is well known that the neuromodulator adenosine, acting through the adenosine A1 receptor subtype, can limit or stop seizures. In 2008, adenosine was proposed as a key component of the anticonvulsant mechanism of the ketogenic diet (KD), a very low carbohydrate diet that can be highly effective in drug-refractory epilepsy. In this study, we review the accumulated data on the intersection among adenosine, ketosis, and anticonvulsant/antiepileptogenic effects. In several rodent models of epilepsy and seizures, antiseizure effects of ketogenic treatments (the KD itself, exogenous ketone bodies, medium-chain triglycerides or fatty acids) are reversed by administration of an adenosine A1 receptor antagonist. In addition, KD treatment elevates extracellular adenosine and tissue adenosine content in brain. Efforts to maintain or mimic a ketogenic milieu in brain slices reveal a state of reduced excitability produced by pre- and postsynaptic adenosine A1 receptor-based effects. Long-lasting seizure reduction may be due to adenosine-based epigenetic effects. In conclusion, there is accumulating evidence for an adenosinergic anticonvulsant action in the ketogenic state. In some cases, the main trigger is mildly but consistently lowered glucose in the brain. More research is needed to investigate the importance of adenosine in the antiepileptogenic and neuroprotective effects of these treatments. Future research may begin to investigate alternative adenosine-promoting strategies to enhance the KD or to find use as treatments themselves.
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Affiliation(s)
- David N Ruskin
- Department of Psychology, Neuroscience Program, Trinity College, Hartford, Connecticut, USA
| | - Masahito Kawamura
- Department of Pharmacology, Jikei University School of Medicine, Minato-ku, Tokyo, Japan
| | - Susan A Masino
- Department of Psychology, Neuroscience Program, Trinity College, Hartford, Connecticut, USA
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Kovács Z, D'Agostino DP, Diamond DM, Ari C. Exogenous Ketone Supplementation Decreased the Lipopolysaccharide-Induced Increase in Absence Epileptic Activity in Wistar Albino Glaxo Rijswijk Rats. Front Mol Neurosci 2019; 12:45. [PMID: 30930744 PMCID: PMC6427924 DOI: 10.3389/fnmol.2019.00045] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2018] [Accepted: 02/05/2019] [Indexed: 12/02/2022] Open
Abstract
It has been demonstrated previously that exogenous ketone supplements such as ketone ester (KE) decreased absence epileptic activity in a well-studied animal model of human absence epilepsy, Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats. It is known that lipopolysaccharide (LPS)-generated changes in inflammatory processes increase absence epileptic activity, while previous studies show that ketone supplement-evoked ketosis can modulate inflammatory processes. Thus, we investigated in the present study whether administration of exogenous ketone supplements, which were mixed with standard rodent chow (containing 10% KE + 10% ketone salt/KS, % by weight, KEKS) for 10 days, can modulate the LPS-evoked changes in absence epileptic activity in WAG/Rij rats. At first, KEKS food alone was administered and changes in spike-wave discharge (SWD) number, SWD time, discharge frequency within SWDs, blood glucose, and beta-hydroxybutyrate (βHB) levels, as well as body weight and sleep-waking stages were measured. In a separate experiment, intraperitoneal (i.p.) injection of LPS (50 μg/kg) alone and a cyclooxygenase 1 and 2 (COX-1 and COX-2) inhibitor indomethacin (10 mg/kg) alone, as well as combined IP injection of indomethacin with LPS (indomethacin + LPS) were applied in WAG/Rij rats to elucidate their influences on SWD number. In order to determine whether KEKS food can modify the LPS-evoked changes in SWD number, KEKS food in combination with IP LPS (50 μg/kg) (KEKS + LPS), as well as KEKS food with IP indomethacin (10 mg/kg) and LPS (50 μg/kg) (KEKS + indomethacin + LPS) were also administered. We demonstrated that KEKS food significantly increased blood βHB levels and decreased not only the spontaneously generated absence epileptic activity (SWD number), but also the LPS-evoked increase in SWD number in WAG/Rij rats. Our results suggest that administration of exogenous ketone supplements (ketogenic foods) may be a promising therapeutic tool in the treatment of epilepsy.
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Affiliation(s)
- Zsolt Kovács
- Department of Biology, ELTE Eötvös Loránd University, Savaria University Centre, Szombathely, Hungary
| | - Dominic P D'Agostino
- Laboratory of Metabolic Medicine, Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, FL, United States.,Institute for Human and Machine Cognition, Ocala, FL, United States
| | - David M Diamond
- Laboratory of Metabolic Medicine, Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, FL, United States.,Comparative Neuroscience Research Laboratory, Department of Psychology, University of South Florida, Tampa, FL, United States
| | - Csilla Ari
- Comparative Neuroscience Research Laboratory, Department of Psychology, University of South Florida, Tampa, FL, United States
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Shah FA, Park DJ, Koh PO. Identification of Proteins Differentially Expressed by Quercetin Treatment in a Middle Cerebral Artery Occlusion Model: A Proteomics Approach. Neurochem Res 2018; 43:1608-1623. [DOI: 10.1007/s11064-018-2576-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2018] [Revised: 06/06/2018] [Accepted: 06/14/2018] [Indexed: 02/06/2023]
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Lindberg D, Shan D, Ayers-Ringler J, Oliveros A, Benitez J, Prieto M, McCullumsmith R, Choi DS. Purinergic signaling and energy homeostasis in psychiatric disorders. Curr Mol Med 2016; 15:275-95. [PMID: 25950756 DOI: 10.2174/1566524015666150330163724] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 02/22/2015] [Accepted: 03/24/2015] [Indexed: 12/11/2022]
Abstract
Purinergic signaling regulates numerous vital biological processes in the central nervous system (CNS). The two principle purines, ATP and adenosine act as excitatory and inhibitory neurotransmitters, respectively. Compared to other classical neurotransmitters, the role of purinergic signaling in psychiatric disorders is not well understood or appreciated. Because ATP exerts its main effect on energy homeostasis, neuronal function of ATP has been underestimated. Similarly, adenosine is primarily appreciated as a precursor of nucleotide synthesis during active cell growth and division. However, recent findings suggest that purinergic signaling may explain how neuronal activity is associated neuronal energy charge and energy homeostasis, especially in mental disorders. In this review, we provide an overview of the synaptic function of mitochondria and purines in neuromodulation, synaptic plasticity, and neuron-glia interactions. We summarize how mitochondrial and purinergic dysfunction contribute to mental illnesses such as schizophrenia, bipolar disorder, autism spectrum disorder (ASD), depression, and addiction. Finally, we discuss future implications regarding the pharmacological targeting of mitochondrial and purinergic function for the treatment of psychiatric disorders.
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Affiliation(s)
| | | | | | | | | | | | | | - D-S Choi
- Neurobiology of Disease Program, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
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9
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Saransaari P, Oja SS. Mechanisms of Inhibitory Amino Acid Release in the Brain Stem Under Normal and Ischemic Conditions. Neurochem Res 2010; 35:1948-56. [DOI: 10.1007/s11064-010-0265-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/08/2010] [Indexed: 12/23/2022]
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10
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Metabolic autocrine regulation of neurons involves cooperation among pannexin hemichannels, adenosine receptors, and KATP channels. J Neurosci 2010; 30:3886-95. [PMID: 20237259 DOI: 10.1523/jneurosci.0055-10.2010] [Citation(s) in RCA: 131] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Metabolic perturbations that decrease or limit blood glucose-such as fasting or adhering to a ketogenic diet-reduce epileptic seizures significantly. To date, the critical links between altered metabolism and decreased neuronal activity remain unknown. More generally, metabolic changes accompany numerous CNS disorders, and the purines ATP and its core molecule adenosine are poised to translate cell energy into altered neuronal activity. Here we show that nonpathological changes in metabolism induce a purinergic autoregulation of hippocampal CA3 pyramidal neuron excitability. During conditions of sufficient intracellular ATP, reducing extracellular glucose induces pannexin-1 hemichannel-mediated ATP release directly from CA3 neurons. This extracellular ATP is dephosphorylated to adenosine, activates neuronal adenosine A(1) receptors, and, unexpectedly, hyperpolarizes neuronal membrane potential via ATP-sensitive K(+) channels. Together, these data delineate an autocrine regulation of neuronal excitability via ATP and adenosine in a seizure-prone subregion of the hippocampus and offer new mechanistic insight into the relationship between decreased glucose and increased seizure threshold. By establishing neuronal ATP release via pannexin hemichannels, and hippocampal adenosine A(1) receptors coupled to ATP-sensitive K(+) channels, we reveal detailed information regarding the relationship between metabolism and neuronal activity and new strategies for adenosine-based therapies in the CNS.
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11
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Li DP, Chen SR, Pan HL. Adenosine inhibits paraventricular pre-sympathetic neurons through ATP-dependent potassium channels. J Neurochem 2010; 113:530-42. [PMID: 20096091 DOI: 10.1111/j.1471-4159.2010.06618.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Adenosine produces cardiovascular depressor effects in various brain regions. However, the cellular mechanisms underlying these effects remain unclear. The pre-sympathetic neurons in the hypothalamic paraventricular nucleus (PVN) play an important role in regulating arterial blood pressure and sympathetic outflow through projections to the spinal cord and brainstem. In this study, we performed whole-cell patch-clamp recordings on retrogradely labeled PVN neurons projecting to the intermediolateral cell column of the spinal cord in rats. Adenosine (10-100 microM) decreased the firing activity in a concentration-dependent manner, with a marked hyperpolarization in 12 of 26 neurons tested. Blockade of A(1) receptors with the adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine or intracellular dialysis of guanosine 5'-O-(2-thodiphosphate) eliminated the inhibitory effect of adenosine on labeled PVN neurons. Immunocytochemical labeling revealed that A(1) receptors were expressed on spinally projecting PVN neurons. Also, blocking ATP-dependent K(+) (K(ATP)) channels with 100 microM glibenclamide or 200 microM tolbutamide, but not the G protein-coupled inwardly rectifying K(+) channels blocker tertiapin-Q, abolished the inhibitory effect of adenosine on the firing activity of PVN neurons. Furthermore, glibenclamide or tolbutamide significantly decreased the adenosine-induced outward currents in labeled neurons. The reversal potential of adenosine-induced currents was close to the K(+) equilibrium potential. In addition, adenosine decreased the frequency of both spontaneous and miniature glutamatergic excitatory post-synaptic currents and GABAergic inhibitory post-synaptic currents in labeled neurons, and these effects were also blocked by 8-cyclopentyl-1,3-dipropylxanthine. Collectively, our findings suggest that adenosine inhibits the excitability of PVN pre-sympathetic neurons through A(1) receptor-mediated opening of K(ATP) channels.
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Affiliation(s)
- De-Pei Li
- Department of Critical Care, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
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12
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Mechanisms of Glycine Release in Mouse Brain Stem Slices. Neurochem Res 2008; 34:286-94. [DOI: 10.1007/s11064-008-9774-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2008] [Accepted: 06/05/2008] [Indexed: 10/21/2022]
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13
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Masino SA, Geiger JD. Are purines mediators of the anticonvulsant/neuroprotective effects of ketogenic diets? Trends Neurosci 2008; 31:273-8. [PMID: 18471903 DOI: 10.1016/j.tins.2008.02.009] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2007] [Revised: 02/16/2008] [Accepted: 02/19/2008] [Indexed: 12/26/2022]
Abstract
Abnormal neuronal signaling caused by metabolic changes characterizes several neurological disorders, and in some instances metabolic interventions provide therapeutic benefits. Indeed, altering metabolism either by fasting or by maintaining a low-carbohydrate (ketogenic) diet might reduce epileptic seizures and offer neuroprotection in part because the diet increases mitochondrial biogenesis and brain energy levels. Here we focus on a novel hypothesis that a ketogenic diet-induced change in energy metabolism increases levels of ATP and adenosine, purines that are critically involved in neuron-glia interactions, neuromodulation and synaptic plasticity. Enhancing brain bioenergetics (ATP) and increasing levels of adenosine, an endogenous anticonvulsant and neuroprotective molecule, might help with understanding and treating a variety of neurological disorders.
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Affiliation(s)
- Susan A Masino
- Neuroscience Program/Psychology Department, Trinity College, Life Sciences Center, 300 Summit Street, Hartford, CT 06106, USA.
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Singh V, Carman M, Roeper J, Bonci A. Brief ischemia causes long-term depression in midbrain dopamine neurons. Eur J Neurosci 2007; 26:1489-99. [PMID: 17880389 DOI: 10.1111/j.1460-9568.2007.05781.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Degeneration of dopamine neurons in the substantia nigra pars compacta (SNc) plays an important role in the pathophysiology of neurodegenerative diseases like Parkinsonism and vascular dementia. SNc dopamine neurons both in vitro and in vivo show sensitivity to hypoxic/ischemic conditions and undergo degeneration. In acute brain slices, these dopamine neurons undergo hyperpolarization during hypoxia and hypoglycemia, which results in silencing of the neurons. However, the role that SNc excitatory synapses play in this process is poorly understood. Here we examined the effect of oxygen/glucose deprivation (OGD) on glutamatergic synaptic transmission in the SNc in a rat midbrain slice preparation. OGD for 5 min caused pre-synaptic ischemic long-term depression (iLTD) of glutamate transmission, as both alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid- and N-methyl-D-aspartate receptor-mediated synaptic currents in SNc dopamine neurons were depressed to a similar extent. This depression began immediately after exposure to OGD and was not recovered upon washout of OGD. Pharmacological studies revealed that the iLTD was triggered by a rise in post-synaptic intracellular calcium and mediated by activation of pre-synaptic adenosine A(1) receptors, which reduced glutamate-dependent synaptic transmission by activating ATP-dependent potassium channels. Furthermore, we observed that iLTD did not occlude tetanic long-term depression (LTD) at the SNc excitatory synapses, suggesting that these two forms of LTD involve different pathways. Taken together, our results showed that brief exposure to hypoxia and hypoglycemia results in LTD of synaptic activity at glutamatergic synapses onto SNc neurons and this phenomenon could represent a protective mechanism by reducing ischemia-induced excitotoxic injury to dopamine neurons.
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Affiliation(s)
- Vineeta Singh
- Department of Neurology, University of California, San Francisco, Ernest Gallo Clinic and Research Center, Emeryville, CA 94608, USA
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15
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Sichardt K, Nieber K. Adenosine A(1) receptor: Functional receptor-receptor interactions in the brain. Purinergic Signal 2007; 3:285-98. [PMID: 18404442 PMCID: PMC2072922 DOI: 10.1007/s11302-007-9065-z] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Accepted: 07/24/2007] [Indexed: 12/20/2022] Open
Abstract
Over the past decade, many lines of investigation have shown that receptor-mediated signaling exhibits greater diversity than previously appreciated. Signal diversity arises from numerous factors, which include the formation of receptor dimers and interplay between different receptors. Using adenosine A1 receptors as a paradigm of G protein-coupled receptors, this review focuses on how receptor-receptor interactions may contribute to regulation of the synaptic transmission within the central nervous system. The interactions with metabotropic dopamine, adenosine A2A, A3, neuropeptide Y, and purinergic P2Y1 receptors will be described in the first part. The second part deals with interactions between A1Rs and ionotropic receptors, especially GABAA, NMDA, and P2X receptors as well as ATP-sensitive K+ channels. Finally, the review will discuss new approaches towards treating neurological disorders.
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Affiliation(s)
- Kathrin Sichardt
- Institute of Pharmacy, University of Leipzig, Talstr. 33, 04103 Leipzig, Germany
| | - Karen Nieber
- Institute of Pharmacy, University of Leipzig, Talstr. 33, 04103 Leipzig, Germany
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