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Sammi SR, Rawat JK, Raghav N, Kumar A, Roy S, Singh M, Gautam S, Yadav RK, Devi U, Pandey R, Kaithwas G. Galantamine attenuates N,N-dimethyl hydrazine induced neoplastic colon damage by inhibiting acetylcholinesterase and bimodal regulation of nicotinic cholinergic neurotransmission. Eur J Pharmacol 2017; 818:174-183. [PMID: 29074413 DOI: 10.1016/j.ejphar.2017.10.036] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Revised: 10/18/2017] [Accepted: 10/19/2017] [Indexed: 02/08/2023]
Abstract
The present study reveals the effect of galantamine (GAL) against 1, 2-dimethylhydrazine (DMH) induced colon cancer. Wistar albino rats were arbitrarily divided into four groups (n = 8). Group 1 served as normal control (normal saline, 3ml/kg/day, p.o.); group 2, 3 and 4 received DMH (20mg/kg/week, s.c.), for 6 weeks; groups 3 and 4 also received GAL (2 and 4mg/kg/day, p.o) for 6 weeks. DMH treated rats showed decreased heart rate variability (HRV) factors, increased incidence of aberrant crypt foci (ACF), increased thiobarbituric acid reactive substances (TBARs) along with the decrease in the enzymatic activity of superoxide dismutase (SOD) and catalase. Increased levels of inflammatory marker cyclooxygenase (COX) and lipoxygenase (LOX) was also evident in DMH treated animals. The colonic surface architecture was studied using scanning electron microscopy revealed aberrant crypts(X500) and neoplastic nodules (X2000). GAL treatment helped to minimize the ACF count, restored oxidative stress and inflammatory markers favorably. To further validate our results, our study was directed to define the effect of GAL on acetylcholine neurotransmission using a simple model organism, Caenorhabditis elegans (C. elegans). Increased synaptic cholinergic transmission by GAL (32µM) was evident in the worms when studied through aldicarb assay. However, GAL (32µM) treatment negatively modulated α7 nicotinic acetylcholine receptor (α7nAch receptor), when evaluated using the levamisole assay. GAL (32µM) treatment down regulated the genomic expression of ace-1, ace-2 along with unc-29, unc-38, and unc-50 (essential components of α7 nAch receptor). GAL by inhibiting AchE and regulating Alpha7nACh activity can improve cholinergic neurotransmission.
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Affiliation(s)
- Shreesh Raj Sammi
- Department of Microbial Technology and Nematology, CSIR-Central Institute of Medicinal and Aromatic Plants, Near Kukrail Picnic Spot, Lucknow, India
| | - Jitendra K Rawat
- Department of Pharmaceutical Sciences, School of Biosciences and Biotechnology, Babasaheb Bhimrao Ambedkar University (A Central University), Lucknow, Uttar Pradesh, India
| | - Neetu Raghav
- Department of Pharmaceutical Sciences, School of Biosciences and Biotechnology, Babasaheb Bhimrao Ambedkar University (A Central University), Lucknow, Uttar Pradesh, India
| | - Ajay Kumar
- Department of Pharmaceutical Sciences, School of Biosciences and Biotechnology, Babasaheb Bhimrao Ambedkar University (A Central University), Lucknow, Uttar Pradesh, India
| | - Subhadeep Roy
- Department of Pharmaceutical Sciences, School of Biosciences and Biotechnology, Babasaheb Bhimrao Ambedkar University (A Central University), Lucknow, Uttar Pradesh, India
| | - Manjari Singh
- Department of Pharmaceutical Sciences, School of Biosciences and Biotechnology, Babasaheb Bhimrao Ambedkar University (A Central University), Lucknow, Uttar Pradesh, India
| | - Swetlana Gautam
- Department of Pharmaceutical Sciences, School of Biosciences and Biotechnology, Babasaheb Bhimrao Ambedkar University (A Central University), Lucknow, Uttar Pradesh, India
| | - Rajnish K Yadav
- Department of Pharmaceutical Sciences, School of Biosciences and Biotechnology, Babasaheb Bhimrao Ambedkar University (A Central University), Lucknow, Uttar Pradesh, India
| | - Uma Devi
- Department of Pharmaceutical Sciences, Faculty of Health Medical Sciences Indigenous and Alternative Medicine, SHIATS- Deemed to be University, Formerly Allahabad Agricultural Institute Naini, Allahabad, U.P., India
| | - Rakesh Pandey
- Department of Microbial Technology and Nematology, CSIR-Central Institute of Medicinal and Aromatic Plants, Near Kukrail Picnic Spot, Lucknow, India
| | - Gaurav Kaithwas
- Department of Pharmaceutical Sciences, School of Biosciences and Biotechnology, Babasaheb Bhimrao Ambedkar University (A Central University), Lucknow, Uttar Pradesh, India.
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Galantamine prevents long-lasting suppression of excitatory synaptic transmission in CA1 pyramidal neurons of soman-challenged guinea pigs. Neurotoxicology 2014; 44:270-8. [PMID: 25064080 DOI: 10.1016/j.neuro.2014.07.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 07/08/2014] [Accepted: 07/15/2014] [Indexed: 12/27/2022]
Abstract
Galantamine, a drug currently approved for the treatment of Alzheimer's disease, has recently emerged as an effective pretreatment against the acute toxicity and delayed cognitive deficits induced by organophosphorus (OP) nerve agents, including soman. Since cognitive deficits can result from impaired glutamatergic transmission in the hippocampus, the present study was designed to test the hypothesis that hippocampal glutamatergic transmission declines following an acute exposure to soman and that this effect can be prevented by galantamine. To test this hypothesis, spontaneous excitatory postsynaptic currents (EPSCs) were recorded from CA1 pyramidal neurons in hippocampal slices obtained at 1h, 24h, or 6-9 days after guinea pigs were injected with: (i) 1×LD50 soman (26.3μg/kg, s.c.); (ii) galantamine (8mg/kg, i.m.) followed 30min later by 1×LD50 soman, (iii) galantamine (8mg/kg, i.m.), or (iv) saline (0.5ml/kg, i.m.). In soman-injected guinea pigs that were not pretreated with galantamine, the frequency of EPSCs was significantly lower than that recorded from saline-injected animals. There was no correlation between the severity of soman-induced acute toxicity and the magnitude of soman-induced reduction of EPSC frequency. Pretreatment with galantamine prevented the reduction of EPSC frequency observed at 6-9 days after the soman challenge. Prevention of soman-induced long-lasting reduction of hippocampal glutamatergic synaptic transmission may be an important determinant of the ability of galantamine to counter cognitive deficits that develop long after an acute exposure to the nerve agent.
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Chen J, Pan H, Chen C, Wu W, Iskandar K, He J, Piermartiri T, Jacobowitz DM, Yu QS, McDonough JH, Greig NH, Marini AM. (-)-Phenserine attenuates soman-induced neuropathology. PLoS One 2014; 9:e99818. [PMID: 24955574 PMCID: PMC4067273 DOI: 10.1371/journal.pone.0099818] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Accepted: 05/15/2014] [Indexed: 11/18/2022] Open
Abstract
Organophosphorus (OP) nerve agents are deadly chemical weapons that pose an alarming threat to military and civilian populations. The irreversible inhibition of the critical cholinergic degradative enzyme acetylcholinesterase (AChE) by OP nerve agents leads to cholinergic crisis. Resulting excessive synaptic acetylcholine levels leads to status epilepticus that, in turn, results in brain damage. Current countermeasures are only modestly effective in protecting against OP-induced brain damage, supporting interest for evaluation of new ones. (-)-Phenserine is a reversible AChE inhibitor possessing neuroprotective and amyloid precursor protein lowering actions that reached Phase III clinical trials for Alzheimer's Disease where it exhibited a wide safety margin. This compound preferentially enters the CNS and has potential to impede soman binding to the active site of AChE to, thereby, serve in a protective capacity. Herein, we demonstrate that (-)-phenserine protects neurons against soman-induced neuronal cell death in rats when administered either as a pretreatment or post-treatment paradigm, improves motoric movement in soman-exposed animals and reduces mortality when given as a pretreatment. Gene expression analysis, undertaken to elucidate mechanism, showed that (-)-phenserine pretreatment increased select neuroprotective genes and reversed a Homer1 expression elevation induced by soman exposure. These studies suggest that (-)-phenserine warrants further evaluation as an OP nerve agent protective strategy.
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Affiliation(s)
- Jun Chen
- Neurology Department, Uniformed Services University of Health Sciences, Bethesda, Maryland, United States of America
| | - Hongna Pan
- Neurology Department, Uniformed Services University of Health Sciences, Bethesda, Maryland, United States of America
| | - Cynthia Chen
- Neurology Department, Uniformed Services University of Health Sciences, Bethesda, Maryland, United States of America
| | - Wei Wu
- Neurology Department, Uniformed Services University of Health Sciences, Bethesda, Maryland, United States of America
| | - Kevin Iskandar
- Neurology Department, Uniformed Services University of Health Sciences, Bethesda, Maryland, United States of America
| | - Jeffrey He
- Neurology Department, Uniformed Services University of Health Sciences, Bethesda, Maryland, United States of America
| | - Tetsade Piermartiri
- Neurology Department, Uniformed Services University of Health Sciences, Bethesda, Maryland, United States of America
| | - David M. Jacobowitz
- Department of Anatomy, Physiology and Genetics, Uniformed Services University of the Health Sciences, Bethesda, Maryland, United States of America
| | - Qian-Sheng Yu
- Drug Design & Development Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - John H. McDonough
- Pharmacology Branch, Research Division, US Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland, United States of America
| | - Nigel H. Greig
- Drug Design & Development Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Ann M. Marini
- Neurology Department, Uniformed Services University of Health Sciences, Bethesda, Maryland, United States of America
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Beggiato S, Tanganelli S, Fuxe K, Antonelli T, Schwarcz R, Ferraro L. Endogenous kynurenic acid regulates extracellular GABA levels in the rat prefrontal cortex. Neuropharmacology 2014; 82:11-8. [PMID: 24607890 DOI: 10.1016/j.neuropharm.2014.02.019] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 02/07/2014] [Accepted: 02/25/2014] [Indexed: 12/17/2022]
Abstract
The tryptophan metabolite kynurenic acid (KYNA) is an endogenous antagonist of the α7 nicotinic acetylcholine receptor (α7nAChR) and, at higher concentrations, inhibits ionotropic glutamate receptors. Increases in KYNA levels are seen in brain and cerebrospinal fluid in individuals with schizophrenia (SZ) and may be causally related to cognitive deficits in SZ and other psychiatric diseases. As dysfunction of circuits involving GABAergic neurons in the prefrontal cortex (PFC) likely plays a role in the cognitive impairments seen in these disorders, we examined the effects of KYNA on extracellular GABA in this brain area. Applied to awake rats for 2 h by reverse dialysis, KYNA concentration-dependently and reversibly reduced extracellular GABA levels, with 300 nM KYNA causing a nadir of ∼45% of baseline concentrations. This effect was not duplicated by reverse dialysis of the selective glycineB receptor antagonist 7-Cl-KYNA (100 nM) or the AMPA/kainate receptor antagonist CNQX (100 μM), and was prevented by co-application of galantamine (5 μM), a positive allosteric modulator of the α7nAChR. Conversely, inhibition of endogenous KYNA formation by reverse dialysis of (S)-4-(ethylsulfonyl)benzoylalanine (ESBA; 5 mM) reversibly increased GABA levels in the PFC, reaching a peak of ∼160% of baseline concentrations. Co-infusion of 30 nM KYNA neutralized this effect. Taken together, these results demonstrate a role for endogenous KYNA in the bi-directional control of GABAergic neurotransmission in the PFC. Pharmacological manipulation of KYNA may therefore be useful in the treatment of GABAergic impairments in SZ and other brain disorders involving the PFC.
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Affiliation(s)
- Sarah Beggiato
- Department of Medical Sciences, University of Ferrara, Italy; Laboratory for the Technology of Advanced Therapies (LTTA Centre), University of Ferrara, Italy.
| | - Sergio Tanganelli
- Department of Medical Sciences, University of Ferrara, Italy; Laboratory for the Technology of Advanced Therapies (LTTA Centre), University of Ferrara, Italy
| | - Kjell Fuxe
- Department of Neuroscience, Karolinska Institute, Stockholm, Sweden
| | - Tiziana Antonelli
- Department of Medical Sciences, University of Ferrara, Italy; Laboratory for the Technology of Advanced Therapies (LTTA Centre), University of Ferrara, Italy
| | - Robert Schwarcz
- Maryland Psychiatric Research Center, Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Luca Ferraro
- Laboratory for the Technology of Advanced Therapies (LTTA Centre), University of Ferrara, Italy; Department of Life Sciences and Biotechnology, University of Ferrara, Italy
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Alkondon M, Albuquerque EX, Pereira EFR. Acetylcholinesterase inhibition reveals endogenous nicotinic modulation of glutamate inputs to CA1 stratum radiatum interneurons in hippocampal slices. Neurotoxicology 2013; 36:72-81. [PMID: 23511125 DOI: 10.1016/j.neuro.2013.02.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2013] [Revised: 02/15/2013] [Accepted: 02/16/2013] [Indexed: 10/27/2022]
Abstract
The involvement of brain nicotinic acetylcholine receptors (nAChRs) in the neurotoxicological effects of soman, a potent acetylcholinesterase (AChE) inhibitor and a chemical warfare agent, is not clear. This is partly due to a poor understanding of the role of AChE in brain nAChR-mediated functions. To test the hypothesis that AChE inhibition builds sufficient acetylcholine (ACh) in the brain and facilitates nAChR-dependent glutamate transmission, we used whole-cell patch-clamp technique to record spontaneous glutamate excitatory postsynaptic currents (EPSCs) from CA1 stratum radiatum interneurons (SRI) in hippocampal slices. First, the frequency, amplitude and kinetics of EPSCs recorded from slices of control guinea pigs were compared to those recorded from slices of guinea pigs after a single injection of the irreversible AChE inhibitor soman (25.2μg/kg, s.c.). Second, EPSCs were recorded from rat hippocampal slices before and after their superfusion with the reversible AChE inhibitor donepezil (100nM). The frequency of EPSCs was significantly higher in slices taken from guinea pigs 24h but not 7 days after the soman injection than in slices from control animals. In 52% of the rat hippocampal slices tested, bath application of donepezil increased the frequency of EPSCs. Further, exposure to donepezil increased both burst-like and large-amplitude EPSCs, and increased the proportion of short (20-100ms) inter-event intervals. Donepezil's effects were suppressed significantly in presence of 10μM mecamylamine or 10nM methyllycaconitine. These results support the concept that AChE inhibition is able to recruit nAChR-dependent glutamate transmission in the hippocampus and such a mechanism can contribute to the acute neurotoxicological actions of soman.
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Affiliation(s)
- Manickavasagom Alkondon
- Division of Translational Toxicology, Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, United States
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Banerjee J, Alkondon M, Albuquerque EX. Kynurenic acid inhibits glutamatergic transmission to CA1 pyramidal neurons via α7 nAChR-dependent and -independent mechanisms. Biochem Pharmacol 2012; 84:1078-87. [PMID: 22889930 DOI: 10.1016/j.bcp.2012.07.030] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Revised: 07/24/2012] [Accepted: 07/26/2012] [Indexed: 01/17/2023]
Abstract
Glutamatergic hypofunction and elevated levels of kynurenic acid (KYNA) in the brain are common features of patients with schizophrenia. In vivo studies indicate that in the hippocampus KYNA decreases glutamate levels, presumably via inhibition of α7 nicotinic receptors (nAChRs). Here we tested the hypothesis that basal synaptic glutamate activity in the hippocampus is regulated by tonically active α7 nAChRs and is sensitive to inhibition by KYNA. To this end, spontaneous excitatory postsynaptic currents (EPSCs), sensitive to AMPA receptor antagonist CNQX (10 μM), were recorded from CA1 pyramidal neurons at -70 mV in rat hippocampal slices. The α7 nAChR antagonists α-bungarotoxin (α-BGT, 100 nM) and methyllycaconitine (MLA, 1-50 nM), and the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV, 50 μM) reduced the frequency of EPSCs. MLA and α-BGT had no effect on miniature EPSCs (mEPSCs). The effect of MLA decreased in the presence of APV (50 μM), with 1 nM MLA becoming completely ineffective. KYNA (1-20 μM) suppressed the frequency of EPSCs, without affecting mEPSCs. The effect of KYNA decreased in the presence of MLA (1 nM) or α-BGT (100 nM), with 1 μM KYNA being devoid of any effect. In the presence of both MLA (10 nM) and APV (50 μM) higher KYNA concentrations (5-20 μM) still reduced the frequency of EPSCs. These results suggest that basal synaptic glutamate activity in CA1 pyramidal neurons is maintained in part by tonically active α7 nAChRs and NMDA receptors and is inhibited by micromolar concentrations of KYNA, acting via α7 nAChR-dependent and -independent mechanisms.
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Affiliation(s)
- Jyotirmoy Banerjee
- Division of Translational Toxicology, Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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Banerjee J, Alkondon M, Pereira EFR, Albuquerque EX. Regulation of GABAergic inputs to CA1 pyramidal neurons by nicotinic receptors and kynurenic acid. J Pharmacol Exp Ther 2012; 341:500-9. [PMID: 22344459 DOI: 10.1124/jpet.111.189860] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Impaired α7 nicotinic acetylcholine receptor (nAChR) function and GABAergic transmission in the hippocampus and elevated brain levels of kynurenic acid (KYNA), an astrocyte-derived metabolite of the kynurenine pathway, are key features of schizophrenia. KYNA acts as a noncompetitive antagonist with respect to agonists at both α7 nAChRs and N-methyl-D-aspartate receptors. Here, we tested the hypothesis that in hippocampal slices tonically active α7 nAChRs control GABAergic transmission to CA1 pyramidal neurons and are sensitive to inhibition by rising levels of KYNA. The α7 nAChR-selective antagonist α-bungarotoxin (α-BGT; 100 nM) and methyllycaconitine (MLA; 10 nM), an antagonist at α7 and other nAChRs, reduced by 51.3 ± 1.3 and 65.2 ± 1.5%, respectively, the frequency of GABAergic postsynaptic currents (PSCs) recorded from CA1 pyramidal neurons. MLA had no effect on miniature GABAergic PSCs. Thus, GABAergic synaptic activity in CA1 pyramidal neurons is maintained, in part, by tonically active α7 nAChRs located on the preterminal region of axons and/or the somatodendritic region of interneurons that synapse onto the neurons under study. L-Kynurenine (20 or 200 μM) or KYNA (20-200 μM) suppressed concentration-dependently the frequency of GABAergic PSCs; the inhibitory effect of 20 μM L-kynurenine had an onset time of approximately 35 min and could not be detected in the presence of 100 nM α-BGT. These results suggest that KYNA levels generated from 20 μM kynurenine inhibit tonically active α7 nAChR-dependent GABAergic transmission to the pyramidal neurons. Disruption of nAChR-dependent GABAergic transmission by mildly elevated levels of KYNA can be an important determinant of the cognitive deficits presented by patients with schizophrenia.
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Affiliation(s)
- Jyotirmoy Banerjee
- Division of Translational Toxicology, Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, USA
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Mamczarz J, Kulkarni GS, Pereira EFR, Albuquerque EX. Galantamine counteracts development of learning impairment in guinea pigs exposed to the organophosphorus poison soman: clinical significance. Neurotoxicology 2011; 32:785-98. [PMID: 21784098 DOI: 10.1016/j.neuro.2011.07.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Revised: 06/19/2011] [Accepted: 07/05/2011] [Indexed: 11/15/2022]
Abstract
Galantamine, a drug used to treat Alzheimer's disease, protects guinea pigs against the acute toxicity and lethality of organophosphorus (OP) compounds, including soman. Here, we tested the hypothesis that a single exposure of guinea pigs to 1xLD50 soman triggers cognitive impairments that can be counteracted by galantamine. Thus, animals were injected intramuscularly with saline (0.5 ml/kg) or galantamine (8 mg/kg) and 30 min later injected subcutaneously with soman (26.3 μg/kg) or saline. Cognitive performance was analyzed in the Morris water maze (MWM) four days or three months after the soman challenge. Fifty percent of the saline-injected animals that were challenged with soman survived with mild-to-moderate signs of acute toxicity that subsided within a few hours. These animals showed no learning impairment and no memory retention deficit, when training in the MWM started four days post-soman challenge. In contrast, animals presented significant learning impairment when testing started three months post-challenge. Though the magnitude of the impairment correlated with the severity of the acute toxicity, animals that presented no or only mild signs of toxicity were also learning impaired. All guinea pigs that were treated with galantamine survived the soman challenge with no signs of acute toxicity and learned the MWM task as control animals, regardless of when testing began. Galantamine also prevented memory extinction in both saline- and soman-challenged animals. In conclusion, learning impairment develops months after a single exposure to 1xLD50 soman, and galantamine prevents both the acute toxicity and the delayed cognitive deficits triggered by this OP poison.
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Affiliation(s)
- Jacek Mamczarz
- Division of Translational Toxicology, Department Epidemiology and Public Health, University of Maryland School of Medicine, 10 S. Pine St. Suite 900, Baltimore, MD 21210, USA.
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Alkondon M, Pereira EFR, Albuquerque EX. Endogenous activation of nAChRs and NMDA receptors contributes to the excitability of CA1 stratum radiatum interneurons in rat hippocampal slices: effects of kynurenic acid. Biochem Pharmacol 2011; 82:842-51. [PMID: 21689641 DOI: 10.1016/j.bcp.2011.06.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Revised: 06/02/2011] [Accepted: 06/02/2011] [Indexed: 10/18/2022]
Abstract
CA1 stratum radiatum interneurons (SRIs) express α7 nicotinic receptors (nAChRs) and receive inputs from glutamatergic neurons/axons that express α3β4β2 nAChRs. To test the hypothesis that endogenously active α7 and/or α3β4β2 nAChRs control the excitability of CA1 SRIs in the rat hippocampus, we examined the effects of selective receptor antagonists on spontaneous fast current transients (CTs) recorded from these interneurons under cell-attached configuration. The frequency of CTs, which represent action potentials, increased in the absence of extracellular Mg(2+) and decreased in the presence of the α3β4β2 nAChR antagonist mecamylamine (3 μM) or the NMDA receptor antagonist APV (50 μM). However, it was unaffected by the α7 nAChR antagonist MLA (10 nM) or the AMPA receptor antagonist CNQX (10 μM). Thus, in addition to synaptically and tonically activated NMDA receptors, α3β4β2 nAChRs that are present on glutamatergic axons/neurons synapsing onto SRIs and are activated by basal levels of acetylcholine contribute to the maintenance of the excitability of these interneurons. Kynurenic acid (KYNA), an astrocyte-derived kynurenine metabolite whose levels are increased in the brains of patients with schizophrenia, also controls the excitability of SRIs. At high micromolar concentrations, KYNA, acting primarily as an NMDA receptor antagonist, decreased the CT frequency recorded from the interneurons. At 2 μM, KYNA reduced the CA1 SRI excitability via mechanisms independent of NMDA receptor block. KYNA-induced reduction of excitability of SRIs may contribute to sensory gating deficits that have been attributed to deficient hippocampal GABAergic transmission and high levels of KYNA in the brain of patients with schizophrenia.
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Affiliation(s)
- Manickavasagom Alkondon
- Division of Translational Toxicology, Department of Epidemiology and Public Health, University of Maryland School of Medicine, 10 S. Pine Street, Suite 900, Baltimore, MD 21201, United States
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Alexandrova EA, Aracava Y, Pereira EFR, Albuquerque EX. Pretreatment of Guinea pigs with galantamine prevents immediate and delayed effects of soman on inhibitory synaptic transmission in the hippocampus. J Pharmacol Exp Ther 2010; 334:1051-8. [PMID: 20554906 DOI: 10.1124/jpet.110.167700] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Galantamine has emerged as a potential antidote to prevent the acute toxicity of organophosphorus (OP) compounds. Changes in inhibitory GABAergic activity in different brain regions can contribute to both induction and maintenance of seizures in subjects exposed to the OP nerve agent soman. Here, we tested the hypothesis that galantamine can prevent immediate and delayed effects of soman on hippocampal inhibitory synaptic transmission. Spontaneous inhibitory postsynaptic currents (IPSCs) were recorded from CA1 pyramidal neurons in hippocampal slices obtained at 1 h, 24 h, or 6 to 9 days after the injection of guinea pigs with saline (0.5 ml/kg i.m.), 1xLD(50) soman (26.3 microg/kg s.c.), galantamine (8 mg/kg i.m.), or galantamine at 30 min before soman. Soman-challenged animals that were not pretreated showed mild, moderate, or severe signs of acute intoxication. At 1 h after the soman injection, the mean IPSC amplitude recorded from slices of mildly intoxicated animals and the mean IPSC frequency recorded from slices of severely intoxicated animals were larger and lower, respectively, than those recorded from slices of control animals. Regardless of the severity of the acute toxicity, at 24 h after the soman challenge the mean IPSC frequency was lower than that recorded from slices of control animals. At 6 to 9 days after the challenge, the IPSC frequency had returned to control levels, whereas the mean IPSC amplitude became larger than control. Pretreatment with galantamine prevented soman-induced changes in IPSCs. Counteracting the effects of soman on inhibitory transmission can be an important determinant of the antidotal effectiveness of galantamine.
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Affiliation(s)
- Elena A Alexandrova
- Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, 655 W. Baltimore St., Baltimore, MD 21201, USA
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Aracava Y, Pereira EFR, Akkerman M, Adler M, Albuquerque EX. Effectiveness of donepezil, rivastigmine, and (+/-)huperzine A in counteracting the acute toxicity of organophosphorus nerve agents: comparison with galantamine. J Pharmacol Exp Ther 2009; 331:1014-24. [PMID: 19741148 DOI: 10.1124/jpet.109.160028] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Galantamine, a centrally acting cholinesterase (ChE) inhibitor and a nicotinic allosteric potentiating ligand used to treat Alzheimer's disease, is an effective and safe antidote against poisoning with nerve agents, including soman. Here, the effectiveness of galantamine was compared with that of the centrally active ChE inhibitors donepezil, rivastigmine, and (+/-)huperzine A as a pre- and/or post-treatment to counteract the acute toxicity of soman. In the first set of experiments, male prepubertal guinea pigs were treated intramuscularly with one of the test drugs and 30 min later challenged with 1.5 x LD(50) soman (42 microg/kg s.c.). All animals that were pretreated with galantamine (6-8 mg/kg), 3 mg/kg donepezil, 6 mg/kg rivastigmine, or 0.3 mg/kg (+/-)huperzine A survived the soman challenge, provided that they were also post-treated with atropine (10 mg/kg i.m.). However, only galantamine was well tolerated. In subsequent experiments, the effectiveness of specific treatment regimens using 8 mg/kg galantamine, 3 mg/kg donepezil, 6 mg/kg rivastigmine, or 0.3 mg/kg (+/-)huperzine A was compared in guinea pigs challenged with soman. In the absence of atropine, only galantamine worked as an effective and safe pretreatment in animals challenged with 1.0 x LD(50) soman. Galantamine was also the only drug to afford significant protection when given to guinea pigs after 1.0 x LD(50) soman. Finally, all test drugs except galantamine reduced the survival of the animals when administered 1 or 3 h after the challenge with 0.6 or 0.7 x LD(50) soman. Thus, galantamine emerges as a superior antidotal therapy against the toxicity of soman.
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Affiliation(s)
- Yasco Aracava
- Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, Maryland, USA
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Molecular and Cellular Actions of Galantamine: Clinical Implications for Treatment of Organophosphorus Poisoning. J Mol Neurosci 2009; 40:196-203. [DOI: 10.1007/s12031-009-9234-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2009] [Accepted: 07/20/2009] [Indexed: 01/09/2023]
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