Article

The combination of donepezil and procyclidine protects against soman-induced seizures in rats

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Abstract

Current treatment of nerve agent poisoning consists of prophylactic administration of pyridostigmine and therapy using atropine, an oxime and a benzodiazepine. Pyridostigmine does however not readily penetrate the blood-brain barrier giving ineffective protection of the brain against centrally mediated seizure activity. In this study, we have evaluated donepezil hydrochloride, a partial reversible inhibitor of acetylcholinesterase (AChE) clinically used for treating Alzheimer's disease, in combination with procyclidine, used in treatment of Parkinson's disease and schizophrenia, as prophylaxis against intoxication by the nerve agent soman. The results demonstrated significant protective efficacy of donepezil (2.5 mg/kg) combined with procyclidine (3 or 6 mg/kg) when given prophylactically against a lethal dose of soman (1.6 x LD(50)) in Wistar rats. No neuropathological changes were found in rats treated with this combination 48 h after soman intoxication. Six hours after soman exposure cerebral AChE activity and acetylcholine (ACh) concentration was 5% and 188% of control, respectively. The ACh concentration had returned to basal levels 24 h after soman intoxication, while AChE activity had recovered to 20% of control. Loss of functioning muscarinic ACh receptors (17%) but not nicotinic receptors was evident at this time point. The recovery in brain AChE activity seen in our study may be due to the reversible binding of donepezil to the enzyme. Donepezil is well tolerated in humans, and a combination of donepezil and procyclidine may prove useful as an alternative to the currently used prophylaxis against nerve agent intoxication.

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... The administration of soman induces seizures. It has been reported that after soman application the administration of donepezil (a partially reversible cholinesterase inhibitor) ( Table 1) and procyclidine (a drug used in schizophrenia and Parkinson's disease) prevents seizures [55]. Soman administration decreases the levels of acetylcholinesterase and increases ACh levels, in comparison with controls, and interferes with muscarinic receptors, but not nicotinic receptors. ...
... Soman administration decreases the levels of acetylcholinesterase and increases ACh levels, in comparison with controls, and interferes with muscarinic receptors, but not nicotinic receptors. The administration of donepezil and procyclidine increases acetylcholinesterase activity and normalizes ACh levels, thus preventing seizures [55]. ...
... Atropine, an M1 receptor antagonist, or donepezil, a partially reversible inhibitor of cholinesterase, exert an anticonvulsant effect. [54,55] Acetylcholine nACh alpha7 ...
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We describe the alterations of classical neurotransmitters and neuropeptides in generalized epilepsy. A neuronal network in this disease is developed. Gamma aminobutyric acid (GABA) hypoactivity induces dopamine hyperactivity because dopaminergic neurons are affected by the inhibitory influence of the GABAergic system through GABA(A) receptors. Glutamate hyperactivity is exerted via presynaptic N-methyl-D-aspartate (NMDA) receptors, which strongly inhibit serotoninergic neurons, and via postsynaptic ionotropic glutaminergic receptors, which can induce epileptic seizures. A collection of specific subreceptors of classical neurotransmitters and neuropeptides involved in epileptogenesis is reported. The question arises whether agonists/antagonists of neuropeptides (neuropeptide Y, galanin…) could have additional antiepileptic properties. The effect of conventional and newer antiepileptic drugs interfering with these subreceptors is discussed on the basis of the neuronal network suggested. From these data, it is concluded that new antiepileptic drugs interfering with other specific subreceptors (GABA(B) antagonists, metabotropic glutaminergic receptors subtype 5 (mGlu5R) antagonists, mGlu2/3R agonists, 5-serotonin (5-HT(7)) agonists) could further stabilize the neuronal network in generalized epilepsy.
... To evaluate the pretreatment efficacy of chosen NMDA receptor antagonists and AChEIs, NMDA receptor antagonists were administered at a dose of 20 mg/kg (memantine) or 6 mg/kg (procyclidine) based on literature data (Haug et al. 2007;Jackson et al. 2019) while the applied doses of reversible AChEIs were established based on previous studies (donepezil at a dose of 2.65 mg/kg; huperzine at a dose of 0.5 mg/kg) (Grunwald et al. 1994;Kosasa et al. 1999). The doses were attributed to approximately 40% brain acetylcholinesterase inhibition (Misik and Kassa 2014). ...
... The neuroprotective efficacy of NMDA-antagonists is based on blocking the excessive glutamate effects (Coleman et al. 2008)). Based on previous studies, combining NMDA-antagonists with other relevant medicines (especially reversible AChEIs) protects against brain damage due to significant synergistic effects in the early stages of the pathological brain cascade (Kim et al. 2002;Haug et al. 2007;Myhrer and Aas 2016). Unlike donepezil, Huperzine A is also a NMDA-receptor antagonist (Coleman et al. 2008). ...
Article
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Organophosphorus nerve agents pose a global threat to both military personnel and civilian population, because of their high acute toxicity and insufficient medical countermeasures. Commonly used drugs could ameliorate the intoxication and overall medical outcomes. In this study, we tested the drugs able to alleviate the symptoms of Alzheimer's disease (donepezil, huperzine A, memantine) or Parkinson's disease (procyclidine). They were administered to mice before soman intoxication in terms of their: i) protection potential against soman toxicity and ii) influence on post-exposure therapy consisting of atropine and asoxime (also known as oxime HI-6). Their pretreatment effect was not significant, when administered alone, but in combination (acetylcholinesterase inhibitor such as denepezil or huperzine A with NMDA antagonist such as memantine or procyclidine) they lowered the soman toxicity more than twice. These combinations also positively influenced the efficacy of post-exposure treatment in a similar fashion; the combinations increased the therapeutic effectiveness of antidotal treatment. In conclusion, the most effective combination - huperzine A and procyclidine - lowered the toxicity three times and improved the post-exposure therapy efficacy more than six times. These results are unprecedented in the published literature.
... Donepezil, galantamine, and Huperzine A (Hup A), a naturally occurring reversible AChE inhibitor, have been shown to protect against soman-induced seizures. [8][9][10][11][12][13] Hup A also provides protection against N-methyl-D-aspartate (NMDA)-induced status epilepticus (SE) 14 and pentylenetetrazole (PTZ)-induced seizures in rats 15 and zebrafish. 16 In addition, we recently demonstrated that Hup A confers robust protection against induced seizures in Scn1a +/À and Scn1a RH/+ mouse models of Dravet syndrome (DS) and genetic epilepsy with febrile seizures plus (GEFS+), respectively. ...
... Recent evidence suggests that reversible AChE inhibitors, such as Huperzine A and donepezil, may be therapeutic in epilepsy as evidenced by their ability to increase resistance to induced seizures [8][9][10][11]15,17 . When compared to Hup A, donepezil similarly conferred robust protection against 6 Hz-, MES-, and PTZ-induced seizures. ...
Article
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De novo loss‐of‐function mutations in SCN1A are the main cause of Dravet syndrome, a catastrophic encephalopathy characterized by recurrent early‐life febrile seizures, a number of other afebrile seizure types that are often refractory to treatment, and behavioral abnormalities including social deficits, motor dysfunction, and cognitive impairment. We previously demonstrated that the reversible acetylcholinesterase inhibitor, Huperzine A, increases seizure resistance in Scn1a mutants. In the present study, we evaluated the therapeutic potential of donepezil, a reversible acetylcholinesterase inhibitor approved by the Food and Drug Administration, in a mouse model of Dravet syndrome (Scn1a+/−). We found that donepezil conferred robust protection against induced seizures in Scn1a+/− mutants.
... Procyclidine possesses broad spectrum of pharmacological properties – antimuscarinic, anti-NMDA receptors and antiglutamatergic activity. Many studies have shown that procyclidine, combined with reversible inhibitor of AChE, is very effective in reducing subconvulsions and convulsions produced by lethal doses of nerve agents (Kim et al., 2002; Myhrer et al., 2004a Myhrer et al., , 2004b Philipens et al., 2006; Haug et al., 2007). At the same time a relationship between convulsions and the rate of lethality in nerve agent poisoned animals have proved (Shih et al., 2003; Haug et al., 2007). ...
... Many studies have shown that procyclidine, combined with reversible inhibitor of AChE, is very effective in reducing subconvulsions and convulsions produced by lethal doses of nerve agents (Kim et al., 2002; Myhrer et al., 2004a Myhrer et al., , 2004b Philipens et al., 2006; Haug et al., 2007). At the same time a relationship between convulsions and the rate of lethality in nerve agent poisoned animals have proved (Shih et al., 2003; Haug et al., 2007). Our results clearly showed that a drug combination of physostigmine and procyclidine demonstrated only limited protective efficacy, independently of the time of prophylaxis, against lethal effects in case of poisoning with 1.5 LD50 soman. ...
Conference Paper
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SUMMARY The main goal of a successful prophylaxis is to minimize or reduce the toxic since caused by nerve agents (tabun, sarin, soman, cyclosarin, VX) and to ensure life saving effect. Such an effect could be achieved by using different drug mixtures consisting of usually 1. Reversible cholinesterase inhibitors and 2. Antimuscarinic compounds or compounds possess ability to affect not only cholinergic but other neuromediators in central neuros system. The purpose of the current study was to investigate prophylactic efficacy of a drug mixtures consisting of physostigmine(0.1 mg/kg) and procyclidine (3 mg/kg) applied 30 and 60 min. before poisoning with lethal doses of soman (1, 1.5 и 2 LD50) with or without additional antidote therapy (HI-6, an oxime reactivator + atropine + midazolam, as a benzodiazepne). The prophylactic efficacy was assessed by 24 hours rate of survival after intoxication.
... and AChE were observed to be very effective in protection against OP intoxication [24, [48][49][50][51][52][53][54][55]. The administration of enzymes as scavengers seems to be very promising: the enzyme is acting at the very beginning of the toxic action, without interaction with the target tissues and without side effects [50,51,[55][56][57][58][59]. Recombinant human BuChE can be produced from milk of transgenic goats [59]. ...
... calcium antagonists (nimodipine), neuromuscular blockers (tubocurarine), adamantanes (memantine), and the opiate antagonist meptazinol [6, [83][84][85] were also tested with different results but they were not very useful for practical use. On the other hand, a positive prophylactic effect has been demonstrated with procyclidine (antimuscarinic, antinicoticnic and the anti-NMDA receptor drug) [86,87], metoclopramide [88], clonidine or procyclidine and donepezil [57,89]. A prophylactic effect of group of drugs with anticholinergic and/or antiglutamatergic properties (benactyzine, biperiden, caramiphen, procyclidine, and trihexyphenidyl) with respect to their anticonvulsant properties was studied to prevent damage of the central nervous systém induced by seizures. ...
Article
Prophylaxis against nerve agent intoxication is based on various approaches: Keeping AChE, key enzyme for toxic action of OP/nerve agents intact (protection of cholinesterases) is a basic requirement for effective prophylaxis. Detoxification realised by administration of the enzymes splitting the OP or evaluating specific enzymes (cholinesterases) is another possibility (scavenger effect). The antidotes currently used for the treatment of OP poisoning including reactivators are to be tested as prophylactics. This principle can be considered as a .,treatment in advance". Moreover, they are uneffective when administered alone; their effect is potentiated when they are administered with anticholinergics. Transdermal administration of reactivator HI-6 was used and prophylactic antidote TRANSANT was developed and introduced into the Czech Army. At present, PYRIDOSTIGMINE seems to be common prophylactic antidote; prophylactics PANPAL (tablets with pyridostigmine, trihexyphenidyle and benactyzine), TRANSANT (transdermal patch containing HI-6) are other means introduced into different armies as prophylactics. TRANSANT is only one prophylactics evaluating reactivator. When administered simultaneously with PANPAL, prophylactic efficacy is increased and represents the best prophylaxis at present.
... The advantage of Huperzine A is reflected in its ability to pass through a blood-brain barrier, which means that AChE in central nerve system can be reached and protected during nerve agent poisoning. [7] Protective effects of FDA-approved drugs for the treatment of Alzheimer's disease, donepezil and galantamine, were also investigated [8][9][10][11][12]. [8]- [12] In this work we present the design, synthesis, NMR characterization, and anticholinesterase activity of four novel nanomolar dual-binding reversible inhibitors of cholinesterases. ...
Conference Paper
Organophosphorous chemical warfare agents (i.e., nerve agents) exhibit toxic effects mainly through covalent, irreversible inhibition of acetylcholinesterase (EC 3.1.1.7), an enzyme that terminates cholinergic neurotransmission, by hydrolyzing acetylcholine at nerve and nerve-muscle junctions. Use of nerve agents is strictly limited to research purposes only and it is under control of Organisation for the Prohibition of Chemical Weapons, OPCW. Despite all efforts to limit the use of nerve agents, unfortunately the danger of nerve agents being used in war aggression and terrorist attacks is still present. The reversible inhibition of AChE was suggested as the pre-treatment option against nerve agents' intoxications. Aiming to investigate novel pre-treatment options, we designed and synthesized the four novel compounds of tacrine and aroylacrylic acid phenylamide moieties, connected via a long methylene chain to target two distinct topologically separated anionic areas on the AChE. The inhibitory activity of the compounds toward the Electric eel AChE's as well as the horse serum BChE was determined by Ellman assay. The designed compounds may represent a new class of promising leads for developing more effective pre-treatment options.
... Donepezil, a centrally acting cholinesterase inhibitor, was used as a positive control. Donepezil hydrochloride was obtained as 10 mg tablets and administered in doses of 2.25 mg/kg based on previous study of Haug et al. [95] (Aricept ® , Pfizer Egypt, S.A.E. Cairo, A.R.E. ...
Article
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Alzheimer’s disease (AD) is a devastating neurodegenerative disorder without a cure. Hence, developing an effective treatment or protective agent is crucial for public health. The present study aims to characterize orange peel extract (OPE) through in vitro and in silico studies. Furthermore, it examines the protective effect of OPE against experimentally-induced Alzheimer’s disease in rats. The total phenolic and flavonoid content of OPE was 255.86 ± 1.77 and 52.06 ± 1.74 (mg/100 g), respectively. Gallic acid, the common polyphenol in OPE detected by HPLC was 3388.60 μg/100 g. OPE antioxidant IC50 was 67.90 ± 1.05, 60.48 ± 0.91, and 63.70 ± 0.30 by DPPH, ABTS and Hydroxyl radical scavenging activity methods, respectively. In vitro anti-acetylcholinesterase (AChE) IC50 was 0.87 ± 0.025 mg/mL for OPE and 2.45 ± 0.001 mg/mL for gallic acid. Molecular docking analysis for human AChE (4EY7) with donepezil, gallic acid, and acetylcholine showed binding energy ΔG values of −9.47, −3.72, and −5.69 Kcal/mol, respectively. Aluminum chloride injection (70 mg/Kg/day for 6 weeks) induced Alzheimer’s-like disease in male rats. OPE (100 and 200 mg/kg/d) and gallic acid (50 mg/kg/d) were administered orally to experimental animals for 6 weeks in addition to aluminum chloride injection (as protective). OPE was found to protect against aluminum chloride-induced neuronal damage by decreasing both gene expression and activity of acetylcholinesterase (AChE) and a decrease in amyloid beta (Aβ42) protein level, thiobarbituric acid-reactive substances (TBARS), and nitric oxide (NO), and increased reduced glutathione (GSH) level and activity of the antioxidant enzymes in the brain tissues. Additionally, gene expressions for amyloid precursor protein (APP) and beta secretase enzyme (BACE1) were downregulated, whereas those for presinilin-2 (PSEN2) and beta cell lymphoma-2 (BCL2) were upregulated. Furthermore, the reverse of mitochondrial alternation and restored brain ultrastructure might underlie neuronal dysfunction in AD. In conclusion, our exploration of the neuroprotective effect of OPE in vivo reveals that OPE may be helpful in ameliorating brain oxidative stress, hence protecting from Alzheimer’s disease progression.
... There is also a prophylactic approach to the use of DON in human and animal studies. One reported the protective effect of pretreatment DON on cognitive deficits of patients undergoing electroconvulsive therapy [65] and another revealed that the combination of DON and procyclidine markedly protects against soman-induced seizures in rats [66]. Concerning cognitive stimulation in humans, growing evidence suggests that premorbid participation in cognitive activities reduces the risk of dementia and AD by increasing cognitive reserve [67]. ...
Article
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Alzheimer's disease (AD) is progressive neurodegeneration known as the most common cause of dementia, and it is the sixth leading cause of death in older people. Given the promising data on the additive effect of combination therapy with donepezil (Aricept), an acetylcholinesterase inhibitor (AChEI), and regarding the similar neuronal mechanisms through which donepezil (DON) and environmental enrichment (EE) exert their enhancing effects on cognition; we asked whether simultaneous treatment with two paradigms in amyloid-beta-induced AD rats may lead to greater protection against the cognitive impairments than either treatment individually. The experimental groups consisted of Alz, sham-operated, Alz + DON, Alz + EE, and Alz + DON + EE. AD was induced by intrahippocampal injection of amyloid-beta (1–42, 6 μg), and DON was orally administrated (4 mg/kg) for 21 days. Environmental enrichment consisted of housing animals in large cages (50 × 50 × 50 cm) containing a running wheel and differently shaped objects for 21 days. Spatial learning and memory were assessed in the Morris water maze (MWM) and Real-time PCR was performed to assess the expression of brain-derived neurotrophic factor (BDNF) and M1 muscarinic acetylcholine receptor (AchM1R) within the hippocampus. Spatial memory was impaired in Alz animals, and while neither pretreatment with DON nor EE alone could significantly restore spatial memory scores in Alz rats, combination therapy was effective. BDNF expression was suppressed in Alz rats and pretreatment with DON plus EE could increase it to the saline levels. The data suggest that a cholinesterase inhibitor and cognitive stimulation can be used effectively in combination to protect cognitive loss in an AD rat model. This additive protective effect may be in part due to the augmented influence of this combination on BDNF levels and cholinergic neuronal system within the hippocampus.
... Therefore, it seems that it is crucial to use prophylactic drugs that protect the brain against the detrimental effects of NAs without serious adverse effects. The combination of donepezil and procyclidine led only to mild cognitive impairments and has shown to have promising protective effects against convulsions, seizures, brain damage, or death following soman poisoning in rats (Haug et al. 2007). Notably, the South Korean research group developed an experimental transdermal patch consisting of procyclidine and physostigmine (Choi et al. 2004). ...
Article
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Organophosphorus compounds (OP) are a constant problem, both in the military and in the civilian field, not only in the form of acute poisoning but also for their long-lasting consequences. No antidote has been found that satisfactorily protects against the toxic effects of organophosphates. Likewise, there is no universal cure to avert damage after poisoning. The key mechanism of organophosphate toxicity is the inhibition of acetylcholinesterase. The overstimulation of nicotinic or muscarinic receptors by accumulated acetylcholine on a synaptic cleft leads to activation of the glutamatergic system and the development of seizures. Further consequences include generation of reactive oxygen species (ROS), neuroinflammation, and the formation of various other neuropathologists. In this review, we present neuroprotection strategies which can slow down the secondary nerve cell damage and alleviate neurological and neuropsychiatric disturbance. In our opinion, there is no unequivocal approach to ensure neuroprotection, however, sooner the neurotoxicity pathway is targeted, the better the results which can be expected. It seems crucial to target the key propagation pathways, i.e., to block cholinergic and, foremostly, glutamatergic cascades. Currently, the privileged approach oriented to stimulating GABAAR by benzodiazepines is of limited efficacy, so that antagonizing the hyperactivity of the glutamatergic system could provide an even more efficacious approach for terminating OP-induced seizures and protecting the brain from permanent damage. Encouraging results have been reported for tezampanel, an antagonist of GluK1 kainate and AMPA receptors, especially in combination with caramiphen, an anticholinergic and anti-glutamatergic agent. On the other hand, targeting ROS by antioxidants cannot or already developed neuroinflammation does not seem to be very productive as other processes are also involved.
... The authors confirmed that the results were promising, but other investigations are needed that include higher doses of more toxic nerve agents such as soman. In another study, Haug et al. (Haug et al., 2007) demonstrated significant protective efficacy of donepezil (2.5 mg/kg) in combination with procyclidine (3 or 6 mg/kg) when given prophylactically against a lethal dose of soman (1.6 3 LD50) in Wistar rats. No neuropathological changes were found in rats treated with this combination 48 h after soman intoxication. ...
Chapter
Nerve agents rapidly inactivate acetylcholinesterase (AChE), leading to the accumulation of acetylcholine in the synaptic cleft, ultimately causing death by respiratory failure. Due to the inefficiency of the standard antidotal therapy consisting of atropine, oxime, and diazepam, the pretreatment option is introduced, given to healthy individuals when a chemical attack is expected. The pyridostigmine bromide is currently the only approved drug for the pretreatment against nerve agent exposure, but in the past few decades, several other AChE inhibitors have been proposed including carbamates (physostigmine and rivastigmine) and the reversible inhibitors AChE used for the treatment of Alzheimer’s disease (huperzine A, donepezil, and galanthamine). In this chapter, we present a comprehensive review of the newest in vitro and in vivo studies of these drugs as pretreatment options, along with the recently designed AChE reversible inhibitors, also tested in vitro for protection of the enzyme against irreversible inhibition by nerve agents. Special attention is paid to the results of the in vitro studies and kinetic behavior of AChE inhibitors and their relation to the protective effects exerted in the in vivo animal models.
... These inhibitors have been used with a limited efficacy in palliative treatment of Alzheimer disease (Moss, 2020). Their potential interest in prophylaxis/pretreatment of nerve agent poisoning has also been demonstrated (Janowsky et al., 2005;Albuquerque et al., 2006;Haug et al., 2007). However, galantamine and donepezil alone or in combination with other molecules may induce cognitive and locomotion impairments as side effects at doses used for protection against nerve agents (Myhrer et al., 2010;Myhrer and Aas, 2016). ...
Article
Certain ligands slowly bind to acetylcholinesterase. As a result, there is a slow establishment of enzyme-inhibitor equilibrium characterized by a slow onset of inhibition prior reaching steady state. Three mechanisms account for slow-binding inhibition: a) slow binding rate constant kon, b) slow ligand induced-fit following a fast binding step, c) slow conformational selection of an enzyme form. The slow equilibrium may be followed by a chemical step. This later that can be irreversible has been observed with certain alkylating agents and substrate transition state analogs. Slow-binding inhibitors present long residence times on target. This results in prolonged pharmacological or toxicological action. Through several well-known molecules (e.g. huperzine) and new examples (tocopherol, trifluoroacetophenone and a 6-methyluracil alkylammonium derivative), we show that slow-binding inhibitors of acetylcholinesterase are promising drugs for treatment of neurological diseases such as Alzheimer disease and myasthenia gravis. Moreover, they may be of interest for neuroprotection (prophylaxis) against organophosphorus poisoning.
... Apparently, the use of M1 receptor antagonists may compensate for the influence of high ACh concentrations on the excitation of Sp cells and hinder increase in their activation, thus resulting in a decrease in the inhibition of GP(e) neurons and an increase in their inhibitory action on neocortical neurons. It was shown that M1 receptor agonists promote generalized epilepsy, whereas M1 receptor antagonists suppress it [103]. ...
Article
We have analyzed the influence of acetylcholine and GABAergic inhibitory transmission on the functioning of parallel topically organized cortico-basal ganglia–thalamo-cortical neural loops including prefrontal and sensory neocortical areas and the hippocampo-basal ganglia–thalamo–hippocampal loop. Abnormal changes in the acetylcholine concentration as well as in the efficiency of excitation and inhibition in these circuits may lead to various types of epilepsy. Epileptiform activity may develop with the participation of long-range GABAergic cells which promote the synchronization of discharges of excitatory neurons in different structures. We discuss the role of GABAergic interactions between the nuclei of the basal ganglia; GABAergic inputs from hippocampal CA1 field to the medial septum and retrosplenial cortex; from the neocortex to the striatum; and from the external segment of the globus pallidus to the striatum and neocortex. We hypothesized that the limited duration of epileptiform activity is a result of the functioning of several negative feedback loops. These loops are under the influence of GABAergic inputs from the pedunculopontine nucleus to the basal forebrain, thalamus, striatum, basal ganglia outputs, and external segment of the globus pallidus. The influence of acetylcholine is complex because different types of cholinoreceptors are present on excitatory and inhibitory neurons in all structures, and different types of receptors show different affinity for acetylcholine. Our analysis suggests that epileptiform activity may be suppressed by reinforcing the negative feedback loop that is formed by the inhibitory input from the external segment of the globus pallidus to the neocortex. This requires a reduction in the activity of striatal GABAergic spiny cells which project to the neurons of the external segment of the globus pallidus. Since this reduction may be achieved by M1 muscarinic receptor antagonists, they may be used to suppress epileptiform activity. The paper discusses possible side effects of targeting muscarinic receptors in the treatment of various diseases including neurodegenerative disorders. In order to reduce side effects caused by M1 receptor antagonists and other antiepileptic drugs, it is suggested to reduce their dose and use adenosine A2A receptor antagonists. Our conclusions are consistent with the known results of experimental and clinical studies, which means that they may be used in a targeted search for drugs that alleviate the symptoms of various types of epilepsy. Keywords: epileptiform activity, acetylcholine, GABAergic inhibition, muscarinic M1 receptors, hippocampus, basal ganglia, negative feedback loop
... Donepezil hydrochloride was obtained as 5 mg tablets. The tablets were crushed, suspended in physiological saline (2 mg/ml) and administered in a dose of 2.25 mg/kg based on the previous studies [13,14]. The rats were subdivided into seven groups, randomly each containing 8 rats. ...
Article
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Some herbal medications like berberine and ipriflavone have a potential effect on Alzheimer. We studied the effect of berberine/ipriflavone mixture on the memory deficit and cognitive dysfunction which are induced by scopolamine and causing Alzheimer-like disease. 56 male Wistar rats were randomly subdivided into seven groups; including, two control groups (one received saline and the other one received polyethylene glycol), induced group, and four different treated groups (berberine, ipriflavone, berberine/ipriflavone mixture, and donepezil). Induced group and treated groups were received 2 mg/kg scopolamine intraperitoneally, once a day for 4 weeks. Berberine or ipriflavone orally administered (50 mg/kg dissolved in 20% polyethylene glycol). Group of berberine/ipriflavone mixture was orally administered 25 mg/kg each dissolved in 20% polyethylene glycol. Donepezil group was orally administered 2.25 mg/kg dissolved in saline. All treatments were continued daily for 4 weeks; afterward, the Morris water maze (MWM) test was initiated. Rats were euthanized 24 hours after probe trial for retention test; then brain tissues were collected from all groups for determination of pro-oxidants, antioxidants, an inflammatory marker, acetylcholine esterase activity, Alzheimer disease markers, and energy profile. Treatment with berberine/ipriflavone mixture improved scopolamine-induced cognitive dysfunctions in the MWM test and was significantly related to the increment in anti-oxidant levels, anti-inflammatory activity, cholinergic function, and brain energy profile. The current study revealed the relation between glucose-6-phosphate dehydrogenase and Alzheimer disease progression. Also, this mixture showed a substantial protective effect against the cognitive impairment induced by scopolamine.
... M 1 muscarinic cholinergic (mACh) receptor agonists exert a proconvulsant effect. In an animal model of generalized epilepsy, it has been reported that M 1 mACh receptor antagonists and donepezil, a reversible cholinesterase inhibitor, have an antiepileptic effect [5]. In a pilocarpine-induced animal model of temporal lobe epilepsy, donepezil exerted diverse effects in influencing neuronal death induced by epileptic seizures. ...
Article
Background In previous works, alterations of neurotransmitters and neuropeptides in the brain areas involved in generalized epilepsy have been reported. Objective We reviewed the alterations of these neurotransmitters and neuropeptides in the following brain areas involved in generalized epilepsy: hippocampus, hypothalamus, thalamus and cerebral cortex. In these brain areas, the neural networks are also actualized. The mechanisms of action of newer antiepileptic drugs in the treatment of generalized epilepsy are also discussed. Results Up-dating the neurotransmitter and neuropeptide alterations, we found that hippocampal GABAergic neurons presynaptically inhibit epileptogenic neurons via GABAB receptors. Epilepsy modulating neuropeptides (galanin, neuropeptide Y, dynorphin) are also involved. GABA deficiency, serotonin hyperactivity, dopamine hyperactivity and glutamate excitotoxicity can enhance ictogenesis: neurons containing these neurotransmitters form the main neural circuit. An increased excitability occurs when the alteration of these neurotransmitters is permanent. Conclusion In preclinical studies, the GABAB receptor agonist GS 39,783 exerted a good antiepileptic effect. Perampanel, an AMPA receptor antagonist, showed good clinical effects in the treatment of partial-onset seizures and primary generalized tonic-clonic seizures. In this treatment, perampanel can be combined with other antiepileptic drugs. Brivaracetam, which shows a high affinity for the synaptic vesicle 2A, exerted a good efficacy in the treatment of adult focal seizures and secondarily generalized tonic-clonic seizures.
... Acetylcholine plays an important role in ictogenesis and exerts its effect upon muscarinic and nicotinic cholinergic receptors. Agonists of the M 1 muscarinic cholinergic receptor exert a proconvulsant effect and M 1 receptor antagonists and donepezil (a reversible inhibitor of cholinesterase) have an antiepileptic effect (Haug et al., 2007). In the hippocampus, alpha7 nicotinic cholinergic (nACh) neurons activate GABAergic neurons and alpha4 beta2 nACh neurons activate D 2 dopaminergic neurons. ...
Chapter
In generalized epilepsy, the alteration of classical neurotransmitters and neuropeptides influences ictogenesis in the hippocampus, thalamus and cerebral cortex. GABAergic interneurons exert a presynaptic inhibitory action and therefore an antiepileptic effect. Neural circuits can be reorganized and then the GABAergic neurons can show an increased excitability. The antiepileptic effect, via GABA A receptors, is reduced during the epileptic seizure. The blockade of ionotropic glutaminergic receptors exerts a stronger antiepileptic effect. A combined pharmacotherapy of GABAergic and glutaminergic antagonists enhanced the antiepileptic effect. Other classical neurotransmitters and neuropeptides also play an important role in ictogenesis. A neural network in the brain regions involved in ictogenesis is described. The mechanisms of action of some recently developed antiepileptic drugs are pointed out according to the neural network suggested. New antiepileptic pharmacological options are derived from this neural network.
... Inductions of epilepsy in rats caused increase the activity of ChE in the brain after 24 hrs these result is disagree with the study of (21) who indicated that administration of pilocarpine induced status epilepticus and leading to a significant decrease in brain ChE activity in adult rats and of (17) who found that induction of epilepsy does not change the activity of ChE in the male rats. Cerebral ChE decreased reversibly in rats soman-induced to epilepsy treated with donepezil and procycledine (34). ...
Article
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The activity of cholinesterase and some biochemical parameters of blood such as glucose, cholesterol and phospholipids were estimated in 52 epilepsy induced females of Wister albino rats. Animals of this experiment were divided into two groups, group (I) regarded as control and group (II) administrated subcutaneously by pentylenetetrazole 100mg/kg and divided in to three sub-groups according to the time of samples collection 3 hrs, 24 hrs and 1 week. The results revealed that epilepsy induction caused a significant inhibition of serum cholinesterase activity 3 hrs after induction while in the brain, the activity of cholinesterase was significantly increased after 24 hrs Serum glucose level was significantly elevated after 3 hrs and 24 hrs of induction, total cholesterol and phospholipids were not changed. From the results obtained in this study, it can be concluded that epilepsy caused significant changes in cholinesterase activity in brain and serum in addition to the glucose level in the serum.
... Acetylcholine, which exerts its effect on muscarinic and nicotinic cholinergic receptors, has a pro-and an anti-convulsant action. The activation of the muscarinic-1 (M1) receptor has a proconvulsant effect [17]. Alpha4beta2 nicotinic cholinergic (alpha4beta2 nAch) neurons activate D2 dopaminergic neurons and alpha7 nAch neurons activate GABAergic neurons located in the hippocampus [18]. ...
Article
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Here, we describe the alterations of neurotransmitters and neuropeptides that act on specific subreceptors in the brain areas involved in generalized epilepsy. A neurotransmitter imbalance between GABAergic and serotonergic neurons with hypoactivity and glutaminergic and dopaminergic neurons with hyperactivity is described. Considering the alterations in neurotransmitters and neuropeptides, neural networks in the hippocampus, hypothalamus, thalamus and cortex are described. The mechanisms of action of some recently developed antiepileptic drugs are addressed. In sum, a multimodal antiepileptic pharmacotherapy acting at several specific subreceptors is suggested. We recommend the development of an antiepileptic drug, that exerts simultaneously a GABAA agonistic and an NMDA antagonistic effect.
... Rivastigmine was also found effective in counteracting cognitive damage following traumatic brain injury and focal ischemia in both animal and human (Chen et al., 1998a(Chen et al., , 1998bCummings, 2000;Giladi et al., 2003;McKeith et al., 2000;Moretti et al., 2001;Silver et al., 2009;Tanaka et al., 1995;Tsujimoto et al., 1993;Wesnes et al., 2002), and was tested for its effects against cognitive deterioration in schizophrenia and drug abuse (Ribeiz et al., 2010;Sofuoglu, 2010;Theunissen et al., 2015). In animal studies, pretreatment with central ChE inhibitors were repeatedly demonstrated to protect against OP nerve agents induced damage (Albuquerque et al., 2006;Alexandrova et al., 2014;Grunwald et al., 2002;Haug et al., 2007;Harris et al., 1991;Janowsky et al., 2004Janowsky et al., , 2005Lallement et al., 2001;Philippens et al., 2000). ...
... The activation of the muscarinic-1 (M 1 ) receptor has a proconvulsant action. Atropine, an M 1 receptor antagonist, and donepezil, a partially reversible inhibitor of cholinesterase, exert an antiepileptic effect [22]. The activation of nAch alpha7Rs, which enhance GABAergic neurotransmission, has an antiepileptic effect [23]. ...
... Huperzine A, a reversible inhibitor of acetylcholinesterase, is able to abolish seizures induced by soman in rats (Tonduli et al., 2001). Wistar rats, exposed to soman, did not have neuropathological sequelae when treated with the partial reversible inhibitor of acetylcholinesterase, donepezil hydrochloride, when used in combination with procyclidine, an anticholinergic compound (Haug et al., 2007). Preor post-treatment with galantamine, a competitive and reversible cholinesterase inhibitor, appeared to reduce lethality and neuropathologic outcomes of guinea pigs exposed to soman (Pereira et al., 2010). ...
Article
Epilepsy is a common neurological disorder characterized by an initial injury due to stroke, traumatic brain injury, brain infection, or febrile seizures causing status epilepticus (SE). This phenomenon precedes recurrent (secondary) seizures, the latent period (period without seizures) and downstream appearance of spontaneous recurrent seizures (SRS). Epilepsy inducers include the organophosphorous (OP) compounds modified as chemical warfare nerve agents, such as soman. SE induced by soman is a result of cholinergic system hyperactivity caused by the irreversible inhibition of acetylcholinesterase, and the subsequent increase in the amount of the neurotransmitter acetylcholine at central and peripheral sites. SE leads to profound, permanent, complex and widespread brain damage and associated cognitive and behavioral deficits, accompanied by impaired neurogenesis. Several anticonvulsant and neuroprotective strategies have been studied in order to avoid the epileptogenesis which occurs after SE caused by soman exposure. In recent studies, we showed that SRS occur post-soman exposure and neuropathology can be reduced with diazepam (DZP) and valproic acid (VPA) when administered in combination treatment. These effects are accompanied by neurogenesis seen 15 days post-exposure in the hippocampal dentate gyrus (DG). This review discusses several findings about epilepsy induced by soman exposure such as behavioral changes, EEG anomalies, neuropathology, neuroinflammation, neurogenesis, possible circuitry changes and current strategies for treatment. The soman seizure model is an important model of temporal lobe epilepsy (TLE) and comparable in certain respects with well studied models in the literature such as pilocarpine and kainic acid. All these models together allow for a greater understanding of the different mechanisms of seizure induction, propagation and options for treatment. These studies are very necessary for current military and civilian treatment regimens, against OP nerve agent exposure, which fail to prevent SE resulting in severe neuropathology and epilepsy.
... , 이결과를 바탕으로 피부부착형 패치 가 설계되었다. . 의 배합에 대한 연구논문 [30] 이 발표된바가 있으며, 특 히 2006년도 화학작용제 해독 워크샵에서 보고된 바 에 의하면, 국과연에서 개발된 패치의 약효 성분이 이 스라엘의 패치성분보다 약효가 우수하고, 인체에 안전 한 것으로 되어있다 [35] . ...
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Nerve agents are irreversible inhibitors of the cholinesterase enzyme. Exposure causes a progression of toxic signs, including hypersecretions, fasciculations, tremor, convulsions, respiratory distress, epileptiform seizures, brain injuries and death. A combined regimen of prophylaxis and therapy is the most effective medical countermeasure for dealing with the threat of nerve agent poisoning to military personnel. In this paper, the author investigated the updated technologies regarding various pre- and post-treatment drugs for nerve agents detoxification which are under development in several countries including Korea. Some characteristics of active ingredients in the formulations of drugs, their action mechanisms, and effectiveness were analyzed. Additionally, part of experimental data on the transdermal patch studied in ADD using beagle dogs was introduced.
... Acute pre-treatment with oral DON, with and without scopolamine, decreased the hypothermic, hypokinetic, and diarrhoea-inducing effects of DFP ( Janowsky et al., 2004Janowsky et al., , 2005. A combined pre-treatment with DON and procyclidine, a muscarinic receptor antagonist, protected against soman-induced seizures ( Haug et al., 2007). ...
Article
Reversible acetylcholinesterase inhibitor donepezil displays prophylactic effects against intoxication with irreversible organophosphorous acetylcholinesterase inhibitors. We used behavioural observation of yawning and epileptic seizures, histochemical acetylcholinesterase staining, and in situ hybridization of the immediate early genes, c-fos and synaptotagmin 4 (Syt4) mRNAs in the brain, to evaluate whether donepezil could protect the brain against the effects of the organophosphate anticholinesterase, diisopropylfluorophosphate, in a rat model of intoxication. Diisopropylfluorophosphatetreated animals exhibited frequent yawning, significant inhibition of acetylcholinesterase staining and upregulation of c-fos mRNA, but not the epileptic seizures or significant change of Syt4 mRNA levels. In order to reduce the threshold for the induction of cholinergic seizures, additional groups of rats were pre-treated with LiCl 24 h before the treatment with diisopropylfluorophosphate. These rats exhibited the seizures, a significant inhibition of acetylcholinesterase staining and significant upregulation of c-fos and Syt4 mRNA levels. All the above-mentioned effects of diisopropylfluorophosphate were inhibited by donepezil pre-treatment. Donepezil pre-treatment by itself induced only a comparatively weaker inhibition of acetylcholinesterase staining and infrequent yawning. We conclude that donepezil protects the brain against diisopropylfluorophosphate-induced effects and that Syt4 mRNA upregulation may serve as a novel marker for organophosphate-induced seizures.
... In the present study, donepezil (3 mg/ kg), ()huperzine A (0.3 mg/kg), or rivastigmine (6 mg/kg) also afforded 100% survival of guinea pigs challenged with 1.5 LD 50 soman and treated with atropine. Other studies have also reported that pretreatment with galantamine, donepezil, or ()huperzine A in combination with post-treatment with a muscarinic antagonist effectively prevents the lethality of high doses of other nerve agents and OP pesticides (Lallement et al., 1997; Albuquerque et al., 2006; Haug et al., 2007; Hilmas et al., 2009). However, as shown here, at therapeutic doses only galantamine is devoid of untoward side effects. ...
Article
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.
... Calcium antagonists (nimodipine), neuromuscular blockers (tubocurarine), adamantanes (memantine), and the opiate antagonist meptazinol [4,[57][58][59] were also tested with different results but they were not very useful for practical use. On the other hand, a positive prophylactic effect has been demonstrated with procyclidine (antimuscarinic, antinicoticnic and the anti-NMDA receptor drug) [61,62], metoclopramide [63], clonidine [64] or procyclidine and donepezil [65]. Special importance can be focused on suramine (a protease inhibitor). ...
Article
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Prophylactic approaches against intoxication with organophosphates (OP)/nerve agents can be based on following principles: keeping acetylcholinesterase (AChE), the key enzyme for toxic action of OP/nerve agents, intact (protection of cholinesterases) is a basic requirement for effective prophylaxis. It can be reached using simple chemicals such as reversible inhibitors (preferably carbamates), which are able to inhibit AChE reversibly. AChE inhibited by carbamates is resistant to OP/nerve agent inhibition. After spontaneous recovery of the activity, normal AChE serves as a source of the active enzyme. Detoxification is realised by administration of the enzymes splitting the OP or exploitating specific enzymes (cholinesterases). OP/nerve agent is bound to the exogenously administered proteins (enzymes) and, thus, the agent level in the organism is decreased ("scavenger" effect). The antidotes currently used for the treatment of OP poisoning (also simple chemicals) can be tested as prophylactics. This principle can be considered as a treatment "in advance". The problem with their use is the timing, duration and achievement of sufficient levels of these antidotes after the administration. At present, PYRIDOSTIGMINE seems to be common prophylactic antidote; prophylactics PANPAL (tablets with pyridostigmine, trihexyphenidyle and benactyzine), TRANSANT (transdermal patch containing HI-6) are other means introduced into different armies as prophylactics. Future development will be focused on scavengers (cholinesterases and other enzymes) acting before the binding of nerve agent to the target sites, and on other drugs reversible cholinesterase inhibitors (e.g. huperzine A, physostigmine, acridine derivatives etc.) including non-traditional routes of administration.
... As a potent cholinesterase inhibitor, soman induces a wide range of deleterious effects including salivation, convulsive seizures, respiratory distress, behavioral impairments and ultimately, death. In general, symptomatic treatment is used against organophosphorus intoxication, for example, donepezil and procyclidine protect against soman-induced seizures (Haug et al., 2007), and atropine reduces secretions. Some oximes as reactivators of inhibited AChE are currently a mainstay of treatment, such as HI-6, TMB-4, K074, etc. Berend et al., 2008;Worek et al., 2007). ...
Article
Soman is an organophosphorus neurotoxin which inhibits the activity of acetylcholinesterase (AChE). The goal of this work was to find out whether antibodies against an organophosphorus hapten could protect mice from soman toxicity. An organophosphorus hapten P6 was synthesized. Its chemical conjugates with limulus polyphemus hemocyanin and bovine serum albumin were used as immune antigen (P6-LPH) and detection antigen (P6-BSA), respectively. Eight hybridoma cell lines secreting monoclonal antibodies (Mabs) were established. The binding reactivities of Mabs with P6 and soman were determined by competitive inhibition enzyme immunoassay (CIEIA). All antibodies recognized P6 and four of them (2C10, 3G1, 3B9 and 3C11) combined with soman. The IC(50) was 10(-6.5) to 10(-5.3)mol/l for P6 and 10(-5) to 10(-3.5)mol/l for soman. Furthermore, Mab 3G1 reduced the inhibition of AChE activity by soman in vitro. When soman was pre-incubated with Mabs before being injected into mice, soman potency was reduced, indicating that Mabs could protect mice from soman toxicity. In an active immunization regimen, mice immunized with P6-LPH and challenged with 0.15mg/kg soman injected subcutaneously, had fewer signs of intoxication and a higher survival rate compared with control mice. These results demonstrate that the anti-soman antibodies have proper characteristics as scavengers in the detoxication of soman poisoning.
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Introduction: Diving utilising closed circuit pure oxygen rebreather systems has become popular in professional settings. One of the hazards the oxygen diver faces is central nervous system oxygen toxicity (CNS-OT), causing potentially fatal convulsions. At the same time, divers frequently travel by boat, often suffering seasickness. The over-the-counter medication meclizine is an anticholinergic and antihistaminergic agent that has gained popularity in the treatment of seasickness. Reports have shown the inhibitory effect that acetylcholine has on glutamate, a main component in the mechanism leading to CNS-OT seizure. The goal of the present study was to test the effect of meclizine on the latency to CNS-OT seizures under hyperbaric oxygen conditions. Methods: Twenty male mice were exposed twice to 608 kPa (6 atmospheres) absolute pressure while breathing oxygen after administration of control solution (carboxymethyl cellulose solvent) or drug solution (meclizine) in a randomised crossover design. Latency to tonic-clonic seizures was visually measured. Results: Mean latency to seizure did not significantly differ between the control group (414 s, standard deviation [SD] 113 s) and meclizine group (434 s, SD 174 s). Conclusions: Based on results from this animal model, meclizine may be an appropriate option for divers suffering from seasickness, who plan on diving using pure oxygen rebreather systems.
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Motivation Drug repositioning is an effective strategy to identify new indications for existing drugs, providing the quickest possible transition from bench to bedside. With the rapid development of deep learning, graph convolutional networks (GCNs) have been widely adopted for drug repositioning tasks. However, prior GCNs based methods exist limitations in deeply integrating node features and topological structures, which may hinder the capability of GCNs. Results In this study, we propose an adaptive GCNs approach, termed AdaDR, for drug repositioning by deeply integrating node features and topological structures. Distinct from conventional graph convolution networks, AdaDR models interactive information between them with adaptive graph convolution operation, which enhances the expression of model. Concretely, AdaDR simultaneously extracts embeddings from node features and topological structures and then uses the attention mechanism to learn adaptive importance weights of the embeddings. Experimental results show that AdaDR achieves better performance than multiple baselines for drug repositioning. Moreover, in the case study, exploratory analyses are offered for finding novel drug–disease associations. Availability and implementation The soure code of AdaDR is available at: https://github.com/xinliangSun/AdaDR.
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Combination therapy has birthed improved treatment possibilities for a number of complex and degenerative diseases in the world, which include cancer, diabetes and cardiovascular disease, and has been encouraged for use in the treatment of Alzheimer’s disease (AD), as a result of its complex pathological pathways. The combination of memantine and donepezil was approved for use to treat moderate-to-severe AD cases in 2014. Studies have however continued to investigate many other possible combination therapies for the treatment of AD. This article highlights some of the recent combination therapies involving the use of donepezil.
Article
The threat of chemical warfare agents like nerve agents requires life saving measures of medical pretreatment combined with treatment after exposure. Pretreatment (pyridostigmine) may cause some side effects in a small number of individuals. A comprehensive research on animals has been performed to clarify effects on behavior. The results from these studies are far from unambiguous, since pyridostigmine may produce adverse effects on behavior in animals in relatively high doses, but not in a consistent way. Other animal studies have examined the potential of drugs like physostigmine, galantamine, benactyzine, trihexyphenidyl, and procyclidine, but they all produce marked behavioral impairment at doses sufficient to contribute to protection against a convulsant dose of soman. Attempts have also been made to develop a combination of drugs capable of assuring full protection (prophylaxis) against nerve agents. However, common to all combinations is that they at anticonvulsant doses cause behavioral deficits. Therefore, the use of limited pretreatment doses may be performed without marked side effects followed by post-exposure therapy with a combination of drugs.
Chapter
The term prophylaxis is sometimes unclear it is limited to medical countermeasures applied just before penetration of a toxic agent into the organism. Prophylaxis focuses on the protection of acetylcholinesterase (AchE) against the inhibition using reversible cholinesterase inhibitors. The level of organophosphates (OP) can be diminished by using enzymes hydrolyzing these agents or enzymes binding the agents and thereby reducing the OP level and inhibition of cholinesterases-AChE and butyrylcholinesterase (scavenger effect) in the organism. Intact AChE is a basic requirement for normal function of the organism and thus for effective prophylaxis. The enzyme is changed in a way that will make it resistant to OP. This can be achieved by using reversible inhibitors, which are able to inhibit AChE reversibly, and after spontaneous recovery of the activity normal AChE serves as a source of an active enzyme. The antidotes currently used for the treatment of OP poisoning in this context include anticholinergics, reactivators, and anticonvulsants.
Chapter
This chapter focuses on the development of novel countermeasures against nerve agents to improve existing prophylactic and postexposure treatments. Nerve agents are regarded as the most toxic among all chemical weapons. Tabun was the first to be synthesized, followed by sarin and soman. VX is another type of nerve agent that was originally developed in the UK during research for new insecticides. The organophosphorus (OP) nerve agents are highly potent irreversible inhibitors of the enzyme acetylcholinesterase (AChE) that hydrolyzes acetylcholine (ACh). Accumulation of ACh in the synaptic cleft results in overstimulation of muscarinic and nicotinic receptors. This cholinergic overactivity can affect all organ systems. The toxic signs in humans include pinpoint pupils (miosis), bronchoconstriction, hypersalivation, increased lung secretions, sweating, diarrhea, loss of consciousness, seizures, and respiratory arrest. Miosis appears to be a very sensitive index of direct exposure, and can be painful for several days. Chest tightness, rhinorrhea, and increased salivation can occur within seconds/minutes of inhalation of nerve agents. If exposure is substantial, death may occur from respiratory arrest within minutes. Oximes should be used for treatment as soon as possible after exposure to nerve agent, because of the short time window of the aging process. Effective prophylactic treatment can be achieved by using a fixed dose of physostigmine in combination with varying doses of procyclidine. Increased lethal doses of soman can be counteracted by a corresponding increase in the procyclidine dose.
Article
During the establishment of a research branch, all relevant matters encountered will be of interest to study. After having acquired a body of basal knowledge, it becomes possible to derive ideas or hypotheses for further elaboration of information. The purpose of the present study was to show that therapies for nerve agent poisoning based on specific neuropharmacological approaches can have greater probability for being successful than treatment regimens based on fragmental research or serendipitous discoveries. By following the guidelines for research in experimental epilepsy, neuronal target areas for nerve agents have been identified through lesion studies, and critical receptors for pharmacological treatment have been specified through microinfusion studies of rats. Subsequent experimentations have shown that the results achieved from microinfusion studies are transferable to systemic administration. It is demonstrated that a treatment regimen developed through the novel approach is more efficacious than regimens derived from conventional research on countermeasures. A therapy consisting of HI-6, levetiracetam, and procyclidine that has been worked out along the new lines, exerts powerful anticonvulsant capacity and appears to have universal utility as a stand-alone therapy against soman intoxication in rats. It would be of great interest to examine whether the latter findings can be expanded to other animal species than rats and other classical nerve agents than soman.
Article
A transdermal patch system containing procyclidine, an N-methyl-d-aspartate receptor antagonist possessing anticholinergic action, and physostigmine, a reversible cholinesterase inhibitor, was developed, and its prophylactic efficacy against soman intoxication was investigated. Male rhesus monkeys were shaved on the dorsal area, attached with a matrix-type patch with various sizes (2×2 to 7×7 cm) for 24 or 72 h, and challenged with 2×LD₅₀ doses (13μg/kg) of soman. The smallest patch size for the protection against lethality induced by soman intoxication was 3×3cm, resulting in blood procyclidine concentration of 10.8 ng/ml, blood physostigmine concentration of 0.54 ng/ml, which are much lower concentrations than maximum sign-free doses, and blood cholinesterase inhibition of 42%. The drug concentrations and enzyme inhibition rate corresponding to a diverging point of survivability were presumably estimated to be around 7 ng/ml for procyclidine, 0.35 ng/ml for physostigmine, and 37% of enzyme inhibition. Separately, in combination with the patch treatment, the post treatment consisting of atropine (0.5 mg/kg) plus 1-[([4-(aminocarbonyl)pyridinio]methoxy)methyl]-2-[(hydroxyimino)methyl]pyridinium (HI-6, 50 mg/kg) exerted protection against 5×LD₅₀ challenge of soman, which means the posttreatment remarkably augmented the efficacy of the patch. Additionally, it was found that brain injuries induced by soman toxicity were effectively prevented by the patch treatment according to histopathological examinations. These results suggest that the patch system could be an effective alternative for diazepam, an anticonvulsant, and the current pyridostigmine pretreatment, and especially in combination with atropine plus HI-6, could be a choice for quality survival from nerve-agent poisoning.
Article
The rapid onset of toxic signs following nerve agent intoxication and the apprehension that current therapy (atropine, oxime, diazepam) may not prevent brain damage, requires supportive pretreatment. Since the current pretreatment drug pyridostigmine fails in protecting brain-AChE, more effective pretreatment is necessary. A main focus of present-day pretreatment research is on bioscavengers, another is on centrally active reversible AChE-inhibitors combined with drugs showing anti-cholinergic, anti-glutamatergic, neuroprotective and non-sedating GABA-ergic activity. Strategies aimed at improving efficacy of pharmacological pretreatment will briefly be discussed. Galantamine, given as a pretreatment or stand-alone therapy, emerged as one of the best medical countermeasures against nerve agent poisoning in guinea pigs. Other preclinical studies demonstrated effective pretreatment consisting of physostigmine combined with procyclidine, scopolamine or bupropion (all single injections), against nerve agent poisoning in guinea pigs. A long sign-free pretreatment with physostigmine (Alzet pump), combined with single injection of procyclidine just before soman poisoning, enhanced the efficacy of a post-poisoning therapy consisting of 3 autoinjector equivalents of HI-6, atropine and diazepam, considerably.
Article
The present study attempts to assess the comparative effects of Bacopa monniera, (40 mg/kg body weight) and donepezil (2.5 mg/kg b. wt) on aluminum (100 mg / kg b. wt. of AlCl3) mediated oxidative damage in the cerebellum of aged rats (24 months) along with the associated dysfunctioning of neuromuscular coordination and motor activity. A significant decrease in the activities of antioxidant enzymes and increased total reacting oxygen species, lipid and protein peroxidation products observed in aluminum exposed rats. We observed that treatment with B. monniera extract restored the altered antioxidant enzyme activities more, when compared with donepezil. However, acetylcholinesterase showed similar effect both in donepezil and B. monniera treated groups. The content of aluminum was increased in all experimental groups, however, iron content was found increased in all groups except the B. monniera treated groups. Moreover, aluminum treated groups of rats exhibited significant changes in behavioral profiles but these changes were in both B. monniera and donepezil treated groups. The light microscopic and ultrastructural studies revealed damaged Purkinje's neurons and altered granular cell layer along with the increased accumulation of lipofuscin granules in aluminum treated animals. These changes were quite less pronounced in B. monniera group than that of donepezil and this may be due to the reduction of excess iron content by B. monniera. On the basis of our results it may be concluded that Al may be linked with cerebellar degeneration and neuromuscular disorders while Bacopa monniera extract helps in reversing these changes.
Article
Acetylcholinesterase inhibitors in combination with an anticholinergic, particularly anticholinergics with antiglutamatergic properties, can effectively protect against nerve agent-induced seizures and lethality. The objective of the present study was to examine potential behavioral side effects of the anticholinesterases physostigmine (0.1mg/kg), galantamine (3mg/kg), huperzine (0.5mg/kg), and donepezil (2.5mg/kg) alone or each drug in combination with anticholinergic procyclidine (3mg/kg). The results showed that rats injected intraperitoneally with galantamine displayed a mild cognitive deficit in terms of reduced preference for novelty that was similarly found among animals treated with procyclidine combined with either galantamine or donepezil. Locomotor activity and rearing were radically depressed in all groups treated with anticholinesterases as well as in combination with procyclidine. Reductions in activity were most prominent for rats injected with galantamine alone. Equalizing effects of cholinesterase inhibitors and anticholinergics were absent in the present context. Findings from previous studies that both systemic and local (amygdala) application of physostigmine cause increased fear-motivated freezing response in rats, may explain the marked reductions in activity among the present rats. In view of these findings, use of anticholinesterases (crossing the blood-brain barrier) as prophylactics against nerve agents must be carefully examined to avoid severe side effects.
Article
Potent cholinesterase inhibitors (e.g., soman, sarin), induce a wide range of deleterious effects including convulsions, behavioral impairments and ultimately, death. Due to the likelihood of various scenarios of military or terrorist attacks by these and other chemical weapons, research has to be aimed at finding optimal therapies. Early accumulation of acetylcholine in synaptic clefts was suggested to trigger an array of toxic events including an excessive release of glutamate, culminating in the activation of its receptors. Stimulation of the N-Methyl-D-Aspartate (NMDA) subtype of these receptors was associated with the neuronal injury that initiates organophosphate-induced brain damage. The notion of a stepwise mechanism yielded treatments based on a combination of an immediate administration of enzyme reactivators and anticholinergic drugs. This strategy dramatically increased survival rates but did not abolish convulsions and failed to prevent the ensuing cognitive dysfunction. Efforts to improve this paradigm by adding anticonvulsants or antiglutamatergic drugs with anti-epileptic characteristics produced dubious results. Under these conditions, benactyzine and caramiphen, agents with anticholinergic and antiglutamatergic properties, provided improved protection when introduced as adjunct agents to oximes, reversible cholinesterase inhibitors and/or specific antimuscarinic drugs such as atropine. In contrast, the specific antimuscarinic drug scopolamine failed to block soman-induced changes in glutamatergic and behavioral parameters even when given prophylactically. These findings along with a large number of additional reports led towards the conclusion that the therapeutic advantage of drugs such as benactyzine and caramiphen could derive from their ability to modulate central cholinergic and glutamate neurotransmission.
Article
In epilepsy research, studies have been made to identify brain areas critical for triggering and/or controlling propagated seizure activity. The purpose of the present study was to focus on a similar approach in nerve agent research by reviewing relevant literature to map potential trigger sites and propagation pathways for seizures. The piriform cortex and medial septal area emerge as prime target areas for soman-induced seizures. The cholinergic hyperactivation in the latter structures seems to induce increased glutamatergic activity in the piriform, entorhinal, and perirhinal cortices along with the hippocampal region. For prophylactic or early treatment, mapping of muscarinic subreceptors in the piriform cortex and medial septum would be guiding for designing anticholinergic drugs with optimal properties. Sustained seizures governed by glutamatergic over-activity may primarily be terminated by drugs with optimal glutamatergic antagonism primarily in the piriform, entorhinal, and perirhinal cortices. Studies of radiolabeled ligands to map subreceptors may provide specification of wanted drug properties to guide the choice among existing agents or to synthesize novel ones.
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Exocytotic release of neurotransmitters requires their accumulation inside preformed secretory vesicles. Distinct vesicular transport activities translocate classical transmitters into synaptic vesicles energized by a H+ electrochemical gradient (Delta(mu(H+))), with subtle but important differences in dependence on the electrical and chemical components. The vesicular transporters also interact with toxic compounds and drugs. They mediate neuroprotection by sequestering toxic compounds as well as neurotransmitters into vesicles, reducing their concentration in the cytosol where they may have detrimental effects. Both therapeutic agents and psychostimulants interfering with vesicular transport have yielded insight into the pathogenesis of psychiatric as well as neurodegenerative diseases. Thus, specific inhibitors have helped to characterize both the physiological role and mechanism of vesicular neurotransmitter transport.
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Soman (pinacolymethylphosphonofluoridate), a highly potent irreversible inhibitor of acetylcholinesterase (AChE), causes seizures and rapidly increases Fos and glial fibrillary acidic protein (GFAP) staining in piriform cortex (PC). This suggests that the inhibition of AChE by soman leads to increased acetylcholine (ACh) and neuronal excitability in PC. The sole source of cholinergic input to PC is from the nucleus of the diagonal band (NDB). To investigate the role of ACh in soman-induced seizures, we lesioned cholinergic neurons in NDB unilaterally with 192-IgG-saporin . By 10 d, saporin eliminated staining for choline acetyltransferase (ChAT), the synthetic enzyme for ACh, in NDB ipsilateral to the lesion. Staining for AChE, the degradative enzyme for ACh, was eliminated in PC ipsilateral to the lesioned NDB. By 45–60 min after soman, increased Fos and GFAP staining in PC was evident only ipsilateral to the unlesioned NDB. By 90–120 min after soman, Fos and GFAP staining increased bilaterally in PC. In a second experiment, electrical stimulation electrodes were implanted unilaterally in the NDB to activate focally the projections to PC in unanesthetized rats. Within 5 min of NDB stimulation, there were clear behavioral and EEG signs of convulsions. After 45–60 min of NDB stimulation, there was increased Fos and GFAP staining in layer II of PC ipsilateral to the stimulation site. Pretreatment with the selective muscarinic receptor antagonist scopolamine blocked the convulsions and prevented increased Fos and GFAP staining in PC. These results suggest that ACh release in PC triggers the initiation of seizures and gliosis after soman administration, predominantly by the activation of muscarinic receptors.
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Donepezil was developed in order to overcome the disadvantages of physostigmine and tacrine. Its use is based on the cholinergic hypothesis. Donepezil is a piperidine-based, reversible acetylcholinesterase inhibitor, that is chemically unrelated to other cholinesterase inhibitors. It was developed for the symptomatic treatment of Alzheimer's disease (AD). Donepezil is highly selective for acetylcholinesterase with a significantly lower affinity for butyrylcholinesterase, which is present predominantly in the periphery. Phase I and II clinical trials demonstrated donepezil's favorable Pharmacokinetic, pharmacodynamic and safety profile. There is no need to modify the dose of donepezil in the elderly or in patients with renal and hepatic failure. Pivotal phase-III trials in the US, European countries, and Japan showed that donepezil significantly improved cognition and global function in patients with mild to moderate AD. In long-term trials, donepezil maintained cognitive and global function for up to 1 year prior to the resumption of gradual deterioration. Donepezil is generally well tolerated; most of its adverse events are mild, transient and cholinergic in nature. Donepezil produces no clinically significant changes in laboratory parameters, including liver function. The drug is approved for the treatment of mild to moderate Alzheimer's disease, but donepezil therapy does not have to be discontinued if a patient continues to deteriorate. Possible new indications for donepezil in psychiatric and neurologic diseases, other than AD, include dementia with Lewy bodies, brain injury, attention deficit hyperactivity, multiple sclerosis, Down's syndrome, delirium, mood disorders, Huntington's disease and sleep disorders.
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This study evaluated the potency and rapidity of some anticholinergics (atropine, biperiden, and trihexyphenidyl) and benzodiazepines (diazepam and midazolam) as an anticonvulsant treatment against seizures induced by six nerve agents (tabun, sarin, soman, cyclosarin, VR, and VX) and summarized the relationship between anticonvulsant activity and nerve agent-induced lethality and neuropathology. Guinea pigs, previously implanted with cortical electrodes for EEG recording, were pretreated with pyridostigmine bromide (0.026 mg/kg im) 30 min prior to challenge with 2x LD50 dose (sc) of a given nerve agent; in a separate experiment, animals were challenged with 5x LD50 sc of soman. One minute after agent challenge the animals were treated im with 2 mg/kg atropine SO(4) admixed with 25 mg/kg 2-PAM Cl. Five minutes after the start of EEG seizures, animals were treated im with different doses of anticholinergics or benzodiazepines and observed for seizure termination. The time to seizure onset, the time to seizure termination, and 24-h lethality were recorded. The anticonvulsant ED50 of each drug for termination of seizures induced by each agent was calculated and compared. Brain tissue from animals that survived 24 h was examined for pathology. All drugs were capable of terminating seizure activity, with midazolam and trihexyphenidyl being significantly more potent than the other drugs, and midazolam being more rapid in controlling seizure than atropine, trihexyphenidyl, or diazepam against each agent. Seizures induced by sarin or VX required lower doses of all the test anticonvulsants. The dose of a given drug that was an effective anticonvulsant against a 2x LD50 challenge of soman was equally effective against seizures induced by a 5x LD50 challenge. All nerve agents were capable of producing neuropathology. Seizure control was strongly associated with protection against acute lethality and brain pathology.
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Smooth pursuit eye movement (SPEM) and antisaccade deficits are observed in the schizophrenia spectrum and have been used to study the pathophysiology as well as the genetic basis of this condition. The neurotransmitter acetylcholine has been implicated in a number of cognitive processes thought to underlie SPEM and antisaccade performance. This study investigates effects on eye movements of procyclidine, an anticholinergic drug often administered to schizophrenic patients. A total of 13 patients completed a double-blind placebo-controlled crossover design, receiving 15 mg procyclidine and placebo. Seven participants received procyclidine first and placebo second, six participants were tested in the reverse order. SPEM and antisaccade (as well as fixation and prosaccade) eye movements were recorded using infrared oculography. Results showed that procyclidine overall, relative to placebo, mildly worsened SPEM performance, as indicated by nonsignificantly reduced gain (p=0.08) and increased frequency of intrusive anticipatory saccades during pursuit (p=0.06). A significant interaction of group and order of administration indicated that procyclidine increased the rate of antisaccade reflexive errors only when administered first; the opposite pattern was observed when placebo was administered first, likely due to the operation of practice effects at second assessment. These findings indicate that acute administration of a clinically relevant dose of procyclidine leads to mild impairments in eye movement performance in schizophrenic patients, suggesting the need to consider this compound in oculomotor studies in schizophrenia. The action of this anticholinergic drug on oculomotor performance is consistent with the hypothesized role of the cholinergic system in the cognitive mechanisms of attention and working memory, processes thought to underlie SPEM and antisaccade performance. Effects of order of administration and practice on the antisaccade task suggest that these factors need to be taken into consideration in future pharmacological studies.
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The use of chemical warfare agents against civilians and unprotected troops in international conflicts or by terrorists against civilians is considered to be a real threat, particularly following the terrorist attacks on 11 September 2001 against the World Trade Center in New York and against the Pentagon in Washington, DC. Over the past 10 years, terrorists have been planning to use or have used chemical warfare agents on several occasions around the world, and the attacks in 2001 illustrate their willingness to use any means of warfare to cause death and destruction among civilians. In spite of new international treaties with strong verification measures and with an aim to prohibit and prevent the use of weapons of mass destruction, nevertheless, some countries and terrorist groups have been able to develop, produce, and use such weapons, particularly nerve agents, in domestic terrorist attacks or during warfare in international conflicts. This article reviews current medical therapy for nerve-agent intoxication and discusses possible future improvement of medical therapies. Present medical counter-measures against nerve agents are not sufficiently effective particularly in protecting the brain. Therefore, new and more effective countermeasures must be developed to enable better medical treatment of civilians and military personnel following exposure to nerve agents. Therefore, it is important with an enhanced effort by all countries, to improve and increase research in medical countermeasures, in the development of protective equipment, and in carrying out regular training of medical and emergency personnel as well as of military nuclear, biological, or chemical (NBC) units. Only then will nations be able to reduce the risk from and prevent the use of such weapons of mass destruction (WMD).
Chapter
Tolerance to AChE inhibitors has been noted using different forms of administration and in several species, such as mice, rats, guinea pigs, and man. Tolerance can develop in several ways. It often occurs because of receptor changes either in the number of receptors or by decreased affinity of the receptor molecule. However, it can also occur because of the presence of other proteins that can bind or inactivate the inhibitor, and thereby make it less readily available. Examples are, binding of the inhibitor to carboxylesterases (CarbEs), buturylcholinesterases (BuChEs), or other binding proteins such as albumin. In addition, tolerance can be achieved through more rapid metabolism of the OP compounds by OP-hydrolyzing enzymes such as paraoxonases (PONs) and somanases. Organophosphates (OPs) inhibit the enzyme AChE, and thereby increase the level of acetylcholine (ACh) in the synaptic gap. The acute toxic effects of OPs are because of accumulation of ACh at the muscarinic and nicotinic receptors. It has been noted by several investigators that during prolonged exposure to an OP, the physiological effects often diminish more than expected from the degree of AChE inhibition, or that repeated additions of OP give lower responses with time. These observations were seen irrespective of inhibition of blood AChE. The decrease in response to repeated administration could not be explained by a reduced inhibitory effect of soman on AChE or by a more rapid de novo synthesis of AChE.
Chapter
The chapter reviews the effects of anti-ChE agents on the thermoregulatory system of mammals and humans, including studies on the central nervous system. The regulation of body temperature is an ideal benchmark to study the toxicity of the anti-ChE insecticides in experimental mammals and humans. The inhibition in acetylcholinesterase (AChE) activity, and subsequent stimulation of cholinergic pathways in the central and peripheral nervous systems is a key mechanism responsible for driving changes in body temperature and activation of thermoregulatory effectors. Body size and ambient temperature are perhaps the most critical factors governing the thermoregulatory effects of these toxicants. Small mammals undergo a marked increase in heat loss and become hypothermic when exposed to anti-ChEs. Small mammals exposed to these agents lower their body temperature by selective activation of heat loss thermoeffectors. This hypothermic response is often protective and increases the likelihood of surviving the toxic insult. Large mammals such as humans are unable to take advantage of this hypothermic response, and it is not clear whether a fever from these toxicants will affect the health effects of these agents. It appears that exercise and/or heat stress will exacerbate the toxic effects of anti-ChE insecticides and nerve gas agents. The redistribution of blood to the skin combined with sweating will increase the cutaneous absorption of OP agents that are applied to the skin. The increase in pulmonary ventilation during exercise combined with higher tissue temperature is bound to increase the intake and toxicity of airborne anti-ChE agents.
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The effects of repeated oral exposures to the organophosphorus insecticide chlorpyrifos (CPS) on brain muscarinic receptor densities, together with cholinesterase (ChE) activity, were studied in early postnatal rats. Initially, the effects on esterases from lactational exposure to CPS were investigated in young rats by administering CPS (100, 150, or 200 mglkg subcutaneously in corn oil) to dams 1 day postpartum, yielding a significant body burden of CPS in the dams for possible excretion in the milk. Brain ChE inhibition in pups was less severe than in dams, whereas liver carboxylesterase (CbxE) inhibition in pups was at the same level as in dams. Because of the limited brain ChE inhibition obtained following lactation, pups were exposed to CPS directly by gavage, using 3 dosing regimens to yield a dose response. The rats were gavaged with CPS in corn oil on alternate days from postnatal day (PND) 1 through PND 21. Rats in the low-dosage group received 11 treatments at 3 mg/kg, those in the medium-dosage group received 3 treatments at 3 mg/kg and 8 at 6 mg/kg, and those in the high dosage group received 3 treatments at 3 mglkg, 4 at 6 mg/kg, and 4 at 12 mg/kg. ChE activity in brain homogenates were inhibited significantly by 29% and 63% in the low- and high-dosage groups, respectively, on PND 22 and by 17% in the high dosage group on PND 40. Muscarinic receptor densities in brain synaptosomes were reduced using 3 H-N-methylscopolamine (NMS) and 3 H-quinuclidinyl benzilate (QNB) as ligands, with the effects more prominent from 3 H-NMS. Densities of both ligands recovered to the control level several days after terminating treatment. The results indicate that pups are apparently exposed to only limited amounts of chlorpyrifos and/or its oxon through the milk when dams are exposed to extremely high chlorpyrifos levels. In addition, repeated direct oral exposures of early postnatal rats to CPS will result in persistent brain ChE inhibition and will transiently reduce muscarinic receptor density.
Article
Beyond 6 to 9 months of treatment with cholinesterase inhibitors (ChE-Is), there is a notable increase in the rate of cognitive decline in Alzheimer disease (AD) patients, and there are few longer-term studies to evaluate this finding. The authors examined whether the ChE-I rivastigmine continued to be therapeutically effective after up to 2 years of treatment in 2,010 patients with probable AD.Methods The clinical course of AD patients treated with rivastigmine was compared with a prediction of their course derived by a baseline-dependent historical model of disease progression developed from data in untreated AD patients. Rivastigmine efficacy data came from four 6-month, placebo-controlled, randomized, controlled trials (RCTs) and two open-label extension studies. Cognitive performance was assessed by various clinician- and caregiver-rated measures.ResultsAfter 2 years on rivastigmine, there was less cognitive deterioration than in historical-control subjects. These effects of rivastigmine on cognitive performance were considered clinically meaningful relative to expected global decline. Treatment-emergent adverse events were the commonly-seen side effects of ChEIs and were similar in frequency to those seen in patients assigned to shorter-term rivastigmine therapy.Conclusion Rivastigmine had a beneficial effect on cognitive performance for up to 2 years in patients with AD, versus no treatment or placebo treatment in historical-control subjects. Caregiver and clinician assessments indicated that the cognitive performance findings were of a magnitude relevant to global patient functioning. Rivastigmine remained safe over this 2-year treatment period.
Article
McDONAGH, J.H., JR., T.-M. SHIH. Neuropharmacological mechanisms of nerve agent-induced seizure and neuropathy. NEUROSCI BIOBEHAV REV 21(5) 559–579, 1997.—This paper proposes a three phase “model” of the neuropharmacological processes responsible for the seizures and neuropathology produced by nerve agent intoxication. Initiation and early expression of the seizures are cholinergic phenomenon; anticholinergics readily terminate seizures at this stage and no neuropathology is evident. However, if not checked, a transition phase occurs during which the neuronal excitation of the seizure per se perturbs other neurotransmitter systems: excitatory amino acid (EAA) levels increase reinforcing the seizure activity; control with anticholinergics becomes less effective; mild neuropathology is occasionally observed. With prolonged epileptiform activity the seizure enters a predominantly non-cholinergic phase: it becomes refractory to some anticholinergics; benzodiazepines and N-methyl-d-aspartate (NMDA) antagonists remain effective as anticonvulsants, but require anticholinergic co-administration; mild neuropathology is evident in multiple brain regions. Excessive influx of calcium due to repeated seizure-induced depolarization and prolonged stimulation of NMDA receptors is proposed as the ultimate cause of neuropathology. The model and data indicate that rapid and aggressive management of seizures is essential to prevent neuropathology from nerve agent exposure. Published by Elsevier Science Ltd.
Article
Data Selection Sources: Medical literature published in any language since 1966 on donepezil, identified using AdisBase (a proprietary database of Adis International, Auckland, New Zealand) and Medline. Additional references were identified from the reference lists of published articles. Bibliographical information, including contributory unpublished data, was also requested from the company developing the drug. Search strategy: AdisBase search terms were 'donepezil' or 'E-2020': Medline search terms were 'donepezil' or 'E-2020': Searches were last updated 12 Jan 2000. Selection: Studies in patients with Alzheimer's disease who received donepezil. inclusion of studies was based mainly on the methods section of the trials. When available, large. well controlled trials with appropriate statistical methodology were preferred. Relevant pharmacodynamic and pharmacokinetic data are also included.
Article
Postnatal changes of nicotinic acetylcholine receptor (nAChR) α2, α3, α4, α7 and β2 subunits mRNAs were investigated in rat brain using ribonuclease protection assay. Multiple developmental patterns were observed: (1) transient expression during the first few postnatal weeks; α2 in the hippocampus and brain stem, α3 in the striatum, cerebellum and cortex, α4 in the hippocampus, striatum and cerebellum, α7 in the cerebellum and β2 in the striatum. (2) Constant expression across development; α2 and α3 in the thalamus, α4 in the cortex, thalamus and brain stem, α7 in the thalamus and brain stem and β2 in all brain regions except striatum. (3) Non-detection across development; α2 in the cortex, striatum and cerebellum. (4) Increase with age; α7 in the cortex and hippocampus. (5) Bell-shaped development; α7 in the striatum. Postnatal changes of nAChR isoforms in different brain regions of rat were investigated by receptor binding assays. The developmental patterns of [3H]epibatidine and (−)-[3H]nicotine binding sites were similar to each other in each brain region, but different from that of [3H]α-bungarotoxin binding sites. No obvious correlation was observed between the developmental patterns of [3H]α-bungarotoxin, [3H]epibatidine and (−)-[3H]nicotine binding sites and corresponding subunits mRNAs. These results indicate that multiple mechanisms are involved in changes of gene expression of nAChRs subunits in the brain of developing rats.
Article
Abstract Injection of sublethal doses of soman in rat intraperitoneally or subcutaneously every 4, 8, 12 or 24 hours led to chronic LD50 doses which were markedly higher than the acute one. When rats were exposed every 24 hrs to half LD50 doses of soman, several of the animals did not show symptoms of soman poisoning and survived a total exposure of 4–7 times the acute LD50 dose. Brain and diaphragm acetylcholinesterase activities declined steadily during the chronic soman exposure. The so-called external acetylcholinesterase activity of the diaphragm was inhibited to a slightly less degree than the total acetylcholinesterase of the same tissue. The ability of the liver to hydrolyze soman was similar in rats which survived several 24 hr doses and untreated rats.
Article
Studies have shown that polychlorinated biphenyls (PCB) may affect cognitive functions both in human and also in experimental animals. We have investigated whether this effect could be caused by an inhibition of the uptake of selected neurotransmitters into rat brain synaptosomes. Ortho-chlorinated biphenyls were found to inhibit transmitter transport into synaptosomes from rat brain. In contrast, several nonortho-chlorinated biphenyls did not inhibit uptake. The uptake of dopamine, glutamate, GABA and serotonin was inhibited by the PCB mixtures, Aroclor 1242 and 1254. Under identical condition, the uptake of dopamine was inhibited more efficient than that of glutamate. The inhibition of neurotransmitter uptake was found to be dependent on the chlorination patterns of the PCB congeners, (i) ortho-chlorinated PCBs with four to five chlorine substituents (with the exception of 2,2′,6,6′-TeCB) were the most effective inhibitors; (ii) hexa- or heptachlorinated PCBs were poor inhibitors or partial inhibitors (e.g. 2,2′,4,4′,5,5′-HCB) of glutamate and GABA uptake. Kinetic studies indicated that Aroclor 1242 inhibited dopamine uptake mainly competitively. The uptake of glutamate and GABA was inhibited in either a mixed competitive or in a non-competitive way, respectively. The neurotoxic concequences of the effect of different PCBs on neurotransmitter uptake on the uptake into synaptosomes are discussed.
Article
The effects of nitric oxide-regulating compounds on convulsions and mortality of rats administered i.p. with diisopropylfluorophosphate was investigated. l-NG-nitroarginine methyl ester, a nitric oxide synthase inhibitor possessing an anticholinergic action, markedly attenuated the intensity of convulsions and significantly reduced the mortality rate. A similar result was obtained with anticholinergic procyclidine, an N-methyl-d-aspartate receptor antagonist. Noteworthy, l-NG-nitroarginine, another inhibitor of nitric oxide synthase, significantly attenuated the seizure intensity when administered in combination with atropine sulfate (5 mg/kg), though either l-NG-nitroarginine or atropine sulfate was inactive alone. It is suggested that nitric oxide may be a proconvulsant or a convulsion-promoting factor in anticholinesterase poisoning, and both the reduction of nitric oxide level and blockade of cholinergic systems may be required for more effective protection of seizures.
Article
The antidotal, anticonvulsant and neuroprotective effects of physostigmine (PhS) and procyclidine (PC), the combinational prophylactics for organophosphate poisoning, were evaluated. For the investigation of dose-response relationship in rats and guinea pigs, various doses (0-6 mg/kg) of PC in combination with a fixed dose (0.1 mg/kg) of PhS were pretreated subcutaneously 30 min prior to subcutaneous poisoning with soman. Procyclidine in combination with PhS exhibited remarkable synergistic effects in a dose-dependent manner, leading to 1.92-5.07 folds of protection ratio in rats and 3.00-4.70 folds in guinea pigs. On the other hand, a low effect (1.65 fold) was achieved with the traditional antidotes atropine (17.4 mg/kg) plus 2-pralidoxime (30 mg/kg) treated immediately after soman poisoning, compared with a marked protection (5.50 fold) with atropine (17.4 mg/kg) plus HI-6 (125 mg/kg) in unpretreated rats. Noteworthy, the combinational prophylactics greatly potentiated the effect of atropine plus 2-pralidoxime to 6.13 or 12.27 folds and that of atropine plus HI-6 to 12.00 or 21.50 folds with 1.0 or 3.0 mg/kg of PC, respectively. A high dose (100 μg/kg, 1.3×LD(50)) of soman induced severe epileptiform seizures in rats pretreated with HI-6 (125 mg/kg), resulting in brain injuries in discrete brain regions under histopathological examination in 24 h. Interestingly, such seizures and excitotoxic brain injuries were fully prevented by pretreatment with PhS (0.1 mg/kg) and PC (1 mg/kg). Taken together, it is proposed that the prophylactics composed of PhS and PC could be a promising regimen for the prevention of lethality, seizures and brain injuries induced by soman poisoning.
Article
A simple, rapid and sensitive method for the detection of acetylcholine and choline in tissue extracts is reported. Acetylcholine and choline are first separated by HPLC then react in a mini-column with acetylcholinesterase and choline oxidase immobilized on Sepharose. The resulting H(2)O(2) produced by choline oxidase is then detected electrochemically. The assay is more sensitive than existing methods. We believe that the principle involved in this method namely the combination of immobilized enzymes and the high sensitivity of electrochemical detection may be applied to other substances that can be converted by immobilized enzymes into an electrochemically detectable compound.
Article
Organic anions of particular importance to biochemistry such as Krebs cycle intermediates, glycolysis intermediates, simple fatty acids, adenine nucleotides and CoA derivatives can be quantitatively extracted from a buffered solution by high-molecular-weight ammonium salts in an organic solvent. Phosphate salts of tertiary amines in chloroform were the most efficient extractants. The isolation procedure was found to be an example of amine neutralization. The effect of pH, different inorganic anions, volume ratios between the two phases, concentration of the isolated anions and concentration of the ammonium salts have been investigated. The extraction technique has been applied to rapid and sensitive radiochemical methods for the determination of acetylcholinesterase and 4-aminobutyrate aminotransferase activities.
Article
The effectiveness of diazepam alone or in the presence of atropine sulfate in reversing soman-induced convulsions, inhibition of blood and brain cholinesterase (ChE) activity, and elevation of brain acetylcholine (ACh) and choline (Ch) concentrations in rats was studied. Diazepam (5 mg/kg, IM) blocked the convulsive activity of soman (100 micrograms/kg, SC) whereas atropine sulfate (12 mg/kg, IM) did not. Inclusion of atropine sulfate enhanced the anticonvulsant effects of diazepam. Neither diazepam nor atropine sulfate alone affected ChE activity in the blood and brain of rats, nor did they alone, or in combination, reverse the ChE inhibition induced by soman. Diazepam by itself caused an increase in ACh concentrations in the striatum and a decrease in Ch concentrations in the cortex and striatum. On the other hand, atropine sulfate produced a decrease in ACh and an increase in Ch concentrations in these two brain regions. With combined treatment, diazepam reversed the effect of atropine sulfate on brain ACh and Ch concentrations. Diazepam attenuated the soman-induced elevation of ACh and Ch concentrations in most of the brain regions studied, while atropine sulfate did not. Only when diazepam was given concurrently with atropine sulfate did the elevated brain ACh or Ch concentrations induced by soman return to normal. These results suggest that the anticonvulsant activity of diazepam in soman poisoning may be partially related to its action on presynaptic cholinergic mechanism.
Article
Physostigmine (Phy) is one of the oldest drug isolated from Calabar beans and successfully used for the treatment of glaucoma in 1864. Since then, it has been widely employed for various therapeutic purposes. Recently, it has gained prominence because of its clinical trials in the treatment of Alzheimer's disease. Phy is also considered to be a potent prophylactic antidote for organophosphate poisoning. It is a reversible cholinesterase (ChE) inhibitor and has a short duration of action. It crosses the blood-brain barrier readily. Hence, it is a centrally acting carbamate. For the last 50 years, numerous authors have shown that pretreatment with Phy would rapidly improve the incapacitating effects of organophosphate intoxication in various animal species. Phy carbamylates to a portion of ChE enzyme and thus protects the enzyme from binding with organophosphate, which are irreversible ChE inhibitors. Organophosphates are metabolized very quickly in the body or bind to non-specific binding sites. The carbamylated ChE enzyme decarbamylates to free the enzyme for normal functioning. The rates of decarbamylation of butyrylcholinesterase (BuChE) in plasma and ChE in brain and muscle are different and are related to the half-life of Phy in these tissues. In addition to ChE inhibition, Phy has got a direct action on acetylcholine (ACh) receptor ionophore complex by interacting with the ACh-gated cation channels. Physostigmine has a half-life of 16, 23 and 30 min in rat, dog and man, respectively. The bioavailability of Phy is very low (about 2%) and it is extensively metabolized in the liver. Less than 4% of Phy is excreted unchanged in the urine and a portion is also eliminated in the bile. Physostigmine has a narrow margin of safety, and a slight increase in dose causes cholinergic symptoms, which can be counteracted by cholinolytic therapy. This review article deals with various aspects of physostigmine such as historical, therapeutic uses, mechanisms of action, methods for the determination, disposition and pharmacokinetics, toxicity and finally as an antidote against organophosphate intoxication.
Article
The pharmacokinetics and pharmacodynamics of procyclidine (10 mg) after oral and intravenous administration were studied in six healthy volunteers. Treatment order was randomised and the study was placebo-controlled and conducted blind. After oral dosing the mean peak plasma concentration was 116 ng/ml and mean bioavailability was 75%. After both oral and intravenous dosing the mean values for the volume of distribution, total body clearance and plasma elimination half-life of procyclidine were in the order of 1 l/kg, 68 ml/min and 12 h respectively. Autonomic effects were maximal within 0.5 h of intravenous administration and at about 1-2 h after oral dosing. Significant effects on pupil diameter, visual near point, salivary secretion and heart rate occurred after intravenous treatment and similar but less marked effects occurred after the oral dose. Significant autonomic effects were still detectable 12 h after both forms of treatment.
Article
This work developed two drug mixtures which alone had no effect on performance of a criterion behavior but when given as a pretreatment would protect against organophosphate-induced lethality and incapacitation. Candidate drugs (alone and together) were given to rats trained to respond on a two-component Fixed Ratio 10 - Extinction (FR10-EXT) schedule. After generating dose response curves for each cholinolytic drug, mixtures of atropine (A) + mecamylamine (M) + pyridostigmine (Py) or physostigmine (Ph) were prepared and a combination of doses that produced no effects on operant performance was determined (Mix I:A = .78, M = .78, Py = .056 mg/kg; Mix II:A = .78, M = .78, Ph = .026 mg/kg). Both pretreatment mixtures provided equivalent protection against the lethal effects of the organophosphate soman; however only Mix II was capable of reversing soman-induced physical incapacitation (PI) as assessed by performance on an accelerating rotarod or FR10 responding. Pretreatment of animals with Mix II resulted in significantly higher levels of brain acetylcholinesterase (AChE) than Mix I pretreated subjects 4 hrs after 1.3 LD50 soman, although peripheral AChE levels were not different. The results indicate organophosphate-induced PI can be attenuated by pretreatment with tertiary carbamates which protect significant amounts of brain AChE from irreversible inhibition.
Article
Recovery of AChE activity in the motor end plate region and end plate free region of the rat diaphragm was studied after irreversible inhibition by soman. Recovery was slow during the first 2 days and only 4 S and 10 S molecular forms of AChE were present in the end plate region. However, cytochemical evidence indicates that synaptic AChE has already started to accumulate and that the synthesis of AChE in muscle and Schwann cell might even be enhanced. Tubular structures, observed underneath the motor end plate, may serve to transport the enzyme from its sites of synthesis in the sarcoplasmic reticulum. Asymmetric molecular forms of AChE in he end plate region appeared later during recovery and, one week after poisoning, their activity was only about 50% of normal value. The limited ability of newly synthesized AChE to attach to the subcellular structures and, therefore, be retained in the muscle, may explain the phase of slow recovery. In accordance with this view, AChE activity in brain recovered in a similar way as in muscle, whereas soluble plasma cholinesterases recovered faster, apparently without a slow initial phase.
Article
Injection of sublethal doses of soman in rat intraperitoneally or subcutaneously every 4, 8, 12 or 24 hours led to chronic LD50 doses which were markedly higher than the acute one. When rats were exposed every 24 hrs to half LD50 doses of soman, several of the animals did not show symptoms of soman poisoning and survived a total exposure of 4-7 times the acute LD50 dose. Brain and diaphragm acetylcholinesterase activities declined steadily during the chronic soman exposure. The so-called external acetylcholinesterase activity of the diaphragm was inhibited to a slightly less degree than the total acetylcholinesterase of the same tissue. The ability of the liver to hydrolyze soman was similar in rats which survived several 24 hr doses and untreated rats.
Article
To study the pharmacokinetic and pharmacodynamic properties of physostigmine in subjects with Alzheimer's disease. Plasma physostigmine concentration and butyrylcholinesterase inhibition were measured in blood samples collected during and after a single high-dose (1 to 1.5 mg for 45 to 60 minutes) and a sustained low-dose steady-state intravenous infusion in nine subjects with Alzheimer's disease. Escalating doses (0.5 to 25 mg/day) were administered during a 2-week period. A dose (2 to 12 mg/day) that optimized cognition in each subject was identified and then administered in a randomized, double-blind, placebo-controlled crossover design for 1 week. The elimination half-life of physostigmine was 16.4 +/- 3.2 (SE) minutes. Clearance and volume of distribution were 7.7 +/- 0.9 (SE) L/min and 2.4 +/- 0.6 (SE) L/kg, respectively. Butyrylcholinesterase inhibition half-life was 83.7 +/- 5.2 (SE) minutes. During sustained steady-state infusion, plasma physostigmine concentration (r = 0.95) and butyrylcholinesterase inhibition (r = 0.99) were linearly correlated with the dose. In five cognitive responders, the memory enhancement was significantly correlated (r = 0.86; p < 0.05) with butyrylcholinesterase inhibition. These results showed that, in cognitive responders, memory enhancement by physostigmine in Alzheimer's disease is correlated directly to the magnitude of plasma cholinesterase inhibition. Furthermore, during single-dose conditions, the dynamic half-life is five-fold longer than the kinetic half-life.
Article
Drugs that act at the N-methyl-D-aspartate (NMDA) receptor complex have the ability to terminate nerve agent-induced seizures and modulate the neuropathologic consequences of agent exposure. Drugs with mixed anticholinergic and anti-NMDA properties potentially provide an ideal class of compounds for development as anticonvulsant treatments for nerve agent casualties. The present experiment evaluated the potential NMDA antagonist activity of 11 anticholinergic drugs by determining whether pretreatment with the compound was capable of protecting mice from the lethal effects of NMDA. The following anticholinergic drugs antagonized NMDA lethality and are ranked according to their potency: mecamylamine > procyclidine = benactyzine > biperiden > trihexyphenidyl. The anticholinergics atropine, aprophen, azaprophen, benztropine, 3-quinuclidinyl benzilate (QNB), and scopolamine failed to show NMDA antagonist properties. In addition, and unexpectedly, diazepam, ethanol, and pentobarbital were also shown to be capable of antagonizing NMDA lethality over a certain range of doses. The advantages and limitations of using antagonism of NMDA lethality in mice as a bioassay for determining the NMDA antagonist properties of drugs are also discussed.
Article
A regime was developed, using mini-osmotic pumps, for the continuous subcutaneous administration of low doses of physostigmine (12.1, 9.7, 4.85 and 2.43 micrograms h-1), in combination with hyoscine (1.94 or 0.39 micrograms h-1), to guinea-pigs for up to 13 days. Physostigmine, in combination with hyoscine, inhibited plasma cholinesterase, and red blood cell and brain acetylcholinesterase, in a concentration-dependent manner, did not affect the normal growth rate of guinea-pigs, and produced no obvious signs of poisoning. A dose rate of 4.85 micrograms h-1 physostigmine and 1.94 micrograms h-1 hyoscine was required to inhibit red cell acetylcholinesterase by 30% and brain acetylcholinesterase by 5-15%, with an accompanying plasma hyoscine concentration of 700-850 pg mL-1. There was an apparent decline in red cell acetylcholinesterase activity during the 13 days. Hyoscine levels were higher in the cholinergic-rich areas of the brain than in the plasma. Continuous pretreatment (1 or 6 days) with physostigmine (4.84 micrograms h-1) and hyoscine (1.94 micrograms h-1) provided complete protection against the lethal effects, and minimized the incapacitation and weight loss produced by soman at a dose equivalent to the LD99 value. Following soman challenge, guinea-pigs exhibited early signs of soman poisoning, but generally these signs of poisoning were minimal by 1-2 h. Extending the pretreatment time to 13 days protected 75% of the guinea-pigs against the lethal effects of soman poisoning. Red cell acetylcholinesterase activity, 24 h after soman poisoning, was higher following continuous pretreatment with physostigmine and hyoscine than after acute treatment with atropine.
Article
The regulation of body temperature is one of many homeostatic functions affected by exposure to anticholinesterase (antiChE) pesticides, and related compounds. In the study of antiChE neurotoxicity, thermoregulatory variables are often used as sensitive physiological indices. Hence, a review on the thermoregulatory aspects of antiChE agents would be useful to researchers in a variety of fields. A reduction in body temperature is a commonly used indicator of antiChE poisoning in laboratory rodents. On the other hand, humans and some other species often shown an elevation in body temperature when exposed to antiChE agents. Hyperthermia has also been noted in animals treated with either low levels of antiChEs or during recovery from high doses of antiChEs. In this review, the literature dealing with the central and peripheral effects of cholinergic agonists and antagonists is reassessed because the thermoregulatory effects of antiChEs are thought to be linked to the activation of cholinergic pathways. This is followed by a thorough review of the studies reporting thermoregulatory responses in laboratory rodents and humans exposed to low and high doses of a variety of antiChE agents, including the organophosphate- (OP) and carbamate- (CB) based pesticides and related drugs. Attention is given to the possible mechanism of action of OPs on thermoregulation in the laboratory rodent including the involvement of behavioral and autonomic processes. The incidence of antiChE-induced hyperthermia (fever) in humans exposed to antiChEs is also addressed. Other topics of antiChE-induced thermoregulatory dysfunction discussed in this review include the role of exercise, heat, and cold stress, tolerance to antiChE agents, and genetic variability. Overall, the mechanism of antiChE-induced changes in body temperature cannot always be explained solely by the immediate consequences of ChE inhibition.
Article
Continuous administration of the carbamate physostigmine, producing approximately 40% serum cholinesterase (ChE) inhibition, provides significant protection against the lethal effects of the organophosphorous nerve agent pinacolyl methylphosphonofluoridate (soman). Rats pretreated with physostigmine were also protected against the development of cholinergic symptoms and loss of body weight. Soman and physostigmine both inhibit ChE, yet animals pretreated with physostigmine exhibited less ChE inhibition in serum and brain than did animals exposed to soman alone. In addition, there did not appear to be any additive effect of presenting both anticholinesterases simultaneously. To further examine the effectiveness of physostigmine, we compared the results of this study with previously collected pyridostigmine data from our laboratory. This comparison indicates that physostigmine is more effective than pyridostigmine in protecting against the detrimental effects of soman.
Article
The object of the study was to determine the pharmacological nature of pinacolyl methylphosphonofluoridate (soman)-induced hypothermia in mice. This was accomplished by examining the soman hypothermia dose response and the effect of various pharmacological antagonists in comparison to the hypothermia responses of muscarinic and nicotinic cholinergic agonists such as oxotremorine and nicotine and another anticholinesterase, physostigmine. Core temperature in mice was monitored by telemetry. In general, atropine antagonized oxotremorine, physostigmine, and soman hypothermia but not nicotine hypothermia whereas mecamylamine antagonized nicotine hypothermia but not that produced by the other agonists. Soman hypothermia was not affected significantly by various pharmacological antagonists, suggesting that other neurotransmitters were not involved in the expression of soman hypothermia. Soman hypothermia appears to be due to muscarinic receptor stimulation and can be effectively antagonized, but not completely, by the use of atropine. Acetylcholinesterase oxime reactivators, such as HI-6 and toxogonin, were ineffective in antagonizing soman-induced hypothermia and reactivating hypothalamic acetylcholinesterase, whereas HI-6 was effective in reactivating soman-inhibited diaphragm acetylcholinesterase when administered up to 10 min after soman, indicating that aging of the soman-inhibited acetylcholinesterase had not occurred. Soman hypothermia appears to be primarily a muscarinic receptor-related event.
Article
The animals used in this study were handled in accordance with the principles stated in the Guide for the Care and Use of Laboratory Animals, proposed by the Committee on Care and Use of Laboratory Animals of the Institute of Laboratory Animal Resources, National Research Council, DHHA, National Institute of Health Publication #85-23, 1985, and the Animal Welfare Act of 1966, as amended, as well as in appropriate laws, Army Regulations, U.S. Army Medical Research and Development Command, and U.S. Army Medical Research Institute of Chemical Defense policies and memoranda. The opinions, or assertions contained herein are the private views of the authors, and are not construed as reflecting the views of the Department of the Army or the Department of Defense.
Article
Fluoro-Jade is an anionic fluorochrome capable of selectively staining degenerating neurons in brain slices. The histochemical application of Fluoro-Jade results in a simple, sensitive and reliable method for staining degenerating neurons and their processes. The technique will detect neuronal degeneration resulting from exposure to a variety of neurotoxic insults. Fluoro-Jade can be combined with other fluorescent methodologies including immunofluorescence, fluorescent axonal tract tracing, and fluorescent Nissl counterstaining. Compared to conventional methodologies, Fluoro-Jade is a more sensitive and definitive marker of neuronal degeneration than hematoxylin and eosin (H&E) or Nissl type stains, while being comparably sensitive yet considerably simpler and more reliable than suppressed silver techniques.
Article
Recent studies concerning management of soman-induced seizures are reviewed. While drugs classically used against epilepsy in hospital appear ineffective against soman, muscarinic receptor blockers are shown to be able to prevent or stop seizures within the first 5 min after their onset. Benzodiazepine could also be considered as an emergency treatment useful during the first 10 min of seizure. Comparatively NMDA antagonists appear to be able to terminate soman-induced seizures even if the treatment is delayed after 40 min of epileptic activity. Drugs with both antimuscarinic and anti-NMDA properties may represent the most adequate pharmacological treatment to treat soman intoxication. However, the results obtained until now with these drugs must be completed in relation with their possible efficacy after i.m. administration. Propositions for future studies are reviewed.
Article
The primary objective of this study was to characterize the pharmacokinetics and pharmacodynamics of single daily doses of donepezil (5 and 10 mg) each evening for 28 consecutive days. A secondary objective was to measure the plasma protein binding of donepezil at steady state. This was a double-blind, randomized, multiple-dose study in healthy male (n=13) and female (n=3) volunteers. Subjects were randomized to receive, once daily, either oral doses of 5 mg donepezil for 28 days or doses of 5 mg donepezil for 7 days followed by 10 mg donepezil for 21 days. All doses were administered in the evening. Donepezil concentrations and protein binding in plasma were determined by HPLC with UV detection and equilibrium dialysis, respectively. Inhibition of acetylcholinesterase (AChE) activity in red blood cell (rbc) membranes was assessed using a specific radioenzyme assay. The pharmacokinetics of donepezil were linear, dose proportional and stationary over the course of the study. Mean Cmax, tmax, AUC(0-24), t1/2 and Vlambda(z)/F at steady state were 34.1 ng ml(-1), 3.0 h, 634.8 ng h ml(-1), 72.7 h, and 11.81 kg(-1), respectively, for the 5 mg group and 60.5 ng ml(-1), 3.9 h, 1127.8 ng h ml(-1), 73.5 h and 11.61 kg(-1), respectively, for the 10 mg group. Accumulation of the drug was observed for 14-21 days, until steady state was achieved. A direct consistent relationship was observed between donepezil plasma concentration and percentage rbc-AChE inhibition during each 24 h evaluation period, indicating no hysteresis in donepezil pharmacodynamics. The pharmacodynamic parameters, Emin, Emax and Ess, were 62.2%, 71.8% and 65.3%, respectively, for the 5 mg donepezil dose, and 74.7%, 83.6% and 77.8%, respectively, for the 10 mg donepezil dose. Donepezil was 95.6% bound to plasma protein at steady state. The binding was high capacity and low affinity, and neither concentration nor time dependent. Both dosage regimens were well tolerated; no clinically significant changes in laboratory or vital sign parameters were observed in any subject. The measured pharmacokinetic and pharmacodynamic parameters for both 5 and 10 mg day(-1) donepezil administered in the evening are in good agreement with previous results obtained with morning administration, indicating no time of dosing effect.
Article
The aim of this study was to characterize the pharmacokinetics and pharmacodynamics of donepezil HCl, a new, chemically distinct and specific acetylcholinesterase (AChE) inhibitor for the treatment of Alzheimer's disease, following multiple-dose administration. This was a double-blind, randomized, placebo-controlled, multiple-dose study in healthy male volunteers (n=27). Three dose levels were investigated in sequential order: 1, 3 and 5 mg. Each dose was administered orally, once a day, for 21 consecutive days. Donepezil concentrations in plasma were quantified by HPLC. Pharmacodynamic activity was determined by the radioenzymatic measurement of erythrocyte membrane acetylcholinesterase (rbc-AChE) inhibition. The pharmacokinetic disposition of donepezil was observed to be dose proportional. The mean terminal disposition half-life was 79.5+/-19.0 h which resulted in a slow approach to steady state (14-21 days). A four- to sixfold increase in donepezil plasma concentration was observed during this time; however, no further increase was evident after achievement of steady state. The mean donepezil plasma concentration at steady state (Css) was 14.2 ng ml(-1). Neither the rate of accumulation nor the rate of clearance was dose dependent. Inhibition of rbc-AChE was directly correlated with donepezil concentration over a wide concentration range, with the higher concentrations showing the expected hyperbolic relationship. Donepezil was well tolerated by all subjects with no clinically significant changes in laboratory or physical parameters observed at any dose. The pharmacokinetics of donepezil were found to be dose proportional following the administration of multiple doses to healthy volunteers. A predictable relationship was also observed between plasma donepezil concentrations and rbc-AChE inhibition. The half-life of donepezil makes it suitable for once-daily dosing.
Article
The aim of this study was to characterize the pharmacokinetic and pharmacodynamic profile of donepezil HCl, a chemically distinct and specific acetylcholinesterase (AChE) inhibitor for the treatment of Alzheimer's disease, following administration of single oral doses. This was a double-blind, randomized, single-dose, placebo-controlled, sequential-group, ascending-dose study in healthy male volunteers (n = 48). Six dose levels were investigated, ranging from 0.3 to 6.0 mg. Donepezil concentrations in plasma were determined by HPLC with UV detection. Pharmacodynamic activity was determined by the radioenzymatic measurement of erythrocyte membrane acetylcholinesterase (rbc-AChE) inhibition. The pharmacokinetic disposition of donepezil was observed to be both linear and dose proportional following single-dose administration. The mean peak plasma concentration (Cmax) of donepezil was observed at 4.1+/-1.5 h. The mean terminal disposition half-life was 81.5+/-22.0 h. The post-absorption phase of the plasma concentration-time curves for the 4.0 mg and 6.0 mg doses appeared to be biphasic, but the rate of donepezil clearance was independent of dose. Plasma concentrations for the 0.3, 0.6 and 0.9 mg dose groups were generally below the level of HPLC detection (2.0 ng ml(-1)), preventing accurate characterization of these doses. A direct correlation was observed between plasma donepezil concentrations and extent of AChE inhibition. For the 4.0 and 6.0 mg donepezil dose groups, maximal AChE inhibition (Emax) ranged from 33% to 35% and there was significant correlation between AChE inhibition and donepezil plasma concentration (P<0.005). The pharmacokinetics of donepezil were found to be linear and dose proportional following the administration of single doses to healthy volunteers. A direct correlation was also observed between plasma donepezil concentrations and AChE inhibition. The extended half-life of donepezil makes it suitable for once-daily dosing.
Article
Postnatal changes of nicotinic acetylcholine receptor (nAChR) alpha 2, alpha 3, alpha 4, alpha 7 and beta 2 subunits mRNAs were investigated in rat brain using ribonuclease protection assay. Multiple developmental patterns were observed: (1) transient expression during the first few postnatal weeks; alpha 2 in the hippocampus and brain stem, alpha 3 in the striatum, cerebellum and cortex, alpha 4 in the hippocampus, striatum and cerebellum, alpha 7 in the cerebellum and beta 2 in the striatum. (2) Constant expression across development; alpha 2 and alpha 3 in the thalamus, alpha 4 in the cortex, thalamus and brain stem, alpha 7 in the thalamus and brain stem and beta 2 in all brain regions except striatum. (3) Non-detection across development; alpha 2 in the cortex, striatum and cerebellum. (4) Increase with age; alpha 7 in the cortex and hippocampus. (5) Bell-shaped development; alpha 7 in the striatum. Postnatal changes of nAChR isoforms in different brain regions of rat were investigated by receptor binding assays. The developmental patterns of [3H]epibatidine and (-)-[3H]nicotine binding sites were similar to each other in each brain region, but different from that of [3H] alpha-bungarotoxin binding sites. No obvious correlation was observed between the developmental patterns of [3H] alpha-bungarotoxin, [3H]epibatidine and (-)-[3H]nicotine binding sites and corresponding subunits mRNAs. These results indicate that multiple mechanisms are involved in changes of gene expression of nAChRs subunits in the brain of developing rats.
Article
Organophosphorus (OP) nerve agents are still used as warfare and terrorism compounds. Classical delayed treatment of victims of organophosphate poisoning includes combined i.v. administration of a cholinesterase reactivator (an oxime), a muscarinic cholinergic receptor antagonist (atropine) and a benzodiazepine anticonvulsant (diazepam). The objective of this study was to evaluate, in a realistic setting, the therapeutic benefit of administration of GK-11 (gacyclidine), an antiglutamatergic compound, as a complement to the above therapy against organophosphate poisoning. Gacyclidine was injected (i.v.) in combination with atropine/diazepam/pralidoxime at man-equivalent doses after a 45- or 30-min latency period to intoxicated primates (2 LD50). The effects of gacyclidine on the animals' survival, electroencephalographic (EEG) activity, signs of toxicity, recovery after challenge and central nervous system histology were examined. The present data demonstrated that atropine/diazepam/pralidoxime alone or combined with gacyclidine did not prevent signs of soman toxicity when treatment was delayed 45 min after poisoning. Atropine/diazepam/pralidoxime also did not control seizures or prevent neuropathology in primates exhibiting severe signs of poisoning when treatment was commenced 30 min after intoxication. However, in this latter case, EEG recordings revealed that additional treatment with gacyclidine was able to stop soman-induced seizures and restore normal EEG activity. This drug also totally prevented the neuropathology observed 5 weeks after soman exposure in animals treated with atropine/diazepam/pralidoxime alone. Overall, in the case of severe OP-poisoning, gacyclidine represents a promising adjuvant therapy to the currently available polymedication to ensure optimal management of organophosphate poisoning in man. This drug is presently being evaluated in a human clinical trial for a different neuroprotective indication. However, it should always be kept in mind that, in the case of severe OP-poisoning, medical intervention must be conducted as early as possible.
Article
The effects of oral administration of the centrally acting acetylcholinesterase (AChE) inhibitors, donepezil hydrochloride (donepezil: E2020: (+/-)-2-[(1-benzylpiperidin-4-yl)methyl]-5,6-dimethoxy-indan-1-one monohydrochloride), tacrine (9-amino-1,2,3,4-tetrahydroacridine hydrochloride) and ENA-713 (rivastigmine: (S)-N-ethyl-3-[(1-dimethyl-amino)ethyl]-N-methyl-phenylcarbamate hydrogentartrate), which have been developed for the treatment of Alzheimer's disease, on the extracellular acetylcholine concentration in the hippocampus of rats were evaluated by using a microdialysis technique without adding cholinesterase inhibitor to the perfusion solution. We also compared the inhibition of brain AChE and the brain concentrations of these drugs. Donepezil at 2.5 mg/kg and tacrine at 5 mg/kg showed significant effects for more than 6 h. At these doses, the maximum increases were observed at about 1.5 h after administration of donepezil, and at about 2 h with tacrine, and were 499% and 422% of the pre-level, respectively. ENA-713 produced significant effects at doses of 0.625, 1.25 and 2.5 mg/kg, which lasted for about 1, 2 and 4 h, respectively. The maximum increases produced by these doses at about 0.5 h after administration were 190, 346 and 458% of the pre-level, respectively. The time courses of brain AChE inhibition with donepezil at 2.5 mg/kg, tacrine at 10 mg/kg and ENA-713 at 2.5 mg/kg were mirror images of the extracellular acetylcholine-increasing action at the same doses. The time courses of the brain concentrations of drugs after oral administration of donepezil at 2.5 mg/kg and tacrine at 10 mg/kg were consistent with those of brain AChE inhibition at the same doses, and there was a linear relation between these parameters. Brain concentration of ENA-713 at 2.5 mg/kg was below the limit of quantification at all time points measured. These results suggest that oral administration of donepezil, tacrine and ENA-713 increases acetylcholine concentration in the synaptic cleft of the hippocampus mostly through AChE inhibition, and that donepezil has a more potent activity than tacrine and a longer-lasting effect than ENA-713 on the central cholinergic system.
Article
1. Donepezil hydrochloride (Aricept) is used for the treatment of Alzheimer's disease. Here the correlation of the intrinsic clearance (Cl(int)) of donepezil between the in vivo and in vitro states was studied in rat, dog and human. 2. In an experiment with 14C-donepezil and human microsomes the routes of metabolism were identified as N-dealkylation and O-demethylation, and no unknown metabolites were detected. 3. The Cl(int) of donepezil in the male rat, female rat, dog and human liver microsomes were 33.7, 13.4, 37.0 and 6.35 microl/min/mg microsomal protein respectively, and sex difference in rat and interspecies difference in the estimated Cl(int) were found. 4. After a single intravenous administration to the male rat, female rat and dog, total plasma clearance (ClP(total)) was 78.6, 29.5 and 88.3 ml/min/kg respectively, and a sex difference was observed in rat. 5. After a single oral administration to the male rat, dog and healthy volunteer, ClP(total) was 140, 105 and 2.35 ml/min/kg respectively, and remarkable differences were observed between animals and man. 6. The contribution of renal clearance to blood clearance (Cl(r)) was low in all species. The predicted in vitro hepatic clearance (Cl(h-pre)) was in the rank order: male rat (15.91 ml/min/kg) > dog (7.96) > female rat (7.67) > human (1.04). Although Cl(h-pre) was underestimated, Cl(h-pre) was significantly correlated with that of ClB(total) in the different animal species and in man, indicating that the in vitro-in vivo ranking order was conserved.
Article
The ability of the nerve agents tabun, sarin, soman, GF, VR, and VX to produce brain seizures and the effectiveness of the anticholinergics biperiden HCl or atropine SO4 as an anticonvulsant treatment were studied in a guinea-pig model. All animals were implanted a week prior to the experiment with cortical electrodes for electroencephalogram (EEG) recordings. On the day of exposure, the animals were pretreated with pyridostigmine (0.026 mg/kg, i.m.) 30 min prior to challenge with a 2 x LD50 dose (s.c.) of a given agent. In separate experiments, animals were challenged with 5 x LD50 (s.c.) of soman. One minute after agent challenge, the animals were treated intramuscularly (i.m.) with 2 mg/kg atropine SO4 admixed with 25 mg/kg 2-PAM Cl and then observed for the onset of seizure activity. Five minutes after the start of nerve agent-induced EEG seizures, animals were treated i.m. with different doses of biperiden HCl or atropine SO4 and observed for seizure termination. The anticonvulsant ED50 of biperiden HCl and atropine SO4 for termination of seizures induced by each nerve agent was calculated and compared. With equally toxic doses (2 x LD50) of these agents, continuous EEG seizures (status epilepticus) developed in all animals challenged with soman, tabun, or VR, and in more than 90% of the animals challenged with GF or sarin. In contrast, only 50% of the animals developed seizures when challenged with VX. The times to onset of seizures for soman, tabun, GF, and sarin were very similar (5-8 min) while for VR, it was about 10 min. In the case of VX, not only was the time to seizure development longer (20.7 min), but the seizure activity in 19% of the animals terminated spontaneously within 5 min after onset and did not return. Under these conditions, the anticonvulsant ED50s of biperiden HCl for soman, GF, VR, tabun, sarin, and VX were 0.57, 0.51, 0.41, 0.2, 0.1, and 0.09 mg/kg, respectively, while those of atropine SO4 for soman, VR, tabun, GF, sarin, and VX were 12.2, 11.9, 10.4, 10.3, 5.1, and 4.1 mg/kg, respectively. In separate experiments, the anticonvulsant ED50 doses of biperiden for animals challenged with 2 or 5 x LD50 of soman were 0.48 (95% confidence limits 0.25-0.73) or 0.57 (95% CI 0.38-0.84) mg/kg, respectively, while the anticonvulsant ED50s for atropine (12.2 mg/kg, i.m.) were identical under these same two challenge conditions. The present study demonstrates that all nerve agents can produce status epilepticus and that the therapeutic effectiveness of atropine and biperiden roughly paralleled the seizurogenic potential of these agents.
Article
Anticholinergic drugs were the first pharmacological agents used in the treatment of Parkinson"s disease. Although levodopa and other centrally acting dopaminergic agonists have largely supplanted their use, they still have a place in treatment of the disease. As a therapeutic class, there is little pharmacokinetic information available for these drugs, which is inclusive of benztropine, biperiden, diphenhydramine, ethopropazine, orphenadrine, procyclidine and trihexyphenidyl. Pharmacokinetic information is largely restricted to studies involving young health volunteers given single doses. In general, this class of drugs is rapidly absorbed after oral administration to humans. Oral bioavailability is variable between the different drugs, ranging from 30% to over 70%. Each of the drugs appears to possess a large Vd in humans and animals, and distribution to tissues is rapid. The drugs are all characterized by relatively low clearance relative to hepatic blood flow, and appear to be extensively metabolized, primarily to N-dealkylated and hydroxylated metabolites. The available information suggests that excretion of parent drug and metabolite is via the urine and bile. Although the existence of a plasma concentration vs. therapeutic effect relationship has not been explored, there is some evidence suggesting a relationship between concentration and peripheral side effects. Elderly tolerate the drugs less well than do younger patients. There is a notable lack of pharmacokinetic information for these drugs in the elderly. The lack of pharmacokinetic information for multiple dose administration and in the elderly may be a possible hindrance in the safe and effective use of these drugs in patients with Parkinson"s disease.
Article
Fluoro-Jade B, like its predecessor Fluoro-Jade, is an anionic fluorescein derivative useful for the histological staining of neurons undergoing degeneration. However, Fluoro-Jade B has an even greater specific affinity for degenerating neurons. This notion is supported by the conspicuous staining of degenerating neuronal elements with minimal background staining. This improved signal-to-noise ratio means that fine neuronal processes including distal dendrites, axons and axon terminals can be more readily detected and documented. Although the staining time and dye concentration are reduced, the method is as rapid, simple and reliable as the original Fluoro-Jade technique. Like Fluoro-Jade, Fluoro-Jade B is compatible with a number of other labeling procedures including immunofluorescent and fluorescent Nissl techniques.
Article
Reducing body temperature of rodents has been found to improve their survival to ischaemia, hypoxia, chemical toxicants, and many other types of insults. Larger species, including humans, may also benefit from a lower body temperature when recovering from CNS ischaemia and other traumatic insults. Rodents subjected to these insults undergo a regulated hypothermic response (that is, decrease in set point temperature) characterised by preference for cooler ambient temperatures, peripheral vasodilatation, and reduced metabolic rate. However, forced hypothermia (that is, body temperature forced below set point) is the only method used in the study and treatment of human pathological insults. The therapeutic efficacy of the hypothermic treatment is likely to be influenced by the nature of the reduction in body temperature (that is, forced versus regulated). Homeostatic mechanisms counter forced reductions in body temperature resulting in physiological stress and decreased efficacy of the hypothermic treatment. On the other hand, regulated hypothermia would seem to be the best means of achieving a therapeutic benefit because thermal homeostatic systems mediate a controlled reduction in core temperature.
Article
The main pharmacological approach for the treatment of Alzheimer's disease (AD) has been based on the use of agents potentiating cholinergic transmission, particularly by inhibiting acetylcholinesterase (AChE), the enzyme that destroys acetylcholine after it has been secreted into the synaptic clefts. Physostigmine is an AChE inhibitor originally extracted from calabar beans. It is licensed in many countries as an agent for reversing the effect of drugs and poisons causing the anticholinergic syndrome. Studies conducted more than 20 years ago suggested that physostigmine could improve memory in people with or without dementia. Investigation of this property has been limited by the very short half-life of physostigmine. Various forms of administering the drug have been tried to overcome this problem, most recently a controlled-release (CR) oral formulation, and a skin patch. It has been proposed as a potential drug for the symptomatic treatment of AD. To determine whether there is evidence of beneficial effects for the use of physostigmine in Alzheimer's disease. To assess the incidence and severity of adverse effects. The Cochrane Controlled Trials Register was searched using the following terms: 'physostigmine', 'physostigmine salicylate', 'Synapton' and 'Antilirium' in accordance with the Cochrane Dementia and Cognitive Improvement Group's search strategy. The pharmaceutical company was contacted. All relevant unconfounded, double-blind, randomized, placebo-controlled trials in which physostigmine was administered for more than one day to patients with dementia of Alzheimer type. Trials in which the allocation to the treatment was not randomized, or in which the allocation to the treatment was not concealed were excluded. Data were extracted independently by two reviewers (JMC & JB), pooled where appropriate and possible, and the weighted or standardized mean differences or Peto odds ratios (95% CI) were estimated. Where possible, intention-to-treat analysis was used. Fifteen studies were included using four different methods of administration of physostigmine. Four studies, involving 29 people in total, used intravenous infusion; seven, involving 131 people, used a conventional oral form; four, involving 1456 participants, used a controlled-release oral form, and one study of 181 people used a verum skin patch. There are no usable results from the intravenous infusion trials, and the few results from the conventional oral form showed no benefit of physostigmine compared with placebo. The results from two of the four studies of the controlled-release physostigmine apply only to a group of patients identified as responders in a pre-randomization titration period. The best dose physostigmine (mean 25mg/day) was associated with a 1.75 point improvement on ADAS-Cog score (mean difference -1.75, 95% confidence interval -2.90, -0.60 on an intention-to-treat basis) and a 0.26 point improvement on the CGIC score (treated as a continuous scale) (mean difference -0.26, 95% confidence interval 0.06, 0.46 on an intention-to-treat basis) compared with placebo at 6 weeks. There were statistically significantly higher numbers of patients from the physostigmine group withdrawing from the trial (22/183 vs 2/183)(OR 5.92, 95% confidence limits 2.59, 13.54) and suffering at least one event of nausea, vomiting, diarhoea, anorexia, dizziness, stomach pain, flatulence or sweating compared with placebo at 6 weeks. The best dose physostigmine (mean 27mg/day) was associated with a 2.0 point improvement on ADAS-Cog score (mean difference -2.02, 95% confidence interval -3.59, -0.45 on an intention to treat basis) compared with placebo at 12 weeks. There were statistically significantly higher numbers of patients from the physostigmine group withdrawing from the trial due to adverse events (13/83 vs 5/93)(OR 3.05, 95% confidence limits 1.15, 8.07) and suffering at least one event of nausea, vomiting, diarhoea, anorexia, dizziness, stomach pain, tremor, asthenia or sweating compared with placebo at 12 weeks. When no attempt was made to identify responders and all relevant patients with Alzheimer's disease were randomized, fixed dose physostigmine (mean 33 mg/day) was associated with a statistically significantly higher number withdrawing (234/358 vs 31/117)(OR 4.82, 95% confidence limits 3.17, 7.33), withdrawing due to adverse events (196/358 vs 10/117) (OR 6.54, 95%confidence limits 4.29, 9.95) and suffering at least one event of nausea, vomiting, diarhoea, anorexia, dizziness, stomach pain, dyspepsia, sweating, asthenia, dyspnoea or abnormal dreaming compared with placebo at 24 weeks. The results from the study of the verum patch physostigmine show that the double dose (delivering mean dose 12mg/day) was associated with statistically significantly higher numbers suffering at least one adverse event of vomiting, nausea or abdominal cramps compared with placebo at 24 weeks, but placebo was associated with statistically significantly greater numbers of gastrointestinal complaints at 24 weeks compared with single-dose physostigmine. The evidence of effectiveness of physostigmine for the symptomatic treatment of Alzheimer's disease is limited. Even in a controlled release formulation designed to overcome the short half-life, physostigmine showed no convincing benefit and adverse effects remained common leading to a high rate of withdrawal.
Article
Changes in the hippocampal theta rhythm were used as a model in which anticonvulsant drugs may be screened for their potential to antagonize soman-induced (1xLD(50)) seizures. The zinc chelator, ethylenediaminetetra acetic acid (EDTA) (300mg/kg), and the NMDA receptor antagonist, HA-966 (60mg/kg), both disrupted the theta rhythm, but did not antagonize soman-induced seizures, neither separately, nor in combination. The anticholinergic and antiglutamatergic procyclidine (6mg/kg) did not influence the theta activity. The GABAergic agonists, diazepam (10mg/kg) and pentobarbital (30mg/kg), both reduced the theta frequency. Procyclidine, diazepam, and pentobarbital did not stop soman-induced seizures when administered separately, but both convulsions and seizure activity terminated when these agents were given together, and the rats slept through the critical convulsion period. This triple therapy was 100% effective, when administered 30-40min following onset of convulsions, and the rats displayed apparently normal behavior the next day. A screening model of potential anticonvulsants cannot be based on alterations in hippocampal EEG activity. Procyclidine, diazepam, and pentobarbital in combination disrupted the theta rhythm like the combination of EDTA and HA-966, but the latter combination did not have anticonvulsant effect. It is concluded that a triple regimen consisting of procyclidine, diazepam, and pentobarbital can effectively terminate soman-induced seizures that have lasted 30min or more.
Article
The combined effects of physostigmine and procyclidine (antagonizing muscarinic, nicotinic, and NMDA receptors) were tested against various doses of soman. Physostigmine (0.1 mg/kg) in combination with procyclidine doses of 1, 3, or 6 mg/kg effectively prevented the development of convulsions and hippocampally monitored seizures when the doses of soman were 1.3, 1.6, or 2 x LD50, respectively. Results from [(3)H]MK-801-binding experiments showed that procyclidine inhibits the phencyclidine site at the NMDA receptor in a concentration-dependent manner. Physostigmine (0.1 mg/kg) and procyclidine in a dose of 1 mg/kg did not prevent convulsions or seizures when the soman dose was 1.6 x LD50. Subsequent treatment with scopolamine in doses of 0.5 or 1 mg/kg immediately after (3 min) seizure onset showed that only the highest dose produced a reliable termination. When scopolamine (1 mg/kg) was given later (10 min) after onset of seizures, no effect was obtained. The sustained seizures were subsequently treated with diazepam (10 mg/kg) and pentobarbital (30 mg/kg) and finally terminated 25 min after onset. In rats given inadequate prophylaxis, both modified convulsions and seizures were seen. It is suggested that moderate doses of prophylactics should be preferred to avoid adverse effects on cognitive functions because insufficient prophylaxis can be compensated for by adjunct treatment.
Article
Beyond 6 to 9 months of treatment with cholinesterase inhibitors (ChE-Is), there is a notable increase in the rate of cognitive decline in Alzheimer disease (AD) patients, and there are few longer-term studies to evaluate this finding. The authors examined whether the ChE-I rivastigmine continued to be therapeutically effective after up to 2 years of treatment in 2,010 patients with probable AD. The clinical course of AD patients treated with rivastigmine was compared with a prediction of their course derived by a baseline-dependent historical model of disease progression developed from data in untreated AD patients. Rivastigmine efficacy data came from four 6-month, placebo-controlled, randomized, controlled trials (RCTs) and two open-label extension studies. Cognitive performance was assessed by various clinician- and caregiver-rated measures. After 2 years on rivastigmine, there was less cognitive deterioration than in historical-control subjects. These effects of rivastigmine on cognitive performance were considered clinically meaningful relative to expected global decline. Treatment-emergent adverse events were the commonly-seen side effects of ChEIs and were similar in frequency to those seen in patients assigned to shorter-term rivastigmine therapy. Rivastigmine had a beneficial effect on cognitive performance for up to 2 years in patients with AD, versus no treatment or placebo treatment in historical-control subjects. Caregiver and clinician assessments indicated that the cognitive performance findings were of a magnitude relevant to global patient functioning. Rivastigmine remained safe over this 2-year treatment period.