Eukaryotic DING proteins are endogenous: an immunohistological study in mouse tissues

Background

DING proteins encompass an intriguing protein family first characterized by their conserved N-terminal sequences. Some of these proteins seem to have key roles in various human diseases, e.g., rheumatoid arthritis, atherosclerosis, HIV suppression. Although this protein family seems to be ubiquitous in eukaryotes, their genes are consistently lacking from genomic databases. Such a lack has considerably hampered functional studies and has fostered therefore the hypothesis that DING proteins isolated from eukaryotes were in fact prokaryotic contaminants.

Principal Findings

In the framework of our study, we have performed a comprehensive immunological detection of DING proteins in mice. We demonstrate that DING proteins are present in all tissues tested as isoforms of various molecular weights (MWs). Their intracellular localization is tissue-dependant, being exclusively nuclear in neurons, but cytoplasmic and nuclear in other tissues. We also provide evidence that germ-free mouse plasma contains as much DING protein as wild-type.

Significance

Hence, data herein provide a valuable basis for future investigations aimed at eukaryotic DING proteins, revealing that these proteins seem ubiquitous in mouse tissue. Our results strongly suggest that mouse DING proteins are endogenous. Moreover, the determination in this study of the precise cellular localization of DING proteins constitute a precious evidence to understand their molecular involvements in their related human diseases.

Long-term behavioral consequences of soman poisoning in mice

We investigated the long-term (up to 90 days) consequences of soman intoxication in mice on weight, motor performances (grip strength, rotarod) and mnemonic cognitive processes (T-maze, Morris water maze test). First, a relative weight loss of 20%, measured 3 days after intoxication, was evidenced as a threshold beyond which neuropathological damage was observed in the hippocampus. Animals were then distributed into either low weight loss (LWL) or high weight loss (HWL) groups according to the relative 20% weight loss threshold. Compared to controls, both groups of poisoned mice quickly exhibited a decrease in their motor performance subsequent to an acute soman toxicity phase. Then, total motor recovery occurred for the LWL group. Comparatively, HWL mice showed only transient recovery prior to a second decrease phase due to soman-induced delayed toxicity. One month after intoxication, mnemonic cognitive performances of the LWL group were similar to controls while the HWL group did not exhibit any learning skill. Three months after poisoning, compared to controls, the LWL group showed similar mnemonic performances in the maze test but a mild deficit in the Morris water maze task. At the same time, learning skills slightly recovered in the HWL group. Mnemonic cognitive data are discussed in relation to the neuropathology, neurogenesis and sprouting occurring in the hippocampus of soman-intoxicated animals.

Soman poisoning induces delayed astrogliotic scar and angiogenesis in damaged mouse brain areas

Gliotic scar formation and angiogenesis are two biological events involved in the tissue reparative process generally occurring in the brain after mechanically induced injury, ischemia or cerebral tumor development. For the first time, in this study, neo-vascularization and glial scar formation were investigated in the brain of soman-poisoned mice over a 3-month period after nerve agent exposure (1.2 LD50 of soman). Using anti-claudin-5 and anti-vascular endothelial growth factor (VEGF) immunostaining techniques on brain sections, blood vessels were quantified and VEGF expression was verified to appraise the level of neo-angiogenesis induced in damaged brain areas. Furthermore, glial scar formation and neuropathology were estimated over time in the same injured brain regions by anti-glial fibrillary acidic protein (GFAP) immunohistochemistry and hemalun-phloxin (H&P) dye staining, respectively. VEGF over-expression was noticed on post-soman day 3 in lesioned areas such as the hippocampal CA1 field and amygdala. This was followed by an increase in the quantity of mature blood vessels, 3 months after soman poisoning, in the same brain areas. On the other hand, massive astroglial cell activation was demonstrated on post-soman day 8. Reactive astroglial cells were located only in damaged cerebral regions where H&P-stained eosinophilic neurons were found. For longer experimental times, astroglial response slowly decreased overtime but remained detectable on post-soman day 90 in some discrete brain regions (i.e. CA1 field and amygdala) evidencing the formation of a glial scar. In this study, we discuss the key role of VEGF in the angiogenic process and in the glial or neuronal response induced by soman poisoning.

Effects of aspirin and mefenamic acid on soman poisoning-induced neuropathology in mice

The efficacy of aspirin and mefenamic acid to counteract soman-induced brain damage was investigated in mice. Neuronal damage was evaluated in the hippocampus and amygdala by performing omega3 receptor density measurements and hemalun-phloxin staining. The effect of both drugs on the proliferation of neural progenitors after soman exposure was also assessed. Mefenamic acid aggravated the soman-induced hippocampal neuropathology. On the other hand, aspirin recorded a weak neuroprotective effect in the amygdala. However, this drug also diminished the proliferation of neural precursor cells. The possible neurochemical mechanisms underlying such differences in the efficacy of the two drugs are also reviewed.

Acetylcholine release, EEG spectral analysis, sleep staging and body temperature studies: A multiparametric approach on freely moving rats

We present a neurochemical, electrophysiological and physiological study on freely moving rats. During 3 days, we have simultaneously monitored acetylcholine (ACh) release in the hippocampus using the microdialysis technique, electroencephalogram (EEG), electromyogram (EMG) and subcutaneous temperature. A spectral analysis of EEG was performed and sleep stages were determined. Energy ratio in the delta (0-4 Hz), slow theta (4-6.5 Hz) and fast theta (6.5-9 Hz) band was calculated. Sleep stages were quantified using an automatic staging method. The circadian cycle of these parameters was observed. Waking, body temperature and ACh release presented synchronized cycles with close acrophases. The relationship between the central cholinergic system and the other parameters is discussed. The influence of handling on the measured parameters, as well as possible artifacts linked to the use of neostigmine in the microdialysis method are considered. Attention was focused on the cholinergic control of EEG theta rhythms.

Early reduction of NeuN antigenicity induced by soman poisoning in mice can be used to predict delayed neuronal degeneration in the hippocampus

The neuronal nuclei (NeuN) antigen is increasingly being used as a specific marker to identify neuronal cell loss under various pathological conditions. However, recent studies pointed out that a decrease in NeuN labeling could also be due to the reduction of protein expression level or loss of antigenicity and this was not necessarily related to neuronal cell disappearance. We also investigated the presence of damaged neurons, the loss of NeuN immunoreactivity and the level of NeuN protein in the brain hippocampus of mice subjected to soman poisoning (1.2 LD50 of soman). Damaged neurons were detected using hemalun-phloxin (H&P) and Fluoro-Jade B (FJB) staining on brain sections. NeuN immunohistochemistry was also performed on adjacent brain sections and NeuN protein level quantified by Western blot analysis. One and eight days after soman exposure, about 49% of hippocampal neurons were damaged, as assessed by H&P or FJB staining. NeuN immunohistochemistry indicated that all these damaged neurons were deprived of NeuN immunoreactivity. Using Western blot analysis, we proved that loss of NeuN immunoreactivity in degenerating neurons was due to reduced NeuN antigenicity rather than a fall in protein expression level. In this study, we discuss the potential use of NeuN immunohistochemistry as a good biomarker to predict delayed neuronal degeneration in the rodent hippocampus after various brain injuries.

Neuronal regeneration partially compensates the delayed neuronal cell death observed in the hippocampal CA1 field of soman-poisoned mice

Soman poisoning induces long-term neuropathology characterized by the presence of damaged neurons up to 2 months after exposure in various central brain areas, especially the hippocampal CA1 layer. Rapid depletion of this layer could therefore be expected. Surprisingly, the CA1 layer remained consistently visible, suggesting delayed death of these damaged neurons, potentially accompanied by neuronal regeneration. To address this issue, mice were exposed to a convulsive dose of soman (110 microg/kg followed by 5.0mg/kg of atropine methyl nitrate (MNA) 1 min later) and brains were collected from day 1 to day 90 post-exposure. Damaged and residual healthy neurons were quantified on brain sections using hemalun-phloxin and fluorojade staining or neuronal nuclei antigen (NeuN) immunohistochemistry. On post-soman day 1, a moderate neuronal cell death was noticed in the hippocampal CA1 layer. In this area, an important and steady quantity of damaged neurons (about 48% of the whole pyramidal neurons) was detected from post-soman day 1 to day 30. Thus, throughout this period, damaged neurons seemed to survive, as confirmed by the unmodified depth of the hippocampal CA1 layer. The dramatic disappearance of the damaged neurons occurred only later during the experiment and was almost complete at day 90 after soman exposure. Interestingly, between day 30 and day 90 following poisoning, an increase in the number of residual healthy pyramidal neurons was observed. These different kinetic patterns related to the density of total, damaged and residual healthy neurons after soman poisoning demonstrate that neuronal regeneration is delayed in the hippocampal CA1 layer and is concomitant to the death of damaged neurons.

Efficacy of the ketamine-atropine combination in the delayed treatment of soman-induced status epilepticus

Nerve agent poisoning is known to induce full-blown seizures, seizure-related brain damage (SRBD), and lethality. Effective and quick management of these seizures is critical. In conditions of delayed treatment, presently available measures are inadequate calling for optimization of therapeutic approaches. The effects of ketamine/atropine sulfate (KET/AS) combinations were thus assessed as potential valuable delayed therapy in soman-poisoned male guinea pigs. Animals received pyridostigmine (26 microg/kg, i.m.) 30 min before soman (62 microg/kg, i.m.) followed by therapy consisting of atropine methyl nitrate (4 mg/kg) 1 min later. KET was then administered i.m. at different times after the onset of seizures, starting at 30 min post-poisoning. KET was always injected with atropine sulfate, itself given at a dose that was unable to modify seizures (2 to 10 mg/kg). Different treatment schemes (dose and time of injection) were evaluated. Sub-anesthetic doses of KET (10 mg/kg) could prevent lethality and stop ongoing seizures only when administered 30 min after challenge. An extended delay before treatment (up to 2 h) called for an increase in KET dose (up to 60 mg/kg three times), thus reaching anesthetic levels but without the need of any ventilation support. KET proved effective in stopping seizures, highly reducing SRBD and allowing survival with a progressive loss of efficacy when treatment was delayed beyond 1 h post-challenge. Preliminary results suggest that association with the benzodiazepine midazolam (1 mg/kg) might be interesting when treatment is initiated 2 h after poisoning, i.e., when KET efficacy is dramatically reduced. All in all, these observations suggest that KET, in association with atropine sulfate and possibly other drugs, may be highly effective in the delayed treatment of severe soman intoxication.

Effect of cytokine treatment on the neurogenesis process in the brain of soman-poisoned mice

We previously described that enhanced proliferation of neural progenitors occurred in the subgranular zone (SGZ) of the dentate gyrus and in the subventricular zone (SVZ) of the mouse brain following soman poisoning. Then, a discrete number of these cells seemed to migrate and engraft into the main damaged brain regions (hippocampus; septum and amygdala) and subsequently differentiate into neurons. In the present study, the effect of a cytokine treatment on the neurogenesis process was evaluated. For this purpose, subcutaneous injection of a cocktail of 40 microg/kg epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) was administered daily to soman-poisoned mice (110 microg/kg soman and 5.0 mg/kg methyl nitrate atropine), from post-soman days 1 to 8. To label replicating neural progenitors, 200 mg/kg bromodeoxyuridine (BrdU) was injected twice a day between post-soman days 6 and 8. Mice were sacrificed on post-soman day 9 or 34. On post-soman day 9, the cytokine treatment had no effect on the proliferation of neural progenitors in the SVZ and SGZ, as assessed by BrdU immunochemistry. However, this treatment seemed to promote the migration of neural precursor cells from the proliferative areas towards damaged brain regions. Indeed, in the CA1 hippocampal layer of soman-poisoned mice, on post-soman day 34, the cytokine treatment increased the number of healthy pyramidal neurons stained by hemalun-eosin dye. The cytokine treatment also augmented the number of BrdU-labeled cells in the CA1 hippocampal layer and amygdala. Interestingly, the administration of cytokines resulted in the differentiation of BrdU-positive cells into new neurons in the CA1 hippocampal layer, whereas astrocytic differentiation was preferentially observed in the amygdala.

Soman poisoning increases neural progenitor proliferation and induces long-term glial activation in mouse brain

To date, only short-term glial reaction has been extensively studied following soman or other warfare neurotoxicant poisoning. In a context of cell therapy by neural progenitor engraftment to repair brain damage, the long-term effect of soman on glial reaction and neural progenitor division was analyzed in the present study. The effect of soman poisoning was estimated in mouse brains at various times ranging from 1 to 90 days post-poisoning. Using immunochemistry and dye staining techniques (hemalun-eosin staining), the number of degenerating neurons, the number of dividing neural progenitors, and microglial, astroglial or oligodendroglial cell activation were studied. Soman poisoning led to rapid and massive (post-soman day 1) death of mature neurons as assessed by hemalun-eosin staining. Following this acute poisoning phase, a weak toxicity effect on mature neurons was still observed for a period of 1 month after poisoning. A massive short-termed microgliosis peaked on day 3 post-poisoning. Delayed astrogliosis was observed from 3 to 90 days after soman poisoning, contributing to glial scar formation. On the other hand, oligodendroglial cells or their precursors were practically unaffected by soman poisoning. Interestingly, neural progenitors located in the subgranular zone of the dentate gyrus (SGZ) or in the subventricular zone (SVZ) of the brain survived soman poisoning. Furthermore, soman poisoning significantly increased neural progenitor proliferation in both SGZ and SVZ brain areas on post-soman day 3 or day 8, respectively. This increased proliferation rate was detected up to 1 month after poisoning.

Effect of soman poisoning on populations of bone marrow and peripheral blood cells in mice

According to recent reports, brain lesions resulting from ischemia, mechanical injury or neurodegenerative diseases can be partially treated using bone marrow-derived stromal cell (BMSC) engraftment approaches. Nevertheless, for brain lesions resulting from organophosphate poisoning, nerve agents such as soman (pinacolyl methylphosphono-fluoridate) could affect blood and bone marrow (BM) micro-environments, thus preventing efficient BMSC migration and engraftment. It is therefore necessary to verify the hematologic response to soman exposure. To assess this issue, the survival of BM cells, in particular hematopoietic progenitor and precursor cells (HPC), as well as distribution of the different populations of peripheral blood cells, were investigated in soman-intoxicated mice. Nine-week-old adult male B6D2F1 mice were treated with 110 microg/kg soman and 5.0 mg/kg methyl nitrate atropine. BM and peripheral blood (PB) samples were collected 1, 4, 8 and 22 days after poisoning. Various parameters were determined such as PB cell counting or, for BM samples, myelogram, in vitro colony-forming cells and phenotypic flow cytometry analysis. On post-soman day 1, a significant decrease in numbers of white blood cells and an increase in erythrocyte and platelet counts were noted. On post-soman day 4, the number of HPC decreased significantly, probably due to reduction of the replication rate of these immature cells. However, the number of more immature cells (Sca1+/Lin- phenotype) remained unchanged. On post-soman day 8 and day 22, the number of monocytes and granulocytes in the blood had considerably increased, probably due to a strong inflammatory reaction in response to soman poisoning. In conclusion, PB cell and BM-derived HPC populations are affected by acute soman poisoning, suggesting particular care, mainly for graft kinetic aspects, during future development of autologous BM stem cell therapy strategy to treat nerve agent-induced brain damage.

[Stem-cell engraftment as delayed therapy to repair organophosphate-induced brain damage]

Amongst organophosphate compounds, both pesticides and warfare neurotoxics are probably the most representative. These compounds are irreversible acetylcholinesterase inhibitors. Usual clinical signs observed after acute poisoning are mainly respiratory distress, convulsions and seizures. Following acute poisoning, an emergency treatment must be provided as soon as possible (maximum delay of 1 hour post-poisoning), to prevent irreversible brain damage and patient death. At the present time, there is no efficient delayed treatment which could be provided if this 1 hour latency is overpassed. However, neurogenesis by stem cell engraftment, eventually complemented by gene therapy strategy, could be a potential therapeutic approach to repair organophosphate-induced brain damage. Main stem cell engraftement strategies successfully used for brain damage of various origins are reviewed in this Article.

Early changes in MAP2 protein in the rat hippocampus following soman intoxication

We investigated the time course of both MAP2 (microtubule-associated protein 2) levels and its phosphorylation degree in the rat hippocampus during the first 90 min following the onset of soman-induced seizures. The quantitative immunoblot analysis of hippocampal extracts revealed that MAP2 increased significantly in response to a sustained epileptic activity (from 60 min of seizure duration). In addition, intense MAP2 dephosphorylation was also observed 60 to 90 min after the onset of seizures. The possible neuropathological consequences of these two early MAP2 changes are discussed in relation to the both excessive stimulation of glutamate receptors and subsequent dendritic spine alterations occurring in hippocampal neurons soon after soman intoxication.

Subchronic administration of pyridostigmine or huperzine to primates: compared efficacy against soman toxicity

Organophosphonate (OP) nerve agents, such as soman, are potent irreversible inhibitors of central and peripheral acetylcholinesterases (AChEs). Pre-treatment of OP poisoning relies on the subchronic administration of a reversible AChE inhibitor. In the present limited study, the protective effects against soman toxicity of such compounds, i.e., the current pre-treatment pyridostigmine and huperzine, a proposed pre-treatment, are compared in primates. This is the first time primates are used to study the potential of pre-treatment with hyperzine. Indeed, previous studies with huperzine used nonprimate models which are not the most appropriate for pre-treatment in humans. Each medication is given via a subcutaneous mini-osmotic pump for 6 days at a delivery rate providing about 20% inhibition of red cell AChE activity. In this trial with only four primates, huperzine selectively inhibits red cell AChE activity whereas pyridostigmine also inhibits plasma butyrylcholinesterase (BuChE). This latter may act as endogenous scavenger of OP compounds helping to confer additional protection against OPs. During intoxication, the cumulative dose of soman needed to produce convulsions and epileptic activity is 1.55-fold higher in the animals pre-treated with huperzine compared to those pre-treated with pyridostigmine. Thus, replacing PYR by HUP for a subchronic pre-treatment of primates gives them better tolerance to the epileptic effects of soman.

Review of the value of huperzine as pretreatment of organophosphate poisoning

Today, organophosphate (OP) nerve agents are still considered as potential threats in both military or terrorism situations. OP agents are potent irreversible inhibitors of central and peripheral acetylcholinesterases. Pretreatment of OP poisoning relies on the subchronic administration of the reversible acetylcholinesterase (AChE) inhibitor pyridostigmine (PYR). Since PYR does not penetrate into the brain, it does not afford protection against seizures and subsequent neuropathology induced by an OP agent such as soman. Comparatively, huperzine (HUP) is a reversible AChE inhibitor that crosses the blood-brain barrier. HUP is presently approved for human use or is in course of clinical trials for the treatment of Alzheimer's disease or myasthenia gravis. HUP is also used as supplementary drug in the USA for correction of memory impairment. Besides, HUP has also been successfully tested for pretreatment of OP poisoning. This review summarizes the therapeutical value of HUP in this field. Moreover, the modes of action of HUP underlying its efficacy against OP agents are described. Efficacy appears mainly related to both the selectivity of HUP for red cell AChE which preserves scavenger capacity of plasma butyrylcholinesterases for OP agents and to the protection conferred by HUP on cerebral AChE. Finally, recent data, showing that HUP seems to be devoid of deleterious effects in healthy subjects, are also presented. Globally, this review reinforces the therapeutical value of HUP for the optimal pretreatment of OP poisoning.

Subchronic administration of various pretreatments of nerve agent poisoning. II. Compared efficacy against soman toxicity

OP nerve agents, such as soman, are potent irreversible inhibitors of central and peripheral acetylcholinesterases. Pretreatment of OP poisoning relies on the subchronic administration of a reversible acetylcholinesterase inhibitor. In the present study, the protective effects against soman toxicity of such compounds i.e. pyridostigmine, physostigmine (alone or associated with scopolamine) or huperzine are compared in guinea-pigs instrumented for EEG recording. Each medication is given via a subcutaneous mini-osmotic pump for 6 days at a delivery rate providing about 30% maximal inhibition of red cell acetylcholinesterase activity. The animals then receive iterative injections of soman (1/3 LD50) every 10 min. With pyridostigmine, reflecting a decreased overall tolerance to the poisoning, the cumulative doses of soman producing either tremors and convulsions or seizures are lower than those found in non-pretreated intoxicated controls. On the other hand, physostigmine does not afford satisfactory protection against the early mortality after intoxication. On this specific point, physostigmine + scopolamine and huperzine, although they do not prevent the appearance of seizures, give best results. The effects of each pretreatment on acetylcholinesterase, butyrylcholinesterase and carboxylesterase (these two latter enzymes may act as endogenous scavengers of OP compounds) are also examined in vitro and in the blood of each animal during subchronic administration. Huperzine appears as a selective inhibitor of red cell acetylcholinesterase activity while pyridostigmine or physostigmine additionally inhibit plasmatic butyrylcholinesterase. Considerations about huperzine or physostigmine + scopolamine as the most appropriate candidate for the pretreatment of OP poisoning are given.

Subchronic administration of various pretreatments of nerve agent poisoning. I. Protection of blood and central cholinesterases, innocuousness towards blood-brain barrier permeability

PYR, a reversible AChE inhibitor, is the current pretreatment against OP intoxication. However, PHY in the presence or absence of SCO on one side, and HUP on the other side, could be considered as potential substitutes for PYR. In the present study, the effects of the subchronic administration of these different current or potential pretreatments on the BBB permeability for blood-borne albumin and on the activity of the blood and central cholinesterases are comparatively evaluated in guinea-pigs. Altogether, although some marginal disruptions of BBB are detected, the different current or potential pretreatments studied seem to have a total innocuousness on the permeability of the BBB for proteins. Finally, at the light of its particular inhibitory effects on blood and central cholinesterases, HUP, compared to the other drugs, seems to be the optimal candidate to be used as pretreatment against OP poisoning.

Compared efficacy of diazepam or avizafone to prevent soman-induced electroencephalographic disturbances and neuropathology in primates: relationship to plasmatic benzodiazepine pharmacokinetics

We performed an experiment to characterize the toxicity of soman in cynomolgus monkeys in which organophosphorus intoxication was followed by treatment with either the current three-drug therapy atropine/pralidoxime/diazepam or a combination of atropine/pralidoxime/avizafone, avizafone being the water soluble prodrug of diazepam. Clinical, electrophysiological, and histological approaches were combined. When benzodiazepines were injected at the similar molar dose of 0.7 micromol/kg, the protection against soman toxicity was better with the atropine/ pralidoxime/diazepam combination than with the atropine/pralidoxime/avizafone one. Pharmacokinetic studies demonstrated that this difference of efficacy could be explained by a lower plasmatic load of diazepam obtained after injection of avizafone at 0.7 micromol/kg, compared to the administration of diazepam at the same molar dose. Moreover, after injection of avizafone, plasmatic levels of diazepam were achieved faster and declined more rapidly than after administration of diazepam. Compared to diazepam given at a dose of 0.7 micromol/kg, injection of 1 micromol avizafone/kg gave a similar plasmatic load of benzodiazepine, but with a lower time to maximum plasma concentration (tmax) and a higher maximum plasma concentration (Cmax) for plasmatic diazepam. We therefore went on to demonstrate that administration of the atropine/pralidoxime/avizafone combination at a dose 1 micromol benzodiazepine/kg to intoxicated monkeys afforded electrophysiological and histological protection similar to that obtained after administration of atropine/pralidoxime/diazepam at a dose of 0.7 micromol diazepam/kg. Reflections on the possible incorporation of avizafone in three-drug emergency treatment are presented.

Soman-induced hypertension in conscious rats is mediated by prolonged central muscarinic stimulation

The acetylcholinesterase inhibitor, soman, induces marked and sustained hypertension and tachycardia associated with a convulsive syndrome in rats. The aims of the present study were to distinguish between the cardiovascular and convulsant effects of soman and to determine whether the maintenance of the soman-induced hypertension and tachycardia depends solely on a central muscarinic effect. To this end, using a computerised analysis of blood pressure (BP) in conscious freely moving rats, we examined the consequences on the increase in mean BP (MBP) and heart rate (HR) induced by soman (60 micrograms/kg, i.v.) of 1) a pre-treatment with the anticonvulsant drug diazepam (3 mg/kg, i.v.) and 2) atropine sulphate (10 mg/kg, i.v.) administered 10 or 60 min after the intoxication. Pretreatment with diazepam prevented the convulsions, assessed by electroencephalogram (EEG) recording, but modified neither the magnitude nor the kinetics of the pressor and tachycardic effects of soman (delta MBP = 74 +/- 2 and 73 +/- 5 mmHg, delta HR = 69 +/- 10 and 79 +/- 7 bpm, maximum MBP = 186 +/- 3 and 182 +/- 6 mmHg, maximum HR = 545 +/- 9 and 522 +/- 16 bpm in solvent- (n = 8) and diazepam- (n = 8) pre-treated rats, respectively). Whatever its time of administration, atropine sulphate fully and immediately reversed the rise in BP induced by soman. The soman-induced tachycardia was also suppressed by atropine administered 10 min after soman whereas it persisted when atropine was injected 60 min after the intoxication. These results show that the cardiovascular effects of soman can occur independently of the convulsive syndrome and that the maintenance of the soman-induced hypertension depends entirely on a permanent central muscarinic stimulation.

Memory impairment after soman intoxication in rat: correlation with central neuropathology. Improvement with anticholinergic and antiglutamatergic therapeutics

The effects of soman, a potent irreversible inhibitor of acetylcholinesterase, on central neuropathology in rats were studied in relation with subsequent spatial memory impairments. In a first step, it was found that, without treatment, neuropathology and learning impairment were observed only in rats which experienced convulsions. Then, treatment consisting of atropine sulfate, and/or TCP and/or NBQX was administered to intoxicated animals at infraanticonvulsant doses to obtain a graded subsequent neuropathology and to appreciate an eventual relation between neuropathology and spatial memory impairment. Thus, a correlation between neuropathology in the hippocampal CA1 region and spatial learning performance was found, the degradation of performance of rat being directly related to the amplitude of their neural damage. A threshold was emphasized : below a certain degree of neural loss, no memory impairment was found. Only treatment with tritherapy (atropine + TCP + NBQX) was able to improve the different parameters of spatial learning, despite no effect on the convulsions of the animals.

Review of the value of gacyclidine (GK-11) as adjuvant medication to conventional treatments of organophosphate poisoning: primate experiments mimicking various scenarios of military or terrorist attack by soman

Today, organophosphorus nerve agents are still considered as potential threats in both military or terrorism situations. These agents act as potent irreversible inhibitors of acetylcholinesterase in both central and peripheral nervous systems. Conventional treatment of organophosphate poisoning includes the combined administration of a cholinesterase reactivator (an oxime), a muscarinic cholinergic receptor antagonist (atropine) and a benzodiazepine anticonvulsant (diazepam). However, numerous studies have demonstrated that the excitatory amino acid glutamate also plays a prominent role in the maintenance of organophosphate-induced seizures and in the subsequent neuropathology especially through an overactivation of the N-methyl-D-aspartate (NMDA) receptor subtype. Contrary to other non-competitive NMDA antagonists successfully tested in rodents exposed to organophosphate, gacyclidine is a novel antiNMDA compound which is in the process of approval for human use in France for neurotraumatology. This review summarizes the therapeutic value of gacyclidine as a complement to the available emergency treatment against severe organophosphate poisoning. Previous data obtained from experiments on primates in several scenarios mimicking military or terrorist attacks, using soman as the nerve agent, were used. Primates pretreated with pyridostigmine and receiving conventional emergency therapy at the first signs of poisoning survive. However, only gacyclidine is able to ensure complete management of nerve agent poisoning for rapid normalization of EEG activity, clinical recovery and neuroprotection. Gacyclidine also ensures optimal management of severe nerve agent poisoning in animals neither pretreated nor receiving emergency therapy likewise during an unexpected exposure. However, this beneficial effect is obtained provided that medical intervention is conducted rapidly after intoxication. Globally, the current lack of any other NMDA receptor antagonist suitable for human use reinforces the therapeutic value of gacyclidine as a central nervous system protective agent for the treatment of OP poisoning.

Acute soman poisoning in primates neither pretreated nor receiving immediate therapy: value of gacyclidine (GK-11) in delayed medical support

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.

Heat stress, even extreme, does not induce penetration of pyridostigmine into the brain of guinea pigs

Stress due to forced swimming was recently shown to allow penetration of pyridostigmine (PYR) into the brain of mice. Accordingly, it was suggested that in troops exposed to emotional stress under conditions of war, as during the Gulf War, the BBB may have unexpectedly become permeable to PYR thus leading to an increased frequency of CNS symptoms. In this study, the entry of PYR into the brain was investigated in guinea pigs subjected to different heat stress levels. In a first group, guinea pigs were maintained at room temperature for 2 hours, their core temperature remaining stable at about 39.8 degrees C. In a second group, animals were placed in a climatic chamber in order to keep their core temperature at 41.5 degrees C for 2 hours. In a third group, animals were subjected to a high ambient temperature (42.6 degrees C) during about 2 hours and developed heatstroke symptoms, their core temperature progressively increasing and reaching around 44.3 degrees C. In each group, the stress of the animals was assessed by measuring the increase of plasma cortisol level. PYR (0.2 mg/kg, s.c.) was injected 90 minutes after beginning the experiment. Penetration of the drug into the brain was examined by measurement of acetylcholinesterase (AChE) activity in the cortex, the striatum and the hippocampus of the animals 30 minutes after PYR administration. A passage of this drug into the brain was also evaluated autoradiographically after i.v. injection of tritiated PYR 90 minutes after the beginning of the experiment (100 microCi/animal). Whatever the group examined, no entry of PYR into the CNS could be detected. Exposure to an ambient temperature at 42.6 degrees C for 2 hours resulted by itself in a partial inhibition of cerebral AChE activity. Our results, which agree with previous data obtained in humans exposed to heat stress, are opposite to the recent research showing a central passage of PYR in mice following a forced swim stress test. This demonstrated that the penetration of PYR into the brain of rodents under stress depends on the experimental conditions used (animal species, nature of the stressor, etc.). Extrapolations to humans of results primarily obtained in rodents about central passage of a drug under stress must thus be done very carefully.

Behavioral effects of NBQX, a competitive antagonist of the AMPA receptors

NBQX, a specific and potent AMPA receptor antagonist has been found to be neuroprotective in various models of ischemia and to have anticonvulsant properties in different models of epilepsy. In this experiment, the neurobehavioral effects of NBQX were studied. In an open field, an important ataxia was emphasized at a dose of 60 mg/kg. In a swimming task, an increase of the escape latencies was noted on the third day at a dose of 40 mg/kg. In a Morris water maze task, doses devoid of effects on locomotion were used (10, 20, and 30 mg/kg). There was no effect on the acquisition of the task at 10 mg/kg and a slight impairment at 20 mg/kg, but the rats did not learn the task at 30 mg/kg. This impairment was reversible, as shown by the increasing performance of this group without treatment. No impairment was noted in the retention phase of the Morris water maze task. The results are discussed relative to the role of the AMPA receptor in memory processes.

Nerve agent poisoning in primates: antilethal, anti-epileptic and neuroprotective effects of GK-11

Organophosphorus nerve agents are still in use today in warfare and as terrorism compounds. Classical emergency treatment of organophosphate poisoning includes the combined administration of a cholinesterase reactivator (an oxime), a muscarinic cholinergic receptor antagonist (atropine) and a benzodiazepine anticonvulsant (diazepam). However, recent experiments with primates have demonstrated that such treatment, even when administered immediately after organophosphate exposure, does not rapidly restore normal electroencephalographic (EEG) activity and fails to totally prevent neuronal brain damage. 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 available emergency therapy against organophosphate poisoning. GK-11 was injected at a dose of 0.1 mg/kg (i.v) after a 45-min latency period to heavily intoxicated (8 LD50) primates. Just after intoxication, man-equivalent doses of one autoinjector containing atropine/pralidoxime/diazepam were administered. The effects of GK-11 were examined on survival, EEG activity, signs of toxicity, recovery after challenge and central nervous system histology. The present data demonstrate that treatment with GK-11 prevents the mortality observed after early administration of classical emergency medication alone. EEG recordings and clinical observations also revealed that GK-11 prevented soman-induced seizures and motor convulsions. EEG analysis within the classical frequency bands (beta, theta, alpha, delta) demonstrated that central activity was totally restored to normal after GK-11 treatment, but remained profoundly altered in animals receiving atropine/pralidoxime/diazepam alone. GK-11 also markedly accelerated clinical recovery of soman-challenged primates. Lastly, this drug totally prevented the neuropathology observed 3 weeks after soman exposure in animals treated with classical emergency treatment alone. GK-11 represents a promising adjuvant therapy to the currently available emergency 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.

Efficacy of huperzine in preventing soman-induced seizures, neuropathological changes and lethality

Huperzine A (HUP) is a potent reversible inhibitor of acetylcholinesterase (AChE) that crosses the blood-brain barrier. Its ability to prevent seizures and subsequent hippocampal neuropathological changes induced by the organophosphate soman was studied in guinea pigs. Results were compared to guinea pigs treated with pyridostigmine (PYR, 0.2 mg/kg, subcutaneously). HUP pretreatment at 0.5 mg/kg, intraperitoneally, totally prevented seizures and ensured the survival of all animals for 24 h after intoxication. Hippocampal tissue was then free of any neuronal damage. Comparatively, all animals pretreated with PYR exhibited epileptic activity after soman poisoning and five of six animals died. Examination of the hippocampus of the only surviving guinea pig pretreated with PYR showed extensive neuropathological changes. Although HUP or PYR induced similar inhibitions of blood AChE activity, only HUP pretreatment led to a decrease in central AChE activity. In binding studies on guinea-pig brain homogenates, HUP had no affinity for muscarinic, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and gamma-aminobutyric acid (GABA)A receptors and only a very low one for N-methyl-D-aspartate (NMDA) receptors. In conclusion, HUP, unlike PYR, protects against soman-induced convulsions and neuropathological changes in the hippocampus. This efficacy seems to be related to a protection by HUP of both peripheral and central stores of AChE.

GK 11: promising additional neuroprotective therapy for organophosphate poisoning

Recent experiments with primates have demonstrated that treatment with atropine/pralidoxime/diazepam, even if administered immediately after organophosphate exposure, does not totally prevent neuronal brain damage. Using primates, we have studied, for the first time, the ability of GK-11 (gacyclidine), an antiglutamatergic drug in the process of agreement for human use, given as an additional therapy, to counteract the neuropathology due to organophosphate exposure that persists after classical treatment with oxime/atropine/benzodiazepine. We have also examined the recovery of the organophosphate-intoxicated primates. Male Cynomolgus monkeys were pretreated 1 hour before poisoning with pyridostigmine, then intoxicated with 8 LD50 of soman and immediately treated with the combination pralidoxime/atropine/diazepam. Some of the animals also received GK-11 at 0.01; 0.03 or 0.1 mg/kg (i.v.) 10 minutes after soman challenge. Recovery of the primates (reflexes, movements, feeding) and the neuropathological changes that occurred three weeks after intoxication (histological examinations and neuronal cell density measurement) were compared in GK-11-treated and control animals. At all doses tested, GK-11 prevented the neuronal rarefaction of the frontoparietal cortex that was observed in soman-intoxicated animals that received only oxime/atropine/diazepam. Moreover, the 0.01 mg/kg dose of GK-11 improved the early recovery of intoxicated primates from 1 day after intoxication. In the view of the most effective management of organophosphate intoxication that is currently available, GK-11 thus appears to be a promising additional neuroprotective therapy. This drug is presently being evaluated in a human clinical trial for a different neuroprotective indication.

Evaluation of dextromethorphan and dextrorphan as a preventive treatment of soman toxicity in mice

Phencyclidine-like drugs are effective against convulsions and brain lesions related to soman intoxication but induce severe side effects. The well tolerated antitussive dextromethorphan (DM) and its metabolite dextrorphan (DX) have antiepileptic and neuroprotective properties that we evaluated in mice against 2 LD50 of soman in a three-drug pretreatment (atropine sulfate and oxime HI-6 plus DM: 20-50 mg/kg or DX: 10-40 mg/kg i.p). Neuroprotection was evaluated by measurement of hippocampal omega 3 binding site density. DM and DX have weak anticonvulsant and neuroprotective activities which are counterbalanced at high doses by an increased mortality due to respiratory distress for DM and by ataxia for DX. Thus DM and DX do not appear to be appropriate for the pretreatment of soman intoxication.

Efficacy of atropine/pralidoxime/diazepam or atropine/HI-6/prodiazepam in primates intoxicated by soman

We performed an experiment to characterize the toxicity of soman in cynomolgus monkeys when the organophosphorus intoxication was followed by a treatment with either the three-drug therapy atropine/pralidoxime/diazepam or the association atropine/HI-6/prodiazepam. Clinical, electrophysiological and histological approaches were combined. Our data demonstrate that the protection afforded against soman toxicity was better with the combination atropine/HI-6/prodiazepam compared to atropine/pralidoxime/diazepam. This was observed transiently in term of vigilance and respiratory function of intoxicated animals, but particularly in term of their EEG- and ECG disturbances. Moreover, compared to those treated with atropine/pralidoxine/diazepam, animals treated with atropine/ HI-6/prodiazepam recovered slightly sooner and did not exhibit prostration 2 days after intoxication although their rapidity of movements was not totally restored. The final recovery observed 3 weeks after intoxication was similar for the two groups. The value of the combination of atropine/HI-6/prodiazepam vs atropine/pralidoxime/diazepam to counteract soman toxicity was also confirmed in term of brain neuroprotection since greater lesions were observed with the second three drug treatment three weeks after intoxication.

The role of nitric oxide in soman-induced seizures, neuropathology, and lethality

The effects of the inhibitors of endothelial and neuronal nitric oxide (NO) synthases, N-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI), respectively, and the precursor of NO, glyceryl trinitrate, on soman-induced seizures, lethality, and neuropathology were studied in rats. It was found that pretreatment of rats with L-NAME and 7-NI potentiated the severity of motor convulsions and enhanced lethality produced by soman. On the other hand, glyceryl trinitrate, administered transdermally at doses ranging from 2.5-5 mg/day 1 day before soman, decreased seizure susceptibility and lethality in soman-intoxicated animals. This was accompanied by a subsequent reduction of central neuronal damage 24 h after soman treatment. Pretreatment with glyceryl trinitrate also reversed seizure latency produced by 7-NI treatment during soman intoxication. These results indicate that neuronal NO may play a prominent role in seizures by acting as an anticonvulsant and neuroprotectant in soman intoxication.

Involvement of non-muscarinic receptors in phosphoinositide signalling during soman-induced seizures

Previous investigations have indicated that soman-induced convulsions involve the inositol lipid signalling system. We previously reported that 10 min after the onset of seizures, inositol 1,4,5-triphosphate (IP3) build-up was coupled to activation of non-muscarinic receptor subtypes. In the present study, we demonstrate that (1) in addition to muscarinic receptors, histamine H1 subtypes and glutamate metabotropic receptors contribute to the first IP3 increase (first 10 min of seizures) and (2) the histamine H1 subtype and glutamate metabotropic receptors are also involved in the second step of inositol phosphate response (after 10 min of seizures). alpha 1-adrenoceptor and 5-HT2 receptors, known to be coupled to phosphoinositide turnover, did not participate in soman-induced IP3 response. Neurochemical interactions between cholinergic, histamine H1 and glutamate metabotropic systems, responsible of the phosphoinositide hydrolysis under soman are envisaged.

Modulation of soman-induced neuropathology with an anticonvulsant regimen

Rat hippocampus and piriform cortex were examined for pathological changes 48 hours after exposure to a convulsant dose of soman. Animals were treated with a low dose of atropine just after soman and were then injected, after 10 or 40 minutes of seizures, with both the anticonvulsant drugs NBQX and TCP. Atropine given alone counteracted the extensive neuronal loss due to soman in both areas without prevention of neuronal suffering. Comparatively, the complete anticonvulsant regimen, given before 40 minutes of seizures, totally prevented hippocampal soman-induced neuropathology. Neurones of piriform cortex were still suffering whatever the time of injection of the drugs. This emphasizes the need for a rapid and definitive anticonvulsant treatment just after soman intoxication to block the subsequent neurotoxic effect of nerve-agent exposure.

Coadministration of atropine, NBQX and TCP against soman-induced seizures

The ability of relatively low doses of atropine, NBQX and TCP administered in combination to prevent or stop seizures induced by soman, was studied in rats. While these drugs injected together early after soman prevented the onset of seizures, their delayed concomitant administration after 5 or 30 min of epileptic activity only mildly attenuated the intensity of seizures. Conversely, a total arrest of epileptic activity was observed in 80 to 100% of animals when NBQX and TCP were given together after 5 to 50 min of seizures to atropine pretreated rats. The large time-window for antiepileptic effectiveness of this 'three drug treatment', provided that atropine is administered early after soman, is discussed in relation to reciprocal potentiations of the antiepileptic effects of atropine, NBQX and TCP in combination.

Antiepileptic effects of NBQX against soman-induced seizures

The ability of NBQX, a potent antagonist of AMPA glutamatergic receptors, to prevent or stop seizures induced by the organophosphate soman, an irreversible inhibitor of AChE, was studied in rats. NBQX administered concomitantly with soman prevents the onset of seizures (ED50: 29.2 mg kg-1, i.p.). Administered 5 min after the onset of seizures, NBQX greatly reduces the intensity of the epileptic activity. The same decrease of epileptic activity is observed, in the presence of atropine, when the administration of NBQX is delayed 15 min after the onset of seizures. NBQX thus appears as a promising antiepileptic candidate against soman-induced seizures. The roles of AMPA and muscarinic receptors in the onset and propagation of soman-induced epileptic activity are discussed.

Transient impairment of the gabaergic function during initiation of soman-induced seizures

The changes in extracellular gamma-aminobutyric acid (GABA) levels, the modifications in binding capacities of GABA-receptor subtypes A and B and of the Cl- ionophore sites localized in the ionic-channel associated to the GABAA receptors were studied in hippocampus of rats subjected to a convulsive dose of the acetylcholinesterase inhibitor soman. Whereas extracellular GABA levels, just as binding on GABAA and GABAB receptors, were not modified under soman, a significant transient decrease in the binding capacities of the Cl- ionophore site of the GABAA receptor complex occurred within the first 10 min of seizures in CA1, CA3 areas, and in the dentate gyrus with return to basal values after 30 min. Accordingly, a transient decrease of the brain muscimol-gated Cl- influx was observed after 10 min of seizures. An increased ability of diazepam to potentiate the GABAA gated Cl- influx occurred at the same time. Altogether, these data demonstrated that an impairment of the GABAA receptor function occurs at the beginning of seizures. This suggests that a temporary decrease of GABAAergic function may contribute to the onset of seizures.

[Evaluation of the anticonvulsant and neuroprotective efficacy of propentofylline during soman poisoning]

The objective of the present study was to evaluate the anticonvulsant and neuroprotective activities of propentofylline against soman, an irreversible acetylcholinesterase inhibitor. In a first step, the ability of propentofylline to inhibit in vitro the hippocampal evoked release of acetylcholine (ACh) and glutamate (Glu), the two major neurotransmitters involved during soman intoxication, was demonstrated. Propentofylline was then given either at single doses from 0.5 to 25 mg/kg or with repetitive injections at 10 mg/kg to mice subjected to soman. Neither tonic-clonic convulsions induced by soman nor subsequent hippocampal damage were reduced in propentofylline-treated mice. This observation suggested that propentofylline did not inhibit the long-lasting hippocampal release of ACh and Glu under soman.

Cholinergic activation of phosphoinositide metabolism during soman-induced seizures

In the present study we investigated the role of the cholinergic pathway in phosphoinositide metabolism activation observed during soman-induced convulsions. We thus studied the effect of atropine sulphate, a muscarinic antagonist (20 mg kg-1, i.p.), on IP3 levels in rat hippocampus. We demonstrated that initially, the increase of IP3 is closely seizure-related. On the other hand, after 10 min of seizures, the IP3 enhancement and the seizure activity are no longer correlated. After 20 min of seizures, atropine failed to inhibit soman-induced IP3 enhancement, suggesting that the activation of another neurotransmitter system(s) linked to PPI turnover succeeds the cholinergic stimulation.

Neuroprotective activity of glutamate receptor antagonists against soman-induced hippocampal damage: quantification with an omega 3 site ligand

Previous investigations have indicated that the measurement of omega 3 (peripheral-type benzodiazepine) binding site densities could be of widespread applicability in the localization and quantification of neural tissue damage in the central nervous system. In the first step of the present study, the suitability of this approach for the assessment of soman-induced brain damage was validated. Autoradiographic study revealed marked increases of omega 3 site densities in several brain areas of convulsing rats 2 days after soman challenge. These increases were well-correlated with the pattern and the amplitude of neuropathological alterations due to soman and closely related to both glial reaction and macrophage invasion of the lesioned tissues. We then used this marker to assess, in mouse hippocampus, the neuroprotective activity against soman-induced brain damage of NBQX and TCP which are respective antagonists of non-NMDA and NMDA glutamatergic receptors. Injection of NBQX at 20 or 40 mg/kg 5 min prior to soman totally prevented the neuronal damage. Comparatively, TCP had neuroprotective efficacy when administered at 1 mg/kg 5 min prior to soman followed by a reinjection 1 h after. These results demonstrate that both NBQX and TCP afford a satisfactory neuroprotection against soman-induced brain damage. Since it is known that the neuropathology due to soman is closely seizure-related, the neuroprotective activities of NBQX and TCP are discussed in relation with the respective roles of non-NMDA and NMDA receptors in the onset and maintenance of soman-induced seizures.

Changes in hippocampal acetylcholine and glutamate extracellular levels during soman-induced seizures: Influence of septal cholinoceptive cells

The changes in extracellular acetylcholine and glutamate levels were determined, during the course of seizures induced by soman, an irreversible inhibitor of acetylcholinesterase, in the CA1 hippocampal area of rats previously injected with atropine or normal saline into septum. The marked increases observed in soman-treated animals were abolished in rats receiving atropine. These data strongly suggest that, during soman intoxication, septal cholinoceptive cells play a key role in controlling the release of acetylcholine and glutamate in hippocampus. The mechanisms underlying this phenomenon are discussed.

Effects of soman-induced seizures on different extracellular amino acid levels and on glutamate uptake in rat hippocampus

Extracellular amino acid levels in CA3 and CA1 fields of rat hippocampus, an area highly sensitive to seizures, were determined by intracranial microdialysis during seizures induced by systemic administration of soman (o-1,2,2-trimethylpropyl methylphosphonofluoridate), a potent inhibitor of acetylcholinesterase. The glutamate uptake level was determined on another series of animals in hippocampus homogenates. An early and transient increase in the extracellular glutamate level occurred in CA3 within 30 min of seizures, with correlated brief elevations of taurine, glycine and glutamine levels. The glutamate level increased early in CA1, declined and then became more sustained (after 50 min of seizures). Apparent elevations of taurine, glycine and glutamine levels in CA1 accompanied changes in glutamate concentrations. Changes of glutamate level correlated with an increase in the glutamate uptake which rapidly declined after 40 min of seizures. The role of the transient release of glutamate in CA3 and of the sustained release in CA1 in prolonged soman-induced seizures is considered. The correlation between glutamate and other amino acid release is studied.

Modulation of the number of muscarinic receptors in mouse neuroblastoma cells by soman

Long-term preincubation at 37 degrees of mouse neuroblastoma cells (clones NS-20 and N1E-115) with soman, a potent and irreversible cholinesterase inhibitor, resulted in a significant decrease in the number of [3H]N-methylscopolamine binding sites and in the inhibition of carbamylcholine-induced cyclic GMP formation. The disappearance of surface muscarinic receptors and the desensitization of the receptor-mediated response seem to occur via accumulation of acetylcholine in the culture medium. The significance of these findings is discussed.