The AF64A model of cholinergic hypofunction: an update

Saporin from Saponaria officinalis as a Tool for Experimental Research, Modeling, and Therapy in Neuroscience

Saporin, which is extracted from Saponaria officinalis, is a protein toxin that inactivates ribosomes. Saporin itself is non-selective toxin but acquires high specificity after conjugation with different ligands such as signaling peptides or antibodies to some surface proteins expressed in a chosen cell subpopulation. The saporin-based conjugated toxins were widely adopted in neuroscience as a convenient tool to induce highly selective degeneration of desired cell subpopulation. Induction of selective cell death is one of approaches used to model neurodegenerative diseases, study functions of certain cell subpopulations in the brain, and therapy. Here, we review studies where saporin-based conjugates were used to analyze cell mechanisms of sleep, general anesthesia, epilepsy, pain, and development of Parkinson’s and Alzheimer’s diseases. Limitations and future perspectives of use of saporin-based toxins in neuroscience are discussed.

Preclinical Models of Alzheimer's Disease: Relevance and Translational Validity

The only drugs currently approved for the treatment of Alzheimer's Disease (AD) are four acetylcholinesterase inhibitors and the NMDA antagonist memantine. Apart from these drugs, which have minimal to no clinical benefit, the 40-year search for effective therapeutics to treat AD has resulted in a clinical failure rate of 100% not only for compounds that prevent brain amyloid deposition or remove existing amyloid plaques but also those acting by a variety of other putative disease-associated mechanisms. This indicates that the preclinical data generated from current AD targets to support the selection, optimization, and translation of new chemical entities (NCEs) and biologics to clinical trials is seriously compromised. While many of these failures reflect flawed hypotheses or a lack of adequate characterization of the preclinical pharmacodynamic and pharmacokinetic (PD/PK) properties of lead NCEs-including their bioavailability and toxicity-the conceptualization, validation, and interrogation of the current animal models of AD represent key limitations. The overwhelming majority of these AD models are transgenic, based on aspects of the amyloid hypothesis and the genetics of the familial form of the disease. As a result, these generally lack construct and predictive validity for the sporadic form of the human disease. The 170 or so transgenic models, perhaps the largest number ever focused on a single disease, use rodents, mainly mice, and in addition to amyloid also address aspects of tau causality with more complex multigene models including other presumed causative factors together with amyloid. This overview discusses the current animal models of AD in the context of both the controversies surrounding the causative role of amyloid in the disease and the need to develop validated models of cognitive function/dysfunction that more appropriately reflect the phenotype(s) of human aged-related dementias. © 2019 by John Wiley & Sons, Inc.

Astroglia in Alzheimer's Disease

Alzheimer's disease is the most common cause of dementia. Cellular changes in the brains of the patients suffering from Alzheimer's disease occur well in advance of the clinical symptoms. At the cellular level, the most dramatic is a demise of neurones. As astroglial cells carry out homeostatic functions of the brain, it is certain that these cells are at least in part a cause of Alzheimer's disease. Historically, Alois Alzheimer himself has recognised this at the dawn of the disease description. However, the role of astroglia in this disease has been understudied. In this chapter, we summarise the various aspects of glial contribution to this disease and outline the potential of using these cells in prevention (exercise and environmental enrichment) and intervention of this devastating disease.

Molecular and Cellular Mechanisms of Sporadic Alzheimer's Disease: Studies on Rodent Models in vivo

In this review, recent data are presented on molecular and cellular mechanisms of pathogenesis of the most widespread (about 95%) sporadic forms of Alzheimer's disease obtained on in vivo rodent models. Although none of the available models can fully reproduce the human disease, several key molecular mechanisms (such as dysfunction of neurotransmitter systems, especially of the acetylcholinergic system, β-amyloid toxicity, oxidative stress, neuroinflammation, mitochondrial dysfunction, disturbances in neurotrophic systems) are confirmed with different models. Injection models, olfactory bulbectomy, and senescence accelerated OXYS rats are reviewed in detail. These three approaches to in vivo modeling of sporadic Alzheimer's disease have demonstrated a considerable similarity in molecular and cellular mechanisms of pathology development. Studies on these models provide complementary data, and each model possesses its specific advantages. A general analysis of the data reported for the three models provides a multifaceted and the currently most complete molecular picture of sporadic Alzheimer's disease. This is highly relevant also from the practical viewpoint because it creates a basis for elaboration and preclinical studies of means for treatment of this disease.

Toxin-Induced Experimental Models of Learning and Memory Impairment

Animal models for learning and memory have significantly contributed to novel strategies for drug development and hence are an imperative part in the assessment of therapeutics. Learning and memory involve different stages including acquisition, consolidation, and retrieval and each stage can be characterized using specific toxin. Recent studies have postulated the molecular basis of these processes and have also demonstrated many signaling molecules that are involved in several stages of memory. Most insights into learning and memory impairment and to develop a novel compound stems from the investigations performed in experimental models, especially those produced by neurotoxins models. Several toxins have been utilized based on their mechanism of action for learning and memory impairment such as scopolamine, streptozotocin, quinolinic acid, and domoic acid. Further, some toxins like 6-hydroxy dopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amyloid-β are known to cause specific learning and memory impairment which imitate the disease pathology of Parkinson's disease dementia and Alzheimer's disease dementia. Apart from these toxins, several other toxins come under a miscellaneous category like an environmental pollutant, snake venoms, botulinum, and lipopolysaccharide. This review will focus on the various classes of neurotoxin models for learning and memory impairment with their specific mechanism of action that could assist the process of drug discovery and development for dementia and cognitive disorders.

The anterior and posterior pedunculopontine tegmental nucleus are involved in behavior and neuronal activity of the cuneiform and entopeduncular nuclei

Loss of cholinergic neurons in the mesencephalic locomotor region, comprising the pedunculopontine nucleus (PPN) and the cuneiform nucleus (CnF), is related to gait disturbances in late stage Parkinson's disease (PD). We investigate the effect of anterior or posterior cholinergic lesions of the PPN on gait-related motor behavior, and on neuronal network activity of the PPN area and basal ganglia (BG) motor loop in rats. Anterior PPN lesions, posterior PPN lesions or sham lesions were induced by stereotaxic microinjection of the cholinergic toxin AF64-A or vehicle in male Sprague-Dawley rats. First, locomotor activity (open field), postural disturbances (Rotarod) and gait asymmetry (treadmill test) were assessed. Thereafter, single-unit and oscillatory activities were measured in the non-lesioned area of the PPN, the CnF and the entopeduncular nucleus (EPN), the BG output region, with microelectrodes under urethane anesthesia. Additionally, ECoG was recorded in the motor cortex. Injection of AF64-A into the anterior and posterior PPN decreased cholinergic cell counts as compared to naive controls (P<0.001) but also destroyed non-cholinergic cells. Only anterior PPN lesions decreased the front limb swing time of gait in the treadmill test, while not affecting other gait-related parameters tested. Main electrophysiological findings were that anterior PPN lesions increased the firing activity in the CnF (P<0.001). Further, lesions of either PPN region decreased the coherence of alpha (8-12 Hz) band between CnF and motor cortex (MCx), and increased the beta (12-30 Hz) oscillatory synchronization between EPN and the MCx. Lesions of the PPN in rats had complex effects on oscillatory neuronal activity of the CnF and the BG network, which may contribute to the understanding of the pathophysiology of gait disturbance in PD.

Latrepirdine: molecular mechanisms underlying potential therapeutic roles in Alzheimer's and other neurodegenerative diseases

Latrepirdine (Dimebon(TM)) was originally marketed as a non-selective antihistamine in Russia. It was repurposed as an effective treatment for patients suffering from Alzheimer's disease (AD) and Huntington's disease (HD) following preliminary reports showing its neuroprotective functions and ability to enhance cognition in AD and HD models. However, latrepirdine failed to show efficacy in phase III trials in AD and HD patients following encouraging phase II trials. The failure of latrepirdine in the clinical trials has highlighted the importance of understanding the precise mechanism underlying its cognitive benefits in neurodegenerative diseases before clinical evaluation. Latrepirdine has shown to affect a number of cellular functions including multireceptor activity, mitochondrial function, calcium influx and intracellular catabolic pathways; however, it is unclear how these properties contribute to its clinical benefits. Here, we review the studies investigating latrepirdine in cellular and animal models to provide a complete evaluation of its mechanisms of action in the central nervous system. In addition, we review recent studies that demonstrate neuroprotective functions for latrepirdine-related class of molecules including the β-carbolines and aminopropyl carbazoles in AD, Parkinson's disease and amyotrophic lateral sclerosis models. Assessment of their neuroprotective effects and underlying biological functions presents obvious value for developing structural analogues of latrepirdine for dementia treatment.

Laser acupuncture improves memory impairment in an animal model of Alzheimer's disease

The burden of Alzheimer's disease is continually rising globally, especially in the Asia-Pacific region. Unfortunately, the efficacy of the therapeutic strategy is still very limited. Because the effect of acupuncture at HT7 can improve learning and memory, the beneficial effect of laser acupuncture, a noninvasive form of acupuncture, at HT7 on memory improvement in patients with Alzheimer's disease has been a focus of research. To elucidate this issue, we used AF64A, a cholinotoxin, to induce memory impairment in male Wistar rats, which weighed 180-220 g. Then, the animals were treated with laser acupuncture either at HT7 or at a sham acupoint once daily for 10 minutes for a period of 14 days. Spatial memory assessments were performed at 1, 7, and 14 days after AF64A administration and at the end of the experiment, and the changes in the malondialdehyde (MDA) level and in the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and acetylcholinesterase (AChE) activities in the hippocampus were recorded. The results showed that laser acupuncture significantly suppressed AChE activity in the hippocampus. Although laser acupuncture enhanced SOD and CAT activities, no reduction in MDA level in this area was observed. Therefore, laser acupuncture at HT7 is a potential strategy to attenuate memory impairment in patients with Alzheimer's disease. However, further research, especially on the toxicity of laser acupuncture following repetitive exposure, is essential.

Animal models for metabolic, neuromuscular and ophthalmological rare diseases

Animal models are important tools in the discovery and development of treatments for rare diseases, particularly given the small populations of patients in which to evaluate therapeutic candidates. Here, we provide a compilation of mammalian animal models for metabolic, neuromuscular and ophthalmological orphan-designated conditions based on information gathered by the European Medicines Agency's Committee for Orphan Medicinal Products (COMP) since its establishment in 2000, as well as from a review of the literature. We discuss the predictive value of the models and their advantages and limitations with the aim of highlighting those that are appropriate for the preclinical evaluation of novel therapies, thereby facilitating further drug development for rare diseases.

Mice with selective elimination of striatal acetylcholine release are lean, show altered energy homeostasis and changed sleep/wake cycle

Cholinergic neurons are known to regulate striatal circuits; however, striatal-dependent physiological outcomes influenced by acetylcholine (ACh) are still poorly under;?>stood. Here, we used vesicular acetylcholine transporter (VAChT)(D2-Cre-flox/flox) mice, in which we selectively ablated the vesicular acetylcholine transporter in the striatum to dissect the specific roles of striatal ACh in metabolic homeostasis. We report that VAChT(D) (2-Cre-flox/flox) mice are lean at a young age and maintain this lean phenotype with time. The reduced body weight observed in these mutant mice is not attributable to reduced food intake or to a decrease in growth rate. In addition, changed activity could not completely explain the lean phenotype, as only young VAChT(D) (2-Cre-flox/flox) mice showed increased physical activity. Interestingly, VAChT(D) (2-Cre-flox/flox) mice show several metabolic changes, including increased plasma levels of insulin and leptin. They also show increased periods of wakefulness when compared with littermate controls. Taken together, our data suggest that striatal ACh has an important role in the modulation of metabolism and highlight the importance of striatum cholinergic tone in the regulation of energy expenditure. These new insights on how cholinergic neurons influence homeostasis open new avenues for the search of drug targets to treat obesity.

Purple rice berry is neuroprotective and enhances cognition in a rat model of Alzheimer's disease

Alzheimer's disease, a neurodegenerative disease characterized by progressive memory loss and cognitive impairment, is the most common type of dementia in aging populations due to severe loss of cholinergic neurons in a specific area. Oxidative stress is known to be involved in the pathogenesis of this condition. Therefore, the cognition-enhancing and neuroprotective effects of rice berry (Oryza sativa), a purple-pigmented rice that is rich in antioxidant substances, was evaluated. Young adult male Wistar rats, weighing 180-220 g, were orally given rice berry once daily at doses of 180, 360, and 720 mg/kg of body weight for a period of 2 weeks before and 1 week after the induction of memory deficit and cholinergic lesions with AF64A, a specific cholinotoxin, via bilateral intracerebroventricular administration. One week following AF64A administration the rats were evaluated for spatial memory, neuron density, acetylcholinesterase activity, and hippocampal lipid peroxidation products. Our results showed that rice berry could significantly prevent memory impairment and hippocampal neurodegeneration in hippocampus. Moreover, it also decreased hippocampal acetylcholinesterase activity and lipid peroxidation product formation. These results suggest that rice berry has potential as an effective agent for neurodegeneration and memory impairment in Alzheimer's disease.

Neurogenesis in Alzheimer's disease

It is widely acknowledged that neural stem cells generate new neurons through the process of neurogenesis in the adult brain. In mammals, adult neurogenesis occurs in two areas of the CNS: the subventricular zone and the subgranular zone of the dentate gyrus of the hippocampus. The newly generated cells display neuronal morphology, generate action potentials and receive functional synaptic inputs, their properties being equivalent to those of mature neurons. Alzheimer's disease (AD) is the widespread cause of dementia, and is an age-related, progressive and irreversible neurodegenerative disease that results in massive neuronal death and deterioration of cognitive functions. Here, we overview the relations between adult neurogenesis and AD, and try to analyse the controversies in the field. We also summarise recent data obtained in the triple transgenic model of AD that show time- and region-specific impairment of neurogenesis, which may account for the early changes in synaptic plasticity and cognitive impairments that develop prior to gross neurodegenerative alterations and that could underlie new rescue therapies.

Cognitive enhancement and neuroprotective effects of Bacopa monnieri in Alzheimer's disease model

ETHNOPHARMACOLOGICAL RELEVANCE

Bacopa monnieri (L.) Wettst., a plant belonging to the family Scrophulariaceae, has been used in the traditional system of Ayurvedic medicine to improve intelligence and memory for a long time. Therefore, the potential of this plant to protect against Alzheimer's disease has been raised but less supported document is available.

AIM OF THE STUDY

To determine the effect of alcoholic extract of Bacopa monnieri on cognitive function and neurodegeneration in animal model of Alzheimer's disease induced by ethylcholine aziridinium ion (AF64A).

MATERIALS AND METHODS

Male Wistar rats were orally given the alcoholic extract of Bacopa monnieri at doses of 20, 40 and 80 mg/kg BW via feeding needle for a period of 2 weeks before and 1 week after the intracerebroventricular administration of AF64A bilaterally. Rats were tested for spatial memory using Morris water maze test and the density of neurons and cholinergic neurons was determined using histological techniques 7 days after AF64A administration.

RESULTS

Bacopa monnieri extract improved the escape latency time (p<.01) in Morris water maze test. Moreover, the reduction of neurons and cholinergic neuron densities were also mitigated.

CONCLUSION

These findings suggest that Bacopa monnieri is a potential cognitive enhancer and neuroprotectant against Alzheimer's disease.

Piperine, the main alkaloid of Thai black pepper, protects against neurodegeneration and cognitive impairment in animal model of cognitive deficit like condition of Alzheimer's disease

Recently, numerous medicinal plants possessing profound central nervous system effects and antioxidant activity have received much attention as food supplement to improve cognitive function against cognitive deficit condition including in Alzheimer's disease condition. Based on this information, the effect of piperine, a main active alkaloid in fruit of Piper nigrum, on memory performance and neurodegeneration in animal model of Alzheimer's disease have been investigated. Adult male Wistar rats (180-220 g) were orally given piperine at various doses ranging from 5, 10 and 20mg/kg BW at a period of 2 weeks before and 1 week after the intracerebroventricular administration of ethylcholine aziridinium ion (AF64A) bilaterally. The results showed that piperine at all dosage range used in this study significantly improved memory impairment and neurodegeneration in hippocampus. The possible underlying mechanisms might be partly associated with the decrease lipid peroxidation and acetylcholinesterase enzyme. Moreover, piperine also demonstrated the neurotrophic effect in hippocampus. However, further researches about the precise underlying mechanism are still required.

Overview on rodent models of Alzheimer's disease

In Alzheimer's disease (AD), characteristic lesions develop in brain regions that subserve cognitive functions, ultimately leading to dementia. There are now several lesioned or transgenic small-animal models of the disease that model select aspects of cognitive deficits and/or recapitulate many, but not all, of the characteristic pathologic lesions observed in AD. This overview describes the most common approaches used to model AD in rodents, highlights their utility, and discusses some of their deficiencies.

Low intracerebroventricular doses of cholinotoxin AF64A do not affect the morphology of gonadotropin hormone-releasing hormone (GnRH)-immunoreactive fibers in the rat septum

Ethylcholine aziridinium (AF64A) induces cholinergic lesion in animal models of AD. Although higher concentrations of AF64A are known to induce nonspecific, cholinergic, and non-cholinergic lesions, low concentrations are believed to be selectively cholinotoxic. However, morphological evidence of this phenomenon has not been demonstrated yet. The present study demonstrates that while AF64A damaged septal cholinergic fibers, periventricular GnRH-immunoreactive fibers remained intact, confirming the highly selective cholinotoxicity of AF64A at appropriate concentrations.

Glycosaminoglycan C3 protects against AF64A-induced cholinotoxicity in a dose-dependent and time-dependent manner

Several studies revealed that proteoglycans (PGs) and glycosaminoglycans (GAGs) play a pivotal role in the pathogenesis of Alzheimer's disease (AD). PGs have affinity to amyloid beta (Abeta) and protect it against proteolysis, and the consequent aggregation is the cause of neurotoxicity. This effect is believed to be attenuated by GAGs. Moreover, a low-molecular-weight GAG C3 derived from unfractionated heparin has been reported to protect against Abeta-induced tau-2 immunoreactivity and cholinergic damage induced by a cholinotoxin, AF64A, in rat. However, the optimal dose and the timeframe of administration of C3 are still unknown. In our studies, we revealed the concentration-dependent and time-dependent effects of C3 on AF64A-induced cholinergic lesion in rat. C3 was administered orally in 5, 10, and 25 mg/kg/day concentration, 7 days before and/or 7 days after intracerebroventricular (i.c.v.) AF64A administration. Our results have shown that 25 mg/kg/day C3 effectively protects against AF64A-generated cholinotoxicity if administered both 7 days before and 7 days after the AF64A injection. In contrast to these findings, administration of 5 or 10 mg/kg/day C3 or 25 mg/kg/day C3, given 7 days before or 7 days after stereotaxic AF64A injection, did not show cholinoprotective effects. In conclusion, the time-dependent effects of C3 on AF64A-induced cholinergic lesion suggest that C3 may act via the processes of both neuroprotection and neurorepair. Moreover, the effects of C3 depend largely on the administered dose of this low-molecular-weight GAG. The present findings also indicate that C3, administered in the effective concentration and timeframe, may play a pivotal role in the treatment of AD.

Protection against inflammatory neurodegeneration and glial cell death by 7β-hydroxy epiandrosterone, a novel neurosteroid

It has been demonstrated that neuroprotective effects of dehydroepiandrosterone (DHEA) may be mediated by its 7alpha- and 7beta-hydroxy derivatives. Epiandrosterone is also converted to 7beta-hydroxy epiandrosterone (7beta-OH EPIA) in numerous tissues. The aim of the present study was to establish whether treatment with 7beta-hydroxy epiandrosterone has a neuroprotective effect in animal models of Alzheimer's disease (AD) lesions. Intra-amygdaloid administration of amyloid beta [Abeta(25-35)] increased the number of tau-positive cells in the ipsilateral hippocampus. Intracerebroventricular administration of ethylcholine aziridinium (AF64A) caused cholinergic damage in the septum, and glial lesions in the lateral septal nucleus and in the lateral zones of the hippocampus. These effects were almost completely prevented when animals were treated subcutaneously (b.i.d.) for 10 days with 0.1 mg/kg 7beta-hydroxy epiandrosterone. These findings indicate that 7beta-hydroxy epiandrosterone has powerful cytoprotective effects suggesting that (a) this neurosteroid may have therapeutic potential in various neurodegenerative conditions such as Alzheimer's disease, and (b) 7beta-hydroxy steroids may constitute a novel class of endogenous neuroprotective agents.

Protective effect of the heparin-derived oligosaccharide C3, on AF64A-induced cholinergic lesion in rats

Alzheimer's disease (AD) literature indicates that glycosaminoglycans (GAGs) may prevent proteoglycan-induced amyloid-beta (Abeta) aggregation, decrease Abeta-induced tau-2 immunoreactivity, and increase the axonal growth and arborization of hippocampal neurons. However, there is no information about the impact of GAGs on cholinergic lesions. Here, AF64A was administered stereotaxically into the lateral ventricles of rats, at doses that are selective for cholinotoxicity (1 and 2 nmol). The heparin-derived oligosaccharide (HDO), C3 (25mg/kg), was administered orally, once daily for 7 days before, and 7 days after AF64A administration. Choline acetyltransferase (ChAT) immunohistochemistry revealed that C3 administration reduced AF64A-induced cholinergic damage in the septum and cingulum bundle. Quantitative neuronal cell counts showed that C3 attenuated, by 60%, the decrease in cell number in the medial septum. Enzyme analysis showed that C3 also significantly restored ChAT (30%) and acetylcholinesterase (AChE) enzyme activity (45%), which had been diminished by AF64A. Our data suggest that, in addition to its effects of anti-Abeta aggregation, anti-Abeta-induced tau-2 immunoreactivity, and neurotrophic effects, C3 also effectively reduces AF64A-induced cholinergic damage; hence it may have potential therapeutic value in AD patients.

Role of NAD(P)H:quinone oxidoreductase in the progression of neuronal cell death in vitro and following cerebral ischaemia in vivo

A direct involvement of the antioxidant enzyme NAD(P)H:quinone oxidoreductase (NQO1) in neuroprotection has not yet been shown. The aim of this study was to examine changes, localization and role of NQO1 after different neuronal injury paradigms. In primary cultures of rat cortex the activity of NQO1 was measured after treatment with ethylcholine aziridinium (AF64A; 40 micro m), inducing mainly apoptotic cell death, or oxygen-glucose deprivation (OGD; 120 min), which combines features of apoptotic and necrotic cell death. After treatment with AF64A a significant NQO1 activation started after 24 h. Sixty minutes after OGD a significant early induction of the enzyme was observed, followed by a second increase 24 h later. Enzyme activity was preferentially localized in glial cells in control and injured cultures, however, expression also occurred in injured neuronal cells. Inhibition of the NQO1 activity by dicoumarol, cibacron blue or chrysin (1-100 nM) protected the cells both after exposure to AF64A or OGD as assessed by the decreased release of lactate dehydrogenase. Comparable results were obtained in vivo using a mouse model of focal cerebral ischaemia. Dicoumarol treatment (30 nmol intracerebroventricular) reduced the infarct volume by 29% (p = 0.005) 48 h after the insult. After chemical induction of NQO1 activity by t-butylhydroquinone in vitro neuronal damage was exaggerated. Our data suggest that the activity of NQO1 is a deteriorating rather than a protective factor in neuronal cell death.

The transport of choline

Choline has many physiological functions throughout the body that are dependent on its available local supply. However, since choline is a charged hydrophilic cation, transport mechanisms are required for it to cross biological membranes. Choline transport is required for cellular membrane construction and is the rate-limiting step for acetylcholine production. Transport mechanisms include: (1) sodium-dependent high-affinity uptake mechanism in synaptosomes, (2) sodium-independent low-affinity mechanism on cellular membranes, and (3) unique choline uptake mechanisms (e.g., blood-brain barrier choline transport). A comprehensive overview of choline transport studies is provided. This review article examines landmark and current choline transport studies, molecular mapping, and molecular identification of these carriers. Information regarding the choline-binding site is presented by reviewing choline structural analog (hemicholinium-3 and 15, and other nitrogen/methyl-hydroxyl compounds) inhibition studies. Choline transport in Alzheimer's disease, brain ischemic events, and aging is also discussed. Emphasis throughout the article is placed on targeting the choline transporter in disease and use of this carrier as a drug delivery vector.

Influences of cholinergic neurotoxin ethylcholine aziridinium ion on circadian rhythms in rats

To investigate whether damages of cholinergic neurons in the brain produce aging-like changes in circadian rhythms, we examined the influences of intracerebroventricular injection of cholinergic neurotoxin ethylcholine aziridinium ion (AF64A, 5 nmol/5 microl) on circadian rhythms in rats, by measuring locomotor activity and body temperature with the automatic behavioral measurement system combined with the telemetry. Daily rhythms in locomotor activity and body temperature were observed in AF64A-treated rats under a 12:12 h light:dark (LD) cycle, however, in AF64A-treated rats, the amplitude of activity and temperature rhythms was significantly decreased, the phase of the both rhythms was advanced and the amount of activity was decreased, compared with control rats. Locomotor activity and body temperature also showed a circadian rhythm in AF64A-treated rats under the constant dark condition with the period similar to that in the control rats. The present findings are in accordance with the observation in aged animals in which cholinergic hypofunction are often observed, suggesting that hypofunctions of the cholinergic systems in the brain might be involved in aging-like changes in the circadian rhythms.

Serotonergic lesion of median raphe nucleus alters nerve growth factor content and vulnerability of cholinergic septohippocampal neurons in rat

About 45% of the serotonergic raphe neurons are reported to express nerve growth factor (NGF) receptors. We therefore investigated whether selective serotonergic lesions of the median or dorsal raphe nuclei are associated with changes in NGF protein levels of the brain and whether the loss of serotonergic function alters the vulnerability of cholinergic septohippocampal neurons. In adult rats the hippocampal NGF content changed in a biphasic way after lesion of the median raphe nucleus by 5,7-dihydroxytryptamine (5,7-DHT), with a significant increase after 2-3 weeks of up to 35%, followed by a significant reduction of 22% below control levels after 7 weeks, and a return to control levels within the following 4 weeks. By contrast, the decrease in hippocampal serotonin and 5-hydroxyindoleacetic acid remained throughout the observation period of 11 weeks, being still reduced to 15 and 30% of the control levels, respectively. In the frontal cortex the partial loss of the serotonergic innervation projecting from the median raphe was associated 5 weeks after 5,7-DHT injection with an increase in NGF protein of 39.7+/-9.6% (P<0.05), which remained elevated up to 11 weeks. At 9 weeks after 5,7-DHT, the lesion of the septohippocampal cholinergic neurons induced by the cholinotoxin ethylcholine aziridinium (AF64A) was exaggerated (P<0.05) as compared to AF64A-treated rats with intact serotonergic innervation. The present data indicate that a serotonergic lesion of the median raphe nucleus results in biphasic changes of NGF protein content and in a delayed increase in the vulnerability of septohippocampal cholinergic neurons.

Selective antibody-induced cholinergic cell and synapse loss produce sustained hippocampal and cortical hypometabolism with correlated cognitive deficits

The physiological interrelationships between cognitive impairments, neurotransmitter loss, amyloid processing and energy metabolism changes in AD, cholinergic dementia and Down's syndrome are largely unknown to date. This report contains novel studies into the association between cognitive function and cerebral metabolism after long-term selective CNS cholinergic neuronal and synaptic loss in a rodent model. We measured local cerebral rates of glucose utilization ((14)C-2-deoxyglucose) throughout the brains of awake rats 4.5 months after bilateral intraventricular injections of a cholinotoxic antibody directed against the low-affinity NGF receptor (p75 NGF) associated with cholinergic neurons (192 IgG-saporin). Permanent cholinergic synapse loss was demonstrated by [(3)H]-vesamicol in vitro autoradiography defining presynaptic vesicular acetylcholine (ACh) transport sites. While other metabolic studies have defined acute and transient glucose use changes after relatively nonspecific lesions of anatomical regions containing cholinergic neurons, our results show sustained reductions in glucose utilization in brain regions impacted by cholinergic synapse loss, including frontal cortical and hippocampal regions, relative to glucose use levels in control rats. In the same animals, impaired cognitive spatial performance in a Morris water maze was correlated with reduced glucose use rates in the cortex and hippocampus at this time point, which is consistent with increased postmortem cortical and hippocampal amyloid precursor protein (APP) levels (45, 46). These results are consistent with the view of cholinergic influence over metabolism, APP processing, and cognition in the cortex and hippocampus.

Differential mechanisms of neuroprotection by 17 beta-estradiol in apoptotic versus necrotic neurodegeneration

The major goal of this study was to compare mechanisms of the neuroprotective potential of 17 beta-estradiol in two models for oxidative stress-independent apoptotic neuronal cell death with that in necrotic neuronal cell death in primary neuronal cultures derived from rat hippocampus, septum, or cortex. Neuronal apoptosis was induced either by staurosporine or ethylcholine aziridinium (AF64A), as models for necrotic cell death glutamate exposure or oxygen-glucose deprivation (OGD) were applied. Long-term (20 hr) pretreatment (0.1 microm 17 beta-estradiol) was neuroprotective in apoptotic neuronal cell death induced by AF64A (40 microm) only in hippocampal and septal neuronal cultures and not in cortical cultures. The neuroprotective effect was blocked by the estrogen antagonists ICI 182,780 and tamoxifen and the phosphatidylinositol 3-kinase (PI3-K) inhibitor LY294002. In glutamate and OGD-induced neuronal damage, long-term pretreatment was not effective. In contrast, short-term (1 hr) pretreatment with 17 beta-estradiol in the dose range of 0.5-1.0 microm significantly reduced the release of lactate dehydrogenase and improved morphology of cortical cultures exposed to glutamate or OGD but was not effective in the AF64A model. Staurosporine-induced apoptosis was not prevented by either long- or short-term pretreatment. The strong expression of the estrogen receptor-alpha and the modulation of Bcl proteins by 17 beta-estradiol in hippocampal and septal but not in cortical cultures indicates that the prevention of apoptotic, but not of necrotic, neuronal cell death by 17 beta-estradiol possibly depends on the induction of Bcl proteins and the density of estrogen receptor-alpha.

Neuroprotective and cognition-enhancing properties of MK-801 flexible analogs. Structure-activity relationships

Neuroprotective and biobehavioral properties of a series of novel open chain MK-801 analogs, as well as their structure-activity relationships have been investigated. Three groups of compounds were synthesized: monobenzylamino, benzhydrylamino, and dibenzylamino (DBA) analogs of MK-801. It was revealed that DBA analogs exhibit pronounced glutamate-induced calcium uptake blocking properties and anti-NMDA activity. The hit compound of DBA series, NT-1505, was investigated for its ability to improve cognition functions in animal model of Alzheimer's disease type dementia, simulated by treating animals with cholinotoxin AF64A. The results from an active avoidance test and a Morris water maze test showed that experimental animals, treated additionally with NT-1505, exhibited much better learning ability and memory than the control group (AF64A treated) and close to that of the vehicle group of animals (treated with physiological solution). Study of NT-1505 influence on locomotor activity revealed that it is characterized by a spectrum of behavioral activity radically different from that of MK-801, and in contrast to the latter one does not produce any psychotomimetic side effects in the therapeutically significant dose interval. The computed docking of MK-801 and its flexible analogs on the NMDA receptor elucidated the crucial role of the hydrogen bond formed between these compounds and the asparagine residue for magnesium binding in the NMDA receptor. It was suggested that strong hydrophobic interaction between MK-801 and the hydrophobic pocket in the NMDA receptor-channel complex determines much higher irreversibility of this adduct compared to the intermediates formed between this site and Mg ions or flexible DBA derivatives, which might explain the absence of PCP-like side effects of the latter compounds.

Glucocorticoid hypersecretion following intracerebroventricular injection of ethylcholine mustard aziridinium ion in rats

To investigate whether cholinergic hypofunctions in the brain influence hypothalamic-pituitary-adrenal activity, we examined the effects of cholinergic neurotoxin ethylcholine mustard aziridinium ion on basal and stress-induced levels of corticosterone in rats. Blood sampling from rats following intracerebroventricular injection of saline (5 microl, as a control) or this neurotoxin (5 nmol/5 microl) was performed over a day in one series, and was taken before, during and after an immobilization stress exposure in another series. Plasma levels of corticosterone and adrenocorticotropin were determined by the radioimmunoassay. The basal levels of plasma corticosterone and adrenocorticotropin over a day were significantly higher in the neurotoxin-treated rats, compared with the control rats (corticosterone, P<0.001; adrenocorticotropin, P<0.05). Further, relative adrenal gland weight of the neurotoxin-treated rats was significantly greater than that of the control rats (P<0.05). However, responses in plasma corticosterone level caused by the immobilization stress in the neurotoxin-treated rats were not different from those in the control rats. The present study demonstrated that damage to the cholinergic neurons in the brain increased hypothalamic-pituitary-adrenal activity over a day, probably due to freedom from inhibitory influences of the hippocampal cholinergic system, but that this damage did not influence stress-induced changes in plasma glucocorticoid level.

The role of acetylcholine in cortical synaptic plasticity

This review examines the role of acetylcholine in synaptic plasticity in archi-, paleo- and neocortex. Studies using microiontophoretic application of acetylcholine in vivo and in vitro and electrical stimulation of the basal forebrain have demonstrated that ACh can produce long-lasting increases in neural responsiveness. This evidence comes mainly from models of heterosynaptic facilitation in which acetylcholine produces a strengthening of a second, noncholinergic synaptic input onto the same neuron. The argument that the basal forebrain cholinergic system is essential in some models of plasticity is supported by studies that have selectively lesioned the cholinergic basal forebrain. This review will examine the mechanisms whereby acetylcholine might induce synaptic plasticity. It will also consider the neural circuitry implicated in these studies, namely the pathways that are susceptible to cholinergic plasticity and the neural regulation of the cholinergic system.

Melatonin is protective in necrotic but not in caspase-dependent, free radical-independent apoptotic neuronal cell death in primary neuronal cultures

To assess the neuroprotective potential of melatonin in apoptotic neuronal cell death, we investigated the efficacy of melatonin in serum-free primary neuronal cultures of rat cortex by using three different models of caspase-dependent apoptotic, excitotoxin-independent neurodegeneration and compared it to that in necrotic neuronal damage. Neuronal apoptosis was induced by either staurosporine or the neurotoxin ethylcholine aziridinium (AF64A) with a delayed occurrence of apoptotic cell death (within 72 h). The apoptotic component of oxygen-glucose deprivation (OGD) unmasked by glutamate antagonists served as a third model. As a model for necrotic cell death, OGD was applied. Neuronal injury was quantified by LDH release and loss of metabolic activity. Although melatonin (0.5 mM) partly protected cortical neurons from OGD-induced necrosis, as measured by a significant reduction in LDH release, it was not effective in all three models of apoptotic cell death. In contrast, exaggeration of neuronal damage by melatonin was observed in native cultures as well as after induction of apoptosis. The present data suggest that the neuroprotectiveness of melatonin strongly depends on the model of neuronal cell death applied. As demonstrated in three different models of neuronal apoptosis, the progression of the apoptotic type of neuronal cell death cannot be withhold or is even exaggerated by melatonin, in contrast to its beneficial effect in the necrotic type of cell death.

Role of nitric oxide in the ethylcholine aziridinium model of delayed apoptotic neurodegeneration in vivo and in vitro

The involvement of nitric oxide in neurodegenerative processes still remains incompletely characterized. Although nitric oxide has been reported to be an important mediator in neuronal degeneration in different models of cell death involving NMDA-receptor activation, increasing evidence for protective mechanisms has been obtained. In this study the role of nitric oxide was investigated in a model of NMDA-independent, delayed apoptotic cell death, induced by the neurotoxin ethylcholine aziridinium ethylcholine aziridinium both in vivo and in vitro. For the in vivo evaluation rats received bilateral intracerebroventricular injections of ethylcholine aziridinium (2nmol/ventricle) or vehicle. In the hippocampus a transient decrease in nitric oxide synthase activity occurred, reaching its lowest levels three days after ethylcholine aziridinium treatment (51.7+/-9.8% of controls). The decrease coincided with the maximal reduction in choline acetyltransferase activity as marker for the extent of cholinergic lesion. The effect of pharmacological inhibition of nitric oxide synthase was tested by application of various nitric oxide synthase inhibitors with different selectivity for the nitric oxide synthase-isoforms. Unspecific nitric oxide synthase inhibition resulted in a significant potentiation of the loss of choline acetyltransferase activity in the hippocampus measured seven days after ethylcholine aziridinium application, whereas the specific inhibition of neuronal or inducible nitric oxide synthase was ineffective. These pharmacological data are suggestive for a neuroprotective role of nitric oxide generated by endothelial nitric oxide synthase. In vitro experiments were performed using serum-free primary neuronal cell cultures from hippocampus, cortex and septum of E15-17 Wistar rat embryos. Ethylcholine aziridinium-application in a range of 5-80microM resulted in delayed apoptotic neurodegeneration with a maximum after three days as confirmed by morphological criteria, life-death assays and DNA laddering. Nitric oxide synthase activity in harvested cells decreased in a dose- and time-dependent manner. Nitric oxide production as determined by measurement of the accumulated metabolite nitrite in the medium was equally low in controls and in ethylcholine aziridinium treated cells (range 0.77-1.86microM nitrite). An expression of inducible nitric oxide synthase messenger RNA could not be detected by semiquantitative RT-PCR 13h after ethylcholine aziridinium application. The present data indicate that in a model of delayed apoptotic neurodegeneration as induced by ethylcholine aziridinium neuronal cell death in vitro and in vivo is independent of the cytotoxic potential of nitric oxide. This is confirmed by a decrease in nitric oxide synthase activity, absence of nitric oxide production and absence of inducible nitric oxide synthase expression. In contrast, evidence for a neuroprotective role of nitric oxide was obtained in vivo as indicated by the exaggeration of the cholinergic lesion after unspecific nitric oxide synthase inhibition by N-nitro-L-arginine methylester.

Accumbens cholinergic interneurons play a role in the regulation of body weight and metabolism

The aims of the present study were (1) to determine whether selective lesions of the accumbens cholinergic interneurons impair feeding and body weight regulation, and (2) to characterize the nature of disturbances using motivational and metabolic challenges. Rats with bilateral cholinotoxic (AF64A) lesions in the nucleus accumbens showed a significant and lasting lag in body weight gain in comparison to the sham-operated controls. This failure to gain weight was not due to a decrease in feeding because lesioned rats actually ate more food and drank more water than controls under basal conditions. Lesion-induced deficits were also exposed when the rats were challenged with food deprivation or cold exposure. Lesioned rats ate less than controls when 24 h food deprived and maintained both a higher core temperature and a higher metabolic rate than controls following either 24-h food deprivation or exposure to cold. Thyroid hormones, insulin, and blood glucose levels were, however, within the physiological range, and no sensory and motor disturbances were observed. The results suggest that the altered body weight regulation is partly due to the enhanced metabolic responsiveness to stress. Possible explanations for the effects of the lesions are also discussed in the context of motivational alterations, including possible dopamine-acetylcholine interactions.

Dimebon improves learning in animals with experimental Alzheimer's disease

Systemic administration of antihistamine drug dimebon improves active avoidance conditioning in rats with chronic partial deprivation of cerebral cholinergic functions caused by intracerebroventricular injections of AF64A. The effects of dimebon on learning are similar to those of tacrine used in the treatment of Alzheimer's disease.

Molecular analysis of non-specific supersensitivity induced by AF64A in rat iris smooth muscle

Characteristics of supersensitivity induced by the pretreatment with AF64A, an inhibitor of choline uptake at parasympathetic nerve endings, were examined in rat iris sphincter. In preparations isolated and skinned by beta-escin after the micro injection of AF64A to eyes in vivo, the amplitude of maximum contraction in pCa 4.5 solution was increased by 180% of the control from the contralateral eyes. The Ca2+ sensitivity of the contractile system was slightly but significantly increased by AF64A injection; the half maximum contraction was obtained at pCa 5.87 and 6.05 in the control and AF64A-injected eyes, respectively. The increase in maximum contraction in AF64A injected ones was neither affected by the addition of calmodulin, GTPgammaS nor H-7. The increase in Ca2+ sensitivity by AF64A injection was not affected by calmodulin, enhanced by GTPgammaS and abolished by H-7. AF64A injection increased the total protein content only by 30% of the control. The contents of contractile proteins per iris were quantified using Western blotting with monoclonal antibodies. The contents of actin and calponin were increased by AF64A, whereas those of myosin, calmodulin and caldesmon were not affected. The results indicate that AF64A-induced enhancement of the maximum contraction is not mainly due to the increase in the contents of major contractile proteins and that the increase in Ca2+ sensitivity could be due to the mechanism in which changes in protein kinase C and/or GTP binding protein activity are involved.

Bis(7)-tacrine, a novel acetylcholinesterase inhibitor, reverses AF64A-induced deficits in navigational memory in rats

The novel dimer bis(7)-tacrine (1,7-N-Heptylene-bis-9,9'-amino-1,2,3, 4-tetrahydroacridine), which exhibits higher potency, selectivity and oral activity on acetylcholinesterase inhibition in vivo than tacrine, was evaluated for its ability to reverse AF64A-induced spatial memory impairment in rats using the Morris water maze. The intracerebroventricular injection of AF64A (3 nmol/side) resulted in a substantial increase in the escape latency to find the platform (F(1,7)=30.2, P<0.01). The observed impairment of spatial memory was paralleled by a 47% decrease in choline acetyltransferase activity in the hippocampus. Oral administration of bis(7)-tacrine (0.22-0.89 micromol/kg) dose-dependently reversed the AF64A-induced latency delay to the level of the saline control group (F(4,28)=7.45, P<0. 05). The present study provides additional evidence of bis(7)-tacrine as an ideal candidate for the palliative treatment of Alzheimer's disease.

Selective neurotoxins, chemical tools to probe the mind: the first thirty years and beyond

For centuries, starting with the advent of the microscope, cytotoxins have been known to non-selectively destroy nerves and other tissue cells. However, neurotoxins restricted in effect to one kind of neuron are an invention of the 20th century. One might reasonably trace the origins of this field to 1960 when the Nobel Laureates, R. Levi- Montalcini and S Cohen, showed that an antibody to nerve growth factor effectively prevented development of sympathetic nerves in the absence of overt changes in dorsal root ganglia and other neural and non-neural tissues. The year 1967 marks discovery of 6-hydroxydopamine, the first of dozens of chemically-selective neurotoxins. As stated by the physiologist W.B. Cannon, neural function can be deduced by denoting absence-deficits. A wealth of knowledge in neuroscience has been realized through use of neurotoxins. In the 21st century we foresee neurotoxins for virtually all neurochemically-identifiable or receptor-specific neurons, acting at/via functional proteins or characteristic DNA sites. These tools will provide us with a better means to probe the mind and thereby lead to a fuller understanding of the intricate roles of identifiable neuronal systems in integrative neuroscience.

Involvement of cholinergic and GABAergic systems in the reversal of memory disruption by NS-105, a cognition enhancer

The effects of (+)-5-oxo-D-prolinepiperidinamide monohydrate (NS-105) on the scopolamine-, electrolytic lesion of the nucleus basalis magnocellularis (NBM)-, AF64A-, baclofen-, cerebral ischemia- and electroconvulsive shock (ECS)-induced memory disruption in the passive avoidance response or radial arm maze tasks were investigated in rats. The effects of NS-105 were compared with those of aniracetam, bifemelane, idebenone, and indeloxazine in two tasks of the passive avoidance response. Furthermore, effects of NS-105 on in vivo release of acetylcholine (ACh) in the cerebral cortex, high-affinity choline uptake (HACU) of the cerebral cortex in rats with lesion of NBM, HACU of the hippocampus in rats treated with pentobarbital and activity of choline acetyltransferase (ChAT) of the cerebral cortex in rats with lesion of NBM were examined. NS-105 showed antiamnestic actions in a variety of animal models of cholinergic dysfunction employed in this study. Aniracetam improved memory disruption caused by scopolamine, but bifemelane, idebenone, and indeloxazine did not. NS-105 (10 mg/kg) showed the increase of ACh release from the cerebral cortex and the enhancement of HACU both in the cerebral cortex and hippocampus, but showed no change in activity of ChAT. NS-105 also reversed memory disruption induced by baclofen, a potent GABA(B) receptor agonist, but all of reference drugs did not. These results suggest that antiamnestic action of NS-105 is due to the facilitation of cholinergic neuronal activity and the suppression of GABA(B) receptor-mediated responses.

Effects of AF64A on gene expression of choline acetyltransferase (ChAT) in the septo-hippocampal pathway and striatum in vivo

AF64A (ethylcholine mustard aziridinium ion) was stereotaxically administered bilaterally (1 nmol/side) into rat lateral cerebral ventricles. Choline acetyltransferase (ChAT) activity and ChAT mRNA levels were measured at predetermined time points in the septo-hippocampal pathway and striatum, both well identified as rich in cholinergic neurons. AF64A caused a rapid but transient increase in ChAT mRNA (167%, P < 0.05) and ChAT activity (164%, P < 0.01) in the septum. By day 7 post treatment, there was a significant decrease in ChAT mRNA (42.5% of control, P < 0.05) in the septum although the ChAT activity still stayed high. This decreased ChAT mRNA level in the septum lasted for at least four weeks, and was paralleled by a long-lasting decrease in ChAT activity in the hippocampus. In the striatum, on the other hand, there were no observed changes in either ChAT activity or ChAT mRNA. These data suggest that the long term effect of AF64A on the septo-hippocampal cholinergic pathway may, at least in part, be due to an action of AF64A on gene expression in the cholinergic neuron. The difference in the response to AF64A between the septo-hippocampal and striatal cholinergic systems might be due to their difference in neuron types.

Long term changes in brain cholinergic markers and nerve growth factor levels after partial immunolesion

There are deficits in cholinergic basal forebrain neurons (CBFNs) in the aged brain and patients suffering Alzheimer's disease associated with a partial loss of the CBFNs. To mimic this partial loss and assess its long term effects on residual cholinergic activity and resultant target-derived nerve growth factor (NGF) levels, we produced a partial immunolesion to CBFNs with 192 IgG-saporin, an immunotoxin selectively taken up by p75NTR-bearing neurons. We measured two cholinergic markers, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity, and NGF protein levels at 10 days, 1, 6 and 12 months postlesion. There were no significant changes in the cholinergic markers and the NGF protein levels in the sham-treated animal controls during the one year experiment. Ten days after 192 IgG-saporin treatment, ChAT activity decreased to 35-50% of controls in the olfactory bulb, hippocampus, and cortex. There was a minor but significant recovery of ChAT activity one year after the immunolesion in the hippocampus. Changes in AChE activity mirrored the ChAT changes but were less robust. There were transient increases in NGF protein levels in the hippocampus and cortex that returned to basal levels at 6 months and 12 months postlesion, respectively. In summary, partial immunolesions resulted in partial region-specific and time-dependent recoveries of cholinergic activity in the target areas of the basal forebrain after a partial elimination of CBFNs and a return to basal levels of NGF protein consistent with the hypothesis that the remaining CBFNs compensated for losses of ChAT and NGF due to changes in cholinergic innervation of basal forebrain target areas.

Cholinergic amacrine cells are not required for the progression and atropine-mediated suppression of form-deprivation myopia

Muscarinic cholinergic pathways have been implicated in the visual control of ocular growth. However, the source(s) of acetylcholine and the tissue(s) which regulate ocular growth via muscarinic acetylcholine receptors (mAChRs) remain unknown. We sought to determine whether retinal sources of acetylcholine and mAChRs contribute to visually guided ocular growth in the chick. Cholinergic amacrine cells were ablated by intraocular injections of either ethylcholine mustard aziridinium ion (ECMA; a selective cholinotoxin) or quisqualic acid (QA; an excitotoxin that destroys many amacrine cells, including those that release acetylcholine). Disruption of cholinergic pathways was assessed immunocytochemically with antibodies to the acetylcholine-synthesizing enzyme choline acetyltransferase (ChAT) and three different isoforms of mAChR, and by biochemical assay for ChAT activity. ECMA (25 nmol) destroyed two of the four subtypes of cholinergic amacrine cells and attenuated retinal ChAT activity, but left retinal mAChR-immunoreactivity intact. QA (200 nmol) destroyed the majority of all four subtypes of cholinergic amacrine cells, and ablated most mAChR-immunoreactivity and ChAT activity in the retina. ECMA and QA had no apparent effect on mAChRs or cholinergic fibres in the choroid, only marginally reduced choroidal ChAT activity, and had little effect on ChAT activity in the anterior segment. Toxin-treated eyes remained emmetropic and responded to form-deprivation by growing excessively and becoming myopic. Furthermore, daily intravitreal injection of 40 microg atropine for 6 days into form-deprived toxin-treated eyes completely prevented ocular elongation and myopia. We conclude that neither cholinergic amacrine cells nor mAChRs in the retina are required for visual regulation of ocular growth, and that atropine may exert its growth-suppressing influence by acting upon extraretinal mAChRs, possibly in the choroid, retinal pigmented epithelium, or sclera.

Invited review: Anticholinesterases: dramatic aspects of their use and misuse

While the lore of anticholinesterases (antiChEs), particularly physostigmine and its natural source, the Calabar bean, is a subject of ethnomedicine and predates our scientific era, the pharmacological development of physostigmine analogues and related agents and of the antiChEs of the organophosphorus (OP) type, is a matter of the last two centuries; this development has reached an exponential character in the last fifty years. This explosion relates to certain uses and misuses of these drugs and this aspect of antiChEs is the main focus of this article. Firstly, there is the matter of Senile Dementia of Alzheimer's Type (SDAT); while there are several clinical applications of antiChEs, their employment in the treatment of SDAT is the last and most intense foray in their medical history and this article will focus on the uses and misuses of antiChEs in this area. Secondly, the applied use of antiChEs as insecticides which coincided with the historical development of OP antiChEs was and is, of major significance for the agricultural economy of both advanced and underdeveloped countries, as this employment may mean the difference between life and starvation. However, there are notable dangers with this application of OP drugs, as will be emphasized in this article. Thirdly, there is the significant and tragic development of the OP drugs as warfare agents and tools for terrorists and rogue states and this article will discuss the several types of toxicity of OP agents and their mechanisms, the enigma of the Persian Gulf War Syndrome being particularly stressed. Altogether, the immense range of antiChE topics includes areas of great basic interest and of practical applications that are of significant benefit to mankind as well as of potential danger.

Effects of tacrine on deficits in active avoidance performance induced by AF64A in rats

Effects of tacrine (1,2,3,4-tetrahydro-9-aminocridine) on memory deficits in rats treated with ethylcholine aziridinium ion (AF64A) were studied using active avoidance test in the two-way shuttle box. Neurotoxin AF64A injected at a dose of 6 nmol (i.c.v., bilaterally) causes nonspecific tissue damage in hippocampal fields CA2 and CA3. Two weeks after treatment with 6 nmol, AF64A active avoidance performance of toxin-treated rats was significantly deteriorated compared to vehicle-treated animals estimated in learning test (68 +/- 3.5 and 83 +/- 3.2% of correct responses, respectively; p < 0.01) and in retention test (53 +/- 5 and 76 +/- 3.6%, respectively; p < 0.01). Under these conditions, chronic treatment with tacrine at a daily dose of 1 mg/kg for 12-14 d reverses the effect of AF64A on the active avoidance performance both in learning (78 +/- 3.2%) and retention (72 +/- 4%) tests. It is supposed that behavioral effects of tacrine considerably depend on a severity of neurodegeneration in the hippocampus.

Induction of apoptosis in vitro and in vivo by the cholinergic neurotoxin ethylcholine aziridinium

The patterns of cell death induced by the cholinergic neurotoxin ethylcholine aziridinium have been investigated in vitro and in vivo. In vitro, the drug induced apoptosis both in neuronal SK-N-MC cells (human neuroblastoma cells) and in non-neuronal 293 cells (a human embryonic kidney cell line). Apoptosis was developed maximally between 15 and 24 h of exposure to ethylcholine aziridinium (100 microM). At the ultrastructural level apoptotic cells were characterized by condensation and margination of nuclear chromatin, fragmentation of nuclei and the formation of apoptotic bodies. Inhibition of endonuclease by zinc almost completely prevented the occurrence of apoptosis. The free radical scavenger Tempol effectively inhibited ethylcholine aziridinium-induced apoptosis by 78.6 +/- 10.3% (n=4), whereas cycloheximide and actinomycin D were only partially effective. In vivo, following injection of ethylcholine aziridinium (2 nmol) into the lateral ventricle of rat brain a high incidence of apoptotic cells as verified by in situ tailing was visible in the periventricular tissue. Neurons as well as glia were affected by the neurotoxin. The number of apoptotic cells peaked two to three days after injection of ethylcholine aziridinium and declined thereafter. Up to one week after ethylcholine aziridinium no signs for the induction of apoptosis in the medial septal nucleus were found. This study provides clear evidence that a neurotoxic compound that induces programmed cell death in vitro is likely to have the same capacity in vivo. Yet, in the case of ethylcholine aziridinium, both the in vitro and the in vivo induction of programmed cell death appears to be an additional feature of ethylcholine aziridinium, which may be independent of the well-established degenerative effect of ethylcholine aziridinium on the cholinergic septohippocampal pathway. The present data indicate that ethylcholine aziridinium provides a useful tool to study molecular mechanisms of neuronal apoptosis.