Effect of hydroalcoholic Echium amoenum extract on scopolamine-induced learning and memory impairment in rats

CONTEXT

Scopolamine, a muscarinic receptor antagonist, causes memory loss that resembles Alzheimer's disease (AD). Echium amoenum L. (Boraginaceae) is a famous medicinal plant of Iran that is traditionally used as a sedative and mood enhancer.

OBJECTIVE

This study evaluates the effect of hydroalcoholic extract of E. amoenum flowers on scopolamine-induced memory impairment in rats.

MATERIALS AND METHODS

Fifty male Wistar rats were randomly divided into five groups. Control group received normal saline, model group received scopolamine (0.7 mg/kg, IP, daily for 21 days), and test groups received E. amoenum extract (50, 75, and 100 mg/kg, IP, daily for 21 days) 30 min before each scopolamine injection. The elevated plus maze (EPM), shuttle box, novel object and rotarod tests were performed after treatment. Brain levels of malondialdehyde (MDA) and total antioxidant capacity (TCA) were also determined.

RESULTS

Scopolamine-treated rats spent more time exploring the novel object compared to the control, and E. amoenum extract at all three doses significantly decreased the time spent exploring the novel object (p < 0.05). E. amoenum extract (75 and 100 mg/kg) significantly elongated the secondary latency in rats receiving scopolamine in the shuttle box test (p < 0.05). In addition, treatment with 75 and 100 mg/kg doses of E. amoenum extract significantly ameliorated scopolamine-induced motor in coordination in rotarod test (p < 0.05). It also significantly increased the time spent in the open arms and reduced the time spent in the closed arms of EPM (p < 0.05). Treatment of scopolamine-exposed rats with E. amoenum extract significantly increased TCA and reduced MDA level of brain (p < 0.05).

DISCUSSION AND CONCLUSIONS

E. amoenum extract shows protective effect against scopolamine-induced impairment and is suggested to be tested in clinical trials to evaluate the efficacy on AD.

Antimuscarinic-induced convulsions in fasted mice after food intake: No evidence of spontaneous seizures, behavioral changes or neuronal damage

Prolonged or repeated seizures have been shown to cause spontaneous recurrent seizures, increased anxiety‑related behavior, locomotor hyperactivity, impaired functions of learning and memory, and neuronal damage in the hippocampus and other brain regions in animals. Mice and rats treated with antimuscarinic drugs after fasting for two days or less develop convulsions after being allowed to eat ad libitum. To address whether such behavioral and neuroanatomic changes occur following these convulsions, mice treated i.p. with saline (control) or 2.4 mg/kg atropine and given food after 24 h of fasting were grouped according to seizure scores for behavioral and histological analysis. Following convulsions, the occurrence of spontaneous recurrent seizures was observed for 30 days. Motor activity and grooming behavior were assessed in the open field, and memory was assessed using the novel object recognition test 4 and 7 days after onset of convulsions, respectively. Animals allocated for the histological analysis were decapitated 7 days after onset of convulsions and hippocampal slices were evaluated for the percentage of degenerating neurons stained with Fluoro‑Jade C. Spontaneous recurrent seizures, locomotor alterations, anxiety‑related behavior, memory impairment, and neuronal loss in the granular layer of the dentate gyrus were not detected in the animals with seizure score 1-2 or 3-5. These results are in accordance with those related to the absence of behavioral changes, cognitive deficits, and hippocampal neuronal damage after single brief seizures in animals and patients with epilepsy.

Sesame indicum, a nutritional supplement, elicits antiamnesic effect via cholinergic pathway in scopolamine intoxicated mice

PURPOSE

Present study was undertaken to evaluate the antiamnesic effect of Sesamum indicum (S. indicum) seeds (standardized for sesamin, a lignan, content) in scopolamine, a muscarinic antagonist intoxicated mice.

METHODS

Male Swiss albino mice (18-22 g bw) were pretreated with methanolic extract of sesame seeds (MSSE) (100 and 200 mg/kg/day, p.o) for a period of 14 days. Scopolamine (0.3 mg/kg, i.p.) was injected on day 14, 45 ± 10 min after MSSE administration. Antiamnesic effect of MSSE was evaluated using step-down latency (SDL) on passive avoidance apparatus and transfer latency (TL) on an elevated plus maze. To unravel the mechanism of action, we examined the effects of MSSE on the genes such as acetyl cholinesterase (AChE), muscarinic receptor M1 subtype (mAChRM₁ ), and brain derived neurotrophic factor (BDNF) expression within hippocampus of experimental mice. Further, its effects on bax and bcl-2 were also evaluated. Histopathological examination of hippocampal CA₁ region was performed using cresyl violet staining.

RESULTS

MSSE treatment produced a significant and dose dependent increase in step down latency in passive avoidance test and decrease in transfer latency in elevated plus maze in scopolamine intoxicated injected mice. MSSE down-regulated AChE and mAChRM₁ and up-regulated BDNF mRNA expression. Further, it significantly down-regulated the bax and caspase 3 and up-regulated bcl-2 expression in scopolamine intoxicated mice brains. Mice treated with MSSE showed increased neuronal counts in hippocampal CA₁ region when compared with scopolamine-vehicle treated mice.

CONCLUSION

Sesame seeds have the ability to interact with cholinergic components involved in memory function/restoration and also an interesting candidate to be considered for future cognitive research. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1955-1963, 2016.

Antidiarrhoeal activity of aqueous leaf extract of Caladium bicolor (Araceae) and its possible mechanisms of action

ETHNOPHARMACOLOGICAL RELEVANCE

Caladium bicolor (Araceae) is a horticulture plant also used by some traditional medicine practitioners in the treatment of diarrhoea and other gastrointestinal disorders. This study was conducted to evaluate the antidiarrhoeal activity of the aqueous leaf extract of C. bicolor and its possible mechanisms of action in rodents.

MATERIALS AND METHODS

Normal and castor oil-induced intestinal transit and castor oil-induced diarrhoea tests were carried out in mice while gastric emptying and enteropooling tests were conducted in rats following the administration of distilled water (10 ml/kg, p.o.), C. bicolor extract (1-50mg/kg, p.o.) and loperamide (5mg/kg, p.o.). The probable mechanisms of action of C. bicolor was investigated following pre-treatment with yohimbine (10mg/kg, s.c.; α2-adrenoceptor antagonist), pilocarpine (1mg/kg, s.c.; non-selective muscarinic receptor agonist), prazosin (1mg/kg, s.c.; α1-adrenoceptor antagonist) and propranolol (1mg/kg, i.p.; non-selective β-adrenoceptor antagonist) 15 min prior to administration of C. bicolor extract (50mg/kg, p.o.). After 30 min of pre-treatment with these drugs, the mice were subjected to the castor oil-induced intestinal transit test.

RESULTS

C. bicolor extract did not produce significant (p>0.05) effect on normal intestinal transit unlike loperamide which caused significant (p<0.001) inhibition (61.57%). The extract caused significant (p<0.001) dose-dependent inhibition of castor oil-induced intestinal transit with peak effect, 100% inhibition, elicited at the dose of 50mg/kg compared to 86.97% inhibition for loperamide. Yohimbine and pilocarpine most significantly (p<0.001) reversed this effect of the extract. In the castor oil-induced diarrhoea test, the extract (1mg/kg) and loperamide significantly (p<0.05, 0.01) delayed the onset of diarrhoea. For diarrhoea score, the extract (1 and 50mg/kg) inhibited diarrhoea development (47.53% and 43.83% inhibition, respectively) like loperamide (5mg/kg; 54.94%). The in vivo antidiarrhoeal index of the extract at 1 and 50mg/kg was 50.07% and 42.81% respectively compared to 58.15% for loperamide.

CONCLUSIONS

The results obtained in this study suggest that the aqueous leaf extract of C. bicolor possess antidiarrhoeal activity due to its anti-motility effect possibly via antagonist action on intestinal muscarinic receptors and agonist action on intestinal α2-adrenoceptors. This justifies the use of the extract in traditional medicine for the treatment of diarrhoea.

The effects of Zibu Piyin Recipe components on scopolamine-induced learning and memory impairment in the mouse

ETHNOPHARMACOLOGICAL RELEVANCE

The Zibu Piyin Recipe (ZBPYR) is derived from Zicheng Decoction, a traditional Chinese medicine formula recorded in the book of Bujuji, written by Wu Cheng in the Qing dynasty and used for clinical treatment of amnesia. Our aim was to study the effects of Zibu Piyin Recipe (ZBPYR) fractions on scopolamine-induced learning and memory impairment in the mouse.

MATERIALS AND METHODS

Crude extracts were prepared using various solvents, and individual fractions produced following D101 macroporous resin column chromatography. The passive avoidance task, step down test and Morris water maze test were then performed in mice for the evaluation of learning and memory alterations. The effective fractions were then analyzed using GC-MS and polysaccharide measurement methods, respectively.

RESULTS

The treatment group latency for the alcohol precipitation from water part (EP) and 95% ethanol part (95%E) following D101 macroporous resin column chromatography was significantly prolonged when compared to that of the scopolamine treated groups for both the passive avoidance task and step down test. In the Morris water maze tests, treatment with EP and 95%E resulted in a significantly shorter escape latency time (from the fourth day and the second day) and swimming distance (on the third day and from the third day) in scopolamine-induced mice. In the memory retention test, treatment with EP and 95%E dramatically shortened the latency to cross platform location and increased the numbers of platform location crosses in the scopolamine-induced mice. The polysaccharide content in EP was determined to be 69.79%. The 95%E was found to mainly contain asarone, α-cadinol, isocalamendiol, 2,4,7,14-tetramethyl-4-vinyl-tricyclo[5.4.3.0(1,8)]tetradecan-6-ol, 3-isopropyl-6,7-dimethyltricyclo[4.4.0.0(2,8)]decane-9,10-diol, 2-methyl-9-(prop-1- -en-3-ol-2-yl)-bicyclo[4.4.0]dec-2-ene-4-ol, diepicedrene-1-oxide, 7-methoxy-6-(3- -methyl-2-oxobutyl)-2H-1-benzopyran-2-one and diisooctyl phthalate when assessed using GC-MS analysis.

CONCLUSION

These findings suggest that the polysaccharide and volatile oil present in ZBPYR exhibit ameliorating effects on scopolamine-induced memory dysfunction.

D-cycloserine in prelimbic cortex reverses scopolamine-induced deficits in olfactory memory in rats

A significant interaction between N-methyl-D-aspartate (NMDA) and muscarinic receptors has been suggested in the modulation of learning and memory processes. The present study further investigates this issue and explores whether d-cycloserine (DCS), a partial agonist at the glycine binding site of the NMDA receptors that has been regarded as a cognitive enhancer, would reverse scopolamine (SCOP)-induced amnesia in two olfactory learning tasks when administered into the prelimbic cortex (PLC). Thus, in experiment 1, DCS (10 µg/site) was infused prior to acquisition of odor discrimination (ODT) and social transmission of food preference (STFP), which have been previously characterized as paradigms sensitive to PLC muscarinic blockade. Immediately after learning such tasks, SCOP was injected (20 µg/site) and the effects of both drugs (alone and combined) were tested in 24-h retention tests. To assess whether DCS effects may depend on the difficulty of the task, in the STFP the rats expressed their food preference either in a standard two-choice test (experiment 1) or a more challenging three-choice test (experiment 2). The results showed that bilateral intra-PLC infusions of SCOP markedly disrupted the ODT and STFP memory tests. Additionally, infusions of DCS alone into the PLC enhanced ODT but not STFP retention. However, the DCS treatment reversed SCOP-induced memory deficits in both tasks, and this effect seemed more apparent in ODT and 3-choice STFP. Such results support the interaction between the glutamatergic and the cholinergic systems in the PLC in such a way that positive modulation of the NMDA receptor/channel, through activation of the glycine binding site, may compensate dysfunction of muscarinic neurotransmission involved in stimulus-reward and relational learning tasks.

Role of central angiotensin receptors in scopolamine-induced impairment in memory, cerebral blood flow, and cholinergic function

RATIONAL

Inhibition of renin-angiotensin system (RAS) improves cognitive functions in hypertensive patients. However, role of AT1 and AT2 receptors in memory impairment due to cholinergic hypofunction is unexplored.

OBJECTIVE

This study investigated the role of AT1 and AT2 receptors in cerebral blood flow (CBF), cholinergic neurotransmission, and cerebral energy metabolism in scopolamine-induced amnesic mice.

METHODS

Scopolamine was given to male Swiss albino mice to induce memory impairment tested in passive avoidance and Morris water maze tests after a week long administration of blocker of AT1 receptor, candesartan, and AT2 receptor, PD123, 319. CBF was measured by laser Doppler flowmetry. Biochemical and molecular studies were done in cortex and hippocampus of mice brain.

RESULTS

Scopolamine caused memory impairment, reduced CBF, acetylcholine (ACh) level, elevated acetylcholinesterase (AChE) activity, and malondialdehyde (MDA). Administration of vehicle had no significant effect on any parameter in comparison to control. Candesartan prevented scopolamine-induced amnesia, restored CBF and ACh level, and decreased AChE activity and MDA level. In contrast, PD123, 319 was not effective. However, the effect of AT1 receptor blocker on memory, CBF, ACh level, and oxidative stress was blunted by concomitant blockade of AT2 receptor. Angiotensin-converting enzyme (ACE) activity, ATP level, and mRNA expression of AT1, AT2, and ACE remained unaltered.

CONCLUSION

The study suggests that activation of AT1 receptors appears to be involved in the scopolamine-induced amnesia and that AT2 receptors contribute to the beneficial effects of candesartan. Theses finding corroborated the number of clinical studies that RAS inhibition in hypertensive patients could be neuroprotective.

Studies on effects of Emblica officinalis (Amla) on oxidative stress and cholinergic function in scopolamine induced amnesia in mice

Emblica officinalis, commonly known as amla, is an important medicinal plant of India. Its fruits have potent antioxidant activity due to the presence of tannoids, tannins, vitamin C and flavonoids. The aim of this study was to investigate the beneficial effect of the hydroalcoholic extract of the fruits of Emblica officinalis (EO) on memory impairment in Swiss albino mice. Scopolamine (1 mg kg(-1), i.p)was administered to induce amnesia and the memory was evaluated by using elevated plus-maze and passive avoidance tests. Piracetam (200 mg kg(-1), i.p.) was used as a standard nootropic agent. The EO extract was administered intraperitoneally in four graded doses (150, 300, 450 and 600 mg kg(-1)) for 7 consecutive days to different groups of mice. The mice were sacrificed on the 8th day following assessment of memory. The brain malondialdehyde (MDA) and glutathione (GSH) as well as acetylcholinesterase (AchE)) activity was determined. It was observed that EO extract reversed the amnesia induced by scopolamine. The mean transfer latency and retention latency in the EO extract 600 mg kg(-1) group vs the vehicle treated scopolamine group was 13.46 sec (p<0.001) and 134.4 sec (p<0.001) vs 23.99 sec and 44.55 sec, respectively. EO extract treatment also significantly (p<0.001) ameliorated the oxidative stress induced by scopolamine administration. The mice brain MDA and GSH levels in the EO extract 600 mg kg(-1) group vs the scopolamine group were 29.95 nmol g(-1) of wet tissue and 51.87 microg g(-1) tissue vs 55.22 nmol g(-1) of wet tissue and 28.33 microg g(-1) tissue, respectively. Further, EO extract (300, 450 and 600 mg kg(-1), i.p) significantly (p<0.001) reversed the rise in brain acetyl cholinesterase (AchE) level induced by scopolamine. The mice brain Ach E levels in the EO extract 600 mg kg(-1) group as compared to the scopolamine group was 70.23 vs 151.49 U mg(-1) protein(-1), respectively. These results suggestthat EO possesses memory enhancing, antioxidant and anti-cholinesterase activity. It may be useful for the treament of cognitive impairments induced by cholinergic dysfunction. Its potential in the management of dementia and Azheimer disease needs to be further explored.

Scopolamine- and diazepam-induced amnesia are blocked by systemic and intraseptal administration of substance P and choline chloride

Systemic (IP) and/or intraseptal (IS) administration of scopolamine (SCP) and diazepam (DZP) induce amnesia, whereas IP injection of the neuropeptide substance P (SP) and choline chloride (ChCl) produce memory facilitation. The septohippocampal cholinergic system has been pointed out as a possible site of SCP and DZP-induced amnesia as well as for the mnemonic effects induced by SP and ChCl. We performed a series of experiments in order to investigate the interactions between cholinergic and GABA/benzodiazepine (GABA/BZD) systems with the SPergic system on inhibitory avoidance retention. Male Wistar rats were trained and tested in a step-down inhibitory avoidance task (1.0 mA footshock). Animals received, pre-training, IP (1.0 mg/kg) or IS (1.0 nM/0.5 microl) injection of DZP, SCP (SCP; 1.0 mg/kg - IP or 0.5 microM/0.5 microl--IS) or vehicle (VEH). Immediately after training they received an IP or IS injections of SP 1-11 (50 microg/kg--IP or 1.0 nM/0.5 microl--IS), SP 1-7 (167 microg/kg--IP or 1.0 nM/0.5 microl--IS), ChCl (20 mg/kg--IP or 0.3 microM/0.5 microl--IS) or VEH. Rats pretreated with SCP and DZP showed amnesia. Post-trial treatments with SP 1-11, SP 1-7 or ChCl blocked the amnesic effects of SCP and DZP. These findings suggest an interaction between SPergic and cholinergic mechanisms with GABAergic systems in the modulation of inhibitory avoidance retention and that the effects of these treatments are mediated, at least in part, by interactions in the septohippocampal pathway.

Aclidinium bromide, a novel long-acting muscarinic M3 antagonist for the treatment of COPD

Aclidinium bromide is a novel, inhaled, long-acting antimuscarinic agent being developed by Almirall Prodesfarma SA and Forest Laboratories Inc as a once-daily treatment for COPD. In preclinical studies, aclidinium bromide demonstrated a comparable profile to tiotropium bromide, with a slightly quicker onset of action but shorter duration of action. Clinical trials have demonstrated an unquestionably interesting pharmacological profile characterized by a faster rate of onset of the smooth muscle relaxing activity than tiotropium bromide and a rapid plasma hydrolysis in human plasma to inactive metabolites that may account for its favorable cardiovascular safety profile. However, the disappointing efficacy results of the recent phase III trials have cast doubt on the real advantage of introducing this drug on the market. Discussions with the FDA concluded that more trials are needed to assess selected dosing regimens, including higher and/or more frequent doses. At the time of publication, further phase III trials with aclidinium bromide were ongoing, and the developing companies were also extending development to combinations of aclidinium bromide with formoterol or an undisclosed inhaled corticosteroid.

[Cytogenetic effects of cholinotropic preparations mixture on Chironomus plumosus (Diptera) larvae in vivo]

Morphometric analysis of changes in nucleolar organizer (NO), Balbiani rings (BR)--BR(B), BR(1G), BR(2G) and chromosome I arm B puff activities, and in chromosome compactness of Chironomus plumosus (Diptera) polytene chromosomes was carried out in acute period under separate and combined influence of atropine and pilocarpine. Supression effect of cholinotropic preparations mixture was revealed. Suppression of NO activity with atropine concentration increase in the mixture served as criterion of toxicity.

A novel compound, maltolyl p-coumarate, attenuates cognitive deficits and shows neuroprotective effects in vitro and in vivo dementia models

To develop a novel and effective drug that could enhance cognitive function and neuroprotection, we newly synthesized maltolyl p-coumarate by the esterification of maltol and p-coumaric acid. In the present study, we investigated whether maltolyl p-coumarate could improve cognitive decline in scopolamine-injected rats and in amyloid beta peptide(1-42)-infused rats. Maltolyl p-coumarate was found to attenuate cognitive deficits in both rat models using passive avoidance test and to reduce apoptotic cell death observed in the hippocampus of the amyloid beta peptide(1-42)-infused rats. We also examined the neuroprotective effects of maltolyl p-coumarate in vitro using SH-SY5Y cells. Cells were pretreated with maltolyl p-coumarate, before exposed to amyloid beta peptide(1-42), glutamate or H2O2. We found that maltolyl p-coumarate significantly decreased apoptotic cell death and reduced reactive oxygen species, cytochrome c release, and caspase 3 activation. Taking these in vitro and in vivo results together, our study suggests that maltolyl p-coumarate is a potentially effective candidate against Alzheimer's disease that is characterized by wide spread neuronal death and progressive decline of cognitive function.

[Changes in proline-specific peptidase activity in experimental model of retrograde amnesia]

Changes in proline-specific peptidase activity in the frontal cortex and hippocampus were studied using the experimental model of retrograde amnesia in rats. In one group, the amnesia was produced by a single injection of M-cholinergic antagonist scopolamine and the other group received the maximal electroconvulsive stimulation (MES). The amnesic effect was evaluated in passive avoidance test. In the amnesia models under consideration, the activity of prolylendopeptidase was significantly increased in both frontal cortex and hippocampus. The activity of dipeptidyl peptidase IV was significantly decreased in the cortex, whereas in the hippocampus it remained unchanged. Pyracetam inhibited prolylendopeptidase in the cortex and hippocampus, whereas dipeptidyl peptidase IV activity remained unchanged.

Prolonged effects of poly(lactic-co-glycolic acid) microsphere-containing huperzine A on mouse memory dysfunction induced by scopolamine

Huperzine A is an anticholinesterase and cognitive enhancer, which is able to alleviate the symptoms of memory dysfunction in the mouse. The fast metabolization rate and narrow therapeutic spectrum makes it unfit for clinical use. Poly(lactic-co-glycolic acid) microsphere as delivery system effectively maintains the blood concentration of huperzine A by a slow-release effect over a long time. In the present article, we investigated the prolonged protective effect of microsphere-containing huperzine A on memory dysfunction induced by scopolamine. Spectrophotometric assay was used to determine the activity of acetylcholinesterase (AChE) and passive avoidance tests to evaluate memory performance. The results show that a bolus dose of microsphere-containing huperzine A (at a dose of 300 microg/kg or 600 microg/kg) administered intramuscularly can effectively maintain drug activity and significantly decrease the activity of AChE from day 3 to 14, the strongest effect seen on day 3 and 7. Accompanying the reduction of the activity of AChE, microsphere-containing huperzine A (300 microg/kg or 600 microg/kg) remarkably increased transfer latency time and no transfer response on the second trial through mitigating the memory impairments induced by scopolamine as compared to the scopolamine model group. Microsphere-containing huperzine A showed cognitive enhancing properties and anticholinesterase activity and may thus be a candidate for treatment of memory impairment.

Insect muscarinic acetylcholine receptor: pharmacological and toxicological profiles of antagonists and agonists

The insect muscarinic acetylcholine receptor (mAChR) is evaluated as a potential target for insecticide action. The mammalian M2/M4-selective antagonist radioligand [3H]AF-DX 384 (a pirenzepine analogue) binds to Drosophila mAChR at a single high-affinity site identical to that for the nonselective antagonist [3H]quinuclidinyl benzilate (QNB) and with a pharmacological profile distinct from that of all mammalian mAChR subtypes. Three nonselective antagonists (QNB, scopolamine, and atropine) show the highest affinity (Ki=0.5-2.4 nM) at the Drosophila target, and AF-DX 384 and M3-selective 4-DAMP (dimethyl-4-(diphenylacetoxy)piperidinium iodide) rank next in potency (Ki=5-18 nM). Eleven muscarinic antagonists generally exhibit higher affinity than eight agonists. On injection into houseflies, the antagonists 4-DAMP and (S)-(+)-dimethindene produce suppressed movement, the agonist (methyloxadiazolyl)quinuclidine causes knockdown and tremors, and all of them inhibit [3H]QNB binding ex vivo, indicating possible mAChR-mediated intoxication. The insect mAChR warrants continuing study in lead generation to discover novel insecticides.

The early toxicology of physostigmine: a tale of beans, great men and egos

Mid-19th century European visitors to Old Calabar, an eastern province of Nigeria, could not avoid becoming aware of native belief in the power of the seeds of a local plant to determine whether individuals were innocent or guilty of some serious misdemeanour. The seeds were those of a previously unknown legume and soon referred to as the ordeal bean of Old Calabar. Their administration was known locally as 'chop nut'. Missionaries who arrived in Calabar in 1846 estimated that chop nut caused some 120 deaths annually and documented the course of poisoning. The latter information and samples of the beans rapidly found their way to Scotland, the home of the missionaries' parent church, explaining why the early toxicology of physostigmine, quantitatively the most important of three active alkaloids in the beans, has such strong Scottish, predominantly Edinburgh, associations. However, it was 1855 before the first of many medical scientists, Robert Christison, a toxicologist of repute, investigated the effects of the beans to the extent of eating part of one himself and documenting the moderate, if not severe, consequences. A further 6 years were to pass before Balfour's comprehensive botanical description of the bean plant appeared. It was he who named it Physostigma venenosum. It was not so long until the next event, one that sparked more intensive and international interest in the beans. In 1863 a young Edinburgh ophthalmologist, Argyll Robertson, published a paper announcing the arrival of the first agent that constricted the pupil of the eye. The drug was an extract of Calabar beans and Argyll Robertson openly admitted that he had been alerted to its unusual property by his physician friend, Thomas Fraser. A minor flood of contributions on the ophthalmic uses of bean extracts followed in the medical press in the next few months; those on their systemic toxicity were fewer. Fraser's MD thesis, submitted to the University of Edinburgh in 1862 and clearly pre-dating Argyll Robertson's involvement with the beans, became generally available a few weeks after the appearance of Argyll Robertson's paper and was the first to address in detail the features of systemic administration of extracts of the beans. A major problem facing all early researchers of the beans was that of deciding how best to extract their active principle, a task made all the more difficult because bioassays were the only means of determining if the toxin was being tracked. The stability of extracts was an inevitable issue and the active principle finally became known as physostigma or physostigmine, after the botanical name of the parent plant. The features of physostigmine toxicity were soon exhaustively documented, both in animals and humans. How they were mediated was another matter altogether. Fraser maintained that muscular paralysis, the cardinal feature, was the result of depression of the spinal cord and was generally, but far from unanimously, supported. Of those who had reservations, Harley was the most prominent. He concluded that paralysis was secondary to effects on the motor nerve endings and, in so doing, came nearest to present-day knowledge at a time when acetylcholine, cholinesterases and cholinesterase inhibitors were not even imagined. Differences of opinion on the mode of action of the beans were to be expected and it is hardly surprising that they were not resolved. No standard formulation of physostigmine was available so the potency of those used would have varied from one investigator to another, the range of animals experimented upon was large while the number used by any researcher was commonly in single figures, more readily available cold-blooded creatures seemed less sensitive to physostigmine toxicity than warm-blooded ones and only Fraser determinedly pursued an answer; in general, the others made one foray into bean research then turned their attentions elsewhere. The same problems would beset other aspects of bean research. While Fraser did not get as close to the mode of action of physostigmine as Harley, he reigns supreme when it comes to antagonism between physostigmine and atropine. By this time, the 1870s had dawned and although the concept of antagonism between therapeutic agents was not new, it had little, if any, reliable scientific foundation. This was about to change; antagonism was becoming exciting and rational. Fraser's firm belief that physostigmine and atropine were mutually antagonistic at a physiological level was contrary to the conventional wisdom of his contemporaries. This alone would earn him a place in history but his contribution goes much, much further. Unlike any other at the time, he investigated it with scientific rigour, experimenting on only one species, ensuring as best he could the animals were the same weight, adjusting the doses of drugs he gave them for bodyweight, determining the minimum lethal dose of each drug before assessing their antagonistic effects, adopting a single, incontrovertible endpoint for efficacy and carrying out sufficient numbers of experiments to appear convincing in a later era where the statistical power of studies is all-important. To crown it all, he presented his results graphically. Fraser never claimed to have discovered the antagonism between physostigmine and atropine. Bartholow in 1873 did, based on work done in 1869. But his data hardly justify it. If anyone can reasonably claim this particular scientific crown it is an ophthalmologist, Niemetschek, working in Prague in 1864. His colleague in the same discipline, Kleinwächter, was faced with treating a young man with atropine intoxication. Knowing of the contrary actions of the two drugs on the pupil, Niemetschek suggested that Calabar bean extract might be useful. Kleinwächter had the courage to take the advice and his patient improved dramatically. Clearly, this evidence is nothing more than anecdotal, but the ophthalmologists were correct and, to the present day, physostigmine has had an intermittent role in the management of anticholinergic poisoning. The converse, giving atropine to treat poisoning with cholinesterase inhibitors, of which physostigmine was the first, has endured more consistently and remains standard practice today. It is salutary to realise that the doses and dosage frequency of atropine together with the endpoints that define they are adequate were formulated by Fraser and others a century and a half ago.

Persistent neurobehavioral effects of early postnatal domoic acid exposure in rats

Domoic acid (DA) is a marine biotoxin, produced by the diatom Pseudo-nitzchia spp., which has been shown to cause cognitive impairment in adults who are exposed via contaminated seafood. The neurobehavioral consequences of developmental exposure are much less well understood. In a previous study, we showed that a single prenatal exposure to DA in rats at mid-gestation caused neurobehavioral changes that persist into adulthood including increased susceptibility to the benchmark amnestic drug scopolamine. In the current study, we examined the lasting neurobehavioral consequences of DA exposure on the first day of postnatal life, a time in rats marking the completion of the major phase of neuroproliferation and corresponding to week 24 of human gestation. The effects of DA exposure at doses from 0.025-0.1 mg/kg (s.c.) twice per day on each of postnatal days 1 and 2 were compared with vehicle-treated controls and rats treated by the same protocol with 1 mg/kg of kainic acid. Following kainic acid exposure, a sex-selective effect was seen with females but not males showing a significant slowing of response latency in the radial-arm maze. The high DA dose of 0.1 mg/kg was quite toxic causing lethality in all of the offspring exposed and this group was excluded from further analysis. When the offspring in the 0.05 mg/kg DA dose group were tested, significant hypoactivity in the Figure-8 maze was observed during adolescence. No significant DA effects were seen in response latency or choice accuracy on the radial-arm maze during either acquisition or with challenge of the amnestic drug scopolamine. Early postnatal DA exposure in the rat can be lethal and sublethal exposure can cause neurobehavioral effects manifest in modest hypoactivity during the adolescent period. However, the sublethal persistent neurobehavioral toxicity appears to be less pervasive than reported effects following DA administered mid-gestation.

Bovine brain phosphatidylserine attenuates scopolamine induced amnesia in mice

This study verifies the effects of bovine brain phosphatidylserine (PS) on passive avoidance (PA) and contextual fear conditioning (CFC) tests in scopolamine-treated mice. Mice received daily i.p. 50 mg/kg PS or 0.2 M Tris pH 7.4 (TRIS) for 5 days. On day 6, mice received saline (TRIS-SAL and PS-SAL) or 1 mg/kg SCO (TRIS-SCO and PS-SCO) i.p. After 20 min, the animals were submitted to PA (experiment 1) or CFC (experiment 2) training sessions, and tests were performed 24 h later. Latency in entering the dark chamber of the PA apparatus presented by TRIS-SCO (but not PS-SCO) group in the test was significantly higher than those presented by controls. Except for TRIS-SCO, all the groups presented higher latencies in the test compared to the training session. In experiment 2, the TRIS-SCO (but not PS-SCO) group presented significantly lower freezing duration than that presented by the TRIS-SAL group in the test. Animals treated with PS alone presented higher freezing duration than that presented by the TRIS-SAL group. The results demonstrate that PS attenuates SCO-induced amnesia in both PA and CFC tests. In addition, PS per se improves retention in the CFC test.

Stimulation of muscarinic receptors mimics experience-dependent plasticity in the honey bee brain

Honey bees begin life working in the hive. At approximately 3 weeks of age, they shift to visiting flowers to forage for pollen and nectar. Foraging is a complex task associated with enlargement of the mushroom bodies, a brain region important in insects for certain forms of learning and memory. We report here that foraging bees had a larger volume of mushroom body neuropil than did age-matched bees confined to the hive. This result indicates that direct experience of the world outside the hive causes mushroom body neuropil growth in bees. We also show that oral treatment of caged bees with pilocarpine, a muscarinic agonist, induced an increase in the volume of the neuropil similar to that seen after a week of foraging experience. Effects of pilocarpine were blocked by scopolamine, a muscarinic antagonist. Our results suggest that signaling in cholinergic pathways couples experience to structural brain plasticity.

Acteoside of Callicarpa dichotoma Attenuates Scopolamine-Induced Memory Impairments

We previously reported that ten phenylethanoid glycosides including acteoside isolated from the leaves and twigs of Callicarpa dichotoma significantly attenuated glutamate-induced neurotoxicity. In the present study, we examined anti-amnesic activity of acteoside using scopolamine-induced (1 mg/kg body weight, s.c.) amnesic mice with both passive avoidance and Morris water maze tests. Acute oral treatment (single administration prior to scopolamine treatment) of mice with acteoside (1.0, 2.5 mg/kg body weight) significantly mitigated scopolamine-induced memory deficits in the passive avoidance test. It is interesting to note that prolonged oral daily treatment of mice with much lower amount (0.1 mg/kg body weight) of acteoside for 10 d reversed the scopolamine-induced memory deficits. In the Morris water maze, prolonged oral treatment with acteoside (prolonged daily administration of 1.0 mg/kg body weight for 10 d) significantly ameliorated scopolamine-induced memory deficits showing the formation of long-term and/or short-term spatial memory. We suggest, therefore, that acteoside has anti-amnesic activity that may ultimately hold significant therapeutic value in alleviating certain memory impairment observed in Alzheimer's disease.

The selective 5-HT6 receptor antagonist Ro4368554 restores memory performance in cholinergic and serotonergic models of memory deficiency in the rat

Antagonists at serotonin type 6 (5-HT(6)) receptors show activity in models of learning and memory. Although the underlying mechanism(s) are not well understood, these effects may involve an increase in acetylcholine (ACh) levels. The present study sought to characterize the cognitive-enhancing effects of the 5-HT(6) antagonist Ro4368554 (3-benzenesulfonyl-7-(4-methyl-piperazin-1-yl)1H-indole) in a rat object recognition task employing a cholinergic (scopolamine pretreatment) and a serotonergic- (tryptophan (TRP) depletion) deficient model, and compared its pattern of action with that of the acetylcholinesterase inhibitor metrifonate. Initial testing in a time-dependent forgetting task employing a 24-h delay between training and testing showed that metrifonate improved object recognition (at 10 and 30 mg/kg, p.o.), whereas Ro4368554 was inactive. Both, Ro4368554 (3 and 10 mg/kg, intraperitoneally (i.p.)) and metrifonate (10 mg/kg, p.o., respectively) reversed memory deficits induced by scopolamine and TRP depletion (10 mg/kg, i.p., and 3 mg/kg, p.o., respectively). In conclusion, although Ro4368554 did not improve a time-related retention deficit, it reversed a cholinergic and a serotonergic memory deficit, suggesting that both mechanisms may be involved in the facilitation of object memory by Ro4368554 and, possibly, other 5-HT(6) receptor antagonists.

Effects of an aqueous extract of Puerariae flos (Thomsonide) on impairment of passive avoidance behavior in mice

The effects of an aqueous extract of Puerariae flos (Thomsonide) on ethanol-induced learning and memory impairment and scopolamine-induced amnesia were investigated. Thomsonide exerted an ameliorating effect on the impairment of both memory registration and memory retrieval induced by ethanol. These results indicate that Thomsonide has an antiamnesic effect on the central nervous system in alcoholic intoxication and support the traditional use of Puerariae flos for the treatment of alcoholic intoxication. Thomsonide also improved the scopolamine-induced impairment of memory registration in passive avoidance behavior in mice. The results of this study suggest that it may be possible to use Thomsonide for the treatment of age-related memory impairment and dementia.

New selective acetylcholinesterase inhibitors designed from natural piperidine alkaloids

Five new piperidine alkaloids were designed from natural (-)-3-O-acetyl-spectaline and (-)-spectaline that were obtained from the flowers of Senna spectabilis (sin. Cassia spectabilis, Leguminosae). Two semi-synthetic analogues (7 and 9) inhibited rat brain acetylcholinesterase, showing IC50 of 7.32 and 15.1 microM, and were 21 and 9.5 times less potent against rat brain butyrylcholinesterase, respectively. Compound 9 (1mg/kg, i.p.) was fully efficacious in reverting scopolamine-induced amnesia in mice. The two active compounds (7 and 9) did not show overt toxic effects at the doses tested in vivo.

Functional changes of nicotinic acetylcholine receptor in muscle and lymphocyte of myasthenic rats following acute dimethoate poisoning

The mechanism underlying intermediate myasthenia syndrome (IMS) following acute organophosphate poisoning remains largely unknown. Previous studies indicated that the mechanism of myasthenia in rats and IMS patients is most likely due to a postsynaptic neurotransmission blocking at neuromuscular junctions (NMJ). Nicotinic acetylcholine receptor (nAChR) is a key postsynaptic component at NMJ. Whether functional changes of nAChR are related to the development of myasthenia has not been demonstrated and addressed in vivo so far. In this study, we attempted to investigate temporal and spatial changes of nAChR in the blood lymphocyte, muscle and brain of rats during the course of myasthenia after acute dimethoate poisoning by using radioligand-binding assay. We found that specific nAChR binding activity in the gastrocnemius muscle and blood lymphocytes of myasthenia rats was significantly increased at 48h after dimethoate poisoning. However, no changes of nAChR binding activity were found in the lymphocytes and muscle of non-myasthenia rats which were sacrificed at 1h after intoxication. Interestingly, no changes of nAChR and muscarinic acetylcholine receptor (mAChR) binding activity were found in the cerebrum and cerebellum of all rats after dimethoate intoxication either at 1 or 48h. The change of nAChR specific binding activity in the lymphocytes is parallel with that in the skeletal muscle during the development of myasthenia. This implied that the changes of nAChR receptor binding activity in the skeletal muscle and lymphocytes are highly associated with the development of myasthenia. The functional changes of nAChR at NMJ might play an important role in the paralysis of skeletal muscle following acute organophosphates (OPs) poisoning.

Correlation between shaking behaviors and seizure severity in five animal models of convulsive seizures

Wet dog shakes (WDS) and head shakes (HS) are associated with experimentally induced convulsive seizures. We sought to determine whether these behaviors are correlated or not with major (status epilepticus (SE) or fully kindled animals) or minor (non-SE or partially kindled animals) seizure severity. WDS are directly correlated with SE induced by intracerebral star fruit extract (Averrhoa carambola) injection and with kindled animals in the amygdala fast kindling model. On the other hand, WDS are inversely correlated with SE induced by intracerebral bicuculline and pilocarpine injections. Systemic pilocarpine in animals pretreated with methyl-scopolamine barely induced WDS or HS. The role of shaking behaviors may vary from ictal to anticonvulsant depending on the experimental seizure model, circuitries involved, and stimulus intensity. The physical presence of acrylic helmets may per se inhibit the HS response. Also, methyl-scopolamine, a drug incapable of crossing the blood-brain barrier, can induce HS in animals without acrylic helmets.

ATROPINE-INDUCED INHIBITION OF SPERM AND SEMEN TRANSPORT IMPAIRS FERTILITY IN MALE RATS

Previous studies revealed that atropine reduced male fertility in rats without any effects on mating performance, sperm production and motility, and testicular morphology. The present study was conducted to investigate whether the impairment of male fertility induced by atropine was related to the inhibition of sperm and semen transports from the vas deferens and seminal vesicle to the urethra during the process of emission. Male rats were treated with atropine at 125 mg/kg/day for 10-17 days prior to mating with untreated females. After confirmation of mating, male rats were euthanized and sperm number in the vas deferens and weights of the seminal vesicle and copulatory plug were determined as indicators of inhibition of sperm and semen transports, respectively. Reproductive status of mated females was determined on gestation days 15-17. A low pregnancy rate associated with a decreased number of implants was observed in females that mated with the atropine-treated males. The average number of sperm in the vas deferens was increased in the atropine-treated males. The average seminal vesicle weight in the atropine-treated males was greater than that of controls. The copulatory plug weights were decreased in the atropine-treated males. These results suggest that inhibitions of sperm and semen transports from the vas deferens and seminal vesicle to the urethra during the process of emission result in reduced male fertility in rats.

Ondansetron amelioration of scopolamine induced cognitive deficits in three-panel runway apparatus in rats

Effect of ondansetron (5-HT3-receptor antagonist) was studied on the working memory deficits induced by scopolamine, a muscarinic receptor antagonist in rats using a three-panel runway apparatus. Varying doses of scopolamine (0.1-0.56mg/kg, ip) were administered alone or in combination with ondansetron (0.01-1.0 mg/kg, ip) and memory errors and latency period of the session were recorded on a three-panel runway apparatus. Treatment with scopolamine (0.56 mg/kg) produced working memory deficits in rats. Treatment with ondansetron (1.0 mg/kg) significantly reduced the scopolamine-induced working memory deficits.

Visual acuity in the water maze: sensitivity to muscarinic receptor blockade in rats and mice

A visual acuity task performed in the water maze in rats [Behav. Brain Res. 119 (2001) 77] was used to reveal the sensitivity of the visual system to muscarinic receptor blockade. Intraperitoneal injection of 0.2 mg/kg scopolamine had no effect, but 2 mg/kg severely compromised visual acuity, but did not affect the swim strategy to solve the task. Spatial learning in a reference memory version of the water maze, however, was impaired by 0.2 mg/kg scopolamine. It was also confirmed that the same visual acuity task is applicable to C57BL6/J mice. The visual deficit induced by 2 mg/kg scopolamine was less severe compared to rats, possibly due to a change in swim strategy in the drug condition. The effect of scopolamine on spatial reference memory in mice was not tested in this study. These data suggest that it may be possible to dissociate drug-induced effects on memory from changes in sensory perception.

Castration in rats impairs performance during acquisition of a working memory task and exacerbates deficits in working memory produced by scopolamine and mecamylamine

RATIONALE

Although much research has focused on the effects of ovarian hormones on learning and memory in females, less information is available regarding the effects of testicular hormones on learning and memory in males. Additionally, despite evidence of an interaction of testicular hormones and the cholinergic system in areas of the brain implicated in learning and memory, no information is available regarding the behavioral consequences of that interaction.

OBJECTIVES

We assessed the effect of castration in male rats on working memory during acquisition of a radial maze. We also assessed the interactive effects of castration and scopolamine, a muscarinic receptor antagonist, as well as mecamylamine, a nicotinic receptor antagonist, on behavior.

METHODS

Young adult male rats were castrated or underwent sham surgeries. Beginning 10 days after surgeries, performance on a task of working memory was assessed across 24 days of acquisition in an eight-arm radial maze. Following acquisition, scopolamine and mecamylamine dose-effect curves were established.

RESULTS

Castration of male rats significantly decreased arm-choice accuracy during acquisition. Castration significantly exacerbated impairments in arm-choice accuracy produced by scopolamine as well as mecamylamine, without altering the disruptive effects of the drugs on the rate at which rats entered the arms of the maze.

CONCLUSIONS

These results indicate that castration in male rats impairs working memory during acquisition of a spatial maze task. Additionally, these results suggest that the absence of testicular hormones increases the sensitivity of male rats to the impairing effects of scopolamine as well as mecamylamine on working memory.

Stability of Atropine Sulfate Prepared for Mass Chemical Terrorism

BACKGROUND

Preparedness for chemical terrorism includes the procurement of the appropriate pharmacological antagonists. A large emphasis has been placed on having a sufficient quantity of atropine available to treat patients exposed to acetylcholinesterase inhibitors such as sarin. Severe exposures may necessitate the administration of large amounts of atropine and dictate the need to prepare significant quantities of extemporaneously compounded atropine solution to respond to mass numbers of casualties over the first 24-48 hours postexposure.

OBJECTIVE

The objective of this project was to determine the stability of a 1 mg/mL atropine solution prepared in multidose IV solutions of 0.9% sodium chloride over a 72-hr period stored at varying temperatures.

METHODS

Atropine sulfate solution 1 mg/mL in 0.9% sodium chloride was prepared from sterile pharmaceutical-grade atropine sulfate powder. Multidose bags of atropine sulfate (100 mL) were stored at controlled temperatures of 4 degrees C to 8 degrees C, 20 degrees C to 25 degrees C, and 32 degrees C to 36 degrees C for 3 days and covered with an amber occlusive cover to minimize exposure to light. Six samples from each bag were drawn at 6, 12, 24, 48, and 72 h after preparation and compared with a time zero control sample. The samples were assayed using United States Pharmacopeia/National Formulary (USP/NF) high-performance liquid chromatography (HPLC) methods for atropine sulfate injection. The USP standard of 95% for atropine sulfate stability was used as the primary endpoint.

RESULTS

Atropine sulfate 1 mg/mL in 0.9% sodium chloride was stable for at least 72hr at 4 degrees C to 8 degrees C (percent initial concentration ranging from 96.5% to 103.4%), 20 degrees C to 25 degrees C (percent initial concentration ranging from 98.7% to 100.2%), and 32 degrees C to 36 degrees C (percent initial concentration ranging from 98.3% to 102.8%). Because the IV bags were protected from light during this study, we recommend this practice after preparing the atropine solution.

CONCLUSIONS

The amount of atropine necessary to treat hundreds to thousands of victims of a chemical attack is immense. The extemporaneous preparation of atropine solution from pharmaceutical-grade powder eliminates concerns about the storage of excessive quantities of atropine. A 1 mg/mL solution is stable for at least 3 days, allowing for use during the most critical treatment periods after exposure.

The 5-HT 1A receptor antagonist WAY 100635 improves rats performance in different models of amnesia evaluated by the object recognition task

The effects of the 5-HT(1A) receptor antagonist WAY 100635 on recognition memory were investigated in two different amnestic models in the rat by using the object recognition task. WAY 100635 at 1 mg/kg, but not at 0.3 mg/kg, counteracted scopolamine-induced performance deficits in the acquisition version of this behavioral paradigm. At the same dose, WAY 100635 antagonized extinction of recognition memory in the normal rat, suggesting that it affected acquisition, storage and retrieval of information. These results support and extend prior findings that interactions between the serotonergic and cholinergic systems are relevant to cognition and indicate that WAY 100635 modulates different aspects of recognition memory.

Ethanol blocks both basic fibroblast growth factor- and carbachol-mediated neuroepithelial cell expansion with differential effects on carbachol-activated signaling pathways

We have expanded neuroepithelial cells dissociated from the embryonic rat telencephalon in serum-free defined medium containing basic fibroblast growth factor (bFGF) in order to generate a model neuroepithelium to study the interaction of ethanol with both growth factor- and transmitter-stimulated proliferation. Ethanol blocked proliferation stimulated by bFGF and by carbachol, an agonist at muscarinic acetylcholine receptors, in a dose-dependent manner. In addition, ethanol attenuated autonomous expansion of neuroepithelial cells occurring following withdrawal of bFGF. The latter effect was associated with an increase in the number of apoptotic cells identified by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling labeling. We studied the effects of ethanol on carbachol-stimulated signaling pathways critical to its proliferative effects. Ethanol significantly reduced carbachol-stimulated Ca(2+) signaling, as well as Erk1/Erk2, Akt and cyclic AMP-response element-binding phosphorylations in a dose-dependent manner. Comparison of the potency of ethanol in attenuating carbachol-stimulated proliferation and signal transduction showed that mitogen-activated protein kinase phosphorylation was less sensitive to ethanol than the other parameters. The results indicate that ethanol's suppression of proliferation induced by carbachol in this model neuroepithelium likely involves multiple signaling pathways. These effects in vitro may help to explain the devastating effects of prenatal ethanol exposure in vivo, which contribute to the fetal alcohol syndrome.

Flumazenil and tacrine increase the effectiveness of ondansetron on scopolamine-induced impairment of spatial learning in rats

RATIONALE

Cholinergic receptor blockade produces memory deficits in animal models. These deficits can be prevented by 5-HT3 receptor antagonists, such as ondansetron, which increases acetylcholine release. We investigated the effects on cognitive performance of combined treatments of ondansetron with either flumazenil, a GABA(A) receptor benzodiazepine site antagonist, or tacrine, a cholinesterase inhibitor, which are also able to prevent scopolamine-induced cognitive impairment.

METHODS

Spatial learning and memory was assessed by studying the effects of single and combined treatments on acquisition and retention of the Morris water maze task in rats.

RESULTS

Scopolamine (0.6 mg/kg) induced significant learning and retention deficits. Both ondansetron (0.1 microg/kg) and tacrine (3 mg/kg) partially prevented the scopolamine-induced learning deficit. A full reversal was only found after the combined treatment of ondansetron with flumazenil (10 mg/kg) and also after tacrine in combination with ondansetron. Likewise, scopolamine-induced retention deficit was fully counteracted by the combined treatment of ondansetron with either flumazenil or tacrine, and only partially by any of the single treatments tested.

CONCLUSIONS

The scopolamine-induced impairment of learning and retention in the water maze is fully prevented by ondansetron when given in combination with either flumazenil or tacrine, suggesting that both combined treatments result in a potentiated cholinergic function and may constitute the basis of a new therapy for cognitive disorders.

Impairment of male fertility induced by muscarinic receptor antagonists in rats

Male rats were treated with a muscarinic receptor antagonist at 3, 10, and 100mg/kg/day for 4 weeks prior to mating with untreated females and their reproductive status was determined on gestation days (GD) 15-17. Treatment-related decreases in the pregnancy rate were observed at 100mg/kg/day without any effects on mating performance. Impairment of male fertility by this compound was also observed after treatment for 1 week, but there were no effects after a 1-week withdrawal period suggesting reversibility of the effect. There were no treatment-related effects on sperm production or motility, or testicular histopathology in any group. In order to determine whether the reduced fertility was a class effect of muscarinic receptor antagonists, atropine was examined. Males received atropine for 1 week at 62.5 and 125 mg/kg/day and were mated with untreated females. A low pregnancy rate associated with a decrease in the number of implantations was observed at 125 mg/kg/day. The effect on implantation was also observed at 62.5mg/kg/day. These findings suggest that the impairment of fertility in male rats induced by muscarinic receptor antagonists is a class effect, and has a relatively short onset of effect and is quickly reversible.

Attenuation of context-specific inhibition on reversal learning of a stimulus-response task in rats with neurotoxic hippocampal damage

Rats with hippocampal or sham lesions were trained on a stimulus-response task developed for the 8-arm radial maze. After reaching a stringent learning criterion, different context manipulations were performed. In Experiment I, the different groups were transferred to an identical radial maze in a different room to determine the context specificity of the discrimination learning. Experiment I revealed that although rats with hippocampal lesions did not show a normal context detection effect, the expression of the discrimination was not context dependent for either the lesion or sham groups. In Experiment II, animals were trained to criterion on the discrimination task and then both groups were divided into sub-groups based on whether they would experience reversal training in the same or different context from original training. Experiment II indicated that animals with hippocampal lesions and shams reversed in a different context were significantly enhanced in reaching the learning criterion compared to either counterparts that were reversed in the same context. Reversal learning in rats with hippocampal lesions was faster than sham animals in the same context suggesting that the context-specific inhibition effect was hippocampal-based. After learning the reversal task, the groups of animals trained and reversed in different contexts were brought back into the original training context to test for competitive effects. Animals with hippocampal lesions that were reversed in the different context, did not show a competition between the most recently acquired discrimination and a context-specific association acquired during original training whereas sham animals in the same condition did. Taken together these results suggest that rats with hippocampal lesions do not acquire normal context-specific inhibition during discrimination learning.

Modulatory role of cyclooxygenase inhibitors in aging- and scopolamine or lipopolysaccharide-induced cognitive dysfunction in mice

Inflammation processes may play a critical role in the pathogenesis of the degenerative changes and cognitive impairments associated with Alzheimer's disease (AD). Non-steroidal anti-inflammatory drugs are reported to be effective in reducing the risk of developing AD or cognitive impairments. Present experiments were performed to study the possible effect of various NSAIDs on cognitive performance of young, aged and scopolamine or lipopolysaccharide (LPS) treated mice (an animal model of AD) using one trial step through type of passive avoidance and in elevated plus maze task. Chronic administration of NSAIDs at the ED(50) doses (nimesulide, rofecoxib and naproxen for 15 days) significantly reversed the age or scopolamine-induced retention deficits in both test paradigms. However, in both the memory paradigms chronic administration of NSAIDs failed to modulate the retention performance of young mice. Acute administration of LPS (50 mcg/mouse, i.p.) significantly exhibited retention deficits after 24 h and seventh day of its administration in both test paradigms. Chronic administration (7 days) of rofecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor (1.92 mg/kg, p.o.) significantly reversed the LPS-induced retention deficits in both tests. The results of this study showed chronic treatment of NSAIDs reverses the cognitive deficits in age and scopolamine or LPS treated mice. These findings establish a link between the central nervous system expression of various pro-inflammatory cytokines and learning impairment in mice.

Toluene inhibits muscarinic receptor-mediated cytosolic Ca2+ responses in neural precursor cells

Toluene is widely used as a component in industrial solvents and many toluene-containing products are abused via inhalation. While many studies have demonstrated its inhibitory effects on neuronal activity, the effects of toluene on receptor signaling in proliferating and differentiating neural precursor cells are presently unclear. Here, using digital video microscopy and Ca2+ imaging, we investigated the effects of acute exposure to toluene on the function of muscarinic acetylcholine receptors (mAChRs) expressed in neural precursor cells. The neural precursor cells were isolatedfrom embryonic day 13 (E13) rat cortex and expanded in serum-free medium containing basic fibroblast growth factor (bFGF). We found that the acetylcholine (ACh) analog carbachol (CCh) induced a dose-dependent increase in cytosolic Ca2+, which was blocked by the muscarinic receptor antagonist atropine in a reversible manner. Toluene was added to the perfusion medium and concentrations of toluene in the medium were determined by gas chromatographic analysis. Following imaging, the cells were fixed and processed for 5-bromo-2'-deoxyuridine (BrdU, cell proliferation marker) and beta-tubulin (TuJ1, neuronal marker) immunostaining. In the 5 day culture, most cells continued to divide (BrdU+), while afew cells differentiated into young neurons (TuJ1-). The CCh-induced Ca2+ elevations in proliferating (BrdU+TuJ1-) neural precursor cells were significantly reduced by acute exposure to 0.15 mM toluene and completely blocked by 10 mM toluene. Toluene's inhibition of muscarinic receptor-mediated Ca2+ signaling was rapid, reversible and dose-dependent with an IC50 value 0.5 mM. Since muscarinic receptors mediate cell proliferation and differentiation during neural precursor cell development, these results suggest that depression of muscarinic signaling may play a role in toluene's teratogenic effect on the developing nervous system.

Receptor mechanisms and circuitry underlying NMDA antagonist neurotoxicity

NMDA glutamate receptor antagonists are used in clinical anesthesia, and are being developed as therapeutic agents for preventing neurodegeneration in stroke, epilepsy, and brain trauma. However, the ability of these agents to produce neurotoxicity in adult rats and psychosis in adult humans compromises their clinical usefulness. In addition, an NMDA receptor hypofunction (NRHypo) state might play a role in neurodegenerative and psychotic disorders, like Alzheimer's disease and schizophrenia. Thus, understanding the mechanism underlying NRHypo-induced neurotoxicity and psychosis could have significant clinically relevant benefits. NRHypo neurotoxicity can be prevented by several classes of agents (e.g. antimuscarinics, non-NMDA glutamate antagonists, and alpha(2) adrenergic agonists) suggesting that the mechanism of neurotoxicity is complex. In the present study a series of experiments was undertaken to more definitively define the receptors and complex neural circuitry underlying NRHypo neurotoxicity. Injection of either the muscarinic antagonist scopolamine or the non-NMDA antagonist NBQX directly into the cortex prevented NRHypo neurotoxicity. Clonidine, an alpha(2) adrenergic agonist, protected against the neurotoxicity when injected into the basal forebrain. The combined injection of muscarinic and non-NMDA Glu agonists reproduced the neurotoxic reaction. Based on these and other results, we conclude that the mechanism is indirect, and involves a complex network disturbance, whereby blockade of NMDA receptors on inhibitory neurons in multiple subcortical brain regions, disinhibits glutamatergic and cholinergic projections to the cerebral cortex. Simultaneous excitotoxic stimulation of muscarinic (m(3)) and glutamate (AMPA/kainate) receptors on cerebrocortical neurons appears to be the proximal mechanism by which the neurotoxic and psychotomimetic effects of NRHypo are mediated.

Attenuation of scopolamine-induced and age-associated memory impairments by the sigma and 5-hydroxytryptamine(1A) receptor agonist OPC-14523 (1-[3-[4-(3-chlorophenyl)-1-piperazinyl]propyl]-5-methoxy-3,4-dihydro-2[1H]-quinolinone monomethanesulfonate)

Sigma and 5-HT(1A) receptor stimulation can increase acetylcholine (ACh) release in the brain. Because ACh release facilitates learning and memory, we evaluated the degree to which OPC-14523 (1-[3-[4-(3-chlorophenyl)-1-piperazinyl]propyl]-5-methoxy-3,4-dihydro-2[1H]-quinolinone monomethane sulfonate), a novel sigma and 5-HT(1A) receptor agonist, can augment ACh release and improve learning impairments in rats due to cholinergic- or age-related deficits. Single oral administration of OPC-14523 improved scopolamine-induced learning impairments in the passive-avoidance task and memory impairment in the Morris water maze. The chronic oral administration of OPC-14523 attenuated age-associated impairments of learning acquisition in the water maze and in the conditioned active-avoidance response test. OPC-14523 did not alter basal locomotion or inhibit acetylcholinesterase (AChE) activity at concentrations up to 100 microM and, unlike AChE inhibitors, did not cause peripheral cholinomimetic responses. ACh release in the dorsal hippocampus of freely moving rats increased after oral delivery of OPC-14523 and after local delivery of OPC-14523 into the hippocampus. The increases in hippocampal ACh release were blocked by the sigma receptor antagonist NE-100 (N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)-phenyl]-ethylamine). Thus, OPC-14523 improves scopolamine-induced and age-associated learning and memory impairments by enhancing ACh release, due to a stimulation of sigma and probably 5-HT(1A) receptors. Combined sigma/5-HT(1A) receptor agonism may be a novel approach to ameliorate cognitive disorders associated with age-associated cholinergic deficits.

Muscarinic receptor antagonist-induced lenticular opacity in rats

Investigations on compound A, an M2-sparing M3 muscarinic receptor antagonist, showed that focal polar anterior subcapsular lenticular opacities, characterized by focal epithelial proliferation, developed in Sprague-Dawley rats. The incidence and bilateral localization of this change increased generally with dose and time, though plateauing after 8 months of treatment; however the severity progressed very slightly. Over a 1-year period, no anterior cortical lens fiber changes or other histological ocular changes developed. A decreased severity of the change and apoptosis suggested some regression after a 26-week recovery period. Two nonselective muscarinic receptor antagonists, atropine and tolterodine, induced similar lenticular changes in rats. A hypothesis in relation to an indirect effect of the drug, such as increased illumination of the lens due to mydriasis observed with all these compounds, was investigated and disproven. Because these opacities are induced by structurally unrelated muscarinic receptor antagonists (atropine and tolterodine), it is likely that these lenticular changes are the result of muscarinic receptor inhibition. However, hypotheses regarding a direct effect of the drug on muscarinic receptors in the lens epithelium, possibly mediated by drug and/or metabolite(s) in the aqueous humor and/or lens epithelium, remain to be investigated. This lenticular opacity is similar to that observed spontaneously in Sprague-Dawley rats, although the latter occur at a lower incidence. No such lenticular opacities have been reported in other animal species, including man, after treatment with muscarinic receptor antagonists.

Evidence for the involvement of the muscarinic cholinergic system in the central actions of pentoxifylline

This study shows that pentoxifylline (ptx), a xanthine derivative, significantly attenuates scopolamine-induced memory impairment in rats, as demonstrated in a passive avoidance task (50 mg/kg intraperitoneally [i.p.]) and in an elevated T-maze (10 and 50 mg/kg i.p.). Ptx (25, 50 and 100 mg/kg i.p.) also potentiates oxotremorine-induced tremors in mice, in a dose-dependent manner, and this effect was completely prevented by atropine. In addition, ptx (50 and 100 mg/kg i.p.) increased the number of animals developing pilocarpine-induced seizures, and potentiated the latency to the first pilocarpine-induced convulsion. Hippocampus homogenates from rats treated with ptx (100 mg/kg) for 1 week and sacrificed 15 min after the last injection showed a significant decrease in the muscarinic receptor numbers, indicative of a downregulation phenomenon. Similar effects were observed when assays were performed 24 h after the last ptx injection (10 and 50 mg/kg i.p.), but not after 72 h. Additionally, in vitro assays showed that ptx inhibits acetylcholinesterase activity in a dose-dependent manner when incubated with homogenates from rat hippocampus. Our data suggest that the muscarinic agonist effect of ptx could possibly depend on factors such as endogenous cholinergic activity.

Doxorubicin affects the cardiac muscarinic system in the rat

During the study on the mechanism of doxorubicin-induced cardiotoxicity, we observed that a long incubation (4 hr) with doxorubicin reduced the maximal negative inotropic effects of a muscarinic receptor agonist, carbachol. The mechanism responsible for this doxorubicin-induced reduction of the efficacy of carbachol was examined in isolated guinea pig hearts. In isolated left atrial muscle preparations, 1 hr incubation with 100 microM doxorubicin caused a parallel right-ward shift of the concentration-response curves for carbachol, but a longer (4 hr) incubation with this agent (30, 100 or 200 microM), caused a significant reduction of the magnitude of the negative inotropic effect of carbachol in addition to the concentration-dependent parallel right-ward shift. The 4-hr incubation with these concentrations of doxorubicin also reduced the maximal negative inotropic effect of an adenosine A1 receptor agonist, R-phenylisopropyl adenosine (R-PIA), without affecting the potency of this agonist. Doxorubicin (1 to 100 microM) reduced [3H]quinuclidinyl benzilate (QNB) binding in a concentration dependent manner, but failed to alter [3HIR-PIA binding. The decrease in the magnitude of the maximal negative inotropic effect by doxorubicin was caused by changes in the muscarinic system at steps common to the transduction of muscarinic and adenosine A1 receptor mechanisms.

Effect of polyacetylenes on the neurite outgrowth of neuronal culture cells and scopolamine-induced memory impairment in mice

Polyacetylenic alcohols and their linoleates isolated from Panax ginseng C. A. MEYER and Cirsium japonicum DC., of which the lipophilic extracts had been found to affect the neuritogenesis of cultured paraneurons, were demonstrated to have a significant neuritogenic effect on PC12h and Neuro2a cells. Panaxynol and the acetylenic triol in particular were highly efficient at concentrations > or = 2 microm. Panaxynol (20 mg/kg/d, i.p., for 3 d) was confirmed to improve scopolamine-induced memory deficit in mice (Y-maze task). It is suggested that the promotion of neuritogenesis in cultured paraneurons by the addition of panaxynol is related its ability to improve memory deficits in animals.

Effect of supplementation of vitamin E and vitamin C on brain acetylcholinesterase activity and neurotransmitter levels in rats treated with scopolamine, an inducer of dementia

In the present study, the effects of vitamins E and C on the levels of neurotransmitters and acetylcholinesterase activity in the brains of rats treated with scopolamine, an inducer of dementia, were examined. Fifty male Sprague-Dawley rats at the age of 5 wk were divided into five groups after 1 wk of adaptation and fed five different diets for 6 wk: a no-scopolamine group, which was a scopolamine-untreated group fed only a basal diet: a scopolamine-treated group fed a basal diet; a vitamin E-supplemented scopolamine-treated group: a vitamin C-supplemented scopolamine-treated group; and a vitamins E and C-supplemented scopolamine-treated group. Scopolamine was twice administered by intraperitoneal injection (300 mg/kg, body weight), 3 d and 20 min prior to sacrifice. Brain acetylcholinesterase activity was markedly reduced by scopolamine injection. However, the supplementation of vitamins E and C in the diet significantly increased the reduced brain acetylcholinesterase activity up to the level of the scopolamine-untreated group. Brain serotonin concentration in the vitamin C-supplemented scopolamine-treated group was significantly higher than that in the scopolamine-treated group. However, there were no significant differences in brain dopamine and norepinephrine concentrations among all groups. In conclusion, supplementation with vitamin E and/or vitamin C might be useful in maintaining brain acetylcholinesterase activity at the normal level and serotonin concentration for some extent under the condition to induce dementia by scopolamine administration.

Hypericum perforatum as a nootropic drug: enhancement of retrieval memory of a passive avoidance conditioning paradigm in mice

Depression, among other non-cognitive symptoms, is common in patients with dementia. The effect of Hypericum perforatum (St. John's Wort) extract, with well-documented antidepressant activity, was tested on memory retrieval 24 h after training on a one-trial passive avoidance task in mice. Acute administration of Hypericum extract (4.0, 8.0, 12.0, and 25.0 mg/kg i.p.) before retrieval testing increased the step-down latency during the test session. The same doses of Hypericum extract, on the other hand, failed to reverse scopolamine-induced amnesia of a two-trial passive avoidance task. The involvement of serotonergic, adrenergic, and dopaminergic mechanisms in the facilitatory effect of Hypericum extract on retrieval memory was investigated. Pretreatment of the animals with serotonergic 5-HT1A receptor antagonist (-)-pindolol (0.3, 1.0, and 3.0 mg/kg), serotonergic 5-HT2A receptor blocker spiperone (0.01, 0.03, and 0.1 mg/kg), alpha adrenoceptor antagonist phentolamine (1, 5, and 10 mg/kg), beta receptor antagonist propranolol (5, 7.5, and 10 mg/kg), dopaminergic D1 receptor antagonist SCH 23390 (0.01, 0.05, and 0.1 mg/kg), and dopaminergic D2 receptor antagonist sulpiride (5, 7.5, and 10 mg/kg) revealed the involvement of adrenergic and serotonergic 5-HT1A receptors in the facilitatory effect of Hypericum extract on retrieval memory. It is concluded that Hypericum extract may be a better alternative for treatment of depression commonly associated with dementia than other antidepressants known to have anticholinergic side effects causing delirium, sedation and even exacerbating already existing impaired cognition. In dementias of old age, Hypericum perforatum would, therefore, serve as one medication targeting both depression and amnesia with lower potential side effects.

A novel nitrate ester reverses the cognitive impairment caused by scopolamine in the Morris water maze

The objective of this study was to test the hypothesis that activation of soluble guanylyl cyclase and increased cGMP formation in the brain would improve task acquisition in cognitively impaired animals. We evaluated the effects of a novel nitrate ester, GT 715 (2,3-dinitrooxy-(2,3-bis-nitrooxypropyldisulfanyl)-propane), in scopolamine-induced impairment of task acquisition in the Morris water maze. GT 715 improved task acquisition in scopolamine-pretreated animals in a time- and dose-dependent manner, whereas the prototypical nitrate ester, glyceryl trinitrate (GTN), was ineffective. GT 715 also was more effective and more potent than GTN for activation of hippocampal guanylyl cyclase. The results of this study therefore suggest that stimulation of cerebral soluble guanylyl cyclase activity may be an effective strategy to improve learning and memory performance in individuals in whom cognitive abilities are impaired by injury, disease, or ageing.

[The evaluation of the specific activity and side effects of the m-cholinergic blocker pentifin compared to other antiparkinson agents]

Experiments on rodents showed that pentifin, a muscarine antagonist belonging to the group of acetylene amines, possesses a pronounced antiparkinsonian activity. Pentifin is superior in the breadth of therapeutic action and tolerance characteristics to the conventional agents used for Parkinson's disease treatment.