Long-lasting antiamnesic effect of a novel anticholinesterase inhibitor (MF268)

In the present study a short (120 min) and long-lasting (360 min) antagonism of scopolamine-induced amnesia in rats was investigated in an eight-arm radial maze, by (3a S, 8a R)-1,2,3,3a,8,8a-hexahydro-1,3a,8-trimethylpyrrolo[2,3-b]indol-5-o l[8-(cis2,6-dimethyl-morpholin-4-yl)octyl]-carbamate L-bitartrate hydrate (MF268), a new cholinesterase inhibitor. Upon completing the training session, the rats were orally administered increasing doses of MF268 (2, 3, 6, 7, and 8 mg/kg) 60 min prior to s.c. injection of scopolamine (0.25 mg/kg). Following a further 60 min the rat was placed in the maze. The reversal of scopolamine-induced impairment was characterized by an inverted U-shaped dose-response curve. A significant reduction in the number of errors, and time taken to complete the maze was observed with a dose of 6 mg/kg. The compound improved memory retention without affecting scopolamine-induced hypermotility. When the same dose was administered 360 min prior to the test a significant reduction in the number of amnesic animals was observed, whereas no cognitive improvement was detected when either 1-Benzil-4-[(5,6-dimethoxy-1-indanon)-2-yl]-methyl piperidine hydrochloride (E2020) (0.25 mg/kg) or tacrine (0.5 mg/kg) were administered 360 min prior to the test. The kinetics of whole-brain cholinesterase confirmed the long-lasting activity for MF268. A clinical relevance for the use of MF268 in AD treatment is suggested.

The influence of ondansetron and m-chlorophenylpiperazine on scopolamine-induced cognitive, behavioral, and physiological responses in young healthy controls

BACKGROUND

There is evidence from animal and human experiments that learning and memory come under the separate influence of both cholinergic and serotonergic pathways. We were interested in learning whether serotonergic drugs could attenuate or exacerbate the memory-impairing effects of anticholinergic blockade in humans.

METHODS

The selective serotonin 5-HT3 receptor antagonist ondansetron (0.15 mg/kg i.v.) and the serotonergic agent m-chlorophenylpiperazine (m-CPP; 0.08 mg/kg i.v.) were administered in combination with the anticholinergic agent scopolamine (0.4 mg PO) and compared to scopolamine alone in 10 young, healthy volunteers. Testing occurred on three separate days.

RESULTS

As expected, i.v. administration of scopolamine induced significant impairments in episodic memory and processing speed; however, these scopolamine-induced cognitive deficits were not attenuated by pretreatment with i.v. ondansetron (0.15 mg/kg), nor were they exacerbated by administration of i.v. m-CPP (0.8 mg/kg) in addition to scopolamine; however, administration of i.v. m-CPP was followed by a significant increase of self-rated functional impairment, altered self-reality, and dysphoria ratings, and scopolamine's effect on pupil size was potentiated.

CONCLUSIONS

Together, these results suggest that in young, healthy volunteers scopolamine-induced changes of cognitive performance are only minimally modulated by the serotonergic effects on ondansetron and m-CPP. Further studies with older controls are needed to test whether these findings may be influenced by age.

The pharmacology of memory

Neurotransmitters play a critical role in the brain circuits involved in various aspects of memory. The importance of acetylcholine is illustrated by the psychopathology of Alzheimer's disease. Cholinergic replacement therapy is now available for treating the cognitive decline associated with this form of degenerative disease. Dopamine in the prefrontal cortex also contributes to information storage, particularly working memory. In both cases efforts have been made to identify the receptor subtype involved and such information is essential if pharmacologically specific drugs are to be developed for cognitive enhancement.

Locomotion and stereotypy induced by scopolamine: contributions of muscarinic receptors near the pedunculopontine tegmental nucleus

In this study, we test whether blockade of muscarinic receptors near mesopontine cholinergic cell groups may contribute to locomotor activation induced by scopolamine. Unilateral or bilateral injections of scopolamine (10-150 micrograms) into the pedunculopontine tegmental nucleus (PPT) increased horizontal locomotion by 2-15 times in a dose-related way. Unilateral or bilateral injections of scopolamine into the PPT increased stereotypic behaviors (such as sniffing in one location or over large areas), self-biting and grooming. Carbachol (4 micrograms) injected into PPT reduced locomotion for 20 min, followed by 70 min of increased locomotion. When carbachol (4 micrograms) was injected into the PPT before scopolamine (3 mg/kg, i.p.), the activating effect of scopolamine was attenuated, but not when carbachol was injected after scopolamine. Therefore, carbachol appears to compete with scopolamine for muscarinic receptors near the PPT that mediate locomotor activating effects of systemic scopolamine. Haloperidol (0.1 mg/kg, i.p.) also attenuated the stereotypy and locomotion induced by scopolamine in the PPT. We hypothesize that scopolamine acts by blocking muscarinic receptors on mesopontine cholinergic neurons, thereby disinhibiting cholinergic neurons that can activate dopamine neurons.

Pharmacological activity of fluoxetine

Some SSRIs like fluvoxamine and zimeldine have already been investigated for their memory improving activity in humans and animals, with positive results. The purpose of this paper is to observe some activities of fluoxetine the known antidepressant on some control neuron system functions [3].

Rolipram and its optical isomers, phosphodiesterase 4 inhibitors, attenuated the scopolamine-induced impairments of learning and memory in rats

We investigated the effects of (+/-)-rolipram, a phosphodiesterase (PDE) 4 inhibitor, and its isomers on scopolamine-induced deficits of learning and memory in rats using an 8-arm radial maze task and a passive avoidance task. 1) In the 8-arm radial maze task, (+/-)-rolipram (0.02-0.2 mg/kg, p.o.), (-)-rolipram (0.01-0.02 and 0.2-0.5 mg/kg, p.o.) and (+)-rolipram (20-50 mg/kg, p.o.) attenuated the scopolamine-induced deficits of spatial cognition. As for the minimum effective dose of each drug, (-)-rolipram was 2 and 2000 times as potent as (+/-)-rolipram and (+)-rolipram, respectively. (-)-Rolipram produced a biphasic dose-response and (+/-)-rolipram produced a broad dose-response. 2) (+/-)-Rolipram and its isomers also attenuated the scopolamine-induced deficits in the passive avoidance response. Also for the minimum effective dose, (-)-rolipram (0.01-0.02 mg/kg) was 2 and 200 times as potent as (+/-)-rolipram (0.02-0.1 mg/kg) and (+)-rolipram (2mg/kg). 3) The behaviorally effective doses of (+/-)-rolipram and its isomers also enhanced the oxotremorine-induced tremors in mice. Comparing these racemic isomers, (-)- and (+/-)-rolipram have more potent effects than (+)-rolipram on scopolamine-induced deficits in the 8-arm radial maze task and passive avoidance task. Especially (+/-)-rolipram has a wide dose range in these behavioral study. These results suggest that the ameliorating effects of rolipram might result from the indirect potentiation of various transmitters including cholinergic and noradrenergic systems by an increase in cAMP with the inhibition of PDE4.

Reduction of dizocilpine and scopolamine-induced deficits in avoidance responding by SCH 54388, a metabolite of felbamate

Felbamate (2-phenyl-1,3-propanediol dicarbamate) is a novel antiepileptic agent with a unique structure and mechanism of action, possibly involving binding sites at the N-methyl-D-aspartate receptor (NMDA) complex. A monocarbomate metabolite of felbamate (SCH 54388) was compared to felbamate using a mouse passive-avoidance paradigm (PAR). SCH 54388 was markedly free of toxic side effects up to doses of 300 mg/kg, sc. SCH 54388 reduced the deficit-producing effects of either scopolamine, a cholinergic antagonist, or dizocilpine (MK-801), an NMDA receptor channel blocker, in a dose-dependent manner. The effective dose range of SCH 54388 was between 0.01 and 10 mg/kg, sc. SCH 54388 was also orally active at doses between 0.1 and 10 mg/kg. Felbamate also reduced scopolamine and dizocilpine antagonism, but was less potent than SCH 54388, reducing scopolamine-induced deficits at 1 to 3 mg/kg, sc. in a dose-dependent manner and reducing deficits induced by dizocilpine at doses of 0.1 and 3 mg/kg, SC. The reduction of dizocilpine-induced deficits by felbamate was not dose dependent. These results suggest that SCH 54388 has a mechanism of action involving either directly or indirectly, glutaminergic and cholinergic central neuronal systems.

Attenuation of the locomotor activating effects of D-amphetamine, cocaine, and scopolamine by potassium channel modulators

1. Locomotor activating effects of D-amphetamine, cocaine, and scopolamine were determined alone and after pretreatment with K-channel modulators in mice. 2. When administered alone, D-amphetamine (1.0- 30 mg/kg) and cocaine (3.0- 56 mg/kg) produced inverted U-shaped dose-effect curves characteristic of psychomotor stimulant drugs. 3. When administered alone, scopolamine (3.0-56 mg/kg) also produced dose-dependent increases in locomotor activity but these effects plateaued with similar increases in locomotor activity induced by 10-56 mg/kg of scopolamine. 4. Pretreatment with the K-channel blockers 4-aminopyridine (0.3-1.7 mg/kg), quinine (30-100 mg/kg) or apamin (0.3-1.0 mg/kg) attenuated the locomotor increases induced by d-amphetamine, cocaine, and scopolamine. 5. Like the K-channel blockers, pretreatment with the K-channel openers cromakalim (1.0-3.0 mg/kg) and pinacidil (3.0-10 mg/kg) also attenuated the locomotor increases induced by D-amphetamine and scopolamine but did not modify the locomotor activating effects of cocaine. 6. These results demonstrate that K-channel modulation modifies the effects of D-amphetamine, cocaine, and scopolamine. 7. The results also demonstrate that K-channel openers can differentially alter the behavioral effects of cocaine and D-amphetamine.

Interleukin-6 affects scopolamine-induced amnesia, but not brain amino acid levels in mice

We have previously shown that, after peripheral administration, different cytokines affect cognitive functions in mice. In this study, we evaluated the effects of mouse interleukin-6 (IL-6) on the classical behavioural test of scopolamine-induced amnesia for a passive avoidance response in the mouse. Pretraining i.p. administration of this cytokine (0.125 and 0.5 microgram/mouse) significantly reduced the amnesic action of the muscarinic receptor antagonist. As it is well known that brain amino acids are deeply involved in the modulation of cognitive processes we measured the levels of glutamine, aspartic acid, glutamic acid and GABA in the hippocampus and hypothalamus of mice treated with IL-6. At both doses which affected the cognitive functions, this cytokine had no effect on brain levels of measured amino acids. Neither nociceptive thresholds to a thermal stimulus, nor spontaneous locomotor activity were modified by the acute administration of IL-6 (0.5 microgram/mouse). Our data confirm previous observations indicating that peripheral administration of cytokines affects some, but not other brain functions and suggest the involvement of IL-6 in the central modifications induced by the immune activation.

Gastrodin and p-hydroxybenzyl alcohol facilitate memory consolidation and retrieval, but not acquisition, on the passive avoidance task in rats

Gastrodin (GAS) and p-hydroxybenzyl alcohol (HBA) which is an aglycone of gastrodin, are active ingredients of Gastrodia elata Blume. In this study, we attempted to investigate the effects of acute administration of GAS and HBA on learning and memory processes such as acquisition, consolidation and retrieval, on the passive avoidance task in rats; piracetam was used as a positive control. Scopolamine, impairing learning acquisition, shortened the step-through latency in the retention test in rats. GAS and HBA did not prolong the step-through latency induced by scopolamine in the passive avoidance task, but piracetam could prolong the step-through latency induced by scopolamine. Cycloheximide, impairing memory consolidation, shortened the step-through latency in the retention test in rats. GAS at 50 mg/kg, HBA at 5 mg/kg and piracetam at 100 mg/kg could prolong the step-through latency induced by cycloheximide in the passive avoidance task. Apomorphine, impairing memory retrieval, shortened the step-through latency in the retention test in rats. GAS at 5 mg/kg, HBA at 1 mg/kg and piracetam at 300 mg/kg could prolong the step-through latency induced by apomorphine in the passive avoidance task. From the above results, we concluded that the facilitating effects of HBA on learning and memory are better than those of GAS. In conclusion, GAS and HBA can improve cycloheximide- and apomorphine-induced amnesia, but not scopolamine-induced acquisition impairment in rats. Thus, GAS and HBA can facilitate memory consolidation and retrieval, but not acquisition. The facilitating effects of GAS and HBA are different from those of piracetam.

Physostigmine reversal of scopolamine-induced hypofrontality

The muscarinic receptor antagonist scopolamine produces a transient memory deficit in healthy humans. This deficit has been offered as a model of the cholinergic deficit of Alzheimer's disease (AD). However, we have previously shown that scopolamine produces a deficit of cortical perfusion maximal in the frontal lobe, dissimilar to the parietal cortex deficit characteristic of AD. The current experiment was aimed at replicating and extending this observation by critically testing the central cholinergic origin of both cognitive and perfusion deficits. Nine healthy subjects participated in regional cerebral blood flow (rCBF) measurements at baseline, after scopolamine (7.2 micrograms/kg i.v.), and after both physostigmine (22 micrograms/kg i.v.) and neostigmine (7 or 11 micrograms/kg i.v.). rCBF was quantified by the xenon 133 inhalation method. As expected, scopolamine reduced cortical perfusion, mainly in the frontal cortex, and produced a memory deficit. Physostigmine, but not neostigmine, reversed all three variables partially or completely. These results support the hypothesis that all three consequences of scopolamine, namely, reduction of mean flow, frontal deficit, and memory impairment, are cholinergically mediated. Furthermore, because neostigmine poorly crosses the blood-brain barrier, these findings confirm that the effect is centrally mediated and cannot be explained by peripheral effects. However, they also confirm the frontal cortex locus of action for both scopolamine and its reversal by physostigmine and therefore suggest a major dissimilarity to the characteristic rCBF appearance of AD. This study extends our previous preliminary findings with tacrine and strengthens the suggestion that only nicotinic receptors are associated with the characteristic parietal deficit of AD.

Pharmacological activity of Guarana (Paullinia cupana Mart.) in laboratory animals

Mice that ingested a suspension of guarana (Paullinia cupana, Sapindaceae) in a dose of 0.3 mg/ml showed a significant increase in physical capacity when subjected to a stressful situation such as forced swimming after 100 and 200 days of treatment. Such an effect, however, was not obtained with a concentration of 3.0 mg/ml, nor with the ingestion of a suspension of ginseng 5.0 mg/ml, nor of a solution of caffeine 0.1 mg/ml. Guarana, both after a single (3.0 and 30 mg/kg) or chronic administrations (0.3 mg/ml), was able to partially reverse the amnesic effect of scopolamine as measured through a passive avoidance test in mice and rats, indicating a positive effect on memory acquisition. However, no effect was observed when an active avoidance task was used in rats, even after 20 days of guarana administration. There was also a tendency of rats treated with 0.3 mg/ml of guarana to better maintain the memory of a Lashley III maze path. The animals had the same average lifespan, indicating a low toxicity of guarana, even after 23 months of treatment.

Effects of D-cycloserine and aniracetam on spatial learning in rats with entorhinal cortex lesions

A great body of behavioural and neurophysiological evidence suggests that excitatory amino acids are involved in mechanisms of learning and memory. Moreover, degeneration of glutamatergic pathways may underlie the cognitive deficits seen in various disorders such as Alzheimer's dementia. As direct stimulation of glutamatergic receptors with agonists may increase the risk of toxicity and accelerate neuropathological changes, a more valid approach seems to be positive modulation of glutamatergic receptors that may reverse the symptoms with a lower risk of excitotoxic effects. Such a possibility offered by partial agonists of the strychnine-insensitive glycine site of the NMDA receptor (Gly-B site) or positive modulators of AMPA receptors, such as aniracetam. In the present study, the effects of d-cycloserine and aniracetam were tested in two animal models of cognitive deficits (entorhinal cortex lesion-induced deficits evaluated in the radial maze and scopolamine-induced amnesia evaluated in passive avoidance test). D-cycloserine (6 mg/kg, for 10 days) had no effect on spatial working memory deficit induced by entorhinal cortex lesions. It did, however, reverse scopolamine-induced deficits in the passive avoidance test when given acutely at the same dose. In contrast, aniracetam (50 mg/kg, for 10 days) produced beneficial effects in the radial maze test in rats with entorhinal cortex lesions, but given at the same dose acutely did not influence scopolamine-induced amnesia. The positive effect of d-cycloserine against scopolamine-induced amnesia may be probably related to the cholinergic-glutamatergic interaction in the hippocampus. The negative data obtained with d-cycloserine in the model of entorhinal cortex lesions-induced cognitive deficits could be taken as a hint that it is probably not suitable for the symptomatological therapy of Alzheimer's disease. The mechanism of positive action of aniracetam cannot be explained on the basis of AMPA receptor modulation, as the dose used (50 mg/kg) is well below that required for the effect at AMPA receptors. Other actions such as peripheral effects or modulation of metabotropic receptors seem more likely.

Dose-related impairment of spatial learning by intrahippocampal scopolamine: antagonism by ondansetron, a 5-HT3 receptor antagonist

To study the role of hippocampal muscarinic receptors in spatial learning, various doses of scopolamine were injected bilaterally into the CA1 region of the dorsal hippocampus of rats trained in a two-platform spatial discrimination task. Scopolamine administered 10 min before each training session at doses ranging from 3.75 to 15 micrograms/microliter impaired choice accuracy, had no effect on choice latency and increased the errors of omission only with 7.5 micrograms on day 1 and with 15 micrograms on days 1 and 2 of training. No dose affected choice accuracy or latency of a non-spatial visual discrimination task. A subcutaneous dose of 1 microgram/kg ondansetron, a 5-HT3 receptor antagonist, 30 min before each training session prevented the impairment of choice accuracy by intrahippocampal 3.75 micrograms scopolamine but 0.1 microgram/kg ondansetron had no such effect. No dose of ondansetron by itself modified the acquisition of spatial learning. The results suggest that relatively low doses of scopolamine in the dorsal hippocampus selectively impair the acquisition of a spatial discrimination task, and that blockade of 5-HT3 receptors prevents the deficit caused by the muscarinic antagonist. The utility of the deficit of spatial learning induced by intrahippocampal scopolamine for modelling some aspects of memory disturbances in Alzheimer's disease is discussed.

Effect of cholinergic activation by physostigmine on working memory failure caused in rats by pharmacological manipulation of hippocampal glutamatergic and 5-HTergic neurotransmission

The muscarinic receptor antagonist scopolamine significantly increased the number of errors in the working memory task with a three-panel runway setup, when injected bilaterally at 3.2 micrograms/side into the dorsal hippocampus. The increase in working memory errors induced by intrahippocampal 3.2 micrograms/side scopolamine was reduced by concurrent injection of the cholinesterase inhibitor physostigmine (1.0 and 3.2 micrograms/side. However, physostigmine (3.2 micrograms/side) did not affect an increase in working memory errors induced by intrahippocampal injection of the competitive N-methyl-D-aspartate (NMDA) receptor antagonist (+/)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) at 32 ng/side. Likewise, physostigmine (3.2 micrograms/side) was ineffective in reducing an increase in working memory errors caused by intrahippocampal administration of the 5-hydroxytryptamine1A (5-HT1A) receptor agonist (+/-)-8-hydroxy-2-(di-n-pro-pylamino)tetralin (8-OH-DPAT) at 10 micrograms/side. These results suggest that the septohippocampal cholinergic activity is necessary for normal working memory processes, but that cholinergic activation neither compensates loss of hippocampal NMDA receptor-mediated neurotransmission nor counteracts the overstimulation of hippocampal 5-HT1A receptors in terms of working memory function.

The neurosteroid pregnenolone sulfate reduces learning deficits induced by scopolamine and has promnestic effects in mice performing an appetitive learning task

The effects of the neurosteroid pregnenolone sulfate (PS) on learning as well as on scopolamine-induced learning deficits were studied in Swiss mice using an appetitively reinforced Go-No Go visual discrimination task. Subcutaneous (SC) administration of scopolamine (0.3-3 mg/kg) after the first session of training dose-dependently impairs learning during the following sessions in this task. Moreover, intracerebroventricular (ICV) administration of PS (0.01-10 nmol) dose-dependently blocks learning deficits induced by scopolamine (3 mg/kg), with the most potent effects at the dose of 0.5 nmol PS. In addition to antagonizing the amnestic effects of scopolamine, PS (0.5 nmol ICV) has a memory-enhancing effect, when administered alone after the first training session. Scopolamine (3 mg/kg SC) also produced substantial deficits on retrieval performance in the Go-No Go visual discrimination task, and caused motor disturbances, when administered 15 min before testing. PS (0.5 nmol ICV) also reduced scopolamine-induced deficits on retrieval but had no effect on scopolamine-induced motor impairments in the traction reflex test. Such a rapid effect of PS on memory processes may be mediated via NMDA and/or GABAA receptors.

Galanin microinjected into the medial septum inhibits scopolamine-induced acetylcholine overflow in the rat ventral hippocampus

Galanin-like immunoreactive terminals hyperinnervate the basal forebrain cholinergic neurons in Alzheimer's disease. To investigate the hypothesis that galanin acts directly on basal forebrain cell bodies, in vivo microdialysis studies were conducted in awake rats which analyzed the actions of galanin on acetylcholine release. Microinjection of galanin into the cholinergic cell body region of the medial septum-diagonal band (MS-DBB) inhibited acetylcholine release in the ventral hippocampus. These results are consistent with an interpretation that galanin terminals synapsing on cholinergic cell bodies of the basal forebrain may serve to inhibit the release of acetylcholine in the terminal fields of the cholinergic neurons.

Aniracetam restores object recognition impaired by age, scopolamine, and nucleus basalis lesions

Object recognition was investigated in adult and aging male rats in a two-trials, unrewarded, test that assessed a form of working-episodic memory. Exploration time in the first trial, in which two copies of the same object were presented, was recorded. In the second trial, in which one of the familiar objects and a new object were presented, the time spent exploring the two objects was separately recorded and a discrimination index was calculated. Adult rats explored the new object longer than the familiar object when the intertrial time ranged from 1 to 60 min. Rats older than 20 months of age did not discriminate between familiar and new objects. Object discrimination was lost in adult rats after scopolamine (0.2 mg/kg SC) administration and with lesions of the nucleus basalis, resulting in a 40% decrease in cortical ChAT activity. Both aniracetam (25, 50, 100 mg/kg os) and oxiracetam (50 mg/kg os) restored object recognition in aging rats, in rats treated with scopolamine, and with lesions of the nucleus basalis. In the rat, object discrimination appears to depend on the integrity of the cholinergic system, and nootropic drugs can correct its disruption.

The effects of a benzodiazepine receptor antagonist beta-carboline ZK-93426 on scopolamine-induced impairment on attention, memory and psychomotor skills

The effects of a single dose of scopolamine alone and in combination with ZK 93426 (a beta-carboline antagonist at the GABAA/BZ receptor complex with weak inverse agonist activity) were tested in two studies. In one study (study 1) the emphasis of enquiry was on different stages of information processing measured by a psychometric battery; in the second study (study 2) performance at different stages of memory and psychomotor abilities was tested and electroencephalogram recordings and video-tracking were also performed. Each study consisted of two parts, part I in which scopolamine (0.5 mg; 1 ml) or placebo were administered subcutaneously, and part II in which scopolamine (0.5 mg; 1 ml) was administered subcutaneously followed by an intravenous injection of ZK 93426 (0.04 mg; 0.04 ml/kg) or placebo. Thirty-six volunteers, who were randomly allocated to receive one of the two treatments (n = 18 per treatment), participated in each part. In study 1 attention was measured by a continuous attention task and a rapid information processing task, vigilance was measured by a visual vigilance task, and working memory and reasoning were evaluated by a logical reasoning task. A visual memory task was also included to measure acquisition and retention. In study 2 acquisition and short term storage and retrieval were measured by a word lists-Buschke restricted reminding procedure, and retention was tested by delayed recall and recognition. Psychomotor performance was assessed by measuring tapping speed (related to gross motoric abilities) and a pegboard task (related to fine motoric abilities). A task to measure working memory, the Pauli test, was also included. In study 1 scopolamine significantly impaired performance in the attentional and vigilance tasks (P < 0.05), but there was no effect in the logical reasoning task main measurements of time and accuracy. In study 2, scopolamine also impaired performance in the psychomotor tasks (P < 0.05) and the Pauli test. ZK 93426 partially antagonised most of the effects of scopolamine on memory and attention, suggesting that an interaction between the GABA-ergic and cholinergic systems is reflected in measurements of both attention and memory. In general a dissociation was found in the effects of scopolamine on memory, i.e. scopolamine impaired performance during all acquisition measurements but left retention unaffected.

Benzodiazepine receptor stimulation blocks scopolamine-induced learning impairments in a water maze task

Central cholinergic (ACh) blockade produces profound cognitive impairments in human and animal subjects. Our previous research demonstrated that ACh blockade exacerbates stress-induced adrenocorticotrophin (ACTH) and corticosterone (CORT) secretion, and increases anxiety-like behavior (ALB) in rats. The fact that all these responses occur following the same manipulation led us to question whether or not increases in ALB might play a part in the cognitive deficits. This issue was all the more intriguing given that anxiolytic agents such as benzodiazepines are reported to produce learning and memory impairments on their own. We reasoned that a low dose of diazepam (DZP) with no apparent cognitive effects itself, might be able to antagonize an impairment induced by scopolamine (SCOP). Adult male Lister rats (n = 6/group) were administered IP either vehicle (VEH), 0.5 mg/kg DZP, 0.25 mg/kg SCOP, or 0.5 mg/kg DZP, followed 20 min later by 0.25 mg/kg SCOP, and tested 20 min later in a water maze for latency to locate a hidden platform and for path length taken to the platform. Rats were tested in an acquisition phase (Day 1) and a retention phase (Day 2), as well as on a visually guided task. On Day 1, SCOP produced a marked acquisition deficit that was unaffected by DZP. DZP by itself had no obvious effect. However, whereas SCOP resulted in a persistent deficit on the retention task (Day 2), pretreatment with DZP prior to SCOP on Day 1 completely abolished the impairment. There were no group differences on the visually cued task. We contend that SCOP-induced cognitive deficits may, in part, be due to increases in ALB. Stimulation of benzodiazepine receptors may offset the loss of cholinergic systems underlying consolidation mechanisms, but not those mediating immediate task performance. Whether this effect of DZP relates to an action on ALB remains to be elucidated.

Effects of thioperamide on the cholinergic system and the step-through passive avoidance test in mice

We investigated the effects of thioperamide, a histamine H3-receptor antagonist, on a scopolamine-induced learning deficit in the step-through passive avoidance test in mice, and on contents of acetylcholine and choline in the brain. In a behavioral study, thioperamide (20 mg/kg) alone slightly ameliorated scopolamine-induced learning deficit, and pretreatment with zolantidine, a histamine H2-receptor antagonist, significantly enhanced the ameliorating effect of thioperamide. This enhanced ameliorating effect of thioperamide was antagonized by pyrilamine, a histamine H1-receptor antagonist and (R)-alpha-methylhistamine, a histamine H3-receptor agonist, suggesting that thioperamide showed the ameliorating effect via histamine H3 receptors and/or histamine H1 receptors. In the biochemical study, thioperamide (20 mg/kg) in combination with zolantidine (20 mg/kg) significantly increased contents of choline in most of brain regions. These findings suggest that there is a close relationship between histaminergic and cholinergic systems in the brain, and that the histaminergic system may play certain important roles in learning and memory.

Caffeine attenuates scopolamine-induced memory impairment in humans

Caffeine consumption can be beneficial for cognitive functioning. Although caffeine is widely recognized as a mild CNS stimulant drug, the most important consequence of its adenosine antagonism is cholinergic stimulation, which might lead to improvement of higher cognitive functions, particularly memory. In this study, the scopolamine model of amnesia was used to test the cholinergic effects of caffeine, administered as three cups of coffee. Subjects were 16 healthy volunteers who received 250 mg caffeine and 2 mg nicotine separately, in a placebo-controlled double-blind cross-over design. Compared to placebo, nicotine attenuated the scopolamine-induced impairment of storage in short-term memory and attenuated the scopolamine-induced slowing of speed of short-term memory scanning. Nicotine also attenuated the scopolamine-induced slowing of reaction time in a response competition task. Caffeine attenuated the scopolamine-induced impairment of free recall from short- and long-term memory, quality and speed of retrieval from long-term memory in a word learning task, and other cognitive and non-cognitive measures, such as perceptual sensitivity in visual search, reading speed, and rate of finger-tapping. On the basis of these results it was concluded that caffeine possesses cholinergic cognition enhancing properties. Caffeine could be used as a control drug in studies using the scopolamine paradigm and possibly also in other experimental studies of cognitive enhancers, as the effects of a newly developed cognition enhancing drug should at least be superior to the effects of three cups of coffee.

Ocular effects of hyoscine in double dose transdermal administration and its reversal by low dose pyridostigmine

The potential of low dose (30 mg t.i.d) pyridostigmine to reduce the ocular side effects of double dose transdermal controlled release hyoscine was evaluated by the study of near visual acuity, accommodation amplitude and pupil diameter in a placebo controlled, double masked study. We studied 47 healthy men (age 18-21 yr) in 3 groups: 16 assigned to placebo hyoscine and placebo pyridostigmine, 15 assigned to double dose hyoscine and placebo pyridostigmine, and 16 to double dose hyoscine and pyridostigmine. Subjects were tested during 48 h of treatment and 48 h of washout period. Blood cholinesterase inhibition level and amount of hyoscine released from the patches were used as parameters of reliability. Difference between groups was assessed using change from baseline scores. Double dose hyoscine caused decrease in near visual acuity to a mean of 14/18. Accommodation amplitude was decreased in the double dose transdermal hyoscine group from 9.19 +/- 1.04 to 4.83 +/- 1.97 diopters of accommodation. This decrease was significant when compared to the placebo group (p < 0.05) and to the pyridostigmine-protected group (p < 0.05). Pyridostigmine, however, did not significantly change the hyoscine-induced mydriasis of 1.47 + 0.15 mm change from baseline (p < 0.05). These results suggest that pyridostigmine administration may be beneficial in shortening recovery time when near vision impairment is experienced following single and double dose transdermal hyoscine administration.

Reversal of scopolamine induced amnesia in rats by the steroid sulfatase inhibitor estrone-3-O-sulfamate

The intent of the study was to determine whether altering the metabolism of neurosteroids via blockade of the enzyme, steroid sulfatase, could enhance retention test performance in rats. The steroid sulfatase inhibitor estrone-3-O-sulfamate (EMATE) was administered alone and in combination with the neurosteroid dehydroepiandrosterone sulfate (DHEAS) to rats which were then tested for the reversal of scopolamine induced amnesia. EMATE enhanced the reversal of amnesia by DHEAS as measured by a passive avoidance test. When administered without DHEAS, as a single acute dose, EMATE had no effect. When administered without DHEAS over 10 consecutive days, however, EMATE significantly improved retention. These results suggest that steroid sulfatase inhibition can potentiate the memory enhancing properties of DHEAS. The study also suggests that increasing the levels of endogenous sulfated neurosteroids via the inhibition of steroid sulfatase activity may enhance learning and/or memory function.