Scopolamine model of dementia: electroencephalogram findings and cognitive performance

Pharmacological models in Alzheimer's disease research

Wider use of pharmacological models would facilitate the development of new drugs for Alzheimer's disease (AD), The two main models currently used are based on the cholinergic and glutamatergic hypotheses of AD, Although they lead to some of the attention and memory impairment observed in AD, they do not fully reproduce the AD pattern. The few studies that used a combination modeling approach, ie, the simultaneous administration of several drugs with the aim of impairing several neurotransmitters or different aspects of a single system, have reported no or marginal cumulative effect. On the basis of current understanding of glutamate and acetylcholine involvement in AD pathophysiology, we suggest that models using selective muscarinic-1 (M(1)) receptor blockers would better mimic the status of the cholinergic system in AD, This kind of model might be suitable for the assessment of drugs that do not act directly on the cholinergic system.

The pharmacological sensitivity of a touchscreen-based visual discrimination task in the rat using simple and perceptually challenging stimuli

RATIONALE

Cognitive testing with touchscreen-equipped operant boxes ('touchscreens') is becoming increasingly popular. Tasks, such as paired associate learning or reversal learning of visual stimuli, have the discrimination of visual stimuli as a fundamental component. However, the effect of drugs commonly used in the study of cognitive mechanisms has yet to be described in a visual discrimination.

OBJECTIVE

The objective of the study was to profile a range of psychoactive agents (glutamatergic, dopaminergic, and cholinergic agonists and antagonists) known to be important in cognitive processing on visual discrimination performance using a touch sensitive computer monitor.

METHODS

Male Lister Hooded rats were trained to a stable level of performance in a simple visual discrimination. In Experiment 1, the effect of MK-801, phencyclidine, memantine, dextroamphetamine sulphate (D-amphetamine) and scopolamine was assessed. In Experiment 2, the stimuli were blended together resulting in a perceptually more demanding discrimination and a reduction in accuracy. The rats used in Experiment 1 were then retested with these 'morphed' stimuli under the influence of the above compounds.

RESULTS

MK-801, PCP, and D-amphetamine induced selective deficits in accuracy in both versions of the task. In contrast, scopolamine and memantine produced non-selective deficits in accuracy. Morphing the stimuli reduced accuracy, but did not alter the observed behavioural profile after compound administration.

CONCLUSION

These data improve our understanding of the basic neuropharmacology of a visual discrimination in cognitive tests employing touchscreens and will aid in the interpretation of pharmacological studies with more cognitively demanding methodologies.

Place and direction learning in a spatial T-maze task by neonatal piglets

Pigs are a valuable animal model for studying neurodevelopment in humans due to similarities in brain structure and growth. The development and validation of behavioral tests to assess learning and memory in neonatal piglets are needed. The present study evaluated the capability of 2-week old piglets to acquire a novel place and direction learning spatial T-maze task. Validity of the task was assessed by the administration of scopolamine, an anti-cholinergic drug that acts on the hippocampus and other related structures, to impair spatial memory. During acquisition, piglets were trained to locate a milk reward in a constant place in space, as well as direction (east or west), in a plus-shaped maze using extra-maze visual cues. Following acquisition, reward location was reversed and piglets were re-tested to assess learning and working memory. The performance of control piglets in the maze improved over time (P < 0.0001), reaching performance criterion (80 % correct) on day 5 of acquisition. Correct choices decreased in the reversal phase (P < 0.0001), but improved over time. In a separate study, piglets were injected daily with either phosphate-buffered saline (PBS; control) or scopolamine prior to testing. Piglets administered scopolamine showed impaired performance in the maze compared to controls (P = 0.03), failing to reach performance criterion after 6 days of acquisition testing. Collectively, these data demonstrate that neonatal piglets can be tested in a spatial T-maze task to assess hippocampal-dependent learning and memory.

Animal models in the drug discovery pipeline for Alzheimer's disease

With increasing feasibility of predicting conversion of mild cognitive impairment to dementia based on biomarker profiling, the urgent need for efficacious disease-modifying compounds has become even more critical. Despite intensive research, underlying pathophysiological mechanisms remain insufficiently documented for purposeful target discovery. Translational research based on valid animal models may aid in alleviating some of the unmet needs in the current Alzheimer's disease pharmaceutical market, which includes disease-modification, increased efficacy and safety, reduction of the number of treatment unresponsive patients and patient compliance. The development and phenotyping of animal models is indeed essential in Alzheimer's disease-related research as valid models enable the appraisal of early pathological processes - which are often not accessible in patients, and subsequent target discovery and evaluation. This review paper summarizes and critically evaluates currently available animal models, and discusses their value to the Alzheimer drug discovery pipeline. Models dealt with include spontaneous models in various species, including senescence-accelerated mice, chemical and lesion-induced rodent models, and genetically modified models developed in Drosophila melanogaster, Caenorhabditis elegans, Danio rerio and rodents. Although highly valid animal models exist, none of the currently available models recapitulates all aspects of human Alzheimer's disease, and one should always be aware of the potential dangers of uncritical extrapolating from model organisms to a human condition that takes decades to develop and mainly involves higher cognitive functions.

Cholinesterase inhibitors improve both memory and complex learning in aged beagle dogs

Similar to patients with Alzheimer's disease (AD), dogs exhibit age-dependent cognitive decline, amyloid-β (Aβ) pathology, and evidence of cholinergic hypofunction. The present study sought to further investigate the role of cholinergic hypofunction in the canine model by examining the effect of the cholinesterase inhibitors phenserine and donepezil on performance of two tasks, a delayed non-matching-to-position task (DNMP) designed to assess working memory, and an oddity discrimination learning task designed to assess complex learning, in aged dogs. Phenserine (0.5 mg/kg; PO) significantly improved performance on the DNMP at the longest delay compared to wash-out and partially attenuated scopolamine-induced deficits (15 μg/kg; SC). Phenserine also improved learning on a difficult version of an oddity discrimination task compared to placebo, but had no effect on an easier version. We also examined the effects of three doses of donepezil (0.75, 1.5, and 6 mg/kg; PO) on performance of the DNMP. Similar to the results with phenserine, 1.5 mg/kg of donepezil improved performance at the longest delay compared to baseline and wash-out, indicative of memory enhancement. These results further extend the findings of cholinergic hypofunction in aged dogs and provide pharmacological validation of the canine model with a cholinesterase inhibitor approved for use in AD. Collectively, these studies support utilizing the aged dog in future screening of therapeutics for AD, as well as for investigating the links among cholinergic function, Aβ pathology, and cognitive decline.

Induction of activity-dependent LTD requires muscarinic receptor activation in medial prefrontal cortex

The medial prefrontal cortex (mPFC) forms part of a neural circuit involved in the formation of lasting associations between objects and places. Cholinergic inputs from the basal forebrain innervate the mPFC and may modulate synaptic processes required for the formation of object-in-place memories. To investigate whether acetylcholine regulates synaptic function in the rat mPFC, whole-cell voltage-clamp recordings were made from pyramidal neurons in layer V. Bath application of the cholinergic agonist carbachol caused a potent and long-term depression (LTD) of synaptic responses that was blocked by the muscarinic receptor antagonist scopolamine and was mimicked, in part, by the M(1) receptor agonists McN-A-343 or AF102B. Furthermore, inhibition of PKC blocked carbachol-mediated LTD. We next determined the requirements for activity-dependent LTD in the prefrontal cortex. Synaptic stimulation that was subthreshold for producing LTD did, however, result in LTD when acetylcholine levels were enhanced by inhibition of acetylcholinesterase or when delivered in the presence of the M(1)-selective positive allosteric modulator BQCA. Increasing the levels of synaptic stimulation resulted in M(1) receptor-dependent LTD without the need for pharmacological manipulation of acetylcholine levels. These results show that synaptic stimulation of muscarinic receptors alone can be critical for plastic changes in excitatory synaptic transmission in the mPFC. In turn, these muscarinic mediated events may be important in the formation of object-in-place memories. A loss of basal forebrain cholinergic neurons is a classic hallmark of Alzheimer's dementia and our results provide a potential explanation for the loss of memory associated with the disease.

The acute effects of dimebolin, a potential Alzheimer's disease treatment, on working memory in rhesus monkeys

BACKGROUND

Dimebolin (latrepirdine), a compound with multiple potential drug targets, is being evaluated in clinical trials for the treatment of Alzheimer's disease (AD) and preliminary results suggest it can slow the disease process. There is also evidence that dimebolin directly improves aspects of cognition. Here we examined the acute effect of dimebolin on components of working memory in non-human primates, young adult (11-17 years old) and aged (20-31 years old) rhesus macaques.

EXPERIMENTAL APPROACH

The effects of dimebolin (3.9-118 µg kg(-1)) on working memory, as measured by performance on delayed matching-to-sample (DMTS), were examined in the normal young adult monkeys and aged adult monkeys. All the monkeys studied were proficient in the performance of a computer-assisted DMTS task. In a subsequent experiment in the same subjects, dimebolin was administered 15 min before a cognitively-impairing dose (20 µg kg(-1)) of scopolamine.

KEY RESULTS

In both the young adult and aged monkeys, dimebolin significantly increased the DMTS task accuracies. In young adults, the task improvement was associated with long (retention/retrieval) delay trials, and a protracted enhancement was observed for sessions run 24 h post administration of a single dose. Dimebolin did not significantly attenuate the scopolamine-induced impairment. In the aged monkeys, dimebolin significantly improved the reduced task accuracies associated with long delay intervals.

CONCLUSIONS AND IMPLICATIONS

Here we demonstrated that dimebolin is able to improve components of working memory in monkeys and to induce a protracted response for at least 24 h after administration of a single dose.

Pharmacokinetic-pharmacodynamic relationships of central nervous system effects of scopolamine in healthy subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• The cholinergic system is important for different central nervous system functions, including memory, learning and attention. Scopolamine, a centrally active muscarinic antagonist, has been used to model dementia and to demonstrate the pharmacological effects of cholinergic drugs, but for most effects the concentration-effect relationships are unknown.

WHAT THIS STUDY ADDS

• We determined the pharmacokinetic-pharmacodynamic relationships of scopolamine using a multidimensional central nervous system test battery in a large group of healthy volunteers. The results suggested there are various functional cholinergic systems with different pharmacological characteristics, which can be used to study the effects of drugs that directly or indirectly modify cholinergic systems. The design of such studies should take the different concentration-effect relationships into account. AIM(S) Although scopolamine is a frequently used memory impairment model, the relationships between exposure and corresponding central nervous system (CNS) effects are mostly unknown. The aim of our study was to characterize these using pharmacokinetic-pharmacodynamic (PK-PD) modelling.

METHODS

In two double-blind, placebo-controlled, four-way crossover studies, 0.5-mg scopolamine was administered i.v. to 90 healthy male subjects. PK and PD/safety measures were monitored pre-dose and up to 8.5 h after administration. PK-PD relationships were modelled using non-linear mixed-effect modelling.

RESULTS

Most PD responses following scopolamine administration in 85 subjects differed significantly from placebo. As PD measures lagged behind the plasma PK profile, PK-PD relationships were modelled using an effect compartment and arbitrarily categorized according to their equilibration half-lives (t(1/2) k(eo) ; hysteresis measure). t(1/2) k(eo) for heart rate was 17 min, saccadic eye movements and adaptive tracking 1-1.5 h, body sway, smooth pursuit, visual analogue scales alertness and psychedelic 2.5-3.5 h, pupil size, finger tapping and visual analogue scales feeling high more than 8 h.

CONCLUSIONS

Scopolamine affected different CNS functions in a concentration-dependent manner, which based on their distinct PK-PD characteristics seemed to reflect multiple distinct functional pathways of the cholinergic system. All PD effects showed considerable albeit variable delays compared with plasma concentrations. The t(1/2) k(eo) of the central effects was longer than of the peripheral effects on heart rate, which at least partly reflects the long CNS retention of scopolamine, but possibly also the triggering of independent secondary mechanisms. PK-PD analysis can optimize scopolamine administration regimens for future research and give insight into the physiology and pharmacology of human cholinergic systems.

Hippocampal M1 receptor function associated with spatial learning and memory in aged female rhesus macaques

Of the acetylcholine muscarinic receptors, the type 1 (M1) and type 2 (M2) receptors are expressed at the highest levels in the prefrontal cortex (PFC) and hippocampus, brain regions important for cognition. As equivocal findings of age-related changes of M1 and M2 in the nonhuman primate brain have been reported, we first assessed age-related changes in M1 and M2 in the PFC and hippocampus using saturation binding assays. Maximum M1 receptor binding, but not affinity of M1 receptor binding, decreased with age. In contrast, the affinity of M2 receptor binding, but not maximum M2 receptor binding, increased with age. To determine if in the elderly cognitive performance is associated with M1 or M2 function, we assessed muscarinic function in elderly female rhesus macaques in vivo using a scopolamine challenge pharmacological magnetic resonance imaging and in vitro using saturation binding assays. Based on their performance in a spatial maze, the animals were classified as good spatial performers (GSP) or poor spatial performers (PSP). In the hippocampus, but not PFC, the GSP group showed a greater change in T(2)*-weighted signal intensity after scopolamine challenge than the PSP group. The maximum M1 receptor binding and receptor binding affinity was greater in the GSP than the PSP group, but no group difference was found in M2 receptor binding. Parameters of circadian activity positively correlated with the difference in T(2)*-weighted signal intensity before and after the challenge, the maximum M1 receptor binding, and the M1 receptor binding affinity. Thus, while in rhesus macaques, there are age-related decreases in M1 and M2 receptor binding, in aged females, hippocampal M1, but not M2, receptor function is associated with spatial learning and memory and circadian activity.

Cholinergic modulation of working memory activity in primate prefrontal cortex

The prefrontal cortex, a cortical area essential for working memory and higher cognitive functions, is modulated by a number of neurotransmitter systems, including acetylcholine; however, the impact of cholinergic transmission on prefrontal activity is not well understood. We relied on systemic administration of a muscarinic receptor antagonist, scopolamine, to investigate the role of acetylcholine on primate prefrontal neuronal activity during execution of working memory tasks and recorded neuronal activity with chronic electrode arrays and single electrodes. Our results indicated a dose-dependent decrease in behavioral performance after scopolamine administration in all the working memory tasks we tested. The effect could not be accounted for by deficits in visual processing, eye movement responses, or attention, because the animals performed a visually guided saccade task virtually error free, and errors to distracting stimuli were not increased. Performance degradation under scopolamine was accompanied by decreased firing rate of the same cortical sites during the delay period of the task and decreased selectivity for the spatial location of the stimuli. These results demonstrate that muscarinic blockade impairs performance in working memory tasks and prefrontal activity mediating working memory.

Vagus nerve stimulation modulates cortical synchrony and excitability through the activation of muscarinic receptors

Vagus nerve stimulation (VNS) is an FDA approved treatment for drug-resistant epilepsy and depression. Recently, we demonstrated the capacity for repeatedly pairing sensory input with brief pulses of VNS to induce input specific reorganization in rat auditory cortex. This was subsequently used to reverse the pathological neural and perceptual correlates of hearing loss induced tinnitus. Despite its therapeutic potential, VNS mechanisms of action remain speculative. In this study, we report the acute effects of VNS on intra-cortical synchrony, excitability, and sensory processing in anesthetized rat auditory cortex. VNS significantly increased and decorrelated spontaneous multi-unit activity, and suppressed entrainment to repetitive noise burst stimulation at 6-8 Hz but not after application of the muscarinic antagonist scopolamine. Collectively, these experiments demonstrate the capacity for VNS to acutely influence cortical synchrony and excitability and strengthen the hypothesis that acetylcholine and muscarinic receptors are involved in VNS mechanisms of action. These results are discussed with respect to their possible implications for sensory processing, neural plasticity, and epilepsy.

Cholinergic receptor subtypes and their role in cognition, emotion, and vigilance control: an overview of preclinical and clinical findings

RATIONALE

The cholinergic system has long been linked to cognitive processes. Two main classes of acetylcholine (ACh) receptors exist in the human brain, namely muscarinic and nicotinic receptors, of which several subtypes occur.

OBJECTIVES

This review seeks to provide an overview of previous findings on the influence of cholinergic receptor manipulations on cognition in animals and humans, with particular emphasis on the role of selected cholinergic receptor subtypes. Furthermore, the involvement of these receptor subtypes in the regulation of emotion and brain electrical activity as measured by electroencephalography (EEG) shall be addressed since these domains are considered to be important modulators of cognitive functioning.

RESULTS

In regard to cognition, the muscarinic receptor subtypes have been implicated mainly in memory functions, but have also been linked to attentional processes. The nicotinic α7 receptor subtype is involved in working memory, whereas the α4β2* subtype has been linked to tests of attention. Both muscarinic and nicotinic cholinergic mechanisms play a role in modulating brain electrical activity. Nicotinic receptors have been strongly associated with the modulation of depression and anxiety.

CONCLUSIONS

Cholinergic receptor manipulations have an effect on cognition, emotion, and brain electrical activity as measured by EEG. Changes in cognition can result from direct cholinergic receptor manipulation or from cholinergically induced changes in vigilance or affective state.

Bacopa monniera Attenuates Scopolamine-Induced Impairment of Spatial Memory in Mice

Scopolamine, an anticholinergic, is an attractive amnesic agent for discerning the action of candidate antiamnesic drugs. Bacopa monniera Linn (Syn. Brahmi) is one such antiamnesic agent that is frequently used in the ancient Indian medical system. We have earlier reported the reversal of diazepam-induced amnesia with B. monniera. In this study we wanted to test if scopolamine-induced impairment of spatial memory can also be ameliorated by B. monniera using water maze mouse model. The objective of study was to study the effect of B. monniera on scopolamine-induced amnesia. We employed Morris water maze scale to test the amnesic effect of scopolamine and its reversal by B. monniera. Rotarod test was conducted to screen muscle coordination activity of mice. Scopolamine significantly impaired the acquisition and retrieval of memory producing both anterograde and retrograde amnesia. Bacopa monniera extract was able to reverse both anterograde and retrograde amnesia. We propose that B. monniera's effects on cholinergic system may be helpful for developing alternative therapeutic approaches for the treatment of Alzheimer's disease.

The cholinergic system, EEG and sleep

Acetylcholine is a potent excitatory neurotransmitter, crucial for cognition and the control of alertness and arousal. Vigilance-specific recordings of the electroencephalogram (EEG) potently reflect thalamo-cortical and brainstem-cortical cholinergic activity that drives theta rhythms and task-specific cortical (de-synchronisation. Additionally, cholinergic projections from the basal forebrain act as a relay centre for the brainstem-cortical arousal system, but also directly modulate cortical activity, and thus promote wakefulness or rapid-eye movement (REM) sleep. Disease states such as sleep disorders, dementia and certain types of epilepsy are a further reflection of the potent cholinergic impact on CNS physiology and function, and highlight the relevance and inter-dependence of sleep and EEG. With novel technologies and computational tools now becoming available, advanced mechanistic insights may be gained and new avenues explored for diagnostics and therapeutics.

Herbal extracts and phytochemicals: plant secondary metabolites and the enhancement of human brain function

Humans consume a wide range of foods, drugs, and dietary supplements that are derived from plants and which modify the functioning of the central nervous sytem (CNS). The psychoactive properties of these substances are attributable to the presence of plant secondary metabolites, chemicals that are not required for the immediate survival of the plant but which are synthesized to increase the fitness of the plant to survive by allowing it to interact with its environment, including pathogens and herbivorous and symbiotic insects. In many cases, the effects of these phytochemicals on the human CNS might be linked either to their ecological roles in the life of the plant or to molecular and biochemical similarities in the biology of plants and higher animals. This review assesses the current evidence for the efficacy of a range of readily available plant-based extracts and chemicals that may improve brain function and which have attracted sufficient research in this regard to reach a conclusion as to their potential effectiveness as nootropics. Many of these candidate phytochemicals/extracts can be grouped by the chemical nature of their potentially active secondary metabolite constituents into alkaloids (caffeine, nicotine), terpenes (ginkgo, ginseng, valerian, Melissa officinalis, sage), and phenolic compounds (curcumin, resveratrol, epigallocatechin-3-gallate, Hypericum perforatum, soy isoflavones). They are discussed in terms of how an increased understanding of the relationship between their ecological roles and CNS effects might further the field of natural, phytochemical drug discovery.

The effects of the glycine reuptake inhibitor R213129 on the central nervous system and on scopolamine-induced impairments in psychomotor and cognitive function in healthy subjects

In this study the effects of R213129, a selective glycine transporter 1 inhibitor, on central nervous system function were investigated in healthy males in the absence and presence of scopolamine. This was a double-blind, placebo-controlled, 4-period crossover ascending dose study evaluating the following endpoints: body sway, saccadic and smooth pursuit eye movements, pupillometry, electroencephalography, visual analogue scales for alertness, mood, calmness and psychedelic effects, adaptive tracking, finger tapping, Visual and Verbal Learning Task, Stroop test, hormone levels and pharmacokinetics. R213129 dose levels were selected based on exposure levels that blocked the GlyT1 sites >50% in preclinical experiments. Forty-three of the 45 included subjects completed the study. Scopolamine significantly affected almost every central nervous system parameter measured in this study. R213129 alone compared with placebo did not elicit pharmacodynamic changes. R213129 had some small effects on scopolamine-induced central nervous system impairments. Scopolamine-induced finger tapping impairment was further enhanced by 3 mg R213129 with 2.0 taps/10 seconds (95% CI -4.0, -0.1), electroencephalography alpha power was increased by 10 mg R213129 with respectively 12.9% (0.7, 26.6%), scopolamine-induced impairment of the Stroop test was partly reversed by 10 mg R213129 with 59 milliseconds (-110, -7). Scopolamine produced robust and consistent effects in psychomotor and cognitive function in healthy volunteers. The most logical reason for the lack of R213129 effects seems to be that the central nervous system concentrations were too low. The effects of higher doses in healthy volunteers and the clinical efficacy in patients remain to be established.

Anti-amnesic effect of Chong-Myung-Tang on scopolamine-induced memory impairments in mice

AIM OF THE STUDY

Chong-Myung-Tang (CMT) consisted of Acorus gramineus Soland, Polygala tenuifolia Willdenow, and Poria cocos Wolf is one of the traditional Korean herbal medicines used for the therapy of learning and memory improvement. The present study was investigated the effect of CMT on learning and memory functions in SCOP-induced memory deficits mice.

MATERIALS AND METHODS

The cognitive-enhancing effect of CMT on amnesic mice induced by SCOP was investigated by assessing the passive avoidance test and the Morris water maze test. In order to confirm the underlying mechanisms of memory enhancing effects of CMT, activities of AChE, choline acetyltransferase (ChAT), and antioxidant enzymes were measured.

RESULTS

Administration of CMT significantly restored memory impairments induced by SCOP in the passive avoidance test and also reduced escape latency during trial sessions in the Morris water maze test. The increased AChE activity produced by SCOP was significantly inhibited by CMT. CMT significantly enhanced ChAT activity. Moreover, treatment with CMT to the amnesic mice induced by SCOP considerably decreased malondialdehyde levels and restored activities of superoxide dismutase and catalase to the control values.

CONCLUSIONS

These results suggest that CMT may be useful for the cognitive improvement via regulation of cholinergic marker enzyme activities and the antioxidant defense system.

Differential role of muscarinic transmission within the entorhinal cortex and basolateral amygdala in the processing of irrelevant stimuli

Cholinergic projections to the entorhinal cortex (EC) and basolateral amygdala (BLA) mediate distinct cognitive processes through muscarinic acetylcholine receptors (mAChRs). In this study, we sought to further differentiate the role of muscarinic transmission in these regions in cognition, using the latent inhibition (LI) phenomenon. LI is a cross-species phenomenon manifested as poorer conditioning to a stimulus experienced as irrelevant during an earlier stage of repeated non-reinforced pre-exposure to that stimulus, and is considered to index the ability to ignore, or to in-attend to, irrelevant stimuli. Given our recent findings that systemic administration of the mAChR antagonist scopolamine can produce two contrasting LI abnormalities in rats, ie, abolish LI under conditions yielding LI in non-treated controls, or produce abnormally persistent LI under conditions preventing its expression in non-treated controls, we tested whether mAChR blockade in the EC and BLA would induce LI abolition and persistence, respectively. We found that intra-EC scopolamine infusion (1, 10 mug per hemisphere) abolished LI when infused in pre-exposure or both pre-exposure and conditioning, but not in conditioning alone, whereas intra-BLA scopolamine infusion led to persistent LI when infused in conditioning or both stages, but not in pre-exposure alone. Although cholinergic innervation of the EC and BLA has long been implicated in attention to novel stimuli and in processing of motivationally significant stimuli, respectively, our results provide evidence that EC mAChRs also have a role in the development of inattention to stimuli, whereas BLA mAChRs have a role in re-attending to previously irrelevant stimuli that became motivationally relevant.

Involvement of phosphoinositide 3-kinase gamma in the neuro-inflammatory response and cognitive impairments induced by beta-amyloid 1-40 peptide in mice

Alzheimer disease (AD) is the most common form of dementia in the elderly, and the neuro-pathological hallmarks of AD include neurofibrillary tangles (NFT), and deposition of beta-amyloid (Abeta) in extracellular plaques. In addition, chronic inflammation due to recruitment of activated glial cells to amyloid plaques are an invariant component in AD, and several studies have reported that the use of non-steroidal anti-inflammatory drugs (NSAIDs) may provide a measure of protection against AD. In this report we have investigated whether phosphoinositide 3-kinase gamma (PI3Kgamma), which is important in inflammatory cell migration, plays a critical role in the neuro-inflammation, synaptic dysfunction, and cognitive deficits induced by intracerebroventricular injection of Abeta(1-40) in mice. We found that the selective inhibitor of PI3Kgamma, AS605240, was able to attenuate the Abeta(1-40)-induced accumulation of activated astrocytes and microglia in the hippocampus, and decrease immuno-staining for p-Akt and cyclooxygenase-2 (COX-2). Interestingly, Abeta(1-40) activated macrophages treated with AS605240 or another PI3Kgamma inhibitor, AS252424, displayed impaired chemotaxis in vitro, but their expression of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) was unaffected. Finally, AS605240 prevented Abeta(1-40)-induced cognitive deficits and synaptic dysfunction, but failed to modify scopolamine-induced amnesia. Our data suggests that inhibition of PI3Kgamma may represent a novel therapeutic target for treating AD patients.

The inhibitory avoidance test optimized for discovery of cognitive enhancers

In the present article, we describe a new protocol for the inhibitory avoidance test, with a dual purpose: (1) to provide a less variable and more reliable assessment of the efficacy of potential cognitive enhancers in antagonizing scopolamine-induced long-term-memory deficits, and (2) to secure a high throughput for pharmacological screening of cognitive enhancers. The new protocol consists of two acquisition trials that are followed 24 h later by a single retention trial. In the present study, this protocol clearly dissociated the frequency distributions of retention latencies between scopolamine- and vehicle-treated groups and allowed validation by means of two acetylcholinesterase inhibitors-tacrine and donepezil-that proved to be active in counteracting the scopolamine-induced memory deficit. This protocol also produced stability of the behavioral response to pharmacological agents over a 3-year period. A statistical power analysis indicated that, depending on the efficacy of the drug/dose, a sample size of 5-12 mice was required in order to show a reversal of the scopolamine-induced memory deficit. The double-trial acquisition protocol is suitable for testing cognitive enhancers, while also providing a clearly enhanced throughput.

Systemic and intrabasalis administration of the orexin-1 receptor antagonist, SB-334867, disrupts attentional performance in rats

RATIONALE

Orexin neurons project to a number of brain regions, including onto basal forebrain cholinergic neurons. Basal forebrain corticopetal cholinergic neurons are known to be necessary for normal attentional performance. Thus, the orexin system may contribute to attentional processing.

OBJECTIVES

We tested whether blockade of orexin-1 receptors would disrupt attentional performance.

METHODS

Rats were trained in a two-lever sustained attention task that required discrimination of a visual signal (500, 100, 25 ms) from trials with no signal presentation. Rats received systemic or intrabasalis administration of the orexin-1 receptor antagonist, SB-334867, prior to task performance.

RESULTS

Systemic administration of the orexin-1 receptor antagonist, SB-334867 (5.0 mg/kg), decreased detection of the longest duration signal. Intrabasalis SB-334867 (0.60 microg) decreased overall accuracy on trials with longer signal durations.

CONCLUSIONS

These findings suggest that orexins contribute to attentional processing, although neural circuits outside of basal forebrain corticopetal cholinergic neurons may mediate some of these effects.

Scopolamine induced deficits in a battery of rat cognitive tests: comparisons of sensitivity and specificity

Despite much research, the cognitive effects of scopolamine hydrobromide, a cholinergic antagonist, remain controversial. Scopolamine affects multiple systems each of which can impact behavior. One way to tease apart the effects of the drug is to determine the effects of low scopolamine doses on different abilities. The present experiments compared the effects of low doses of scopolamine on a single group of rats conducting a battery of behavioral tasks: Morris water maze, radial arm maze, delayed non-matching to position tasks, and fixed ratio 5 bar pressing. The behavioral battery ranged from tasks having little cognitive demand to those thought to be based more on attention and spatial-working memory. Control experiments using additional groups of rats assessing peripheral versus central effects were conducted with both liquid and dry reinforcement and with methyl scopolamine. Furthermore, the 5-choice serial reaction time test assessed scopolamine effects on attention. The data show a wide spectrum of central and peripheral cholinergic involvement. The central effects include attention and motor initiation, both of which impact and interact with the mnemonic function of acetylcholine. These results show that a limited disruption of the central cholinergic system can have profound effects on attention and/or psychomotor control before any measurable mnemonic disruption.

Ibuprofen treatment modifies cortical sources of EEG rhythms in mild Alzheimer's disease

OBJECTIVE

Non-steroidal anti-inflammatory drugs such as ibuprofen have a protective role on risk of Alzheimer's disease (AD). Here we evaluated the hypothesis that long-term ibuprofen treatment affects cortical sources of resting electroencephalographic (EEG) rhythms in mild AD patients.

METHODS

Twenty-three AD patients (13 treated AD IBUPROFEN; 10 untreated AD PLACEBO) were enrolled. Resting EEG data were recorded before and 1 year after the ibuprofen/placebo treatment. EEG rhythms were delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), and beta 2 (20-30 Hz). LORETA was used for EEG source analysis.

RESULTS

In the AD PLACEBO group, amplitude of delta sources was globally greater at follow-up than baseline. Instead, amplitude of delta sources remained stable or decreased in the majority of the AD IBUPROFEN patients. Clinical (CDR) but not global cognitive status (MMSE) reflected EEG results.

CONCLUSIONS

These results suggest that in mild AD patients, a long-term ibuprofen treatment slightly slows down the progressive increment of delta rhythms as a sign of contrast against the neurodegenerative processes.

SIGNIFICANCE

They motivate future investigations with larger population and extended neuropsychological testing, to study the relationships among ibuprofen treatment, delta cortical sources, and higher order functions.

Mangiferin ameliorates scopolamine-induced learning deficits in mice

The aim of this study was to evaluate the effects of Anemarrhena asphodeloides BUNGE (AA) on cholinergic memory deficits in mice. This agent has previously been used as an antipyretic, anti-inflammatory, anti-diabetic, and antidepressant in traditional Chinese medicine. Mangiferin was isolated from AA and showed a dose-dependent inhibition of acetylcholinesterase (AChE) activity (IC(50) value, 62.8 microM). Cholinergic dysfunction was induced in mice by administering scopolamine, and the animals were then tested using the passive avoidance test as well as the Morris water maze test. Mangiferin (20 mg/kg, p.o.) significantly reversed scopolamine-induced deficits in the passive avoidance test, and also improved escape latencies in training trials and increased swimming times in the Morris water maze test (p<0.05). Mangiferin also reduced acetylcholine and tumor necrosis factor (TNF)-alpha levels induced by scopolamine in mice brain (p<0.05) and inhibited nuclear factor (NF)-kappaB activation in scopolamine or TNF-alpha-stimulated BV-2 microglial cells. These results suggest that mangiferin can improve long-term cholinergic memory deficits by AChE inhibition or cholinergic receptor stimulation and inhibition of NF-kappaB activation.

KD-501, a standardized extract of Scrophularia buergeriana has both cognitive-enhancing and antioxidant activities in mice given scopolamine

AIM OF THE STUDY

The cognitive-enhancing and antioxidant activities of KD-501, a standardized extract of the roots of Scrophularia buergeriana Miquel (Scrophulariceae) were investigated.

MATERIALS AND METHODS

KD-501 was orally administered to amnesic mice induced by scopolamine and we performed passive avoidance and the Morris water maze tests. To elucidate the mechanism of cognitive-enhancing activity, the effects of KD-501 on the activities of acetylcholinesterase and antioxidant enzymes within the cortex and hippocampus of mice were evaluated.

RESULTS

Acute and prolonged oral administration of KD-501 significantly ameliorated scopolamine-induced amnesia in passive avoidance test. In the Morris water maze test, acute and prolonged administration of KD-501 improved the impairment of spatial memory induced by scopolamine indicated by the formation of reference and working memories. The activity of acetylcholinesterase was significantly inhibited by KD-501 within the cortex and hippocampus. Moreover, the reduced activities or contents of glutathione reductase, superoxide dismutase (SOD) and reduced GSH within the cortex and hippocampus caused by scopolamine were elevated by the treatment of KD-501.

CONCLUSIONS

Taken together, it could be postulated that KD-501 may exert its potent cognitive-enhancing activity through both anti-acetylcholinesterase and antioxidative actions.

Serum anticholinergic activity and cerebral cholinergic dysfunction: an EEG study in frail elderly with and without delirium

Background

Delirium increases morbidity, mortality and healthcare costs especially in the elderly. Serum anticholinergic activity (SAA) is a suggested biomarker for anticholinergic burden and delirium risk, but the association with cerebral cholinergic function remains unclear. To clarify this relationship, we prospectively assessed the correlation of SAA with quantitative electroencephalography (qEEG) power, delirium occurrence, functional and cognitive measures in a cross-sectional sample of acutely hospitalized elderly (> 80 y) with high dementia and delirium prevalence.

Methods

61 consecutively admitted patients over 80 years underwent an extensive clinical and neuropsychological evaluation. SAA was determined by using radio receptor assay as developed by Tune, and standard as well as quantitative EEGs were obtained.

Results

15 patients had dementia with additional delirium (DD) according to expert consensus using DSM-IV criteria, 31 suffered from dementia without delirium (D), 15 were cognitively unimpaired (CU). SAA was clearly detectable in all patients but one (mean 10.9 ± 7.1 pmol/ml), but was not associated with expert-panel approved delirium diagnosis or cognitive functions. Delirium-associated EEG abnormalities included occipital slowing, peak power and alpha decrease, delta and theta power increase and slow wave ratio increase during active delirious states. EEG measures correlated significantly with cognitive performance and delirium severity, but not with SAA levels.

Conclusion

In elderly with acute disease, EEG parameters reliable indicate delirium, but SAA does not seem to reflect cerebral cholinergic function as measured by EEG and is not related to delirium diagnosis.

Modelling of the concentration--effect relationship of THC on central nervous system parameters and heart rate -- insight into its mechanisms of action and a tool for clinical research and development of cannabinoids

Pharmacokinetics after pulmonary administration of delta-9-tetrahydrocannabinol (THC) and its major metabolites 11-OH-THC and 11-nor-9-COOH-THC was quantified. Additionally, the relationship between THC and its effects on heart rate, body sway and several visual analogue scales was investigated using pharmacokinetic-pharmacodynamic (PK-PD) modelling. This provided insights useful for the research and development of novel cannabinoids and the physiology and pharmacology of cannabinoid systems. First, the PK-PD model gave information reflecting various aspects of cannabinoid systems. The delay between THC concentration and effect was quantified in equilibration half-lives of 7.68 min for heart rate and from 39.2 to 84.8 min for the CNS responses. This suggests that the effect of THC on the different responses could be due to different sites of action or different physiological mechanisms. Differences in the shape of the concentration-effect relationship could indicate various underlying mechanisms. Second, the PK-PD model can be used for prediction of THC concentration and effect profiles. It is illustrated how this can be used to optimise studies with entirely different trial designs. Third, many new cannabinoid agonists and antagonists are in development. PK-PD models for THC can be used as a reference for new agonists or as tools to quantitate the pharmacological properties of cannabinoid antagonists.

Histamine H1-receptor blockade in humans affects psychomotor performance but not memory

Results from recent animal studies suggest an important role for histamine in memory functioning. Histaminergic drugs might prove beneficial for people suffering from memory impairment. To determine if histamine is involved in memory functioning this study evaluates the effects of histaminergic dysfunction on memory performance by administrating a H1-antagonist to humans. The study was conducted according to a 4-way, double-blind, crossover design in 20 healthy female volunteers, aged 18-45 years. On each test day subjects completed three test sessions: before and around 2 and 4 h after administration of single oral doses of dexchlorpheniramine 2 mg or 4 mg, scopolamine 1 mg or placebo. Drug effects were assessed using tests of memory, psychomotor and attention performance, and subjective alertness. Results showed that dexchlorpheniramine impaired performance in tests of spatial learning, reaction time, tracking and divided attention but showed no effects on working memory, visual memory, word learning or memory scanning. Scopolamine induced a similar pattern of effects. In addition, both drugs decreased subjective alertness. In conclusion results show that dexchlorpheniramine and scopolamine clearly impaired performance on psychomotor and attention tasks but do not suggest a specific role of the histaminergic system in learning and memory in humans.

The scopolamine-reversal paradigm in rats and monkeys: the importance of computer-assisted operant-conditioning memory tasks for screening drug candidates

RATIONALE

The scopolamine-reversal model is enjoying a resurgence of interest in clinical studies as a reversible pharmacological model for Alzheimer's disease (AD). The cognitive impairment associated with scopolamine is similar to that in AD. The scopolamine model is not simply a cholinergic model, as it can be reversed by drugs that are noncholinergic cognition-enhancing agents.

OBJECTIVES

The objective of the study was to determine relevance of computer-assisted operant-conditioning tasks in the scopolamine-reversal model in rats and monkeys.

MATERIALS AND METHODS

Rats were evaluated for their acquisition of a spatial reference memory task in the Morris water maze. A separate cohort was proficient in performance of an automated delayed stimulus discrimination task (DSDT). Rhesus monkeys were proficient in the performance of an automated delayed matching-to-sample task (DMTS).

RESULTS

The AD drug donepezil was evaluated for its ability to reverse the decrements in accuracy induced by scopolamine administration in all three tasks. In the DSDT and DMTS tasks, the effects of donepezil were delay (retention interval)-dependent, affecting primarily short delay trials. Donepezil produced significant but partial reversals of the scopolamine-induced impairment in task accuracies after 2 mg/kg in the water maze, after 1 mg/kg in the DSDT, and after 50 microg/kg in the DMTS task.

CONCLUSIONS

The two operant-conditioning tasks (DSDT and DMTS) provided data most in keeping with those reported in clinical studies with these drugs. The model applied to nonhuman primates provides an excellent transitional model for new cognition-enhancing drugs before clinical trials.

5,19-cyclo-9beta,10xi-androstane-3,17-dione promotes neurotrophic factor biosynthesis in 1321N1 human astrocytoma cells and improves passive avoidance learning impairment

Since neurotrophic factors are essential for neurons to form neuronal networks and maintain neuronal functions, neurotrophic factor-like substances or inducers of neurotrophic factors can be useful for the treatment of serious neuronal diseases such as Alzheimer's and Parkinson's diseases. In the present study, we examined an effect of 5,19-cyclo-9beta,10xi-androstane-3,17-dione (CAD) on neurotrophic factor synthesis in glial cells and scopolamine-induced impairment of learning in mice. 1321N1 human astrocytoma cells promoted secretion of certain neurotrophic factors in response to CAD with no cytotoxicity, which caused dramatic neurite outgrowth in rat pheochromocytoma (PC12) cells. In fact, CAD significantly enhanced nerve growth factor (NGF) secretion and its gene expression in 1321N1 cells, in a time and concentration-dependent manner. Because second messengers such as cAMP, inositol 1,4,5-trisphosphates and Ca(2+) induce NGF gene expression, we measured activities of adenylyl cyclase and phospholipase C and intracellular Ca(2+) concentration in 1321N1 cells. However, CAD changed neither second messenger levels. CAD enhanced the gene expression of proto-oncogene, c-fos that is one of the components of transcription factor (AP-1). In addition to those above, the in vivo effects of CAD were also examined. Although injection of muscarinic receptor antagonist scopolamine impaired passive avoidance learning in mice, pretreatment with CAD significantly reversed the adverse effect in a dose-dependent manner. Taking these results together, CAD has enormous therapeutic potential for serious neuronal diseases.