Cholinergic function and intellectual decline in Alzheimer's disease

Neuroprotective effects of chlorogenic acid on scopolamine-induced amnesia via anti-acetylcholinesterase and anti-oxidative activities in mice

Chlorogenic acid is a major polyphenolic component of many plants and beverages, and is particularly abundant in coffee. We evaluated the neuroprotective effects of chlorogenic acid on learning and memory impairment induced by scopolamine (0.5 mg/kg, i.p.), a muscarinic antagonist, using the Y-maze, passive avoidance, and Morris water maze tests. The chlorogenic acid significantly improved the impairment of short-term or working memory induced by scopolamine in the Y-maze test, and significantly reversed cognitive impairments in mice as measured by the passive avoidance test. In addition, chlorogenic acid decreased escape latencies in the Morris water maze test. In a probe trial session, chlorogenic acid increased the latency time in the target quadrant in a dose-dependent manner. Ex vivo, chlorogenic acid inhibited acetylcholinesterase activity in the hippocampus and frontal cortex. Chlorogenic acid also decreased malondialdehyde levels in the hippocampus and frontal cortex. In vitro, chlorogenic acid was found to inhibit acetylcholinesterase activity (IC₅₀=98.17 μg/ml) and free radical scavenging activity (IC₅₀=3.09 μg/ml) in a dose-dependent manner. These results indicate that chlorogenic acid may exert anti-amnesic activity via inhibition of acetylcholinesterase and malondialdehyde in the hippocampus and frontal cortex.

Carbachol-induced long-term synaptic depression is enhanced during senescence at hippocampal CA3-CA1 synapses

Dysregulation of the cholinergic transmitter system is a hallmark of Alzheimer's disease and contributes to an age-associated decline in memory performance. The current study examined the influence of carbachol, a cholinergic receptor agonist, on synaptic transmission over the course of aging. Extracellular excitatory postsynaptic field potentials were recorded from CA3-CA1 synapses in acute hippocampal slices obtained from young adult (5-8 mo) and aged (22-24 mo) male Fischer 344 rats. Bath application of carbachol elicited a transient depression of synaptic transmission, which was followed by a long-lasting depression (CCh-LTD) observed 90 min after carbachol cessation in both age groups. However, the magnitude of CCh-LTD was significantly larger in senescent animals and was attenuated by N-methyl-D-aspartate receptor blockade in aged animals. Blockade of L-type Ca(2+) channels inhibited CCh-LTD to a greater extent in aged animals compared to young adults. Finally, the expression of CCh-LTD was dependent on protein synthesis. The results indicate that altered Ca(2+) homeostasis or muscarinic activation of Ca(2+) signaling contribute to the enhanced CCh-LTD during senescence.

Mechanisms of chronic nicotine treatment-induced enhancement of the sensitivity of cortical neurons to the neuroprotective effect of donepezil in cortical neurons

We have previously shown that chronic donepezil treatment induces nicotinic acetylcholine receptor up-regulation and enhances the sensitivity of the neurons to the neuroprotective effect of donepezil. Further analyses revealed that the nicotinic receptor is involved in this enhancement. In this study, we examined whether nicotinic receptor stimulation is sufficient to make neurons more sensitive to donepezil. We treated primary cultures of rat cortical neurons with nicotine and confirmed that chronic nicotine treatment induced nicotinic receptor up-regulation and made the neurons more sensitive to the neuroprotective effects of donepezil. Analyses with receptor antagonists and kinase inhibitors revealed that the effects of chronic nicotine treatment are mediated by nicotinic receptors and their downstream effectors including phosphatidylinositol 3-kinase. In contrast to chronic donepezil treatment that enhanced the level of nicotine-induced Ca(2+) influx, chronic nicotine treatment did not significantly alter the level of Ca(2+) influx.

Thinking about repairing thinking

The work of Sinden et al. suggests that it may be possible to produce improvement in the “highest” areas of brain function by transplanting brain tissue. What appears to be the limiting factor is not the complexity of the mental process under consideration but the discreteness of the lesion which causes the impairment and the appropriateness and accuracy of placement of the grafted tissue.

Therapeutic uses for neural grafts: Progress slowed but not abandoned

In spite of Stein and Glasier's justifiable conclusion that initial optimism concerning the immediate clinical applicability of neural transplantation was premature, there exists much experimental evidence to support the potential for incorporating this procedure into a therapeutic arsenal in the future. To realize this potential will require continued evolution of our knowledge at multiple levels of the clinical and basic neurosciences.

The structure, operation, and functionality of intracerebral grafts

The concept of structure, operation, and functionality, as they may be understood by clinicians or researchers using neural transplantation techniques, are briefly defined. Following Stein & Glasier, we emphasize that the question of whether an intracerebral graft is really functional should be addressed not only in terms of what such a graft does in a given brain structure, but also in terms of what it does at the level of the organism.

The NGF superfamily of neurotrophins: Potential treatment for Alzheimer's and Parkinson's disease

Stein & Glasier suggest embryonic neural tissue grafts as a potential treatment strategy for Alzheimer's and Parkinson's disease. As an alternative, we suggest that the family of nerve growth factor-related neurotrophins and their trk (tyrosine kinase) receptors underlie cholinergic basal forebrain (CBF) and dopaminergic substantia nigra neuron degeneration in these diseases, respectively. Therefore, treatment approaches for these disorders could utilize neurotrophins.

Some practical and theoretical issues concerning fetal brain tissue grafts as therapy for brain dysfunctions

Grafts of embryonic neural tissue into the brains of adult patients are currently being used to treat Parkinson's disease and are under serious consideration as therapy for a variety of other degenerative and traumatic disorders. This target article evaluates the use of transplants to promote recovery from brain injury and highlights the kinds of questions and problems that must be addressed before this form of therapy is routinely applied. It has been argued that neural transplantation can promote functional recovery through the replacement of damaged nerve cells, the reestablishment of specific nerve pathways lost as a result of injury, the release of specific neurotransmitters, or the production of factors that promote neuronal growth. The latter two mechanisms, which need not rely on anatomical connections to the host brain, are open to examination for nonsurgical, less intrusive therapeutic use. Certain subjective judgments used to select patients who will receive grafts and in assessment of the outcome of graft therapy make it difficult to evaluate the procedure. In addition, little long-term assessment of transplant efficacy and effect has been done in nonhuman primates. Carefully controlled human studies, with multiple testing paradigms, are also needed to establish the efficacy of transplant therapy.

Models of neurological defects and defects in neurological models

The transition from research to patient following advances in transplantation research is likely to be disappointing unless it includes a better understanding of critically relevant characteristics of the neurological disorder and improvements in the animal models, particularly the behavioral features. The appropriateness of the model has less to do with the species than with how the species is used.

Change of cholinergic transmission and memory deficiency induced by injection of beta-amyloid protein into NBM of rats

The change of cholinergic transmission of beta-amyloid protein (beta-AP) treated rats was studied by intracerebral microdialysis sampling combined with HPLC analysis. beta-AP(1-40) was injected into nucleus basalis magnocellularis (NBM). Passive avoidance response test (step-down test) and delayed alternation task were used for memory testing. The impairment of memory after injection of beta-AP(1-40) into NBM exhibited mainly the deficiency of short-term working memory. One week after injection of beta-AP(1-40) the release of acetylcholine (ACh) from frontal cortex of freely-moving rats decreased significantly, and the response of cholinergic nerve ending to the action of high [K(+)] solution was rather weak. In control animals the percentage of increase of ACh-release during behavioral performance was 57%, while in beta-AP(1-40)-treated rats it was 34%. The temporary increase of the ACh-release of the rat put into a new place was also significantly diminished in beta-AP(1-40) -treated rats. The results show that the injection of beta-AP(1-40) into NBM impairs the cholinergic transmission in frontal cortex, and the impairment of cholinergic transmission may be the main cause of the deficit of working memory.

MRI-based volumetric measurement of the substantia innominata in amnestic MCI and mild AD

The substantia innominata (SI) contains the nucleus basalis of Meynert, which provides the major cholinergic innervation to the entire cortical mantel and the amygdala; degeneration of nucleus basalis neurons correlates with cognitive decline in Alzheimer's disease (AD). However, whether SI atrophy occurs in individuals with amnestic mild cognitive impairment (aMCI) has not been examined thoroughly in vivo. In the present study, we developed a new protocol to measure volumetric changes in the SI from magnetic resonance imaging (MRI) scans. Participants consisted of 27 elderly controls with no cognitive impairment (NCI); 33 individuals with aMCI; and 19 patients with mild AD. SI volumes were traced on three consecutive gapless 1mm thick coronal slices. Results showed that SI volume was significantly reduced in the mild AD group compared to both NCI and aMCI participants; however, the NCI and aMCI groups did not differ from each other. Furthermore, a decrease in SI volume was related to impaired performance on declarative memory tasks even when attention was controlled.

Cognitive-enhancing activity of loganin isolated from Cornus officinalis in scopolamine-induced amnesic mice

We examined anti-amnesic activity of the methanolic extract of Cornus officinalis fruits (COT) and a major constituent, loganin using scopolamine-induced (1 mg/kg body weight, s.c.) amnesic mice with both passive avoidance and the Morris water maze tests. Oral treatment of mice with COT (100 mg/kg body weight) and loganin (1 and 2 mg/kg body weight) significantly mitigated scopolamine-induced memory deficits in passive avoidance test. In the Morris water maze test, oral treatment of loganin significantly ameliorated scopolamine-induced memory deficits showing the formation of long-term and/or short-term spatial memory. Moreover, loganin (2 mg/kg body weight) significantly inhibited acetylcholinesterase activity by as much as 45% of control in the mouse hippocampus. These results indicate that loganin may exert antiamnesic activity in in vivo through acetylcholinesterase inhibition.

Improving effects of the mushroom Yamabushitake (Hericium erinaceus) on mild cognitive impairment: a double-blind placebo-controlled clinical trial

A double-blind, parallel-group, placebo-controlled trial was performed on 50- to 80-year-old Japanese men and women diagnosed with mild cognitive impairment in order to examine the efficacy of oral administration of Yamabushitake (Hericium erinaceus), an edible mushroom, for improving cognitive impairment, using a cognitive function scale based on the Revised Hasegawa Dementia Scale (HDS-R). After 2 weeks of preliminary examination, 30 subjects were randomized into two 15-person groups, one of which was given Yamabushitake and the other given a placebo. The subjects of the Yamabushitake group took four 250 mg tablets containing 96% of Yamabushitake dry powder three times a day for 16 weeks. After termination of the intake, the subjects were observed for the next 4 weeks. At weeks 8, 12 and 16 of the trial, the Yamabushitake group showed significantly increased scores on the cognitive function scale compared with the placebo group. The Yamabushitake group's scores increased with the duration of intake, but at week 4 after the termination of the 16 weeks intake, the scores decreased significantly. Laboratory tests showed no adverse effect of Yamabushitake. The results obtained in this study suggest that Yamabushitake is effective in improving mild cognitive impairment.

Anti-amnesic properties of (+/-)-PPCC, a novel sigma receptor ligand, on cognitive dysfunction induced by selective cholinergic lesion in rats

Previous studies have reported that selective sigma-1 agonists may improve cognitive abilities in experimental animals possibly via a cholinergic mechanism. However, the issue of a direct action on to sigma-1 receptors in memory-related brain areas has been much less investigated. The newly synthetised compound methyl(1R,2S/1S,2R)-2-[4-hydroxy-4-phenylpiperidin-1-yl)methyl]-1-(4-methylphenyl) cyclopropanecarboxylate [(+/-)-PPCC] has recently been shown to possess high affinity for the sigma-1 receptor where it specifically acts as an agonist. Here, the functional effects of (+/-)-PPCC were investigated in rat models of mild or severe cognitive dysfunction based on a sub-total (<or= 70-80%) or complete (>or= 90-95%) central cholinergic depletion induced by different doses of the selective immunotoxin 192 IgG-saporin injected intraventricularly. At 5-6 weeks post-surgery, the lesioned animals exhibited dose-dependent deficits in reference memory, as assessed using the Morris water maze task, whereas working memory abilities, evaluated using the radial arm water maze task, appeared equally impaired in the two dose groups. Daily treatment with (+/-)-PPCC significantly improved both reference and working memory performance in all lesioned animals but it did not affect intact or sham-lesioned subjects. In a separate test, treatment with (+/-)-PPCC reversed the learning deficits induced by the muscarinic receptor antagonist atropine sulphate in both control and mild-lesioned rats. The effect was blocked in lesioned, but not normal animals by pre-treatment with the sigma-1 antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine. The results suggest that (+/-)-PPCC may efficiently ameliorate perturbed cognitive abilities, and that these anti-amnesic effects most probably occur via a direct interaction of the compound with sigma-1 receptors.

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.

Nerve growth factor-inducing activity of Hericium erinaceus in 1321N1 human astrocytoma cells

Neurotrophic factors are essential to maintain and organize neurons functionally; thereby neurotrophic factor-like substances or their inducers are expected to be applied to the treatment of neurodegenerative diseases such as Alzheimer's disease. In the present study, we firstly examined the effects of ethanol extracts of four edible mushrooms, Hericium erinaceus (Yamabushitake), Pleurotus eryngii (Eringi), Grifola frondosa (Maitake), and Agaricus blazei (Himematsutake), on nerve growth factor (NGF) gene expression in 1321N1 human astrocytoma cells. Among the four mushroom extracts, only H. erinaceus extract promoted NGF mRNA expression in a concentration-dependent manner. In addition, secretion of NGF protein from 1321N1 cells was enhanced by H. erinaceus extracts, and the conditioned medium of 1321N1 cells incubated with H. erinaceus extract enhanced the neurite outgrowth of PC12 cells. However, hericenones C, D and E, constituents of H. erinaceus, failed to promote NGF gene expression in 1321N1 cells. The enhancement of NGF gene expression by H. erinaceus extracts was inhibited by the c-jun N-terminal kinase (JNK) inhibitor SP600125. In addition, H. erinaceus extracts induced phosphorylation of JNK and its downstream substrate c-Jun, and increased c-fos expression, suggesting that H. erinaceus promotes NGF gene expression via JNK signaling. Furthermore we examined the efficacy of H. erinaceus in vivo. ddY mice given feed containing 5% H. erinaceus dry powder for 7 d showed an increase in the level of NGF mRNA expression in the hippocampus. In conclusion, H. erinaceus contains active compounds that stimulate NGF synthesis via activation of the JNK pathway; these compounds are not hericenones.

Functional convergence of dopaminergic and cholinergic input is critical for hippocampus-dependent working memory

Although Parkinson's disease is a movement disorder, in many patients cognitive dysfunction is an important clinical sign. It is not yet clear whether this is attributable solely to a decrease in dopamine levels, or whether other neurotransmitter systems might be involved as well. In the present study, the importance of the mesocorticolimbic dopamine pathway and a possible convergence with forebrain cholinergic projections to neocortex and hippocampus in the regulation of learning and memory abilities were investigated by using specific lesion paradigms in one or both systems. Lesioning of dopaminergic neurons in the ventral tegmental area resulted in an impaired performance in the reference memory task, whereas the execution of the working memory tasks appeared to be unaffected in the Morris water maze. Analysis of the swim paths revealed that the dopamine-depleted animals were capable of adapting a search strategy on a given testing day but failed to transfer this information to the next day, suggesting a deficit in information storage and/or recall. In contrast, cholinergic lesions alone were without effect in all test paradigms. However, when both dopamine and acetylcholine were depleted, animals were also impaired in the working memory task, indicating that a functional convergence of the inputs from these systems was critical for acquisition of spatial memory. Interestingly, such an additional acquisition deficit appeared only after hippocampal cholinergic depletion regardless of a concurrent disruption of basalo cortical cholinergic afferents. Thus, further analyses of cholinergic alterations may prove useful in better understanding the cognitive symptoms in Parkinson's disease.

Coactivation of M(1) muscarinic and alpha1 adrenergic receptors stimulates extracellular signal-regulated protein kinase and induces long-term depression at CA3-CA1 synapses in rat hippocampus

Intact cholinergic innervation from the medial septum and noradrenergic innervation from the locus ceruleus are required for hippocampal-dependent learning and memory. However, much remains unclear about the precise roles of acetylcholine (ACh) and norepinephrine (NE) in hippocampal function, particularly in terms of how interactions between these two transmitter systems might play an important role in synaptic plasticity. Previously, we reported that activation of either muscarinic M(1) or adrenergic alpha1 receptors induces activity- and NMDA receptor-dependent long-term depression (LTD) at CA3-CA1 synapses in acute hippocampal slices, referred to as muscarinic LTD (mLTD) and norepinephrine LTD (NE LTD), respectively. In this study, we tested the hypothesis that mLTD and NE LTD are independent forms of LTD, yet require activation of a common Galphaq-coupled signaling pathway for their induction, and investigated the net effect of coactivation of M(1) and alpha1 receptors on the magnitude of LTD induced. We find that neither mLTD nor NE LTD requires phospholipase C activation, but both plasticities are prevented by inhibiting the Src kinase family and extracellular signal-regulated protein kinase (ERK) activation. Interestingly, LTD can be induced when M(1) and alpha1 agonists are coapplied at concentrations too low to induce LTD when applied separately, via a summed increase in ERK activation. Thus, because ACh and NE levels in vivo covary, especially during periods of memory encoding and consolidation, cooperative signaling through M(1) and alpha1 receptors could function to induce long-term changes in synaptic function important for cognition.

Mechanisms of alpha7-nicotinic receptor up-regulation and sensitization to donepezil induced by chronic donepezil treatment

alpha7-nicotinic acetylcholine receptors are one of the most abundant subtypes of nicotinic receptors in the brain and have been shown to be involved in the neuroprotective effect of donepezil. Recently, we showed that in primary culture of rat cortical neurons, chronic donepezil treatment (10 muM, 4 days) (1) induces the up-regulation of alpha7-nicotinic receptors, (2) enhances the nicotine-induced increase in [Ca(2+)](i) and (3) enhances the sensitivity to the neuroprotective effect of donepezil. Here we demonstrate the involvement of alpha7-nicotinic receptors in these three effects. Concomitant treatment with nicotinic receptor antagonist inhibited the up-regulation of alpha7-nicotinic receptor, enhancement of the increase in [Ca(2+)](i) induced by nicotine, and enhancement of sensitivity to the neuroprotective effect of donepezil. Next, using inhibitors of phosphatidylinositol 3-kinase and mitogen-activated protein kinase signaling pathways, we demonstrate the involvement of these pathways in the up-regulation of alpha7-nicotinic receptors and in making the neurons more sensitive to the neuroprotective effects of donepezil. Concomitant chronic donepezil treatment with inhibitors of phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways inhibited nicotinic receptor up-regulation and enhancement of the response to nicotine, and enhanced the sensitivity to donepezil. This study increases understanding of the less-studied mechanism of chronic donepezil treatment-induced nicotinic receptor up-regulation and increased sensitivity to donepezil.

Strategies for molecular imaging dementia and neurodegenerative diseases

Dementia represents a heterogeneous term that has evolved to describe the behavioral syndromes associated with a variety of clinical and neuropathological changes during continuing degenerative disease of the brain. As such, there lacks a clear consensus regarding the neuropsychological and other constituent characteristics associated with various cerebrovascular changes in this disease process. But increasing this knowledge has given more insights into memory deterioration in patients suffering from Alzheimer's disease and other subtypes of dementia. The author reviews current knowledge of the physiological coupling between cerebral blood flow and metabolism in the light of state-of-the-art-imaging methods and its changes in dementia with special reference to Alzheimer's disease. Different imaging techniques are discussed with respect to their visualizing effect of biochemical, cellular, and/or structural changes in dementia. The pathophysiology of dementia in advanced age is becoming increasingly understood by revealing the underlying basis of neuropsychological changes with current imaging techniques, genetic and pathological features, which suggests that alterations of (neuro) vascular regulatory mechanisms may lead to brain dysfunction and disease. The current view is that cerebrovascular deregulation is seen as a contributor to cerebrovascular pathologies, such as stroke, but also to neurodegenerative conditions, such as Alzheimer's disease. The better understanding of these (patho) physiological mechanisms may open an approach to new interventional strategies in dementia to enhance neurovascular repair and to protect neurovascular coupling.

Water-soluble derivative of propolis mitigates scopolamine-induced learning and memory impairment in mice

The water-soluble derivative of propolis (WSDP) was prepared from fresh Chinese propolis. Its major constituents were identified by high performance liquid chromatography (HPLC) analysis. It has been reported that propolis possessed a broad spectrum of biological activities but including few studies on learning and memory by now. Thus, this study was aimed to investigate the effect of WSDP on scopolamine-induced learning and memory impairment in mice. WSDP (50 mg/kg, 100 mg/kg) was given by intragastric administration (i.g.) 40 min prior to the intraperitoneal (i.p.) injection of scopolamine (1 mg/kg). The effect on amnesia was investigated with both hidden-platform acquisition training and probe trial testing in Morris water maze test. The results from 100 mg/kg WSDP group showed significant mitigation scopolamine-induced amnesia in mice. Furthermore, WSDP's effect on the acetylcholinesterase (AChE) activity in the cerebral cortex and hippocampus was also assayed. As a result, WSDP (100 mg/kg) significantly inhibited AChE activity in the hippocampus of scopolamine-treated mice. These results indicated that WSDP may mitigate amnesia in vivo through inhibition of AChE activity in the hippocampus, which suggested propolis may have potential as a pharmaceutical of brain protection with elderly population for preventing Alzheimer's disease (AD) and other neurodegenerative diseases.

Phenserine

Phenserine, a derivative of physostigmine, was first described as an inhibitor of acetylcholinesterase (AChE) and was shown to improve cognition in various experimental paradigms in rodents and dogs. It was clinically tested for Alzheimer's disease, with moderate success in initial Phase II studies. Phenserine deserves attention for an additional quality of action: in addition to inhibiting AChE, it modulates the amount of beta-amyloid precursor protein (APP) in neuronal cell culture by reducing APP translation. This effect probably involves interaction of phenserine with a regulatory element in the 5'-untranslated region of the APP gene that controls APP expression. Phenserine apparently reduces translational efficiency of APP mRNA into protein, a process that may involve an interaction with iron and/or an iron-responsive element. As a consequence, phenserine reduces beta-amyloid peptide (Abeta) formation in vitro and in vivo. Phenserine is also unique because of differing actions of its enantiomers: (-)-phenserine is the active enantiomer for inhibition of AChE, whereas (+)-phenserine ('posiphen') has weak activity as an AChE inhibitor and can be dosed much higher. Both enantiomers are equipotent in downregulating APP expression. (+)-Posiphen may be a promising drug, either alone or in combination with (-)-phenserine, to attenuate the progression of Alzheimer's disease.

Lesions to the nucleus basalis magnocellularis lower performance but do not block the retention of a previously acquired learning set

Rats were first trained to acquire an olfactory discrimination learning set (ODLS) on 40 olfactory-unique discrimination problems. Following acquisition of ODLS, animals were lesioned bilaterally in the nucleus basalis magnocellularis (nBM) using either quisqualic acid (QUIS) or 192 IgG-saporin (SAP). QUIS animals performed significantly worse than control animals following surgery and SAP animals performed transiently worse than control animals. Despite lowered performances, both QUIS and SAP animals performed significantly better than expected by chance on trial 2 indicating retention of the ODLS previously acquired. Implications for the role of the nBM in aspects of cognitive flexibility and its role in acquisition versus retention are discussed.

Genetic and pharmacological approaches to evaluate the interaction between the cannabinoid and cholinergic systems in cognitive processes

BACKGROUND AND PURPOSE

The objective of this study was to investigate the possible interactions between the cannabinoid and cholinergic systems in memory and learning processes by using genetic and pharmacological approaches in two different behavioural models, the active avoidance and the object recognition test.

EXPERIMENTAL APPROACH

The effects induced by nicotine, physostigmine and scopolamine were studied in CB(1) receptor knockout and wild-type mice in the active avoidance paradigm. In addition, the effects of pretreatment with the CB(1) receptor antagonist rimonabant were evaluated on the responses induced by nicotine in the active avoidance and the object recognition tasks in wild-type mice.

KEY RESULTS

Nicotine (0.5 mg kg(-1) s.c.) did not modify the performance of CB(1) knockout and wild-type mice in this model, whereas scopolamine (0.5 mgkg(-1) i.p.) impaired the performance in both genotypes. Physostigmine (0.1 mg kg(-1) i.p.) increased the active avoidance performance in wild-type but not in CB(1) knockout mice. Rimonabant (0.3, 1, 3, and 10 mg kg(-1)) did not modify the performance in the active avoidance test, given alone or co-administered with nicotine. In contrast, nicotine enhanced the performance in the object recognition task but this response was attenuated by rimonabant co-administration.

CONCLUSIONS AND IMPLICATIONS

The present findings revealed that the cognitive effects of nicotine and physostigmine were attenuated in the absence of CB(1) receptor activity. Scopolamine effects were independent from CB(1) receptors.

Excessive hippocampal acetylcholine levels in acetylcholinesterase-deficient mice are moderated by butyrylcholinesterase activity

Central cholinergic systems are involved in a plethora of brain functions and are severely and selectively damaged in neurodegenerative diseases such as Alzheimer's disease and dementia with Lewy bodies. Cholinergic dysfunction is treated with inhibitors of acetylcholinesterase (AChE) while the role of butyrylcholinesterase (BChE) for brain cholinergic function is unclear. We have used in vivo microdialysis to investigate the regulation of hippocampal acetylcholine (ACh) levels in mice that are devoid of AChE (AChE-/- mice). Extracellular ACh levels in the hippocampus were 60-fold elevated in AChE-/- mice compared with wild-type (AChE+/+) animals. In AChE-/- mice, calcium-free conditions reduced hippocampal ACh levels by 50%, and infusion of tetrodotoxin by more than 90%, indicating continuous ACh release. Infusion of a selective AChE inhibitor (BW284c51) caused a dose-dependent, up to 16-fold increase of extracellular ACh levels in AChE+/+ mice but did not change ACh levels in AChE-/- mice. In contrast, infusion of a selective inhibitor of BChE (bambuterol) caused up to fivefold elevation of ACh levels in AChE-/- mice, but was without effect in AChE+/+ animals. These results were corroborated with two other specific inhibitors of AChE and BChE, tolserine and bis-norcymserine, respectively. We conclude that lack of AChE causes dramatically increased levels of extracellular ACh in the brain. Importantly, in the absence of AChE, the levels of extracellular ACh in the brain are controlled by the activity of BChE. These results point to a potential usefulness of BChE inhibitors in the treatment of central cholinergic dysfunction in which brain AChE activity is typically reduced.

[Development of anti-dementia drugs related to neurotrophic factors]

Neurotrophic factor-like substances and inducers of neurotrophic factor biosynthesis have enormous therapeutic potential for serious neuronal diseases such as Alzheimer's disease. Here, we discuss about the pharmacological effects of scabronines and beta-eudesmol as promising candidates of leading compounds against the dementia. In addition, we discuss about the signaling pathway of nerve growth factor and cyclic AMP in order to seek the signaling molecules as targets of drug development.

Coexistence of muscarinic long-term depression with electrically induced long-term potentiation and depression at CA3-CA1 synapses

Our laboratory recently characterized a form of long-term depression (LTD) at CA3-CA1 synapses mediated by M1 muscarinic receptors (mAChRs), termed muscarinic LTD (mLTD). mLTD is both activity and NMDAR dependent, characteristics shared by forms of synaptic plasticity thought to be relevant to learning and memory, including long-term potentiation (LTP) induced by high-frequency stimulation (HFS-LTP) and long-term depression induced by low-frequency stimulation (LFS-LTD). However, it remains unclear whether mLTD can occur sequentially with these electrically induced forms of hippocampal plasticity or whether mLTD might interact with them. The first goal of this study was to examine the interplay of mLTD and HFS-LTP. We report that mLTD expression does not alter subsequent induction of HFS-LTP and, further, at synapses expressing HFS-LTP, mLTD can mediate a novel form of depotentiation. The second goal was to determine whether mLTD would alter LFS-LTD induction and/or expression. Although we show that mLTD is occluded by saturation of LFS-LTD, suggesting mechanistic similarity between these two plasticities, saturation of mLTD does not occlude LFS-LTD. Surprisingly, however, the LFS-LTD that follows cholinergic receptor activation is NMDAR independent, indicating that application of muscarinic agonist induces a change in the induction mechanism required for LFS-LTD. These data demonstrate that mLTD can coexist with electrically induced forms of synaptic plasticity and support the hypothesis that mLTD is one of the mechanisms by which the cholinergic system modulates hippocampal function.

On the molecular basis linking Nerve Growth Factor (NGF) to Alzheimer's disease

1. Alzheimer's disease (AD) is pathologically defined by the deposition of amyloid peptide and neurofibrillary tangles and is characterized by a progressive loss of cognition and memory function, due to marked cortical cholinergic depletion. 2. Cholinergic cortical innervation is provided by basal forebrain cholinergic neurons. The neurotrophin Nerve Growth Factor (NGF) promotes survival and differentiation of basal forebrain cholinergic neurons. 3. This assertion has been at the basis of the hypothesis developed in the last 20 years, whereby NGF deprivation would be one of the factor involved in the etiology of sporadic forms of AD. 4. In this review, we shall summarize data that lead to the production and characterization of a mouse model for AD (AD11 anti-NGF mice), based on the expression of transgenic antibodies neutralizing NGF. The AD-like phenotype of AD11 mice will be discussed on the basis of recent studies that have posed NGF and its precursor pro-NGF back to the stage of AD-like neurodegeneration, showing the involvement of the precursor pro-NGF in one of the cascades leading to AD neurodegeneration.

Choline pivaloyl ester strengthened the benefit effects of Tacrine and Galantamine on electroencephalographic and cognitive performances in nucleus basalis magnocellularis-lesioned and aged rats

The aim of the present work was the assessment of the effects produced on the electroencephalographic (EEG) activity and the cognitive and memory performances of nucleus basalis magnocellularis (NBM)-lesioned or aged rats by the combined treatment with [2-(2,2-dimethylpropionyloxy)ethyl]trimethylammonium 2,2-dimethylpropionate (choline pivaloyl ester) (CPE) and the Cholinesterase inhibitors (ChEIs) Tacrine (THA) and Galantamine (GAL). Intraperitoneal administration of CPE combined with THA or GAL to both NBM-lesioned or aged rats, produced EEG desynchronisation, and a significant decrease in the energy of the total EEG spectrum and the lower frequency bands (delta 0.25-3 and theta 4-7 Hz) lasting many minutes. Furthermore, drug associations reversed in aged rats the scopolamine (0.2 mg/kg, i.p.)-induced increase in EEG power, slow waves and high-voltage spindle (HVS). Furthermore, the combined administration of CPE and Cholinesterase inhibitors in both NBM-lesioned or aged animals, improved performances in all behavioural tasks, enhancing object discrimination, increasing locomotory activity and alternation choice in T-maze, ameliorating retention in passive avoidance and decreasing escape latency in Morris water maze. In all test, AChEIs and CPE combinations proved to be more effective than CPE, THA or GAL given alone. In conclusion, the present work shows the ability of choline pivaloyl ester in strengthening the positive cerebral activity of THA and GAL.

Gomisin A improves scopolamine-induced memory impairment in mice

Gomisin A is a component of the fruits of Schizandra chinesis which are widely used as a tonic in traditional Chinese medicine. In the present study, we assessed the effect of gomisin A on the learning and memory impairments induced by scopolamine. The cognition-enhancing effect of gomisin A was investigated using a passive avoidance test, the Y-maze test, and the Morris water maze test in mice. Drug-induced amnesia was induced by treating animals with scopolamine (1 mg/kg, i.p.). Gomisin A (5 mg/kg, p.o.) administration significantly reversed scopolamine-induced cognitive impairments in mice by the passive avoidance test and the Y-maze test (P<0.05), and also improved escape latency in the Morris water maze test at 5 mg/kg (P<0.05). Moreover, in an in vitro study, gomisin A was found to inhibit acetylcholinesterase activity in a dose-dependent manner (IC50 value; 15.5 microM). These results suggest that gomisin A may be a useful cognitive impairment treatment, and its beneficial effects are mediated, in part, via enhancing the cholinergic nervous system.

Combined Blockade of Cholinergic Receptors Shifts the Brain from Stimulus Encoding to Memory Consolidation

High central nervous system levels of acetylcholine (ACh) are commonly regarded as crucial for learning and memory, and a decline in cholinergic neurotransmission is associated with Alzheimer's dementia. However, recent findings revealed exceptions to this rule: The low ACh tone characterizing slowwave sleep (SWS) has proven necessary for consolidation of hippocampus-dependent declarative memories during this sleep stage. Such observations, together with recent models of a hippocampal-neocortical dialogue underlying systems memory consolidation, suggest that high levels of ACh support memory encoding, whereas low levels facilitate consolidation. We tested this hypothesis in human subjects by blocking cholinergic neurotransmission during wakefulness, starting 30 min after learning. Subjects received the muscarinic antagonist scopolamine (4 µg/kg bodyweight intravenously) and the nicotinic antagonist mecamylamine (5 mg orally). Compared to placebo, combined muscarinic and nicotinic receptor blockade significantly improved consolidation of declarative memories tested 10 hr later, but simultaneously impaired acquisition of similar material. Consolidation of procedural memories, which are not dependent on hippocampal functioning, was unaffected. Neither scopolamine nor mecamylamine alone enhanced declarative memory consolidation. Our findings support the notion that ACh acts as a switch between modes of acquisition and consolidation. We propose that the natural shift in central nervous system cholinergic tone from high levels during wakefulness to minimal levels during SWS optimizes declarative memory consolidation during a period with no need for new memory encoding.

The object recognition task in rats and mice: a simple and rapid model in safety pharmacology to detect amnesic properties of a new chemical entity

INTRODUCTION

The aim of the present study was to evaluate the potential usefulness of the object recognition learning paradigm to detect the potential amnesic properties of a new drug for use in the characterisation of its safety pharmacology profile.

METHODS AND RESULTS

In the first experiment, the time-dependent decay of object recognition memory was characterised in Sprague-Dawley rats and C57Bl/6J mice. Under our experimental conditions, it takes between 3 and 4 post-training hours for the rats and between 1 and 2 post-training hours for the mice to forget the respective value of the objects. In the second experiment, the effects of scopolamine (0.03-1 mg/kg) were investigated in both rats and mice when administered 30 min prior to training in the object recognition task. Memory retention was tested 2 h after training in rats and 1 h after training in mice. Scopolamine impairs the object recognition memory at doses of 0.1, 0.3, and 1 mg/kg in rats and at doses of 0.3 and 1 mg/kg in mice. In the last experiment, effects of two benzodiazepines (alprazolam and diazepam) were assessed in the mouse model of object recognition task. Diazepam and alprazolam were intraperitoneally administered 30 min prior to training and memory retention was tested 10 min and 1 h after training. At 0.2 mg/kg, both benzodiazepines impair object recognition memory when testing is performed 1 h after training. However, when testing is performed 10 min after training, both benzodiazepines at 0.2 mg/kg failed to disrupt memory processes.

DISCUSSION

Taken together, these results show that the object recognition task can easily be performed in rats and mice for safety pharmacology studies related to CNS function. Because of the ageing population and the increasing number of drugs prescribed to elderly patients, it becomes important to evaluate the potential side effects of a new chemical entity on memory function during evaluation of its safety profile. The object recognition task, which is simple, rapid, and reliable, should be of great use in safety pharmacology to detect amnesic properties of new compounds.

Daidzein activates choline acetyltransferase from MC-IXC cells and improves drug-induced amnesia

The choline acetyltransferase (ChAT) activator, which enhances cholinergic transmission via an augmentation of the enzymatic production of acetylcholine (ACh), is an important factor in the treatment of Alzheimer's disease (AD). Methanolic extracts from Pueraria thunbergiana exhibited an activation effect (46%) on ChAT in vitro. Via the sequential isolation of Pueraria thunbergiana, the active component was ultimately identified as daidzein (4',7-dihydroxy-isoflavone). In order to investigate the effects of daidzein from Pueraria thunbergiana on scopolamine-induced impairments of learning and memory, we conducted a series of in vivo tests. Administration of daidzein (4.5 mg/kg body weight) to mice was shown significantly to reverse scopolamine-induced amnesia, according to the results of a Y-maze test. Injections of scopolamine into mice resulted in impaired performance on Y-maze tests (a 37% decreases in alternation behavior). By way of contrast, mice treated with daidzein prior to the scopolamine injections were noticeably protected from this performance impairment (an approximately 12%-21% decrease in alternation behavior). These results indicate that daidzein might play a role in acetylcholine biosynthesis as a ChAT activator, and that it also ameliorates scopolamine-induced amnesia.

Long-term effects of immunotoxic cholinergic lesions in the septum on acquisition of the cone-field task and noncognitive measures in rats

In rats, nonspecific mechanical or neurotoxic lesions of the septum impair spatial memory in, e.g., Morris water- and radial-maze tasks. Unfortunately, the lack of specificity of such lesions limits inferences about the role of the cholinergic hippocampal projections in spatial cognition. We therefore tested the effects of septal lesions produced by 192 IgG-saporin in rats, which is highly selective for basal forebrain cholinergic neurons, on home cage activity, noncognitive tests (modified Irwin test, open field and forced swimming tests, and various sensorimotor tasks), and the cone-field spatial learning task. The immunotoxic lesion reduced acetylcholine (ACh) levels in the septum (-61%) and hippocampus (>-75%). Rats with lesions showed mild home-cage hyperactivity at 4 weeks postlesion, but no noncognitive deficits at 13 weeks postsurgery. In the cone-field task, rats with septal lesions made more working- and reference-memory errors than the controls, but acquisition curves were parallel in both groups. The speed of visiting cones was faster in the rats with lesions, indicative of disturbed attention or increased motivation. These data support the growing evidence that involvement of the septohippocampal cholinergic system in spatial learning and memory may have been overestimated in studies that used lesions with poor selectivity.

Does cholesterol act as a protector of cholinergic projections in Alzheimer's disease?

The relationship between Alzheimer's disease (AD) and progressive degeneration of the forebrain cholinergic system is very well established, whereas mechanisms linking this disease with cholesterol, apolipoprotein E (apoE) phenotype, and amyloid precursor protein (APP) metabolism have not been fully elucidated even though there is a plethora of publications separately on each of these issues. The intention of this hypothesis is to unify knowledge coming from all of these areas. It is based on an assumption that the process of APP hypermetabolism is a neuroprotective response for age-related cholinergic deterioration. In some individuals this initially positive process becomes highly overregulated by genetic or/and epigenetic risk factors and after many years of accumulations lead eventually to AD. I hypothesise that neuroprotective role of APP-hypermetabolism might be related to enrichment of neuronal membranes (lipid rafts in particular) in cholesterol in order to compensate for decrease in presynaptic cholinergic transmission and/or AD-related decrease in cholesterol levels. The above is consistent with findings indicating that activity of both muscarinic and nicotinic cholinergic receptors is correlated in a positive manner with cholesterol plasmalemmal content. Briefly – APP metabolism together with transport of cholesterol in apoE containing lipoproteins seem to play a key role in mobilising cholesterol into neuronal membranes.

Natural and hybrid (“chimeric”) stable regulatory glyproline peptides

The present concept of relative instability of regulatory peptides (RPs) in organisms must be amended. The recently characterized family of glyprolines and some other prolyl-glycyl-proline (PGP)-containing oligopeptides show the stability quite comparable with those of major pharmacological preparations. The ability of glyprolines to pass gastro-enteric tract barriers opens ways to per-oral administration of this new group of drugs such as semax, selank and their fragments. The most interesting approach is the creation of hybrid ("chimeric") peptide drugs combining the unmodified representatives of various natural RPs that distinctly manifest their inherent physiological activities and cooperate with each other in stabilization of whole peptide in vivo. As the result, the activity of such peptides as semax and selank may have value in a vide variety of pathological processes.