Alteration in nicotine binding sites in Parkinson's disease, Lewy body dementia and Alzheimer's disease: possible index of early neuropathology

Quantification of nicotinic acetylcholine receptors in Parkinson's disease with (123)I-5IA SPECT

We quantified in vivo brain nicotinic acetylcholine receptor (nAChR) distributions in patients with Parkinson's disease (PD) and evaluated correlations between nAChR distributions and clinical variables of the patients, especially dopaminergic medications. Ten patients with PD without dementia underwent 5-(123)I-iodo-3-(2(S)-azetidinylmethoxy)pyridine ((123)I-5IA) single photon emission computed tomography (SPECT) and the data were compared with those of 10 age-matched healthy volunteers. Correlation analyses between (123)I-5IA distribution volumes (DVs) in each brain region and clinical variables of the patients were also performed. The PD group showed a statistically significant decrease (20-25%) in the brainstem and frontal cortex as compared with the control group. Although age, duration of disease, daily dose of levodopa, duration of PD medication use, and scores on the motor section of Unified Parkinson's Disease Rating Scale were not significantly correlated with DV values in any brain regions, high daily doses of dopamine agonist showed a significant negative correlation with DVs in the cerebellum, and temporal, parietal and occipital cortices. These findings suggest that patients with PD without dementia can show reductions especially in the brainstem and frontal cortex. They also suggest that dopamine agonists can have a negative influence on the distribution of nAChRs.

DLB and PDD boundary issues: diagnosis, treatment, molecular pathology, and biomarkers

For more than a decade, researchers have refined criteria for the diagnosis of dementia with Lewy bodies (DLB) and at the same time have recognized that cognitive impairment and dementia occur commonly in patients with Parkinson disease (PD). This article addresses the relationship between DLB, PD, and PD with dementia (PDD). The authors agreed to endorse "Lewy body disorders" as the umbrella term for PD, PDD, and DLB, to promote the continued practical use of these three clinical terms, and to encourage efforts at drug discovery that target the mechanisms of neurodegeneration shared by these disorders of alpha-synuclein metabolism. We concluded that the differing temporal sequence of symptoms and clinical features of PDD and DLB justify distinguishing these disorders. However, a single Lewy body disorder model was deemed more useful for studying disease pathogenesis because abnormal neuronal alpha-synuclein inclusions are the defining pathologic process common to both PDD and DLB. There was consensus that improved understanding of the pathobiology of alpha-synuclein should be a major focus of efforts to develop new disease-modifying therapies for these disorders. The group agreed on four important priorities: 1) continued communication between experts who specialize in PDD or DLB; 2) initiation of prospective validation studies with autopsy confirmation of DLB and PDD; 3) development of practical biomarkers for alpha-synuclein pathologies; 4) accelerated efforts to find more effective treatments for these diseases.

Emerging concepts: novel integration of in vivo approaches to localize the function of nicotinic receptors

Nicotinic acetylcholine receptors (nAChRs) are important targets of the neuromodulator acetylcholine (ACh) and the drug nicotine. The role of their different subunits has been analysed for a decade by the creation of knock-out (KO) mice using homologous recombination. This technique shows that a given subunit is necessary for a given function. However, for ubiquitously expressed genes, it cannot demonstrate the localization for a given subunit in which its expression is sufficient, especially for behavioural phenotypes. Sufficient in this context means that the brain region requiring the expression of the gene product has been localized. Novel strategies have therefore been developed to re-express, region specifically, nAChR subunits on a KO background using lentiviral vectors. Localized regeneration of fully functional high-affinity nAChRs in defined brain regions has proven that these receptors are sufficient to restore a variety of functions: nicotine-induced dopamine release, nicotine self-administration in mice, dopamine neuron firing patterns, and exploratory and locomotor behaviours in a sequential locomotor task testing executive function were thus defined as depending exclusively on the 'knock-back' of beta2*-nAChRs into the ventral tegmental area. These analyses highlight the important role of endogenous cholinergic regulation of a variety of functions. The novel integrated use of restricted re-expressed nAChR subunits with in vivo electrophysiology and automated quantitative behavioural analysis enables the further analysis of defined neuronal circuits in nicotine addiction and higher cognitive function.

Differential nicotinic regulation of the nigrostriatal and mesolimbic dopaminergic pathways: implications for drug development

Neuronal nicotinic acetylcholine receptors (nAChRs) modulate dopaminergic function. Discovery of their multiplicity has lead to the search for subtype-selective nAChR agonists that might be therapeutically beneficial in diseases linked to brain dopaminergic pathways. The regulation and responses of the nigrostriatal and mesolimbic dopaminergic pathways are often similar, but some differences do exist. The cerebral distribution and characteristics of various nAChR subtypes differ between nigrostriatal and mesolimbic dopaminergic pathways. Comparison of nicotine and epibatidine, two nAChR agonists whose relative affinities for various nAChR subtypes differ, revealed differences in the nAChR-mediated regulation of dopaminergic activation between these dopamine systems. Nicotine preferentially stimulates the mesolimbic pathway, whereas epibatidine's stimulatory effect falls on the nigrostriatal pathway. Thus, it may be possible to stimulate the nigrostriatal pathway with selective nAChR agonists that do not significantly affect the mesolimbic pathway, and thus lack addictive properties. Furthermore, dopamine uptake inhibition revealed a novel inhibitory effect of epibatidine on accumbal dopamine release, which could form a basis for novel antipsychotics that could alleviate the elevated accumbal dopaminergic tone found in schizophrenia during the active psychotic state. Different regulation of nigrostriatal and mesolimbic dopaminergic pathways by nAChRs could be an important basis for developing novel drugs for treatment of Parkinson's disease and schizophrenia.

New multipotent tetracyclic tacrines with neuroprotective activity

The synthesis and the biological evaluation (neuroprotection, voltage dependent calcium channel blockade, AChE/BuChE inhibitory activity and propidium binding) of new multipotent tetracyclic tacrine analogues (5-13) are described. Compounds 7, 8 and 11 showed a significant neuroprotective effect on neuroblastoma cells subjected to Ca(2+) overload or free radical induced toxicity. These compounds are modest AChE inhibitors [the best inhibitor (11) is 50-fold less potent than tacrine], but proved to be very selective, as for most of them no BuChE inhibition was observed. In addition, the propidium displacement experiments showed that these compounds bind AChE to the peripheral anionic site (PAS) of AChE and, consequently, are potential agents that can prevent the aggregation of beta-amyloid. Overall, compound 8 is a modest and selective AChE inhibitor, but an efficient neuroprotective agent against 70mM K(+) and 60microM H(2)O(2). Based on these results, some of these molecules can be considered as lead candidates for the further development of anti-Alzheimer drugs.

Partial agonists as therapeutic agents at neuronal nicotinic acetylcholine receptors

Improved understanding of how brain function is altered in neurodegenerative disease states, pain and conditions, such as schizophrenia and attention deficit disorder, has highlighted the role of nicotinic acetylcholine receptors (nAChRs) in these conditions and identified them as promising therapeutic targets. nAChRs are widely expressed throughout the peripheral and central nervous system, and this widespread nature underlines the need for new ligands with different selectivities and pharmacological profiles if we are to avoid the adverse side effects associated with many of the nAChR modulators currently identified. Partial agonists have the unique property of being able to act both as agonists or antagonists depending on the concentration of endogenous neurotransmitter. Moreover, the agonist action of partial agonists has a 'ceiling' effect, giving them a large safety margin and making them an attractive proposition for therapeutic molecules. Partial agonists of nAChRs are currently being developed as a nicotine replacement therapy for smoking cessation and for the treatment of a number of neurological diseases associated with a loss of cholinergic function. This commentary will discuss the pharmacological properties of partial agonists and review recent research developments in the field of partial agonists acting at nicotinic receptors.

Neuroprotective effects of galanthamine and tacrine against glutamate neurotoxicity

We examined the mechanisms of the neuroprotective effects of two central-type acetylcholinesterase inhibitors, galanthamine and tacrine, on nitric oxide-mediated glutamate neurotoxicity using primary cultures from the cerebral cortex of fetal rats. Galanthamine and tacrine showed prominent protective effects against glutamate neurotoxicity. Mecamylamine, a nicotinic acetylcholine receptor antagonist, but not scopolamine, a muscarinic acetylcholine receptor antagonist, inhibited the protective effects of these inhibitors on glutamate neurotoxicity. Furthermore, dihydro-beta-erythroidine, an alpha4-nicotinic receptor antagonist, and methyllycaconitine, an alpha7-nicotinic receptor antagonist, inhibited the neuroprotective effects of galanthamine but not tacrine. Next, we investigated the site of action where galanthamine and tacrine prevent glutamate neurotoxicity. Both these acetylcholinesterase inhibitors prevented glutamate- and ionomycin-induced neurotoxicity, but only tacrine prevented S-nitrosocysteine-induced neurotoxicity. These results suggest that galanthamine and tacrine protect cortical neurons from glutamate neurotoxicity via different mechanisms.

Age-related alterations of GABAergic input to CA1 pyramidal neurons and its control by nicotinic acetylcholine receptors in rat hippocampus

The aim of this study was to determine whether age-associated alterations in the GABAergic input to pyramidal neurons in the hippocampus are due to a dysfunction of GABAergic interneurons, and/or a decrease in their cholinergic control via nicotinic receptors (nAChRs). Electrophysiological recordings were obtained from pyramidal cells in the CA1 area of hippocampal slices from young (3-4 months old) and aged (25-30 months old) Sprague-Dawley rats. Synaptic GABA(A) receptor-mediated inhibitory postsynaptic currents and inhibitory postsynaptic potentials induced by stimulation of the stratum oriens were significantly smaller in aged rats. The frequency (but not amplitude) of spontaneous and miniature GABA inhibitory postsynaptic currents (IPSCs) was reduced in aged rats, suggesting a presynaptic alteration. Tetanic stimulation of cholinergic afferents to release endogenous acetylcholine, or an exogenous application of the nAChR agonist cytisine, increased the frequency of spontaneous IPSCs in young rats; however these effects were not evident in aged rats, indicating that the nicotinic control of GABA release is lowered during aging. None of these age-related alterations were reversed by a chronic treatment with donepezil, a cholinesterase inhibitor. Immunofluorescent labeling of GABA interneurons with somatostatin (SOM), parvalbumin (PV) or calbindin (CB), together with the vesicular acetylcholine transporter VAChT, revealed a selective loss of subpopulations of SOM and CB positive interneurons. This loss was associated with a general decrease in density of the cholinergic network in aged rats. Thus, the lower GABAergic inhibition observed in the aged rat hippocampus is due to a selective loss/dysfunction of subpopulations of GABAergic interneurons, associated with a widespread cholinergic deficit.

Altered synaptic function in Alzheimer's disease

Alzheimer's disease is the leading cause of dementia in the elderly, presenting itself clinically by progressive loss of memory and learning. Since synaptic density correlates more closely with cognitive impairment than any other pathological lesion observable in the disease pathology, an increased understanding of the mechanisms behind synaptic disconnection is of vital importance. Our lab investigated the neurotransmitter-specific status of distinct cortical presynaptic bouton populations in various transgenic mouse models of the Alzheimer's-like amyloid pathology in order to assess their involvement throughout the progression of the pathology. These studies have revealed that the amyloid pathology appears to progress in a neurotransmitter-specific manner where the cholinergic terminals appear most vulnerable, followed by the glutamatergic terminals and finally by the somewhat more resilient GABAergic terminals. This review will discuss additional studies which also provide evidence of a neurotransmitter-specific pathology as well as comment on the potential explanations for the observed vulnerabilities, touching upon metabolic demand, trophic support and receptor mediated activation.

Nicotine regulates SH-SY5Y neuroblastoma cell proliferation through the release of brain-derived neurotrophic factor

Nicotine has been shown to produce some beneficial effects in neurodegenerative disorders, and several studies have suggested that these effects may be mediated in part through the action of the neurotrophic factor BDNF. To further elucidate the interaction between nicotine and BDNF, we examined the effect of nicotine on the proliferation of the neuroblastoma cell line SH-SY5Y, which, following differentiation with retinoic acid, expresses both nicotinic receptors and the receptor for BDNF, TrkB. Both nicotine and the nicotinic alpha-7 selective agonist AR-17779 significantly increased cell proliferation albeit with bell-shaped dose-response kinetics. The blockade of this effect with either the alpha-7 nicotinic antagonist methyllycaconitine or the non-selective nicotinic antagonist mecamylamine indicated that the effect was mediated by nicotinic receptors. Prior addition of neutralising BDNF antibodies or of the tyrosine kinase inhibitor K252A (200 nM) completely blocked nicotine-induced proliferation, suggesting the involvement of TrkB signalling in the mediation of the effect. Nicotine also enhanced both the secretion of BDNF from the SH-SY5Y and cell surface density of TrkB receptors. These effects were abolished by pretreatment with MLA. These data indicate that activation of nicotinic receptors has effects upon the BDNF-TrkB pathway, inducing cell proliferation by promoting the release of BDNF, which in turn activates TrkB receptors.

Neurosteroids and cholinergic systems: implications for sleep and cognitive processes and potential role of age-related changes

RATIONALE

The neurosteroids pregnenolone sulfate (PREGS), dehydroepiandrosterone sulfate (DHEAS) and allopregnanolone (3alpha,5alpha THPROG) have been implicated as powerful modulators of memory processes and sleep states in young and aged subjects with memory impairment. As these processes depend on the integrity of cholinergic systems, a specific effect of neurosteroids on these systems may account for their effects on sleep and memory.

OBJECTIVE

To review the evidence for a specific and differential effect of neurosteroids on cholinergic systems.

METHODS

We carried out keyword searches in "Medline" to identify articles concerning (1) the effects of neurosteroids on cholinergic systems, sleep and memory processes, and (2) changes in neurosteroid concentrations during aging. Few results are available for humans. Most data concerned rodents.

RESULTS

Peripheral and central administrations of PREGS, DHEAS, and 3alpha,5alpha THPROG modulate the basal forebrain and brainstem projection cholinergic neurons but not striatal cholinergic interneurons. Local administration of neurosteroids to the basal forebrain and brainstem cholinergic neurons alters sleep and memory in rodents. There are a few conflicting reports concerning the effects of aging on neurosteroid concentrations in normal and pathological conditions.

CONCLUSIONS

The specific modulation of basal forebrain and brainstem cholinergic systems by neurosteroids may account for the effects of these compounds on sleep and memory processes. To improve our understanding of the role of neurosteroids in cholinergic systems during normal and pathological aging, we need to determine whether there is specific regionalization of neurosteroids, and we need to investigate the relationship between neurosteroid concentrations in cholinergic nuclei and age-related sleep and memory impairments.

Cholinergic and glutamatergic drugs in Alzheimer's disease therapy

The pathology and clinical symptoms of Alzheimer's disease are well known and include plaques, tangles, cell loss and dysfunction. The target of current treatments is to improve neuronal dysfunction and produce symptomatic benefits based on a clear understanding of neurotransmitter biochemistry. The purpose of this review is to examine the scientific background to currently available treatments, discuss the clinical experience of employing these drugs in Alzheimer's disease patients and review the socioeconomic influences on their use in the future.

The role of nicotinic acetylcholine receptors in Alzheimer’s disease

The two hallmark lesions of Alzheimer's disease (AD) are extracellular amyloid plaques, mainly formed by a small peptide called amyloid-beta (Abeta), and neurofibrillary tangles, which are intracellular inclusions formed by aggregates of hyperphosphorylated tau protein. One of the major neurochemical features of AD is the marked reduction of nicotinic acetylcholine receptors in disease-relevant brain regions such as the cerebral cortex and hippocampus. This loss is further compounded by the loss of cholinergic cells, which contributes to the cognitive dysfunction. This observation has had a major impact on therapeutic treatments, as efforts to restore cholinergic function such as the administration of acetylcholinesterase inhibitors have been, until recently, the major treatment options available for AD. Understanding the relationship of these hallmark lesions with the plethora of other changes that occur in the AD brain has proven to be a difficult challenge to resolve. The utilization of transgenic mouse models, that recapitulate one or more neuropathological and neurochemical features of the AD brain is providing some inroads, as they offer a means to gain mechanistic insights into the disease process in an in vivo setting. In this review, we consider the role of nicotinic acetylcholine receptors in transgenic models and in AD.

α7 Nicotinic acetylcholine receptor as a target to rescue deficit in hippocampal LTP induction in β-amyloid infused rats

Continuous intracerebroventricular infusion of beta-amyloid peptide 1-40 (Abeta(1-40)) in animal models induces learning and memory impairment associated with dysfunction of the cholinergic neuronal system, which has been considered to be a pathological model of Alzheimer's disease [Nitta, A., Itoh, A., Hasegawa, T., Nabeshima, T., 1994. Beta-amyloid protein-induced Alzheimer's disease animal model. Neurosci. Lett. 170, 63-66.]. Here, using a real-time optical recording technique, we demonstrate that basal synaptic transmission and several forms of synaptic plasticity, including long-term potentiation (LTP), post-tetanic potentiation (PTP) and paired-pulse facilitation (PPF) are deficient at the Schaffer collateral-CA1 synapse in hippocampal slices from Abeta-infused brain. Throughout this study, an effort was made to address whether the alpha7 nicotinic acetylcholine receptor (alpha7nAChR), which is believed to be a primary target of Abeta [Wang, H.Y., Lee, D.H., Davis, C.B., Shank, R.P., 2000a. Amyloid peptide Abeta (1-42) binds selectively and with picomolar affinity to alpha 7 nicotinic acetylcholine receptors. J. Neurochem. 75, 1155-1161.], is responsible for the deficits in synaptic plasticity observed in the Abeta-infused rats. First, we found that Abeta-infusion markedly depressed the response of alpha7nAChR to a selective alpha7nAChR agonist [3-(2,4-dimethoxybenzylidene)-anabaseine] (DMXB). Second, blockade of alpha7nAChR with either methyllycaconitine (MLA) or alpha-bungarotoxin (alpha-BTX) in control rats inhibited LTP induction, suggesting that the activation of alpha7nAChR is required for LTP induction. Finally, pre-treatment of the slices from Abeta-infused rats with 10 microM DMXB rescued CA1 synapses from the deficit in LTP and PPF. These results suggest that Abeta-impaired LTP and PPF arise as a consequence of dysfunctional alpha7nAChR, and that alpha7nAChR may be an important target to help ameliorate AD patient cognitive deficits.

Simplified quantification of nicotinic receptors with 2[18F]F-A-85380 PET

INTRODUCTION

Neuronal nicotinic acetylcholine receptors (nAChRs), widely distributed in the human brain, are implicated in various neurophysiological processes as well as being particularly affected in neurodegenerative conditions such as Alzheimer's disease. We sought to evaluate a minimally invasive method for quantification of nAChR distribution in the normal human brain, suitable for routine clinical application, using 2[(18)F]F-A-85380 and positron emission tomography (PET).

METHODS

Ten normal volunteers (four females and six males, aged 63.40+/-9.22 years) underwent a dynamic 120-min PET scan after injection of 226 MBq 2[(18)F]F-A-85380 along with arterial blood sampling. Regional binding was assessed through standardized uptake value (SUV) and distribution volumes (DV) obtained using both compartmental (DV(2CM)) and graphical analysis (DV(Logan)). A simplified approach to the estimation of DV (DV(simplified)), defined as the region-to-plasma ratio at apparent steady state (90-120 min post injection), was compared with the other quantification approaches.

RESULTS

DV(Logan) values were higher than DV(2CM). A strong correlation was observed between DV(simplified), DV(Logan) (r=.94) and DV(2CM) (r=.90) in cortical regions, with lower correlations in thalamus (r=.71 and .82, respectively). Standardized uptake value showed low correlation against DV(Logan) and DV(2CM).

CONCLUSION

DV(simplified) determined by the ratio of tissue to metabolite-corrected plasma using a single 90- to 120-min PET acquisition appears acceptable for quantification of cortical nAChR binding with 2[(18)F]F-A-85380 and suitable for clinical application.

Mechanisms of Neuroprotective Effects of Therapeutic Acetylcholinesterase Inhibitors Used in Treatment of Alzheimer's Disease

Donepezil, galanthamine, and tacrine are therapeutic acetylcholinesterase (AChE) inhibitors used for the treatment of Alzheimer's disease. The aim of this paper is to review recent findings on their neuroprotective properties and the mechanisms of neuroprotection against glutamate neurotoxicity in rat cortical neurons. First, the hallmark of neurotoxicity induced by two different glutamate treatment conditions was examined, revealing that acute glutamate treatment (1 mM, 10 min) induces necrotic neuronal death and that moderate glutamate treatment (100 microM, 24 hr) induces apoptotic neuronal death. Next, we showed that therapeutic AChE inhibitors protect cortical neurons from glutamate neurotoxicity in a time- and concentration-dependent manner. We examined the mechanism of this neuroprotective effect and found that the neuroprotective effects against both acute and moderate glutamate treatments are mediated through nicotinic acetylcholine receptors (nAChRs), or more specifically, the effects of donepezil and galanthamine are mediated through alpha4- and alpha7-nAChR. We also showed that donepezil and galanthamine protect cortical neurons against acute glutamate treatment-induced neurotoxicity at steps before, and that tacrine protects at steps after, nitric oxide radical formation. On the other hand, the neuroprotective effects of donepezil and galanthamine, but not of tacrine, against neurotoxicity induced by moderate glutamate treatment were mediated through the phosphatidylinositol 3-kinase-Akt pathway. These findings unveiled the hitherto unknown neuroprotective effects of therapeutic AChE inhibitors and provided valuable insights into its neuroprotective mechanisms. They may very likely form the basis for a novel treatment strategy against Alzheimer's disease.

Chronic pre-treatment with nicotine enhances nicotine-evoked striatal dopamine release and α6 and β3 nicotinic acetylcholine receptor subunit mRNA in the substantia nigra pars compacta of the rat

Whilst local intrastriatal infusion of nicotine consistently elicits striatal dopamine release, systemic administration often fails to do so. Since chronic nicotine administration is known to result in desensitisation-induced upregulation of nicotinic acetylcholine receptors (nAChRs), the present study investigated whether chronic pre-treatment could enhance the response to systemic nicotine and, if so, whether increases in specific nAChR subunit mRNA levels in the substantia nigra pars compacta (SNc) may underlie this effect. In vivo microdialysis studies in male Sprague-Dawley rats revealed that following 4 days pre-treatment with nicotine (0.8 mg kg(-1)s.c.), local intrastriatal nicotine infusion (3 mM) elicited significantly higher dopamine efflux compared to vehicle pre-treated controls (peak release: 1273 +/- 199% basal versus 731 +/- 113% basal), whereas systemic nicotine challenge (0.8 mg kg(-1)s.c.) elicited no response. In contrast, following 8 days pre-treatment with nicotine (0.8 mg kg(-1)s.c.), systemic nicotine challenge (0.8 mg kg(-1)s.c.) now produced significantly higher dopamine efflux than that of vehicle pre-treated controls (147 +/- 30% basal versus 91 +/- 5% basal). Eight days pre-treatment with nicotine also significantly elevated the levels of alpha6 (approximately 55%) and beta3 (approximately 43%) nAChR subunit mRNA in the SNc, suggesting that up-regulation of these nAChR subunit genes in the nigrostriatal tract may contribute to the enhanced nicotine-evoked striatal dopamine release.

From ligand design to therapeutic efficacy: the challenge for nicotinic receptor research

S-Nicotine, the principal psychoactive constituent of Nicotiana tabacum, underpins addiction to tobacco smoking. Although tobacco consumption is a leading cause of death worldwide, nicotine itself is also proposed to have potential therapeutic benefits for a diverse range of conditions. Nicotine interacts with its cognate receptors in the central nervous system to exert a predominantly modulatory influence, making neuronal nicotinic receptors attractive therapeutic targets. Here, we focus on three natural products as lead compounds for drug discovery programs, nicotine, epibatidine and cytisine, and consider the aims and limitations that shape these drug discovery endeavors.

A comparison of the efficacy of donepezil in Parkinson's disease with dementia and dementia with Lewy bodies

BACKGROUND

Parkinson's disease with dementia (PDD) and dementia with Lewy bodies (DLB) overlap in phenomenology and neurochemical deficits. We hypothesised they would not differ in their response to the cholinesterase inhibitor donepezil.

METHODS

We recruited 70 subjects, 30 DLB and 40 PDD, in an open label study to compare the efficacy of donepezil in these two patient groups. They were assessed at baseline, 4, 12 and 20 weeks. The main outcome measures were the Mini-Mental State Examination (MMSE), Neuropsychiatric Inventory (NPI) and motor sub-section of the Unified Parkinson's Disease Rating Scale (UPDRS III).

RESULTS

PDD patients were younger than DLB and had more severe parkinsonism at baseline. The groups were similar on all other variables of interest. By 20 weeks the mean MMSE score increased by 3.9 points in the DLB group and by 3.2 points in PDD. The mean NPI score reduced by 14.6 points for DLB and 12.0 points for PDD. These treatment effects were all significant compared to baseline (p < 0.001) but there were no significant between-group treatment differences (MMSE p = 0.56, NPI p = 0.39). UPDRS III motor scores did not change significantly from baseline values in either group. Although adverse effects were common (69%) they were usually mild and 64 patients (91%) completed the study. The four patients who did withdraw with adverse effects all had a PDD diagnosis.

CONCLUSIONS

Donepezil produced similar improvements in cognition and behaviour in DLB and PDD. This supports the hypothesis that the two disorders are closely related clinically and neurobiologically. Larger scale, placebo controlled clinical trials are needed to provide an evidence base to guide the clinical use of cholinesterase inhibitors in Lewy body disease.

Impaired metabotropic glutamate receptor/phospholipase C signaling pathway in the cerebral cortex in Alzheimer's disease and dementia with Lewy bodies correlates with stage of Alzheimer's-disease-related changes

The aim of the present work was to analyze the status of metabotropic glutamate receptors (mGluRs) in the frontal cortex (area 8) from ten cases with common form DLB (cDLB) and eleven cases with pure AD in comparison with five age-matched controls. mGluRs, determined by radioligand binding assays, were significantly decreased in cerebral cortex in cDLB. This decrease was already present in cases with early AD changes not involving the frontal cortex, but dramatically correlated with AD neuropathological changes, at its greatest in isocortical stages, which was associated with a decrease in the expression levels of mGluR1 detected by Western blotting. Moreover, mGluRs analyzed in pure AD were lower than those obtained in cDLB and also correlated with progression of illness. On the other hand, the expression levels of phospholipase Cbeta1 (PLCbeta1) isoform, which is the effector of group I mGluRs, was decreased in parallel in cDLB cases. Finally, the PLCbeta1 decrease was associated with reduced GTP- and l-glutamate-stimulated PLC activity in both cDLB and AD cases. These results show that group I mGluRs/PLC signaling are down-regulated and desensitized in the frontal cortex in cDLB and AD cases and that these modifications worsen with progression of AD changes in the cerebral neocortex. Therefore, group I mGluR dysfunction may be implicated in the pathogenesis of cognitive impairment and dementia in common form of DLB and pure AD.

Effect of repeated nicotine exposure on high-affinity nicotinic acetylcholine receptor density in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHRs) are often used as a model of attention deficit hyperactivity disorder (ADHD) and to investigate the effects of hypertension on cognitive function. Further, they appear to have reduced numbers of central nicotinic acetylcholine receptors (nAChRs) and, therefore, may be useful to model certain aspects of Alzheimer's disease (AD) and other forms of dementia given that a decrease in nAChRs is thought to contribute to cognitive decline in these disorders. In the present study, based on reports that chronic nicotine exposure increases nAChRs in several mammalian models, we tested the hypothesis that repeated exposures to a relatively low dose of the alkaloid would ameliorate the receptor deficits in SHR. Thus, young-adult SHRs and age-matched Wistar-Kyoto (WKY) control rats were treated with either saline or nicotine twice a day for 14 days (total daily dose = 0.7 mg/kg nicotine base) and then sacrificed. Quantitative receptor autoradiography with [125I]-IPH, an epibatidine analog, revealed: (1) that high-affinity nAChRs were higher in saline-treated WKY (control) rats compared to saline-treated SHRs in 18 of the 19 brain region measured, although statistically different only in the mediodorsal thalamic nuclei, (2) that nicotine significantly increased nAChR binding in WKY rats in six brain areas including cortical regions and the anterior thalamic nucleus, (3) that there were no cases where nicotine significantly increased nAChR binding in SHRs. These results indicate that subjects deficient in nAChRs may be less sensitive to nAChR upregulation with nicotine than normal subjects and require higher doses or longer periods of exposure.

Galantamine modulates nicotinic receptor and blocks Abeta-enhanced glutamate toxicity

Galantamine is a plant alkaloid that is used in the treatment of Alzheimer's disease. We have studied the effects of galantamine on beta-amyloid-enhanced glutamate toxicity using primary rat cultured cortical neurons. Nicotine and galantamine alone, and in combination, protected neurons against this neurotoxicity. The protection was not blocked by alpha4beta2 nicotinic acetylcholine receptor (nAChR) antagonists, but was partially blocked by alpha7 nAChR antagonists. Galantamine induced phosphorylation of Akt, an effector of phosphatidylinositol 3-kinase (PI3K), while PI3K inhibitors blocked the protective effect and Akt phosphorylation. The antibody FK1, which selectively blocks the allosterically potentiating ligand site on nAChR, significantly reduced the galantamine-induced protection and Akt phosphorylation. Furthermore, suppression of alpha7 nAChR using an RNA interference technique reduced Akt phosphorylation induced by galantamine. Our data suggest that neuroprotection by galantamine is mediated, at least in part, by alpha7 nAChR-PI3K cascade.

Nicotinic acetylcholine receptor immunohistochemistry in Alzheimer's disease and dementia with Lewy bodies: differential neuronal and astroglial pathology

Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) are common forms of dementia in the elderly. The neuropathology of AD and DLB is related to cholinergic dysfunctions, and both alpha4 and alpha7 nicotinic acetylcholine receptor (nAChR) subunits are decreased in several brain areas in both diseases. In this immunohistochemical study, we compared neuronal and astroglial alpha4 and alpha7 subunits in AD, DLB and age-matched controls in the hippocampal formation. The numbers of alpha4 reactive neurons were decreased in layer 3 of the entorhinal cortex of AD and DLB, whereas those of alpha7 reactive neurons were decreased in layer 2 of the subiculum of AD and DLB and in layer 3 of the entorhinal cortex of DLB. In contrast, the intensity of alpha7 reactive neuropil was significantly higher in AD than in controls or DLB in a number of areas of the hippocampus (CA3/4 and stratum granulosum), subiculum and entorhinal cortex. An increase in alpha7 immunoreactivity in AD was also associated with astrocytes. The number of astrocytes double-labelled with alpha7 and glial fibrillary acidic protein (GFAP) antibodies was increased in most areas of the hippocampus and entorhinal cortex in AD compared with controls and DLB. Increased astrocyte alpha7 nAChRs in AD may be associated with inflammatory mechanisms related to degenerative processes specific to this disease.

Involvement of α6/α3 neuronal nicotinic acetylcholine receptors in neuropsychiatric features of Dementia with Lewy bodies: [125I]-α-conotoxin MII binding in the thalamus and striatum

Dementia with Lewy bodies (DLB) is a neurodegenerative disease associated with a range of neuropsychiatric symptoms and reduced expression of neuronal nicotinic acetylcholine receptors (nAChRs) in neocortex, hippocampus, thalamus and basal ganglia. To determine whether there are selective associations between alterations in alpha6/alpha3 neuronal nicotinic acetylcholine receptors (nAChRs) and the two key neuropsychiatric features of DLB, impaired consciousness (IC) and visual hallucinations (VH), quantitative [(125)I]-alpha-conotoxin MII ([(125)I]-alpha-Ctx MII) autoradiography was undertaken on 28 people with DLB and 15 control cases from the Newcastle Brain Bank. There was a highly significant overall trend for reduced thalamic [(125)I]-alpha-Ctx MII binding in DLB (p < 0.001), with significant deficits in the centromedian, ventral lateral and ventroposterior medial thalamic nuclei (p < 0.05), together with caudate and putamen (p < 0.001). [(125)I]-alpha-Ctx MII binding was significantly lower in DLB cases with IC than without IC in the putamen (p < 0.05), however there was no significant association between [(125)I]-alpha-Ctx MII binding and VH. Reductions in [(125)I]-alpha-Ctx MII binding in caudate and putamen were paralleled by similar reductions in [(125)I]PE2I binding. [(125)I]PE2I binding was also significantly lower in DLB cases with IC than without IC in the caudate (p < 0.05) and putamen (p < 0.001). These results demonstrate that deficits in alpha6/alpha3 nAChRs occur in specific brain regions in DLB, may in part be related to the loss of dopaminergic neurons and may contribute to the development of impaired consciousness in the disorder.

Aging and subcellular localization of m2 muscarinic autoreceptor in basalocortical neurons in vivo

By using immunohistochemical approaches at the light and electron microscopic levels, we have shown that aging modifies the subcellular distribution of the m2 muscarinic autoreceptor (m2R) differentially at somato-dendritic postsynaptic sites and at axonal presynaptic sites in cholinergic basalocortical neurons, in vivo. In cholinergic perikarya and dendrites of the nucleus basalis magnocellularis (NBM), aging is associated with a decrease of the density of m2R at the plasma membrane and in the cytoplasm, suggesting a decrease of the total number of m2R in the somato-dendritic field. In contrast, the number of substance P receptors per somato-dendritic surface was not affected. In the frontal cortex (FC), we have shown a decrease of cytoplasmic m2R density also leading to a decrease of the number of m2R per surface of varicosities but with no change of the density of m2R at the membrane. Our results suggest that the decrease of m2R in the somato-dendritic field of the NBM, but not a modification of the number of presynaptic m2 autoreceptors at the plasma membrane in the FC, could contribute to the decrease of the efficacy of cholinergic transmission observed with aging in the rat.

Effects of galantamine in patients with mild Alzheimer's disease

BACKGROUND

Galantamine is an acetylcholinesterase inhibitor that modulates nicotinic receptors. It is effective in mild to moderate Alzheimer's disease (AD) but no trial has focused exclusively on mild AD. We performed a post-hoc sub-set analysis using data from four randomised trials to explore the efficacy of galantamine versus placebo in mild AD.

METHODS

Participants in all studies met NINCDS-ADRDA criteria for probable AD. We examined data from patients with baseline Mini Mental State Examination (MMSE) 21-24 who received galantamine 24 mg/day (GAL) or placebo (PLAC). Scores for the Alzheimer's Disease Assessment Scale-cognitive subset (ADAS-cog), Clinician's Interview-Based Impression of Change (CIBIC), Disability Assessment for Dementia (DAD), and ACDS-ADL scales were compared.

RESULTS

Of the 694 patients (362 GAL, 332 PLAC, mean baseline MMSE 22.4 +/- 1.1, mean age 74 +/- 7.9 years), 65% completed 6 months treatment (223 GAL, 229 PLAC). Mean change in ADAS-cog at 6 months was -1.5 (95% confidence interval -2.2, -0.8, p < 0.001) for GAL and +0.2 (-0.6, 0.9, p = 0.72) for PLAC. This difference was statistically significant (p = 0.001). Significantly more patients receiving galantamine were classified as 'improved' using the CIBIC (26.9% GAL vs 14.3% PLAC, p < 0.001). Galantamine was generally well tolerated; most common adverse events were nausea, vomiting and diarrhoea.

CONCLUSIONS

Pooled data from four randomised trials of patients with mild AD indicate that patients who received galantamine 24 mg/day for 6 months improved cognition more often than those who received placebo and that a higher proportion receiving galantamine were globally improved. This suggests that patients with mild AD benefit from galantamine treatment.

Pharmacotherapeutic approaches to the treatment of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD), a progressive degenerative disorder of the brain, is the most common cause of cognitive impairment in the elderly. The pharmacotherapy of AD is evolving rapidly. Cholinergic stabilization with cholinesterase-inhibitor (ChEI) therapy implies neuroprotection and a resultant slowing of disability and disease progression. The moderate-affinity N-methyl-d-aspartate (NMDA)-receptor antagonist memantine may block neural excitotoxicity.

OBJECTIVE

The purpose of this review was to examine the evidence for the responsiveness to pharmacotherapy of established AD; specifically, the extent to which the benefits of therapy have been proved, the extent to which currently available ChEIs support cholinergic neurotransmission, and the extent to which currently available ChEIs and memantine provide neuroprotection.

METHODS

Relevant studies were identified through a comprehensive search of MEDLINE for articles published between January 1999 and February 2004 using the terms Alzheimer's pharmacotherapy, cholinesterase inhibitor therapy, Alzheimer's disease, donepezil, rivastigmine, galantamine, glutamatergic system modifiers, and memantine; a search of the reference lists of identified articles; and a manual search of pertinent journals. Articles were selected that contained higher-level evidence, based on explicit validated criteria.

RESULTS

ChEI therapy was associated with quality-of-life improvements that included enhanced performance of activities of daily living, reduced behavioral disturbances, stabilized cognitive impairment, decreased caregiver stress, and delay in the first dementia-related nursing home placement. In large clinical trials in moderate to severe AD (a stage that is associated with distress for patients and caregiver burden, and for which other treatments are not available), memantine showed an ability to delay cognitive and functional deterioration. The combination of memantine and ChEI therapy was significantly more efficacious than ChEI therapy alone (P < 0.001) and was well tolerated.

CONCLUSIONS

The idea that AD is pharmacologically unresponsive appears to be changing. With the use of ChEI and NMDA-receptor antagonist therapy, the symptoms and outcomes of this devastating neurodegenerative disease can be improved and its course altered.

Effects of galantamine on behavioural and psychological disturbances and caregiver burden in patients with Alzheimer's disease

BACKGROUND

Behavioural and psychological disturbances occur in up to 90% of patients with Alzheimer's disease (AD), have a substantial impact on both patients and caregivers, and are often associated with the decision to institutionalise patients. Galantamine (Reminyl) is a dual-acting cholinergic treatment that improves cognitive and functional performance, delays the onset of behavioural symptoms and decreases behaviour-associated caregiver distress.

OBJECTIVE

To assess the impact of galantamine on behavioural disturbances and associated caregiver burden in non-institutionalised patients with AD.

METHODS

This was a 3-month, open-label, multicentre study in Switzerland. Patients with mild-to-moderate AD received galantamine (escalated from 8 to 24 mg/day over 8 weeks). The primary outcome was the Neuropsychiatric Inventory (NPI) for patients who completed 3 months treatment (observed cases, OC). Secondary outcomes included the Nurses' Observation Scale for Geriatric patients (NOSGER), and the Clinical Global Impression (CGI) of change.

RESULTS

124 patients (mean age 75.2 years, 55.6% women) received galantamine and were included in the intention-to-treat (ITT) safety analysis. Significant improvements in NPI scores versus baseline were seen in the OC analysis (p < 0.05, N = 91); mean total NPI scores (+/- SE) were reduced from 14.9 +/- 1.2 at baseline to 11.3 +/- 1.2 at month 3. Eleven out of 12 NPI domains were improved. Anxiety, aberrant motor behaviour, delusions, euphoria and night-time-behaviour all improved by > 30%. Symptoms with the highest baseline frequency and severity improved by 19-27%. A significant reduction in total NPI caregiver burden was observed at month 3 (p < 0.05). Despite this short assessment period the NOSGER evaluation and physicians' CGI also showed improvement. Adverse events (AEs) were mostly gastrointestinal.

CONCLUSION

Galantamine significantly reduced behavioural disturbances after 3 months in this population and this had a positive impact on behaviour-related caregiver burden. Galantamine showed the expected safety profile and was well tolerated.

Studies toward Labeling Cytisine with [11C]Phosgene: Rapid Synthesis of a δ-Lactam Involving a New Chemoselective Lithiation−Annulation Method

With the aim of the radiolabeling of cytisine, a potent agonist of nicotinic receptors, with [(11)C]phosgene, the rapid synthesis of a lactam model of our target has been studied. The key step of the delta-lactam formation is a new chemoselective lithiation-annulation method, under high dilution, of a suitable piperidinylcarbamoyl chloride. This precursor was obtained from (2-hydroxyethyl)piperidine in a linear synthetic sequence involving a Corey-Fuchs olefination of the corresponding aldehyde, followed by a selective reduction, using a diimide equivalent, of an iodoalkyne into a (Z)-iodopropene piperidine. This alkene served as main precursor to study the cyclization according to several procedures using phosgene as the required carbonylating reagent.

Galantamine prevents apoptosis induced by beta-amyloid and thapsigargin: involvement of nicotinic acetylcholine receptors

Galantamine is currently used to treat Alzheimer's disease patients; it behaves as a mild blocker of acetylcholinesterase (AChE) and has an allosteric modulating action on nicotinic acetylcholine receptors (nAChRs). In this study, we observed that galantamine prevented cell death induced by the peptide beta-amyloid(1-40) and thapsigargin in the human neuroblastoma cell line SH-SY5Y, as well as in bovine chromaffin cells. The protective effect of galantamine was concentration-dependent in both cell types; maximum protection was produced at 300 nM. The antiapoptotic effect of galantamine at 300 nM, against beta-amyloid(1-40) or thapsigargin-induced toxicity, was reversed by alpha-bungarotoxin. At neuroprotective concentrations, galantamine caused a mild and sustained elevation of the cytosolic concentration of calcium, [Ca2+]c, measured in single cells loaded with Fura-2. Incubation of the cells for 48 h with 300 nM galantamine doubled the density of alpha7 nicotinic receptors and tripled the expression of the antiapoptotic protein Bcl-2. These results strongly suggest that galantamine can prevent apoptotic cell death by inducing neuroprotection through a mechanism related to that described for nicotine, i.e. activation of nAChRs and upregulation of Bcl-2. These findings might explain the long-term beneficial effects of galantamine in patients suffering of Alzheimer's disease.

Loss of alpha-conotoxinMII- and A85380-sensitive nicotinic receptors in Parkinson's disease striatum

Multiple nicotinic receptors are present in rodent and monkey striatum, with a selective localization of alpha-conotoxinMII-sensitive sites in the striatum and preferential declines in their numbers after nigrostriatal damage. Here we report the presence of 125I-alpha-conotoxinMII and alpha-conotoxinMII-sensitive 125I-epibatidine nicotinic receptors in human control and Parkinson's disease striatum. 125I-alpha-ConotoxinMII bound to control striatum with the characteristics of a nicotinic receptor ligand although the number of sites was approximately fivefold lower than in rodent and monkey. Competition analyses of alpha-conotoxinMII with 125I-epibatidine showed that toxin-sensitive sites comprised approximately 15% of nicotinic receptors in human striatum. In Parkinson's disease caudate, there was a approximately 50% decline in 125I-alpha-conotoxinMII sites with a similar decline in the dopamine transporter. In putamen, there were substantially greater losses of the dopamine transporter (80-90%) but only 50-60% decreases in 125I-alpha-conotoxinMII sites with corresponding declines in alpha-conotoxinMII-sensitive 125I-epibatidine sites, 125I-epibatidine (multiple) sites and 125I-A85380 (beta2-containing) nicotinic receptors. The greater loss of the transporter compared with nicotinic sites suggests that only a subpopulation of nicotinic receptors is located pre-synaptically on striatal dopaminergic neurons in man. Correlation analyses between changes in nicotinic receptors and the dopamine transporter in Parkinson's disease striatum suggest that alpha-conotoxinMII-sensitive 125I-epibatidine sites (low-affinity sites), 125I-A85380 and 125I-epibatidine sites are localized in part to dopaminergic terminals. In summary, these results show that alpha-conotoxinMII-sensitive sites are present in human striatum and that there are high- and low-affinity subtypes which are both decreased in Parkinson's disease.

α7-Nicotinic acetylcholine receptors mediate an Aβ1−42-induced increase in the level of acetylcholinesterase in primary cortical neurones

The beta-amyloid protein (Abeta) is the major protein component of amyloid plaques found in the Alzheimer brain. Although there is a loss of acetylcholinesterase (AChE) from both cholinergic and non-cholinergic neurones in the brain of Alzheimer patients, the level of AChE is increased around amyloid plaques. Previous studies using P19 cells in culture and transgenic mice which overexpress human Abeta have suggested that this increase may be due to a direct action of Abeta on AChE expression in cells adjacent to amyloid plaques. The aim of the present study was to examine the mechanism by which Abeta increases levels of AChE in primary cortical neurones. Abeta1-42 was more potent than Abeta1-40 in its ability to increase AChE in primary cortical neurones. The increase in AChE was unrelated to the toxic effects of the Abeta peptides. The effect of Abeta1-42 on AChE was blocked by inhibitors of alpha7 nicotinic acetylcholine receptors (alpha7 nAChRs) as well as by inhibitors of L- or N-type voltage-dependent calcium channels (VDCCs), whereas agonists of alpha7 nAChRs (choline, nicotine) increased the level of AChE. The results demonstrate that the effect of Abeta1-42 on AChE is due to an agonist effect of Abeta1-42 on the alpha7 nAChR.

Donepezil modulates nicotinic receptors of substantia nigra dopaminergic neurones

1. The effects of donepezil, one of the most common cholinesterase inhibitors used for treatment of Alzheimer's disease, were studied on nicotinic receptors (nAChRs)-mediated postsynaptic currents, in dopaminergic neurons of the substantia nigra pars compacta, using the patch-clamp recording technique in slice preparations. 2. Donepezil (10-100 microM) selectively and reversibly depressed nicotine currents, induced by brief puffer pulses, through a glass micropipette positioned above the slice. 3. The peak amplitude fading of the responses generated by repeated test applications of low doses of nicotine was accelerated by donepezil, while it slowed the recovery of nicotine currents after a large, desensitising, dose of the same agonist. 4. Donepezil depressed even maximal responses to nicotine, revealing a noncompetitive mechanism of action; moreover, the inhibition of nAChRs was voltage and time independent. 5. Pretreatment with vesamicol or methamidophos did not prevent the reduction of nicotine-induced currents. The data indicated direct effect on nAChR, independent from the activity of donepezil as cholinesterase inhibitor.

Visual inspection time in Parkinson’s disease: deficits in early stages of cognitive processing

Inspection time (IT) is a simple information processing paradigm dependent on a participant's ability to identify physical properties of a stimulus presented for a specified time interval. In contrast with reaction time (RT) studies, the dependent variable of interest in IT is not related to the motoric speed with which the individual is able to respond, but rather the minimum presentation time necessary for participants to reliably identify physical properties of the stimulus. It is well documented that individuals with Parkinson's disease (PD) experience significant impairment on tests of simple RT, but it is unclear whether such deficits can be interpreted as 'pure' slowness of information processing, or a delay in the selection and output of a motor response. In the first experiment described here, a sample of 'optimally medicated' PD patients was compared with an age-matched control group, on an IT task. Results of this experiment suggested that individuals with PD required significantly longer stimulus presentation times than healthy participants. The second experiment compared a sample of PD patients (tested both "ON" and "OFF" their typical dopaminergic medications), with an age-matched control group, on the same test of IT. Results again indicated a significant IT deficit in participants with PD, and suggested that these deficits do not significantly resolve with levodopa treatment. Overall, the results of these two experiments suggest that information processing deficits associated with PD are distinct from motor impairment. These findings are further discussed in terms of existing neurochemical models of information processing ability.

Lack of efficacy of a nicotine transdermal treatment on motor and cognitive deficits in Parkinson's disease

Studies assessing the efficacy of nicotine in Parkinson's disease (PD) have generated contradictory results. The controversy seems to stem from uncontrolled factors including the lack of objective measures, the practice effect in a test-retest design, and the absence of plasmatic dosage. This study aimed at further controlling these factors using transdermal nicotine in PD.

METHODS

Twenty-two nonsmoking PD patients received a transdermal nicotine treatment over 25 days in increasing titrated doses. Motor and cognitive assessments were carried out on days 11 and 25 (low-dose and high-dose assessments, respectively) and after a 14-day washout period.

RESULTS

Patients tolerated nicotine poorly. Thirteen (59%) withdrew, mostly because of acute side effects. In the remaining nine patients, nicotine neither improved nor worsened motor or cognitive functioning in comparison with 10 age, gender and education matched controls.

CONCLUSIONS

Transdermal nicotine is not effective in treating motor and cognitive deficits in PD. The results obtained with our objective measures confirm a recent double-blind, placebo-controlled study that used clinical measures. It is possible that nicotine lacks specificity in targeting critical nicotinic receptors that might be involved in PD pathophysiology. The low tolerability may be related to such a lack of specificity of nicotine, which would directly stimulate the autonomic nervous system.

Nicotinic acetylcholine receptor distribution in Alzheimer's disease, dementia with Lewy bodies, Parkinson's disease, and vascular dementia: in vitro binding study using 5-[(125)i]-a-85380

Nicotinic acetylcholine receptors (nAChRs) have been implicated in a number of neurological disorders. 5-Iodo-3-[2(S)-2-azetidinylmethoxy]pyridine (5-I-A-85380) is a novel nAChR marker, binding predominantly to the alpha4beta2 subtype. This in vitro autoradiography study describes the distribution of 5-[(125)I]-A-85380 binding in post-mortem brain tissue from normal elderly individuals and from cases with age-associated dementias of both neurodegenerative and vascular types. The binding distribution of 5-[(125)I]-A-85380 in normal brain tissue was found to be consistent with the reported distribution of other high-affinity nicotinic ligands. In addition to high thalamic and moderate striatal and temporal cortex density, moderate 5-[(125)I]-A-85380 binding was also seen in white matter tracts in cingulate, occipital, and temporal areas, indicating the presence of nAChRs along nerve fiber tracts, which has not been reported in other high-affinity nicotinic agonist distribution studies. In Parkinson's disease (PD), loss of striatal 5-[(125)I]-A-85380 binding closely parallels the loss of nigrostriatal dopaminergic markers previously observed. In dementia with Lewy bodies (DLB) reduced striatal 5-[(125)I]-A-85380 binding density, comparable to that in PD, may be a marker of early degeneration in nigrostriatal inputs, while in Alzheimer's disease (AD) reduced striatal 5-[(125)I]-A-85380 binding could be related to reduced cortical inputs. The reductions of nAChRs seen in AD, DLB, and PD were not apparent in vascular dementia (VaD). In conclusion, 5-I-A-85380 is clearly a useful ligand for both in vitro and in vivo single photon emission tomography human studies investigating disease symptoms and progression, response to acetylcholinesterase-inhibiting drugs and in differentiating primary degenerative dementia from VaD.

Synthesis and evaluation of iodinated TZTP-derivatives as potential radioligands for imaging of muscarinic M2 receptors with SPET

A series of iodinated thiadiazolyltetrahydro-1-methyl-pyridine (TZTP) compounds was synthesized and evaluated in vitro and in vivo as potential radioligands for imaging of the muscarinic M2 receptor subtype with SPET. One of these compounds, 5-(E)-iodopentenylthio-TZTP, has high in vitro affinity (Ki = 4.9 nM) and moderate selectivity for the muscarinic M2 receptor subtype. Although the uptake pattern in the biodistribution studies in rats is consistent with muscarinic M2 receptor disribution, specific in vivo binding to these receptors could not be demonstrated. The usefulness of this tracer in human SPET imaging may therefore be limited.

Nicotinic acetylcholine receptors: from structure to brain function

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels and can be divided into two groups: muscle receptors, which are found at the skeletal neuromuscular junction where they mediate neuromuscular transmission, and neuronal receptors, which are found throughout the peripheral and central nervous system where they are involved in fast synaptic transmission. nAChRs are pentameric structures that are made up of combinations of individual subunits. Twelve neuronal nAChR subunits have been described, alpha2-alpha10 and beta2-beta4; these are differentially expressed throughout the nervous system and combine to form nAChRs with a wide range of physiological and pharmacological profiles. The nAChR has been proposed as a model of an allosteric protein in which effects arising from the binding of a ligand to a site on the protein can lead to changes in another part of the molecule. A great deal is known about the structure of the pentameric receptor. The extracellular domain contains binding sites for numerous ligands, which alter receptor behavior through allosteric mechanisms. Functional studies have revealed that nAChRs contribute to the control of resting membrane potential, modulation of synaptic transmission and mediation of fast excitatory transmission. To date, ten genes have been identified in the human genome coding for the nAChRs. nAChRs have been demonstrated to be involved in cognitive processes such as learning and memory and control of movement in normal subjects. Recent data from knockout animals has extended the understanding of nAChR function. Dysfunction of nAChR has been linked to a number of human diseases such as schizophrenia, Alzheimer's and Parkinson's diseases. nAChRs also play a significant role in nicotine addiction, which is a major public health concern. A genetically transmissible epilepsy, ADNFLE, has been associated with specific mutations in the gene coding for the alpha4 or beta2 subunits, which leads to altered receptor properties.

Poor tolerability of a transdermal nicotine treatment in Parkinson's disease

Studies assessing the effect of transdermal nicotine in Parkinson's disease (PD) have generated mixed results regarding its efficacy to treat motor and cognitive deficits. These studies generally reported good tolerability in nonsmoking PD patients. The authors report the tolerability data of an open trial with transdermal nicotine in PD. Twenty-two therapeutically well-controlled nonsmoking PD patients received a transdermal nicotine treatment over 25 days according to the following fixed titration schedule: 7 mg for the first 11 days, 14 mg for the next 11 days, and 21 mg for the last 3 days. Fourteen PD patients (64%) had side effects such as nausea, vomiting, and dizziness, and 10 of them withdrew from the study. Factors such as age, body mass index, disease duration, and motor disability were not related to this intolerance. Transdermal nicotine can produce unpleasant adverse effects in patients with PD. Given that similar doses of nicotine were better tolerated in previous studies, the authors suspect the pharmacokinetic profile of the transdermal delivery system to be a determining factor in the effect of nicotine treatment in PD.

Update on Alzheimer drugs (galantamine)

BACKGROUND

Deficient cholinergic function contributes to the cognitive and behavioral signs and symptoms of Alzheimer disease (AD). A successful treatment approach in AD has been the enhancement of cholinergic function by cholinesterase inhibitors.

REVIEW SUMMARY

Galantamine is a cholinesterase inhibitor and allosteric modulating ligand at nicotinic cholinergic receptors. Galantamine 24 mg/d has been demonstrated consistently effective compared with placebo for the cognitive, functional, and behavioral aspects of Alzheimer's disease in large multicenter trials. Cognition and function on average are preserved for 12 months in Alzheimer disease patients receiving galantamine. It is safe and very well tolerated when dosage is escalated gradually.

CONCLUSIONS

Galantamine is a valuable addition to agents available for the pharmacologic treatment of AD.

Nicotine enhances contextual fear conditioning in C57BL/6J mice at 1 and 7 days post-training

Nicotine has been demonstrated to enhance learning processes. The present experiments extend these results to examine the effects of nicotine on acquisition and consolidation of contextual and cued fear conditioning, and the duration of nicotine's enhancement of conditioned fear. C57BL/6 mice were trained with two pairings of an auditory CS and a foot shock US. Multiple doses of nicotine were given before or immediately after training and on testing day (0.0, 0.050, 0.125, 0.250, and 0.375 mg/kg, i.p). Freezing to both the context and auditory CS was measured 24h after training and again 1 week after training. Mice did not receive nicotine for the 1-week retest. Nicotine (0.125 and 0.250 mg/kg) given on both training and testing days enhanced freezing to the context at 24h. In addition, elevated freezing to the context was seen 1 week post-training in mice previously treated with 0.125 and 0.250 mg/kg nicotine. Thus, nicotine-treated mice did show elevated levels of freezing when retested 1 week later, even though no nicotine was administered at the 1-week retest. Mice that received nicotine on training day or testing day only and mice that received nicotine with mecamylamine, a nicotinic receptor antagonist, were not different from saline-treated mice. In addition, post-training administration of nicotine did not enhance fear conditioning. The present results indicate that nicotine enhancement of contextual fear conditioning depends on administration of nicotine on training and test days but results in a long-lasting enhancement of memories of contextual fear conditioning that remains in the absence of nicotine.

The beneficial effect of donepezil on visual hallucinations in three patients with Parkinson's disease

Visual hallucinations (VHs) are common psychiatric symptoms in patients with long-standing Parkinson's disease (PD). Treatment with neuroleptics or withdrawal of anti-PD drugs may improve VHs but will worsen motor dysfunctions. The authors report on 3 patients with long-standing PD who were treated with the cholinesterase inhibitor donepezil for the treatment of VHs. Each received a daily dose of 5 mg of donepezil, after reducing or discontinuing anti-PD medications had failed to relieve the VHs. In 2 patients (patient 1, 2), donepezil decreased VHs without worsening motor dysfunctions. In addition, the cognitive status of patient 2 improved. In patient 3, donepezil also resolved VHs, but delusions developed during treatment. After discontinuing donepezil, delusions disappeared and VHs reappeared. Donepezil may ameliorate visual hallucinations in PD patients, but controlled, double-blind trials are necessary to further clarify the effect of this drug on VHs in PD.

Nicotinic acetylcholine receptor-mediated neuroprotection by donepezil against glutamate neurotoxicity in rat cortical neurons

Donepezil is a potent and selective acetylcholinesterase (AChE) inhibitor developed for the treatment of Alzheimer's disease. To elucidate whether donepezil shows neuroprotective action in addition to amelioration of cognitive deficits, we examined the effects of donepezil on glutamate-induced neurotoxicity using primary cultures of rat cortical neurons. A 10-min exposure of cultures to glutamate followed by a 1-h incubation with glutamate-free medium caused a marked loss of viability, as determined by Trypan blue exclusion. Glutamate neurotoxicity was prevented by 24-h pretreatment of donepezil in a concentration-dependent manner. Among AChE inhibitors examined, donepezil and certain AChE inhibitors such as tacrine and galanthamine showed potent neuroprotective action, although physostigmine did not affect glutamate neurotoxicity. Neuroprotective action of donepezil was antagonized by mecamylamine, a nicotinic acetylcholine receptor (nAChR) antagonist, but not by scopolamine, a muscarinic acetylcholine receptor antagonist. Furthermore, both dihydro-beta-erythroidine, an alpha4beta2-neuronal nAChR antagonist, and methyllycaconitine, an alpha7-nAChR antagonist, each also significantly antagonized the effect of donepezil. Next, we examined the effects of donepezil on glutamate-induced apoptosis. Exposure of 100 microM glutamate to cortical neurons for 24 h induced apoptotic neuronal death and nuclear fragmentation. Donepezil for 24 h before and 24 h during glutamate exposure prevented nuclear fragmentation and glutamate-induced apoptosis. These results suggest that donepezil not only protects cortical neurons against glutamate neurotoxicity via alpha4beta2- and alpha7-nAChRs but also prevents apoptotic neuronal death.

Impaired modulation of GABAergic transmission by muscarinic receptors in a mouse transgenic model of Alzheimer's disease

It has long been recognized that muscarinic acetylcholine receptors (mAChRs) are crucial for the control of cognitive processes, and drugs that activate mAChRs are helpful in ameliorating cognitive deficits of Alzheimer's disease (AD). On the other hand, GABAergic transmission in prefrontal cortex (PFC) plays a key role in "working memory" via controlling the timing of neuronal activity during cognitive operations. To test whether the muscarinic and gamma-aminobutyric acid (GABA) system are interconnected in normal cognition and dementia, we examined the muscarinic regulation of GABAergic transmission in PFC of an animal model of AD. Transgenic mice overexpressing a mutant gene for beta-amyloid precursor protein (APP) show behavioral and histopathological abnormalities resembling AD and, therefore, were used as an AD model. Application of the mAChR agonist carbachol significantly increased the spontaneous inhibitory postsynaptic current (sIPSC) frequency and amplitude in PFC pyramidal neurons from wild-type animals. In contrast, carbachol failed to increase the sIPSC amplitude in APP transgenic mice, whereas the carbachol-induced increase of the sIPSC frequency was not significantly changed in these mutants. Similar results were obtained in rat PFC slices pretreated with the beta-amyloid peptide (Abeta). Inhibiting protein kinase C (PKC) blocked the carbachol enhancement of sIPSC amplitudes, implicating the PKC dependence of this mAChR effect. In APP transgenic mice, carbachol failed to activate PKC despite the apparently normal expression of mAChRs. These results show that the muscarinic regulation of GABA transmission is impaired in the AD model, probably due to the Abeta-mediated interference of mAChR activation of PKC.

Combined uridine and choline administration improves cognitive deficits in spontaneously hypertensive rats

Rationale. Hypertension is considered a risk factor for the development of cognitive disorders, because of its negative effects on cerebral vasculature and blood flow. Genetically induced hypertension in rats has been associated with a range of cognitive impairments. Therefore, spontaneously hypertensive rats (SHR) can potentially be used as a model for cognitive deficits in human subjects. Consecutively, it can be determined whether certain food components can improve cognition in these rats. Objective. The present study aimed to determine whether SHR display specific deficits in attention, learning, and memory function. Additionally, effects of chronic uridine and choline administration were studied. Methods. 5-7 months old SHR were compared with normotensive Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats. (a) The operant delayed non-matching-to-position (DNMTP) test was used to study short-term memory function. (b) The five-choice serial reaction time (5-CSRT) task was used to assess selective visual attention processes. (c) Finally, the Morris water maze (MWM) acquisition was used as a measure for spatial learning and mnemonic capabilities. Results. (1) SHR exhibited significantly impaired performance in the 5-CSRT test in comparison with the two other rat strains. Both the SHR and WKY showed deficits in spatial learning when compared with the SD rats. (2) Uridine and choline supplementation normalized performance of SHR in the 5-CSRT test. (3) In addition, uridine and choline treatment improved MWM acquisition in both WKY and SHR rats. Conclusion. The present results show that the SHR have a deficiency in visual selective attention and spatial learning. Therefore, the SHR may provide an interesting model in the screening of substances with therapeutic potential for treatment of cognitive disorders. A combination of uridine and choline administration improved selective attention and spatial learning in SHR.

Cholinergic nicotinic receptors: competitive ligands, allosteric modulators, and their potential applications

Discovery of the important role played by nicotinic acetylcholine receptors (nAChRs) in several CNS disorders has called attention to these membrane proteins and to ligands able to modulate their functions. The existence of different subtypes at multiple levels has complicated the understanding of this receptor's physiological role, but at the same time has increased the efforts to discover selective compounds in order to improve the pharmacological characterization of this kind of receptor and to make the possible therapeutical use of its modulators safer. This review focuses on the structure of new ligands for nAChRs, agonists, antagonists and allosteric modulators, and on their possible applications.