Monoamine neurons in aging and Alzheimer's disease

Biogenesis and secretion of mitovesicles, small extracellular vesicles of mitochondrial origin at the crossroads between brain health and disease

In the brain, mitochondrial components are released into the extracellular space via several mechanisms, including a recently identified type of extracellular vesicles called mitovesicles. While vesiculation of neuronal mitochondria yields various intracellular types of vesicles, with either a single or a double membrane, mitovesicles secreted into the extracellular space are a unique subtype of these mitochondria-derived vesicles, with a double membrane and a specific set of mitochondrial DNA, RNA, proteins, and lipids. Based on the most relevant literature describing mitochondrial vesiculation and mitochondrial exocytosis, we propose a model for their secretion when the amphisome, a hybrid endosome-autophagosome organelle, fuses with the plasma membrane, releasing mitovesicles and exosomes into the extracellular space. In aging and neurodegenerative disorders, mitochondrial dysfunction, in association with endolysosomal abnormalities, alter mitovesicle number and content, with downstream effect on brain health.

Mitovesicles secreted into the extracellular space of brains with mitochondrial dysfunction impair synaptic plasticity

BACKGROUND

Hypometabolism tied to mitochondrial dysfunction occurs in the aging brain and in neurodegenerative disorders, including in Alzheimer's disease, in Down syndrome, and in mouse models of these conditions. We have previously shown that mitovesicles, small extracellular vesicles (EVs) of mitochondrial origin, are altered in content and abundance in multiple brain conditions characterized by mitochondrial dysfunction. However, given their recent discovery, it is yet to be explored what mitovesicles regulate and modify, both under physiological conditions and in the diseased brain. In this study, we investigated the effects of mitovesicles on synaptic function, and the molecular players involved.

METHODS

Hippocampal slices from wild-type mice were perfused with the three known types of EVs, mitovesicles, microvesicles, or exosomes, isolated from the brain of a mouse model of Down syndrome or of a diploid control and long-term potentiation (LTP) recorded. The role of the monoamine oxidases type B (MAO-B) and type A (MAO-A) in mitovesicle-driven LTP impairments was addressed by treatment of mitovesicles with the irreversible MAO inhibitors pargyline and clorgiline prior to perfusion of the hippocampal slices.

RESULTS

Mitovesicles from the brain of the Down syndrome model reduced LTP within minutes of mitovesicle addition. Mitovesicles isolated from control brains did not trigger electrophysiological effects, nor did other types of brain EVs (microvesicles and exosomes) from any genotype tested. Depleting mitovesicles of their MAO-B, but not MAO-A, activity eliminated their ability to alter LTP.

CONCLUSIONS

Mitovesicle impairment of LTP is a previously undescribed paracrine-like mechanism by which EVs modulate synaptic activity, demonstrating that mitovesicles are active participants in the propagation of cellular and functional homeostatic changes in the context of neurodegenerative disorders.

Activation of 5-HT1A Receptors Normalizes the Overexpression of Presynaptic 5-HT1A Receptors and Alleviates Diabetic Neuropathic Pain

Neuropathic pain is a well-documented phenomenon in experimental and clinical diabetes; however, current treatment is unsatisfactory. Serotoninergic-containing neurons are key components of the descending autoinhibitory pathway, and a decrease in their activity may contribute at least in part to diabetic neuropathic pain (DNP). A streptozotocin (STZ)-treated rat was used as a model for type 1 diabetes mellitus (T1DM). Pain transmission was evaluated using well-established nociceptive-based techniques, including the Hargreaves apparatus, cold plate and dynamic plantar aesthesiometer. Using qRT-PCR, Western blotting, immunohistochemistry, and HPLC-based techniques, we also measured in the central nervous system and peripheral nervous system of diabetic animals the expression and localization of 5-HT1A receptors (5-HT1AR), levels of key enzymes involved in the synthesis and degradation of tryptophan and 5-HT, including tryptophan hydroxylase-2 (Tph-2), tryptophan 2,3-dioxygenase (Tdo), indoleamine 2,3-dioxygenase 1 (Ido1) and Ido2. Moreover, spinal concentrations of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA, a metabolite of 5-HT) and quinolinic acid (QA, a metabolite of tryptophan) were also quantified. Diabetic rats developed thermal hyperalgesia and cold/mechanical allodynia, and these behavioral abnormalities appear to be associated with the upregulation in the levels of expression of critical molecules related to the serotoninergic nervous system, including presynaptic 5-HT1AR and the enzymes Tph-2, Tdo, Ido1 and Ido2. Interestingly, the level of postsynaptic 5-HT1AR remains unaltered in STZ-induced T1DM. Chronic treatment of diabetic animals with 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT), a selective 5-HT1AR agonist, downregulated the upregulation of neuronal presynaptic 5-HT1AR, increased spinal release of 5-HT (↑ 5-HIAA/5-HT) and reduced the concentration of QA, decreased mRNA expression of Tdo, Ido1 and Ido2, arrested neuronal degeneration and ameliorated pain-related behavior as exemplified by thermal hyperalgesia and cold/mechanical allodynia. These data show that 8-OH-DPAT alleviates DNP and other components of the serotoninergic system, including the ratio of 5-HIAA/5-HT and 5-HT1AR, and could be a useful therapeutic agent for managing DNP.

Structure, Function, and Molecular Landscapes of the Aging Retina

Because the central nervous system is largely nonrenewing, neurons and their synapses must be maintained over the lifetime of an individual to ensure circuit function. Age is a dominant risk factor for neural diseases, and declines in nervous system function are a common feature of aging even in the absence of disease. These alterations extend to the visual system and, in particular, to the retina. The retina is a site of clinically relevant age-related alterations but has also proven to be a uniquely approachable system for discovering principles that govern neural aging because it is well mapped, contains diverse neuron types, and is experimentally accessible. In this article, we review the structural and molecular impacts of aging on neurons within the inner and outer retina circuits. We further discuss the contribution of non-neuronal cell types and systems to retinal aging outcomes. Understanding how and why the retina ages is critical to efforts aimed at preventing age-related neural decline and restoring neural function.

Impact of aging on animal models of Parkinson's disease

Aging is the biggest risk factor for developing Parkinson's disease (PD), the second most common neurodegenerative disorder. Several animal models have been developed to explore the pathophysiology underlying neurodegeneration and the initiation and spread of alpha-synuclein-related PD pathology, and to investigate biomarkers and therapeutic strategies. However, bench-to-bedside translation of preclinical findings remains suboptimal and successful disease-modifying treatments remain to be discovered. Despite aging being the main risk factor for developing idiopathic PD, most studies employ young animals in their experimental set-up, hereby ignoring age-related cellular and molecular mechanisms at play. Consequently, studies in young animals may not be an accurate reflection of human PD, limiting translational outcomes. Recently, it has been shown that aged animals in PD research demonstrate a higher susceptibility to developing pathology and neurodegeneration, and present with a more disseminated and accelerated disease course, compared to young animals. Here we review recent advances in the investigation of the role of aging in preclinical PD research, including challenges related to aged animal models that are limiting widespread use. Overall, current findings indicate that the use of aged animals may be required to account for age-related interactions in PD pathophysiology. Thus, although the use of older animals has disadvantages, a model that better represents clinical disease within the elderly would be more beneficial in the long run, as it will increase translational value and minimize the risk of therapies failing during clinical studies. Furthermore, we provide recommendations to manage the challenges related to aged animal models.

Alzheimer's disease neuropathology is exacerbated following traumatic brain injury. Neuroprotection by co-administration of nanowired mesenchymal stem cells and cerebrolysin with monoclonal antibodies to amyloid beta peptide

Military personnel are prone to traumatic brain injury (TBI) that is one of the risk factors in developing Alzheimer's disease (AD) at a later stage. TBI induces breakdown of the blood-brain barrier (BBB) to serum proteins into the brain and leads to extravasation of plasma amyloid beta peptide (ΑβP) into the brain fluid compartments causing AD brain pathology. Thus, there is a need to expand our knowledge on the role of TBI in AD. In addition, exploration of the novel roles of nanomedicine in AD and TBI for neuroprotection is the need of the hour. Since stem cells and neurotrophic factors play important roles in TBI and in AD, it is likely that nanodelivery of these agents exert superior neuroprotection in TBI induced exacerbation of AD brain pathology. In this review, these aspects are examined in details based on our own investigations in the light of current scientific literature in the field. Our observations show that TBI exacerbates AD brain pathology and TiO₂ nanowired delivery of mesenchymal stem cells together with cerebrolysin-a balanced composition of several neurotrophic factors and active peptide fragments, and monoclonal antibodies to amyloid beta protein thwarted the development of neuropathology following TBI in AD, not reported earlier.

Exploring the Role of Monoamine Oxidase Activity in Aging and Alzheimer's Disease

Monoamine oxidases (MAOs) are a family of flavin adenine dinucleotide-dependent enzymes that exert a crucial role in the metabolism of neurotransmitters of the central nervous system. The impaired function of MAOs is associated with copious brain diseases. The alteration of monoamine metabolism is a characteristics feature of aging. MAO plays a crucial role in the pathogenesis of Alzheimer's disease (AD) - a progressive neurodegenerative disorder associated with an excessive accumulation of amyloid-beta (Aβ) peptide and neurofibrillary tangles (NFTs). Activated MAO has played a critical role in the development of amyloid plaques from Aβ, as well as the formation of the NFTs. In the brain, MAO mediated metabolism of monoamines is the foremost source of reactive oxygen species formation. The elevated level of MAO-B expression in astroglia has been reported in the AD brains adjacent to amyloid plaques. Increased MAO-B activity in the cortical and hippocampal regions is associated with AD. This review describes the pathogenic mechanism of MAOs in aging as well as the development and propagation of Alzheimer's pathology.

The protective effect of Indian Catechu methanolic extract against aluminum chloride-induced neurotoxicity, A rodent model of Alzheimer's disease

Alzheimer's disease (AD) is the commonest neurodegenerative disorder with a wide array of manifestations, courses, and contributing causes. Despite being clinically characterized a long time ago; no treatment has been developed that could improve the pathology or slow down the disease manifestation- so far. Indian Catechu methanolic extract (ICME) has proved to have multiple beneficial effects that support its use in several disorders- especially those with complex etiology. In the present study, we evaluated the neuroprotective effect of ICME in a rat model of AD using Aluminum Chloride (AlCl3). The results showed that ICME could have a positive impact on the course of AD through its anticholinesterase effect and significant antioxidant effect which was reflected on the animals both on behavioral tests as well as hallmark pathological findings.

A comprehensive review of monoamine oxidase inhibitors as Anti-Alzheimer's disease agents: A review

Monoamine oxidases (MAO-A and MAO-B) are mammalian flavoenzyme, which catalyze the oxidative deamination of several neurotransmitters like norepinephrine, dopamine, tyramine, serotonin, and some other amines. The oxidative deamination produces several harmful side products like ammonia, peroxides, and aldehydes during the biochemical reaction. The concentration of biochemical neurotransmitter alteration in the brain by MAO is directly related with several neurological disorders like Alzheimer's disease and Parkinson's disease (PD). Activated MAO also contributes to the amyloid beta (Aβ) aggregation by two successive cleft β-secretase and γ-secretase of amyloid precursor protein (APP). Additionally, activated MAO is also involved in aggregation of neurofibrillary tangles and cognitive destruction through the cholinergic neuronal damage and disorder of the cholinergic system. MAO inhibition has general anti-Alzheimer's disease effect as a consequence of oxidative stress reduction prompted by MAO enzymes. In this review, we outlined and addressed recent understanding on MAO enzymes such as their structure, physiological function, catalytic mechanism, and possible therapeutic goals in AD. In addition, it also highlights the current development and discovery of potential MAO inhibitors (MAOIs) from various chemical scaffolds.

Gene expression of serotonergic markers in peripheral blood mononuclear cells of patients with late-onset Alzheimer's disease

Serotonin or 5-hydroxytryptamine (5-HT) is primarily involved in the regulation of learning and memory. Pathological changes in metabolism or functional imbalance of 5-HT has been associated with Alzheimer's disease (AD). The hypothesis tested is that in peripheral blood, markers of the serotonergic pathway can be used as a diagnostic tool for AD. The current study measured the relative expression of 5-HT receptors (5-HTR2A and 5-HTR3A) as well as the 5-HT catalytic enzyme, Monoamine oxidase A (MAO-A) mRNA in Peripheral Blood Mononuclear Cells (PBMCs) of patients with late-onset Alzheimer's disease (LOAD) and age-matched controls. 5-HTR2A, 5-HTR3A, and MAO-A mRNA expressions were examined in PBMCs of 30 patients with LOAD and 30 control individuals. Real-time quantitative PCR was used to measure mRNA expression. The dementia status of patients in this study was assessed using a Mini-Mental State Examination (MMSE). Mean data of relative mRNA expression of 5-HTR2A, 5-HTR3A and MAO-A were significantly lower in PBMCs of patients with LOAD compared with controls. Based on the down-regulation of serotonergic markers in PBMCs, our findings may be another claim to the systemic nature of LOAD. The role of peripheral serotonergic downregulation, in the pathogenesis of AD, needs to be further studied. Given the extremely convenient access to PBMCs, these molecular events may represent more complete dimensions of AD neuropathophysiology or possibly lead to a new direction in studies focused on blood-based markers.

Neuroprotective effects of Sophora secundiflora, Sophora tomentosa leaves and formononetin on scopolamine-induced dementia

Five flavonoids were isolated from the ethyl acetate fraction of leaves of Sophora secundiflora; formononetin (1), 5-hydroxy-4'-methoxyflavone (2), genistein (3), 5-hydroxy-8-(1-hydroxy-1-methyl-ethyl)-2-(4-hydroxyphenyl)-4H-furo-[2, 3-h]-chromen-4-one (4) and ononin (5). Additionally, LC-ESI-MS/MS analysis of the ethyl acetate fraction of S. secundiflora leaves had led to tentative identification of eighteen compounds. Formononetin, S. tomentosa and S. secundiflora leaves methanolic extract were evaluated in vivo for their neuroprotective activity where formononetin and S. tomentosa showed promising neuroprotective activity with reduction in acetylcholine esterase (AchE) enzyme activity and elevation of acetylcholine (Ach) and glutathione(GSH) brain levels and attenuation of dopamine (DA), nor-adrenaline (NA) and malonedialdehyde (MDA) brain level significantly, However S. secundiflora leaves methanolic extract didn't attenuate the AchE enzyme activity, DA and NA brain levels.[Formula: see text].

Chronic Polyphenon-60 or Catechin Treatments Increase Brain Monoamines Syntheses and Hippocampal SIRT1 Levels Improving Cognition in Aged Rats

Polyphenolic compounds from green tea have great interest due to its large CONSUMPTION and therapeutic potential on the age-associated brain decline. The current work compares a similar dose regimen of a whole-green-tea extract and catechin in old rats over the course of 36 days. Results showed a significant improvement in visuo-spatial working memory and episodic memory of old rats after polyphenolic compounds administration assessed by behavioral tests. No effects were observed on the age-associated motor coordination decline. Statistically, results were correlated with significant improvements, mainly in hippocampal and striatal noradrenergic and serotonergic systems, but also with the striatal dopaminergic system. Both polyphenolic treatments also reverted the age-associated reduction of the neuroinflammation by modulating protein sirtuin 1 (SIRT1) expression in hippocampus, but no effects were observed in the usual reduction of the histone-binding protein RBAP46/48 protein linked to aging. These results are in line with previous ones obtained with other polyphenolic compounds, suggesting a general protective effect of all these compounds on the age-associated brain decline, pointing to a reduction of the oxidative stress and neuroinflammatory status reduction as the leading mechanisms. Results also reinforce the relevance of SIRT1-mediated mechanism on the neuroprotective effect and rule out the participation of RBAP46/48 protein.

Surface Fouling of Ultrananocrystalline Diamond Microelectrodes during Dopamine Detection: Improving Lifetime via Electrochemical Cycling

In this work, we report the electrochemical response of a boron-doped ultrananocrystalline diamond (BDUNCD) microelectrode during long-term dopamine (DA) detection. Specifically, changes to its electrochemical activity and electroactive area due to DA byproducts and surface oxidation are studied via scanning electron microscopy, energy dispersive spectroscopy, electrochemical impedance spectroscopy, and silver deposition imaging (SDI). The fouling studies with amperometry (AM) and fast scan cyclic voltammetry (FSCV) methods suggest that the microelectrodes are heavily fouled due to poor DA-dopamine- o-quinone cyclization rates followed by a combination of polymer formation and major changes in their surface chemistry. SDI data confirms the presence of the insulating polymer with sparsely distributed tiny electroactive regions. This resulted in severely distorted DA signals and a 90% loss in signal starting as early as 3 h for AM and a 56% loss at 6.5 h for FSCV. This underscores the need for cleaning of the fouled microelectrodes if they have to be used long-term. Out of the three in vivo suitable electrochemical cycling cleaning waveforms investigated, the standard waveform (-0.4 V to +1.0 V) provides the best cleaned surface with a fully retained voltammogram shape, no hysteresis, no DA signal loss (a 90 ± 0.72 nA increase), and the smallest charge transfer resistance value of 0.4 ± 0.02 MΩ even after 6.5 h of monitoring. Most importantly, this is the same waveform that is widely used for in vivo detection with carbon fiber microelectrodes. Future work to test these microelectrodes for more than 24 h of DA detection is anticipated.

T-type calcium channel enhancer SAK3 promotes dopamine and serotonin releases in the hippocampus in naive and amyloid precursor protein knock-in mice

T-type calcium channels in the brain mediate the pathophysiology of epilepsy, pain, and sleep. Recently, we developed a novel therapeutic candidate, SAK3 (ethyl 8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo[1,2-a] pyridine]-2-ene-3-carboxylate), for Alzheimer's disease (AD). The cognitive improvement by SAK3 is closely associated with enhanced acetylcholine (ACh) release in the hippocampus. Since monoamines such as dopamine (DA), noradrenaline (NA), and serotonin (5-HT) are also involved in hippocampus-dependent learning and psychomotor behaviors in mice, we investigated the effects of SAK3 on these monoamine releases in the mouse brain. Oral administration of SAK3 (0.5 mg/kg, p.o.) significantly promoted DA and 5-HT releases in the naive mouse hippocampal CA1 region but not in the medial prefrontal cortex (mPFC), while SAK3 did not affect NA release in either brain region. The T-type calcium channel-specific inhibitor, NNC 55-0396 (1 μM) significantly antagonized SAK3-enhanced DA and 5-HT releases in the hippocampus. Interestingly, the α7 nicotinic ACh receptor (nAChR) antagonist, methyllycaconitine (1 nM) significantly inhibited DA release, and the α4 nAChR antagonist, dihydro-β-erythroidine (100 μM) significantly blocked both DA and 5-HT releases following SAK3 (0.5 mg/kg, p.o.) administration in the hippocampus. SAK3 did not alter basal monoamine contents both in the mPFC and hippocampus. SAK3 (0.5 mg/kg, p.o.) administration also significantly elevated DA and 5-HT releases in the hippocampal CA1 region of amyloid-precursor protein (APP)NL-GF knock-in (KI) mice. Moreover, hippocampal DA and 5-HT contents were significantly decreased in APPNL-GF KI mice. Taken together, our data suggest that SAK3 promotes monoamine DA and 5-HT releases by enhancing the T-type calcium channel and nAChR in the mouse hippocampus.

Association between serotonin denervation and resting-state functional connectivity in mild cognitive impairment

Resting-state functional connectivity alterations have been demonstrated in Alzheimer's disease (AD) and mild cognitive impairment (MCI) before the observation of AD neuropathology, but mechanisms driving these changes are not well understood. Serotonin neurodegeneration has been observed in MCI and AD and is associated with cognitive deficits and neuropsychiatric symptoms, but the role of the serotonin system in relation to brain network dysfunction has not been a major focus of investigation. The current study investigated the relationship between serotonin transporter availability (SERT; measured using positron emission tomography) and brain network functional connectivity (measured using resting-state functional MRI) in 20 participants with MCI and 21 healthy controls. Two SERT regions of interest were selected for the analysis: the Dorsal Raphe Nuclei (DRN) and the precuneus which represent the cell bodies of origin and a cortical target of projections of the serotonin system, respectively. Both regions show decreased SERT in MCI compared to controls and are the site of early AD pathology. Average resting-state functional connectivity did not differ between MCI and controls. Decreased SERT in DRN was associated with lower hippocampal resting-state connectivity in MCI participants compared to controls. Decreased SERT in the right precuneus was also associated with lower resting-state connectivity of the retrosplenial cortex to the dorsal lateral prefrontal cortex and higher resting-state connectivity of the retrosplenial cortex to the posterior cingulate and in patients with MCI but not in controls. These results suggest that a serotonergic mechanism may underlie changes in brain functional connectivity in MCI. Hum Brain Mapp 38:3391-3401, 2017. © 2017 Wiley Periodicals, Inc.

Causes, consequences, and cures for neuroinflammation mediated via the locus coeruleus: noradrenergic signaling system

Aside from its roles in as a classical neurotransmitter involved in regulation of behavior, noradrenaline (NA) has other functions in the CNS. This includes restricting the development of neuroinflammatory activation, providing neurotrophic support to neurons, and providing neuroprotection against oxidative stress. In recent years, it has become evident that disruption of physiological NA levels or signaling is a contributing factor to a variety of neurological diseases and conditions including Alzheimer's disease (AD) and Multiple Sclerosis. The basis for dysregulation in these diseases is, in many cases, due to damage occurring to noradrenergic neurons present in the locus coeruleus (LC), the major source of NA in the CNS. LC damage is present in AD, multiple sclerosis, and a large number of other diseases and conditions. Studies using animal models have shown that experimentally induced lesion of LC neurons exacerbates neuropathology while treatments to compensate for NA depletion, or to reduce LC neuronal damage, provide benefit. In this review, we will summarize the anti-inflammatory and neuroprotective actions of NA, summarize examples of how LC damage worsens disease, and discuss several approaches taken to treat or prevent reductions in NA levels and LC neuronal damage. Further understanding of these events will be of value for the development of treatments for AD, multiple sclerosis, and other diseases and conditions having a neuroinflammatory component. The classical neurotransmitter noradrenaline (NA) has critical roles in modulating behaviors including those involved in sleep, anxiety, and depression. However, NA can also elicit anti-inflammatory responses in glial cells, can increase neuronal viability by inducing neurotrophic factor expression, and can reduce neuronal damage due to oxidative stress by scavenging free radicals. NA is primarily produced by tyrosine hydroxylase (TH) expressing neurons in the locus coeruleus (LC), a relatively small brainstem nucleus near the IVth ventricle which sends projections throughout the brain and spinal cord. It has been known for close to 50 years that LC neurons are lost during normal aging, and that loss is exacerbated in neurological diseases including Parkinson's disease and Alzheimer's disease. LC neuronal damage and glial activation has now been documented in a variety of other neurological conditions and diseases, however, the causes of LC damage and cell loss remain largely unknown. A number of approaches have been developed to address the loss of NA and increased inflammation associated with LC damage, and several methods are being explored to directly minimize the extent of LC neuronal cell loss or function. In this review, we will summarize some of the consequences of LC loss, consider several factors that likely contribute to that loss, and discuss various ways that have been used to increase NA or to reduce LC damage. This article is part of the 60th Anniversary special issue.

Basal Forebrain Cholinergic System and Memory

Basal forebrain cholinergic neurons constitute a way station for many ascending and descending pathways. These cholinergic neurons have a role in eliciting cortical activation and arousal. It is well established that they are mainly involved in cognitive processes requiring increased levels of arousal, attentive states and/or cortical activation with desynchronized activity in the EEG. These cholinergic neurons are modulated by several afferents of different neurotransmitter systems. Of particular importance within the cortical targets of basal forebrain neurons is the hippocampal cortex. The septohippocampal pathway is a bidirectional pathway constituting the main septal efferent system, which is widely known to be implicated in every memory process investigated. The present work aims to review the main neurotransmitter systems involved in modulating cognitive processes related to learning and memory through modulation of basal forebrain neurons.

Neuroprotective effects of multifaceted hybrid agents targeting MAO, cholinesterase, iron and β-amyloid in ageing and Alzheimer's disease

Alzheimer's disease (AD) is accepted nowadays as a complex neurodegenerative disorder with multifaceted cerebral pathologies, including extracellular deposition of amyloid β peptide-containing plaques, intracellular neurofibrillary tangles, progressive loss of cholinergic neurons, metal dyshomeostasis, mitochondrial dysfunction, neuroinflammation, glutamate excitoxicity, oxidative stress and increased MAO enzyme activity. This may explain why it is currently widely accepted that a more effective therapy for AD would result from the use of multifunctional drugs, which may affect more than one brain target involved in the disease pathology. The current review will discuss the potential benefits of novel multimodal neuroprotective, brain permeable drugs, recently developed by Youdim and collaborators, as a valuable therapeutic approach for AD treatment. The pharmacological and neuroprotective properties of these multitarget-directed ligands, which target MAO enzymes, the cholinergic system, iron accumulation and amyloid β peptide generation/aggregation are described, with a special emphasis on their potential therapeutic value for ageing and AD-associated cognitive functions. This review is conceived as a tribute to the broad neuropharmacology work of Professor Moussa Youdim, Professor Emeritus in the Faculty of Medicine and Director of Eve Topf Center of Excellence in Technion-Israel Institute of Technology, and Chief Scientific Officer of ABITAL Pharma Pipeline Ltd., at the occasion of his 75th birthday.

LINKED ARTICLES

This article is part of a themed section on Updating Neuropathology and Neuropharmacology of Monoaminergic Systems. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.13/issuetoc.

Neurotoxin-induced DNA damage is persistent in SH-SY5Y cells and LC neurons

Degeneration of the noradrenergic neurons has been reported in the brain of patients suffering from neurodegenerative diseases. However, their pathological characteristics during the neurodegenerative course and underlying mechanisms remain to be elucidated. In the present study, we used the neurotoxin camptothecin (CPT) to induce the DNA damage response in neuroblastoma SH-SY5Y cells, normal fibroblast cells, and primarily cultured locus coeruleus (LC) and raphe neurons to examine cellular responses and repair capabilities after neurotoxin exposure. To our knowledge, the present study is the first to show that noradrenergic SH-SY5Y cells are more sensitive to CPT-induced DNA damage and deficient in DNA repair, as compared to fibroblast cells. Furthermore, similar to SH-SY5Y cells, primarily cultured LC neurons are more sensitive to CPT-induced DNA damage and show a deficiency in repairing this damage. Moreover, while N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) exposure also results in DNA damage in cultured LC neurons, neither CPT nor DSP4 induce DNA damage in neuronal cultures from the raphe nuclei. Taken together, noradrenergic SH-SY5Y cells and LC neurons are sensitive to CPT-induced DNA damage and exhibit a repair deficiency, providing a mechanistic explanation for the pathological characteristics of LC degeneration when facing endogenous and environmental DNA-damaging insults in vivo.

Depressive-like behavior is paired to monoaminergic alteration in a murine model of Alzheimer's disease

BACKGROUND

Neuropsychiatric signs are critical in primary caregiving of Alzheimer patients and have not yet been fully investigated in murine models.

METHODS

18-month-old 3×Tg-AD male mice and their wild-type male littermates (non-Tg) were used. The open field test and the elevated plus maze test were used to evaluate anxiety-like behaviors, whereas the Porsolt forced swim test, the tail suspension test, and the sucrose preference test for antidepressant/depression-coping behaviors. Neurochemical study was conducted by microdialysis in freely-moving mice, analyzing the basal and K(+)-stimulated monoamine output in the frontal cortex and ventral hippocampus. Moreover by immunohistochemistry, we analysed the expression of Tyrosin hydroxylase and Tryptophan hydroxylase, which play a key role in the synthesis of monoamines.

RESULTS

Aged 3×Tg-AD mice exhibited a higher duration of immobility in the forced swim and tail suspension tests (predictors of depression-like behavior) which was not attenuated by a noradrenaline reuptake inhibitor, desipramine. In the sucrose preference test, 3×Tg-AD mice showed a significantly lower sucrose preference compared to the non-Tg group, without any difference in total fluid intake. In contrast, the motor functions and anxiety-related emotional responses of 3×Tg-AD mice were normal, as detected by the open-field and elevated plus-maze tests. To strengthen these results, we then evaluated the monoaminergic neurotransmissions by in vivo microdialysis and immunohistochemistry. In particular, with the exception of the basal hippocampal dopamine levels, 3×Tg-AD mice exhibited a lower basal extracellular output of amines in the frontal cortex and ventral hippocampus and also a decreased extracellular response to K(+) stimulation. Such alterations occur with obvious local amyloid-β and tau pathologies and without gross alterations in the expression of Tyrosin and Tryptophan hydroxylase.

CONCLUSIONS

These results suggest that 3×Tg-AD mice exhibit changes in depression-related behavior involving aminergic neurotrasmitters and provide an animal model for investigating AD with depression.

Novel Therapeutic Strategies for Delirium in Patients With Cancer

To compare the efficacy of antipsychotics (APs) for delirium treatment in patients with cancer, 27 patients treated with 1 of the 4 APs, haloperidol (HPD), risperidone (RIS), olanzapine (OLZ), and quetiapine (QTP), were divided into 2 groups: long half-life (T1/2; HPD, RIS, and OLZ) versus short T1/2 (QTP) or the multiacting receptor-targeted APs (MARTAs; OLZ and QTP) versus the non-MARTA (HPD and RIS). The symptom severity was evaluated by the memorial delirium rating scale (MDAS) on days 0, 3, and 7 following intervention. Significant improvements in total MDAS scores were found in all groups on day 3. However, on day 7, only the short T1/2 group and MARTA group showed significant improvement. Consideration of an AP’s pharmacological properties may be helpful for improving the outcomes of pharmacological delirium intervention in patients with cancer.

Monoamine oxidase inhibitors: promising therapeutic agents for Alzheimer's disease (Review)

Activated monoamine oxidase (MAO) has a critical role in the pathogenesis of Alzheimer's disease (AD), including the formation of amyloid plaques from amyloid β peptide (Aβ) production and accumulation, formation of neurofibrillary tangles, and cognitive impairment via the destruction of cholinergic neurons and disorder of the cholinergic system. Several studies have indicated that MAO inhibitors improve cognitive deficits and reverse Aβ pathology by modulating proteolytic cleavage of amyloid precursor protein and decreasing Aβ protein fragments. Thus, MAO inhibitors may be considered as promising therapeutic agents for AD.

Increase in tetrahydrobiopterin concentration with aging in the cerebral cortex of the senescence-accelerated mouse prone 10 strain caused by abnormal regulation of tetrahydrobiopterin biosynthesis

6R-L-Erythro-5,6,7,8-tetrahydrobiopterin (BH4) is an essential cofactor for tyrosine hydroxylase (TH) activity and is a risk factor for cognitive decline and brain atrophy. Previous studies have shown that the decline in TH activity in the cerebral cortex of senescence-accelerated mouse prone 10 (SAMP10) mice is caused, at least in part, by a decrease in Fe, ferritin, and TH phosphorylation. We determined the concentrations of BH4 and the enzymes GTP cyclohydrolase-1,6-pyruvoyltetrahydropterin synthase and sepiapterin reductase (SPR) in the de novo pathway of BH4 biosynthesis. Dihydrofolate reductase (DHFR), which converts BH2 to BH4 in the salvage pathway of BH4 synthesis was also determined in the cerebral cortex of SAM mice at 3 and 12 months of age. The BH4 concentration was measured by HPLC, and the protein levels of enzymes involved in BH4 synthesis were measured by western blot analysis. At 12 months of age, BH4 concentration in the cerebral cortex of SAMP10 mice showed significantly higher values as compared to that of control mice. Further, the protein level of SPR in SAMP10 mice was significantly higher than that in SAMR1 mice at 3 and 12 months of age. In contrast to SPR, the protein level of DHFR in SAMP10 mice was significantly lower than that in SAMR1 mice. These results indicate that abnormal regulation of BH4 metabolism occurs in the cerebral cortex of SAMP10 where the dysfunction of the salvage pathway of BH4 synthesis may cause overproduction of BH4 through the de novo pathway, which is considered characteristic in the cerebral cortex of SAMP10 with aging. Therefore, there is a possibility that the excess amounts of BH4 lead to age-related brain dysfunction in the cerebral cortex of SAMP10.

Cognitive abnormalities and hippocampal alterations in monoamine oxidase A and B knockout mice

The monoamine oxidase isoenzymes (MAOs) A and B play important roles in the homeostasis of monoaminergic neurotransmitters. The combined deficiency of MAO A and B results in significantly elevated levels of serotonin (5-hydroxytryptamine), norepinephrine, dopamine, and β-phenylethylamine; in humans and mice, these neurochemical changes are accompanied by neurodevelopmental perturbations as well as autistic-like responses. Ample evidence indicates that normal levels of monoamines in the hippocampus, amygdala, frontal cortex, and cerebellum are required for the integrity of learning and memory. Thus, in the present study, the cognitive status of MAO A/B knockout (KO) mice was examined with a wide array of behavioral tests. In comparison with male wild-type littermates, MAO A/B KO mice exhibited abnormally high and overgeneralized fear conditioning and enhanced eye-blink conditioning. These alterations were accompanied by significant increases in hippocampal long-term potentiation and alterations in the relative expression of NMDA glutamate receptor subunits. Our data suggest that chronic elevations of monoamines, because of the absence of MAO A and MAO B, cause functional alterations that are accompanied with changes in the cellular mechanisms underlying learning and memory. The characteristics exhibited by MAO A/B KO mice highlight the potential of these animals as a useful tool to provide further insight into the molecular bases of disorders associated with abnormal monoaminergic profiles.

Effects of Lifelong Ethanol Consumption on Brain Monoamine Transmitters in Alcohol-Preferring Alko Alcohol (AA) Rats

The purpose of the present study was to examine the combined effects of aging and lifelong ethanol exposure on the levels of monoamine neurotransmitters in different regions of the brain. This work is part of a project addressing interactions of aging and lifelong ethanol consumption in alcohol-preferring AA (Alko Alcohol) line of rats, selected for high voluntary consumption of ethanol. Intake of ethanol on the level of 4.5–5 g/kg/day for about 20 months induced only limited changes in the neurotransmitter levels; the concentration of noradrenaline was significantly reduced in the frontal cortex. There was also a trend towards lower levels of dopamine and 5-hydroxytryptamine (5-HT) in the frontal cortex, and towards a lower noradrenaline level in the dorsal cortex. Aging was associated with a decreased concentration of dopamine in the dorsal cortex and with a declining trend in the striatum. The levels of 5-HT in the limbic forebrain were higher in the aged than in the young animals, and in the striatum, there was a trend towards higher levels in older animals. The data suggest that a continuous intake of moderate amounts of ethanol does not enhance the age-related alterations in brain monoamine neurotransmission, while the decline in the brain level of dopamine associated with aging may be a factor contributing to age-related neurological disorders.

Development of amyloid burden in African Green monkeys

The vervet is an old world monkey increasingly being used as a model for human diseases. In addition to plaques and tangles, an additional hallmark of Alzheimer's disease is damage to neurons that synthesize noradrenaline (NA). We characterized amyloid burden in the posterior temporal lobe of young and aged vervets, and compared that with changes in NA levels and astrocyte activation. Total amyloid beta (Aβ)40 and Aβ42 levels were increased in the aged group, as were numbers of amyloid plaques detected using antibody 6E10. Low levels of Aβ42 were detected in 1 of 5 younger animals, although diffusely stained plaques were observed in 4 of these. Increased glial fibrillary acidic protein staining and messenger RNA levels were significantly correlated with increased age, as were cortical NA levels. Levels of Aβ42 and Aβ40, and the number of 6E10-positive plaques, were correlated with NA levels. Interestingly messenger RNA levels of glial derived neurotrophic factor, important for noradrenergic neuronal survival, were reduced with age. These findings suggest that amyloid pathology in aged vervets is associated with astrocyte activation and higher NA levels.

A strategy for developing new treatment paradigms for neuropsychiatric and neurocognitive symptoms in Alzheimer's disease

Successful disease modifying drug development for Alzheimer's disease (AD) has hit a roadblock with the recent failures of amyloid-based therapies, highlighting the translational disconnect between preclinical animal models and clinical outcome. Although disease modifying therapies are the Holy Grail to pursue, symptomatic therapies addressing cognitive and neuropsychiatric aspects of the disease are also extremely important for the quality of life of patients and caregivers. Despite the fact that neuropsychiatric problems in Alzheimer patients are the major driver for costs associated with institutionalization, no good preclinical animal models with predictive validity have been documented. We propose a combination of quantitative systems pharmacology (QSP), phenotypic screening and preclinical animal models as a novel strategy for addressing the bottleneck in both cognitive and neuropsychiatric drug discovery and development for AD. Preclinical animal models such as transgene rats documenting changes in neurotransmitters with tau and amyloid pathology will provide key information that together with human imaging, pathology and clinical data will inform the virtual patient model. In this way QSP modeling can partially overcome the translational disconnect and reduce the attrition of drug programs in the clinical setting. This approach is different from target driven drug discovery as it aims to restore emergent properties of the networks and therefore likely will identify multitarget drugs. We review examples on how this hybrid humanized QSP approach has been helpful in predicting clinical outcomes in schizophrenia treatment and cognitive impairment in AD and expand on how this strategy could be applied to neuropsychiatric symptoms in dementia. We believe such an innovative approach when used carefully could change the Research and Development paradigm for symptomatic treatment in AD.

Sleep disturbances in Alzheimer's and Parkinson's diseases

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative disorders and exact a burden on our society greater than cardiovascular disease and cancer combined. While cognitive and motor symptoms are used to define AD and PD, respectively, patients with both disorders exhibit sleep disturbances including insomnia, hypersomnia and excessive daytime napping. The molecular basis of perturbed sleep in AD and PD may involve damage to hypothalamic and brainstem nuclei that control sleep-wake cycles. Perturbations in neurotransmitter and hormone signaling (e.g., serotonin, norepinephrine and melatonin) and the neurotrophic factor BDNF likely contribute to the disease process. Abnormal accumulations of neurotoxic forms of amyloid β-peptide, tau and α-synuclein occur in brain regions involved in the regulation of sleep in AD and PD patients, and are sufficient to cause sleep disturbances in animal models of these neurodegenerative disorders. Disturbed regulation of sleep often occurs early in the course of AD and PD, and may contribute to the cognitive and motor symptoms. Treatments that target signaling pathways that control sleep have been shown to retard the disease process in animal models of AD and PD, suggesting a potential for such interventions in humans at risk for or in the early stages of these disorders.

Deficiency of catecholamine syntheses caused by downregulation of phosphorylation of tyrosine hydroxylase in the cerebral cortex of the senescence-accelerated mouse prone 10 strain with aging

The purpose of this study was to elucidate the alteration of catecholamine metabolism and the contribution of catecholamines to the decline of learning and memory in the brain of the senescence-accelerated mouse prone 10 (SAMP10) with aging. Catecholamines and their metabolites in the cerebral cortex were measured by HPLC-ECD. The protein levels of tyrosine hydroxylase (TH) as well as TH phosphorylated at Ser19 or Ser40, dopamine-β-hydroxylase (DβH), and cAMP-dependent protein kinase (PKA) were determined by western blot analysis. Dopamine (DA) and norepinephrine (NE) levels in SAMP10 were significantly lower than those in control animals. However, no significant difference was observed in catecholamine metabolite levels between SAMP10 and control mice. The level of TH phosphorylation at Ser40 in SAMP10 was significantly lower than that in control mice, but no significant difference was observed in the levels of TH, TH phosphorylated at Ser19, or DβH. The amount of PKA, which regulates the phosphorylation of TH at Ser40, was significantly lower in SAMP10 than in control mice. The present study demonstrated that a decline in DA and NE concentrations was observed in the cerebral cortex of SAMP10 with aging, and this decrease of catecholamine levels was caused by impairment of their synthetic pathway. These impairments are considered to be caused by downregulation of TH phosphorylation at Ser40 as a result of PKA deficiency. The present study suggests that the decline of learning and memory abilities of SAMP10 is caused by a decrease in catecholamine synthesis in the cerebral cortex with aging.

The noradrenaline precursor L-DOPS reduces pathology in a mouse model of Alzheimer's disease

Damage to noradrenergic neurons in the locus coeruleus (LC) is a hallmark of Alzheimer's disease (AD) and may contribute to disease progression. In 5xFAD transgenic mice, which accumulate amyloid burden at early ages, the LC undergoes stress as evidenced by increased astrocyte activation, neuronal hypertrophy, reduced levels of LC-enriched messenger RNAs (mRNAs), and increased inflammatory gene expression. Central nervous system (CNS) noradrenaline (NA) levels in 5-month-old male 5xFAD mice were increased using the NA precursor L-threo-3,4-dihydroxyphenylserine (L-DOPS). After 1 month, L-DOPS treatment improved learning in the Morris water maze test compared with vehicle-treated mice. L-DOPS increased CNS NA levels, and average latency times in the water maze test were inversely correlated to NA levels. L-DOPS reduced astrocyte activation and Thioflavin-S staining; increased mRNA levels of neprilysin and insulin degrading enzyme, and of several neurotrophins; and increased brain-derived neurotrophic factor protein levels. These data demonstrate the presence of LC stress in a robust mouse model of AD, and suggest that raising CNS NA levels could provide benefit in AD.

Locus coeruleus damage and noradrenaline reductions in multiple sclerosis and experimental autoimmune encephalomyelitis

The endogenous neurotransmitter noradrenaline exerts anti-inflammatory and neuroprotective effects in vitro and in vivo. Several studies report that noradrenaline levels are altered in the central nervous system of patients with multiple sclerosis and rodents with experimental autoimmune encephalomyelitis, which could contribute to pathology. Since the major source of noradrenaline are neurons in the locus coeruleus, we hypothesized that alterations in noradrenaline levels are a consequence of stress or damage to locus coeruleus neurons. In C57BL/6 mice immunized with myelin oligodendrocyte glycoprotein peptide 35-55 to develop chronic disease, cortical and spinal cord levels of noradrenaline were significantly reduced versus control mice. Immunohistochemical staining revealed increased astrocyte activation in the ventral portion of the locus coeruleus in immunized mice. The immunized mice showed neuronal damage in the locus coeruleus detected by a reduction of average cell size of tyrosine hydroxylase stained neurons. Analysis of the locus coeruleus of multiple sclerosis and control brains showed a significant increase in astrocyte activation, a reduction in noradrenaline levels, and neuronal stress indicated by hypertrophy of tyrosine hydroxylase stained cell bodies. However, the magnitude of these changes was not correlated with extent of demyelination or of cellular infiltrates. Together these findings demonstrate the presence of inflammation and neuronal stress in multiple sclerosis as well as in experimental autoimmune encephalomyelitis. Since reduced noradrenaline levels could be permissive for increased inflammation and neuronal damage, these results suggest that methods to raise noradrenaline levels or increase locus coeruleus function may be of benefit in treating multiple sclerosis.

Aging, Neurodegenerative Disease and the Brain

L'eorganisation anatomique et chimique du cerveau humain subit de nombreux changements au cours du vieillissement. Certains neurons meurent, d'autres s'atrophient et ily a une réduction marquée du nombre de synapses dans des régions spécifiques du cerveau. Des diminutions du métabolisme du glucose et des effets pré- et post-synaptiques des neurotransmetteurs ont aussi été rapportées. À l'exception de certaines structures sous-corticales, il existe cependant une controverse quant à la sévérité des changements dans l'ensemble du cerveau. De plus, les effets du vieillissement sont très variables d'une région du cerveau à l'autre ainsi que d'un individu à l'autre. Certains phénomènes observès dans le vieillissement normal, tels la perte des neurones dopaminergique de la substance noire et celle des neurones cholinergiques du prosencé;phale basal, apparaissent sous une forme grandement exacerbées dans diverses pathologies neurodégénératives comme les maladies de Parkinson et d'Alzeimer. Les faibles altérations qui surviennent au niveau de ces systémes lors du vieillissement normal pourraient étre responsables des troubles d'équilibre, de la pauvreté de mouvement et des pertes de mémoires que l'on observent chez les gens âgés. Cependant, l'inflammation chronique du cerveau semble être une caractéristique typique des individus atteints de maladies neurodégénératives. L'hypothèse voulant que cette inflammation puisse être ralentie par un traitement avec des agents anti-inflammatoires a été supportée par les résultats de 19 études épidémiologiques ainsi que par un essai clinique de moindre envergure. Cependant, d'Autres études cliniques devront ètre réalisées et une attention particulière devra être portée aux effets secondaires de la thérapie anti-inflammatoire conventionnelle afin d'en arriver à une conclusion définitive.

Development of an efficient therapeutic agent for Alzheimer's disease: design and synthesis of dual inhibitors of acetylcholinesterase and serotonin transporter

To date, acetylcholinesterase (AChE) inhibitors have been clinically effective drugs for the palliative treatment of Alzheimer's disease, but their clinical efficacy is limited, mainly due to their adverse effects on peripheral organs. Since patients of Alzheimer's disease often exhibit depression as well as memory impairment, dual inhibitors of AChE and serotonin transporter (SERT) would be a better therapeutic method. Anti-depressive effects based on SERT inhibition would reduce the dose-related side effects of AChE inhibitors. Such dual inhibitors were designed by the hybridization of rivastigmine and fluoxetine based on a hypothetical model of the AChE active site. Various derivatives were synthesized and evaluated for their in vitro inhibition, and then (S)-5j (RS-1259), which possessed balanced inhibitory activities of AChE (IC(50)=101 nM) and SERT (IC(50)=42 nM), was successfully obtained. An ex vivo experiment in mice indicated that (S)-5j (RS-1259) simultaneously inhibited AChE and SERT in the brain following an oral administration. The simultaneous elevation of extracellular levels of acetylcholine and serotonin in the rat hippocampus was actually confirmed by microdialysis.

Tackling sleeplessness: psychological treatment options for insomnia in older adults

This paper provides a broad review of the extant literature involving the treatment of sleeplessness in older adults with insomnia. First, background information (including information regarding key issues in late-life insomnia and epidemiology of late-life insomnia) pertinent to achieving a general understanding of insomnia in the elderly is presented. Next, theories of insomnia in older adults are examined and discussed in relation to treatment of insomnia in late-life. With a general knowledge base provided, empirical evidence for both pharmacological (briefly) and psychological treatment options for insomnia in late-life are summarized. Recent advances in the psychological treatment of insomnia are provided and future directions are suggested. This review is not meant to be all-inclusive; however, it is meant to provide professionals across multiple disciplines (physicians; psychologists; applied and basic researchers) with a mix of breadth and depth of knowledge related to insomnia in late-life. It is our hope that readers will see the evidence in support of psychological treatments for late-life insomnia, and the utility in continuing to investigate this treatment modality.

Antidepressants are a rational complementary therapy for the treatment of Alzheimer's disease

There is a high prevalence rate (30-50%) of Alzheimer's disease (AD) and depression comorbidity. Depression can be a risk factor for the development of AD or it can be developed secondary to the neurodegenerative process. There are numerous documented diagnosis and treatment challenges for the patients who suffer comorbidity between these two diseases. Meta analysis studies have provided evidence for the safety and efficacy of antidepressants in treatment of depression in AD patients. Preclinical and clinical studies show the positive role of chronic administration of selective serotonin reuptake inhibitor (SSRI) antidepressants in hindering the progression of the AD and improving patient performance. A number of clinical studies suggest a beneficial role of combinatorial therapies that pair antidepressants with FDA approved AD drugs. Preclinical studies also demonstrate a favorable effect of natural antidepressants for AD patients. Based on the preclinical studies there are a number of plausible antidepressants effects that may modulate the progression of AD. These effects include an increase in neurogenesis, improvement in learning and memory, elevation in the levels of neurotrophic factors and pCREB and a reduction of amyloid peptide burden. Based on this preclinical and clinical evidence, antidepressants represent a rational complimentary strategy for the treatment of AD patients with depression comorbidity.

Regulation of cortical acetylcholine release: insights from in vivo microdialysis studies

Acetylcholine release links the activity of presynaptic neurons with their postsynaptic targets and thus represents the intercellular correlate of cholinergic neurotransmission. Here, we review the regulation and functional significance of acetylcholine release in the mammalian cerebral cortex, with a particular emphasis on information derived from in vivo microdialysis studies over the past three decades. This information is integrated with anatomical and behavioral data to derive conclusions regarding the role of cortical cholinergic transmission in normal behavioral and how its dysregulation may contribute to cognitive correlates of several neuropsychiatric conditions. Some unresolved issues regarding the regulation and significance of cortical acetylcholine release and the promise of new methodology for advancing our knowledge in this area are also briefly discussed.

Neurochemical basis for symptomatic treatment of Alzheimer's disease

Neuron and synapse loss together with neurotransmitter dysfunction have, along with Abeta deposition and neurofibrillary tangles, been recognized as hallmarks of Alzheimer's disease (AD). Furthermore, clinical and preclinical studies point to neuronal loss and associated neurochemical alterations of several transmitter systems as a main factor underlying both cognitive and neuropsychiatric symptoms. Treatment for the cognitive decline in AD, based on early findings of a cholinergic deficit, has been in the clinic for more than a decade but provides only modest benefit in most patients. Therefore there is still considerable scope for new treatments that demonstrate greater efficacy against cognitive dysfunction in spite of the fact that the mainstays of current treatments, the cholinesterase inhibitors Aricept, Exelon and Reminyl (Razadyne) will become generic over the next few years. However, the most important area for drug development is for the treatment of behavioural disturbance in AD since many existing treatments have limited efficacy and have potentially life-threatening side effects. This review examines the neurochemical underpinning of both cognitive and neuropsychiatric symptoms in dementia and provides some basis for rational drug development.

A dual-hit animal model for age-related parkinsonism

Parkinson's disease is a neurological disorder which afflicts an increasing number of individuals. If the wider complex of extrapyramidal symptoms referred to as "age-related parkinsonism" is included, the incidence is near 50% of the population above 80 years of age. This review summarizes recent studies from our laboratories as well as other research groups in the quest to explore the multi-faceted etiology of age-related neurodegeneration, in general, and degeneration of the substantia nigra dopaminergic neurons, in particular. Our work during recent years has focused on assessment of potential interactive effects of a reduction in glial cell line-derived neurotrophic factor (GDNF) and the aging process (intrinsic factors) and early neurotoxin exposure (an extrinsic factor) on dopamine (DA) systems and the behaviors they mediate. The guiding hypothesis directing the research to be described was that a combination of the two factors would exacerbate the decline in the DA transmitter system function that occurs during aging. The results obtained were consistent with the well-established aging-related decline in function and structure of neurons utilizing DA as a transmitter and motor function, and extended knowledge by establishing that the genetic reduction of Gdnf exacerbated these aging related changes. Thus, GDNF reduction appears to increase the vulnerability of the DA neurons to the many different challenges associated with the aging process. Assessment of methamphetamine effects on young Gdnf(+/-) mice indicated that reduced GDNF availability increased the vulnerability of DA systems to this well-established neurotoxin. The work discussed in this review is consistent with earlier work demonstrating the importance of GDNF for maintenance of DA neurons and also provides a novel model for progressive DA degeneration and motor dysfunction.

Mosaic aging

Although all multicellular organisms undergo structural and functional deterioration with age, senescence is not a uniform process. Rather, each organism experiences a constellation of changes that reflect the heterogeneous effects of age on molecules, cells, organs and systems, an idiosyncratic pattern that we refer to as mosaic aging. Varying genetic, epigenetic and environmental factors (local and extrinsic) contribute to the aging phenotype in a given individual, and these agents influence the type and rate of functional decline, as well as the likelihood of developing age-associated afflictions such as cardiovascular disease, arthritis, cancer, and neurodegenerative disorders. Identifying key factors that drive aging, clarifying their activities in different systems, and in particular understanding how they interact will enhance our comprehension of the aging process, and could yield insights into the permissive role that senescence plays in the emergence of acute and chronic diseases of the elderly.

Theta bursts in the olfactory nerve paired with beta-adrenoceptor activation induce calcium elevation in mitral cells: a mechanism for odor preference learning in the neonate rat

Odor preference learning in the neonate rat follows pairing of odor input and noradrenergic activation of beta-adrenoceptors. Odor learning is hypothesized to be supported by enhanced mitral cell activation. Here a mechanism for enhanced mitral cell signaling is described. Theta bursts in the olfactory nerve (ON) produce long-term potentiation (LTP) of glomerular excitatory postsynaptic potentials (EPSPs) and of excitatory postsynaptic currents (EPSCs) in the periglomerular (PG) and external tufted (ET) cells. Theta bursts paired with beta-adrenoceptor activation significantly elevate mitral cell (MC) calcium. Juxtaglomerular inhibitory network depression by beta-adrenoceptor activation appears to increase calcium in MCs in response to theta burst stimulation.

Characterization of 2,5-diaryl-1,3,4-oxadiazolines by multinuclear magnetic resonance and density functional theory calculations. Investigation on a case of very remote Hammett correlation

Two series of 2,5-diaryl-1,3,4-oxadiazolines have been studied by multinuclear magnetic resonance and density functional theory calculations. A full NMR spectroscopic characterization has been performed and excellent remote Hammett correlations (sigma(p) or sigma(p)+) have been found for para substitution in the two aryl rings through at least 11 bonds, notwithstanding the presence in the path of atoms that should act as insulators and a lack of correlation for some of the intermediate atoms. The computational investigation on the electronic delocalization, performed with the ACID (anisotropy of the induced current density) method, reveals indeed that electrons are delocalized in almost the entire molecule despite the presence of the insulators.

Cholinergic modulation of the cerebral metabolic response to citalopram in Alzheimer's disease

Pre-clinical and human neuropharmacological evidence suggests a role of cholinergic modulation of monoamines as a pathophysiological and therapeutic mechanism in Alzheimer's disease. The present study measured the effects of treatment with the cholinesterase inhibitor and nicotinic receptor modulator, galantamine, on the cerebral metabolic response to the selective serotonin reuptake inhibitor, citalopram. Seven probable Alzheimer's disease patients and seven demographically comparable controls underwent two positron emission tomography (PET) glucose metabolism scans, after administration of a saline placebo infusion (Day 1) and after citalopram (40 mg, IV, Day 2). The scan protocol was repeated in the Alzheimer's disease patients 2 months after titration to a 24 mg galantamine dose. At baseline, cerebral glucose metabolism was reduced in Alzheimer's disease patients relative to controls in right middle temporal, left posterior cingulate and parietal cortices (precuneus and inferior parietal lobule), as expected. Both groups demonstrated acute decreases in cerebral glucose metabolism after citalopram to a greater extent in the Alzheimer's disease patients. In the patients, relative to the controls, citalopram decreased glucose metabolism to a greater extent in middle frontal gyrus (bilaterally), left middle temporal gyrus and right posterior cingulate prior to treatment. Galantamine treatment alone increased metabolism in the right precuneus, right inferior parietal lobule and right middle occipital gyrus. In contrast, during galantamine treatment, citalopram increased metabolism in the right middle frontal gyrus, right post-central gyrus, right superior and middle temporal gyrus and right cerebellum. The combined cerebral metabolic effects of galantamine and citalopram suggest, consistent with preclinical data, a synergistic interaction of cholinergic and serotonergic systems.