Locus ceruleus degeneration promotes Alzheimer pathogenesis in amyloid precursor protein 23 transgenic mice

Ascending monoaminergic systems alterations in Alzheimer's disease. translating basic science into clinical care

Extensive neuropathological studies have established a compelling link between abnormalities in structure and function of subcortical monoaminergic (MA-ergic) systems and the pathophysiology of Alzheimer's disease (AD). The main cell populations of these systems including the locus coeruleus, the raphe nuclei, and the tuberomamillary nucleus undergo significant degeneration in AD, thereby depriving the hippocampal and cortical neurons from their critical modulatory influence. These studies have been complemented by genome wide association studies linking polymorphisms in key genes involved in the MA-ergic systems and particular behavioral abnormalities in AD. Importantly, several recent studies have shown that improvement of the MA-ergic systems can both restore cognitive function and reduce AD-related pathology in animal models of neurodegeneration. This review aims to explore the link between abnormalities in the MA-ergic systems and AD symptomatology as well as the therapeutic strategies targeting these systems. Furthermore, we will examine possible mechanisms behind basic vulnerability of MA-ergic neurons in AD.

Comprehensive behavioral characterization of an APP/PS-1 double knock-in mouse model of Alzheimer's disease

INTRODUCTION

Despite the extensive mechanistic and pathological characterization of the amyloid precursor protein (APP)/presenilin-1 (PS-1) knock-in mouse model of Alzheimer's disease (AD), very little is known about the AD-relevant behavioral deficits in this model. Characterization of the baseline behavioral performance in a variety of functional tasks and identification of the temporal onset of behavioral impairments are important to provide a foundation for future preclinical testing of AD therapeutics. Here we perform a comprehensive behavioral characterization of this model, discuss how the observed behavior correlates with the mechanistic and pathological observations of others, and compare this model with other commonly used AD mouse models.

METHODS

FOUR DIFFERENT GROUPS OF MICE RANGING ACROSS THE LIFESPAN OF THIS MODEL (TEST GROUPS: 7, 11, 15, and 24 months old) were run in a behavioral test battery consisting of tasks to assess motor function (grip strength, rotor rod, beam walk, open field ambulatory movement), anxiety-related behavior (open field time spent in peripheral zone vs. center zone, elevated plus maze), and cognitive function (novel object recognition, radial arm water maze).

RESULTS

There were no differences in motor function or anxiety-related behavior between APP/PS-1 knock-in mice and wild-type counterpart mice for any age group. Cognitive deficits in both recognition memory (novel object recognition) and spatial reference memory (radial arm water maze) became apparent for the knock-in animals as the disease progressed.

CONCLUSION

This is the first reported comprehensive behavioral analysis of the APP/PS1 knock-in mouse model of AD. The lack of motor/coordination deficits or abnormal anxiety levels, coupled with the age/disease-related cognitive decline and high physiological relevance of this model, make it well suited for utilization in preclinical testing of AD-relevant therapeutics.

Rapid β-amyloid deposition and cognitive impairment after cholinergic denervation in APP/PS1 mice

Although extensive evidence supports the role of β-amyloid (Aβ) in Alzheimer disease (AD), the neurotoxic mechanisms underlying AD pathogenesis are not understood. On the other hand, neuronal loss is the pathologic feature that best correlates with cognitive impairment. We hypothesized that cholinergic neurodegeneration may lead to Aβ deposition and tested this by inducing selective cholinergic lesions in APPswe/PS1dE9 mice with murine p75 saporin (mu p75-SAP). Intracerebroventricular lesions that removed approximately 50% of cholinergic innervation to the cortex and hippocampus were induced in animals with incipient (∼3 months) and marked (∼7 months of age) Aβ deposition. Cranial windows were implanted, and Aβ deposition was monitored in vivo using multiphoton microscopy. Deposition of Aβ was increased as soon as 7 days after the lesion, and this effect was maintained up to 3 months later. Postmortem studies using immunohistochemistry with an anti-Aβ antibody corroborated these findings in both cerebral cortex and hippocampus. Tau phosphorylation was also significantly increased after the lesions. Cholinergic denervation resulted in early memory impairment at 3 months of age that worsened with age (∼7 months); there was a synergistic effect between cholinergic denervation and the presence of APP/PS1 transgenes. Altogether, our data suggest that cholinergic denervation may trigger Aβ deposition and synergistically contribute to cognitive impairment in AD patients.

Targeting norepinephrine in mild cognitive impairment and Alzheimer's disease

The Alzheimer's disease (AD) epidemic is a looming crisis, with an urgent need for new therapies to delay or prevent symptom onset and progression. There is growing awareness that clinical trials must target stage-appropriate pathophysiological mechanisms to effectively develop disease-modifying treatments. Advances in AD biomarker research have demonstrated changes in amyloid-beta (Aβ), brain metabolism and other pathophysiologies prior to the onset of memory loss, with some markers possibly changing one or two decades earlier. These findings suggest that amyloid-based therapies would optimally be targeted at the earliest clinically detectable stage (such as mild cognitive impairment (MCI)) or before. Postmortem data indicate that tau lesions in the locus coeruleus (LC), the primary source of subcortical norepinephrine (NE), may be the first identifiable pathology of AD, and recent data from basic research in animal models of AD indicate that loss of NE incites a neurotoxic proinflammatory condition, reduces Aβ clearance and negatively impacts cognition - recapitulating key aspects of AD. In addition, evidence linking NE deficiency to neuroinflammation in AD also exists. By promoting proinflammatory responses, suppressing anti-inflammatory responses and impairing Aβ degradation and clearance, LC degeneration and NE loss can be considered a triple threat to AD pathogenesis. Remarkably, restoration of NE reverses these effects and slows neurodegeneration in animal models, raising the possibility that treatments which increase NE transmission may have the potential to delay or reverse AD-related pathology. This review describes the evidence supporting a key role for noradrenergic-based therapies to slow or prevent progressive neurodegeneration in AD. Specifically, since MCI coincides with the onset of clinical symptoms and brain atrophy, and LC pathology is already present at this early stage of AD pathogenesis, MCI may offer a critical window of time to initiate novel noradrenergic-based therapies aimed at the secondary wave of events that lead to progressive neurodegeneration. Because of the widespread clinical use of drugs with a NE-based mechanism of action, there are immediate opportunities to repurpose existing medications. For example, NE transport inhibitors and NE-precursor therapies that are used for treatment of neurologic and psychiatric disorders have shown promise in animal models of AD, and are now prime candidates for early-phase clinical trials in humans.

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.

Selective loss of noradrenaline exacerbates early cognitive dysfunction and synaptic deficits in APP/PS1 mice

BACKGROUND

Degeneration of the locus coeruleus (LC), the major noradrenergic nucleus in the brain, occurs early and is ubiquitous in Alzheimer's disease (AD). Experimental lesions to the LC exacerbate AD-like neuropathology and cognitive deficits in several transgenic mouse models of AD. Because the LC contains multiple neuromodulators known to affect amyloid β toxicity and cognitive function, the specific role of noradrenaline (NA) in AD is not well understood.

METHODS

To determine the consequences of selective NA deficiency in an AD mouse model, we crossed dopamine β-hydroxylase (DBH) knockout mice with amyloid precursor protein (APP)/presenilin-1 (PS1) mice overexpressing mutant APP and PS1. Dopamine β-hydroxylase (-/-) mice are unable to synthesize NA but otherwise have normal LC neurons and co-transmitters. Spatial memory, hippocampal long-term potentiation, and synaptic protein levels were assessed.

RESULTS

The modest impairments in spatial memory and hippocampal long-term potentiation displayed by young APP/PS1 or DBH (-/-) single mutant mice were augmented in DBH (-/-)/APP/PS1 double mutant mice. Deficits were associated with reduced levels of total calcium/calmodulin-dependent protein kinase II and N-methyl-D-aspartate receptor 2A and increased N-methyl-D-aspartate receptor 2B levels and were independent of amyloid β accumulation. Spatial memory performance was partly improved by treatment with the NA precursor drug L-threo-dihydroxyphenylserine.

CONCLUSIONS

These results indicate that early LC degeneration and subsequent NA deficiency in AD may contribute to cognitive deficits via altered levels of calcium/calmodulin-dependent protein kinase II and N-methyl-D-aspartate receptors and suggest that NA supplementation could be beneficial in early AD.

Death by a thousand cuts in Alzheimer's disease: hypoxia--the prodrome

A wide range of clinical consequences may be associated with obstructive sleep apnea (OSA) including systemic hypertension, cardiovascular disease, pulmonary hypertension, congestive heart failure, cerebrovascular disease, glucose intolerance, impotence, gastroesophageal reflux, and obesity, to name a few. Despite this, 82 % of men and 93 % of women with OSA remain undiagnosed. OSA affects many body systems, and induces major alterations in metabolic, autonomic, and cerebral functions. Typically, OSA is characterized by recurrent chronic intermittent hypoxia (CIH), hypercapnia, hypoventilation, sleep fragmentation, peripheral and central inflammation, cerebral hypoperfusion, and cerebral glucose hypometabolism. Upregulation of oxidative stress in OSA plays an important pathogenic role in the milieu of hypoxia-induced cerebral and cardiovascular dysfunctions. Strong evidence underscores that cerebral amyloidogenesis and tau phosphorylation--two cardinal features of Alzheimer's disease (AD), are triggered by hypoxia. Mice subjected to hypoxic conditions unambiguously demonstrated upregulation in cerebral amyloid plaque formation and tau phosphorylation, as well as memory deficit. Hypoxia triggers neuronal degeneration and axonal dysfunction in both cortex and brainstem. Consequently, neurocognitive impairment in apneic/hypoxic patients is attributable to a complex interplay between CIH and stimulation of several pathological trajectories. The framework presented here helps delineate the emergence and progression of cognitive decline, and may yield insight into AD neuropathogenesis. The global impact of CIH should provide a strong rationale for treating OSA and snoring clinically, in order to ameliorate neurocognitive impairment in aged/AD patients.

Selective ablation of dopamine β-hydroxylase neurons in the brain by immunotoxin-mediated neuronal targeting: new insights into brain catecholaminergic circuitry and catecholamine-related diseases

The locus coeruleus (LC) has been implicated in a variety of physiological functions including sleep/wakefulness, cognition/memory, stress/emotion, and pain. Marked loss of LC-noradrenergic (NAergic) neurons is observed in autopsy specimens of patients with Alzheimer's disease and Parkinson's disease (PD), and part of the clinical symptoms of these diseases may be related to dysfunction of the LC. Neurotoxins have been utilized to ablate LC-NAergic neurons in experimental animals for elucidating the pathophysiological implication of the loss of LC, but there are methodological drawbacks in previously utilized methods. We employed immunotoxin-mediated neuronal targeting to overcome these problems. Following complete disruption of the LC-NAergic neurons by immunotoxin, mice showed behavioral changes, which resembled the nonmotor symptoms of PD. The LC-NAergic neurons did not regenerate following ablation, so the immunotoxin-mediated neuronal targeting may be useful especially for studying the long-term effects of the loss of LC-NAergic neurons on brain functions.

The locus coeruleus-norepinephrine network optimizes coupling of cerebral blood volume with oxygen demand

Given the brain's uniquely high cell density and tissue oxygen levels bordering on hypoxia, the ability to rapidly and precisely match blood flow to constantly changing patterns in neural activity is an essential feature of cerebrovascular regulation. Locus coeruleus-norepinephrine (LC-NE) projections innervate the cerebral vasculature and can mediate vasoconstriction. However, function of the LC-mediated constriction in blood-flow regulation has never been addressed. Here, using intrinsic optical imaging coupled with an anesthesia regimen that only minimally interferes with LC activity, we show that NE enhances spatial and temporal aspects of functional hyperemia in the mouse somatosensory cortex. Increasing NE levels in the cortex using an α(2)-adrenergic receptor antagonist paradoxically reduces the extent of functional hyperemia while enhancing the surround blood-flow reduction. However, the NE-mediated vasoconstriction optimizes spatial and temporal focusing of the hyperemic response resulting in a sixfold decrease in the disparity between blood volume and oxygen demand. In addition, NE-mediated vasoconstriction accelerated redistribution to subsequently active regions, enhancing temporal synchronization of blood delivery. These observations show an important role for NE in optimizing neurovascular coupling. As LC neuron loss is prominent in Alzheimer and Parkinson diseases, the diminished ability to couple blood volume to oxygen demand may contribute to their pathogenesis.

Bupropion and Citalopram in the APP23 Mouse Model of Alzheimer's Disease: A Study in a Dry-Land Maze

Background. Incipient Alzheimer's disease is often disguised as depressive disorder. Over the course of AD, depressive symptoms are even more frequent. Hence, treatment with antidepressants is common in AD. It was the goal of the present study to assess whether two common antidepressants with different mechanisms of action affect spatial learning in a transgenic animal model of Alzheimer's disease. Methods. We assessed spatial memory of male wild-type and B6C3-Tg(APPswe,PSEN1dE9)85Dbo (APP23) transgenic animals in a complex dry-land maze. Animals were treated with citalopram (10 mg/kg) and bupropion (20 mg/kg). Results. Moving and resting time until finding the goal zone decreased in 4.5-month-old sham-treated wild-type animals and, to a lesser extent, in APP23 animals. Compared with sham-treated APP23 animals, treatment with bupropion reduced resting time and increased speed. On treatment with citalopram, moving and resting time were unchanged but speed decreased. Length of the path to the goal zone did not change on either bupropion or citalopram. Conclusion. Bupropion increases psychomotor activity in APP23 transgenic animals, while citalopram slightly reduces psychomotor activity. Spatial learning per se is unaffected by treatment with either bupropion or citalopram.

Long-term proteasomal inhibition in transgenic mice by UBB(+1) expression results in dysfunction of central respiration control reminiscent of brainstem neuropathology in Alzheimer patients

Aging and neurodegeneration are often accompanied by a functionally impaired ubiquitin–proteasome system (UPS). In tauopathies and polyglutamine diseases, a mutant form of ubiquitin B (UBB⁺¹) accumulates in disease-specific aggregates. UBB⁺¹ mRNA is generated at low levels in vivo during transcription from the ubiquitin B locus by molecular misreading. The resulting mutant protein has been shown to inhibit proteasome function. To elucidate causative effects and neuropathological consequences of UBB⁺¹ accumulation, we used a UBB⁺¹ expressing transgenic mouse line that models UPS inhibition in neurons and exhibits behavioral phenotypes reminiscent of Alzheimer’s disease (AD). In order to reveal affected organs and functions, young and aged UBB⁺¹ transgenic mice were comprehensively phenotyped for more than 240 parameters. This revealed unexpected changes in spontaneous breathing patterns and an altered response to hypoxic conditions. Our findings point to a central dysfunction of respiratory regulation in transgenic mice in comparison to wild-type littermate mice. Accordingly, UBB⁺¹ was strongly expressed in brainstem regions of transgenic mice controlling respiration. These regions included, e.g., the medial part of the nucleus of the tractus solitarius and the lateral subdivisions of the parabrachial nucleus. In addition, UBB⁺¹ was also strongly expressed in these anatomical structures of AD patients (Braak stage #6) and was not expressed in non-demented controls. We conclude that long-term UPS inhibition due to UBB⁺¹ expression causes central breathing dysfunction in a transgenic mouse model of AD. The UBB⁺¹ expression pattern in humans is consistent with the contribution of bronchopneumonia as a cause of death in AD patients.

Cognitive and non-cognitive behaviors in the triple transgenic mouse model of Alzheimer's disease expressing mutated APP, PS1, and Mapt (3xTg-AD)

3xTg-AD mutant mice are characterized by parenchymal Aβ plaques and neurofibrillary tangles resembling those found in patients with Alzheimer's disease. The mutants were compared with non-transgenic controls in sensorimotor and learning tests. 3xTg-AD mutants were deficient in T-maze reversal, object recognition, and passive avoidance learning. In addition, the mutants showed hypoactivity in two open-field tests, fewer fecal boli in an observation jar, and reduced enclosed arm entries and head-dipping in the elevated plus-maze. On the contrary, the mutants did not differ from controls in pain thresholds, nest-building, and various reflexes determined by the SHIRPA primary screen and were even better on the rotorod test of motor coordination.

Reduced tissue levels of noradrenaline are associated with behavioral phenotypes of the TgCRND8 mouse model of Alzheimer's disease

Noradrenergic cell loss is well documented in Alzheimer's disease (AD). We have measured the tissue levels of catecholamines in an amyloid precursor protein-transgenic 'TgCRND8' mouse model of AD and found reductions in noradrenaline (NA) within hippocampus, temporoparietal and frontal cortices, and cerebellum. An age-related increase in cortical NA levels was observed in non-Tg controls, but not in TgCRND8 mice. In contrast, NA levels declined with aging in the TgCRND8 hippocampus. Dopamine levels were unaffected. Reductions in the tissue content of NA were found to coincide with altered expression of brain-derived neurotrophic factor (BDNF) mRNA and to precede the onset of object memory impairment and behavioral despair. To test whether these phenotypes might be associated with diminished NA, we treated mice with dexefaroxan, an antagonist of presynaptic inhibitory α(2)-adrenoceptors on noradrenergic and cholinergic terminals. Mice 12 weeks of age were infused systemically for 28 days with dexefaroxan or rivastigmine, a cholinesterase inhibitor. Both dexefaroxan and rivastigmine improved TgCRND8 behavioral phenotypes and increased BDNF mRNA expression without affecting amyloid-β peptide levels. Our results highlight the importance of noradrenergic depletion in AD-like phenotypes of TgCRND8 mice.

Norepinephrine differentially modulates the innate inflammatory response provoked by amyloid-β peptide via action at β-adrenoceptors and activation of cAMP/PKA pathway in human THP-1 macrophages

Evidence indicates that norepinephrine (NE) has antiinflammatory activities and plays a neuroprotective role where inflammatory events contribute to Alzheimer's disease pathology. Here, we evaluated the effects of NE on amyloid beta 1-42 (Aβ1-42)-induced cytotoxicity and proinflammatory cytokine/chemokine secretion, and determined the mechanisms through which NE exerts its actions in human THP-1 macrophages. NE clearly reduced the Aβ1-42-mediated production of the proinflammatory chemokine, monocytic chemotactic protein-1 (MCP-1/CCL2). In contrast to its ability to reduce MCP-1 secretion, NE enhanced the amounts of the proinflammatory cytokine interleukin (IL)-1β secreted from Aβ1-42 treated cells. NE significantly reduced the Aβ1-42-induced cytotoxicity in situations where it contributed to the increased IL-1β and decreased MCP-1 during Aβ1-42 stimulation. The ability of NE to differentially modulate the Aβ1-42-induced immune responses was mediated by β-adrenoceptors, as the aforementioned effects were replicated by the β-adrenoceptor agonist, isoproterenol, and blocked by the β-adrenoceptor antagonist, dl-propranolol. Of note, the NE effects on Aβ1-42-induced responses were mimicked by dbcAMP and forskolin, but significantly blocked by H89, an inhibitor of PKA. Moreover, NE abolished Aβ1-42-mediated decline of CREB phosphorylation. Overall, NE suppresses Aβ1-42-mediated cytotoxicity and MCP-1 secretion, but enhances Aβ-mediated IL-1β secretion through action at β-adrenoceptors, accompanied by activation of cAMP/PKA pathway and CREB in human microglia-like THP-1 cells.

APP transgenic mice for modelling behavioural and psychological symptoms of dementia (BPSD)

The discovery of gene mutations responsible for autosomal dominant Alzheimer's disease has enabled researchers to reproduce in transgenic mice several hallmarks of this disorder, notably Aβ accumulation, though in most cases without neurofibrillary tangles. Mice expressing mutated and wild-type APP as well as C-terminal fragments of APP exhibit variations in exploratory activity reminiscent of behavioural and psychological symptoms of Alzheimer dementia (BPSD). In particular, open-field, spontaneous alternation, and elevated plus-maze tasks as well as aggression are modified in several APP transgenic mice relative to non-transgenic controls. However, depending on the precise murine models, changes in open-field and elevated plus-maze exploration occur in either direction, either increased or decreased relative to controls. It remains to be determined which neurotransmitter changes are responsible for this variability, in particular with respect to GABA, 5HT, and dopamine.

Age-related neurodegeneration and memory loss in down syndrome

Down syndrome (DS) is a condition where a complete or segmental chromosome 21 trisomy causes variable intellectual disability, and progressive memory loss and neurodegeneration with age. Many research groups have examined development of the brain in DS individuals, but studies on age-related changes should also be considered, with the increased lifespan observed in DS. DS leads to pathological hallmarks of Alzheimer's disease (AD) by 40 or 50 years of age. Progressive age-related memory deficits occurring in both AD and in DS have been connected to degeneration of several neuronal populations, but mechanisms are not fully elucidated. Inflammation and oxidative stress are early events in DS pathology, and focusing on these pathways may lead to development of successful intervention strategies for AD associated with DS. Here we discuss recent findings and potential treatment avenues regarding development of AD neuropathology and memory loss in DS.

Butyrylcholinesterase genotype and gender influence Alzheimer's disease phenotype

Retrospective data are presented to support a spectrum of early Alzheimer's disease (AD) along a continuum defined by gender and genotype. The putative neurodegenerative mechanisms driving distinct phenotypes at each end of the spectrum are glial hypoactivity associated with early failure of synaptic cholinergic neurotransmission and glial overactivation associated with loss of neural network connectivity due to accelerated age-related breakdown of myelin. In early AD, male butyrylcholinesterase K-variant carriers with one or two apolipoprotein ɛ4 alleles have prominent medial temporal atrophy, synaptic failure, cognitive decline, and accumulation of aggregated beta-amyloid peptide. Increasing synaptic acetylcholine in damaged but still functional cholinergic synapses improves cognitive symptoms, whereas increasing the ability of glia to support synapses and to clear beta-amyloid peptide might be disease-modifying. Conversely, chronic glial overactivation can also drive degenerative processes and in butyrylcholinesterase K-variant negative females generalized glial overactivation may be the main driver from mild cognitive impairment to AD. Females are more likely than males to have accelerated age-related myelin breakdown, more widespread white matter loss, loss of neural network connectivity, whole brain atrophy, and functional decline. Increasing extracellular acetylcholine levels blocks glial activation, reduces myelin loss and damage to neural network connectivity, and is disease-modifying. Between extremes characterized by gender, genotype, and age, pathophysiology may be mixed and this spectrum may explain much of the heterogeneity of amnestic mild cognitive impairment. Preservation of the functional integrity of the neural network may be an important component of strengthening cognitive reserve and significantly delaying the onset and progression of dementia, particularly in females. Prospective confirmation of these hypotheses is required. Implications for future research and therapeutic opportunities are discussed.

The vincamine derivative vindeburnol provides benefit in a mouse model of multiple sclerosis: effects on the Locus coeruleus

The endogenous neurotransmitter noradrenaline (NA) plays several roles in maintaining brain homeostasis, including exerting anti-inflammatory and neuroprotective effects. The primary source of NA in the CNS are tyrosine hydroxylase (TH)-positive neurons located in the Locus coeruleus (LC) which send projections throughout the brain and spinal cord. We recently demonstrated that dysregulation of the LC:Noradrenergic system occurs in experimental autoimmune encephalomyelitis as well as in MS patients, associated with damage occurring to LC neurons. Vindeburnol, a structural analog of the cerebral vasodilator vincamine, was previously reported to increase TH expression and activity in LC neurons. Female C57BL/6 mice were immunized with myelin oligodendrocyte glycoprotein (MOG)(35-55) peptide, and treated with vindeburnol at the first appearance of clinical signs. Clinical signs continued to increase for about 1 week, at which point mice in the vehicle group continued to worsen while vindeburnol-treated mice showed improvement. Pro-inflammatory cytokine production from splenic T cells was not reduced by vindeburnol suggesting primarily central actions of treatment. In the cerebellum, vindeburnol decreased astrocyte activation and reduced the number of demyelinated regions. Vindeburnol reduced astrocyte activation in the LC, reduced TH+ neuronal hypertrophy, increased expression of several genes involved in LC survival and maturation, and increased NA levels in the spinal cord. These results suggest that treatments with drugs such as vindeburnol which target LC survival or function could be of benefit in MS patients.

Recruiting adaptive cellular stress responses for successful brain ageing

Successful ageing is determined in part by genetic background, but also by experiential factors associated with lifestyle and culture. Dietary, behavioural and pharmacological interventions have been identified as potential means to slow brain ageing and forestall neurodegenerative disease. Many of these interventions recruit adaptive cellular stress responses to strengthen neuronal networks and enhance plasticity. In this Science and Society article, we describe several determinants of healthy and pathological brain ageing, with insights into how these processes are accelerated or prevented. We also describe the mechanisms underlying the neuroprotective actions of exercise and nutritional interventions, with the goal of recruiting these molecular targets for the treatment and prevention of neurodegenerative disease.

Dysfunctional nucleus tractus solitarius: its crucial role in promoting neuropathogenetic cascade of Alzheimer's dementia--a novel hypothesis

The pathophysiological mechanism(s) underlying Alzheimer's disease (AD) still remain unclear, and no disease-modifying or prophylactic therapies are currently available. Unraveling the fundamental neuropathogenesis of AD is an important challenge. Several studies on AD have suggested lesions in a number of CNS areas including the basal forebrain, hippocampus, entorhinal cortex, amygdale/insula, and the locus coeruleus. However, plausible unifying studies on the upstream factors that involve these heterogeneous regions and herald the onset of AD pathogenesis are not available. The current article presents a novel nucleus tractus solitarius (NTS) vector hypothesis that underpins several disparate biological mechanisms and neural circuits, and identifies relevant hallmarks of major presumptive causative factor(s) linked to the NTS, in older/aging individuals. Aging, obesity, infection, sleep apnea, smoking, neuropsychological states, and hypothermia-all activate inflammatory cytokines and oxidative stress. The synergistic impact of systemic proinflammatory mediators activates microglia and promotes neuroinflammation. Acutely, the innate immune response is protective defending against pathogens/toxins; however, when chronic, it causes neuroinflammation and neuronal dysfunction, particularly in brainstem and neocortex. The NTS in the brainstem is an essential multiple signaling hub, and an extremely important central integration site of baroreceptor, chemoreceptor, and a multitude of sensory afferents from gustatory, gastrointestinal, cardiac, pulmonary, and upper airway systems. Owing to persistent neuroinflammation, the dysfunctional NTS exerts deleterious impact on nucleus ambiguus, dorsal motor nucleus of vagus, hypoglossal, parabrachial, locus coeruleus and many key nuclei in the brainstem, and the hippocampus, entorhinal cortex, prefrontal cortex, amygdala, insula, and basal forebrain in the neocortex. The neuronal and synaptic dysfunction emanating from the inflamed NTS may affect its interconnected pathways impacting almost the entire CNS--which is already primed by neuroinflammation, thus promoting cognitive and neuropsychiatric symptoms. The upstream factors discussed here may underpin the neuropathopgenesis of AD. AD pathology is multifactorial; the current perspective underscores the value of attenuating disparate upstream factors--in conjunction with anticholinesterase, anti-inflammatory, immunosuppressive, and anti-oxidant pharmacotherapy. Amelioration of the NTS pathology may be of central importance in countering the neuropathological cascade of AD. The NTS, therefore, may be a potential target of novel therapeutic strategies.

A noradrenergic lesion exacerbates neurodegeneration in a Down syndrome mouse model

Individuals with Down syndrome (DS) acquire Alzheimer's-like dementia (AD) and associated neuropathology earlier and at significantly greater rates than age-matched normosomic individuals. However, biological mechanisms have not been discovered and there is currently limited therapy for either DS- or AD-related dementia. Segmental trisomy 16 (Ts65Dn) mice provide a useful model for many of the degenerative changes which occur with age in DS including cognitive deficits, neuroinflammation, and degeneration of basal forebrain cholinergic neurons. Loss of noradrenergic locus coeruleus (LC) neurons is an early event in AD and in DS, and may contribute to the neuropathology. We report that Ts65Dn mice exhibit progressive loss of norepinephrine (NE) phenotype in LC neurons. In order to determine whether LC degeneration contributes to memory loss and neurodegeneration in Ts65Dn mice, we administered the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4; 2 doses of 50 mg/kg, i.p.) to Ts65Dn mice at four months of age, prior to working memory loss. At eight months of age, Ts65Dn mice treated with DSP-4 exhibited an 80% reduction in hippocampal NE, coupled with a marked increase in hippocampal neuroinflammation. Noradrenergic depletion also resulted in accelerated cholinergic neuron degeneration and a further impairment of memory function in Ts65Dn mice. In contrast, DSP-4 had minimal effects on normosomic littermates, suggesting a disease-modulated vulnerability to NE loss in the DS mouse model. These data suggest that noradrenergic degeneration may play a role in the progressive memory loss, neuroinflammation, and cholinergic loss occurring in DS individuals, providing a possible therapeutic avenue for future clinical studies.

Increased regional cerebral glucose uptake in an APP/PS1 model of Alzheimer's disease

Alzheimer's disease (AD), the most common age-related neurodegenerative disorder, is characterized by the invariant cerebral accumulation of β-amyloid peptide. This event occurs early in the disease process. In humans, [18F]-fluoro-2-deoxy-D-glucose ([18F]-FDG) positron emission tomography (PET) is largely used to follow-up in vivo cerebral glucose utilization (CGU) and brain metabolism modifications associated with the Alzheimer's disease pathology. Here, [18F]-FDG positron emission tomography was used to study age-related changes of cerebral glucose utilization under resting conditions in 3-, 6-, and 12-month-old APP(SweLon)/PS1(M146L), a mouse model of amyloidosis. We showed an age-dependent increase of glucose uptake in several brain regions of APP/PS1 mice but not in control animals and a higher [18F]-FDG uptake in the cortex and the hippocampus of 12-month-old APP/PS1 mice as compared with age-matched control mice. We then developed a method of 3-D microscopic autoradiography to evaluate glucose uptake at the level of amyloid plaques and showed an increased glucose uptake close to the plaques rather than in amyloid-free cerebral tissues. These data suggest a macroscopic and microscopic reorganization of glucose uptake in relation to cerebral amyloidosis.

Stages of granulovacuolar degeneration: their relation to Alzheimer's disease and chronic stress response

Granulovacuolar degeneration (GVD) is characterized by the presence of vacuolar cytoplasmic lesions in nerve cells of the medial temporal lobe. These changes occur in older non-diseased individuals as well as in patients with Alzheimer's disease (AD), progressive supranuclear palsy (PSP), Pick's, sporadic Parkinson's (PD), and Guam diseases. We stained representative paraffin sections from all parts of the brain with anti-pTDP43, anti-CK1δ or anti-CK1ε from 14 non-demented elderly, 19 AD, 17 non-AD tauopathy, 9 sporadic PD, and 5 TDP43-proteinopathy [amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD)] cases. Our results showed five stages of GVD based on its distribution pattern: GVD began in the hippocampal subfields CA1, CA2, and the subiculum. In a second stage, entorhinal cortex, and CA4 neurons exhibited GVD. Additional neurons were involved in the temporal neocortex in stage 3, whereas the affection of the amygdala and/or the hypothalamus marked stage 4. A fifth and final stage was characterized by additional GVD in the cingulate cortex and occasionally in the frontal and parietal cortices as well as in the oral raphe and pedunculopontine tegmental nuclei. The GVD stages correlated with neurofibrillary tangle stages, Consortium to Establish a Registry for AD (CERAD) scores for neuritic plaque pathology, amyloid β-protein deposition phases, cerebral amyloid angiopathy stages, and clinical dementia rating (CDR) scores. No associations were seen between GVD stage and the presence of non-AD tauopathies, PD, ALS, or FTLD cases. In conclusion, GVD affects neurons in a hierarchical sequence that allows the distinction of five stages. The topographic distribution of GVD restricted to regions involved in response to chronic stress could indicate a link between GVD and chronically stressful influences. Moreover, the association of the GVD stages with those of AD-related pathology but not with other neurodegenerative disorders points to a possible role of GVD and the response to chronic stress in the pathogenesis of AD.

A comparative study of five mouse models of Alzheimer's disease: cell cycle events reveal new insights into neurons at risk for death

Ectopic cell cycle events (CCEs) in postmitotic neurons link the neurodegenerative process in human Alzheimer's disease (AD) with the brain phenotype of transgenic mouse models with known familial AD genes. Most reports on the mouse models use the appearance of brain amyloid pathology as a key outcome measure. In the current paper, we focus on the induction of neurodegeneration using CCEs as markers for impending neuronal loss. We compare 5 mouse models of familial AD for the appearance of CCEs in subcortical regions—deep cerebellar nuclei, amygdala, locus coeruleus, hippocampus, and dorsal raphe. We find that the models differ in their CCE involvement as well as in the appearance of phosphorylated tau and amyloid deposition, suggesting that each model represents a different disease phenotype. Comparison with the pattern of neuron death in human AD suggests that each may represent a distinctly different disease model when used in preclinical trials.

Amyloid beta peptide-(1-42) induces internalization and degradation of beta2 adrenergic receptors in prefrontal cortical neurons

Emerging evidence indicates that amyloid β peptide (Aβ) initially induces subtle alterations in synaptic function in Alzheimer disease. We have recently shown that Aβ binds to β(2) adrenergic receptor (β(2)AR) and activates protein kinase A (PKA) signaling for glutamatergic regulation of synaptic activities. Here we show that in the cerebrums of mice expressing human familial mutant presenilin 1 and amyloid precursor protein genes, the levels of β(2)AR are drastically reduced. Moreover, Aβ induces internalization of transfected human β(2)AR in fibroblasts and endogenous β(2)AR in primary prefrontal cortical neurons. In fibroblasts, Aβ treatment also induces transportation of β(2)AR into lysosome, and prolonged Aβ treatment causes β(2)AR degradation. The Aβ-induced β(2)AR internalization requires the N terminus of the receptor containing the peptide binding sites and phosphorylation of β(2)AR by G protein-coupled receptor kinase, not by PKA. However, the G protein-coupled receptor kinase phosphorylation of β(2)AR and the receptor internalization are much slower than that induced by βAR agonist isoproterenol. The Aβ-induced β(2)AR internalization is also dependent on adaptor protein arrestin 3 and GTPase dynamin, but not arrestin 2. Functionally, pretreatment of primary prefrontal cortical neurons with Aβ induces desensitization of β(2)AR, which leads to attenuated response to subsequent stimulation with isoproterenol, including decreased cAMP levels, PKA activities, PKA phosphorylation of serine 845 on α-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid (AMPA) receptor subunit 1 (GluR1), and AMPA receptor-mediated miniature excitatory postsynaptic currents. This study indicates that Aβ induces β(2)AR internalization and degradation leading to impairment of adrenergic and glutamatergic activities.

CCL2/MCP-1 modulation of microglial activation and proliferation

Background

Monocyte chemoattractant protein (CCL2/MCP-1) is a chemokine that attracts cells involved in the immune/inflammatory response. As microglia are one of the main cell types sustaining inflammation in brain, we proposed here to analyze the direct effects of MCP-1 on cultured primary microglia.

Methods

Primary microglia and neuronal cultures were obtained from neonatal and embryonic Wistar rats, respectively. Microglia were incubated with different concentrations of recombinant MCP-1 and LPS. Cell proliferation was quantified by measuring incorporation of bromodeoxyuridine (BrdU). Nitrite accumulation was measured using the Griess assay. The expression and synthesis of different proteins was measured by RT-PCR and ELISA. Cell death was quantified by measuring release of LDH into the culture medium.

Results

MCP-1 treatment (50 ng/ml, 24 h) did not induce morphological changes in microglial cultures. Protein and mRNA levels of different cytokines were measured, showing that MCP-1 was not able to induce proinflammatory cytokines (IL-1β, IL6, MIP-1α), either by itself or in combination with LPS. A similar lack of effect was observed when measuring inducible nitric oxide synthase (NOS2) expression or accumulation of nitrites in the culture media as a different indicator of microglial activation. MCP-1 was also unable to alter the expression of different trophic factors that were reduced by LPS treatment. In order to explore the possible release of other products by microglia and their potential neurotoxicity, neurons were co-cultured with microglia: no death of neurons could be detected when treated with MCP-1. However, the presence of MCP-1 induced proliferation of microglia, an effect opposite to that observed with LPS.

Conclusion

These data indicate that, while causing migration and proliferation of microglia, MCP-1 does not appear to directly activate an inflammatory response in this cell type, and therefore, other factors may be necessary to cause the changes that result in the neuronal damage commonly observed in situations where MCP-1 levels are elevated.

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.

Anomalies in social behaviors and exploratory activities in an APPswe/PS1 mouse model of Alzheimer's disease

Alzheimer's disease is characterized by deficits in social communication, associated with generalized apathy or agitation, as well as social memory. To assess social behaviors in 6-month-old male APPswe/PS1 bigenics relative to non-transgenic controls, the 3-chamber test was used, together with open-field and elevated plus-maze tests of exploration. APPswe/PS1 mice were less willing to engage in social interaction than wild-type, avoiding an unfamiliar stimulus mouse, probably not due to generalized apathy because in both tests of exploratory activity the mutants were hyperactive. This study reveals reduced "sociability" combined with hyperactivity in an APPswe/PS1 mouse model of Alzheimer dementia.

Image analysis tools for evaluation of microscopic views of immunohistochemically stained specimen in medical research-a review

The aim of this study is to review the methods being used for image analysis of microscopic views of immunohistochemically stained specimen in medical research. The solutions available range from general purpose software to commercial packages. Many studies have developed their own custom written programs based on some general purpose software available. Many groups have reported development of computer aided image analysis programs aiming at obtaining faster, simpler and cheaper solutions. Image analysis tools namely Aperio, Lucia, Metaview, Metamorph, ImageJ, Scion, Adobe Photoshop, Image Pro Plus are also used for evaluation of expressions using immunohistochemical staining. An overview of such methods used for image analysis is provided in this paper. This study concludes that there is good scope for development of freely available software for staining intensity quantification, which a medical researcher could easily use without requiring high level computer skills.

Image analysis tools for evaluation of microscopic views of immunohistochemically stained specimen in medical research-a review

The aim of this study is to review the methods being used for image analysis of microscopic views of immunohistochemically stained specimen in medical research. The solutions available range from general purpose software to commercial packages. Many studies have developed their own custom written programs based on some general purpose software available. Many groups have reported development of computer aided image analysis programs aiming at obtaining faster, simpler and cheaper solutions. Image analysis tools namely Aperio, Lucia, Metaview, Metamorph, ImageJ, Scion, Adobe Photoshop, Image Pro Plus are also used for evaluation of expressions using immunohistochemical staining. An overview of such methods used for image analysis is provided in this paper. This study concludes that there is good scope for development of freely available software for staining intensity quantification, which a medical researcher could easily use without requiring high level computer skills.

Interleukin-1alpha and HMGB1 mediate hippocampal dysfunction in SIGIRR-deficient mice

Single-Ig-interleukin-1 related receptor (SIGIRR) is a member of the interleukin (IL)-1/Toll-like receptor (TLR) family. It negatively regulates inflammation, rendering SIGIRR(-/-) mice more susceptible to inflammatory challenge. This susceptibility extends to the brain, where increased responsiveness to lipopolysaccharide has been observed in SIGIRR-deficient mice. While this is likely due to enhanced TLR4-mediated signaling, the functional consequences of these changes have not yet been described. In the current study, we have investigated the impact of SIGIRR deficiency on hippocampal function, and show that novel object recognition, spatial reference memory, and long-term potentiation (LTP) were impaired in SIGIRR(-/-) mice. These changes were accompanied by increased expression of IL-1RI and TLR4, and upregulation of their downstream signaling events, namely IRAK1 (IL-1R-associated kinase 1), c-Jun N-terminal protein kinase (JNK), and nuclear factor κB (NF-κB). The deficit in LTP was attenuated by the endogenous IL-1 receptor antagonist (IL-1ra) and an anti-TLR4 antibody, and also by inhibition of JNK and NF-κB. We propose that IL-1RI is activated by IL-1α and TLR4 is activated by the endogenous agonist, high mobility group box 1 (HMGB1), as we identified enhanced expression of both cytokines in the hippocampus of SIGIRR(-/-) mice. Additionally, application of HMGB1 increased the activation of JNK and NF-κB and was found to be detrimental to LTP in a TLR4-dependent manner. These findings highlight the functional role of SIGIRR in regulating inflammatory-mediated synaptic and cognitive decline, and describe evidence of the key role of HMGB1 in this process.

VMAT2-Deficient Mice Display Nigral and Extranigral Pathology and Motor and Nonmotor Symptoms of Parkinson's Disease

Dopamine is transported into synaptic vesicles by the vesicular monoamine transporter (VMAT2; SLC18A2). Disruption of dopamine storage has been hypothesized to damage the dopamine neurons that are lost in Parkinson's disease. By disrupting vesicular storage of dopamine and other monoamines, we have created a progressive mouse model of PD that exhibits catecholamine neuron loss in the substantia nigra pars compacta and locus coeruleus and motor and nonmotor symptoms. With a 95% reduction in VMAT2 expression, VMAT2-deficient animals have decreased motor function, progressive deficits in olfactory discrimination, shorter latency to behavioral signs of sleep, delayed gastric emptying, anxiety-like behaviors at younger ages, and a progressive depressive-like phenotype. Pathologically, the VMAT2-deficient mice display progressive neurodegeneration in the substantia nigra (SNpc), locus coeruleus (LC), and dorsal raphe (DR) coupled with α-synuclein accumulation. Taken together, these studies demonstrate that reduced vesicular storage of monoamines and the resulting disruption of the cytosolic environment may play a role in the pathogenesis of parkinsonian symptoms and neurodegeneration. The multisystem nature of the VMAT2-deficient mice may be useful in developing therapeutic strategies that go beyond the dopamine system.

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.

Effect of neocortical and hippocampal amyloid deposition upon galaninergic and cholinergic neurites in AβPPswe/PS1ΔE9 mice

Amyloid-β (Aβ) plaques occur in close apposition to thickened or swollen cholinergic and galaninergic neurites within the neocortex and hippocampus in Alzheimer's disease (AD). Despite this observation, the effect of Aβ deposition upon cholinergic and galaninergic dystrophic neurite formation remains unclear. Therefore, the purpose of this study was to evaluate the interaction between Aβ deposition within the neocortex and hippocampus upon cholinergic and galaninergic dystrophic neurite formation. Neocortical and hippocampal tissue harvested from 3- and 12-month-old amyloid-β protein precursor (AβPP)swe/PS1ΔE9 transgenic (Tg) mice were dual-immunolabeled with antibodies against either choline acetyltransferace and Aβ (10D5) or galanin (Gal) and Aβ. Stereology was used to quantify amyloid plaques and cholinergic or galaninergic dystrophic neurites. Plaque number was assessed using the optical fractionator; plaque area was calculated with the Cavalieri estimator, and dystrophic neurite numbers and thickness were manually measured. Neither amyloid nor dystrophic neuritic profiles were seen in the brains of 3-month-old Tg mice. In contrast, quantitative analysis revealed significantly more plaques in neocortex than hippocampus, with no difference in regional plaque size in 12-month-old Tg mice. Significantly more cholinergic than galaninergic dystrophic neurites-per-plaque occurred in the neocortex and hippocampus. Additionally, cholinergic dystrophic neurites were thicker than galaninergic dystrophic neurites in both regions. These data suggest that amyloid plaque deposition has a greater impact upon cholinergic than galaninergic dystrophic neurite formation in the neocortex and hippocampus in AβPPswe/PS1ΔE9 Tg mice. These data are also compatible with the hypothesis that galanin is neuroprotective and reduces dystrophic neurite formation in the face of amyloid toxicity.

Distinct adrenergic system changes and neuroinflammation in response to induced locus ceruleus degeneration in APP/PS1 transgenic mice

Degeneration of locus ceruleus (LC) neurons and subsequent reduction of norepinephrine (NE) in LC projection areas represent an early pathological indicator of Alzheimer's disease (AD). In order to study the effects of NE depletion on cortical and hippocampal adrenergic system changes, LC degeneration was induced in 3-month-old APP/PS1 mice by the neurotoxin N-(2-chloroethyl)-N-ethyl-bromo-benzylamine (dsp4). Dsp4 induced a widespread loss of norepinephrine transporter binding in multiple brain structures already at 4.5 months. This was accompanied by changes of α-1-, α-2-, and β-1-adreneroceptor binding sites as well as altered adrenoceptor mRNA expression. In parallel, we observed increased micro- and astrogliosis in cortical and hippocampal structures in dsp4-treated groups. In addition, the expression of the pro-inflammatory cytokines CCL2 and IL-1β were induced in both, dsp4-treated and APP/PS1-transgenic mice, whereas IL-1α was only up-regulated in dsp4-treated APP/PS1 mice. Concerning amyloid β (Aβ) deposition, we observed an elevation of Aβ1-42 levels in aged dsp4-treated APP/PS1 mice. These data support the hypothesis that LC degeneration leads to dysregulation of adrenergic receptors and exacerbation of Aβ-induced neuroinflammation, both of which are exploitable for early disease marker development.

Ablation of the locus coeruleus increases oxidative stress in tg-2576 transgenic but not wild-type mice

Mice transgenic for production of excessive or mutant forms of beta-amyloid differ from patients with Alzheimer's disease in the degree of inflammation, oxidative damage, and alteration of intermediary metabolism, as well as the paucity or absence of neuronal atrophy and cognitive impairment. Previous observers have suggested that differences in inflammatory response reflect a discrepancy in the state of the locus coeruleus (LC), loss of which is an early change in Alzheimer's disease but which is preserved in the transgenic mice. In this paper, we extend these observations by examining the effects of the LC on markers of oxidative stress and intermediary metabolism. We compare four groups: wild-type or Tg2576 Aβ transgenic mice injected with DSP4 or vehicle. Of greatest interest were metabolites different between ablated and intact transgenics, but not between ablated and intact wild-type animals. The Tg2576_DSP4 mice were distinguished from the other three groups by oxidative stress and altered energy metabolism. These observations provide further support for the hypothesis that Tg2576 Aβ transgenic mice with this ablation may be a more congruent model of Alzheimer's disease than are transgenics with an intact LC.

Norepinephrine promotes microglia to uptake and degrade amyloid beta peptide through upregulation of mouse formyl peptide receptor 2 and induction of insulin-degrading enzyme

Locus ceruleus (LC) is the main subcortical site of norepinephrine synthesis. In Alzheimer's disease (AD) patients and rodent models, degeneration of LC neurons and reduced levels of norepinephrine in LC projection areas are significantly correlated with the increase in amyloid plaques, neurofibrillary tangles, and severity of dementia. Activated microglia play a pivotal role in the progression of AD by either clearing amyloid beta peptide (Abeta) deposits through uptake of Abeta or releasing cytotoxic substances and proinflammatory cytokines. Here, we investigated the effect of norepinephrine on Abeta uptake and clearance by murine microglia and explored the underlying mechanisms. We found that murine microglia cell line N9 and primary microglia expressed beta(2) adrenergic receptor (AR) but not beta(1) and beta(3)AR. Norepinephrine and isoproterenol upregulated the expression of Abeta receptor mFPR2, a mouse homolog of human formyl peptide receptor FPR2, through activation of beta(2)AR in microglia. Norepinephrine also induced mFPR2 expression in mouse brain. Activation of beta(2)AR in microglia promoted Abeta(42) uptake through upregulation of mFPR2 and enhanced spontaneous cell migration but had no effect on cell migration in response to mFPR2 agonists. Furthermore, activation of beta(2)AR on microglia induced the expression of insulin-degrading enzyme and increased the degradation of Abeta(42). Mechanistic studies showed that isoproterenol induced mFPR2 expression through ERK1/2-NF-kappaB and p38-NF-kappaB signaling pathways. These findings suggest that noradrenergic innervation from LC is needed to maintain adequate Abeta uptake and clearance by microglia, and norepinephrine is a link between neuron and microglia to orchestrate the host response to Abeta in AD.

Distinct glutaminyl cyclase expression in Edinger-Westphal nucleus, locus coeruleus and nucleus basalis Meynert contributes to pGlu-Abeta pathology in Alzheimer's disease

Glutaminyl cyclase (QC) was discovered recently as the enzyme catalyzing the pyroglutamate (pGlu or pE) modification of N-terminally truncated Alzheimer’s disease (AD) Aβ peptides in vivo. This modification confers resistance to proteolysis, rapid aggregation and neurotoxicity and can be prevented by QC inhibitors in vitro and in vivo, as shown in transgenic animal models. However, in mouse brain QC is only expressed by a relatively low proportion of neurons in most neocortical and hippocampal subregions. Here, we demonstrate that QC is highly abundant in subcortical brain nuclei severely affected in AD. In particular, QC is expressed by virtually all urocortin-1-positive, but not by cholinergic neurons of the Edinger–Westphal nucleus, by noradrenergic locus coeruleus and by cholinergic nucleus basalis magnocellularis neurons in mouse brain. In human brain, QC is expressed by both, urocortin-1 and cholinergic Edinger–Westphal neurons and by locus coeruleus and nucleus basalis Meynert neurons. In brains from AD patients, these neuronal populations displayed intraneuronal pE-Aβ immunoreactivity and morphological signs of degeneration as well as extracellular pE-Aβ deposits. Adjacent AD brain structures lacking QC expression and brains from control subjects were devoid of such aggregates. This is the first demonstration of QC expression and pE-Aβ formation in subcortical brain regions affected in AD. Our results may explain the high vulnerability of defined subcortical neuronal populations and their central target areas in AD as a consequence of QC expression and pE-Aβ formation.

Neuroinflammatory processes in Alzheimer's disease

Generation of neurotoxic amyloid beta peptides and their deposition along with neurofibrillary tangle formation represent key pathological hallmarks in Alzheimer's disease (AD). Recent evidence suggests that inflammation may be a third important component which, once initiated in response to neurodegeneration or dysfunction, may actively contribute to disease progression and chronicity. Various neuroinflammatory mediators including complement activators and inhibitors, chemokines, cytokines, radical oxygen species and inflammatory enzyme systems are expressed and released by microglia, astrocytes and neurons in the AD brain. Degeneration of aminergic brain stem nuclei including the locus ceruleus and the nucleus basalis of Meynert may facilitate the occurrence of inflammation in their projection areas given the antiinflammatory and neuroprotective action of their key transmitters norepinephrine and acetylcholine. While inflammation has been thought to arise secondary to degeneration, recent experiments demonstrated that inflammatory mediators may stimulate amyloid precursor protein processing by various means and therefore can establish a vicious cycle. Despite the fact that some aspects of inflammation may even be protective for bystander neurons, antiinflammatory treatment strategies should therefore be considered. Non-steroidal anti-inflammatory drugs have been shown to reduce the risk and delay the onset to develop AD. While, the precise molecular mechanism underlying this effect is still unknown, a number of possible mechanisms including cyclooxygenase 2 or gamma-secretase inhibition and activation of the peroxisome proliferator activated receptor gamma may alone or, more likely, in concert account for the epidemiologically observed protection.

Mouse models in neurological disorders: applications of non-invasive imaging

Neuroimaging techniques represent powerful tools to assess disease-specific cellular, biochemical and molecular processes non-invasively in vivo. Besides providing precise anatomical localisation and quantification, the most exciting advantage of non-invasive imaging techniques is the opportunity to investigate the spatial and temporal dynamics of disease-specific functional and molecular events longitudinally in intact living organisms, so called molecular imaging (MI). Combining neuroimaging technologies with in vivo models of neurological disorders provides unique opportunities to understand the aetiology and pathophysiology of human neurological disorders. In this way, neuroimaging in mouse models of neurological disorders not only can be used for phenotyping specific diseases and monitoring disease progression but also plays an essential role in the development and evaluation of disease-specific treatment approaches. In this way MI is a key technology in translational research, helping to design improved disease models as well as experimental treatment protocols that may afterwards be implemented into clinical routine. The most widely used imaging modalities in animal models to assess in vivo anatomical, functional and molecular events are positron emission tomography (PET), magnetic resonance imaging (MRI) and optical imaging (OI). Here, we review the application of neuroimaging in mouse models of neurodegeneration (Parkinson's disease, PD, and Alzheimer's disease, AD) and brain cancer (glioma).

Intraneuronal beta-amyloid accumulation and synapse pathology in Alzheimer's disease

The aberrant accumulation of aggregated beta-amyloid peptides (Abeta) as plaques is a hallmark of Alzheimer's disease (AD) neuropathology and reduction of Abeta has become a leading direction of emerging experimental therapies for the disease. The mechanism(s) whereby Abeta is involved in the pathophysiology of the disease remain(s) poorly understood. Initially fibrils, and subsequently oligomers of extracellular Abeta have been viewed as the most important pathogenic form of Abeta in AD. More recently, the intraneuronal accumulation of Abeta has been described in the brain, although technical considerations and its relevance in AD have made this a controversial topic. Here, we review the emerging evidence linking intraneuronal Abeta accumulation to the development of synaptic pathology and plaques in AD, and discuss the implications of intraneuronal beta-amyloid for AD pathology, biology, diagnosis and therapy.