Beta-amyloid(1-42)-induced cholinergic lesions in rat nucleus basalis bidirectionally modulate serotonergic innervation of the basal forebrain and cerebral cortex

Emerging Nanotechnology for the Treatment of Alzheimer's Disease

Nanotechnology is a great choice for medical research, and the green synthesis approach is a novel and better way to synthesize nanoparticles. Biological sources are cost-effective, environmentally friendly, and allow large-scale production of nanoparticles. Naturally obtained 3 β-hydroxy-urs- 12-en-28-oic acids reported for neuroprotective and dendritic structure are reported as solubility enhancers. Plants are free from toxic substances and act as natural capping agents. In this review, the pharmacological properties of ursolic acid (UA) and the structural properties of the dendritic structure are discussed. UA acid appears to have negligible toxicity and immunogenicity, as well as favorable biodistribution, according to the current study, and the dendritic structure improves drug solubility, prevents drug degradation, increases circulation time, and potentially targets by using different pathways with different routes of administration. Nanotechnology is a field in which materials are synthesized at the nanoscale. Nanotechnology could be the next frontier of humankind's technological advancement. Richard Feynman first used the term 'Nanotechnology' in his lecture, "There is Plenty of Room at the Bottom", on 29th December, 1959, and since then, interest has increased in the research on nanoparticles. Nanotechnology is capable of helping humanity by solving major challenges, particularly in neurological disorders like Alzheimer's disease (AD), the most prevalent type, which may account for 60-70% of cases. Other significant forms of dementia include vascular dementia, dementia with Lewy bodies (abnormal protein aggregates that form inside nerve cells), and a number of illnesses that exacerbate frontotemporal dementia. Dementia is an acquired loss of cognition in several cognitive domains that are severe enough to interfere with social or professional functioning. However, dementia frequently co-occurs with other neuropathologies, typically AD with cerebrovascular dysfunction. Clinical presentations show that neurodegenerative diseases are often incurable because patients permanently lose some neurons. A growing body of research suggests that they also advance our knowledge of the processes that are probably crucial for maintaining the health and functionality of the brain. Serious neurological impairment and neuronal death are the main features of neurodegenerative illnesses, which are also extremely crippling ailments. The most prevalent neurodegenerative disorders cause cognitive impairment and dementia, and as average life expectancy rises globally, their effects become more noticeable.

Protein Misfolding and Aggregation in the Brain: Common Pathogenetic Pathways in Neurodegenerative and Mental Disorders

Mental disorders represent common brain diseases characterized by substantial impairments of social and cognitive functions. The neurobiological causes and mechanisms of psychopathologies still have not been definitively determined. Various forms of brain proteinopathies, which include a disruption of protein conformations and the formation of protein aggregates in brain tissues, may be a possible cause behind the development of psychiatric disorders. Proteinopathies are known to be the main cause of neurodegeneration, but much less attention is given to the role of protein impairments in psychiatric disorders' pathogenesis, such as depression and schizophrenia. For this reason, the aim of this review was to discuss the potential contribution of protein illnesses in the development of psychopathologies. The first part of the review describes the possible mechanisms of disruption to protein folding and aggregation in the cell: endoplasmic reticulum stress, dysfunction of chaperone proteins, altered mitochondrial function, and impaired autophagy processes. The second part of the review addresses the known proteins whose aggregation in brain tissue has been observed in psychiatric disorders (amyloid, tau protein, α-synuclein, DISC-1, disbindin-1, CRMP1, SNAP25, TRIOBP, NPAS3, GluA1, FABP, and ankyrin-G).

Serotonergic mechanisms in spinal cord injury

Spinal cord injury (SCI) is a tragic event causing irreversible losses of sensory, motor, and autonomic functions, that may also be associated with chronic neuropathic pain. Serotonin (5-HT) neurotransmission in the spinal cord is critical for modulating sensory, motor, and autonomic functions. Following SCI, 5-HT axons caudal to the lesion site degenerate, and the degree of axonal degeneration positively correlates with lesion severity. Rostral to the lesion, 5-HT axons sprout, irrespective of the severity of the injury. Unlike callosal fibers and cholinergic projections, 5-HT axons are more resistant to an inhibitory milieu and undergo active sprouting and regeneration after central nervous system (CNS) traumatism. Numerous studies suggest that a chronic increase in serotonergic neurotransmission promotes 5-HT axon sprouting in the intact CNS. Moreover, recent studies in invertebrates suggest that 5-HT has a pro-regenerative role in injured axons. Here we present a brief description of 5-HT discovery, 5-HT innervation of the CNS, and physiological functions of 5-HT in the spinal cord, including its role in controlling bladder function. We then present a comprehensive overview of changes in serotonergic axons after CNS damage, and discuss their plasticity upon altered 5-HT neurotransmitter levels. Subsequently, we provide an in-depth review of therapeutic approaches targeting 5-HT neurotransmission, as well as other pre-clinical strategies to promote an increase in re-growth of 5-HT axons, and their functional consequences in SCI animal models. Finally, we highlight recent findings signifying the direct role of 5-HT in axon regeneration and suggest strategies to further promote robust long-distance re-growth of 5-HT axons across the lesion site and eventually achieve functional recovery following SCI.

Effect of flavonoids rich extract of Capparis spinosa on inflammatory involved genes in amyloid-beta peptide injected rat model of Alzheimer's disease

OBJECTIVES

Alzheimer's disease (AD) is one of the most common forms of neurodegenerative diseases. Despite vast ongoing researches focusing on the area, little is known about novel treatments. In this study, we aimed to survey the effects of Capparis spinosa (C. spinosa) extract on amyloid-beta peptide (Aβ)-injected rat.

METHODS

For this purpose, hydroalcoholic extracts of caper leaf and fruit were prepared. Total phenolic content, DPPH, and FRAP assay were accomplished to determine antioxidant activity of C. spinosa. HPLC analysis was conducted to measure rutin and quercetin content of selected parts of the plant. Higher levels of flavonoids were observed in leaves of the plant. Twelve male Wistar Aβ-induced rats were randomly divided in four groups of (1) Aβ^-/DW⁺: Sham-operated group (2) Aβ⁺/DW⁺: Aβ-injected group (3) Aβ⁺/RU⁺: Standard rutin treatment (4) Aβ⁺/CS⁺: C. spinosa extract treatment. After 6 weeks of oral administration, real-time qPCR were conducted to determine APP, BACE-1, PSEN-1, and PSEN-2 genes expression in the hippocampus of rats.

RESULTS

HPLC analysis showed high levels of rutin and quercetin in leaves of Capparis. Rutin was 16939.2 ± 0.01 and quercetin was 908.93 ± 0.01 µg/g fresh weight. In fruit, 1019.52 ± 0.01 rutin and 97.86 ± 0.01 µg/g FW quercetin were measured. Expression of BACE-1, APP, PSEN-1, and PSEN-2 genes in comparison with the control group showed significant down regulation.

DISCUSSION

Results of the study demonstrated that C. spinosa has the potential to down regulate inflammation-involved genes in AD, due to its high levels of flavonoids and could be beneficial as a dietary complement in AD patients.

Hazelnut and neuroprotection: Improved memory and hindered anxiety in response to intra-hippocampal Aβ injection

OBJECTIVES

Corylus avellana L. (hazelnut) is known to be a delicious and nutritious food. This study was carried out to evaluate the use of hazelnut as a therapy for memory impairment because in Iranian traditional medicine, it is recommended for those suffering from a particular type of dementia, with symptoms of Alzheimer's disease.

METHODS

In this study, rats were fed with hazelnut kernel [(without skin) 800 mg/kg/day] during 1 week before stereotaxic surgery to 24 hours before behavioral testing (in general, for 16 consecutive days) and the effect of hazelnut eating on memory, anxiety, neuroinflammation and apoptosis was assessed in the amyloid beta-injected rat.

RESULTS

The results of this study showed that feeding with hazelnut improved memory, (which was examined by using Y-maze test and shuttle box apparatus), and reduced anxiety-related behavior, that was evaluated using elevated plus maze. Also, western blotting analysis of cyclooxygenase-2, interleukin-1β, tumor necrosis factor-α, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein, and caspase-3 showed that hazelnut has an ameliorating effect on the neuroinflammation and apoptosis caused by Aβ.

DISCUSSION

These findings suggest that hazelnut, as a dietary supplement, improves healthy aging and could be a beneficial diet for the treatment of AD.

β-Amyloid: the key peptide in the pathogenesis of Alzheimer's disease

The amyloid β peptide (Aβ) is a critical initiator that triggers the progression of Alzheimer's Disease (AD) via accumulation and aggregation, of which the process may be caused by Aβ overproduction or perturbation clearance. Aβ is generated from amyloid precursor protein through sequential cleavage of β- and γ-secretases while Aβ removal is dependent on the proteolysis and lysosome degradation system. Here, we overviewed the biogenesis and toxicity of Aβ as well as the regulation of Aβ production and clearance. Moreover, we also summarized the animal models correlated with Aβ that are essential in AD research. In addition, we discussed current immunotherapeutic approaches targeting Aβ to give some clues for exploring the more potentially efficient drugs for treatment of AD.

Geldanamycin Reduces Aβ-Associated Anxiety and Depression, Concurrent with Autophagy Provocation

Neurodegenerative disorders are generally characterized by abnormal aggregation and deposition of specific proteins. Amyloid beta (Aβ)-associated neurodegenerative disorder is characterized by an oxidative damage that, in turn, leads to some behavioral changes before the establishment of dementia such as depression and anxiety. In the current study, we investigated the effect of heat shock protein 90 inhibitor geldanamycin (GA) administration 24 h before Aβ injection. In our experiment, 7 days after Aβ injection, elevated plus maze and forced swimming test were conducted to assess anxiety and depression-like behaviors. Levels of autophagy markers and malondialdehyde (MDA) and also activity of catalase in the hippocampus of rats were evaluated. Our behavioral analyses demonstrated that GA pretreatment can significantly decrease anxiety- and depression-like behaviors in Aβ-injected rats. Also, levels of autophagy markers including Atg12, Atg7, and LC3-II increased, while MDA level decreased and the activity of catalase increased in rats pretreated with GA compared to Aβ-injected rats. Thus, we assumed that GA, at least in part, ameliorated Aβ-mediated anxiety and depression by inducing autophagy and improving antioxidant defense system.

Modeling Alzheimer's disease in transgenic rats

Alzheimer's disease (AD) is the most common form of dementia. At the diagnostic stage, the AD brain is characterized by the accumulation of extracellular amyloid plaques, intracellular neurofibrillary tangles and neuronal loss. Despite the large variety of therapeutic approaches, this condition remains incurable, since at the time of clinical diagnosis, the brain has already suffered irreversible and extensive damage. In recent years, it has become evident that AD starts decades prior to its clinical presentation. In this regard, transgenic animal models can shed much light on the mechanisms underlying this "pre-clinical" stage, enabling the identification and validation of new therapeutic targets. This paper summarizes the formidable efforts to create models mimicking the various aspects of AD pathology in the rat. Transgenic rat models offer distinctive advantages over mice. Rats are physiologically, genetically and morphologically closer to humans. More importantly, the rat has a well-characterized, rich behavioral display. Consequently, rat models of AD should allow a more sophisticated and accurate assessment of the impact of pathology and novel therapeutics on cognitive outcomes.

Acetyl-CoA the key factor for survival or death of cholinergic neurons in course of neurodegenerative diseases

Glucose-derived pyruvate is a principal source of acetyl-CoA in all brain cells, through pyruvate dehydogenase complex (PDHC) reaction. Cholinergic neurons like neurons of other transmitter systems and glial cells, utilize acetyl-CoA for energy production in mitochondria and diverse synthetic pathways in their extramitochondrial compartments. However, cholinergic neurons require additional amounts of acetyl-CoA for acetylcholine synthesis in their cytoplasmic compartment to maintain their transmitter functions. Characteristic feature of several neurodegenerating diseases including Alzheimer’s disease and thiamine diphosphate deficiency encephalopathy is the decrease of PDHC activity correlating with cholinergic deficits and losses of cognitive functions. Such conditions generate acetyl-CoA deficits that are deeper in cholinergic neurons than in noncholinergic neuronal and glial cells, due to its additional consumption in the transmitter synthesis. Therefore, any neuropathologic conditions are likely to be more harmful for the cholinergic neurons than for noncholinergic ones. For this reason attempts preserving proper supply of acetyl-CoA in the diseased brain, should attenuate high susceptibility of cholinergic neurons to diverse neurodegenerative conditions. This review describes how common neurodegenerative signals could induce deficts in cholinergic neurotransmission through suppression of acetyl-CoA metabolism in the cholinergic neurons.

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.

Increased hippocampal CA1 density of serotonergic terminals in a triple transgenic mouse model of Alzheimer's disease: an ultrastructural study

Alzheimer's disease (AD) is a neurodegenerative pathology that deteriorates mnesic functions and associated brain regions including the hippocampus. Serotonin (5-HT) has an important role in cognition. We recently demonstrated an increase in 5-HT transporter (SERT) fibre density in the hippocampal CA1 in an AD triple transgenic mouse model (3xTg-AD). Here, we analyse the ultrastructural localisation, distribution and numerical density (N_v) of hippocampal SERT axons (SERT-Ax) and terminals (SERT-Te) and their relationship with SERT fibre sprouting and altered synaptic N_v in 3xTg-AD compared with non-transgenic control mice. 3xTg-AD animals showed a significant increase in SERT-Te N_v in CA1 at both, 3 (95%) and 18 months of age (144%), being restricted to the CA1 stratum moleculare (S. Mol; 227% at 3 and 180% at 18 months). 3xTg-AD animals also exhibit reduced N_v of perforated axospinous synapses (PS) in CA1 S. Mol (56% at 3 and 52% at 18 months). No changes were observed in the N_v of symmetric and asymmetrical synapses or SERT-Ax. Our results suggest that concomitant SERT-Te N_v increase and PS reduction in 3xTg-AD mice may act as a compensatory mechanism maintaining synaptic efficacy as a response to the AD cognitive impairment.

Behavioural and cellular effects of exogenous amyloid-β peptides in rodents

A better understanding of Alzheimer's disease (AD) and the development of disease modifying therapies are some of the biggest challenges of the 21st century. One of the core features of AD are amyloid plaques composed of amyloid-beta (Aβ) peptides. The first hypothesis proposed that cognitive deficits are linked to plaque-development and transgenic mice have been generated to study this link, thereby providing a good model to develop new therapeutic approaches. Since later it was recognised that in AD patients the cognitive deficit is rather correlated to soluble amyloid levels, consequently, a new hypothesis appeared associating the earliest amyloid toxicity to these soluble species. The purpose of this review is to give a summary of behavioural and cellular data obtained after soluble Aβ peptide administration into rodents' brain, thereby showing that this model is a valid tool to investigate AD pathology when no plaques are present. Additionally, this method offers an excellent, efficient model to test compounds which could act at such early stages of the disease.

Effects of estrogen on beta-amyloid-induced cholinergic cell death in the nucleus basalis magnocellularis

Alzheimer disease is characterized by accumulation of β-amyloid (Aβ) and cognitive dysfunctions linked to early loss of cholinergic neurons. As estrogen-based hormone replacement therapy has beneficial effects on cognition of demented patients, and it may prevent memory impairments, we investigated the effect of estrogen-pretreatment on Aβ-induced cholinergic neurodegeneration in the nucleus basalis magnocellularis (NBM). We tested which Aβ species induces the more pronounced cholinotoxic effect in vivo. We injected different Aβ assemblies in the NBM of mice, and measured cholinergic cell and cortical fiber loss. Spherical Aβ oligomers had the most toxic effect. Pretreatment of ovariectomized mice with estrogen before Aβ injection decreased cholinergic neuron loss and partly prevented fiber degeneration. By using proteomics, we searched for proteins involved in estrogen-mediated protection and in Aβ toxicity 24 h following injection. The change in expression of, e.g., DJ-1, NADH ubiquinone oxidoreductase, ATP synthase, phosphatidylethanolamine-binding protein 1, protein phosphatase 2A and dimethylarginine dimethylaminohydrolase 1 support our hypothesis that Aβ induces mitochondrial dysfunction, decreases MAPK signaling, and increases NOS activation in NBM. On the other hand, altered expression of, e.g., MAP kinase kinase 1 and 2, protein phosphatase 1 and 2A by Aβ might increase MAPK suppression and NOS signaling in the cortical target area. Estrogen pretreatment reversed most of the changes in the proteome in both areas. Our experiments suggest that regulation of the MAPK pathway, mitochondrial pH and NO production may all contribute to Aβ toxicity, and their regulation can be prevented partly by estrogen pretreatment.

Effects of yokukansan and donepezil on learning disturbance and aggressiveness induced by intracerebroventricular injection of amyloid β protein in mice

The effects of yokukansan and donepezil on learning disturbance and aggressiveness were examined in amyloid β protein (Aβ)-injected mice. Intellicage tests showed that both yokukansan and donepezil ameliorated Aβ-induced learning disturbance, but the ameliorating effect of donepezil was not enhanced by concomitant administration of yokukansan. On the other hand, a social interaction test showed that Aβ-induced aggressiveness was ameliorated by yokukansan, but not by donepezil. Co-administration of both drugs also ameliorated aggressiveness, as did yokukansan alone. In vitro binding assays revealed that yokukansan did not bind to choline receptors or transporters. In vitro enzyme assays revealed that yokukansan did not affect choline acetyltransferase activity or inhibit acetylcholinesterase activity, as did donepezil. These results suggest that yokukansan might ameliorate aggressiveness without interfering with the pharmacological efficacy (antidementia effect) of donepezil and also that concomitant administration of yokukansan might be useful for amelioration of aggressiveness, which was not lessened by donepezil. The difference in the efficacies of both drugs may be due to a difference in their pharmacological mechanisms.

Serotonin fibre sprouting and increase in serotonin transporter immunoreactivity in the CA1 area of hippocampus in a triple transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that deteriorates cognitive functions and associated brain regions such as the hippocampus, being the primary cause of dementia. Serotonin (5-HT) is widely present in the hippocampus, being an important neurotransmitter involved in learning and memory. Although recent evidence suggests alterations in 5-HT neurotransmission in AD, it is not clear how hippocampal 5-HT innervation is modified. Here, we studied hippocampal 5-HT innervation by analysing: (i) the expression, density and distribution of 5-HT transporter (SERT)-immunoreactive fibres; (ii) the specific morphological characteristics of serotonergic fibres and their relation to amyloid plaques; and (iii) the total number of 5-HT neurons within the raphe nuclei in triple transgenic mouse model of AD. We used quantitative light microscopy immunohistochemistry comparing transgenic and non-transgenic animals of different ages (3, 6, 9, 12 and 18 months). The transgenic animals showed a significant increase in SERT fibres in the hippocampus in a subfield-, strata- and age-specific manner. The increase in SERT fibres was specific to the CA1 stratum lacunosum-moleculare. An increase in SERT fibres in transgenic animals was observed at 3 months (by 61%) and at 18 months (by 74%). No changes, however, were found in the total number of raphe 5-HT neurons at any age. Our results indicate that triple transgenic mice display changes in the expression of SERT and increased SERT fibres sprouting, which may account for imbalanced serotonergic neurotransmission associated with (or linked to) AD cognitive impairment.

Ameliorative effects of yokukansan, a traditional Japanese medicine, on learning and non-cognitive disturbances in the Tg2576 mouse model of Alzheimer's disease

AIM OF THIS STUDY

Aim of the present study is to clarify the effects of yokukansan (TJ-54) on learning and non-cognitive disturbances in the Tg2576 mouse expressing the human form of the APP695SWE (APP-Tg mice), which is considered to be an animal model of Alzheimer's disease.

MATERIALS AND METHODS

Powdered diets containing 0.5 and 1.0% TJ-54 were given to the mice for 10 months (from 5 to 15 months old). The Morris water-maze test, elevated plus-maze test, and open-field test were performed for evaluation of learning and non-cognitive disturbances.

RESULTS

Treatment with 1.0% TJ-54 for 5 months shortened the time it took for APP-Tg positive (+) mice to reach the platform in the Morris water-maze test. In the elevated plus-maze test, treatment with 1.0% TJ-54 for 2 months significantly reduced the increased number of entries and the time spent in open arms observed in APP-Tg(+) mice. In an open-field test, treatment of 1.0% TJ-54 for 9 months significantly suppressed the increase in locomotion observed in APP-Tg(+) mice.

CONCLUSION

These results suggest the possibility that TJ-54 ameliorates learning deficits and non-cognitive defects including a decrease in the anxiety (or disinhibition) and an increase in locomotor activity (hyperactivity) observed in APP-Tg(+) mice.

Reduced 5-HT2A receptor binding in patients with mild cognitive impairment

Previous studies of patients with Alzheimer's disease (AD) have described reduced brain serotonin 2A (5-HT(2A)) receptor density. It is unclear whether this abnormality sets in early in the course of the disease and whether it is related to early cognitive and neuropsychiatric symptoms. We assessed cerebral 5-HT(2A) receptor binding in patients with mild cognitive impairment (MCI) and related 5-HT(2A) receptor binding to clinical symptoms. Sixteen patients with MCI of the amnestic type (mean age 73, mean MMSE 26.1) and 17 age and sex matched control subjects were studied with MRI and [(18)F]altanserin PET in a bolus-infusion approach. A significant global reduction of 20-30% in 5-HT(2A) binding (atrophy corrected) was found in most neocortical areas. Reduced 5-HT(2A) binding in the striatum correlated significantly with Neuropsychiatric Inventory depression and anxiety scores. We conclude that widespread reductions in 5-HT(2A) receptor binding were found in amnestic MCI, pointing at the presence of serotonergic dysfunction in prodromal AD. This may provide some of the pathophysiological background for the neuropsychiatric symptoms found in early AD.

Huperzine A reverses cholinergic and monoaminergic dysfunction induced by bilateral nucleus basalis magnocellularis injection of beta-amyloid peptide (1-40) in rats

(1) Huperzine A, a promising therapeutic agent for Alzheimer's disease (AD), was tested for its effects on cholinergic and monoaminergic dysfunction induced by injecting beta-amyloid peptide-(1-40) into nucleus basalis magnocellularis of the rat. (2) Bilateral injection of 10 microg beta-amyloid peptide-(1-40) into nucleus basalis magnocellularis produced local deposits of amyloid plaque and functional abnormalities detected by microdialysis. In medial prefrontal cortex, reductions in the basal levels and stimulated release of acetylcholine, dopamine, norepinephrine, and 5-hydroxytryptamine were observed. However, oral huperzine A (0.18 mg/kg, once daily for 21 consecutive days) markedly reduced morphologic abnormalities at the injection site in rats infused with beta-amyloid peptide-(1-40). Likewise, this treatment ameliorated the beta-amyloid peptide-(1-40)-induced deficits in extracellular acetylcholine, dopamine, and norepinephrine (though not 5-hydroxytryptamine) in medial prefrontal cortex, and lessened the reduction in nicotine or methoctramine-stimulated release of acetylcholine and K(+)-evoked releases of acetylcholine and dopamine. (3) The present results provide the first direct evidence that huperzine A acts to oppose neurotoxic effects of beta-amyloid peptide on cholinergic, dopaminergic, and noradrenergic systems of the rat forebrain.

Abeta(1-42) injection causes memory impairment, lowered cortical and serum BDNF levels, and decreased hippocampal 5-HT(2A) levels

Aggregation of the beta-amyloid protein (Abeta) is a hallmark of Alzheimer's disease (AD) and is believed to be causally involved in a neurodegenerative cascade. In patients with AD, reduced levels of serum Brain Derived Neurotrophic Factor (BDNF) and cortical 5-HT(2A) receptor binding has recently been reported but it is unknown how these changes are related to beta-amyloid accumulation. In this study we examined in rats the effect of intrahippocampal injections of aggregated Abeta(1-42) (1 microg/microl) on serum and brain BDNF or 5-HT(2A) receptor levels. A social recognition test paradigm was used to monitor Abeta(1-42) induced memory impairment. Memory impairment was seen 22 days after injection of Abeta(1-42) in the experimental group and until termination of the experiments. In the Abeta(1-42) injected animals we saw an abolished increase in serum BDNF levels that was accompanied by significant lower BDNF levels in frontal cortex and by an 8.5% reduction in hippocampal 5-HT(2A) receptor levels. A tendency towards lowered cortical 5-HT(2A) was also observed. These results indicate that the Abeta(1-42) associated memory deficit is associated with an impaired BDNF regulation, which is reflected in lower cortical BDNF levels, and changes in hippocampal 5-HT(2A) receptor levels. This suggests that the BDNF and 5-HT2A changes observed in AD are related to the presence of Abeta(1-42) deposits.

Beta-amyloid peptide-induced modifications in alpha7 nicotinic acetylcholine receptor immunoreactivity in the hippocampus of the rat: relationship with GABAergic and calcium-binding proteins perikarya

The effects of the injected beta-amyloid (Abeta) protein on the alpha7 subtype of nicotinic acetylcholine receptor protein (alpha7nAChR) in the hippocampus were studied in rats. Injections of Abeta into the retrosplenial cortex resulted in a decrease in alpha7nAChR-immunoreactivity in the hippocampus. Quantitative analysis revealed a significant reduction in alpha7nAChR-immunoreactivity in the dorsal part of the CA1 ipsilateral to the Abeta-injected side as compared to the corresponding hemisphere of non-treated control animals and with that seen in the contralateral hemisphere, which corresponds to the control (PBS)-injected side. A significant decrease in alpha7nAChR-immunoreactivity was also found in the dorsal part of the ipsilateral CA1 as compared with that in the ventral part of the CA1, in CA2, and in CA3 ipsilateral to the Abeta-injected side. The analysis also revealed a significant decrease in alpha7nAChR-immunoreactivity in the dentate gyrus ipsilateral to the Abeta-injected side as compared to the corresponding hemisphere of non-treated control animals and with that in the PBS-injected side co-localization studies showed that the alpha7nAChR protein is highly localized in GABA- and Parv-immunoreactive cells, while only few Calb-positive cells expressed immunoreactivity for alpha7nAChR. In addition, injections of Abeta protein resulted in a significant reduction in the number of GABA- and Parv-immunoreactive cells in the dorsal part of the ipsilateral CA1 as compared to the corresponding region of non-treated control animals and with that in the corresponding region of the PBS-injected side. Our findings suggest that Abeta induces a reduction in alpha7nAChR-containing cells, which may contribute to impairment of GABAergic synaptic transmission in the hippocampus.

Effects of beta-amyloid protein on M1 and M2 subtypes of muscarinic acetylcholine receptors in the medial septum-diagonal band complex of the rat: relationship with cholinergic, GABAergic, and calcium-binding protein perikarya

Cortical cholinergic dysfunction has been correlated with the expression and processing of beta-amyloid precursor protein. However, it remains unclear as to how cholinergic dysfunction and beta-amyloid (Abeta) formation and deposition might be related to one another. Since the M1- and M2 subtypes of muscarinic acetylcholine receptors (mAChRs) are considered key molecules that transduce the cholinergic message, the purpose of the present study was to assess the effects of the injected Abeta peptide on the number of M1mAchR- and M2mAChR-immunoreactive cells in the medial septum-diagonal band (MS-nDBB) complex of the rat. Injections of Abeta protein into the retrosplenial cortex resulted in a decrease in M1mAChR and M2mAChR immunoreactivity in the MS-nDBB complex. Quantitative analysis revealed a significant reduction in the number of M1mAChR- and M2mAChR-immunoreactive cells in the medial septum nucleus (MS) and in the horizontal nucleus of the diagonal band of Broca (HDB) as compared to the corresponding hemisphere in control animals and with that seen in the contralateral hemisphere, which corresponds to the PBS-injected side. Co-localization studies showed that the M1mAChR protein is localized in GABA-immunoreactive cells of the MS-nDBB complex, in particular those of the MS nucleus, while M2mAChR protein is localized in both the cholinergic and GABAergic cells. Moreover, GABAergic cells containing M2mAChR are mainly localized in the MS nucleus, while cholinergic cells containing M2mAChR are localized in the MS and the HDB nuclei. Our findings suggest that Abeta induces a reduction in M1mAChR- and M2mAChR-containing cells, which may contribute to impairments of cholinergic and GABAergic transmission in the MS-nDBB complex.

Effect of nucleus basalis magnocellularis cholinergic lesions on fear-like and anxiety-like behavior

Previous research has suggested that cholinergic neurons in the nucleus basalis magnocellularis and substantia innominata (NBM/SI) may be important in mediating aversive states. The authors investigated the effect of NBM/SI cholinergic lesions, induced with 192 IgG saporin, on behavioral measures of aversive states in rats. Behavior in the elevated plus maze and behavioral suppression induced by 2 fear-conditioned stimuli, a tone and a light, were evaluated. Lesions had no effect on any measures in the elevated plus maze but attenuated operant suppression induced by the light and attenuated freezing induced by the tone, though this last effect was not statistically significant. The results of the study suggest that NBM/SI cholinergic neurons may be important in mediating selective aspects of aversive states.

Redox proteomics in some age-related neurodegenerative disorders or models thereof

Neurodegenerative diseases cause memory loss and cognitive impairment. Results from basic and clinical scientific research suggest a complex network of mechanisms involved in the process of neurodegeneration. Progress in treatment of such disorders requires researchers to better understand the functions of proteins involved in neurodegenerative diseases, to characterize their role in pathogenic disease mechanisms, and to explore their roles in the diagnosis, treatment, and prevention of neurodegenerative diseases. A variety of conditions of neurodegenerative diseases often lead to post-translational modifications of proteins, including oxidation and nitration, which might be involved in the pathogenesis of neurodegenerative diseases. Redox proteomics, a subset of proteomics, has made possible the identification of specifically oxidized proteins in neurodegenerative disorders, providing insight into a multitude of pathways that govern behavior and cognition and the response of the nervous system to injury and disease. Proteomic analyses are particularly suitable to elucidate post-translational modifications, expression levels, and protein-protein interactions of thousands of proteins at a time. Complementing the valuable information generated through the integrative knowledge of protein expression and function should enable the development of more efficient diagnostic tools and therapeutic modalities. Here we review redox proteomic studies of some neurodegenerative diseases.

Sleep and circadian abnormalities in a transgenic mouse model of Alzheimer's disease: a role for cholinergic transmission

The Tg2576 mouse model of Alzheimer's disease (AD) exhibits age-dependent amyloid beta (Abeta) deposition in the brain. We studied electroencephalographically defined sleep and the circadian regulation of waking activities in Tg2576 mice to determine whether these animals exhibit sleep abnormalities akin to those in AD. In Tg2576 mice at all ages studied, the circadian period of wheel running rhythms in constant darkness was significantly longer than that of wild type mice. In addition, the increase in electroencephalographic delta (1-4 Hz) power that occurs during non-rapid eye movement sleep after sleep deprivation was blunted in Tg2576 mice relative to controls at all ages studied. Electroencephalographic power during non-rapid eye movement sleep was shifted to higher frequencies in plaque-bearing mice relative to controls. The wake-promoting efficacy of the acetylcholinesterase inhibitor donepezil was lower in plaque-bearing Tg2576 mice than in controls. Sleep abnormalities in Tg2576 mice may be due in part to a cholinergic deficit in these mice. At 22 months of age, two additional deficits emerged in female Tg2576 mice: time of day-dependent modulation of sleep was blunted relative to controls and rapid eye movement sleep as a percentage of time was lower in Tg2576 than in wild type controls. The rapid eye movement sleep deficit in 22 month-old female Tg2576 mice was abolished by brief passive immunization with an N-terminal antibody to Abeta. The Tg2576 model provides a uniquely powerful tool for studies on the pathophysiology of and treatments for sleep deficits and associated cholinergic abnormalities in AD.

Effects of beta-amyloid protein on serotoninergic, noradrenergic, and cholinergic markers in neurons of the pontomesencephalic tegmentum in the rat

The effects on serotoninergic, noradrenergic and cholinergic markers on neurons of the pontomesencephalic tegmentum nuclei were studied in rats following local administration of fibrillar beta-amyloid peptide (Abeta1-40) into the left retrosplenial cortex. Focal deposition of Abeta in the retrosplenial cortex resulted in a loss of serotoninergic neurons in the dorsal and median raphe nuclei. The dorsal raphe nucleus showed a statistically significant reduction of 31.7% in the number of serotoninergic neurons and a decrease (up to 17.38%) in neuronal density in comparison with the same parameters in uninjected controls. A statistically significant reduction of 50.3%, together with a significant decrease of 53.94% in the density of serotoninergic neurons, was also observed in the median raphe nucleus as compared with control animals. Furthermore, a significant reduction of 35.07% in the number of noradrenergic neurons as well as a statistically significant decrease of 56.55% in the density of dopamine-beta-hydroxylase-immunoreactive neurons were also found in the locus coeruleus as compared with the corresponding hemisphere in uninjected controls. By contrast, a reduction of 24.37% in the number of choline acetyltransferase-positive neurons and a slight decrease (up to 22.28%) in the density of cholinergic neurons, which were not statistically significant, was observed in the laterodorsal tegmental nucleus in comparison with the same parameters in control animals. These results show that three different neurochemically defined populations of neurons in the pontomesencephalic tegmentum are affected by the neurotoxicity of Abeta in vivo and that Abeta might indirectly affect serotoninergic, noradrenergic and cholinergic innervation in the retrosplenial cortex.

Ovariectomy combined with amyloid beta(1-42) impairs memory by decreasing acetylcholine release and alpha 7nAChR expression without induction of apoptosis in the hippocampus CA1 neurons of rats

In this study, the effect of ovariectomy and amyloid Beta(1-42) (ABeta(1-42))on eight-armed radial maze performance, acetylcholine (ACh) release, Alpha7nACh receptor (Alpha7nAChr), glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression, and apoptosis of CA1 neurons in the dorsal hippocampus were investigated in rat. The results showed that the dorsal hippocampus of sham rats contains 136.7 -/+ 16.7 to 160.4 -/+ 21.1 fmol/microl ACh, and respective 201 -/+ 22.9 and 416.6 -/+ 66.3 expression of mRNA for a7nAChR and GAPDH. Ovariectomy alone, after 4 weeks, did not impair memory, and neither induced apoptosis nor changed the basal ACh release. On the other hand, ABeta(1-42) (600 pmol/10 microl/body/day i.c.v. for 7 days) impaired memory, an effect characterized by increased error choices and reduced (50-59%) ACh release, but only with slight apoptosis. Moreover, ovariectomy combined with ABeta(1-42) induced memory impairment characterized by decreased numbers of correct choices and increased numbers of errors. This effect was accompanied by a decrease of the basal ACh level (67%), a7nAChR mRNA expression (52%) and a7nAChR/GAPDH ratio (44%) without induction of apoptosis in the dorsal hippocampus. The high K+-evoked ACh release was not altered in ovariectomized rats, but was decreased by ABeta(1-42) (43%) and ovariectomy + ABeta(1-42) (80%). These results suggest that ovariectomy-induced hormonal deprivation after 4 weeks, when accompanied by ABeta(1-42) accumulation in the dorsal hippocampus, could impair memory by decreasing ACh release and a7nAChR expression without inducing apoptosis in the CA1 field of the dorsal hippocampus.

Functional recovery of cholinergic basal forebrain neurons under disease conditions: old problems, new solutions?

Recognition of the involvement of cholinergic neurons in the modulation of cognitive functions and their severe dysfunction in neurodegenerative disorders, such as Alzheimer's disease, initiated immense research efforts aimed at unveiling the anatomical organization and cellular characteristics of the basal forebrain (BFB) cholinergic system. Concomitant with our unfolding knowledge about the structural and functional complexity of the BFB cholinergic projection system, multiple pharmacological strategies were introduced to rescue cholinergic nerve cells from noxious attacks; however, a therapeutic breakthrough is still awaited. In this review, we collected recent findings that significantly contributed to our better understanding of cholinergic functions under disease conditions, and to the design of effective means to restore lost or damaged cholinergic functions. To this end, we first provide a brief survey of the neuroanatomical organization of BFB nuclei with emphasis on major evolutionary differences among mammalian species, in particular rodents and primates, and discuss limitations of the translation of experimental data to human therapeutic applications. Subsequently, we summarize the involvement of cholinergic dysfunction in the pathogenesis of severe neurological conditions, including stroke, traumatic brain injury, virus encephalitis and Alzheimer's disease, and emphasize the critical role of pro-inflammatory cytokines as common mediators of cholinergic neuronal damage. Moreover, we review leading functional concepts on the limited recovery of cholinergic neurons and their impaired plastic re-modeling, as well as on the hampered interplay of the ascending cholinergic and monoaminergic projection systems under neurodegenerative conditions. In addition, recent advances in the dynamic labeling of living cholinergic neurons by fluorochromated antibodies, referred to as in vivo labeling, and novel neuroimaging approaches as potential diagnostic tools of progressive cholinergic decline are surveyed. Finally, the potential of cell replacement strategies using embryonic and adult stem cells, and multipotent neural progenitors, as a means to recover damaged cholinergic functions, is discussed.

Post-lesion administration of 5-HT1A receptor agonist 8-OH-DPAT protects cholinergic nucleus basalis neurons against NMDA excitotoxicity

Recent evidence indicates that serotonin (5-HT)1A receptor agonists may abrogate excitotoxic brain damage. We investigated whether a single i.p. injection of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), at a dose of 2.5 mg/kg, protects cholinergic neurons of the rat magnocellular nucleus basalis (MBN) against NMDA excitotoxicity when administered at post-injury intervals ranging from 6 to 96 h. Drug effects on passive avoidance learning and on the density of cortical cholinergic innervation, a measure of neuronal survival in the damaged MBN, were analyzed. Our results demonstrate that 8-OH-DPAT, when administered up to 24 h post-lesion, significantly attenuates both behavioral and neuroanatomical consequences of NMDA excitotoxicity on cholinergic MBN neurons; and support the hypothesis that 5-HT1A receptor agonists may interfere with delayed neuronal death in vivo that is of significance in the pharmacological treatment of neurological disorders associated with excitotoxic neuronal damage.