Altered brain serotonin transporter and associated glucose metabolism in Alzheimer disease

Alzheimer Disease-Link With Major Depressive Disorder and Efficacy of Antidepressants in Modifying its Trajectory

Alzheimer disease (AD) is a devastating neurodegenerative disorder that affects millions of individuals worldwide, with no effective cure. The main symptoms include learning and memory loss, and the inability to carry out the simplest tasks, significantly affecting patients' quality of life. Over the past few years, tremendous progress has been made in research demonstrating a link between AD and major depressive disorder (MDD). Evidence suggests that MDD is commonly associated with AD and that it can serve as a precipitating factor for this disease. Antidepressants such as selective serotonin reuptake inhibitors, which are the first line of treatment for MDD, have shown great promise in the treatment of depression in AD, although their effectiveness remains controversial. The goal of this review is to summarize current knowledge regarding the association between AD, MDD, and antidepressant treatment. It first provides an overview of the interaction between AD and MDD at the level of genes, brain regions, neurotransmitter systems, and neuroinflammatory markers. The review then presents current evidence regarding the effectiveness of various antidepressants for AD-related pathophysiology and then finally discusses current limitations, challenges, and future directions.

Photoactivatable Agonist-Antagonist Pair as a Tool for Precise Spatiotemporal Control of Serotonin Receptor 2C Signaling

Orthogonal recreation of the signaling profile of a chemical synapse is a current challenge in neuroscience. This is due in part to the kinetics of synaptic signaling, where neurotransmitters are rapidly released and quickly cleared by active reuptake machinery. One strategy to produce a rapid rise in an orthogonally controlled signal is via photocaged compounds. In this work, photocaged compounds are employed to recreate both the rapid rise and equally rapid fall in activation at a chemical synapse. Specifically, a complementary pair of photocages based on BODIPY were conjugated to a 5-HT2C subtype-selective agonist, WAY-161503, and antagonist, N-desmethylclozapine, to generate "caged" versions of these drugs. These conjugates release the bioactive drug upon illumination with green light (agonist) or red light (antagonist). We report on the synthesis, characterization, and bioactivity testing of the conjugates against the 5-HT2C receptor. We then characterize the kinetics of photolysis quantitatively using HPLC and qualitatively in cell culture conditions stimulating live cells. The compounds are shown to be stable in the dark for 48 h at room temperature, yet photolyze rapidly when irradiated with visible light. In live cells expressing the 5-HT2C receptor, precise spatiotemporal control of the degree and length of calcium signaling is demonstrated. By loading both compounds in tandem and leveraging spectral multiplexing as a noninvasive method to control local small-molecule drug availability, we can reproducibly initiate and suppress intracellular calcium flux on a timescale not possible by traditional methods of drug dosing. These tools enable a greater spatiotemporal control of 5-HT2C modulation and will allow for more detailed studies of the receptors' signaling, interactions with other proteins, and native physiology.

Effects of Sideritis scardica Extract on Scopolamine-Induced Learning and Memory Impairment in Mice

BACKGROUND

The neurodegenerative process in Alzheimer's disease, one of the most common types of dementia worldwide, mostly affects the cholinergic neurotransmitter system and, to a lesser extent, the monoaminergic one. The antioxidant acetylcholinesterase (AChE) and triple monoamine reuptake inhibitory activity of Sideritis scardica (S. scardica) and other Sideritis species has already been reported.

OBJECTIVE

To investigate the effects of S. scardica water extracts on the learning and memory processes, anxiety-like behavior, and locomotor activities in scopolamine (Sco)-induced dementia in mice.

METHODS

Male Albino IRC mice were used. The plant extract was administered for 11 consecutive days in the presence or absence of Sco (1 mg/kg, i.p). The behavioural performance of the animals was evaluated by passive avoidance, T-maze, and hole-board tests. The effects of extract on AChE activity, brain noradrenalin (NA), and serotonin (Sero) content, and antioxidant status were also monitored.

RESULTS

Our experimental data revealed that the S. scardica water extract caused a reduction in degree of memory impairment and anxiety-like behaviour in mice with scopolamine-induced dementia. The extract did not affect changed by the Sco AChE activity but impact reduced brain NA and Sero levels and demonstrated moderate antioxidant activity. In healthy mice we did not confirm the presence of anxiolytic-like and AChE inhibitory effects of the S. scardica water extract. The extract did not change the control Sero brain levels and reduce those of NA.

CONCLUSION

S. scardica water extract demonstrated memory preserving effect in mice with scopolamine-induced dementia and deserve further attention.

Regional serotonin terminal density in aging human brain: A [11C]DASB PET study

There are conflicting results regarding regional age-related changes in serotonin terminal density in human brain. Some imaging studies suggest age-related declines in serotoninergic terminals and perikarya. Other human imaging studies and post-mortem biochemical studies suggest stable brain regional serotoninergic terminal densities across the adult lifespan. In this cross-sectional study, we used [11C]3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile positron emission tomography to quantify brain regional serotonin transporter density in 46 normal subjects, ranging from 25 to 84 years of age. Both voxel-based analyses, using sex as a covariate, and volume-of-interest-based analyses were performed. Both analyses revealed age-related declines in [11C]3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile binding in numerous brain regions, including several neocortical regions, striatum, amygdala, thalamus, dorsal raphe, and other subcortical regions. Similar to some other neurotransmitter systems of subcortical origin, we found evidence of age-related declines in regional serotonin terminal density in both cortical and subcortical regions.

State-of-the-art imaging of neuromodulatory subcortical systems in aging and Alzheimer's disease: Challenges and opportunities

Primary prevention trials have shifted their focus to the earliest stages of Alzheimer's disease (AD). Autopsy data indicates that the neuromodulatory subcortical systems' (NSS) nuclei are specifically vulnerable to initial tau pathology, indicating that these nuclei hold great promise for early detection of AD in the context of the aging brain. The increasing availability of new imaging methods, ultra-high field scanners, new radioligands, and routine deep brain stimulation implants has led to a growing number of NSS neuroimaging studies on aging and neurodegeneration. Here, we review findings of current state-of-the-art imaging studies assessing the structure, function, and molecular changes of these nuclei during aging and AD. Furthermore, we identify the challenges associated with these imaging methods, important pathophysiologic gaps to fill for the AD NSS neuroimaging field, and provide future directions to improve our assessment, understanding, and clinical use of in vivo imaging of the NSS.

Associations of depressive symptoms with white matter abnormalities and regional cerebral blood flow in patients with amnestic mild cognitive impairment

AIM

Depressive symptoms are one of the most common neuropsychiatric symptoms in patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD), although the pathophysiologies of the depressive symptoms that occur in these diseases have not been elucidated to date. In this study, we therefore investigated the associations between depressive symptoms and cognitive performance, white matter abnormalities, and regional cerebral blood flow (rCBF) in amnestic MCI patients.

METHODS

Thirty-eight patients with amnestic MCI were analyzed. The volumes of periventricular hyperintensities (PVH) and deep white matter hyperintensities (DWMH) were measured on T2-fluid-attenuated inversion recovery magnetic resonance imaging using the imaging software 3D-slicer. Associations between the Geriatric Depression Scale (GDS) score and other neuropsychological test scores on the one hand and the PVH and DWMH volumes on the other were analyzed. Voxel-wise correlations of rCBF with GDS score, after controlling for the effects of age, were investigated using SPM8 software.

RESULTS

Significant correlations were identified between GDS score, Trail Making Test B and apathy scale scores on the one hand and PVH volume on the other. A significant negative association between GDS score and rCBF was identified in the right dominant bilateral dorsolateral prefrontal cortex (DLPFC).

CONCLUSIONS

Depressive symptoms are significantly associated with PVH volume in MCI patients. The rCBF of the DLPFC was significantly associated with depressive symptoms, suggesting that this area might be closely involved in the pathogenesis of the depressive symptoms observed in MCI patients. Geriatr Gerontol Int 2022; 22: 846-850.

Pathological mechanisms and therapeutic strategies for Alzheimer's disease

Alzheimer's disease is a rather complex neurodegenerative disease, which is attributed to a combination of multiple factors. Among the many pathological pathways, synaptic dysfunctions, such as synapses loss and deficits in synaptic plasticity, were thought to be strongly associated with cognitive decline. The deficiencies in various sorts of neurotransmissions are responsible for the multifarious neurodegenerative symptoms in Alzheimer's disease, for example, the cholinergic and glutamatergic deficits for cognitive decline, the excitatory and inhibitory neurotransmission dyshomeostasis for synaptic plasticity deficits and epileptiform symptoms, and the monoamine neurotransmission for neuropsychiatric symptoms. Amyloid cascade hypothesis is the most popular pathological theory to explain Alzheimer's disease pathogenesis and attracts considerable attention. Multiple lines of genetic and pathological evidence support the predominant role of amyloid beta in Alzheimer's disease pathology. Neurofibrillary tangles assembled by microtubule-associated protein tau are other important histopathological characteristics in Alzheimer's disease brains. Cascade of tau toxicity was proved to lead to neuron damage, neuroinflammation and oxidative stress in brain. Ageing is the main risk factor of neurodegenerative diseases, and is associated with inflammation, oxidative stress, reduced metabolism, endocrine insufficiencies and organ failures. These aging related risk factors were also proved to be some of the risk factors contributing to Alzheimer's disease. In Alzheimer's disease drug development, many good therapeutic strategies have been investigated in clinical evaluations. However, complex mechanism of Alzheimer's disease and the interplay among different pathological factors call for the come out of all-powerful therapies with multiple curing functions. This review seeks to summarize some of the representative treatments targeting different pathological pathways currently under clinical evaluations. Multi-target therapies as an emerging strategy for Alzheimer's disease treatment will be highlighted.

Integration of System Biology Tools to Investigate Huperzine A as an Anti-Alzheimer Agent

Aim: The present study aimed to investigate huperzine A as an anti-Alzheimer agent based on the principle that a single compound can regulate multiple proteins and associated pathways, using system biology tools. Methodology: The simplified molecular-input line-entry system of huperzine A was retrieved from the PubChem database, and its targets were predicted using SwissTargetPrediction. These targets were matched with the proteins deposited in DisGeNET for Alzheimer disease and enriched in STRING to identify the probably regulated pathways, cellular components, biological processes, and molecular function. Furthermore, huperzine A was docked against acetylcholinesterase using AutoDock Vina, and simulations were performed with the Gromacs package to take into account the dynamics of the system and its effect on the stability and function of the ligands. Results: A total of 100 targets were predicted to be targeted by huperzine A, of which 42 were regulated at a minimum probability of 0.05. Similarly, 101 Kyoto Encyclopedia of Genes and Genomes pathways were triggered, in which neuroactive ligand-receptor interactions scored the least false discovery rate. Also, huperzine A was predicted to modulate 54 cellular components, 120 molecular functions, and 873 biological processes. Furthermore, huperzine A possessed a binding affinity of -8.7 kcal/mol with AChE and interacted within the active site of AChE via H-bonds and hydrophobic interactions.

Positron emission tomography imaging of serotonin degeneration and beta-amyloid deposition in late-life depression evaluated with multi-modal partial least squares

Depression in late-life is associated with increased risk of cognitive decline and development of all-cause dementia. The neurobiology of late-life depression (LLD) may involve both neurochemical and neurodegenerative mechanisms that are common to depression and dementia. Transgenic amyloid mouse models show evidence of early degeneration of monoamine systems. Informed by these preclinical data, the hypotheses were tested that a spatial covariance pattern of higher beta-amyloid (Aβ) and lower serotonin transporter availability (5-HTT) in frontal, temporal, and parietal cortical regions would distinguish LLD patients from healthy controls and the expression of this pattern would be associated with greater depressive symptoms. Twenty un-medicated LLD patients who met DSM-V criteria for major depression and 20 healthy controls underwent PET imaging with radiotracers for Aβ ([11C]-PiB) and 5-HTT ([11C]-DASB). A voxel-based multi-modal partial least squares (mmPLS) algorithm was applied to the parametric PET images to determine the spatial covariance pattern between the two radiotracers. A spatial covariance pattern was identified, including higher Aβ in temporal, parietal and occipital cortices associated with lower 5-HTT in putamen, thalamus, amygdala, hippocampus and raphe nuclei (dorsal, medial and pontine), which distinguished LLD patients from controls. Greater expression of this pattern, reflected in summary 5-HTT/Aβ mmPLS subject scores, was associated with higher levels of depressive symptoms. The mmPLS method is a powerful approach to evaluate the synaptic changes associated with AD pathology. This spatial covariance pattern should be evaluated further to determine whether it represents a biological marker of antidepressant treatment response and/or cognitive decline in LLD patients.

Fungi and Algae as Sources of Medicinal and Other Biologically Active Compounds: A Review

Many species of fungi including lichenized fungi (lichens) and algae have the ability to biosynthesize biologically active compounds. They produce, among others, polysaccharides with anticancer and immunostimulatory properties: (1) Background: This paper presents the characteristics of the most important bioactive compounds produced by fungi and algae; (2) Methods: Based on the example of the selected species of mushrooms, lichens and algae, the therapeutic properties of the secondary metabolites that they produce and the possibilities of their use are presented; (3) Results: The importance of fungi, especially large-fruited mushrooms, lichens and algae, in nature and human life is discussed, in particular, with regard to their use in the pharmaceutical industry and their nutritional value; (4) Conclusions: The natural organisms, such as fungi, lichenized fungi and algae, could be used as supplementary medicine, in the form of pharmaceutical preparations and food sources. Further advanced studies are required on the pharmacological properties and bioactive compounds of these organisms.

Nutritional, Medicinal, and Cosmetic Value of Bioactive Compounds in Button Mushroom (Agaricus bisporus): A Review

Fungi are vital to numerous industrial and household processes, especially producing cheeses, beer, wine, and bread, and they are accountable for breaking down organic matter. The remarkable medicinal and nutritional values of the mushrooms have increased their consumption. Agaricus bisporus belongs to the Agaricaceae family, and it is a top-ranked cultivated mushroom that is well known for its edibility. A. bisporus is rich in nutrients such as carbohydrates, amino acids, fats, and minerals and has potential anticancer, antioxidant, anti-obesity, and anti-inflammation properties. The bioactive compounds extracted from this mushroom can be used for the treatment of several common human diseases including cancer, bacterial and fungal infections, diabetes, heart disorder, and skin problems. A. bisporus has opened new horizons for the world to explore mushrooms as far as their culinary and medicinal values are concerned. In recent years, tyrosinase and ergothioneine have been extracted from this mushroom, which has made this mushroom worth considering more for nutritional and medicinal purposes. To emphasize various aspects of A. bisporus, a comprehensive review highlighting the nutritional, medicinal, and cosmetic values and finding out the research gaps is presented. In this way, it would be possible to improve the quality and quantity of bioactive compounds in A. bisporus, ultimately contributing to the discovery of new drugs and the responsible mechanisms. In the present review, we summarize the latest advancements regarding the nutritional, pharmaceutical, and cosmetic properties of A. bisporus. Moreover, research gaps with future research directions are also discussed.

Brain mechanisms underlying neuropsychiatric symptoms in Alzheimer's disease: a systematic review of symptom-general and -specific lesion patterns

Neuropsychiatric symptoms (NPSs) are common in patients with Alzheimer's disease (AD) and are associated with accelerated cognitive impairment and earlier deaths. This review aims to explore the neural pathogenesis of NPSs in AD and its association with the progression of AD. We first provide a literature overview on the onset times of NPSs. Different NPSs occur in different disease stages of AD, but most symptoms appear in the preclinical AD or mild cognitive impairment stage and develop progressively. Next, we describe symptom-general and -specific patterns of brain lesions. Generally, the anterior cingulate cortex is a commonly damaged region across all symptoms, and the prefrontal cortex, especially the orbitofrontal cortex, is also a critical region associated with most NPSs. In contrast, the anterior cingulate-subcortical circuit is specifically related to apathy in AD, the frontal-limbic circuit is related to depression, and the amygdala circuit is related to anxiety. Finally, we elucidate the associations between the NPSs and AD by combining the onset time with the neural basis of NPSs.

Carbon-11: Radiochemistry and Target-Based PET Molecular Imaging Applications in Oncology, Cardiology, and Neurology

The positron emission tomography (PET) molecular imaging technique has gained its universal value as a remarkable tool for medical diagnosis and biomedical research. Carbon-11 is one of the promising radiotracers that can report target-specific information related to its pharmacology and physiology to understand the disease status. Currently, many of the available carbon-11 (t_1/2 = 20.4 min) PET radiotracers are heterocyclic derivatives that have been synthesized using carbon-11 inserted different functional groups obtained from primary and secondary carbon-11 precursors. A spectrum of carbon-11 PET radiotracers has been developed against many of the upregulated and emerging targets for the diagnosis, prognosis, prediction, and therapy in the fields of oncology, cardiology, and neurology. This review focuses on the carbon-11 radiochemistry and various target-specific PET molecular imaging agents used in tumor, heart, brain, and neuroinflammatory disease imaging along with its associated pathology.

Markers for the central serotonin system correlate to verbal ability and paralinguistic social voice processing in autism spectrum disorder

Impairment in verbal communication abilities has been reported in autism spectrum disorder (ASD). Dysfunction of the serotonergic system has also been reported in ASD. However, it is still unknown how the brain serotonergic system relates to impairment in verbal communication abilities in individuals with ASD. In the present study, we investigated the correlation between brain serotonergic condition and brain sensitivity to paralinguistic stimuli (i.e., amplitude in the human voice prosodic change-evoked mismatch field) measured by magnetoencephalography (MEG) or verbal ability in 10 adults with ASD. To estimate the brain serotonergic condition, we measured the serotonin transporter nondisplaceable binding potential cerebrum-wide using positron emission tomography with [11C]N,N-dimethyl-2-(2-amino-4-cyanophenylthio)benzylamine ([11C] DASB). The results demonstrated a significant positive correlation between brain activity to paralinguistic stimuli and brain serotonin transporter binding potential in the left lingual gyrus, left fusiform gyrus and left calcarine cortex. In addition, there were significant positive correlations between verbal ability and serotonergic condition in the right anterior insula, right putamen and right central operculum. These results suggested that the occipital cortex is implicated in recognition of the prosodic change in ASD, whereas the right insula-involved serotonergic system is important in nurturing verbal function in ASD.Trial registration: UMIN000011077.

Synthesis and evaluation of 2-(2'-((dimethylamino)methyl)-4'-(2-fluoroethoxy-substituted)phenylthio)benzenamine derivatives as potential positron emission tomography imaging agents for serotonin transporters

A series of diphenylsulfide derivatives with various substitutions at the 4-position on phenyl ring A and different lengths of the 2-fluoroethoxy-substituted side-chain at the 4'-position on ring B were synthesized and evaluated as potential positron emission tomography (PET) imaging agents for serotonin transporters (SERT). These ligands exhibited high SERT binding affinities (K_i = 0.11-1.3 nM) and the 4-methyl-substituted (4-Me) compounds 7a and 8a displayed excellent selectivity for SERT versus norepinephrine transporters (NET) (392- and 700-fold, respectively). In the parallel artificial membrane permeability assay (PAMPA), these ligands demonstrated moderate to high brain penetration, and the 4-Me analogs showed higher BBB permeability than the corresponding 4-F analogs. The 2-fluoroethoxy-substituted ligands showed higher metabolic stability and lower lipophilicity than 4-F-ADAM. [¹⁸F]7a-c were readily prepared using an automatic synthesizer and exhibited significant uptake and slow washout in rat brains. At 120 min after iv injection, [¹⁸F]7a exhibited the highest uptake in the midbrain, whereas [¹⁸F]7b exhibited the highest uptake in the hypothalamus and midbrain. After treatment with citalopram, a SERT-selective ligand, the uptake of [¹⁸F]7a in the hypothalamus and striatum was significantly decreased. The potent and highly selective SERT binding and the selective and reversible accumulation in SERT-rich brain regions suggested that [¹⁸F]7a is a promising lead for the further development of novel [¹⁸F]-labeled PET imaging agents for SERT binding sites in the brain.

AD molecular: Molecular imaging of Alzheimer's disease: PET imaging of neurotransmitter systems

Current understanding of Alzheimer's disease (AD) pathogenesis relies on the observed accumulations of amyloid β and phosphorylated tau aggregates that are thought to play key roles in initiating or propagating disease. However, other processes including changes in synaptic proteins and neurotransmitter loss have been suggested as important etiologies or contributors. Positron emission tomography (PET) imaging allows in vivo investigations of molecular changes associated with AD. PET imaging with multiple radiotracers can be used in combination with other modalities such as magnetic resonance imaging (MRI), and with assessments of cognition and neuropsychiatric symptoms to investigate the molecular underpinnings of AD. Studies of synaptic protein changes may improve the understanding of disease mechanisms and provide valuable markers of disease progression and therapeutic efficacy. This chapter will illustrate the importance of in vivo molecular imaging in the study of AD with a specific emphasis on PET and radioligands for several non-amyloid targets.

Cerebral serotonin transporter measurements with [11C]DASB: A review on acquisition and preprocessing across 21 PET centres

Positron Emission Tomography (PET) imaging has become a prominent tool to capture the spatiotemporal distribution of neurotransmitters and receptors in the brain. The outcome of a PET study can, however, potentially be obscured by suboptimal and/or inconsistent choices made in complex processing pipelines required to reach a quantitative estimate of radioligand binding. Variations in subject selection, experimental design, data acquisition, preprocessing, and statistical analysis may lead to different outcomes and neurobiological interpretations. We here review the approaches used in 105 original research articles published by 21 different PET centres, using the tracer [¹¹C]DASB for quantification of cerebral serotonin transporter binding, as an exemplary case. We highlight and quantify the impact of the remarkable variety of ways in which researchers are currently conducting their studies, while implicitly expecting generalizable results across research groups. Our review provides evidence that the foundation for a given choice of a preprocessing pipeline seems to be an overlooked aspect in modern PET neuroscience. Furthermore, we believe that a thorough testing of pipeline performance is necessary to produce reproducible research outcomes, avoiding biased results and allowing for better understanding of human brain function.

Diagnosis and Management of Neuropsychiatric Symptoms in Alzheimer's Disease

PURPOSE OF REVIEW

To explore the most recent developments in the effective diagnosis and treatment of neuropsychiatric symptoms (NPS) in Alzheimer's disease (AD).

RECENT FINDINGS

The clinical diagnosis of NPS in AD is facilitated by the use of the Neuropsychiatric Inventory (NPI). CT and MRI scans can be useful for detecting structural changes indicating AD. Other promising diagnostic methodologies that are less frequently used in the clinical setting include positron emission tomography (PET) scans for detecting amyloid and blood tests for detecting serum biomarkers. Numerous pharmaceutical agents have been studied for their use in managing NPS, with antipsychotics being popular for managing agitation but also having significant side effects. Non-pharmacological interventions, such as reminiscence therapy and the Describe, Investigate, Create, Evaluate (DICE) approach may be able to provide treatment without such adverse effects. Diagnosing AD and the comorbid NPS remains primarily a clinical endeavor with CT and MRI scans sometimes used, but evidence is amassing for the use of other imaging modalities and different lab tests for convenient and empiric diagnosis of AD to distinguish it from other psychiatric illnesses. The number of pharmacologic treatments for NPS that are safe as well as efficacious remains limited, yet non-pharmacologic interventions have clear clinical utility. In addition to searching for more successful pharmacological treatments, further research should focus on novel diagnostic tests and non-pharmacologic therapies.

Alterations in Phase-Related Prefrontal Activation During Cognitive Tasks and Nicotinic α4β2 Receptor Availability in Alzheimer's Disease

BACKGROUND

Evidence shows that the cholinergic system plays an important role in regulating working memory and that working memory-related prefrontal activation decreases with age and neuronal degeneration, such as Alzheimer's disease (AD). However, the relation between attention-related α4β2 nicotinic cholinergic function and task-induced prefrontal activation especially time course-related activation remains to be explored.

OBJECTIVE

We aimed to elucidate the relationship between changes in task-induced oxy-hemoglobin concentration (cerebral blood flow, CBF) in the prefrontal cortex and the availability of α4β2 nicotinic receptors in the brain of AD patients in light of their task performance.

METHODS

Eleven mild-to-moderate AD patients and eleven normal elderly subjects underwent the near-infrared spectroscopy during easy and difficult working memory tasks for estimating prefrontal CBF changes and positron emission tomography with the α4β2 tracer [18F]2FA-85380 ([18F]2FA) for measuring the α4β2 nicotinic receptor binding.

RESULTS

Significant correlations between mean oxy-hemoglobin concentration in the channels with significant [group] main effects and prefrontal [18F]2FA binding were observed during the early easy task period in the normal group and during the late difficult task in the AD group. In addition, those prefrontal CBF responses were significantly correlated with not correct performance but the execution time to spend.

CONCLUSION

The α4β2 nicotinic acetylcholine receptors in the prefrontal cortex play an important role in increasing prefrontal activation when attending to novel stimuli, irrespective of the accuracy of the outcome. A delay in the cholinergic-induced increase in prefrontal activation in AD patients might explain their delayed responses in the cognitive task.

Association Study and Meta-Analysis of Polymorphisms, Methylation Profiles, and Peripheral mRNA Expression of the Serotonin Transporter Gene in Patients with Alzheimer's Disease

BACKGROUND/AIM

The aim of this study was to elucidate the relationship between Alzheimer's disease (AD) and the serotonin transporter gene (SLC6A4).

METHODS

AD subjects (n = 43) and controls (n = 47) were recruited and evaluated. In leukocytes, we evaluated two polymorphisms in SLC6A4, the serotonin transporter length polymorphic region (5-HTT-LPR) and rs25531, as well as methylation rates of the SLC6A4 promoter region and the SLC6A4 mRNA expression level. We also performed a meta-analysis to examine the relationship between the frequency of the L allele and the risk of AD.

RESULTS

The distributions of 5-HTT-LPR and rs25531 polymorphisms in AD subjects were not different from those of controls. Although the methylation rates in AD subjects were not significantly different from those of controls, the expression level in AD subjects was significantly higher than in controls. Additionally, the expression level in AD subjects was significantly correlated with apathy. Meta-analysis revealed that the L/L genotype significantly reduced the risk of AD, but only in the Caucasian population.

CONCLUSION

Higher SLC6A4 mRNA expression in leukocytes in AD was associated with apathy regardless of SLC6A4 genotypes and methylation rates of the promoter region. The L/L genotype may reduce the risk of AD in the Caucasian population.

Molecular imaging of serotonin degeneration in mild cognitive impairment

Neuropathological and neuroimaging studies have consistently demonstrated degeneration of monoamine systems, especially the serotonin system, in normal aging and Alzheimer's disease. The evidence for degeneration of the serotonin system in mild cognitive impairment is limited. Thus, the goal of the present study was to measure the serotonin transporter in vivo in mild cognitive impairment and healthy controls. The serotonin transporter is a selective marker of serotonin terminals and of the integrity of serotonin projections to cortical, subcortical and limbic regions and is found in high concentrations in the serotonergic cell bodies of origin of these projections (raphe nuclei). Twenty-eight participants with mild cognitive impairment (age 66.6±6.9, 16 males) and 28 healthy, cognitively normal, demographically matched controls (age 66.2±7.1, 15 males) underwent magnetic resonance imaging for measurement of grey matter volumes and high-resolution positron emission tomography with well-established radiotracers for the serotonin transporter and regional cerebral blood flow. Beta-amyloid imaging was performed to evaluate, in combination with the neuropsychological testing, the likelihood of subsequent cognitive decline in the participants with mild cognitive impairment. The following hypotheses were tested: 1) the serotonin transporter would be lower in mild cognitive impairment compared to controls in cortical and limbic regions, 2) in mild cognitive impairment relative to controls, the serotonin transporter would be lower to a greater extent and observed in a more widespread pattern than lower grey matter volumes or lower regional cerebral blood flow and 3) lower cortical and limbic serotonin transporters would be correlated with greater deficits in auditory-verbal and visual-spatial memory in mild cognitive impairment, not in controls. Reduced serotonin transporter availability was observed in mild cognitive impairment compared to controls in cortical and limbic areas typically affected by Alzheimer's disease pathology, as well as in sensory and motor areas, striatum and thalamus that are relatively spared in Alzheimer's disease. The reduction of the serotonin transporter in mild cognitive impairment was greater than grey matter atrophy or reductions in regional cerebral blood flow compared to controls. Lower cortical serotonin transporters were associated with worse performance on tests of auditory-verbal and visual-spatial memory in mild cognitive impairment, not in controls. The serotonin system may represent an important target for prevention and treatment of MCI, particularly the post-synaptic receptors (5-HT4 and 5-HT6), which may not be as severely affected as presynaptic aspects of the serotonin system, as indicated by the observation of lower serotonin transporters in MCI relative to healthy controls.

The Lateral Occipito-temporal Cortex Is Involved in the Mental Manipulation of Body Part Imagery

The lateral occipito-temporal cortex (LOTC), including the extrastriate body area, is known to be involved in the perception of body parts. Although still controversial, recent studies have demonstrated the role of the LOTC in higher-level body-related cognition in humans. This study consisted of two experiments (E1 and E2). The first (E1) was an exploratory experiment to find the neural correlate of the mental manipulation of body part imagery, in which brain cerebral glucose metabolic rates and the performance of mental rotation of the hand were measured in 100 subjects who exhibited a range of symptoms of cognitive decline. In E1, we found that the level of glucose metabolism in the right LOTC was significantly correlated with performance in a task involving mental manipulation of the hand. Next, in E2, we performed a randomized, double-blind, controlled intervention study (clinical trial number: UMIN 000018310) in younger healthy adults to test whether right occipital (corresponding to the right LOTC) anodal stimulation using transcranial direct current stimulation (tDCS) could enhance the mental manipulation of the hand. In E2, we demonstrated a significant effect of tDCS on the accuracy rate in a task involving mental manipulation of the hand. Although further study is necessary to answer the question of whether these results are specific for the mental manipulation of body parts but not non-body parts, E1 demonstrated a possible role of the LOTC in carrying out the body mental manipulation task in patients with dementia, and E2 suggested the possible effect of tDCS on this task in healthy subjects.

In vitro cultures of Bacopa monnieri and an analysis of selected groups of biologically active metabolites in their biomass

CONTEXT

Bacopa monnieri L. Pennell (Scrophulariaceae) is one of the most important plants in the system of Indian medicine (Ayurveda).

OBJECTIVE

This paper studies the optimal growth of B. monnieri for effective accumulation of metabolites. Biomass growth of this plant could be accomplished in liquid cultures on Murashige & Skoog medium.

MATERIALS AND METHODS

Powdered shoots of in vitro cultures of B. monnieri were extracted by methanol for indole compounds, phenolic compounds and bacosides for RP-HPLC analysis. Fatty acid analysis was performed via gas chromatography. Anti-inflammatory effect of B. monnieri extracts was evaluated in the A549 cells. COX-2 and cPGES expression was analyzed using Western blots.

RESULTS

l-Tryptophan and serotonin were found in biomass from in vitro cultures of B. monnieri on MS medium and in biomass from the MS mediums enriched with the different additions such as of 0.1 g/L magnesium sulphate, 0.1 g/L zinc hydroaspartate, 0.1 g/L l-tryptophan, 0.25 g/L serine, 0.5 g/L serine and 0.5 mg/L anthranilic acid. The content of l-tryptophan and serotonin compounds was significant in biomass from medium with the addition of 0.1 g/L zinc hydroaspartate (0.72 mg/g dry weight and 1.19, respectively). Phenolic compounds identified in biomass from the same variants of MS medium were chlorogenic acid (ranging from 0.20 to 0.70 mg/g dry weight), neochlorogenic acid (ranging from 0.11 to 0.40 mg/g dry weight) and caffeic acid (ranging from 0.01 to 0.04 mg/g dry weight). The main group of fatty acids in biomass was saturated fatty acids (53.4%). The predominant fatty acid was palmitic acid. A significant decrease of COX-2 and cPGES expression was observed in the A549 cells activated with LPS and treated with B. monnieri extracts.

DISCUSSION AND CONCLUSIONS

As far as we know, this is the first analysis of indole compounds and phenolic acids in this plant. The multi-therapeutic effect of B. monnieri is expressed by the activity of bacosides. Information about the presence of indole and phenolic compounds, and fatty acids in this plant is limited, but the content of these compounds might participate in the physiological activity of B. monnieri.

Drug Development in Alzheimer's Disease: The Contribution of PET and SPECT

Clinical trials aiming to develop disease-altering drugs for Alzheimer’s disease (AD), a neurodegenerative disorder with devastating consequences, are failing at an alarming rate. Poorly defined inclusion-and outcome criteria, due to a limited amount of objective biomarkers, is one of the major concerns. Non-invasive molecular imaging techniques, positron emission tomography and single photon emission (computed) tomography (PET and SPE(C)T), allow visualization and quantification of a wide variety of (patho)physiological processes and allow early (differential) diagnosis in many disorders. PET and SPECT have the ability to provide biomarkers that permit spatial assessment of pathophysiological molecular changes and therefore objectively evaluate and follow up therapeutic response, especially in the brain. A number of specific PET/SPECT biomarkers used in support of emerging clinical therapies in AD are discussed in this review.

In Vivo Evaluation of Blood Based and Reference Tissue Based PET Quantifications of [11C]DASB in the Canine Brain

This first-in-dog study evaluates the use of the PET-radioligand [¹¹C]DASB to image the density and availability of the serotonin transporter (SERT) in the canine brain. Imaging the serotonergic system could improve diagnosis and therapy of multiple canine behavioural disorders. Furthermore, as many similarities are reported between several human neuropsychiatric conditions and naturally occurring canine behavioural disorders, making this tracer available for use in dogs also provide researchers an interesting non-primate animal model to investigate human disorders. Five adult beagles underwent a 90 minutes dynamic PET scan and arterial whole blood was sampled throughout the scan. For each ROI, the distribution volume (V_T), obtained via the one- and two- tissue compartment model (1-TC, 2-TC) and the Logan Plot, was calculated and the goodness-of-fit was evaluated by the Akaike Information Criterion (AIC). For the preferred compartmental model BP_ND values were estimated and compared with those derived by four reference tissue models: 4-parameter RTM, SRTM2, MRTM2 and the Logan reference tissue model. The 2-TC model indicated in 61% of the ROIs a better fit compared to the 1-TC model. The Logan plot produced almost identical V_T values and can be used as an alternative. Compared with the 2-TC model, all investigated reference tissue models showed high correlations but small underestimations of the BP_ND-parameter. The highest correlation was achieved with the Logan reference tissue model (Y = 0.9266 x + 0.0257; R² = 0.9722). Therefore, this model can be put forward as a non-invasive standard model for future PET-experiments with [¹¹C]DASB in dogs.

Agaricus bisporus and its in vitro culture as a source of indole compounds released into artificial digestive juices

The popularity of Agaricus bisporus results not only from the quality of the flavors, but also from the content of many substances of therapeutic properties. This paper presents a study on RP-HPLC determination of the content of indole compounds released from the lyophilized biomass from in vitro cultures of A. bisporus into artificial digestive juices at 37°C. A. bisporus in vitro cultures were grown on media enriched with zinc salts. The release of 5-hydroxy-l-tryptophan and l-tryptophan was found in the greatest number of samples. The content of 5-hydroxy-l-tryptophan in the investigated samples ranged from 86.62 to 531 mg/100g d.w. The amount of l-tryptophan was determined within the range of 1.63-4.68 mg/100g d.w. and for melatonin 0.43-0.64 mg/100g d.w. It was demonstrated for the first time that in vitro cultures of A. bisporus release indole compounds in conditions simulating the human digestive tract.

Nicotine Administration Attenuates Methamphetamine-Induced Novel Object Recognition Deficits

BACKGROUND

Previous studies have demonstrated that methamphetamine abuse leads to memory deficits and these are associated with relapse. Furthermore, extensive evidence indicates that nicotine prevents and/or improves memory deficits in different models of cognitive dysfunction and these nicotinic effects might be mediated by hippocampal or cortical nicotinic acetylcholine receptors. The present study investigated whether nicotine attenuates methamphetamine-induced novel object recognition deficits in rats and explored potential underlying mechanisms.

METHODS

Adolescent or adult male Sprague-Dawley rats received either nicotine water (10-75 μg/mL) or tap water for several weeks. Methamphetamine (4 × 7.5mg/kg/injection) or saline was administered either before or after chronic nicotine exposure. Novel object recognition was evaluated 6 days after methamphetamine or saline. Serotonin transporter function and density and α4β2 nicotinic acetylcholine receptor density were assessed on the following day.

RESULTS

Chronic nicotine intake via drinking water beginning during either adolescence or adulthood attenuated the novel object recognition deficits caused by a high-dose methamphetamine administration. Similarly, nicotine attenuated methamphetamine-induced deficits in novel object recognition when administered after methamphetamine treatment. However, nicotine did not attenuate the serotonergic deficits caused by methamphetamine in adults. Conversely, nicotine attenuated methamphetamine-induced deficits in α4β2 nicotinic acetylcholine receptor density in the hippocampal CA1 region. Furthermore, nicotine increased α4β2 nicotinic acetylcholine receptor density in the hippocampal CA3, dentate gyrus and perirhinal cortex in both saline- and methamphetamine-treated rats.

CONCLUSIONS

Overall, these findings suggest that nicotine-induced increases in α4β2 nicotinic acetylcholine receptors in the hippocampus and perirhinal cortex might be one mechanism by which novel object recognition deficits are attenuated by nicotine in methamphetamine-treated rats.

Molecular imaging of neuropsychiatric symptoms in Alzheimer's and Parkinson's disease

Neuropsychiatric symptoms (NPS) are very common in neurodegenerative diseases and are a major contributor to disability and caregiver burden. There is accumulating evidence that NPS may be a prodrome and/or a "risk factor" of neurodegenerative diseases. The medications used to treat these symptoms in younger patients are not very effective in patients with neurodegenerative disease and may have serious side effects. An understanding of the neurobiology of NPS is critical for the development of more effective intervention strategies. Targeting these symptoms may also have implications for prevention of cognitive or motor decline. Molecular brain imaging represents a bridge between basic and clinical observations and provides many opportunities for translation from animal models and human post-mortem studies to in vivo human studies. Molecular brain imaging studies in Alzheimer's disease (AD) and Parkinson's disease (PD) are reviewed with a primary focus on positron emission tomography studies of NPS. Future directions for the field of molecular imaging in AD and PD to understand the neurobiology of NPS will be discussed.

Principles and management of neuropsychiatric symptoms in Alzheimer's dementia

Neuropsychiatric symptoms of Alzheimer's disease (NPS-AD) are highly prevalent and lead to poor medical and functional outcomes. In spite of the burdensome nature of NPS-AD, we are continuing to refine the nosology and only beginning to understand the underlying pathophysiology. Cluster analyses have frequently identified three to five subsyndromes of NPS-AD: behavioral dysfunction (for example, agitation/aggressiveness), psychosis (for example, delusions and hallucinations), and mood disturbance (for example, depression or apathy). Recent neurobiological studies have used new neuroimaging techniques to elucidate behaviorally relevant circuits and networks associated with these subsyndromes. Several fronto-subcortical circuits, cortico-cortical networks, and neurotransmitter systems have been proposed as regions and mechanisms underlying NPS-AD. Common to most of these subsyndromes is the broad overlap of regions associated with the salience network (anterior cingulate and insula), mood regulation (amygdala), and motivated behavior (frontal cortex). Treatment strategies for dysregulated mood syndromes (depression and apathy) have primarily targeted serotonergic mechanisms with antidepressants or dopaminergic mechanisms with psychostimulants. Psychotic symptoms have largely been targeted with anti-psychotic medications despite controversial risk/benefit tradeoffs. Management of behavioral dyscontrol, including agitation and aggression in AD, has encompassed a wide range of psychoactive medications as well as non-pharmacological approaches. Developing rational therapeutic approaches for NPS-AD will require a firmer understanding of the underlying etiology in order to improve nosology as well as provide the empirical evidence necessary to overcome regulatory and funding challenges to further study these debilitating symptoms.

Platelets, a reliable source for peripheral Alzheimer's disease biomarkers?

Peripheral biomarkers play an indispensable role in quick and reliable diagnoses of any kind of disease. With the population ageing, the number of people suffering from age-related diseases is expected to rise dramatically over the coming decades. In particular, all types of cognitive deficits, such as Alzheimer's disease, will increase. Alzheimer's disease is characterised mainly by coexistence of amyloid plaques and neurofibrillary tangles in brain. Reliable identification of such molecular characteristics antemortem, however, is problematic due to restricted availability of appropriate sample material and definitive diagnosis is only possible postmortem. Currently, the best molecular biomarkers available for antemortem diagnosis originate from cerebrospinal fluid. Though, this is not convenient for routine diagnosis because of the required invasive lumbar puncture. As a consequence, there is a growing demand for additional peripheral biomarkers in a more readily accessible sample material. Blood platelets, due to shared biochemical properties with neurons, can constitute an attractive alternative as discussed here. This review summarises potential platelet Alzheimer's disease biomarkers, their role, implication, and alteration in the disease. For easy comparison of their performance, the Hedge effect size was calculated whenever data were available.

Monoaminergic neurotransmitter alterations in postmortem brain regions of depressed and aggressive patients with Alzheimer's disease

Depression and aggression in Alzheimer's disease (AD) are 2 of the most severe and prominent neuropsychiatric symptoms (NPS). Altered monoaminergic neurotransmitter system functioning has been implicated in both NPS, although their neurochemical etiology remains to be elucidated. Left frozen hemispheres of 40 neuropathologically confirmed AD patients were regionally dissected. Dichotomization based on depression and aggression scores resulted in depressed/nondepressed (AD + D/AD - D) and aggressive/nonaggressive (AD + Agr/AD - Agr) groups. Concentrations of dopamine, serotonin (5-HT), (nor)epinephrine ((N)E), and respective metabolites were determined using reversed-phase high-performance liquid chromatography. Significantly lower 3-methoxy-4-hydroxyphenylglycol (MHPG) and higher homovanillic acid levels were observed in Brodmann area (BA) 9 and 10 of AD + D compared with AD - D. In AD + Agr, 5-hydroxy-3-indoleacetic acid (5-HIAA) levels in BA9, 5-HIAA to 5-HT ratios in BA11, and MHPG, NE, and 5-HIAA levels in the hippocampus were significantly decreased compared with AD - Agr. These findings indicate that brain region-specific altered monoamines and metabolites may contribute to the occurrence of depression and aggression in AD.

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.

Normative database of the serotonergic system in healthy subjects using multi-tracer PET

The highly diverse serotonergic system with at least 16 different receptor subtypes is implicated in the pathophysiology of most neuropsychiatric disorders including affective and anxiety disorders, obsessive compulsive disorder, post-traumatic stress disorder, eating disorders, sleep disturbance, attention deficit/hyperactivity disorder, drug addiction, suicidal behavior, schizophrenia, Alzheimer, etc. Alterations of the interplay between various pre- and postsynaptic receptor subtypes might be involved in the pathogenesis of these disorders. However, there is a lack of comprehensive in vivo values using standardized procedures. In the current PET study we quantified 3 receptor subtypes, including the major inhibitory (5-HT(1A) and 5-HT(1B)) and excitatory (5-HT(2A)) receptors, and the transporter (5-HTT) in the brain of healthy human subjects to provide a database of standard values. PET scans were performed on 95 healthy subjects (age=28.0 ± 6.9 years; 59% males) using the selective radioligands [carbonyl-(11)C]WAY-100635, [(11)C]P943, [(18)F]altanserin and [(11)C]DASB, respectively. A standard template in MNI stereotactic space served for region of interest delineation. This template follows two anatomical parcellation schemes: 1) Brodmann areas including 41 regions and 2) AAL (automated anatomical labeling) including 52 regions. Standard values (mean, SD, and range) for each receptor and region are presented. Mean cortical and subcortical binding potential (BP) values were in good agreement with previously published human in vivo and post-mortem data. By means of linear equations, PET binding potentials were translated to post-mortem binding (provided in pmol/g), yielding 5.89 pmol/g (5-HT(1A)), 23.5 pmol/g (5-HT(1B)), 31.44 pmol/g (5-HT(2A)), and 11.33 pmol/g (5-HTT) being equivalent to the BP of 1, respectively. Furthermore, we computed individual voxel-wise maps with BP values and generated average tracer-specific whole-brain binding maps. This knowledge might improve our interpretation of the alterations taking place in the serotonergic system during neuropsychiatric disorders.

Alzheimer's disease: pathological mechanisms and the beneficial role of melatonin

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD.

Factors associated with a depressive disorder in Alzheimer's disease are different from those found for other dementia disorders

Background

This study explores factors associated with depression in Alzheimer's disease (AD) compared with mild cognitive impairment (MCI) and other dementia disorders.

Method

In a prospective study we included 195 patients: 31 with MCI, 112 with AD and 52 with other dementias.

Results

According to the ICD-10 and the DSM-IV criteria, 88 (44.1%) and 59 (30.3%), respectively, had a depressive disorder. An adjusted multiple regression analysis showed that previous depression (p < 0.05) was significantly associated with depression in AD patients. Severity of dementia (p < 0.05) was significantly associated with a depressive disorder in a group of patients with frontotemporal dementia, vascular dementia, or dementia due to Lewy Body disease or Parkinson's disease.

Conclusion

We found different factors associated with a depressive disorder in AD compared to those found for other dementia disorders.

Effects of brain amyloid deposition and reduced glucose metabolism on the default mode of brain function in normal aging

Brain β-amyloid (Aβ) deposition during normal aging is highlighted as an initial pathogenetic event in the development of Alzheimer's disease. Many recent brain imaging studies have focused on areas deactivated during cognitive tasks [the default mode network (DMN), i.e., medial frontal gyrus/anterior cingulate cortex and precuneus/posterior cingulate cortex], where the strength of functional coordination was more or less affected by cerebral Aβ deposits. In the present positron emission tomography study, to investigate whether regional glucose metabolic alterations and Aβ deposits seen in nondemented elderly human subjects (n = 22) are of pathophysiological importance in changes of brain hemodynamic coordination in DMN during normal aging, we measured cerebral glucose metabolism with [(18)F]FDG, Aβ deposits with [(11)C]PIB, and regional cerebral blood flow during control and working memory tasks by H(2)(15)O on the same day. Data were analyzed using both region of interest and statistical parametric mapping. Our results indicated that the amount of Aβ deposits was negatively correlated with hemodynamic similarity between medial frontal and medial posterior regions, and the lower similarity was associated with poorer working memory performance. In contrast, brain glucose metabolism was not related to this medial hemodynamic similarity. These findings suggest that traceable Aβ deposition, but not glucose hypometabolism, in the brain plays an important role in occurrence of neuronal discoordination in DMN along with poor working memory in healthy elderly people.

Brain serotonergic circuitries

Brain serotonergic circuitries interact with other neurotransmitter systems on a multitude of different molecular levels. In humans, as in other mammalian species, serotonin (5-HT) plays a modulatory role in almost every physiological function. Furthermore, serotonergic dysfunction is thought to be implicated in several psychiatric and neurodegenerative disorders. We describe the neuroanatomy and neurochemistry of brain serotonergic circuitries. The contribution of emergent in vivo imaging methods to the regional localization of binding site receptors and certain aspects of their functional connectivity in correlation to behavior is also discussed. 5-HT cell bodies, mainly localized in the raphe nuclei, send axons to almost every brain region. It is argued that the specificity of the local chemocommunication between 5-HT and other neuronal elements mainly depends on mechanisms regulating the extracellular concentration of 5-HT the diversity of high-affinity membrane receptors, and their specific transduction modalities.

The role of serotonin in respiratory function and dysfunction

Serotonin (5-HT) is a neuromodulator-transmitter influencing global brain function. Past and present findings illustrate a prominent role for 5-HT in the modulation of ponto-medullary autonomic circuits. 5-HT is also involved in the control of neurotrophic processes during pre- and postnatal development of neural circuits. The functional implications of 5-HT are particularly illustrated in the alterations to the serotonergic system, as seen in a wide range of neurological disorders. This article reviews the role of 5-HT in the development and control of respiratory networks in the ponto-medullary brainstem. The review further examines the role of 5-HT in breathing disorders occurring at different stages of life, in particular, the neonatal neurodevelopmental diseases such as Rett, sudden infant death and Prader-Willi syndromes, adult diseases such as sleep apnoea and mental illness linked to neurodegeneration.

Effects of S100B on Serotonergic Plasticity and Neuroinflammation in the Hippocampus in Down Syndrome and Alzheimer's Disease: Studies in an S100B Overexpressing Mouse Model

S100B promotes development and maturation in the mammalian brain. However, prolonged or extensive exposure can lead to neurodegeneration. Two important functions of S100B in this regard, are its role in the development and plasticity of the serotonergic neurotransmitter system, and its role in the cascade of glial changes associated with neuroinflammation. Both of these processes are therefore accelerated towards degeneration in disease processes wherein S100B is increased, notably, Alzheimer's disease (AD) and Down syndrome (DS). In order to study the role of S100B in this context, we have examined S100B overexpressing transgenic mice. Similar to AD and DS, the transgenic animals show a profound change in serotonin innervation. By 28 weeks of age, there is a significant loss of terminals in the hippocampus. Similarly, the transgenic animals show neuroinflammatory changes analogous with AD and DS. These include decreased numbers of mature, stable astroglial cells, increased numbers of activated microglial cells and increased microglial expression of the cell surface receptor RAGE. Eventually, the S100B transgenic animals show neurodegeneration and the appearance of hyperphosphorylated tau structures, as seen in late stage DS and AD. The role of S100B in these conditions is discussed.