5-HT7 receptors in Alzheimer's disease.

Even though the involvement of serotonin (5-hydroxytryptamine; 5-HT) and its receptors in Alzheimer's disease (AD) is widely accepted, data on the expression and the role of 5-HT7 receptors in AD is relatively limited. Therefore, the objective of the present work was to study the expression of serotonergic 5-HT7 receptors in postmortem samples of AD brains and correlate it with neurotransmitter levels, cognition and behavior. The study population consisted of clinically well-characterized and neuropathologically confirmed AD patients (n = 42) and age-matched control subjects (n = 18). Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) and high-performance liquid chromatography were performed on Brodmann area (BA) 7, BA10, BA22, BA24, hippocampus, amygdala, thalamus and cerebellum to measure mRNA levels of 5-HT7 receptors (HTR7), as well as the concentrations of various monoamine neurotransmitters and their metabolites. Decreased levels of HTR7 mRNA were observed in BA10. A significant association was observed between HTR7 levels in BA10 and BEHAVE-AD cluster B (hallucinations) (rs(28) = 0.444, P < 0.05). In addition, a negative correlation was observed between HTR7 levels in BA10 and both MHPG concentrations in this brain region (rs(45) = -0.311; P < 0.05), and DOPAC levels in the amygdala (rs(42) = -0.311; P < 0.05). Quite surprisingly, no association was found between HTR7 levels and cognitive status. Altogether, this study supports the notion of the involvement of 5-HT7 receptors in psychotic symptoms in AD, suggesting the interest of testing antagonist acting at this receptor to specifically treat psychotic symptoms in this illness.

Monoaminergic and Kynurenergic Characterization of Frontotemporal Dementia and Amyotrophic Lateral Sclerosis in Cerebrospinal Fluid and Serum.

Exploring the neurochemical continuum between frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) with respect to monoamines and kynurenines in cerebrospinal fluid (CSF) and serum, may be useful to identify possible new research/therapeutic targets. Hence, we analysed monoamines and kynurenines in CSF and serum derived from patients with FTD (n = 39), ALS (n = 23), FTD-ALS (n = 4) and age-matched control subjects (n = 26), using reversed-phase ultra-high performance liquid chromatography (RP-UHPLC) with electrochemical detection (ECD) and liquid chromatography tandem mass spectrometry, respectively. We noted a shared dopaminergic disturbance in FTD and ALS when compared to CONTR, with significantly increased serum DA levels and decreased DOPAC concentrations, as well as decreased DOPAC/DA ratios in both disease groups. In CSF, significantly reduced DOPAC concentrations in FTD and ALS were observed as well. Here, a significant increase in DA levels and decrease in DOPAC/DA ratios was only found in FTD relative to CONTR. With respect to the kynurenine pathway (KP), we only found decreased HK/XA ratios, indicative for vitamin B6 status, in serum of ALS subjects compared to FTD. The dopaminergic commonalities observed in FTD and ALS might relate to a disturbance of dopaminergic nerve terminals in projection areas of the substantia nigra and/or ventral tegmental area, although these findings should first be confirmed in brain tissue. Lastly, based on the results of this work, the KP does not hold promise as a research/therapeutic target in FTD and ALS.

Sampling issues of cerebrospinal fluid and plasma monoamines: Investigation of the circadian rhythm and rostrocaudal concentration gradient.

Biomarkers for neurodegenerative dementias offer interesting prospects regarding diagnosis and disease monitoring. Monoamines such as dopamine, (nor)adrenaline, serotonin (5-hydroxytryptamine or 5-HT), and their respective metabolites homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylglycol (MHPG), and 5-hydroxyindoleacetic acid (5-HIAA), were shown to be altered in dementia, including Alzheimer's disease (AD). Biomarker research is hampered by potential confounds including the influence of time of day and volume of cerebrospinal fluid (CSF) collected. Therefore, the possibility of a circadian rhythm in CSF and plasma, and the presence of a rostrocaudal concentration gradient (RCG) in CSF for aforementioned monoamines/metabolites, were investigated. Circadian rhythmicity was assessed using reversed-phase ultra-high performance liquid chromatography with electrochemical detection (RP-UHPLC-ECD) to measure monoamine/metabolite concentrations in 271 paired CSF and plasma samples, successively collected over a period of 30 h and derived from eight healthy subjects. Plasma samples were also analyzed for melatonin, serving as positive control analyte, using ELISA. The RCG examination entailed RP-UHPLC-ECD analyses on five consecutive CSF samples derived from 10 patients with AD and 10 non-AD/control subjects. Besides a diurnal rhythm for melatonin, we found a similar rhythmicity for plasma HVA, with acrophases occurring between 02:00 and 06:00 h, in four out of seven subjects. Three and two subjects showed a circadian rhythm for CSF HVA and 5-HIAA, respectively. No rhythmicity was observed in any other compound. We found that only CSF MHPG, HVA and 5-HIAA levels differed across CSF fractions, and that these changes in 5-HIAA levels varied in the AD versus non-AD/control group. Positive correlations between CSF volume and HVA and 5-HIAA levels, indicative of a RCG, were also observed. Such a RCG could not be detected for the other monoamines/metabolites. Our results stress the importance of standardizing sampling procedures of biological fluids with respect to time of day, volume and number of samples.

Evaluating the applicability of mouse SINEs as an alternative normalization approach for RT-qPCR in brain tissue of the APP23 model for Alzheimer's disease.

BACKGROUND: The choice of appropriate reference genes (RGs) for use in reverse transcription quantitative polymerase chain reaction (RT-qPCR) has been thoroughly investigated, since the inclusion of unstable RGs might cause inaccurate gene expression results. NEW METHOD: Short interspersed nuclear elements (SINEs) such as B elements, might represent an alternative solution given the high occurrence of these repetitive elements in the rodent genome and transcriptome. We performed RT-qPCR to investigate the stability of nine commonly used RGs and two B elements, B1 and B2, across different age- and genotype-related experimental conditions in the hippocampus and cortex of the APP23 amyloidosis mouse model for Alzheimer's disease. Gene stability was assessed using geNorm, NormFinder and BestKeeper. Human amyloid precursor protein (APP) levels in transgenic versus wild-type animals were also determined to validate the use of B elements as an alternative normalization approach. RESULTS: Whereas B elements were stably expressed in the hippocampus, they were ranked as least stable in the cortex. The optimal normalization factor (NF) in hippocampus was a combination of Gapdh and Rpl13a, whereas in cortex, Actb and Tbp constituted the ideal NF. COMPARISON WITH EXISTING METHOD: When comparing B1 and B2 as NFs for APP with the optimal panel of RGs in hippocampus, we found that B1 and B2 performed similarly to the optimal NF, while these SINEs performed less well in cortex. CONCLUSIONS: Although B elements are suitable as an alternative normalization strategy in the hippocampus, they do not represent a universal normalization approach in the APP23 model.

The validation of Short Interspersed Nuclear Elements (SINEs) as a RT-qPCR normalization strategy in a rodent model for temporal lobe epilepsy.

BACKGROUND: In gene expression studies via RT-qPCR many conclusions are inferred by using reference genes. However, it is generally known that also reference genes could be differentially expressed between various tissue types, experimental conditions and animal models. An increasing amount of studies have been performed to validate the stability of reference genes. In this study, two rodent-specific Short Interspersed Nuclear Elements (SINEs), which are located throughout the transcriptome, were validated and assessed against nine reference genes in a model of Temporal Lobe Epilepsy (TLE). Two different brain regions (i.e. hippocampus and cortex) and two different disease stages (i.e. acute phase and chronic phase) of the systemic kainic acid rat model for TLE were analyzed by performing expression analyses with the geNorm and NormFinder algorithms. Finally, we performed a rank aggregation analysis and validated the reference genes and the rodent-specific SINEs (i.e. B elements) individually via Gfap gene expression. RESULTS: GeNorm ranked Hprt1, Pgk1 and Ywhaz as the most stable genes in the acute phase, while Gusb and B2m were ranked as the most unstable, being significantly upregulated. The two B elements were ranked as most stable for both brain regions in the chronic phase by geNorm. In contrast, NormFinder ranked the B1 element only once as second best in cortical tissue for the chronic phase. Interestingly, using only one of the two algorithms would have led to skewed conclusions. Finally, the rank aggregation method indicated the use of the B1 element as the best option to normalize target genes, independent of the disease progression and brain region. This result was supported by the expression profile of Gfap. CONCLUSION: In this study, we demonstrate the potential of implementing SINEs -notably the B1 element- as a stable normalization factor in a rodent model of TLE, independent of brain region or disease progression.

Serotonergic Dysfunction in Amyotrophic Lateral Sclerosis and Parkinson's Disease: Similar Mechanisms, Dissimilar Outcomes.

Amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD) share similar pathophysiological mechanisms. From a neurochemical point of view, the serotonin (5-hydroxytryptamine; 5-HT) dysfunction in both movement disorders-related to probable lesioning of the raphe nuclei-is profound, and, therefore, may be partially responsible for motor as well as non-motor disturbances. More specifically, in ALS, it has been hypothesized that serotonergic denervation leads to loss of its inhibitory control on glutamate release, resulting into glutamate-induced neurotoxicity in lower and/or upper motor neurons, combined with a detrimental decrease of its facilitatory effects on glutamatergic motor neuron excitation. Both events then may eventually give rise to the well-known clinical motor phenotype. Similarly, disruption of the organized serotonergic control on complex mesencephalic dopaminergic connections between basal ganglia (BG) nuclei and across the BG-cortico-thalamic circuits, has shown to be closely involved in the onset of parkinsonian symptoms. Levodopa (L-DOPA) therapy in PD largely seems to confirm the influential role of 5-HT, since serotonergic rather than dopaminergic projections release L-DOPA-derived dopamine, particularly in extrastriatal regions, emphasizing the strongly interwoven interactions between both monoamine systems. Apart from its orchestrating function, the 5-HT system also exerts neuroprotective and anti-inflammatory effects. In line with this observation, emerging therapies have recently focused on boosting the serotonergic system in ALS and PD, which may provide novel rationale for treating these devastating conditions both on the disease-modifying, as well as symptomatic level.

Cerebrospinal fluid and serum MHPG improve Alzheimer's disease versus dementia with Lewy bodies differential diagnosis.

INTRODUCTION: Given the challenges concerning the differential diagnosis of dementia, we investigated the possible added value of monoaminergic compounds to the standard cerebrospinal fluid (CSF) Alzheimer's disease (AD) biomarkers. Particularly, regarding the AD versus dementia with Lewy bodies (DLB) comparison, monoamines or their metabolites might have added discriminative value as there is a more severe neuropathological burden in the locus coeruleus of DLB patients, the principal site of noradrenaline synthesis. METHODS: We applied enzyme-linked immunosorbent assay (ELISA) to analyze CSF amyloid ß peptide of 42 amino acids, total tau, and tau phosphorylated at threonine 181, in patients with AD, frontotemporal dementia, DLB/Parkinson's disease dementia, and controls. Reversed-phase high-performance liquid chromatography with electrochemical detection was implemented to study monoamine and metabolite levels in CSF and serum. Stepwise forward conditional logistic regression and receiver operating characteristic (ROC) curve analyses were performed to assess the diagnostic accuracy of these newly fitted models containing the most discriminative indicators of disease status. RESULTS: Most significant differences in CSF and serum were confined to the noradrenergic system. More specifically, CSF 3-methoxy-4-hydroxyphenylglycol (MHPG) levels were higher, whereas serum MHPG levels were lower, in DLB patients compared with all other groups. Addition of CSF and serum MHPG levels to the CSF AD biomarker panel significantly increased diagnostic accuracy between DLB/Parkinson's disease dementia and AD. Interestingly, a model only including CSF and serum MHPG without the classic AD biomarker panel reached similar area under the curve values. DISCUSSION: We hypothesize that varying degrees of neuronal loss in the locus coeruleus of DLB/Parkinson's disease dementia versus AD patients result in differentially altered MHPG levels, making this metabolite a valuable biomarker.

Brain Serotonergic and Noradrenergic Deficiencies in Behavioral Variant Frontotemporal Dementia Compared to Early-Onset Alzheimer's Disease.

Routinely prescribed psychoactive drugs in behavioral variant frontotemporal dementia (FTD) for improvement of (non)cognitive symptoms are primarily based on monoamine replacement or augmentation strategies. These were, however, initially intended to symptomatically treat other degenerative, behavioral, or personality disorders, and thus lack disease specificity. Moreover, current knowledge on brain monoaminergic neurotransmitter deficiencies in this presenile disorder is scarce, particularly with reference to changes in Alzheimer's disease (AD). The latter hence favors neurochemical comparison studies in order to elucidate the monoaminergic underpinnings of FTD compared to early-onset AD, which may contribute to better pharmacotherapy. Therefore, frozen brain samples, i.e., Brodmann area (BA) 6/8/9/10/11/12/22/24/46, amygdala, and hippocampus, of 10 neuropathologically confirmed FTD, AD, and control subjects were analyzed by means of reversed-phase high-performance liquid chromatography. Levels of serotonergic, dopaminergic, and noradrenergic compounds were measured. In nine brain areas, serotonin (5-HT) concentrations were significantly increased in FTD compared to AD patients, while 5-hydroxyindoleacetic acid/5-HT ratios were decreased in eight regions, also compared to controls. Furthermore, in all regions, noradrenaline (NA) levels were significantly higher, and 3-methoxy-4-hydroxyphenylglycol/NA ratios were significantly lower in FTD than in AD and controls. Contrarily, significantly higher dopamine (DA) levels and reduced homovanillic acid/DA ratios were only found in BA12 and BA46. Results indicate that FTD is defined by distinct serotonergic and noradrenergic deficiencies. Additional research regarding the interactions between both monoaminergic networks is required. Similarly, clinical trials investigating the effects of 5-HT1A receptor antagonists or NA-modulating agents, such as α1/2/ß1-blockers, seem to have a rationale and should be considered.