Different mechanisms promote astrocyte Ca2+ waves and spreading depression in the mouse neocortex

Cortical spreading depression (CSD) is thought to play an important role in different pathological conditions of the human brain. Here we investigated the interaction between CSD and Ca2+ waves within the astrocyte population in slices from mouse neocortex (postnatal days 10-14). After local KCl ejection as a trigger for CSD, we recorded the propagation of Ca2+ increases within a large population of identified astrocytes in synchrony with CSD measured as intrinsic optical signal (IOS) or negative DC-potential shift. The two events spread with 39.2 +/- 3.3 mum/sec until the IOS and negative DC-potential shift decayed after approximately 1 mm. However, the astrocyte Ca2+ wave continued to propagate for up to another 500 microm but with a reduced speed of 18.3 +/- 2.5 microm/sec that is also typical for glial Ca2+ waves in white matter or culture. While blocking CSD using MK-801 (40 microm), an NMDA-receptor antagonist, the astrocyte Ca2+ wave persisted with a reduced speed (13.2 +/- 1.5 microm/sec). The specific gap junction blocker carbenoxolon (100 microm) did not prevent CSD but decelerated the speed (2.9 +/- 0.9 microm/sec) of the astrocyte Ca2+ wave in the periphery of CSD. We also found that interfering with intracellular astrocytic Ca2+ signaling by depletion of internal Ca2+ stores does not affect the spread of the IOS. We conclude that CSD determines the velocity of an accompanying astrocytic Ca2+ response, but the astrocyte Ca2+ wave penetrates a larger territory and by this represents a self-reliant phenomenon with a different mechanism of propagation

Plasma amyloid concentration in Alzheimer's disease: performance of a high-throughput amyloid assay in distinguishing Alzheimer's disease cases from controls

BACKGROUND: Collection of cerebrospinal fluid (CSF) for measurement of amyloid-β (Aβ) species is a gold standard in Alzheimer's disease (AD) diagnosis, but has risks. Thus, establishing a low-risk blood Aβ test with high AD sensitivity and specificity is of outmost interest. OBJECTIVE: We evaluated the ability of a commercially available plasma Aβ assay to distinguish AD patients from biomarker-healthy controls. METHOD: In a case-control design, we examined plasma samples from 44 AD patients (A + N+) and 49 controls (A-N-) from a memory clinic. AD was diagnosed using a combination of neuropsychological examination, CSF biomarker analysis and brain imaging. Total Aβ40 and total Aβ42 in plasma were measured through enzyme-linked immunosorbent assay (ELISA) technology using ABtest40 and ABtest42 test kits (Araclon Biotech Ltd.). Receiver operating characteristic (ROC) analyses with outcome AD were performed, and sensitivity and specificity were calculated. RESULTS: Plasma Aβ42/40 was weakly positively correlated with CSF Aβ42/40 (Spearman's rho 0.22; p = 0.037). Plasma Aβ42/40 alone was not able to statistically significantly distinguish between AD patients and controls (AUC 0.58; 95% CI 0.46, 0.70). At a cut-point of 0.076 maximizing sensitivity and specificity, plasma Aβ42/40 had a sensitivity of 61.2% and a specificity of 63.6%. CONCLUSION: In this sample, the high-throughput blood Aβ assay was not able to distinguish well between AD patients and controls. Whether or not the assay may be useful in large-scale epidemiological settings remains to be seen

Value of neuropsychological tests to identify patients with depressive symptoms on the Alzheimer's disease continuum

BACKGROUND: Depressive symptoms often co-occur with Alzheimer's disease (AD) and can impact neuropsychological test results. In early stages of AD, disentangling cognitive impairments due to depression from those due to neurodegeneration often poses a challenge. OBJECTIVE: We aimed to identify neuropsychological tests able to detect AD-typical pathology while taking into account varying degrees of depressive symptoms. METHODS: A battery of neuropsychological tests (CERAD-NP) and the Geriatric Depression Scale (GDS) were assessed, and cerebrospinal fluid (CSF) biomarkers were obtained. After stratifying patients into CSF positive or negative and into low, moderate, or high GDS score groups, sensitivity and specificity and area under the curve (AUC) were calculated for each subtest. RESULTS: 497 participants were included in the analyses. In patients with low GDS scores (≤10), the highest AUC (0.72) was achieved by Mini-Mental State Examination, followed by Constructional Praxis Recall and Wordlist Total Recall (AUC = 0.714, both). In patients with moderate (11-20) and high (≥21) GDS scores, Trail Making Test-B (TMT-B) revealed the highest AUCs with 0.77 and 0.82, respectively. CONCLUSION: Neuropsychological tests showing AD-typical pathology in participants with low GDS scores are in-line with previous results. In patients with higher GDS scores, TMT-B showed the best discrimination. This indicates the need to focus on executive function rather than on memory task results in depressed patients to explore a risk for AD

Apolipoprotein E4 disrupts the neuroprotective action of sortilin in neuronal lipid metabolism and endocannabinoid signaling

INTRODUCTION: Apolipoprotein E (apoE) is a carrier for brain lipids and the most important genetic risk factor for Alzheimer's disease (AD). ApoE binds the receptor sortilin, which mediates uptake of apoE‐bound cargo into neurons. The significance of this uptake route for brain lipid homeostasis and AD risk seen with apoE4, but not apoE3, remains unresolved. METHODS: Combining neurolipidomics in patient specimens with functional studies in mouse models, we interrogated apoE isoform–specific functions for sortilin in brain lipid metabolism and AD. RESULTS: Sortilin directs the uptake and conversion of polyunsaturated fatty acids into endocannabinoids, lipid‐based neurotransmitters that act through nuclear receptors to sustain neuroprotective gene expression in the brain. This sortilin function requires apoE3, but is disrupted by binding of apoE4, compromising neuronal endocannabinoid metabolism and action. DISCUSSION: We uncovered the significance of neuronal apoE receptor sortilin in facilitating neuroprotective actions of brain lipids, and its relevance for AD risk seen with apoE4

Expression und Funktion von Neurotransmitterrezeptoren auf Astrozyten im intakten Hirngewebe der Maus [Expression and function of neurotransmitter receptors on astrocytes in the intact mouse brain]

Im Gehirn von Saeugetieren bilden Gliazellen die groesste Zellpopulation. Die Nervenzellen, die Informationen schnell durch elektrische Aktivitaet und Transmitterfreisetung weiterleiten, sind fuer eine funktionierende Signalweiterleitung auf die Funktionen von Gliazellen angewiesen. Die Astrozyten, welche die groesste Untergruppe der Gliazellen bilden, sind in engem morphologischen Kontakt mit Synapsen sowie auch mit Blutgefaessen und sind fuer den Naehrstofftransport aus dem Blut zu den Neuronen zustaendig. Die Integration der Astrozyten in die Signalweiterleitung zwischen Neuronen und die interastrozytaere Kommunikation sind bisher wenig erforscht. Im Rahmen dieser Arbeit wurde untersucht, ob Astrozyten im intakten Hirngewebe der Maus NMDA-Rezeptoren exprimieren und somit in der Lage sind, nach Ausschuettung von Glutamat aus Neuronen, Calciumsignale zu generieren. Desweiteren wurde die Kommunikation zwischen Astrozyten untereinander in Form von Calciumwellen im akuten Hirngewebe charakterisiert. Es konnte gezeigt werden, dass Astrozyten funktionelle NMDA-Rezeptoren exprimieren und nach Rezeptoraktivierung mit einem Calciumsignal reagieren. Im Gegensatz zu Neuronen ist der astrozytaere NMDA-Rezeptor bei physiologischen Mg2+-Konzentrationen als Ionenpore aktivierbar, womit keine vorherige Depolarisation der Membran fuer einen Calciumeinstrom noetig ist. Den Astrozyten ist somit die Moeglichkeit gegeben, auf die Ausschuettung von Glutamat zu reagieren. Desweiteren konnte gezeigt werden, dass Astrozyten im Maushirn innerhalb der weissen Substanz in Form von Calciumwellen miteinander kommunizieren. Es sind jedoch auch andere Gliazelltypen an dieser Kommunikationsform beteiligt, wie Vorlaeuferzellen und Mikrogliazellen. Die Welle wird durch eine Freisetzung von ATP in den Extrazellulaerraum getragen, wodurch alle Zellen des Hirngewebes auch Neurone durch diese astrozytaere Aktivitaet beeinflusst werden koennen. Es konnte somit im Rahmen dieser Arbeit gezeigt werden, dass Astrozyten die Voraussetzung haben, zum einen auf neuronale Aktivitaet zu reagieren und ueber ein eigenes System zu kommunizieren, was ihnen die Moeglichkeit gibt, plastisch auf physiologische wie auch pathologische Vorgaenge im Gehirn einzuwirken. [In the mammalian brain, the major cell population is not comprised of neurons, but of glia cells. Functional signal transmission in between neurons is only possible in a functioning glial network. Astrocytes, the largest subgroup of glia cells, are in intimate morphological contact with neurons, especially at synapses. In addition, they are responsible for the glucose uptake from the blood and supply neurons with other nutrients and metabolic subtances. The integration of astrocytes into neuronal signal transmission and the inter-astrocytic communication have not been investigated in great detail yet. Here, I investigated if astrocytes in brain tissue express NMDA type glutamate receptors. Thereby, they would be able to respond with a calcium signal to extracellular accumulation of glutamate. Furthermore, communication in between astrocytes via propagation of calcium waves in intact brain tissue was characterized. I could show that astrocytes express functional NMDA receptors and activation of those receptors leads to a rise in intracellular calcium levels in those cells. In contrast to the neuronal NMDA receptor, the astrocytic receptor can open at physiological Mg2+ concentrations. Thus, no prior depolarisation is needed for the receptor to open. Astrocytes thereby have the ability to respond to extracellular glutamate immediately. Secondly, I could show that astrocytes in white matter within the mouse brain communicate via propagation of calcium waves. The wave is propagating via release of ATP into the extracellular space. Thus, all cells expressing purinergic receptors within the brain parenchmyma also neurons can be influenced functionally by this astrocytic activity. Taken together, I could show that astrocytes are able to respond to neuronal activity, and that they are able to communicate via their own communication system. This allows them to react to physiological and pathophysiological situations in the brain.

Liquordiagnostik bei Demenzen [CSF biomarkers in dementia]

The clinical diagnosis of dementia today is mainly based on the results of different neuro psychometric tests and cranial CT or MRT. Biomarker quantification in cerebrospinal fluid (CSF) may indicate and substantiate the presence of neurodegenerative processes especially in Alzheimer's disease. In the course of neurodegenerative processes, such as dementia, certain protein levels in CSF may change. The increased rate of neuronal cell death which is common to all types of dementia may cause elevated levels of the Tau protein. CSF biomarker analysis is especially helpful to differentiate between cognitive deficits due to major depressive disorders without neurodegeneration and dementia. To substantiate the diagnosis of Alzheimer's disease, the amyloid metabolism should be analyzed. Alzheimer's disease leads to the deposition of amyloid plaques in the brain and is accompanied by a decrease of the peptide A{beta}1-42 in CSF and stable levels of the peptide A{beta}1-40

Antidepressants act on glial cells: SSRIs and serotonin elicit astrocyte calcium signaling in the mouse prefrontal cortex

One important target in the treatment of major depressive disorder (MDD) is the serotonin (5-hydroxytryptamine, 5-HT) system. Selective serotonin reuptake inhibitors (SSRI) are used to treat MDD. Yet, the mode of action of these drugs is not completely understood. There is evolving evidence for a role of glutamate in mood disorder and its signaling. Astrocytes are involved in glutamate metabolism and play an active role in memory processing but their role in mood disorders is still largely unknown. A modulation of astrocytic signaling by SSRIs or 5-HT has not been investigated up to now. We investigated astrocytic calcium signaling with the calcium indicator dye Fluo-4. Using a confocal microscope, we imaged astrocytes in the medial prefrontal cortex of acute mouse brain slices after the application of the SSRIs citalopram and fluoxetine. In the same way, we studied the effects of serotonin and the modulation of this signaling by glutamate in astrocytes. We found that astrocyte calcium signaling can be elicited by 5-HT. Also, the SSRIs citalopram and fluoxetine induce calcium signals in about 1/3 of all astrocytes, even when neuronal signal propagation is inhibited. Astrocytic responses to 5-HT have a unique pattern and they could mostly not be evoked twice. We determined that glutamate is a substance that can interfere with 5-HT-induced calcium signals in astrocytes since after stimulation by glutamate, astrocytes did not show a response to 5-HT. Astrocytic calcium signaling is elicited by SSRIs and 5-HT. They may serve as integrators, linking the serotonergic and glutamatergic signaling pathways