Plaque contact and unimpaired Trem2 is required for the microglial response to amyloid pathology.

Using spatial cell-type-enriched transcriptomics, we compare plaque-induced gene (PIG) expression in microglia-touching plaques, neighboring plaques, and far from plaques in an aged Alzheimer's mouse model with late plaque development. In 18-month-old APPNL-F/NL-F knockin mice, with and without the Alzheimer's disease risk mutation Trem2R47H/R47H, we report that expression of 38/55 PIGs have plaque-induced microglial upregulation, with a subset only upregulating in microglia directly contacting plaques. For seven PIGs, including Trem2, this upregulation is prevented in APPNL-F/NL-FTrem2R47H/R47H mice. These TREM2-dependent genes are all involved in phagocytic and degradative processes that we show correspond to a decrease in phagocytic markers and an increase in the density of small plaques in Trem2-mutated mice. Furthermore, despite the R47H mutation preventing increased Trem2 gene expression, TREM2 protein levels and microglial density are still marginally increased on plaques. Hence, both microglial contact with plaques and functioning TREM2 are necessary for microglia to respond appropriately to amyloid pathology.

Knock-in models related to Alzheimer's disease: synaptic transmission, plaques and the role of microglia.

BACKGROUND: Microglia are active modulators of Alzheimer's disease but their role in relation to amyloid plaques and synaptic changes due to rising amyloid beta is unclear. We add novel findings concerning these relationships and investigate which of our previously reported results from transgenic mice can be validated in knock-in mice, in which overexpression and other artefacts of transgenic technology are avoided. METHODS: AppNL-F and AppNL-G-F knock-in mice expressing humanised amyloid beta with mutations in App that cause familial Alzheimer's disease were compared to wild type mice throughout life. In vitro approaches were used to understand microglial alterations at the genetic and protein levels and synaptic function and plasticity in CA1 hippocampal neurones, each in relationship to both age and stage of amyloid beta pathology. The contribution of microglia to neuronal function was further investigated by ablating microglia with CSF1R inhibitor PLX5622. RESULTS: Both App knock-in lines showed increased glutamate release probability prior to detection of plaques. Consistent with results in transgenic mice, this persisted throughout life in AppNL-F mice but was not evident in AppNL-G-F with sparse plaques. Unlike transgenic mice, loss of spontaneous excitatory activity only occurred at the latest stages, while no change could be detected in spontaneous inhibitory synaptic transmission or magnitude of long-term potentiation. Also, in contrast to transgenic mice, the microglial response in both App knock-in lines was delayed until a moderate plaque load developed. Surviving PLX5266-depleted microglia tended to be CD68-positive. Partial microglial ablation led to aged but not young wild type animals mimicking the increased glutamate release probability in App knock-ins and exacerbated the App knock-in phenotype. Complete ablation was less effective in altering synaptic function, while neither treatment altered plaque load. CONCLUSIONS: Increased glutamate release probability is similar across knock-in and transgenic mouse models of Alzheimer's disease, likely reflecting acute physiological effects of soluble amyloid beta. Microglia respond later to increased amyloid beta levels by proliferating and upregulating Cd68 and Trem2. Partial depletion of microglia suggests that, in wild type mice, alteration of surviving phagocytic microglia, rather than microglial loss, drives age-dependent effects on glutamate release that become exacerbated in Alzheimer's disease.

Following spatial Aß aggregation dynamics in evolving Alzheimer's disease pathology by imaging stable isotope labeling kinetics.

ß-Amyloid (Aß) plaque formation is the major pathological hallmark of Alzheimer's disease (AD) and constitutes a potentially critical, early inducer driving AD pathogenesis as it precedes other pathological events and cognitive symptoms by decades. It is therefore critical to understand how Aß pathology is initiated and where and when distinct Aß species aggregate. Here, we used metabolic isotope labeling in APPNL-G-F knock-in mice together with mass spectrometry imaging to monitor the earliest seeds of Aß deposition through ongoing plaque development. This allowed visualizing Aß aggregation dynamics within single plaques across different brain regions. We show that formation of structurally distinct plaques is associated with differential Aß peptide deposition. Specifically, Aß1-42 is forming an initial core structure followed by radial outgrowth and late secretion and deposition of Aß1-38. These data describe a detailed picture of the earliest events of precipitating amyloid pathology at scales not previously possible.

Prodromal neuroinflammatory, cholinergic and metabolite dysfunction detected by PET and MRS in the TgF344-AD transgenic rat model of AD: a collaborative multi-modal study.

Mouse models of Alzheimer's disease (AD) are valuable but do not fully recapitulate human AD pathology, such as spontaneous Tau fibril accumulation and neuronal loss, necessitating the development of new AD models. The transgenic (TG) TgF344-AD rat has been reported to develop age-dependent AD features including neuronal loss and neurofibrillary tangles, despite only expressing APP and PSEN1 mutations, suggesting an improved modelling of AD hallmarks. Alterations in neuronal networks as well as learning performance and cognition tasks have been reported in this model, but none have combined a longitudinal, multimodal approach across multiple centres, which mimics the approaches commonly taken in clinical studies. We therefore aimed to further characterise the progression of AD-like pathology and cognition in the TgF344-AD rat from young-adults (6 months (m)) to mid- (12 m) and advanced-stage (18 m, 25 m) of the disease. Methods: TgF344-AD rats and wild-type (WT) littermates were imaged at 6 m, 12 m and 18 m with [18F]DPA-714 (TSPO, neuroinflammation), [18F]Florbetaben (Aß) and [18F]ASEM (α7-nicotinic acetylcholine receptor) and with magnetic resonance spectroscopy (MRS) and with (S)-[18F]THK5117 (Tau) at 15 and 25 m. Behaviour tests were also performed at 6 m, 12 m and 18 m. Immunohistochemistry (CD11b, GFAP, Aß, NeuN, NeuroChrom) and Tau (S)-[18F]THK5117 autoradiography, immunohistochemistry and Western blot were also performed. Results: [18F]DPA-714 positron emission tomography (PET) showed an increase in neuroinflammation in TG vs wildtype animals from 12 m in the hippocampus (+11%), and at the advanced-stage AD in the hippocampus (+12%), the thalamus (+11%) and frontal cortex (+14%). This finding coincided with strong increases in brain microgliosis (CD11b) and astrogliosis (GFAP) at these time-points as assessed by immunohistochemistry. In vivo [18F]ASEM PET revealed an age-dependent increase uptake in the striatum and pallidum/nucleus basalis of Meynert in WT only, similar to that observed with this tracer in humans, resulting in TG being significantly lower than WT by 18 m. In vivo [18F]Florbetaben PET scanning detected Aß accumulation at 18 m, and (S)-[18F]THK5117 PET revealed subsequent Tau accumulation at 25m in hippocampal and cortical regions. Aß plaques were low but detectable by immunohistochemistry from 6 m, increasing further at 12 and 18 m with Tau-positive neurons adjacent to Aß plaques at 18 m. NeuroChrom (a pan neuronal marker) immunohistochemistry revealed a loss of neuronal staining at the Aß plaques locations, while NeuN labelling revealed an age-dependent decrease in hippocampal neuron number in both genotypes. Behavioural assessment using the novel object recognition task revealed that both WT & TgF344-AD animals discriminated the novel from familiar object at 3 m and 6 m of age. However, low levels of exploration observed in both genotypes at later time-points resulted in neither genotype successfully completing the task. Deficits in social interaction were only observed at 3 m in the TgF344-AD animals. By in vivo MRS, we showed a decrease in neuronal marker N-acetyl-aspartate in the hippocampus at 18 m (-18% vs age-matched WT, and -31% vs 6 m TG) and increased Taurine in the cortex of TG (+35% vs age-matched WT, and +55% vs 6 m TG). Conclusions: This multi-centre multi-modal study demonstrates, for the first time, alterations in brain metabolites, cholinergic receptors and neuroinflammation in vivo in this model, validated by robust ex vivo approaches. Our data confirm that, unlike mouse models, the TgF344-AD express Tau pathology that can be detected via PET, albeit later than by ex vivo techniques, and is a useful model to assess and longitudinally monitor early neurotransmission dysfunction and neuroinflammation in AD.

Trem2 promotes anti-inflammatory responses in microglia and is suppressed under pro-inflammatory conditions.

Genome-wide association studies have reported that, amongst other microglial genes, variants in TREM2 can profoundly increase the incidence of developing Alzheimer's disease (AD). We have investigated the role of TREM2 in primary microglial cultures from wild type mice by using siRNA to decrease Trem2 expression, and in parallel from knock-in mice heterozygous or homozygous for the Trem2 R47H AD risk variant. The prevailing phenotype of Trem2 R47H knock-in mice was decreased expression levels of Trem2 in microglia, which resulted in decreased density of microglia in the hippocampus. Overall, primary microglia with reduced Trem2 expression, either by siRNA or from the R47H knock-in mice, displayed a similar phenotype. Comparison of the effects of decreased Trem2 expression under conditions of lipopolysaccharide (LPS) pro-inflammatory or IL-4 anti-inflammatory stimulation revealed the importance of Trem2 in driving a number of the genes up-regulated in the anti-inflammatory phenotype. RNA-seq analysis showed that IL-4 induced the expression of a program of genes including Arg1 and Ap1b1 in microglia, which showed an attenuated response to IL-4 when Trem2 expression was decreased. Genes showing a similar expression profile to Arg1 were enriched for STAT6 transcription factor recognition elements in their promoter, and Trem2 knockdown decreased levels of STAT6. LPS-induced pro-inflammatory stimulation suppressed Trem2 expression, thus preventing TREM2's anti-inflammatory drive. Given that anti-inflammatory signaling is associated with tissue repair, understanding the signaling mechanisms downstream of Trem2 in coordinating the pro- and anti-inflammatory balance of microglia, particularly mediating effects of the IL-4-regulated anti-inflammatory pathway, has important implications for fighting neurodegenerative disease.

Negative Regulator of Ubiquitin-Like Protein 1 modulates the autophagy-lysosomal pathway via p62 to facilitate the extracellular release of tau following proteasome impairment.

Negative regulator of ubiquitin-like protein 1 (NUB1) and its longer isoform NUB1L are ubiquitin-like (UBL)/ubiquitin-associated (UBA) proteins that facilitate the targeting of proteasomal substrates, including tau, synphilin-1 and huntingtin. Previous data revealed that NUB1 also mediated a reduction in tau phosphorylation and aggregation following proteasome inhibition, suggesting a switch in NUB1 function from targeted proteasomal degradation to a role in autophagy. Here, we delineate the mechanisms of this switch and show that NUB1 interacted specifically with p62 and induced an increase in p62 levels in a manner facilitated by inhibition of the proteasome. NUB1 moreover increased autophagosomes and the recruitment of lysosomes to aggresomes following proteasome inhibition. Autophagy flux assays revealed that NUB1 affected the autophagy-lysosomal pathway primarily via the UBA domain. NUB1 localized to cytosolic inclusions with pathological forms of tau, as well as LAMP1 and p62 in the hippocampal neurons of tauopathy mice. Finally, NUB1 facilitated the extracellular release of tau following proteasome inhibition. This study thus shows that NUB1 plays a role in regulating the autophagy-lysosomal pathway when the ubiquitin proteasome system is compromised, thus contributing to the mechanisms targeting the removal of aggregation-prone proteins upon proteasomal impairment.

A Unifying Hypothesis for Alzheimer's Disease: From Plaques to Neurodegeneration.

Evidence suggests that amyloid ß is highly toxic to synapses in a phospho-Tau-dependent manner. Here, I present a hypothesis that links previous evidence from the first rise of amyloid ß through to Tau tangles and neurodegeneration. In the immediate vicinity of plaques, concentrated soluble amyloid ß occurs in equilibrium with deposited forms. Initially, plaques cover only a small percentage of brain volume. Microglia, by efficiently removing damaged synapses, may prevent spread of damage along the axon, restricting damage to the immediate vicinity of plaques. However, as plaque load increases, as seen in Alzheimer's disease, an individual axon may suffer multiple points of damage, leading to dissociation of Tau, formation of a tangle, and loss of the axon. As more axons suffer this fate, the network eventually degenerates. According to this hypothesis, the degree of plaque load that an individual can tolerate would depend on the efficiency of their microglia in removing amyloid-ß-damaged synapses and the distribution of plaques, relative to axon trajectories, would determine the eventual cognitive symptoms.

Effects of rising amyloidß levels on hippocampal synaptic transmission, microglial response and cognition in APPSwe/PSEN1M146V transgenic mice.

BACKGROUND: Progression of Alzheimer's disease is thought initially to depend on rising amyloidß and its synaptic interactions. Transgenic mice (TASTPM; APPSwe/PSEN1M146V) show altered synaptic transmission, compatible with increased physiological function of amyloidß, before plaques are detected. Recently, the importance of microglia has become apparent in the human disease. Similarly, TASTPM show a close association of plaque load with upregulated microglial genes. METHODS: CA1 synaptic transmission and plasticity were investigated using in vitro electrophysiology. Microglial relationship to plaques was examined with immunohistochemistry. Behaviour was assessed with a forced-alternation T-maze, open field, light/dark box and elevated plus maze. FINDINGS: The most striking finding is the increase in microglial numbers in TASTPM, which, like synaptic changes, begins before plaques are detected. Further increases and a reactive phenotype occur later, concurrent with development of larger plaques. Long-term potentiation is initially enhanced at pre-plaque stages but decrements with the initial appearance of plaques. Finally, despite altered plasticity, TASTPM have little cognitive deficit, even with a heavy plaque load, although they show altered non-cognitive behaviours. INTERPRETATION: The pre-plaque synaptic changes and microglial proliferation are presumably related to low, non-toxic amyloidß levels in the general neuropil and not directly associated with plaques. However, as plaques grow, microglia proliferate further, clustering around plaques and becoming phagocytic. Like in humans, even when plaque load is heavy, without development of neurofibrillary tangles and neurodegeneration, these alterations do not result in cognitive deficits. Behaviours are seen that could be consistent with pre-diagnosis changes in the human condition. FUNDING: GlaxoSmithKline; BBSRC; UCL; ARUK; MRC.

Improving Mouse Models for Dementia. Are All the Effects in Tau Mouse Models Due to Overexpression?

Mouse models of Alzheimer's disease have commonly used transgenic overexpression of genes involved in production of amyloid ß (APP and/or PSEN1/2) or Tau (MAPT) with mutations that result in familial forms of dementia. We discuss possible improvements that may create full models while avoiding the problems of overexpression and report synaptic results in APPKI models. We stress use of inappropriate controls without overexpression of the normal human protein and the mismatch between the learning deficits reported in mice with plaques but no tangles and the human condition. We focus on Tau overexpression, including new data that support previous reports of the grossly nonlinear relationship between Tau overexpression and neurofibrillary tangle load, with a twofold increase in Tau protein, resulting in a 100-fold increase in tangle density. These data also support the hypothesis that a high concentration of soluble Tau, in overexpression models, plays an important direct role in neurodegeneration, rather than only via aggregation. Finally, we hypothesize that there is an optimal concentration range over which Tau can bind to microtubules and a threshold beyond which much of the overexpressed protein is unable to bind. The excess thus causes toxicity in ways not necessarily related to the process in human dementias.

Neuronal and Peripheral Pentraxins Modify Glutamate Release and may Interact in Blood-Brain Barrier Failure.

Neuronal pentraxin 1 (NPTX1) has been implicated in Alzheimer's disease, being present in and around dystrophic neurons in plaques, affecting glutamatergic transmission postsynaptically and mediating effects of amyloidß. Here, we confirm the presence of NPTX1 around plaques in postmortem Alzheimer's disease brain and report that acutely applied human NPTX1 increases paired-pulse ratio at mouse CA3-CA1 hippocampal synapses, indicating a decrease in glutamate release. In contrast, chronic exposure to NPTX1, NPTX2, or NPTX receptor decreases paired-pulse ratio, mimicking some of the earliest changes in mice expressing familial Alzheimer's disease genes. The peripheral pentraxin, serum amyloid P component (SAP), causes similar synaptic effects to NPTX1. The presence of SAP on amyloid plaques in Alzheimer's disease confirms that it can enter the brain. We show that SAP and neuronal pentraxins can interact and that SAP can enter the brain if the blood-brain barrier is compromised, suggesting that peripheral pentraxins could affect central synaptic transmission via this interaction, especially in the event of blood-brain barrier breakdown.

Large and Small Dendritic Spines Serve Different Interacting Functions in Hippocampal Synaptic Plasticity and Homeostasis.

The laying down of memory requires strong stimulation resulting in specific changes in synaptic strength and corresponding changes in size of dendritic spines. Strong stimuli can also be pathological, causing a homeostatic response, depressing and shrinking the synapse to prevent damage from too much Ca(2+) influx. But do all types of dendritic spines serve both of these apparently opposite functions? Using confocal microscopy in organotypic slices from mice expressing green fluorescent protein in hippocampal neurones, the size of individual spines along sections of dendrite has been tracked in response to application of tetraethylammonium. This strong stimulus would be expected to cause both a protective homeostatic response and long-term potentiation. We report separation of these functions, with spines of different sizes reacting differently to the same strong stimulus. The immediate shrinkage of large spines suggests a homeostatic protective response during the period of potential danger. In CA1, long-lasting growth of small spines subsequently occurs consolidating long-term potentiation but only after the large spines return to their original size. In contrast, small spines do not change in dentate gyrus where potentiation does not occur. The separation in time of these changes allows clear functional differentiation of spines of different sizes.

First effects of rising amyloid-ß in transgenic mouse brain: synaptic transmission and gene expression.

Detecting and treating Alzheimer's disease, before cognitive deficits occur, has become the health challenge of our time. The earliest known event in Alzheimer's disease is rising amyloid-ß. Previous studies have suggested that effects on synaptic transmission may precede plaque deposition. Here we report how relative levels of different soluble amyloid-ß peptides in hippocampus, preceding plaque deposition, relate to synaptic and genomic changes. Immunoprecipitation-mass spectrometry was used to measure the early rise of different amyloid-ß peptides in a mouse model of increasing amyloid-ß ('TASTPM', transgenic for familial Alzheimer's disease genes APP/PSEN1). In the third postnatal week, several amyloid-ß peptides were above the limit of detection, including amyloid-ß40, amyloid-ß38 and amyloid-ß42 with an intensity ratio of 6:3:2, respectively. By 2 months amyloid-ß levels had only increased by 50% and although the ratio of the different peptides remained constant, the first changes in synaptic currents, compared to wild-type mice could be detected with patch-clamp recordings. Between 2 and 4 months old, levels of amyloid-ß40 rose by ∼7-fold, but amyloid-ß42 rose by 25-fold, increasing the amyloid-ß42:amyloid-ß40 ratio to 1:1. Only at 4 months did plaque deposition become detectable and only in some mice; however, synaptic changes were evident in all hippocampal fields. These changes included increased glutamate release probability (P < 0.001, n = 7-9; consistent with the proposed physiological effect of amyloid-ß) and loss of spontaneous action potential-mediated activity in the cornu ammonis 1 (CA1) and dentate gyrus regions of the hippocampus (P < 0.001, n = 7). Hence synaptic changes occur when the amyloid-ß levels and amyloid-ß42:amyloid-ß40 ratio are still low compared to those necessary for plaque deposition. Genome-wide microarray analysis revealed changes in gene expression at 2-4 months including synaptic genes being strongly affected but often showing significant changes only by 4 months. We thus demonstrate that, in a mouse model of rising amyloid-ß, the initial deposition of plaques does not occur until several months after the first amyloid-ß becomes detectable but coincides with a rapid acceleration in the rise of amyloid-ß levels and the amyloid-ß42:amyloid-ß40 ratio. Prior to acceleration, however, there is already a pronounced synaptic dysfunction, reflected as changes in synaptic transmission and altered gene expression, indicating that restoring synaptic function early in the disease progression may represent the earliest possible target for intervention in the onset of Alzheimer's disease.

A genome-wide gene-expression analysis and database in transgenic mice during development of amyloid or tau pathology.

We provide microarray data comparing genome-wide differential expression and pathology throughout life in four lines of "amyloid" transgenic mice (mutant human APP, PSEN1, or APP/PSEN1) and "TAU" transgenic mice (mutant human MAPT gene). Microarray data were validated by qPCR and by comparison to human studies, including genome-wide association study (GWAS) hits. Immune gene expression correlated tightly with plaques whereas synaptic genes correlated negatively with neurofibrillary tangles. Network analysis of immune gene modules revealed six hub genes in hippocampus of amyloid mice, four in common with cortex. The hippocampal network in TAU mice was similar except that Trem2 had hub status only in amyloid mice. The cortical network of TAU mice was entirely different with more hub genes and few in common with the other networks, suggesting reasons for specificity of cortical dysfunction in FTDP17. This Resource opens up many areas for investigation. All data are available and searchable at http://www.mouseac.org.

Multiphoton microfabrication of conducting polymer-based biomaterials.

We report the application of multiphoton microfabrication to prepare conducting polymer (CP)-based biomaterials that were capable of drug delivery and interacting with brain tissue ex vivo, thereby highlighting the potential of multiphoton lithography to prepare electroactive biomaterials which may function as implantable neural biointerfaces (e.g. electrodes).

Dynamic range of GSK3α not GSK3ß is essential for bidirectional synaptic plasticity at hippocampal CA3-CA1 synapses.

Glycogen synthase kinase-3 (GSK3), particularly the isoform GSK3ß, has been implicated in a wide range of physiological systems and neurological disorders including Alzheimer's Disease. However, the functional importance of GSK3α has been largely untested. The multifunctionality of GSK3 limits its potential as a drug target because of inevitable side effects. Due to its greater expression in the CNS, GSK3ß rather than GSK3α has also been assumed to be of primary importance in synaptic plasticity. Here, we investigate bidirectional long-term synaptic plasticity in knockin mice with a point mutation in GSK3α or GSK3ß that prevents their inhibitory regulation. We report that only the mutation in GSK3α affects long-term potentiation (LTP) and depression (LTD). This stresses the importance of investigating isoform specificity for GSK3 in all systems and suggests that GSK3α should be investigated as a drug target in cognitive disorders including Alzheimer's Disease.

Corticosterone reduces dendritic complexity in developing hippocampal CA1 neurons.

Although prolonged stress and corticosteroid exposure induce morphological changes in the hippocampal CA3 area, the adult CA1 area is quite resistant to such changes. Here we addressed the question whether elevated corticosteroid hormone levels change dendritic complexity in young, developing CA1 cells. In organotypic cultures (prepared from P5 rats) that were 14-21 days cultured in vitro, two doses of corticosterone (30 and 100 nM) were tested. Dendritic morphology of CA1 neurons was established by imaging neurons filled with the fluorescent dye Alexa. Application of 100 nM corticosterone for 20 minutes induced atrophy of the apical dendritic tree 1-4 hours later. Fractal analysis showed that total neuronal complexity was reduced twofold when compared with vehicle-treated neurons. Exposing organotypic slices to 30 nM corticosterone reduced apical length in a more delayed manner: only neurons examined more than 2 hours after exposure to corticosterone showed atrophy of the apical dendritic tree. Neither dose of corticosterone affected the length of basal dendrites or spine density. Corticosterone was ineffective in changing morphology of the apical dendrites when tested in the presence of the glucocorticoid receptor antagonist RU38486. These results suggest that high physiological levels of corticosterone, via activation of the glucocorticoid receptor, can, during the course of only a few hours, reduce the dendritic complexity of CA1 pyramidal neurons in young, developing hippocampal tissue. These findings suggest that it is relevant to maintain plasma corticosterone levels low during hippocampal development.

GABA release by basket cells onto Purkinje cells, in rat cerebellar slices, is directly controlled by presynaptic purinergic receptors, modulating Ca2+ influx.

In many brain regions, Ca(2+) influx through presynaptic P2X receptors influences GABA release from interneurones. In patch-clamp recordings of Purkinje cells (PCs) in rat cerebellar slices, broad spectrum P2 receptor antagonists, PPADS (30microM) or suramin (12microM), result in a decreased amplitude and increased failure rate of minimal evoked GABAergic synaptic currents from basket cells. The effect is mimicked by desensitizing P2X1/3-containing receptors with alpha,beta-methylene ATP. This suggests presynaptic facilitation of GABA release via P2XR-mediated Ca(2+) influx activated by endogenously released ATP. In contrast, activation of P2Y4 receptors (using UTP, 30microM, but not P2Y1 or P2Y6 receptor ligands) results in inhibition of GABA release. Immunological studies reveal the presence of most known P2Rs in >or=20% of GABAergic terminals in the cerebellum. P2X3 receptors and P2Y4 receptors occur in approximately 60% and 50% of GABAergic synaptosomes respectively and are localized presynaptically. Previous studies report that PC output is also influenced by postsynaptic purinergic receptors located on both PCs and interneurones. The high Ca(2+) permeability of the P2X receptor and the ability of ATP to influence intracellular Ca(2+) levels via P2Y receptor-mediated intracellular pathways make ATP the ideal transmitter for the multisite bidirectional modulation of the cerebellar cortical neuronal network.

Differential development of neuronal physiological responsiveness in two human neural stem cell lines.

BACKGROUND: Neural stem cells (NSCs) are powerful research tools for the design and discovery of new approaches to neurodegenerative disease. Overexpression of the myc family transcription factors in human primary cells from developing cortex and mesencephalon has produced two stable multipotential NSC lines (ReNcell VM and CX) that can be continuously expanded in monolayer culture. RESULTS: In the undifferentiated state, both ReNcell VM and CX are nestin positive and have resting membrane potentials of around -60 mV but do not display any voltage-activated conductances. As initially hypothesized, using standard methods (stdD) for differentiation, both cell lines can form neurons, astrocytes and oligodendrocytes according to immunohistological characteristics. However it became clear that this was not true for electrophysiological features which designate neurons, such as the firing of action potentials. We have thus developed a new differentiation protocol, designated 'pre-aggregation differentiation' (preD) which appears to favor development of electrophysiologically functional neurons and to lead to an increase in dopaminergic neurons in the ReNcell VM line. In contrast, the protocol used had little effect on the differentiation of ReNcell CX in which dopaminergic differentiation was not observed. Moreover, after a week of differentiation with the preD protocol, 100% of ReNcell VM featured TTX-sensitive Na+-channels and fired action potentials, compared to 25% after stdD. Currents via other voltage-gated channels did not appear to depend on the differentiation protocol. ReNcell CX did not display the same electrophysiological properties as the VM line, generating voltage-dependant K+ currents but no Na+ currents or action potentials under either stdD or preD differentiation. CONCLUSION: These data demonstrate that overexpression of myc in NSCs can be used to generate electrophysiologically active neurons in culture. Development of a functional neuronal phenotype may be dependent on parameters of isolation and differentiation of the cell lines, indicating that not all human NSCs are functionally equivalent.

Enriching the environment of alphaCaMKIIT286A mutant mice reveals that LTD occurs in memory processing but must be subsequently reversed by LTP.

alphaCaMKII(T286A) mutant mice lack long-term potentiation (LTP) in the hippocampal CA1 region and are impaired in spatial learning. In situ hybridization confirms that the mutant mice show the same developmental expression of alphaCaMKII as their wild-type littermates. A simple hypothesis would suggest that if LTP is a substrate for learning, then enriching the environment should cause learning-dependent changes in wild-type mice that have LTP. Such changes would not be seen in LTP-deficient alphaCaMKII(T286A) mutants. Excitatory synaptic currents in CA1 neurons, recorded with patch clamp in brain slices, revealed that enrichment induces an increase in glutamate release probability and a decreased miniature current amplitude. Confocal microscopy also showed dendritic spine density to be reduced. However, contrary to the hypothesis above, these enrichment-induced changes occur only in the mutant mice and are not detectable in wild-type littermates. We suggest that enrichment induces alphaCaMKII-independent changes in both wild-type and mutant mice. Such changes may be subsequently reversed in wild-type animals via alphaCaMKII-dependent mechanisms, such as LTP. Reversal of plasticity has long been hypothesized to be essential for the hippocampus to maintain its role in memory processing. The inability to reverse plasticity in alphaCaMKII(T286A) mutant mice would then result in impairment of spatial learning.

The ducky(2J) mutation in Cacna2d2 results in reduced spontaneous Purkinje cell activity and altered gene expression.

The mouse mutant ducky and its allele ducky(2J) represent a model for absence epilepsy characterized by spike-wave seizures and cerebellar ataxia. These mice have mutations in Cacna2d2, which encodes the alpha2delta-2 calcium channel subunit. Of relevance to the ataxic phenotype, alpha2delta-2 mRNA is strongly expressed in cerebellar Purkinje cells (PCs). The Cacna2d2(du2J) mutation results in a 2 bp deletion in the coding region and a complete loss of alpha2delta-2 protein. Here we show that du(2J)/du(2J) mice have a 30% reduction in somatic calcium current and a marked fall in the spontaneous PC firing rate at 22 degrees C, accompanied by a decrease in firing regularity, which is not affected by blocking synaptic input to PCs. At 34 degrees C, du(2J)/du(2J) PCs show no spontaneous intrinsic activity. Du(2J)/du(2J) mice also have alterations in the cerebellar expression of several genes related to PC function. At postnatal day 21, there is an elevation of tyrosine hydroxylase mRNA and a reduction in tenascin-C gene expression. Although du(2J)/+ mice have a marked reduction in alpha2delta-2 protein, they show no fall in PC somatic calcium currents or increase in cerebellar tyrosine hydroxylase gene expression. However, du(2J)/+ PCs do exhibit a significant reduction in firing rate, correlating with the reduction in alpha2delta-2. A hypothesis for future study is that effects on gene expression occur as a result of a reduction in somatic calcium currents, whereas effects on PC firing occur as a long-term result of loss of alpha2delta-2 and/or a reduction in calcium currents and calcium-dependent processes in regions other than the soma.