bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Spiking Working Memory Model Based on Hebbian Short-Term Potentiation
Authors: Fiebig Florian , Lansner Anders 
Published: November 2016

A dominant theory of working memory (WM), referred to as the persistent activity hypothesis, holds that recurrently connected neural networks, presumably located in the prefrontal cortex, encode and maintain WM memory items through sustained elevated activity. Reexamination of experimental data has shown that prefrontal cortex activity in single units during delay periods is much more variable than predicted by such a theory and associated computational models. Alternative models of WM maintenance based on synaptic plasticity, such as short-term nonassociative (non-Hebbian) synaptic facilitation, have been suggested but cannot account for encoding of novel associations. Here we test the hypothesis that a recently identified fast-expressing form of Hebbian synaptic plasticity (associative short-term potentiation) is a possible mechanism for WM encoding and maintenance. Our simulations using a spiking neural network model of cortex reproduce a range of cognitive memory effects in the classical multi-item WM task of encoding and immediate free recall of word lists. Memory reactivation in the model occurs in discrete oscillatory bursts rather than as sustained activity. We relate dynamic network activity as well as key synaptic characteristics to electrophysiological measurements. Our findings support the hypothesis that fast Hebbian short-term potentiation is a key WM mechanism.SIGNIFICANCE STATEMENTWorking memory (WM) is a key component of cognition. Hypotheses about the neural mechanism behind WM are currently under revision. Reflecting recent findings of fast Hebbian synaptic plasticity in cortex, we test whether a cortical spiking neural network model with such a mechanism can learn a multi-item WM task (word list learning). We show that our model can reproduce human cognitive phenomena and achieve comparable memory performance in both free and cued recall while being simultaneously compatible with experimental data on structure, connectivity, and neurophysiology of the underlying cortical tissue. These findings are directly relevant to the ongoing paradigm shift in the WM field.
Regulatory B Cells Induce Formation of IL-10-Expressing T Cells in Mice with Autoimmune Neuroinflammation
Authors: Pennati Andrea , Ng Spencer , Wu Yuanqiang , Murphy Jordan R. , Deng Jiusheng , Rangaraju Srikant , Asress Seneshaw , Blanchfield Jennifer L. , Evavold Brian , Galipeau Jacques 
Published: November 2016

Although B cells are traditionally known for their role in propagating proinflammatory immune responses, their immunosuppressive effects have only recently begun to be appreciated. How these regulatory B cells (Bregs) suppress the immune response remains to be worked out in detail. In this article, we show that Bregscan induce the formation of conventional FoxP3+regulatory T cells (Tregs), as well as a more recently described CD49b+CD223+regulatory T-cell subset, known as type 1 regulatory T cells (Tr1s). When Bregsare transferred into mice with experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis, they home to the spleen and mesenteric lymph nodes, leading to an expansion of Tregsand Tr1in vivo. Tregsand Tr1s are also found in greater proportions in the CNS of mice with EAE treated with Bregsand are correlated with the remission of symptoms. The discovery that Bregsinduce the formation of regulatory T-cell subsetsin vivomay herald their use as immunosuppressive agents in adoptive cellular therapies for autoimmune pathologies.SIGNIFICANCE STATEMENTAlthough B cells are traditionally known for their role in propagating proinflammatory immune responses, their immunosuppressive effects have only recently begun to be appreciated. How regulatory B cells (Bregs) suppress the immune response remains to be fully understood. In this article, we show that Bregscan induce the formation of conventional regulatory T cells (Tregs) as well as type 1 regulatory T cells (Tr1s). When Bregsare transferred into mice with experimental autoimmune encephalomyelitis (EAE), they home to secondary lymphoid organs, leading to an expansion of Tregsand Tr1sin vivo. Tregsand Tr1s are also found in greater proportions in the CNS of mice with EAE treated with Bregsand are correlated with the remission of symptoms.
Immunotherapy with Aducanumab Restores Calcium Homeostasis in Tg2576 Mice
Authors: Kastanenka Ksenia V. , Bussiere Thierry , Shakerdge Naomi , Qian Fang , Weinreb Paul H. , Rhodes Ken , Bacskai Brian J. 
Published: November 2016

Calcium homeostasis plays a major role in maintaining neuronal function under physiological conditions. Amyloid-β (Aβ) initiates pathological processes that include disruption in intracellular calcium levels, so amelioration of the calcium alteration could serve as an indirect functional indicator of treatment efficacy. Therefore, calcium dynamics were used as a measure of functional outcome. We evaluated the effects of the anti-Aβ antibody aducanumab on calcium homeostasis and plaque clearance in aged Tg2576 mice within vivomultiphoton imaging. Acute topical application of aducanumab to the brain resulted in clearance of amyloid plaques. Although chronic systemic administration of aducanumab in 22-month-old mice did not clear existing plaques, calcium overload was ameliorated over time. Therefore, this antibody likely restores neuronal network function that possibly underlies cognitive deficits, indicating promise as a clinical treatment. In addition, functional readouts such as calcium overload may be a more useful outcome measure to monitor treatment efficacy in models of Alzheimer's disease compared with amyloid burden alone.SIGNIFICANCE STATEMENTAlzheimer's disease (AD) is a progressive neurodegenerative disorder that is currently without a cure. Aducanumab is an anti-amyloid-β antibody being developed for the treatment of AD. Interim analyses of a phase 1b clinical trial have suggested potential beneficial effects on amyloid pathology and cognitive status in patients treated with aducanumab (Sevigny et al., 2016). Here, we show that a murine analog of aducanumab clears amyloid plaques in an acute setting and restores calcium homeostasis disrupted in a mouse model of AD upon chronic treatment. Therefore, we demonstrate that aducanumab reverses a functional outcome measure reflective of neural network activity.
The Effects of Peripheral and Central High Insulin on Brain Insulin Signaling and Amyloid-β in Young and Old APP/PS1 Mice
Authors: Stanley Molly , Macauley Shannon L. , Caesar Emily E. , Koscal Lauren J. , Moritz Will , Robinson Grace O. , Roh Joseph , Keyser Jennifer , Jiang Hong , Holtzman David M. 
Published: November 2016

Hyperinsulinemia is a risk factor for late-onset Alzheimer's disease (AD).In vitroexperiments describe potential connections between insulin, insulin signaling, and amyloid-β (Aβ), butin vivoexperiments are needed to validate these relationships under physiological conditions. First, we performed hyperinsulinemic-euglycemic clamps with concurrent hippocampal microdialysis in young, awake, behavingAPPswe/PS1dE9transgenic mice. Both a postprandial and supraphysiological insulin clamp significantly increased interstitial fluid (ISF) and plasma Aβ compared with controls. We could detect no increase in brain, ISF, or CSF insulin or brain insulin signaling in response to peripheral hyperinsulinemia, despite detecting increased signaling in the muscle. Next, we delivered insulin directly into the hippocampus of youngAPP/PS1mice via reverse microdialysis. Brain tissue insulin and insulin signaling was dose-dependently increased, but ISF Aβ was unchanged by central insulin administration. Finally, to determine whether peripheral and central high insulin has differential effects in the presence of significant amyloid pathology, we repeated these experiments in olderAPP/PS1mice with significant amyloid plaque burden. Postprandial insulin clamps increased ISF and plasma Aβ, whereas direct delivery of insulin to the hippocampus significantly increased tissue insulin and insulin signaling, with no effect on Aβ in old mice. These results suggest that the brain is still responsive to insulin in the presence of amyloid pathology but increased insulin signaling does not acutely modulate Aβin vivobefore or after the onset of amyloid pathology. Peripheral hyperinsulinemia modestly increases ISF and plasma Aβ in young and old mice, independent of neuronal insulin signaling.SIGNIFICANCE STATEMENTThe transportation of insulin from blood to brain is a saturable process relevant to understanding the link between hyperinsulinemia and AD.In vitroexperiments have found direct connections between high insulin and extracellular Aβ, but these mechanisms presume that peripheral high insulin elevates brain insulin significantly. We found that physiological hyperinsulinemia in awake, behaving mice does not increase CNS insulin to an appreciable level yet modestly increases extracellular Aβ. We also found that the brain of agedAPP/PS1mice was not insulin resistant, contrary to the current state of the literature. These results further elucidate the relationship between insulin, the brain, and AD and its conflicting roles as both a risk factor and potential treatment.
Distinct Regions within Medial Prefrontal Cortex Process Pain and Cognition
Authors: Jahn Andrew , Nee Derek Evan , Alexander William H. , Brown Joshua W. 
Published: November 2016

Neuroimaging studies of the medial prefrontal cortex (mPFC) suggest that the dorsal anterior cingulate cortex (dACC) region is responsive to a wide variety of stimuli and psychological states, such as pain, cognitive control, and prediction error (PE). In contrast, a recent meta-analysis argues that the dACC is selective for pain, whereas the supplementary motor area (SMA) and pre-SMA are specifically associated with higher-level cognitive processes (Lieberman and Eisenberger, 2015). To empirically test this claim, we manipulated effects of pain, conflict, and PE in a single experiment using human subjects. We observed a robust dorsal-ventral dissociation within the mPFC with cognitive effects of PE and conflict overlapping dorsally and pain localized more ventrally. Classification of subjects based on the presence or absence of a paracingulate sulcus showed that PE effects extended across the dorsal area of the dACC and into the pre-SMA. These results begin to resolve recent controversies by showing the following: (1) the mPFC includes dissociable regions for pain and cognitive processing; and (2) meta-analyses are correct in localizing cognitive effects to the dACC, although these effects extend to the pre-SMA as well. These results both provide evidence distinguishing between different theories of mPFC function and highlight the importance of taking individual anatomical variability into account when conducting empirical studies of the mPFC.SIGNIFICANCE STATEMENTDecades of neuroimaging research have shown the mPFC to represent a wide variety of stimulus processing and cognitive states. However, recently it has been argued whether distinct regions of the mPFC separately process pain and cognitive phenomena. To address this controversy, this study directly compared pain and cognitive processes within subjects. We found a double dissociation within the mPFC with pain localized ventral to the cingulate sulcus and cognitive effects localized more dorsally within the dACC and spreading into the pre-supplementary motor area. This provides empirical evidence to help resolve the current debate about the functional architecture of the mPFC.
Activity Induces Fmr1-Sensitive Synaptic Capture of Anterograde Circulating Neuropeptide Vesicles
Authors: Cavolo Samantha L. , Bulgari Dinara , Deitcher David L. , Levitan Edwin S. 
Published: November 2016

Synaptic neuropeptide and neurotrophin stores are maintained by constitutive bidirectional capture of dense-core vesicles (DCVs) as they circulate in and out of the nerve terminal. Activity increases DCV capture to rapidly replenish synaptic neuropeptide stores following release. However, it is not known whether this is due to enhanced bidirectional capture. Here experiments at theDrosophilaneuromuscular junction, where DCVs contain neuropeptides and a bone morphogenic protein, show that activity-dependent replenishment of synaptic neuropeptides following release is evident after inhibiting the retrograde transport with the dynactin disruptor mycalolide B or photobleaching DCVs entering a synaptic bouton by retrograde transport. In contrast, photobleaching anterograde transport vesicles entering a bouton inhibits neuropeptide replenishment after activity. Furthermore, tracking of individual DCVs moving through boutons shows that activity selectively increases capture of DCVs undergoing anterograde transport. Finally, upregulating fragile X mental retardation 1 protein (Fmr1, also called FMRP) acts independently of futsch/MAP-1B to abolish activity-dependent, but not constitutive, capture. Fmr1 also reduces presynaptic neuropeptide stores without affecting activity-independent delivery and evoked release. Therefore, presynaptic motoneuron neuropeptide storage is increased by a vesicle capture mechanism that is distinguished from constitutive bidirectional capture by activity dependence, anterograde selectivity, and Fmr1 sensitivity. These results show that activity recruits a separate mechanism than used at rest to stimulate additional synaptic capture of DCVs for future release of neuropeptides and neurotrophins.SIGNIFICANCE STATEMENTSynaptic release of neuropeptides and neurotrophins depends on presynaptic accumulation of dense-core vesicles (DCVs). At rest, DCVs are captured bidirectionally as they circulate throughDrosophilamotoneuron terminals by anterograde and retrograde transport. Here we show that activity stimulates further synaptic capture that is distinguished from basal capture by its selectivity for anterograde DCVs and its inhibition by overexpression of the fragile X retardation protein Fmr1. Fmr1 dramatically lowers DCV numbers in synaptic boutons. Therefore, activity-dependent anterograde capture is a major determinant of presynaptic peptide stores.
Functional Synaptic Integration of Forebrain GABAergic Precursors into the Adult Spinal Cord
Authors: Etlin Alex , Bráz Joao M. , Kuhn Julia A. , Wang Xidao , Hamel Katherine A. , Llewellyn-Smith Ida J. , Basbaum Allan I. 
Published: November 2016

Spinal cord transplants of embryonic cortical GABAergic progenitor cells derived from the medial ganglionic eminence (MGE) can reverse mechanical hypersensitivity in the mouse models of peripheral nerve injury- and paclitaxel-induced neuropathic pain. Here, we used electrophysiology, immunohistochemistry, and electron microscopy to examine the extent to which MGE cells integrate into host circuitry and recapitulate endogenous inhibitory circuits. Whether the transplants were performed before or after nerve injury, the MGE cells developed into mature neurons and exhibited firing patterns characteristic of subpopulations of cortical and spinal cord inhibitory interneurons. Conversely, the transplanted cells preserved cortical morphological and neurochemical properties. We also observed a robust anatomical and functional synaptic integration of the transplanted cells into host circuitry in both injured and uninjured animals. The MGE cells were activated by primary afferents, including TRPV1-expressing nociceptors, and formed GABAergic, bicuculline-sensitive, synapses onto host neurons. Unexpectedly, MGE cells transplanted before injury prevented the development of mechanical hypersensitivity. Together, our findings provide direct confirmation of an extensive, functional synaptic integration of MGE cells into host spinal cord circuits. This integration underlies normalization of the dorsal horn inhibitory tone after injury and may be responsible for the prophylactic effect of preinjury transplants.SIGNIFICANCE STATEMENTSpinal cord transplants of embryonic cortical GABAergic interneuron progenitors from the medial ganglionic eminence (MGE), can overcome the mechanical hypersensitivity produced in different neuropathic pain models in adult mice. Here, we examined the properties of transplanted MGE cells and the extent to which they integrate into spinal cord circuitry. Using electrophysiology, immunohistochemistry, and electron microscopy, we demonstrate that MGE cells, whether transplanted before or after nerve injury, develop into inhibitory neurons, are activated by nociceptive primary afferents, and form GABA-A-mediated inhibitory synapses with the host. Unexpectedly, cells transplanted into naive spinal cord prevented the development of nerve-injury-induced mechanical hypersensitivity. These results illustrate the remarkable plasticity of adult spinal cord and the potential of cell-based therapies against neuropathic pain.
Tau Isoforms Imbalance Impairs the Axonal Transport of the Amyloid Precursor Protein in Human Neurons
Authors: Lacovich Valentina , Espindola Sonia L. , Alloatti Matías , Pozo Devoto Victorio , Cromberg Lucas E. , Čarná Mária E. , Forte Giancarlo , Gallo Jean-Marc , Bruno Luciana , Stokin Gorazd B. , Avale M. Elena , Falzone Tomás L. 
Published: November 2016

Tau, as a microtubule (MT)-associated protein, participates in key neuronal functions such as the regulation of MT dynamics, axonal transport, and neurite outgrowth. Alternative splicing of exon 10 in the tau primary transcript gives rise to protein isoforms with three (3R) or four (4R) MT binding repeats. Although tau isoforms are balanced in the normal adult human brain, imbalances in 3R:4R ratio have been tightly associated with the pathogenesis of several neurodegenerative disorders, yet the underlying molecular mechanisms remain elusive. Several studies exploiting tau overexpression and/or mutations suggested that perturbations in tau metabolism impair axonal transport. Nevertheless, no physiological model has yet demonstrated the consequences of altering the endogenous relative content of tau isoforms over axonal transport regulation. Here, we addressed this issue using atrans-splicing strategy that allows modulating tau exon 10 inclusion/exclusion in differentiated human-derived neurons. Upon changes in 3R:4R tau relative content, neurons showed no morphological changes, but live imaging studies revealed that the dynamics of the amyloid precursor protein (APP) were significantly impaired. Single trajectory analyses of the moving vesicles showed that predominance of 3R tau favored the anterograde movement of APP vesicles, increasing anterograde run lengths and reducing retrograde runs and segmental velocities. Conversely, the imbalance toward the 4R isoform promoted a retrograde bias by a significant reduction of anterograde velocities. These findings suggest that changes in 3R:4R tau ratio has an impact on the regulation of axonal transport and specifically in APP dynamics, which might link tau isoform imbalances with APP abnormal metabolism in neurodegenerative processes.SIGNIFICANCE STATEMENTThe tau protein has a relevant role in the transport of cargos throughout neurons. Dysfunction in tau metabolism underlies several neurological disorders leading to dementia. In the adult human brain, two tau isoforms are found in equal amounts, whereas changes in such equilibrium have been associated with neurodegenerative diseases. We investigated the role of tau in human neurons in culture and found that perturbations in the endogenous balance of tau isoforms were sufficient to impair the transport of the Alzheimer's disease-related amyloid precursor protein (APP), although neuronal morphology was normal. Our results provide evidence of a direct relationship between tau isoform imbalance and defects in axonal transport, which induce an abnormal APP metabolism with important implications in neurodegeneration.
NR2A-Containing NMDARs in the Prefrontal Cortex Are Required for Working Memory and Associated with Age-Related Cognitive Decline
Authors: McQuail Joseph A. , Beas B. Sofia , Kelly Kyle B. , Simpson Kailey L. , Frazier Charles J. , Setlow Barry , Bizon Jennifer L. 
Published: November 2016

Working memory, the ability to temporarily maintain representational knowledge, is a foundational cognitive process that can become compromised in aging and neuropsychiatric disease. NMDA receptor (NMDAR) activation in prefrontal cortex (PFC) is necessary for the pyramidal neuron activity believed to enable working memory; however, the distinct biophysical properties and localization of NMDARs containing NR2A and NR2B subunits suggest unique roles for NMDAR subtypes in PFC neural activity and working memory. Experiments herein show that working memory depends on NR2A- but not NR2B-NMDARs in PFC of rats and that NR2A-NMDARs mediate the majority of evoked NMDAR currents on layer 2/3 PFC pyramidal neurons. Moreover, attenuated expression of the NR2A but not the NR2B subunit in PFC associates with naturally occurring working memory impairment in aged rats. Finally, NMDAR currents and working memory are enhanced in aged rats by promoting activation of the NR2A-enriched synaptic pool of PFC NMDARs. These results implicate NR2A-NMDARs in normal working memory and suggest novel treatment strategies for improving working memory in cognitive disorders.SIGNIFICANCE STATEMENTWorking memory, the ability to hold information “in mind,” requires persistent activity of pyramidal neurons in prefrontal cortex (PFC) mediated by NMDA receptor (NMDAR) activation. NMDAR loss in PFC may account for working memory impairments in aging and psychiatric disease. Our studies demonstrate that NMDARs containing the NR2A subunit, but not the NR2B subunit, are required for working memory and that loss of NR2A predicts severity of age-related working memory impairment. The importance of NR2A to working memory is likely due its abundant contribution to pyramidal neuron activity and location at synaptic sites in PFC. This information is useful in designing new therapies to treat working memory impairments by enhancing the function of NR2A-containing NMDARs.