Neuroscience Center at Dartmouth

Dartmouth, Lebanon

Neuroscience Center at Dartmouth

Dartmouth, Lebanon
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Jacobs V.L.,Neuroscience Center at Dartmouth | De Leo J.A.,Neuroscience Center at Dartmouth | De Leo J.A.,Emmanuel College at Boston
Journal of Neuro-Oncology | Year: 2013

Glioblastoma multiform is one of the most common and aggressive primary brain tumors in adults. High glutamate levels are thought to contribute to glioma growth. While research has focused on understanding glutamate signaling in glioma cells, little is known about the role of glutamate between glioma and astrocyte interactions. To study the relationship between astrocytes and tumor cells, the CNS-1 rodent glioma cell line was used. We hypothesized increased glutamate uptake by astrocytes would negatively affect CNS-1 cell growth. Primary rodent astrocytes and CNS-1 cells were co-cultured for 7 days in a Boyden chamber in the presence of 5 mM glutamate. Cells were treated with propentofylline, an atypical synthetic methylxanthine known to increase glutamate transporter expression in astrocytes. Our results indicate astrocytes can increase glutamate uptake through the GLT-1 transporter, leading to less glutamate available for CNS-1 cells, ultimately resulting in increased CNS-1 cell apoptosis. These data suggest that astrocytes in the tumor microenvironment can be targeted by the drug, propentofylline, affecting tumor cell growth. © 2013 Springer Science+Business Media New York.

Jacobs V.L.,Neuroscience Center at Dartmouth | de Leo J.A.,Neuroscience Center at Dartmouth | de Leo J.A.,Emmanuel College at Boston
PLoS ONE | Year: 2012

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain cancer, with a median survival of less than 2 years after diagnosis with current available therapies. The tumor microenvironment serves a critical role in tumor invasion and progression, with microglia as a critical player. Our laboratory has previously demonstrated that propentofylline, an atypical methylxanthine with central nervous system glial modulating and anti-inflammatory actions, significantly decreases tumor growth in a GBM rodent model by preferentially targeting microglia. In the present study, we used the CNS-1 rat glioma model to elucidate the mechanisms of propentofylline. Here we demonstrate that propentofylline targets TROY, a novel signaling molecule up-regulated in infiltrating microglia, and not macrophages, in response to CNS-1 cells. We identify Pyk2, Rac1 and pJNK as the downstream signaling molecules of TROY through western blot analysis and siRNA transfection. We demonstrate that inhibition of TROY expression in microglia by siRNA transfection significantly inhibits microglial migration towards CNS-1 cells similar to 10 μM propentofylline treatment. These results identify TROY as a novel molecule expressed in microglia, involved in their migration and targeted by propentofylline. Furthermore, these results describe a signaling molecule that is differentially expressed between microglia and macrophages in the tumor microenvironment. © 2012 Jacobs et al.

Jacobs V.L.,Dartmouth College | Valdes P.A.,Dartmouth College | de Leo J.A.,Neuroscience Center at Dartmouth | de Leo J.A.,Dartmouth Hitchcock Medical Center
ASN Neuro | Year: 2011

GBM (glioblastoma multiforme) is a highly aggressive brain tumour with very poor prognosis despite multi-modalities of treatment. Furthermore, recent failure of targeted therapy for these tumours highlights the need of appropriate rodent models for preclinical studies. In this review, we highlight the most commonly used rodent models (U251, U86, GL261, C6, 9L and CNS-1) with a focus on the pathological and genetic similarities to the human disease. We end with a comprehensive review of the CNS-1 rodent model. © 2011 The Author(s).

Horvath R.J.,Neuroscience Center at Dartmouth | Romero-Sandoval E.A.,Neuroscience Center at Dartmouth | Romero-Sandoval E.A.,Dartmouth Hitchcock Medical Center | Leo J.A.D.,Neuroscience Center at Dartmouth | Leo J.A.D.,Dartmouth Hitchcock Medical Center
Pain | Year: 2010

Anti-nociceptive tolerance to opioids is a well-described phenomenon, which severely limits the clinical efficacy of opioids for the treatment of chronic pain syndromes. The mechanisms that drive anti-nociceptive tolerance, however, are less well understood. We have previously shown that glia have a central role in the development of morphine tolerance and that administration of a glial modulating agent attenuated tolerance formation. Recently, we have demonstrated that morphine enhances microglial Iba1 expression and P2X4 receptor-mediated microglial migration via direct μ opioid receptor signaling in in vitro microglial cultures. We hypothesize that P2X4 receptors drive morphine tolerance and modulate morphine-induced spinal glial reactivity. Additionally, we hypothesize that perivascular microglia play a role in morphine tolerance and that P2X4 receptor expression regulates perivascular microglia ED2 expression. To test these hypotheses, rats were implanted with osmotic minipumps releasing morphine or saline subcutaneously for seven days. Beginning three days prior to morphine treatment, P2X4 receptor antisense oligonucleotide (asODN) was injected intrathecally daily, to selectively inhibit P2X4 receptor expression. P2X4 receptor asODN treatment inhibited morphine-induced P2X4 receptor expression and blocked anti-nociceptive tolerance to systemically administered morphine. P2X4 receptor asODN treatment also attenuated the morphine-dependent increase of spinal ionized calcium binding protein (Iba1), glial fibrillary acidic protein (GFAP) and μ opioid receptor protein expression. Chronic morphine also decreased perivascular microglial ED2 expression, which was reversed by P2X4 receptor asODN. Together, these data suggest that the modulation of P2X4 receptor expression on microglia and perivascular microglia may prove an attractive target for adjuvant therapy to attenuate opioid-induced anti-nociceptive tolerance. © 2010 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

Isaeva E.,Neuroscience Center at Dartmouth | Isaeva E.,Bogomoletz Institute of Physiology | Hernan A.,Neuroscience Center at Dartmouth | Isaev D.,Neuroscience Center at Dartmouth | And 2 more authors.
Annals of Neurology | Year: 2012

Objective: An epileptic seizure is frequently the presenting sign of intracerebral hemorrhage (ICH) caused by stroke, head trauma, hypertension, and a wide spectrum of disorders. However, the cellular mechanisms responsible for occurrence of seizures during ICH have not been established. During intracerebral bleeding, blood constituents enter the neuronal tissue and produce both an acute and a delayed effect on brain functioning. Among the blood components, only thrombin has been shown to evoke seizures immediately after entering brain tissue. In the present study, we tested the hypothesis that thrombin increases neuronal excitability in the immature brain through alteration of voltage-gated sodium channels. Methods: The thrombin effect on neuronal excitability and voltage-gated sodium channels was assessed using extracellular and intracellular recording techniques in the hippocampal slice preparation of immature rats. Results: We show that thrombin increased neuronal excitability in the immature hippocampus in an N-methyl-D-aspartate-independent manner. Application of thrombin did not alter transient voltage-gated sodium channels and action potential threshold. However, thrombin significantly depolarized the membrane potential and produced a hyperpolarizing shift of tetrodotoxin-sensitive persistent voltage-gated sodium channel activation. This effect of thrombin was attenuated by application of protease-activated receptor-1 and protein kinase C antagonists. Interpretation: Our data indicate that thrombin amplifies the persistent voltage-gated sodium current affecting resting membrane potential and seizure threshold at the network level. Our results provide a novel explanation as to how ICH in newborns results in seizures, which may provide avenues for therapeutic intervention in the prevention of post-ICH seizures. Copyright © 2012 American Neurological Association.

Holmes G.L.,Neuroscience Center at Dartmouth
Epilepsia | Year: 2013

Cognitive impairment is a common and often devastating comorbidity of pharmacoresistent epilepsy. The cognitive comorbidity can be both chronic, primarily due to the underlying etiology of the epilepsy, and dynamic or evolving because of recurrent seizures or interictal spikes. There is now considerable evidence that interictal spikes can contribute to cognitive impairment. Interictal spikes in both rodents and humans result in transient impairment of memory retrieval, whereas in immature animals, interictal spikes can result in long-term adverse effects on brain development. Interictal spikes therefore contribute to the cognitive impairment in the pharmacoresistant epilepsies. Effective treatment of pharmacoresistant epilepsy needs to target not only the overt seizures but interictal electroencephalography (EEG) abnormalities as well. Wiley Periodicals, Inc. © 2013 International League Against Epilepsy.

Kulandaivel K.,Neuroscience Center at Dartmouth | Holmes G.L.,Neuroscience Center at Dartmouth
Epilepsy and Behavior | Year: 2011

There is increasing evidence that there is a strong relationship between brain oscillations and neurocognitive function. We used EEG power spectral analysis to determine if frequency and power provide an independent measure of developmental impairment in infants. We examined the spectral power of EEGs in 200 infants between 6 and 24. months of age who were evaluated for seizures. Infants were stratified into three age groups 6-12, 12-18, and 18-24. months, and development assessments were coded as normal, moderately delayed, and severely delayed. Compared with the normal infants, children with developmental delay had lower mean frequencies and greater delta and less theta and alpha power. Delta/theta and theta/alpha ratios were highly significant indicators of developmental status. This study demonstrates that frequency and power of brain oscillations during wakefulness is a strong predictor of development in infants. The findings support the concept that normal oscillatory activity is critical for normal cognitive function during development. © 2011 Elsevier Inc.

Bender A.C.,Neuroscience Center at Dartmouth | Morse R.P.,Neuroscience Center at Dartmouth | Morse R.P.,Childrens Hospital at Dartmouth | Scott R.C.,Neuroscience Center at Dartmouth | And 4 more authors.
Epilepsy and Behavior | Year: 2012

Dravet syndrome (DS) is a childhood disorder associated with loss-of-function mutations in SCN1A and is characterized by frequent seizures and severe cognitive impairment. Animal studies have revealed new insights into the mechanisms by which mutations in this gene, encoding the type I voltage-gated sodium channel (Na v1.1), may lead to seizure activity and cognitive dysfunction. In this review, we further consider the function of fast-spiking GABAergic neurons, one cell type particularly affected by these mutations, in the context of the temporal coordination of neural activity subserving cognitive functions. We hypothesize that disruptions in GABAergic firing may directly contribute to the poor cognitive outcomes in children with DS, and discuss the therapeutic implications of this possibility. © 2011 Elsevier Inc.

Isaeva E.,Neuroscience Center at Dartmouth | Isaeva E.,Bogomoletz Institute of Physiology | Isaev D.,Neuroscience Center at Dartmouth | Isaev D.,Bogomoletz Institute of Physiology | And 3 more authors.
European Journal of Neuroscience | Year: 2010

Neonatal seizures are associated with a high likelihood of adverse neurological outcomes, including mental retardation, behavioral disorders, and epilepsy. Early seizures typically involve the neocortex, and post-neonatal epilepsy is often of neocortical origin. However, our understanding of the consequences of neonatal seizures for neocortical function is limited. In the present study, we show that neonatal seizures induced by flurothyl result in markedly enhanced susceptibility of the neocortex to seizure-like activity. This change occurs in young rats studied weeks after the last induced seizure and in adult rats studied months after the initial seizures. Neonatal seizures resulted in reductions in the amplitude of spontaneous inhibitory postsynaptic currents and the frequency of miniature inhibitory postsynaptic currents, and significant increases in the amplitude and frequency of spontaneous excitatory postsynaptic currents (sEPSCs) and in the frequency of miniature excitatory postsynaptic currents (mEPSCs) in pyramidal cells of layer 2/3 of the somatosensory cortex. The selective N-methyl-d-aspartate (NMDA) receptor antagonist d-2-amino-5-phosphonovalerate eliminated the differences in amplitude and frequency of sEPSCs and mEPSCs in the control and flurothyl groups, suggesting that NMDA receptors contribute significantly to the enhanced excitability seen in slices from rats that experienced recurrent neonatal seizures. Taken together, our results suggest that recurrent seizures in infancy result in a persistent enhancement of neocortical excitability. © Federation of European Neuroscience Societies and Blackwell Publishing Ltd.

Kleen J.K.,Neuroscience Center at Dartmouth | Scott R.C.,Neuroscience Center at Dartmouth | Scott R.C.,University College London | Holmes G.L.,Neuroscience Center at Dartmouth | Lenck-Santini P.P.,Neuroscience Center at Dartmouth
Annals of Neurology | Year: 2010

Objective: Cognitive impairment is common in epilepsy, particularly in memory function. Interictal spikes (IISs) are thought to disrupt cognition, but it is difficult to delineate their contribution from general impairments in memory produced by etiology and seizures. We investigated the transient impact of focal IISs on the hippocampus, a structure crucial for learning and memory and yet highly prone to IISs in temporal lobe epilepsy (TLE). Methods: Bilateral hippocampal depth electrodes were implanted into 14 Sprague-Dawley rats, followed by intrahippocampal pilocarpine or saline infusion unilaterally. Rats that developed chronic spikes were trained in a hippocampal-dependent operant behavior task, delayed-match-to-sample. Depth-electroencephalogram (EEG) was recorded during 5,562 trials among five rats, and within-subject analyses evaluated the impact of hippocampal spikes on short-term memory operations. Results: Hippocampal spikes that occurred during memory retrieval strongly impaired performance (p < 0.001). However, spikes that occurred during memory encoding or memory maintenance did not affect performance in those trials. Hippocampal spikes also affected response latency, adding approximately 0.48 seconds to the time taken to respond (p < 0.001). Interpretation: We found that focal IIS-related interference in cognition extends to structures in the limbic system, which required intrahippocampal recordings. Hippocampal spikes seem most harmful if they occur when hippocampal function is critical, extending human studies showing that cortical spikes are most disruptive during active cortical functioning. The cumulative effects of spikes could therefore impact general cognitive functioning. These results strengthen the argument that suppression of IISs may improve memory and cognitive performance in patients with epilepsy. © 2010 American Neurological Association.

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