Neuronal Synaptic Activity Research Articles

Supporting evidence for using perispinal etanercept to inhibit TNFα when treating neuropathologies including dementia, chronic stroke, neuropathic pain or traumatic brain injury: Clinical outcomes and role of TNF in neuropathologies other than Alzheimer’s Dementia (Part III)

Part III examines the evidence for the involvement of the pro-inflammatory cytokine, Tumour Necrosis Factoralpha (TNFα) in neuropathologies other than Alzheimer’s Dementia (AD), and for using an anti-TNF therapy, Etanercept (ENBREL), to target and treat these health problems, including chronic stroke, neuropathic pain or traumatic brain injury (TBI). All of these can become chronic illnesses and are of major incidence with a grossly unmet need to improve their treatment. The three-part review presents the overwhelming scientific and medical basis as to why research studies and more trials to evaluate the use of the perispinally administered anti-TNFα drug, Etanercept, are justified to allow it to become a front-line standard therapy. Part I established the role of TNFα as a direct regulator of neuronal synaptic activity. It is in this context, as detailed below, that targeting TNF in the brain holds major significance, not only for treating the dementias, but also its great benefits in reducing long term pain during rehabilitation from TBI or chronic stroke. Given the increasing numbers of families afflicted with Alzheimer’s disease, chronic stroke, neuropathic pain or TBI, clinical studies are now imperative to improve the treatment of these life-threatening and debilitating illnesses.

Neurophysiological evidence for the presence of cannabinoid CB1 receptors in the laterodorsal tegmental nucleus.

Marijuana, which acts within the endocannabinoid (eCB) system as an agonist of the cannabinoid type1 receptor (CB1R), exhibits addictive properties and has powerful actions on the state of arousal of an organism. The laterodorsal tegmental nucleus (LDT), as a component of the reticular activating system, is involved in cortical activation and is important in the development of drug addiction-associated behaviours. Therefore, eCBs might exert behavioural effects by actions on the LDT; however, it is unknown whether eCBs have actions on neurons in this nucleus. Accordingly, whole-cell voltage- and current-clamp recordings were conducted from mouse brain slices, and responses of LDT neurons to the CB1R agonist WIN-2 were monitored. Our results showed that WIN-2 decreased the frequency of spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs). Ongoing activity of endogenous eCBs was confirmed as AM251, a potent CB1R antagonist, elicited sIPSCs. WIN-2 reduced the firing frequency of LDT neurons. In addition, our RT-PCR studies confirmed the presence of CB1R transcript in the LDT. Taken together, we conclude that CB1Rs are functionally active in the LDT, and their activation changes the firing frequency and synaptic activity of neurons in this nucleus. Therefore, endogenous eCB transmission could play a role in processes involving the LDT, such as cortical activation and motivated behaviours and, further, behavioural actions of marijuana are probably mediated, in part, via cellular actions within the LDT induced by this addictive and behavioural state-altering drug.

Phosphorylation of Cyclin-dependent Kinase 5 (Cdk5) at Tyr-15 Is Inhibited by Cdk5 Activators and Does Not Contribute to the Activation of Cdk5

Cdk5 is a member of the cyclin-dependent kinase (Cdk) family. In contrast to other Cdks that promote cell proliferation, Cdk5 plays a role in regulating various neuronal functions, including neuronal migration, synaptic activity, and neuron death. Cdks responsible for cell proliferation need phosphorylation in the activation loop for activation in addition to binding a regulatory subunit cyclin. Cdk5, however, is activated only by binding to its activator, p35 or p39. Furthermore, in contrast to Cdk1 and Cdk2, which are inhibited by phosphorylation at Tyr-15, the kinase activity of Cdk5 is reported to be stimulated when phosphorylated at Tyr-15 by Src family kinases or receptor-type tyrosine kinases. We investigated the activation mechanism of Cdk5 by phosphorylation at Tyr-15. Unexpectedly, however, it was found that Tyr-15 phosphorylation occurred only on monomeric Cdk5, and the coexpression of activators, p35/p25, p39, or Cyclin I, inhibited the phosphorylation. In neuron cultures, too, the activation of Fyn tyrosine kinase did not increase Tyr-15 phosphorylation of Cdk5. Further, phospho-Cdk5 at Tyr-15 was not detected in the p35-bound Cdk5. In contrast, expression of active Fyn increased p35 in neurons. These results indicate that phosphorylation at Tyr-15 is not an activation mechanism of Cdk5 but, rather, indicate that tyrosine kinases could activate Cdk5 by increasing the protein amount of p35. These results call for reinvestigation of how Cdk5 is regulated downstream of Src family kinases or receptor tyrosine kinases in neurons, which is an important signaling cascade in a variety of neuronal activities.

Projection target‐specific action of nicotine in the caudal nucleus of the solitary tract

The brainstem nucleus of the solitary tract (NTS) is the key integrating relay in the central processing of sensory information from the thoracic and from most subdiaphragmatic viscera. Modulation of neuronal excitability and synaptic activity in the NTS by nicotinic agents can have potent effects on vital physiological functions, such as feeding, digestion, respiration, and blood circulation. Caudal NTS neurons demonstrate considerable heterogeneity in projection targets, synaptic properties, and expression of nicotinic acetylcholine receptors (nAChRs). However, despite its heterogeneity, the caudal NTS may contain discrete subsets of neurons with unique projection target-specific properties. To test this hypothesis, we used in vivo fluorescent tracing and ex vivo patch-clamp electrophysiology to evaluate responsiveness to nicotine of anatomically identified caudal NTS neurons that project to the hypothalamic paraventricular nucleus (PVN) and the brainstem caudal ventrolateral medulla (CVLM). The results of this study demonstrate that responsiveness to nicotine correlates with where the neurons project. Specifically, PVN-projecting caudal NTS neurons respond to nicotine only presynaptically (i.e., via activation of presynaptic nAChRs and potentiation of synaptic release of glutamate), suggesting indirect, glutamate-dependent effects of nicotine on the PVN-projecting NTS circuitry. By contrast, CVLM-projecting caudal NTS neurons exhibit only limited presynaptic, but dominant somatodendritic, responsiveness to nicotine, suggesting that the effects of nicotine on the CVLM-projecting NTS circuitry are direct and largely glutamate independent. Understanding the relationships among function-specific brainstem/hypothalamic neuronal networks, nuclei, and individual neurons could help develop therapies targeting identifiable neuronal circuits to offset impaired autonomic homeostasis.

Stoichiometry and specific assembly of Best ion channels.

Human Bestrophin 1 (hBest1) is a calcium-activated chloride channel that regulates neuronal excitability, synaptic activity, and retinal homeostasis. Mutations in hBest1 cause the autosomal-dominant Best macular dystrophy (BMD). Because hBest1 mutations cause BMD, but a knockout does not, we wondered if hBest1 mutants exert a dominant negative effect through interaction with other calcium-activated chloride channels, such as hBest2, 3, or 4, or transmembrane member 16A (TMEM16A), a member of another channel family. The subunit architecture of Best channels is debated, and their ability to form heteromeric channel assemblies is unclear. Using single-molecule subunit analysis, we find that each of hBest1, 2, 3, and 4 forms a homotetrameric channel. Despite considerable conservation among hBests, hBest1 has little or no interaction with other hBests or mTMEM16A. We identify the domain responsible for assembly specificity. This domain also plays a role in channel function. Our results indicate that Best channels preferentially self-assemble into homotetramers.

Persistent Pain Facilitates Response to Morphine Reward by Downregulation of Central Amygdala GABAergic Function

Opioid-based analgesics are widely used for treating chronic pain, but opioids are highly addictive when repeatedly used because of their strong rewarding effects. In recent years, abuse of prescription opioids has dramatically increased, including incidences of misuse of opioid drugs prescribed for pain control. Despite this issue in current clinical pain management, it remains unknown how pain influences the abuse liability of prescription opioids. Pain as aversive experience may affect opioid reward of positive emotion through common brain sites involved in emotion processing. In this study, on a rat model of chronic pain, we determined how persistent pain altered behavioral responses to morphine reward measured by the paradigm of unbiased conditioned place preference (CPP), focusing on GABAergic synaptic activity in neurons of the central nucleus of the amygdala (CeA), an important brain region for emotional processing of both pain and reward. We found that pain reduced the minimum number of morphine-conditioning sessions required for inducing CPP behavior. Both pain and morphine conditioning that elicited CPP inhibited GABA synaptic transmission in CeA neurons. Pharmacological activation of CeA GABAA receptors reduced the pain and inhibited CPP induced both by an effective dose of morphine and by a sub-threshold dose of morphine under pain condition. Furthermore, inhibition of CeA GABAA receptors mimicked the pain effect, rendering the sub-threshold dose of morphine effective in CPP induction. These findings suggest that pain facilitates behavioral responses to morphine reward by predisposing the inhibitory GABA function in the CeA circuitry involved in the behavior of opioid reward.

Downregulation of Homer1b/c improves neuronal survival after traumatic neuronal injury

Homer protein, a member of the post-synaptic density protein family, plays an important role in the neuronal synaptic activity and is extensively involved in neurological disorders. The present study investigates the role of Homer1b/c in modulating neuronal survival by using an in vitro traumatic neuronal injury model, which was achieved by using a punch device that consisted of 28 stainless steel blades joined together and produced 28 parallel cuts. Downregulation of Homer1b/c by specific siRNA significantly (p<0.05) alleviated the cytoplasmic calcium levels and neuron lactate dehydrogenase release, and ultimately decreased the apoptotic rate after traumatic neuronal injury compared with non-targeting siRNA control treatment in cultured rat cortical neurons. Moreover, the expression of metabotropic glutamate receptor 1a (mGluR1a) was significantly (p<0.05) reduced in the Homer1b/c siRNA-transfected neurons after injury. Therefore, Homer1b/c not only modulated the mGluR1a-inositol 1,4,5-triphosphate receptors-Ca2+ signal transduction pathway, but also regulated the expression of mGluR1a in mechanical neuronal injury. These findings indicate that the suppression of Homer1b/c expression potentially protects neurons from glutamate excitotoxicity after injury and might be an effective intervention target in traumatic brain injury.

Permeability Transition Pore-Mediated Mitochondrial Superoxide Flashes Regulate Cortical Neural Progenitor Differentiation

In the process of neurogenesis, neural progenitor cells (NPCs) cease dividing and differentiate into postmitotic neurons that grow dendrites and an axon, become excitable, and establish synapses with other neurons. Mitochondrial biogenesis and aerobic metabolism provide energy substrates required to support the differentiation, growth and synaptic activity of neurons. Mitochondria may also serve signaling functions and, in this regard, it was recently reported that mitochondria can generate rapid bursts of superoxide (superoxide flashes), the frequency of which changes in response to environmental conditions and signals including oxygen levels and Ca2+ fluxes. Here we show that the frequency of mitochondrial superoxide flashes increases as embryonic cerebral cortical neurons differentiate from NPCs, and provide evidence that the superoxide flashes serve a signaling function that is critical for the differentiation process. The superoxide flashes are mediated by mitochondrial permeability transition pore (mPTP) opening, and pharmacological inhibition of the mPTP suppresses neuronal differentiation. Moreover, superoxide flashes and neuronal differentiation are inhibited by scavenging of mitochondrial superoxide. Conversely, manipulations that increase superoxide flash frequency accelerate neuronal differentiation. Our findings reveal a regulatory role for mitochondrial superoxide flashes, mediated by mPTP opening, in neuronal differentiation.

Shot Noise analysis of subthreshold membrane potential activity in neurons

Shot noise is one of the most extensively harnessed phenomena used to model different aspects of neural activity in neuroscience. Shot noise processes [1] display very characteristic fluctuations that correspond to the sum of causal system responses to unitary event arrivals that follow a Poisson distribution. In general, applications of shot noise [2-4] have been confined to the so-called Campbell Limit corresponding to steady-state regime, or to specific post-synaptic responses that make the process Markovian or with the assumption of homogeneous Poisson event arrivals. In this work we go beyond this context to show that the shot-noise formalism can be used to analyze the synaptic activity of neurons beyond the Campbell limit, for any type of bounded post-synaptic response function and non-homogeneous Poisson event arrivals. This enhancement of technique allows for two main applications. 1) Computation of the full density for current synapses and statistical moments for conductance synapses. This yields a statistical description of the subthreshold membrane potential. This includes considering distributions on the afferent populations over biological parameters such as peak intensity, number of independent channels, or dynamical parameters such as distribution of incoming firing rate or variable incoming firing rate. The picture obtained is of particular interest for various applications such as calculating the transfer function. 2) Under stationarity assumptions, this technique offers the potential to reverse the moments of membrane potential integration. This offers a candidate method to infer characteristics of the synaptic activity (and therefore of the network activity) from the analysis of the subthreshold variations of the membrane potential. This application is of particular interest for the analysis of intracellular recordings in vivo. We illustrate these techniques by comparing analytic expressions with numerical estimates, as well as to neurons subject to a large range of synaptic activity (including low release rate far from the diffusion limit). In conclusion, due to their flexibility as a modeling tool, shot noise analysis appears as a very useful tool in computational neuroscience to model post-synaptic and sub-threshold membrane potential responses to incoming network activity, and also as a tool for electrophysiological analysis of network activity from intracellular recordings.

선조체에서 3-nitropropionic acid 투여 후 calponin 3의 발현 연구

Calponin 3는 F-actin과 결합하는 단백질로 신경계의 가소성과 시냅스 활성을 조절하는데 중요한 역할을 하는 것으로 알려져 있다. 평활근과 심장근에 발현되는 calponin 1과 calponin 2와는 다르게 calponin 3는 뇌 조직에 많이 발현되어 있는 것으로 보고되고 있다. 본 연구는 마우스에서 3-nitropropionic acid를 투여하여 선조체에 비가역적 신경 손상을 주었을 때 calponin 3의 발현 양상을 알아보기 위하여 진행되었다. 본 연구 결과 3-nitropropionic acid를 마우스에 투여하였을 때 선조체에서 신경조직의 괴사가 일어남을 관찰하였으며 calponin 3는 약물 투여 후 1.5일부터 서서히 발현되는 것을 확인하였다. 특히, calponin 3는 신경조직의 괴사가 일어나는 부위의 주변부에서 발현되는 것을 확인하였으며 형광 이중면역 염색법으로 확인한 결과 GFAP를 발현하는 별아교세포에서 발현됨을 최초로 밝혔다. 따라서, calponin 3가 3-nitropropionic acid의 독성에 저항성을 나타내는 부위에서 별아교세포에서만 특이적으로 발현되는 것으로 보아 calponin 3는 별아교세포에 의한 신경아교증에 중요한 역할을 하는 것으로 추측된다. Calponin 3 is an F-actin-binding protein and plays a key role in regulating spine plasticity and synaptic activity in neurons. Unlike the other subtypes, calponin 1 and 2, which are expressed in smooth and cardiac muscle cells, calponin 3 is highly expressed in the brain. The goal of this study was to elucidate the spatiotemporal expression pattern of calponin 3 following repeated administration of 3-nitropropionic acid in mice. The repeated administration of 3-nitropropionic acid generated necrotic neuronal cell death in the striatum. Calponin 3 was up-regulated in the neuroprotective penimbral region from 1.5 days after the last injection and thereafter. Double immunofluorescence study revealed that calponin 3 was induced in GFAP-positive astrocytes. These results suggest that calponin 3 induction in the neuroprotective penumbral area following 3-nitropropionic acid intoxication may play a key role in reactive astrogliosis in the striatum.

Channel-mediated astrocytic glutamate release via Bestrophin-1 targets synaptic NMDARs

BackgroundAstrocytes regulate neuronal excitability and synaptic activity by releasing gliotransmitters such as glutamate. Our recent study demonstrated that astrocytes release glutamate upon GPCR activation via Ca2+ activated anion channel, Bestrophin-1 (Best1). The target of Best1-mediated astrocytic glutamate has been shown to be the neuronal NMDA receptors (NMDAR). However, whether it targets synaptically or extra-synaptically localized NMDAR is not known.FindingsWe recorded spontaneous miniature excitatory postsynaptic currents (mEPSCs) from CA1 pyramidal cells to test whether Best1-mediated astrocytic glutamate targets synaptic NMDAR. An agonist of protease activated receptor 1 (PAR1) was used to induce astrocytic Ca2+ increase and glutamate release. Firstly, we found that activation of PAR1 and subsequent release of glutamate from astrocyte does not alone increase the frequency of mEPSCs. Secondly, we found that mEPSC rise time is variable depending on the different electrotonic distances from the somatic recording site to the synaptic region where each mEPSC occurs. Two subgroups of mEPSC from CA1 pyramidal neuron by rise time were selected and analyzed. One group is fast rising mEPSCs with a rise time of 1 ~ 5 ms, representing synaptic activities arising from proximal dendrites. The other group is slowly rising mEPSCs with a rise time of 5 ~ 10 ms, representing synaptic events arising from glutamate release at synapses located in the distal dendrites. We used cell-type specific Best1 gene silencing system by Cre-loxP cleavage to dissociate the effect of neuronal and astrocytic Best1. Astrocytic Best1-mediated glutamate release by PAR1 activation did not affect decay kinetics, frequency, and amplitude of fast rising mEPSC. In contrast, PAR1 activation resulted in an NMDA receptor component to be present on slowly rising mEPSC, but did not alter frequency or amplitude.ConclusionsOur results indicate that astrocytic glutamate via Best1 channel targets and activates synaptic NMDARs.

SPIN90 Phosphorylation Modulates Spine Structure and Synaptic Function

The correct rearrangement of postsynaptic components in dendritic spines is important for driving changes of spine structure and synaptic function. SPIN90 plays an essential role in many cellular processes including actin polymerization, endocytosis, growth cone formation and dendritic spine morphogenesis. Here, we demonstrate that SPIN90, which is a binding partner of PSD95 and Shank in spines, is targeted to synapses and leads to enhanced synaptic activity in neurons. We show, using in vitro and in vivo kinase assays, that SPIN90 is tyrosine phosphorylated by Src kinase. SPIN90 that was tyrosine-phosphorylated by Src was targeted to dendritic spines in cultured hippocampal neurons. Moreover, a SPIN90 phospho-deficient mutant was unable to accumulate at dendritic spines whereas SPIN90 WT and a phospho-mimicking mutant were localized at spines and bound PSD95 and Shank with increased efficiency. Consistent with these findings, hippocampal neurons that overexpressed SPIN90 WT or a phospho-mimicking mutant had enlarged spine heads, leading to enhanced postsynaptic function in terms of both amplitude and frequency. Together, our findings show that SPIN90 modulates synaptic activity in neurons as a result of its phosphorylation.

Synaptic Activity in Serotonergic Neurons Is Required for Air-Puff Stimulated Flight in Drosophila melanogaster

BackgroundFlight is an integral component of many complex behavioral patterns in insects. The giant fiber circuit has been well studied in several insects including Drosophila. However, components of the insect flight circuit that respond to an air-puff stimulus and comprise the flight central pattern generator are poorly defined. Aminergic neurons have been implicated in locust, moth and Drosophila flight. Here we have investigated the requirement of neuronal activity in serotonergic neurons, during development and in adults, on air-puff induced flight in Drosophila.Methodology/Principal FindingsTo target serotonergic neurons specifically, a Drosophila strain that contains regulatory regions from the TRH (Tryptophan Hydroxylase) gene linked to the yeast transcription factor GAL4 was used. By blocking synaptic transmission from serotonergic neurons with a tetanus toxin transgene or by hyperpolarisation with Kir2.1, close to 50% adults became flightless. Temporal expression of a temperature sensitive Dynamin mutant transgene (Shits) suggests that synaptic function in serotonergic neurons is required both during development and in adults. Depletion of IP3R in serotonergic neurons via RNAi did not affect flight. Interestingly, at all stages a partial requirement for synaptic activity in serotonergic neurons was observed. The status of serotonergic neurons was investigated in the central nervous system of larvae and adults expressing tetanus toxin. A small but significant reduction was observed in serotonergic cell number in adult second thoracic segments from flightless tetanus toxin expressing animals.ConclusionsThese studies show that loss of synaptic activity in serotonergic neurons causes a flight deficit. The temporal focus of the flight deficit is during pupal development and in adults. The cause of the flight deficit is likely to be loss of neurons and reduced synaptic function. Based on the partial phenotypes, serotonergic neurons appear to be modulatory, rather than an intrinsic part of the flight circuit.

S4‐04‐02: APP‐mediated regulation of neuronal cholesterol turnover and synaptic activity: A new therapeutic target for the treatment of Alzheimer's disease

S4‐04‐02: APP‐mediated regulation of neuronal cholesterol turnover and synaptic activity: A new therapeutic target for the treatment of Alzheimer's disease

Nesfatin‐1 Alters Synaptic Activity in Neurons in the Nucleus of the Solitary Tract

Nesfatin‐1 (nes‐1) is a recently discovered neuropeptide that decreases food intake and is expressed in the medullary nucleus of the solitary tract (NTS). In order to begin elucidating the mechanisms of nes‐1 actions, we studied the effect of nes‐1 on synaptic activity in NTS neurons using whole‐cell voltage clamp recordings. Bath applied nes‐1 (10nM) did not influence the frequency (freq, 157±49 vs 163±48 events/100s, p=0.85) nor amplitude (amp, 29±4 vs 51±13 pA, p=0.11) of EPSCs recorded from rat medial NTS neurons (n=8) in slice. Nes‐1 did, however, induce an increase in freq (144±45 vs 224±53 events/100s, p=0.03) and amp (57±9 vs 74±12 pA, p=0.02) of IPSCs in 8/9 cells. We next used tetrodotoxin to study spontaneous miniature EPSCs and IPSCs. 10nM nes‐1 did not affect freq (305±68 vs 275±45 events/100s, p=0.37) nor amp (30±2 vs 34±4 pA, p=0.25) of mEPSCs (n=7). Neither the freq (335±102 vs 385±90 events/100s, p=0.41) nor amp (85±12 vs 92±12 pA, p=0.31) of mIPSCs was affected (n=9) by nes‐1. Our findings identify NTS as a site where nes‐1 acts to selectively enhance GABAergic tone and increase inhibitory synaptic events to potentially modify food intake.Research support: NSERC, FQRNT, CIHR.

Quantitative analysis of in vivo phosphorylation of Cyclin-dependent kinase activator p35 by Phos-tag SDS-PAGE/immunoblotting

Phosphorylation is a major post-translational modification widely used in regulation of many cellular processes. Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine kinase activated by activation subunit p35. Cdk5-p35 regulates various neuronal activities such as neuronal migration, synaptic activity, and cell death. The kinase activity of Cdk5 is regulated by proteolysis of p35: proteasomal degradation causes downregulation of Cdk5 whereas cleavage of p35 by calpain causes overactivation of Cdk5. Phosphorylation of p35 determines the proteolytic pathway. We have previously identified Ser8 and Thr138 as major phosphorylation sites using metabolic labeling of cultured cells followed by 2D-phosphopeptide mapping and phospho-specific antibodies. However, these approaches cannot determine the extent of p35 phosphorylation in vivo. Here we report the use of Phos-tag SDS-PAGE to reveal the in vivo phosphorylation states of p35. Using Phos-tag acrylamide, electrophoretic mobility of phosphorylated p35 was delayed because it is trapped at Phos-tag sites. We constructed phosphorylation-dependent banding profiles of p35 and Ala substitution mutants at phosphorylation sites co-expressed with Cdk5 in COS-7 cells. Using the standard banding profiles, we assigned respective bands of endogenous p35 with combinations of phosphorylation states, and quantified Ser8, Ser91 and Thr138 phosphorylation. This is the first quantitative and site-specific measurements of phosphorylation of p35, demonstrating the usefulness of Phos-tag SDS-PAGE for analysis of phosphorylation states of in vivo proteins.

Calcium Signaling and Gliotransmission in Normal vs. Reactive Astrocytes

A prominent area of neuroscience research over the past 20 years has been the acute modulation of neuronal synaptic activity by Ca2+-dependent release of the transmitters ATP, D-serine, and glutamate (called gliotransmitters) by astrocytes. Although the physiological relevance of this mechanism is under debate, emerging evidence suggests that there are critical factors in addition to Ca2+ that are required for gliotransmitters to be released from astrocytes. Interestingly, these factors include activated microglia and the proinflammatory cytokine Tumor Necrosis Factor α (TNFα), chemotactic cytokine Stromal cell-Derived Factor-1α (SDF-1α), and inflammatory mediator prostaglandin E2 (PGE2). Of note, microglial activation and release of inflammatory molecules from activated microglia and reactive astrocytes can occur within minutes of a triggering stimulus. Therefore, activation of astrocytes by inflammatory molecules combined with Ca2+ elevations may lead to gliotransmitter release, and be an important step in the early sequence of events contributing to hyperexcitability, excitotoxicity, and neurodegeneration in the damaged or diseased brain. In this review, we will first examine evidence questioning Ca2+-dependent gliotransmitter release from astrocytes in healthy brain tissue, followed by a close examination of recent work suggesting that Ca2+-dependent gliotransmitter release occurs as an early event in the development of neurological disorders and neuroinflammatory and neurodegenerative diseases.

The Neuroprotective Effect of a Specific P2X7 Receptor Antagonist Derives from its Ability to Inhibit Assembly of the NLRP3 Inflammasome in Glial Cells

Release of interleukin (IL)-1β from immunocompetent cells requires formation of the NACHT, LLR and PYD domains-containing protein 3 (NLRP3) inflammasome and caspase 1 activation. Adenosine 5'-triphosphate (ATP), acting on the P2X(7) receptor, is one factor that stimulates inflammasome assembly. We show that a novel specific P2X(7) receptor antagonist, GSK1370319A, inhibits ATP-induced increase in IL-1β release and caspase 1 activation in lipopolysaccharide (LPS)-primed mixed glia by blocking assembly of the inflammasome in a pannexin 1-dependent manner. GSK1370319A also inhibits ATP-induced subregion-specific neuronal loss in hippocampal organotypic slice cultures, which is dependent on its ability to prevent inflammasome assembly in glia. Significantly, GSK1370319A attenuates age-related deficits in long-term potentiation (LTP) and inhibits the accompanying age-related caspase 1 activity. We conclude that inhibiting P2X(7) receptor-activated NLRP3 inflammasome formation and the consequent IL-1β release from glia preserve neuronal viability and synaptic activity.

WIP Is a Negative Regulator of Neuronal Maturation and Synaptic Activity

Wiskott-Aldrich syndrome protein (WASP) -interacting protein (WIP) is an actin-binding protein involved in the regulation of actin polymerization in cells, such as fibroblasts and lymphocytes. Despite its recognized function in non-neuronal cells, the role of WIP in the central nervous system has not been examined previously. We used WIP-deficient mice to examine WIP function both in vivo and in vitro. We report here that WIP(-)(/-) hippocampal neurons exhibit enlargement of somas as well as overgrowth of neuritic and dendritic branches that are more evident in early developmental stages. Dendritic arborization and synaptogenesis, which includes generation of postsynaptic dendritic spines, are actin-dependent processes that occur in parallel at later stages. WIP deficiency also increases the amplitude and frequency of miniature excitatory postsynaptic currents, suggesting that WIP(-)(/-) neurons have more mature synapses than wild-type neurons. These findings reveal WIP as a previously unreported regulator of neuronal maturation and synaptic activity.

Mitochondria and cortical gamma oscillations: food for thought?

Increasingly, modalities such as functional MRI and positron emission tomography are finding their place in clinical neurological practice. These techniques provide a unique window into the collective behaviour of neuronal networks; and provide useful information concerning both physiological and pathophysiological modes of operation in particular regions of the brain. A contentious issue is whether or not inferences can be made about neuronal spiking or synaptic activity from measurements of brain-blood flow and energy metabolism (Logothetis and Wandell, 2004). In order to obtain this level of information, electrophysiological techniques such as intracranial EEG, using subdural and/or depth electrodes, are needed. However, this type of invasive approach is not widely used, being suitable only in patients suffering from intractable epilepsy. Recently, a number of research groups have combined techniques such as functional MRI with EEG. This powerful combinatory approach permits experimenters to overcome limitations in terms of discriminating spatial, temporal and spectral features when compared with EEG recordings alone. Such an approach has been fruitful in revealing a significant positive correlation between a particular type of EEG rhythm and haemodynamic responses in the visual cortex (Niessing et al ., 2005). This particular EEG rhythm, the gamma frequency oscillation (γ-oscillation), occurs in many cortical regions and is suggested to play a role in several cognitive processes including memory formation (Fell et al ., 2001), attention (Fries et al ., 2001) and perception (Fries et al ., 2007; Uhlhaas et al ., 2008). The γ-oscillations are therefore highly likely to be important in a wide range of human diseases disrupting normal brain function. At the level of the cortical microcircuit, γ-oscillations are generated through an interplay between cortical inhibitory (gamma-aminobutyric acid releasing) interneurons and excitatory (glutamate releasing) principal neurons. Both in vivo (Atallah and Scanziani, 2009) and in vitro (Traub and Whittington, 2010 …