Acute Neuronal Loss Research Articles

Neuroinflammation and microglial activation as target for therapeutic strategy: in vitro and in vivo models of study

AbstractBackgroundAlzheimer's disease (AD) is characterized by the extracellular accumulation of senile plaques composed of beta‐amyloid (Aβ) and the intracellular deposition of neurofibrillary tangles composed of hyperphosphorylated tau (Tp). Aβ oligomers (AβO) induce damage beginning with loss of synapses, followed by neurite network disorganization and neuronal death. Neuroinflammation plays an essential role in the disease. In AD patient brains, reactive microglia are closely colocalized with amyloid plaques, indicating their close link. Aβ‐activated microglia produce neurotoxic cytokines/chemokines which subsequently cause neuronal dysfunction and death.MethodUsing rat primary cultures of cortical neurons and microglial cells, generating a solution of AβO/protofibrils, playing with the concentration and time of exposure, we were able to mimic the early effects (acute neuronal loss) and the neuroinflammatory response.ResultAt the beginning of the exposure, we observed a Aβ phagocytosis, followed by a strong increase of TREM2/OX41 marker associated with cytokines release and CD206 (M2 marker) decrease over the time.In addition, microglial activation was deeply studied in the hippocampus of aged mice infused with the AβO/protofibril preparation. We observed progressive Tp accumulation associated with neurodegeneration and progressive activation of microglial cells (transition from a phagocytosis stage to a pro‐inflammatory stage with over‐expression of IBA1, CD68 immunoreactivity and production of pro‐inflammatory cytokines).ConclusionIn this work, we proposed vitro/vivo models showing differential and consecutive microglial responses to Aβ. These models are useful for targeting microglial in the pre‐disease period (in vitro) and for modulating the microglial response in the brain once the disease process is underway, and hold promise as a disease‐modifying treatment strategy.

Müller Glia maintain their regenerative potential despite degeneration in the aged zebrafish retina.

Ageing is a significant risk factor for degeneration of the retina. Müller glia cells (MG) are key for neuronal regeneration, so harnessing the regenerative capacity of MG in the retina offers great promise for the treatment of age‐associated blinding conditions. Yet, the impact of ageing on MG regenerative capacity is unclear. Here, we show that the zebrafish retina undergoes telomerase‐independent, age‐related neurodegeneration but that this is insufficient to stimulate MG proliferation and regeneration. Instead, age‐related neurodegeneration is accompanied by MG morphological aberrations and loss of vision. Mechanistically, yes‐associated protein (Yap), part of the Hippo signalling, has been shown to be critical for the regenerative response in the damaged retina, and we show that Yap expression levels decline with ageing. Despite this, morphologically and molecularly altered aged MG retain the capacity to regenerate neurons after acute light damage, therefore, highlighting key differences in the MG response to high‐intensity acute damage versus chronic neuronal loss in the zebrafish retina.

Acute minocycline administration reduces brain injury and improves long-term functional outcomes after delayed hypoxemia following traumatic brain injury

Clinical trials of therapeutics for traumatic brain injury (TBI) demonstrating preclinical efficacy for TBI have failed to replicate these results in humans, in part due to the absence of clinically feasible therapeutic windows for administration. Minocycline, an inhibitor of microglial activation, has been shown to be neuroprotective when administered early after experimental TBI but detrimental when administered chronically to human TBI survivors. Rather than focusing on the rescue of primary injury with early administration of therapeutics which may not be clinically feasible, we hypothesized that minocycline administered at a clinically feasible time point (24 h after injury) would be neuroprotective in a model of TBI plus delayed hypoxemia. We first explored several different regimens of minocycline dosing with the initial dose 24 h after injury and 2 h prior to hypoxemia, utilizing short-term neuropathology to select the most promising candidate. We found that a short course of minocycline reduced acute microglial activation, monocyte infiltration and hippocampal neuronal loss at 1 week post injury. We then conducted a preclinical trial to assess the long-term efficacy of a short course of minocycline finding reductions in hippocampal neurodegeneration and synapse loss, preservation of white matter myelination, and improvements in fear memory performance at 6 months after injury. Timing in relation to injury and duration of minocycline treatment and its impact on neuroinflammatory response may be responsible for extensive neuroprotection observed in our studies.

Xenon treatment after severe traumatic brain injury improves locomotor outcome, reduces acute neuronal loss and enhances early beneficial neuroinflammation: a randomized, blinded, controlled animal study

BackgroundTraumatic brain injury (TBI) is a major cause of morbidity and mortality, but there are no clinically proven treatments that specifically target neuronal loss and secondary injury development following TBI. In this study, we evaluate the effect of xenon treatment on functional outcome, lesion volume, neuronal loss and neuroinflammation after severe TBI in rats.MethodsYoung adult male Sprague Dawley rats were subjected to controlled cortical impact (CCI) brain trauma or sham surgery followed by treatment with either 50% xenon:25% oxygen balance nitrogen, or control gas 75% nitrogen:25% oxygen. Locomotor function was assessed using Catwalk-XT automated gait analysis at baseline and 24 h after injury. Histological outcomes were assessed following perfusion fixation at 15 min or 24 h after injury or sham procedure.ResultsXenon treatment reduced lesion volume, reduced early locomotor deficits, and attenuated neuronal loss in clinically relevant cortical and subcortical areas. Xenon treatment resulted in significant increases in Iba1-positive microglia and GFAP-positive reactive astrocytes that was associated with neuronal preservation.ConclusionsOur findings demonstrate that xenon improves functional outcome and reduces neuronal loss after brain trauma in rats. Neuronal preservation was associated with a xenon-induced enhancement of microglial cell numbers and astrocyte activation, consistent with a role for early beneficial neuroinflammation in xenon’s neuroprotective effect. These findings suggest that xenon may be a first-line clinical treatment for brain trauma.

Neuronal Parasitism, Early Myenteric Neurons Depopulation and Continuous Axonal Networking Damage as Underlying Mechanisms of the Experimental Intestinal Chagas' Disease.

There is a growing consensus that the balance between the persistence of infection and the host immune response is crucial for chronification of Chagas heart disease. Extrapolation for chagasic megacolon is hampered because research in humans and animal models that reproduce intestinal pathology is lacking. The parasite-host relationship and its consequence to the disease are not well-known. Our model describes the temporal changes in the mice intestine wall throughout the infection, parasitism, and the development of megacolon. It also presents the consequence of the infection of primary myenteric neurons in culture with Trypanosoma cruzi (T. cruzi). Oxidative neuronal damage, involving reactive nitrogen species induced by parasite infection and cytokine production, results in the denervation of the myenteric ganglia in the acute phase. The long-term inflammation induced by the parasite's DNA causes intramuscular axonal damage, smooth muscle hypertrophy, and inconsistent innervation, affecting contractility. Acute phase neuronal loss may be irreversible. However, the dynamics of the damages revealed herein indicate that neuroprotection interventions in acute and chronic phases may help to eradicate the parasite and control the inflammatory-induced increase of the intestinal wall thickness and axonal loss. Our model is a powerful approach to integrate the acute and chronic events triggered by T. cruzi, leading to megacolon.

Blast exposure predisposes the brain to increased neurological deficits in a model of blast plus blunt traumatic brain injury

Soldiers are often exposed to more than one traumatic brain injury (TBI) over the course of their service. In recent years, more attention has been drawn to the increased risk of neurological deficits caused by the ‘blast plus’ polytrauma, which typically is a blast trauma combined with other forms of TBI. In this study, we investigated the behavioral and neuronal deficits resulting from a blast plus injury involving a mild-moderate blast followed by a mild blunt trauma using the fluid percussion injury model. We identified that the blast injury predisposed the brain to increased cognitive deficits, chronic ventricular enlargement, increased neurodegeneration at acute time points and chronic neuronal loss. Interestingly, a single blast and single blunt injury differed in their onset and manifestation of cognitive and regional neuronal loss. We also identified the presence of cleaved RIP1 from caspase 8 mediated apoptosis in the blunt injury while the blast injury did not activate immediate apoptosis but led to decreased hilar neuronal survival over time.

Abstract TP120: Complement Activation Contributes to Malignant Transformation of Stroke and Limits Cognitive Recovery After Reperfusion Therapy

Introduction: Ischemic stroke involves an ischemic event followed by post-ischemic neuroinflammation, leading to acute mortality, neuronal loss, and impaired recovery. Standard of care reperfusion therapy (thrombolysis or thrombectomy) has a limited treatment window due to risk of hemorrhage, and leads to functional independence in only a subset of patients. We studied the role of complement and neuroinflammation in the pathophysiology behind the major clinical challenges of reperfusion therapy; the risk of hemorrhage and limited cognitive recovery. Methods: We used 3 stroke models, namely transient middle cerebral artery occlusion (MCAO), permanent MCAO and microembolic models, to investigate the effects of t-PA, mechanical reperfusion, rehabilitation therapy, and complement inhibition in mice. We used B4-Crry, a site-targeted inhibitor of C3 activation that specifically localizes to neoepitopes expressed in the post-ischemic brain following its intravenous administration. A retrospective analysis was also performed for cognitive and motor recovery in human patients following reperfusion therapy. Results: Complement inhibition with B4-Crry improved the safety, efficacy and treatment window of reperfusion therapy, decreased hemorrhagic transformation, and improved cognitive recovery. Despite reperfusion with t-PA, there was ongoing complement-dependent microglial activation and phagocytosis of hippocampal synapses for at least 30 days leading to pronounced long-term cognitive deficits. Administration of B4Crry, alone or in combination with thrombolytic therapy, limited complement deposition in the perilesional brain, and reduced microgliosis and synaptic uptake. Reperfusion therapy alone did not improve cognitive outcomes, even when combined with rehabilitation therapy. Reperfusion therapy did not improve cognitive outcomes in stroke patients. Conclusions: Although post-stroke reperfusion therapy limits the size of injury and improves motor deficits, post-reperfusion complement activation and neuroinflammation contribute to the malignant transformation of stroke acutely and seeds a chronic neurodegenerative inflammatory response. Complement modulation may be a promising adjuvant to reperfusion therapy.

Assessment of systemic administration of PEGylated IGF-1 in a mouse model of traumatic brain injury.

Traumatic brain injury can result in lasting cognitive dysfunction due to degeneration of mature hippocampal neurons as well as the loss of immature neurons within the dentate gyrus. While endogenous neurogenesis affords a partial recovery of the immature neuron population, hippocampal neurogenesis may be enhanced through therapeutic intervention. Insulin-like growth factor-1 (IGF-1) has the potential to improve cognitive function and promote neurogenesis after TBI, but its short half-life in the systemic circulation makes it difficult to maintain a therapeutic concentration. IGF-1 modified with a polyethylene glycol moiety (PEG-IGF-1) exhibits improved stability and half-life while retaining its ability to enter the brain from the periphery, increasing its viability as a translational approach. The goal of this study was to evaluate the ability of systemic PEG-IGF-1 administration to attenuate acute neuronal loss and stimulate the recovery of hippocampal immature neurons in brain-injured mice. In a series of studies utilizing a well-established contusion brain injury model, PEG-IGF-1 was administered subcutaneously after injury. Serum levels of PEG were verified using ELISA and histological staining was used to investigate numbers of degenerating neurons and cortical contusion size at 24 h after injury. Immunofluorescent staining was used to evaluate numbers of immature neurons at 10 d after injury. Although subcutaneous injections of PEG-IGF-1 increased serum IGF-1 levels in a dose-dependent manner, no effects were observed on cortical contusion size, neurodegeneration within the dentate gyrus, or recovery of hippocampal immature neuron numbers. In contrast to its efficacy in rodent models of neurodegenerative diseases, PEG- IGF-1 was not effective in ameliorating early neuronal loss after contusion brain trauma.

Identifying the Role of Complement in Triggering Neuroinflammation after Traumatic Brain Injury.

The complement system is implicated in promoting acute secondary injury after traumatic brain injury (TBI), but its role in chronic post-traumatic neuropathology remains unclear. Using various injury-site targeted complement inhibitors that block different complement pathways and activation products, we investigated how complement is involved in neurodegeneration and chronic neuroinflammation after TBI in a clinically relevant setting of complement inhibition. The current paradigm is that complement propagates post-TBI neuropathology predominantly through the terminal membrane attack complex (MAC), but the focus has been on acute outcomes. Following controlled cortical impact in adult male mice, we demonstrate that although inhibition of the MAC (with CR2-CD59) reduces acute deficits, inhibition of C3 activation is required to prevent chronic inflammation and ongoing neuronal loss. Activation of C3 triggered a sustained degenerative mechanism of microglial and astrocyte activation, reduced dendritic and synaptic density, and inhibited neuroblast migration several weeks after TBI. Moreover, inhibiting all complement pathways (with CR2-Crry), or only the alternative complement pathway (with CR2-fH), provided similar and significant improvements in chronic histological, cognitive, and functional recovery, indicating a key role for the alternative pathway in propagating chronic post-TBI pathology. Although we confirm a role for the MAC in acute neuronal loss after TBI, this study shows that upstream products of complement activation generated predominantly via the alternative pathway propagate chronic neuroinflammation, thus challenging the current concept that the MAC represents a therapeutic target for treating TBI. A humanized version of CR2fH has been shown to be safe and non-immunogenic in clinical trials.SIGNIFICANCE STATEMENT Complement, and specifically the terminal membrane attack complex, has been implicated in secondary injury and neuronal loss after TBI. However, we demonstrate here that upstream complement activation products, generated predominantly via the alternative pathway, are responsible for propagating chronic inflammation and injury following CCI. Chronic inflammatory microgliosis is triggered by sustained complement activation after CCI, and is associated with chronic loss of neurons, dendrites and synapses, a process that continues to occur even 30 d after initial impact. Acute and injury-site targeted inhibition of the alternative pathway significantly improves chronic outcomes, and together these findings modify the conceptual paradigm for targeting the complement system to treat TBI.

Activation of G-protein coupled estrogen receptor 1 improves early-onset cognitive impairment via PI3K/Akt pathway in rats with traumatic brain injury

Previous studies experimentally reveal that G-protein coupled estrogen receptor 1(GPER) has neuroprotection against ischemic injury. However, its effect on traumatic brain injury (TBI) is less well-established. Cognitive impairment following human TBI is a common clinical observation, and TBI is considered as a risk factor for Alzheimer's disease (AD). This study aimed to observe the possible protective effect of GPER on early-onset cognitive impairment after a single TBI and investigate the cellular mechanism underlying its actions. We found that selective GPER agonist G-1 significantly reduced hippocampal CA1 neuronal loss and improved cognitive impairment in TBI rats. Although previous studies have shown that AD-like tau pathology occurs many years after both repetitive and single TBI, accumulation of hyperphosphorylated tau was not observed within days (detected at 24 h and 7d) after TBI. Furthermore, tau phosphorylation was not altered by G-1 treatment. It was found that G-1 administration caused an increase in p-Akt level. However, the neuroprotective effects of G-1 on spatial cognition and neuronal death were attenuated by PI3K/Akt inhibitor LY294002. These findings indicate that GPER agonist G-1 had protection on cognitive function via activation of PI3K/Akt signaling. Early-onset cognitive impairment following a single TBI was closely associated with acute hippocampal neuronal loss rather than tau pathology. This study suggests that early activation of GPER might be a promising therapeutic strategy for improvement of TBI-induced cognitive outcomes.

Etanercept, an inhibitor of TNF-a, prevents propofol-induced neurotoxicity in the developing brain

Propofol can induce acute neuronal apoptosis, neuronal loss or long-term cognitive impairment when exposed in neonatal rodents, but the mechanisms by which propofol induces developmental neurotoxicity are unclear. Recent studies have demonstrated that propofol can increase the TNF-α level in the developing brain, but there is a lack of direct evidence to show whether TNF-α is partially or fully involved in propofol-induced neurotoxicity. The present study shows that propofol exposure in neonatal rats induces an increase of TNF-α in the cerebral spinal fluid, hippocampus and prefrontal cortex (PFC). Etanercept, a TNF-α inhibitor, prevents propofol-induced short- or long-term neuronal apoptosis, neuronal loss, synaptic loss and long-term cognitive impairment. Furthermore, mTNF-α (precursor of TNF-α) expression in microglia cells is increased after propofol anaesthesia in either the hippocampus or PFC, but mTNF-α expression in neurons is only increased in the PFC. These findings suggest that TNF-α may mediate propofol-induced developmental neurotoxicity, and etanercept can provide neural protection. Microglia are the main cellular source of TNF-α after propofol exposure, while the synthesis of TNF-α in neurons is brain-region selective.

Involvement of the neuronal phosphotyrosine signal adaptor N-Shc in kainic acid-induced epileptiform activity.

BDNF-TrkB signaling is implicated in experimental seizures and epilepsy. However, the downstream signaling involved in the epileptiform activity caused by TrkB receptor activation is still unknown. The aim of the present study was to determine whether TrkB-mediated N-Shc signal transduction was involved in kainic acid (KA)-induced epileptiform activity. We investigated KA-induced behavioral seizures, epileptiform activities and neuronal cell loss in hippocampus between N-Shc deficient and control mice. There was a significant reduction in seizure severity and the frequency of epileptiform discharges in N-Shc deficient mice, as compared with wild-type and C57BL/6 mice. KA-induced neuronal cell loss in the CA3 of hippocampus was also inhibited in N-Shc deficient mice. This study demonstrates that the activation of N-Shc signaling pathway contributes to an acute KA-induced epileptiform activity and neuronal cell loss in the hippocampus. We propose that the N-Shc-mediated signaling pathway could provide a potential target for the novel therapeutic approaches of epilepsy.

Time-dependent effects of CX3CR1 in a mouse model of mild traumatic brain injury

BackgroundNeuroinflammation is an important secondary mechanism that is a key mediator of the long-term consequences of neuronal injury that occur in traumatic brain injury (TBI). Microglia are highly plastic cells with dual roles in neuronal injury and recovery. Recent studies suggest that the chemokine fractalkine (CX3CL1, FKN) mediates neural/microglial interactions via its sole receptor CX3CR1. CX3CL1/CX3CR1 signaling modulates microglia activation, and depending upon the type and time of injury, either protects or exacerbates neurological diseases.MethodsIn this study, mice deficient in CX3CR1 were subjected to mild controlled cortical impact injury (CCI), a model of TBI. We evaluated the effects of genetic deletion of CX3CR1 on histopathology, cell death/survival, microglia activation, and cognitive function for 30 days post-injury.ResultsDuring the acute post-injury period (24 h–15 days), motor deficits, cell death, and neuronal cell loss were more profound in injured wild-type than in CX3CR1−/− mice. In contrast, during the chronic period of 30 days post-TBI, injured CX3CR1−/− mice exhibited greater cognitive dysfunction and increased neuronal death than wild-type mice. The protective and deleterious effects of CX3CR1 were associated with changes in microglia phenotypes; during the acute phase CX3CR1−/− mice showed a predominant anti-inflammatory M2 microglial response, with increased expression of Ym1, CD206, and TGFβ. In contrast, increased M1 phenotypic microglia markers, Marco, and CD68 were predominant at 30 days post-TBI.ConclusionCollectively, these novel data demonstrate a time-dependent role for CX3CL1/CX3CR1 signaling after TBI and suggest that the acute and chronic responses to mild TBI are modulated in part by distinct microglia phenotypes.

Aligned carbon nanotube reinforced polymeric scaffolds with electrical cues for neural tissue regeneration

In this article, the challenge of providing electrical cue through a soft polymeric neural scaffold for directional neuron growth has been studied. Aligned multiwalled carbon nanotube (MWCNT) chitosan composite scaffolds are successfully fabricated using electric field alignment technique. Uniform distribution and alignment of 0.5 wt% MWCNTs in the chitosan matrix, good interfacial bonding, and aligned network of carbon nanotubes (CNTs) help to improve the elastic modulus, yield strength, and ultimate tensile strength by 12.7%, 21.9%, and 11.2%, respectively, as compared with the random MWCNT–chitosan scaffold. Alignment of MWCNTs introduces highly anisotropic electrical conductivity (100,000 times higher) along its direction, as compared to the transverse direction of the scaffold. This is the ideal requirement for a neural scaffold to guide cells in the appropriate direction. Interactions of HT-22 hippocampal neurons with MWCNT–chitosan matrix prove the scaffolds to be highly biocompatible with a notable increase in viability. In addition, 50–60% of neurons are found to be aligned in the MWCNT alignment direction of the scaffold. These results indicate that aligned MWCNT–chitosan scaffold is a potential design to control the directional cell migration on the scaffold, which opens up the possibility of its use in repopulating cells in regions of acute neuronal loss.

Histopathological evidence that hippocampal atrophy following status epilepticus is a result of neuronal necrosis

Medial temporal lobe epilepsy is commonly associated with hippocampal atrophy on MRI and hippocampal sclerosis on histopathological examination of surgically-resected specimens. Likewise, it is well-established that prolonged seizures and status epilepticus can lead to hippocampal edema as noted on MRI.In this paper, the authors present an unusual patient with prolonged refractory status epilepticus, due to limbic encephalitis associated with anti-GAD antibody, who underwent palliative epilepsy surgery. Bilateral hippocampal edema was noted on preoperative MRI. Histologic evaluation confirmed presence of acute necrosis and neuronal loss in the left hippocampal formation. Follow-up MRI several months after surgery demonstrated severe atrophy of the contralateral right hippocampus.This is the first clear histopathological evidence that hippocampal atrophy following status epilepticus is the result of acute neuronal necrosis and cell loss.

Pregabalin Attenuates Excitotoxicity in Diabetes

Diabetes can exacerbate seizures and worsen seizure-related brain damage. In the present study, we aimed to determine whether the standard antiepileptic drug pregabalin (PGB) protects against pilocarpine-induced seizures and excitotoxicity in diabetes. Adult male Sprague-Dawley rats were divided into either a streptozotocin (STZ)-induced diabetes group or a normal saline (NS) group. Both groups were further divided into subgroups that were treated intravenously with either PGB (15 mg/kg) or a vehicle; all groups were treated with subcutaneous pilocarpine (60 mg/kg) to induce seizures. To evaluate spontaneous recurrent seizures (SRS), PGB-pretreated rats were fed rat chow containing oral PGB (450 mg) for 28 consecutive days; vehicle-pretreated rats were fed regular chow. SRS frequency was monitored for 2 weeks from post-status epilepticus day 15. We evaluated both acute neuronal loss and chronic mossy fiber sprouting in the CA3 area. In addition, we performed patch clamp recordings to study evoked excitatory postsynaptic currents (eEPSCs) in hippocampal CA1 neurons for both vehicle-treated rats with SRS. Finally, we used an RNA interference knockdown method for Kir6.2 in a hippocampal cell line to evaluate PGB's effects in the presence of high-dose ATP. We found that compared to vehicle-treated rats, PGB-treated rats showed less severe acute seizure activity, reduced acute neuronal loss, and chronic mossy fiber sprouting. In the vehicle-treated STZ rats, eEPSC amplitude was significantly lower after PGB administration, but glibenclamide reversed this effect. The RNA interference study confirmed that PGB could counteract the ATP-sensitive potassium channel (KATP)-closing effect of high-dose ATP. By opening KATP, PGB protects against neuronal excitotoxicity, and is therefore a potential antiepileptogenic in diabetes. These findings might help develop a clinical algorithm for treating patients with epilepsy and comorbid metabolic disorders.

Direct detection of alpha synuclein oligomers in vivo

BackgroundRat models of Parkinson’s disease are widely used to elucidate the mechanisms underlying disease etiology or to investigate therapeutic approaches. Models were developed using toxins such as MPTP or 6-OHDA to specifically target dopaminergic neurons resulting in acute neuronal loss in the substantia nigra or by using viral vectors to induce the specific and gradual expression of alpha synuclein in the substantia nigra. The detection of alpha- synuclein oligomers, the presumed toxic species, in these models and others has been possible using only indirect biochemical approaches to date. Here we coinjected AAVs encoding alpha-synuclein fused to the N- or C-terminal half of VenusYFP in rat substantia nigra pars compacta and describe for the first time a novel viral vector rodent model with the unique ability to directly detect and track alpha synuclein oligomers ex vivo and in vivo.ResultsViral coinjection resulted in widespread VenusYFP signal within the nigrostriatal pathway, including cell bodies in the substantia nigra and synaptic accumulation in striatal terminals, suggestive of in vivo alpha-synuclein oligomers formation. Transduced rats showed alpha-synuclein induced dopaminergic neuron loss in the substantia nigra, the appearance of dystrophic neurites, and gliosis in the striatum. Moreover, we have applied in vivo imaging techniques in the living mouse to directly image alpha-synuclein oligomers in the cortex.ConclusionWe have developed a unique animal model that provides a tool for the Parkinson’s disease research community with which to directly detect alpha- synuclein oligomers in vivo and screen therapeutic approaches targeting alpha-synuclein oligomers.

Local disruption of glial adenosine homeostasis in mice associates with focal electrographic seizures: A first step in epileptogenesis?

Astrogliosis and associated dysfunction of adenosine homeostasis are pathological hallmarks of the epileptic brain and thought to contribute to seizure generation in epilepsy. The authors hypothesized that astrogliosis-an early component of the epileptogenic cascade-might be linked to focal seizure onset. To isolate the contribution of astrogliosis to ictogenesis from other pathological events involved in epilepsy, the authors used a minimalistic model of epileptogenesis in mice, based on a focal onset status epilepticus triggered by intra-amygdaloid injection of kainic acid. The authors demonstrate acute neuronal cell loss restricted to the injected amygdala and ipsilateral CA3, followed 3 weeks later by focal astrogliosis and overexpression of the adenosine-metabolizing enzyme adenosine kinase (ADK). Using synchronous electroencephalographic recordings from multiple depth electrodes, the authors identify the KA-injected amygdala and ipsilateral CA3 as two independent foci for the initiation of non-synchronized electrographic subclinical seizures. Importantly, seizures remained focal and restricted to areas of ADK overexpression. However, after systemic application of a non-convulsive dose of an adenosine A(1) -receptor antagonist, seizures in amygdala and CA3 immediately synchronized and spread throughout the cortex, leading to convulsive seizures. This focal seizure phenotype remained stable over at least several weeks. We conclude that astrogliosis via disruption of adenosine homeostasis per se and in the absence of any other overt pathology, is associated with the emergence of spontaneous recurrent subclinical seizures, which remain stable over space and time. A secondary event, here mimicked by brain-wide disruption of adenosine signaling, is likely required to turn pre-existing subclinical seizures into a clinical seizure phenotype.

Kappa opioid receptor activation blocks progressive neurodegeneration after kainic acid injection

We recently demonstrated that endogenous prodynorphin-derived peptides mediate anticonvulsant, antiepileptogenic and neuroprotective effects via kappa opioid receptors (KOP). Here we show acute and delayed neurodegeneration and its pharmacology after local kainic acid injection in prodynorphin knockout and wild-type mice and neuroprotective effect(s) of KOP activation in wild-type mice. Prodynorphin knockout and wild-type mice were injected with kainic acid (3 nmoles in 50 nl saline) into the stratum radiatum of CA1 of the right dorsal hippocampus. Knockout mice displayed significantly more neurodegeneration of pyramidal cells and interneurons than wild-type mice 2 days after treatment. This phenotype could be mimicked in wild-type animals by treatment with the KOP antagonist GNTI and rescued in knockout animals by the KOP agonist U-50488. Minor differences in neurodegeneration remained 3 weeks after treatment, mostly because of higher progressive neurodegeneration in wild-type mice compared with prodynorphin-deficient animals. In wild-type mice progressive neurodegeneration, but not acute neuronal loss, could be mostly blocked by U-50488 treatment. Our data suggest that endogenous prodynorphin-derived peptides sufficiently activate KOP receptors during acute seizures, and importantly in situations of reduced dynorphinergic signaling-like in epilepsy-the exogenous activation of KOP receptors might also have strong neuroprotective effects during excitotoxic events.

Neonatal astrocyte damage is sufficient to trigger progressive striatal degeneration in a rat model of glutaric acidemia-I.

BackgroundWe have investigated whether an acute metabolic damage to astrocytes during the neonatal period may critically disrupt subsequent brain development, leading to neurodevelopmental disorders. Astrocytes are vulnerable to glutaric acid (GA), a dicarboxylic acid that accumulates in millimolar concentrations in Glutaric Acidemia I (GA-I), an inherited neurometabolic childhood disease characterized by degeneration of striatal neurons. While GA induces astrocyte mitochondrial dysfunction, oxidative stress and subsequent increased proliferation, it is presently unknown whether such astrocytic dysfunction is sufficient to trigger striatal neuronal loss.Methodology/Principal FindingsA single intracerebroventricular dose of GA was administered to rat pups at postnatal day 0 (P0) to induce an acute, transient rise of GA levels in the central nervous system (CNS). GA administration potently elicited proliferation of astrocytes expressing S100β followed by GFAP astrocytosis and nitrotyrosine staining lasting until P45. Remarkably, GA did not induce acute neuronal loss assessed by FluoroJade C and NeuN cell count. Instead, neuronal death appeared several days after GA treatment and progressively increased until P45, suggesting a delayed onset of striatal degeneration. The axonal bundles perforating the striatum were disorganized following GA administration. In cell cultures, GA did not affect survival of either striatal astrocytes or neurons, even at high concentrations. However, astrocytes activated by a short exposure to GA caused neuronal death through the production of soluble factors. Iron porphyrin antioxidants prevented GA-induced astrocyte proliferation and striatal degeneration in vivo, as well as astrocyte-mediated neuronal loss in vitro.Conclusions/SignificanceTaken together, these results indicate that a transient metabolic insult with GA induces long lasting phenotypic changes in astrocytes that cause them to promote striatal neuronal death. Pharmacological protection of astrocytes with antioxidants during encephalopatic crisis may prevent astrocyte dysfunction and the ineluctable progression of disease in children with GA-I.