c-Fos, N-methyl-d-aspartate receptor 2C, GABA-A-alpha1 immonoreactivity, seizure latency and neuronal injury following single or recurrent neonatal seizures in hippocampus of Wistar rat

Genetic Inhibition of Plppr5 Aggravates Hypoxic-Ischemie-Induced Cortical Damage and Excitotoxic Phenotype

Hypoxia-ischemia (HI) is the most common acute brain threat in neonates and a leading cause of neurodevelopmental impairment. Exploring the new molecular mechanism of HI brain injury has important clinical translational significance for the next clinical intervention research. Lipid phosphatase-related proteins (PLPPRs) are regulators of mitochondrial membrane integrity and energy metabolism. We recently found that Plppr5 knockout exacerbated HI impairment in some aspects and partially attenuated the neuroprotective effects of melatonin, suggesting that Plppr5 may be a novel intervention target for HI. The present study aimed to determine the long-term effects of gene knockout of Plppr5 on HI brain injury, focusing on the neuronal excitability phenotype, and to determine the effect of Plppr5 gene silencing on neuronal zinc metabolism and mitochondrial function in vitro. 10-day-old wild type (WT) mice and Plppr5-deficient (Plppr5–/–) mice were subjected to hypoxia-ischemia. Lesion volumes and HI-induced neuroexcitotoxic phenotypes were quantified together with ZnT1 protein expression in hippocampus. In addition, HT22 (mouse hippocampal neuronal cells) cell model was established by oxygen–glucose deprivation/reoxygenation (OGD/R) treatment and was treated with medium containing LV-sh_Plppr5 or control virus. Mitochondrial oxidative stress indicator ROS, mitochondrial ZnT1 protein expression and zinc ion content were detected.

Results

Plppr5-deficient mice subjected to hypoxia-ischemia at postnatal day 10 present significantly higher cerebral infarction. Plppr5-deficient mice were endowed with a more pronounced superexcitability phenotype at 4 weeks after HI, manifested as a reduced seizure threshold. ZnT1 protein was also found reduced in Plppr5-deficient mice as well as in mice subjected to HI excitotoxicity. Plppr5 knockout in vivo exacerbates HI brain injury phenotypes, including infarct volume and seizure threshold. In addition, knockout of the Plppr5 gene reduced the MFS score to some extent. In vitro Plppr5 silencing directly interferes with neuronal zinc metabolism homeostasis and exacerbates hypoxia-induced mitochondrial oxidative stress damage. Taken together, our findings demonstrate for the first time that Plppr5-deficient mouse pups exposed to neuronal hypoxia and ischemia exhibit aggravated acute brain injury and long-term brain excitability compared with the same treated WT pups, which may be related to the disruption of zinc and mitochondria-dependent metabolic pathways in the hippocampus. These data support further investigation into novel approaches targeting Plppr5-mediated zinc and mitochondrial homeostasis in neonatal HIE.

Long-Term Effects of Early Life Seizures on Endogenous Local Network Activity of the Mouse Neocortex

Understanding the long term impact of early life seizures (ELS) is of vital importance both for researchers and clinicians. Most experimental studies of how seizures affect the developing brain have drawn their conclusions based on changes detected at the cellular or behavioral level, rather than on intermediate levels of analysis, such as the physiology of neuronal networks. Neurons work as part of networks and network dynamics integrate the function of molecules, cells and synapses in the emergent properties of brain circuits that reflect the balance of excitation and inhibition in the brain. Therefore, studying network dynamics could help bridge the cell-to-behavior gap in our understanding of the neurobiological effects of seizures. To this end we investigated the long-term effects of ELS on local network dynamics in mouse neocortex. By using the pentylenetetrazole (PTZ)-induced animal model of generalized seizures, single or multiple seizures were induced at two different developmental stages (P9-15 or P19-23) in order to examine how seizure severity and brain maturational status interact to affect the brain's vulnerability to ELS. Cortical physiology was assessed by comparing spontaneous network activity (in the form of recurring Up states) in brain slices of adult (>5 mo) mice. In these experiments we examined two distinct cortical regions, the primary motor (M1) and somatosensory (S1) cortex in order to investigate regional differences in vulnerability to ELS. We find that the effects of ELSs vary depending on (i) the severity of the seizures (e.g., single intermittent ELS at P19-23 had no effect on Up state activity, but multiple seizures induced during the same period caused a significant change in the spectral content of spontaneous Up states), (ii) the cortical area examined, and (iii) the developmental stage at which the seizures are administered. These results reveal that even moderate experiences of ELS can have long lasting age- and region-specific effects in local cortical network dynamics.

IL-33 Provides Neuroprotection through Suppressing Apoptotic, Autophagic and NF-κB-Mediated Inflammatory Pathways in a Rat Model of Recurrent Neonatal Seizure

Interleukin-33 (IL-33) is a novel identified chromatin-associated cytokine of IL-1 family cytokines. It signals through a heterodimer comprised of ST2L and IL-1RAcp, and plays a crucial role in many diseases. However, very little is known about the role and underlying intricate mechanisms of IL-33 in recurrent neonatal seizure (RNS). To determine whether IL-33 plays an important regulatory role, we established a neonatal seizure model in this study. Rats were subjected to recurrent seizures induced by inhaling volatile flurothyl. Recombinant IL-33 or PBS were also administered by intraperitoneally (IP) before surgery, respectively. Here, our current results indicated that RNS contributed to a significant reduction in IL-33 and its specific receptor (ST2L) expressions in cortex. While, in hippocampus, RNS induced an increase in IL-33 and ST2L evidently, compared with Sham group. After injection with IL-33, however, a remarkable increase in total IL-33 was detected both in brain cortex and hippocampus. In addition, IL-33 was mainly co-localized in the nuclear of GFAP⁺ astrocytes and the cytoplasm of the Iba-1⁺ microglia and IL-33⁺/NeuN⁺ merged cells. In parallel, ST2L was expressed mainly in the membrane of GFAP⁺ astrocytes, Iba-1⁺ microglia and NeuN⁺ neurons, respectively. Furthermore, administration of IL-33 improved RNS-induced behavioral deficits, promoted bodyweight gain, and ameliorated spatial learning and memory ability. Moreover, IL-33 pretreatment blocked the activation of NF-κB, resisted inflammatory cytokines IL-1β and TNF-α increase, as well as suppressed apoptosis and autophagy activation after RNS. Collectively, IL-33 provides potential neuroprotection through suppressing apoptosis, autophagy and at least in part by NF-κB-mediated inflammatory pathways after RNS.

Long-Term Effects of Ketogenic Diet on Subsequent Seizure-Induced Brain Injury During Early Adulthood: Relationship of Seizure Thresholds to Zinc Transporter-Related Gene Expressions

The divalent cation zinc is associated with cortical plasticity. However, the mechanism of zinc in the pathophysiology of cortical injury-associated neurobehavioral damage following neonatal seizures is uncertain. We have previously shown upregulated expression of ZnT-3; MT-3 in hippocampus of neonatal rats submitted to flurothyl-induced recurrent seizures, which was restored by pretreatment with ketogenic diet (KD). In this study, utilizing a novel "twist" seizure model by coupling early-life flurothyl-induced seizures with later exposure to penicillin, we further investigated the long-term effects of KD on cortical expression of zinc homeostasis-related genes in a systemic scale. Ten Sprague-Dawley rats were assigned each averagely into the non-seizure plus normal diet (NS + ND), non-seizure plus KD (NS + KD), recurrent seizures plus normal diet (RS + ND) and recurrent seizures plus KD (RS + KD) group. Recurrent seizures were induced by volatile flurothyl during P9-P21. During P23-P53, rats in NS + KD and RS + KD groups were dieted with KD. Neurological behavioral parameters of brain damage (plane righting reflex, cliff avoidance reflex, and open field test) were observed at P43. At P63, we examined seizure threshold using penicillin, then the cerebral cortex were evaluated for real-time RT-PCR and western blot study. The RS + ND group showed worse performances in neurological reflex tests and reduced latencies to myoclonic seizures induced by penicillin compared with the control, which was concomitant with altered expressions of ZnT-7, MT-1, MT-2, and ZIP7. Specifically, there was long-term elevated expression of ZIP7 in RS + ND group compared with that in NS + ND that was restored by chronic ketogenic diet (KD) treatment in RS + KD group, which was quite in parallel with the above neurobehavioral changes. Taken together, these findings indicate that the long-term altered expression of the metal transporter ZIP7 in adult cerebral cortex might correlate with neurobehavioral damage and reduced seizure threshold following recurrent neonate seizures and further highlights ZIP7 as a candidate for therapeutic target of KD for the treatment of neonatal seizure-induced long-term brain damage.

Neuroprotection Mediated through GluN2C-Containing N-methyl-D-aspartate (NMDA) Receptors Following Ischemia

Post-ischemic activation of NMDA receptors (NMDARs) has been linked to NMDAR subunit-specific signaling that mediates pro-survival or pro-death activity. Although extensive studies have been performed to characterize the role of GluN2A and GluN2B following ischemia, there is less understanding regarding the regulation of GluN2C. Here, we show that GluN2C expression is increased in acute hippocampal slices in response to ischemia. Strikingly, GluN2C knockout mice, following global cerebral ischemia, exhibit greater neuronal death in the CA1 area of the hippocampus and reduced spatial working memory compared to wild-type mice. Moreover, we find that GluN2C-expressing hippocampal neurons show marked resistance to NMDA-induced toxicity and reduced calcium influx. Using both in vivo and in vitro experimental models of ischemia, we demonstrate a neuroprotective role of GluN2C, suggesting a mechanism by which GluN2C is upregulated to promote neuronal survival following ischemia. These results may provide insights into development of NMDAR subunit-specific therapeutic strategies to protect neurons from excitotoxicity.

Long-term expression of zinc transporters in hippocampus following penicillin-induced developmental seizures and its regulation by E-64d

Autophagy has been shown to be involved in the pathophysiology of developmental seizure-induced brain damage. The present study aimed to examine whether E-64d, an autophagy inhibitor, was able to facilitate developmental seizure-induced hippocampal mossy fiber sprouting, in particular sprouting-associated zinc transporter signals. Recurrent seizures were induced by penicillin every other day in Sprague-Dawley rats from postnatal day 21 (P21). Rats were randomly assigned into the control group (CONT), recurrent seizure group (RS) and the seizure plus E-64d group (E64D). The expression levels of beclin-1 and B-cell lymphoma 2 were analyzed at 1.5, 3, 6 and 24 h after the last seizures using western blot analysis. At P51, mossy fiber sprouting and the mRNA expression levels of zinc transporter 2 (ZnT-2), ZnT-4, ZnT-5, ZnT-6, ZnT-7, divalent cation transporter 1, Zrt-Irt-like protein 6 (ZIP-6), ZIP-7, cathepsin D and cathepsin L in the rat hippocampus were assessed using Timm staining and reverse transcription-quantitative polymerase chain reaction analysis, respectively. Reduced hippocampal mossy fiber sprouting were detected in the E-64d-treated rats compared with the non-treated control. In parallel with these observations, there was a marked reduction in the mRNA expression levels of ZnT-4 at P51 in the E-64d-treated rat hippocampus compared with the non-treated seizure group. Linear correlation analysis showed significant inter-relationship among ZIP-7, ZnT-4, ZnT-5, ZnT-7, cathepsin D and cathepsin L. These results indicate that the ZnT-4/ZIP-7/cathepsin signaling pathway serves a crucial function in the neuroprotective effects of E-64d. Thus, E-64d may offer a novel strategy for the development of therapeutic interventions for developmental seizure-induced brain damage.

Neurobehavioral Deficits in a Rat Model of Recurrent Neonatal Seizures Are Prevented by a Ketogenic Diet and Correlate with Hippocampal Zinc/Lipid Transporter Signals

The ketogenic diet (KD) has been shown to be effective as an antiepileptic therapy in adults, but it has not been extensively tested for its efficacy in neonatal seizure-induced brain damage. We have previously shown altered expression of zinc/lipid metabolism-related genes in hippocampus following penicillin-induced developmental model of epilepsy. In this study, we further investigated the effect of KD on the neurobehavioral and cognitive deficits, as well as if KD has any influence in the activity of zinc/lipid transporters such as zinc transporter 3 (ZnT-3), MT-3, ApoE, ApoJ (clusterin), and ACAT-1 activities in neonatal rats submitted to flurothyl-induced recurrent seizures. Postnatal day 9 (P9), 48 Sprague-Dawley rats were randomly assigned to two groups: flurothyl-induced recurrent seizure group (EXP) and control group (CONT). On P28, they were further randomly divided into the seizure group without ketogenic diet (EXP1), seizure plus ketogenic diet (EXP2), the control group without ketogenic diet (CONT1), and the control plus ketogenic diet (CONT2). Neurological behavioral parameters of brain damage (plane righting reflex, cliff avoidance reflex, and open field test) were observed from P35 to P49. Morris water maze test was performed during P51-P57. Then hippocampal mossy fiber sprouting and the protein levels of ZnT3, MT3, ApoE, CLU, and ACAT-1 were detected by Timm staining and Western blot analysis, respectively. Flurothyl-induced neurobehavioral toxicology and aberrant mossy fiber sprouting were blocked by KD. In parallel with these behavioral changes, rats treated with KD (EXP2) showed a significant down-regulated expression of ZnT-3, MT-3, ApoE, clusterin, and ACAT-1 in hippocampus when compared with the non-KD-treated EXP1 group. Our findings provide support for zinc/lipid transporter signals being potential targets for the treatment of neonatal seizure-induced brain damage by KD.

Oxidative stress induced by epileptic seizure and its attenuation by melatonin

An epileptic seizure and postictal period in addition to well-known features are also characterized by massive consumption of energy. This is thought to lead to oxidative stress and increased generation of free radicals, which is reflected by increased levels of oxidative products. Our previous work described the neuroprotective effects of melatonin in preventing cognitive worsening after a single epileptic seizure. This work was aimed on direct measurement of free radicals in brain tissue using the EPR method 1, 15 and 60 minutes after seizure. The measurement was performed in adult male Wistar rats at the mentioned intervals after a single tonic-clonic seizure induced by flurothyl. In comparison to control animals there was a significant increase in hydroxyl and nitroxyl radicals 60 minutes after the seizure. The levels of hydroxyl radicals were significantly lower in animals that received melatonin 60 minutes before seizure induction compared to animals without preventive treatment. Therefore, melatonin affected the generation of the measured free radicals differently. An important finding was the delayed increase in free radicals after a single seizure in the later phases of recovery.

Sex-specific consequences of early life seizures

Seizures are very common in the early periods of life and are often associated with poor neurologic outcome in humans. Animal studies have provided evidence that early life seizures may disrupt neuronal differentiation and connectivity, signaling pathways, and the function of various neuronal networks. There is growing experimental evidence that many signaling pathways, like GABAA receptor signaling, the cellular physiology and differentiation, or the functional maturation of certain brain regions, including those involved in seizure control, mature differently in males and females. However, most experimental studies of early life seizures have not directly investigated the importance of sex on the consequences of early life seizures. The sexual dimorphism of the developing brain raises the question that early seizures could have distinct effects in immature females and males that are subjected to seizures. We will first discuss the evidence for sex-specific features of the developing brain that could be involved in modifying the susceptibility and consequences of early life seizures. We will then review how sex-related biological factors could modify the age-specific consequences of induced seizures in the immature animals. These include signaling pathways (e.g., GABAA receptors), steroid hormones, growth factors. Overall, there are very few studies that have specifically addressed seizure outcomes in developing animals as a function of sex. The available literature indicates that a variety of outcomes (histopathological, behavioral, molecular, epileptogenesis) may be affected in a sex-, age-, region-specific manner after seizures during development. Obtaining a better understanding for the gender-related mechanisms underlying epileptogenesis and seizure comorbidities will be necessary to develop better gender and age appropriate therapies.

Expression profiles of hippocampal regenerative sprouting-related genes and their regulation by E-64d in a developmental rat model of penicillin-induced recurrent epilepticus

E-64d (a calpain and autophagy inhibitor) has previously been shown safe for the treatment of Alzheimer's disease in humans. In the present study, the potential protective mechanism of E-64d on hippocampal aberrant mossy fiber sprouting was examined in a developmental rat model of penicillin-induced recurrent epilepticus. A seizure was induced by penicillin every other day in Sprague-Dawley rats from postnatal day 21 (P21). The rats were randomly assigned into the control group (CONT1), the control plus E-64d (CONT2), the seizure group (EXP1) and the seizure plus E-64d (EXP2). On P51, mossy fiber sprouting and related gene expression in hippocampus were assessed by Timm staining and real-time RT-PCR methods, respectively. To validate the RT-PCR results, western blot analysis was performed on selected genes. E-64d obviously suppressed the aberrant mossy fiber sprouting in the supragranular region of dentate gyrus and CA3 subfield of hippocampus. Among the total twelve genes, six genes were strongly up- (MT-3, ACAT1, clusterin and ApoE) or down- (ZnT-1 and PRG-3) regulated by developmental seizures (EXP1) compared with that in the CONT1. Up-regulation of ApoE and Clusterin was blocked by pretreatment with E-64d both in mRNA and protein levels. Further, E-64d-pretreated seizure rats (EXP2) showed a significant downregulation of mRNA expression of PRG-1, PRG-3 and PRG-5, cathepsin B and ApoE, as well as up-regulated nSMase and ANX7 in hippocampus when compared with EXP1 rats. The results of the present study suggest that E-64d, an elective inhibitor of calpain and autophagy, is potentially useful in the treatment of developmental seizure-induced brain damage both by regulating abnormal zinc signal transduction and through the modulation of altered lipid metabolism via ApoE/clusterin pathway in hippocampus.

NMDA receptor signaling: death or survival?

Glutamate-induced neuronal damage is mainly caused by overactivation of N-methyl-D-aspartate (NMDA) receptors. Conversely, normal physiological brain function and neuronal survival require adequate activation of NMDA receptors. Studies have revealed that NMDA receptor-induced neuronal death or survival is mediated through distinct subset of NMDA receptors triggering different intracellular signaling pathways. Here we discuss recent advances in the characterization of NMDA receptors in neuronal protection, emphasizing subunit-specific role, which contributes to temporal-spatial distribution, subcellular localization and diverse channel properties of NMDA receptors.

Long-term effects of recurrent neonatal seizures on neurobehavioral function and related gene expression and its intervention by inhibitor of cathepsin B

Cathepsins are families of proteases that have been reported to play the key roles in neuroexcitotoxicity. The present study was sought to determine the effect of CBI, a cathepsin B inhibitor, in the prevention of neurobehavioral deficits after inhalant flurothyl-induced recurrent neonatal seizures in rats. We examined the expression pattern of autophagy-related genes at acute phase after the last seizures using western blot method, and evaluated behavioral deficits during postnatal day 28 (P28) to P35. The results showed improved neurological scores and learning ability in CBI-treated rats compared with the nontreated control. Flurothyl-induced increases in the ratio of LC3-II/LC3-I, Beclin-1 and Cathepsin-B were blocked by pre-treatment with CBI at 1.5, 3, 6 and 24 h after the last seizures in hippocampus and cerebral cortex by western blot analysis. Meanwhile, CBI also reversed flurothyl-induced down-regulation of Bcl-2 protein levels. Furthermore, in the long-term time point of 35 days (P35), PRG-1 mRNA and protein level in hippocampus and cerebral cortex of recurrent seizure group were up-regulated when compared to the control rats; meanwhile, the up-regulated expression of PRG-1 were robustly inhibited by CBI. These date demonstrated, for the first time, that lysosomal enzymes participate in neonatal seizure-induced brain damage and that modulation of cathepsin B may offer a new strategy for the development of therapeutic interventions for treatment of developmental seizure-induced brain damage.

Altered GABA signaling in early life epilepsies

The incidence of seizures is particularly high in the early ages of life. The immaturity of inhibitory systems, such as GABA, during normal brain development and its further dysregulation under pathological conditions that predispose to seizures have been speculated to play a major role in facilitating seizures. Seizures can further impair or disrupt GABA_A signaling by reshuffling the subunit composition of its receptors or causing aberrant reappearance of depolarizing or hyperpolarizing GABA_A receptor currents. Such effects may not result in epileptogenesis as frequently as they do in adults. Given the central role of GABA_A signaling in brain function and development, perturbation of its physiological role may interfere with neuronal morphology, differentiation, and connectivity, manifesting as cognitive or neurodevelopmental deficits. The current GABAergic antiepileptic drugs, while often effective for adults, are not always capable of stopping seizures and preventing their sequelae in neonates. Recent studies have explored the therapeutic potential of chloride cotransporter inhibitors, such as bumetanide, as adjunctive therapies of neonatal seizures. However, more needs to be known so as to develop therapies capable of stopping seizures while preserving the age- and sex-appropriate development of the brain.

Effects of penicillin-induced developmental epilepticus on hippocampal regenerative sprouting, related gene expression and cognitive deficits in rats

For the purpose of investigating the long-term effects of seizures in developmental rats on spatial learning ability and hippocampal mossy fiber sprouting related gene expressions in adult rat brain, a seizure was induced by penicillin quaque die alterna in Sprague-Dawley rats from postnatal day 29 (P29). Rats were assigned into the recurrent seizure group (RS, seizures were induced in 11 consecutive days) and the control group. During P51-P56, P81-P84 and P92-P95, the rats were tested for spatial learning ability with the Morris water maze task. On P95, the authors examined mossy fiber sprouting and gene expression of zinc transporters 1 and 3 (ZnT-1, ZnT-3), calcium/calmodulin-dependent protein kinase IIalpha (CaMK-IIalpha), NMDA receptor 2C (NR2C) and glutamate receptor 2 (GluR2) in hippocampus by Timm staining and real-time RT-PCR analysis. The escape latencies from the water maze of the rats in the RS group were significantly longer than those of the control rats at d5 of the first test, at d1 of the second test, and at d2 of the third test. In the spatial probe test, the ratio between the swim time in the third quadrant and the total swim time in control group was significantly higher than RS group (p<0.05) in the entire three probe tests. The Timm scores in CA3 and dentate gyrus in the RS animals were significantly higher than that in the control. Compared with the control rats, the expressions of ZnT-1, CaMK-IIalpha and GluR2 transcripts in the hippocampus of the RS group was significantly decreased while unchanged in transcriptional levels of ZnT-3 and NR2C. There were positive linear correlations among ZnT-3, CaMKIIalpha, and NR2C in control group and among CaMKIIalpha, ZnT-1 and GluR2 in RS group. The results suggest that recurrent seizures induced in developmental rats could cause long-term disturbance on the hippocampal mossy fiber sprouting related gene expressions, which might play an important role in long-term cognitive deficit and hippocampal aberrant mossy fiber sprouting.

Neonatal seizures: do they damage the brain?

Seizures are an early sign of brain injury in newborns. These seizures are in most cases repetitive or associated with asymptomatic electrographic seizures. Despite the relative resistance of the immature brain to seizure-induced brain damage, there is more and more evidence that neonatal seizures impair normal brain development. This review addresses the changes associated with neonatal seizures and discusses current and future potential neuroprotective strategies.

JunB is a repressor of MMP-9 transcription in depolarized rat brain neurons

Matrix Metalloproteinase-9 (MMP-9) is an extracellularly operating enzyme involved in the synaptic plasticity, hippocampal-dependent long term memory and neurodegeneration. Previous studies have shown its upregulation following seizure-evoking stimuli. Herein, we show that in the rat brain, MMP-9 mRNA expression in response to pentylenetetrazole-evoked neuronal depolarization is transient. Furthermore, we demonstrate that in the rat hippocampus neuronal activation strongly induces JunB expression, simultaneously leading to an accumulation of JunB/FosB complexes onto the -88/-80 bp site of the rat MMP-9 gene promoter in vivo. Surprisingly, manipulations with JunB expression levels in activated neurons revealed its moderate repressive action onto MMP-9 gene expression. Therefore, our study documents the active repressive influence of AP-1 onto MMP-9 transcriptional regulation by the engagement of JunB.