Brief seizure activity alters Ca2+/calmodulin dependent protein kinase II dephosphorylation and subcellular distribution in rat brain for several hours

Gentiopicroside Attenuates Lithium/Pilocarpine-Induced Epilepsy Seizures by Down-Regulating NR2B/CaMKII/CREB and TLR4/NF-κB Signaling Pathways in the Hippocampus of Mice

Background: Epilepsy is a prevalent and disabling neurological condition characterized by recurrent seizures. Approximately 50% of adults with active epilepsy have at least one comorbidity and they are at a greater risk of premature death than the general population. Gentiopicroside (Gent) is a primary component of Gentiana macrophylla Pall. that has been shown to have diverse pharmacological properties. However, its role in epileptic seizures in adult mice and its underlying mechanism of action remain obscure. We aimed to explore the anti-epileptic effect and mechanism of Gent on lithium/pilocarpine (Pilo)-induced epilepsy seizures in mice. Methods: In this study, we established a lithium/Pilo-induced epilepsy model, and Gent was first given to mice 30 min before Pilo administration. Then, we detected behavioral and histopathological changes through electrocorticographic (ECoG) measurements, Nissl staining, Fluoro-Jade B (FJB) staining, and immunohistochemical staining. We then used molecular biology techniques, such as Western blotting, quantitative polymerase chain reaction (qPCR) analysis, and the enzyme-linked immunosorbent assay (ELISA) to investigate the mechanisms of Gent in lithium/Pilo-induced epileptic seizures in mice and lipopolysaccharide (LPS)-induced inflammatory astrocytes. Results: We confirmed that Gent could prevent abnormal ECoG activity, behavioral changes, and neurodegeneration. Subsequently, we found Gent could downregulate the factors that could promote apoptosis (i.e., the NR2B/CaMKII/CREB signaling cascade) and neuroinflammatory-related factors (i.e., the TLR4/NF-κB signaling cascade). Conclusions: Gent could be a potential therapeutic agent for epilepsy, offering possibilities for both prevention and treatment. Our research establishes a preliminary experimental framework for ongoing studies into Gent's efficacy as a treatment for epilepsy.

Behavioral and Molecular Responses to Exogenous Cannabinoids During Pentylenetetrazol-Induced Convulsions in Male and Female Rats

Epilepsy is a disabling, chronic brain disease,affecting ~1% of the World’s population, characterized by recurrent seizures (sudden, uncontrolled brain activity), which may manifest with motor symptoms (e.g., convulsions) or non-motor symptoms. Temporal lobe epilepsies (TLE) compromising the hippocampus are the most common form of focal epilepsies. Resistance in ~1/3 of epileptic patients to the first line of treatment, i.e., antiepileptic drugs (AEDs), has been an important motivation to seek alternative treatments. Among these, the plant Cannabis sativa (commonly known as marihuana) or compounds extracted from it (cannabinoids) have gained widespread popularity. Moreover, sex differences have been proposed in epilepsy syndromes and in cannabinoid action. In the hippocampus, cannabinoids interact with the CB1R receptor whose membrane levels are regulated by β-Arrestin2, a protein that promotes its endocytosis and causes its downregulation. In this article, we evaluate the modulatory role of WIN 55,212-2 (WIN), a synthetic exogenous cannabinoid on behavioral convulsions and on the levels of CB1R and β-Arrestin2 in female and male adolescent rats after a single injection of the proconvulsant pentylenetetrazol (PTZ). As epilepsies can have a considerable impact on synaptic proteins that regulate neuronal toxicity, plasticity, and cognition, we also measured the levels of key proteins markers of excitatory synapses, in order to examine whether exogenous cannabinoids may prevent such pathologic changes after acute seizures. We found that the exogenous administration of WIN prevented convulsions of medium severity in females and males and increased the levels of phosphorylated CaMKII in the hippocampus. Furthermore, we observed a higher degree of colocalization between CB1R and β-Arrestin2 in the granule cell layer.

Pentylenetetrazol and Morphine Interaction in a State-dependent Memory Model: Role of CREB Signaling

Introduction:

State-dependent (STD) memory is a process, in which the learned information can be optimally retrieved only when the subject is in the state similar to the encoding phase. This phenomenon has been widely studied with morphine. Several studies have reported that Pentylenetetrazole (PTZ) impairs memory in experimental animal models. Due to certain mechanistic interactions between morphine and PTZ, it is hypothesized that PTZ may interfere with the morphine-STD. The cyclic adenosine monophosphate Response Element-Binding (CREB) is considered as the main downstream marker for long-term memory. This study was designed to determine the possible interaction between PTZ and morphine STD and the presumable changes in CREB mRNA.

Methods:

In an Inhibitory Avoidance (IA) model, posttraining morphine (2.5, 5, and 7.5 mg/ kg-i.p.) was used. The pre-test morphine was evaluated for morphine-induced STD memory. Moreover, the effect of a pre-test PTZ (60 mg/kg-i.p.) was studied along with morphine STD. Locomotion testing was carried out using open-field. Eventually, using real-time-PCR, the CREB mRNA changes in the hippocampus were evaluated.

Results:

Posttraining MOR (7.5 mg/kg-i.p.) impaired IA memory (P<0.001). The pre-test injection of similar doses of morphine recovered the morphine-induced memory impairment (P<0.001). The pre-test PTZ impaired the IA memory recall (P<0.001); however, the pre-test PTZ along with morphine STD potentiated the morphine-induced STD (P<0.001). Alterations in CREB mRNA were observed in all groups. No difference was seen in the locomotor activity.

Conclusion:

Presumably, the certain interactive effect of PTZ on morphine-induced STD is mediated through gamma-aminobutyric acid and opioid systems via CREB signaling.

Modeling psychiatric comorbid symptoms of epileptic seizures in zebrafish

Epilepsy is a debilitating neurological disorder characterized by recurrent unprovoked seizures. Anxiety, cognitive deficits, depressive-like symptoms, and social dysfunction are psychiatric comorbidities with high prevalence in epileptic patients. Due to the genetic and behavioral tractability, the zebrafish is a promising model organism to understand the neural bases involved in epilepsy-related comorbidities. Here, we aimed to characterize some behavioral phenotypes paralleling those observed in epilepsy-related comorbidities after a single pentylenetetrazole (PTZ) exposure in zebrafish. We also analyzed the influence of whole-body cortisol levels in the behavioral responses measured. Fish were exposed to 10 mM PTZ for 20 min to induce epileptic seizures. After 24 h recovery period, locomotion and anxiety-like responses (novel tank and light-dark tests), social interaction (shoaling behavior task), and memory retention (inhibitory avoidance protocol) were assessed. Basically, PTZ impaired habituation to novelty stress, evoked anxiogenic-like behaviors, disrupted shoaling, and caused memory consolidation deficits in zebrafish without changing whole-body cortisol levels. In conclusion, our novel findings further validate the use of zebrafish as a suitable tool for modeling epilepsy-related comorbidities in translational neuropsychiatric research.

Voltage-Dependent Calcium Channels, Calcium Binding Proteins, and Their Interaction in the Pathological Process of Epilepsy

As an important second messenger, the calcium ion (Ca²⁺) plays a vital role in normal brain function and in the pathophysiological process of different neurodegenerative diseases including Alzheimer’s disease (AD), Parkinson’s disease (PD), and epilepsy. Ca²⁺ takes part in the regulation of neuronal excitability, and the imbalance of intracellular Ca²⁺ is a trigger factor for the occurrence of epilepsy. Several anti-epileptic drugs target voltage-dependent calcium channels (VDCCs). Intracellular Ca²⁺ levels are mainly controlled by VDCCs located in the plasma membrane, the calcium-binding proteins (CBPs) inside the cytoplasm, calcium channels located on the intracellular calcium store (particular the endoplasmic reticulum/sarcoplasmic reticulum), and the Ca²⁺-pumps located in the plasma membrane and intracellular calcium store. So far, while many studies have established the relationship between calcium control factors and epilepsy, the mechanism of various Ca²⁺ regulatory factors in epileptogenesis is still unknown. In this paper, we reviewed the function, distribution, and alteration of VDCCs and CBPs in the central nervous system in the pathological process of epilepsy. The interaction of VDCCs with CBPs in the pathological process of epilepsy was also summarized. We hope this review can provide some clues for better understanding the mechanism of epileptogenesis, and for the development of new anti-epileptic drugs targeting on VDCCs and CBPs.

Multiple forms of metaplasticity at a single hippocampal synapse during late postnatal development

Metaplasticity refers to adjustment in the requirements for induction of synaptic plasticity based on the prior history of activity. Numerous forms of developmental metaplasticity are observed at Schaffer collateral synapses in the rat hippocampus at the end of the third postnatal week. Emergence of spatial learning and memory at this developmental stage suggests possible involvement of metaplasticity in the final maturation of the hippocampus. Three distinct metaplastic phenomena are apparent. (1) As transmitter release probability increases with increasing age, presynaptic potentiation is reduced. (2) Alterations in the composition and channel conductance properties of AMPARs facilitate the induction of postsynaptic potentiation with increasing age. (3) Low frequency stimulation inhibits subsequent induction of potentiation in animals older but not younger than 3 weeks of age. Thus, many forms of plasticity expressed at SC-CA1 synapses are different in rats younger and older than 3 weeks of age, illustrating the complex orchestration of physiological modifications that underlie the maturation of hippocampal excitatory synaptic transmission. This review paper describes three late postnatal modifications to synaptic plasticity induction in the hippocampus and attempts to relate these metaplastic changes to developmental alterations in hippocampal network activity and the maturation of contextual learning.

Emerging role of CaMKII in neuropsychiatric disease

Although it has been known for decades that hippocampal calcium/calmodulin (CaM)-dependent protein kinase II (CaMKII) plays an essential role in learning and memory consolidation, the roles of CaMKII in other brain regions are only recently being explored in depth. A series of recent studies suggest that CaMKII dysfunction throughout the brain may underlie myriad neuropsychiatric disorders, including drug addiction, schizophrenia, depression, epilepsy, and multiple neurodevelopmental disorders, perhaps through maladaptations in glutamate signaling and neuroplasticity. I review here the structure, function, subcellular localization, and expression patterns of CaMKII isoforms, as well as recent advances demonstrating that disturbances in these properties may contribute to psychiatric disorders.

Anti-epileptic effect of Ganoderma lucidum polysaccharides by inhibition of intracellular calcium accumulation and stimulation of expression of CaMKII α in epileptic hippocampal neurons

Purpose

To investigate the mechanism of the anti-epileptic effect of Ganoderma lucidum polysaccharides (GLP), the changes of intracellular calcium and CaMK II α expression in a model of epileptic neurons were investigated.

Method

Primary hippocampal neurons were divided into: 1) Control group, neurons were cultured with Neurobasal medium, for 3 hours; 2) Model group I: neurons were incubated with Mg²⁺ free medium for 3 hours; 3) Model group II: neurons were incubated with Mg²⁺ free medium for 3 hours then cultured with the normal medium for a further 3 hours; 4) GLP group I: neurons were incubated with Mg²⁺ free medium containing GLP (0.375 mg/ml) for 3 hours; 5) GLP group II: neurons were incubated with Mg²⁺ free medium for 3 hours then cultured with a normal culture medium containing GLP for a further 3 hours. The CaMK II α protein expression was assessed by Western-blot. Ca²⁺ turnover in neurons was assessed using Fluo-3/AM which was added into the replacement medium and Ca²⁺ turnover was observed under a laser scanning confocal microscope.

Results

The CaMK II α expression in the model groups was less than in the control groups, however, in the GLP groups, it was higher than that observed in the model group. Ca²⁺ fluorescence intensity in GLP group I was significantly lower than that in model group I after 30 seconds, while in GLP group II, it was reduced significantly compared to model group II after 5 minutes.

Conclusion

GLP may inhibit calcium overload and promote CaMK II α expression to protect epileptic neurons.

Neuronal excitability and calcium/calmodulin-dependent protein kinase type II: location, location, location

Calcium/calmodulin-dependent protein kinase type II (CaMKII) is a highly abundant serine/threonine kinase comprising a significant fraction of total protein in mammalian forebrain and forming a major component of the postsynaptic density. CaMKII is essential for certain forms of synaptic plasticity and memory consolidation and this is mediated through substrate binding and intramolecular phosphorylation of holoenzyme subunits. CaMKII is multifunctional; it targets a variety of cellular substrates, and this diversity depends on holoenzyme subunit composition. CaMKII comprises homooligomeric and heterooligomeric complexes generated from four subunits (α, β, δ, and γ) encoded by separate genes that are further expanded by extensive alternative splicing to more than 30 different isoforms. Much attention has been paid to understanding the regulation of CaMKII function through its structural diversity and/or substrate specificity. However, given the importance of subunit composition to holoenzyme activity, it is likely that specificity of cellular expression of CaMKII isoforms also plays a major role in regulation of enzyme function. Herein we review the cellular colocalization of CaMKII isoforms with special regard to the cell-type specificity of isoform expression in brain. In addition, we highlight the remarkable specificity of subcellular localization by the CaMKIIα isoform. In addition, we discuss the role that this cellular specificity of expression might play in propagating the type of recurrent neuronal activity associated with disorders such as temporal lobe epilepsy.

Bi-directional regulation of CaMKIIα phosphorylation at Thr286 by NMDA receptors in cultured cortical neurons

The N-methyl-D-aspartate (NMDA) receptor (NMDAR)-stimulated autophosphorylation of calmodulin-dependent kinase IIα at Thr286 may regulate many aspects of neuroplasticity. Here, we show that low NMDA concentration (20 μM) up-regulated Thr286 phosphorylation, and high concentration (100 μM) caused dephosphorylation. We next modulated the strength of NMDAR activation by manipulating NMDAR 2A subunit (NR2A) and NMDAR 2B subunit (NR2B), which represent the major NMDAR subtypes in forebrain regions. Pharmacological inhibition and molecular knockdown of NR2A or NR2B blocked 20 μM NMDA-induced phosphorylation. Conversely, over-expression of NR2A or NR2B enhanced phosphorylation by 20 μM NMDA. The 100 μM NMDA-induced dephosphorylation was suppressed by inhibition or knockdown of NR2A or NR2B, and enhanced by over-expression of NR2A or NR2B. Compared to NR2A, NR2B showed a higher impact on the NMDA-stimulated bi-directional regulation of Thr286 phosphorylation. We further found that activation of NR2A and NR2B by 100 μM NMDA-induced dephosphorylation through protein phosphatases (PP) that are inhibited by high concentration okadaic acid (1 μM), but not by PP2A and PP2B inhibitors. This novel function of NMDAR in dynamic regulation of calmodulin-dependent kinase IIα activity provides new evidence to support the current understanding that, depending on the degree of activation, NMDAR may lead to different and even opposing effects on intracellular signaling.

Effects of pentylenetetrazol-induced brief convulsive seizures on spatial memory and fear memory

Previous studies have demonstrated that in the pentylenetetrazol (PTZ) kindling model, recurrent seizures either impair or have no effect on learning and memory. However, the effects of brief seizures on learning and memory remain unknown. Here, we found that a single injection of a convulsive dose of PTZ (50 mg/kg, ip) induced brief seizures in Sprague-Dawley rats. Administration of PTZ before training impaired the acquisition of spatial memory in the Morris water maze (MWM) and fear memory in contextual fear conditioning. However, the administration of PTZ immediately after training did not affect memory consolidation in either task. These findings suggest that brief seizures have different effects on acquisition and consolidation of spatial and fear memory.

Transient activation of protein phosphatase 2A induced by electroconvulsive shock in the rat frontal cortex

We have attempted to determine the effects of electroconvulsive shock (ECS) on protein phosphatase 2A (PP2A) in the frontal cortices of rats. PP2A exhibited a 30% increase in activity immediately after ECS treatment. Immunoblot analysis revealed that phosphorylation signals, including protein kinase B (Akt/PKB), glycogen synthase kinase-3beta (GSK-3beta), and cyclic adenosine monophosphate response element binding protein (CREB) were reduced immediately after ECS treatment. When an additional ECS was administered after the activation of these kinases, the immediate reactivation of PP2A overrode the kinase activity. ECS induces transient PP2A activation prior to kinase activation, and this pattern of activity may induce the biphasic phosphorylation of substrate proteins.

Effect of pentylenetetrazol-induced epileptic seizure on thiol redox state in the mouse cerebral cortex

In the present study we examined the effects of pentylenetetrazol (PTZ) administration on the thiol redox state (TRS), lipid peroxidation and protein oxidation in left and right mouse cerebral cortex in order (a) to quantitate the major components of the thiol redox state and relate them with oxidative stress and cortical laterality, and (b) to investigate whether neuronal activation without synchronization, induced by subconvulsive doses of PTZ, can cause similar qualitative effects on the thiol redox state. Specifically, we examined the TRS components [glutathione (GSH), glutathione disulfide (GSSG), cysteine (CSH), protein (P) thiols (PSH) and protein and non-protein (NP) mixed/symmetric disulfides (PSSR, NPSSR, NPSSC, PSSP)]. At 15 min after seizure, GSH, GSSG, CSH, NPSSC, PSSR and PSSC levels are decreased in left (14-50%) and right (11-53%) cortex while PSSP levels are increased in both left (1400%) and right (1600%) cortex. At 30 min after seizure, GSSG, CSH, NPSSC, PSSR and PSSC levels are decreased in left (14-51%) and right (18-56%) cortex while PSSP and protein carbonyl levels are increased in left (2300% and 20%, respectively) and right (2800% and 21%, respectively) cortex. At 24 h after seizure, the TRS components return to normal and protein carbonyl levels are decreased in left (16%) and right (20%) cortex. The significant decrease in GSH, GSSG, CSH, NPSSC, PSSR and PSSC, as well as the increase in protein carbonyl and the high increase in PSSP levels after PTZ-induced seizure indicate increased oxidative stress in cerebral cortex of mice, and of similar magnitude and TRS-component profiles between left and right cerebral cortex.

Prolonged changes in Ca2+/calmodulin-dependent protein kinase II after a brief pentylenetetrazol seizure; potential role in kindling

This study evaluated the alteration of CaMKII autophosphorylation and distribution in rat brain following a single, brief pentylenetetrazol (PTZ) seizure and during PTZ kindling. Total CaMKII alpha subunit (alpha-CaMKII) and alpha-CaMKII phosphorylated at Thr(286) were detected by immunoblot. A large decrease in CaMKII Thr(286) phosphorylation, as well as CaMKII translocation from particulate to soluble fraction was observed in both cerebral cortex and hippocampus 0.5-4 h after the brief PTZ convulsion. These changes reverted to control values by 12 h. These long-lasting changes in CaMKII autophosphorylation and subcellular distribution after a brief seizure suggested that CaMKII could be involved in carrying forward the signal resulting from brief seizure activity, at least for a few hours, as would be required for kindling to occur. In PTZ kindled rats, convulsions produced changes in CaMKII Thr(286) phosphorylation and distribution in the same direction and of similar magnitude as after the acute convulsion, but lasting for a much longer time. In fact, reduced Thr(286) phosphorylation of alpha-CaMKII was observed up to 48 h, completely bridging the interval between PTZ injections. Similar, but intermediate changes were found in tissue from rats that were only partially kindled. These results implicate CaMKII as a molecular messenger in the acquisition of PTZ kindling.