Chronic inhibition of Ca(2+)/calmodulin kinase II activity in the pilocarpine model of epilepsy

The Traf2 and NcK interacting kinase inhibitor NCB-0846 suppresses seizure activity involving the decrease of GRIA1

Epilepsy, one of the most common neurological disorders, is characterized by spontaneous recurrent seizures. Temporal lobe epilepsy (TLE) is one of the most common medically intractable seizure disorders. Traf2-and NcK-interacting kinase (TNIK) has recently attracted attention as a critical modulation target of many neurological and psychiatric disorders, but its role in epilepsy remains unclear. In this study, we hypothesized the involvement of TNIK in epilepsy and investigated TNIK expression in patients with intractable TLE and in a pilocarpine-induced rat model of epilepsy by western blotting, immunofluorescence, and immunohistochemistry. A pentylenetetrazole (PTZ)-induced epilepsy rat model was used to determine the effect of the TNIK inhibitor NCB-0846 on behavioral manifestations of epilepsy. Coimmunoprecipitation (Co-IP)/mass spectrometry (MS) was used to identify the potential mechanism. Through Co-IP, we detected and confirmed the main potential TNIK interactors. Subcellular fractionation was used to establish the effect of NCB-0846 on the expression of the main interactors in postsynaptic density (PSD) fractions. We found that TNIK was primarily located in neurons and decreased significantly in epilepsy model rats and TLE patients compared with controls. NCB-0846 delayed kindling progression and decreased seizure severity. Co-IP/MS identified 63 candidate TNIK interactors in rat hippocampi, notably CaMKII. Co-IP showed that TNIK might correlate with endogenous GRIA1, SYN2, PSD-95, CaMKIV, GABRG1, and GABRG2. In addition, the significant decrease in GRIA1 in hippocampal total lysate and PSDs after NCB-0846 treatment might help modify the progression of PTZ kindling. Our results suggest that TNIK contributes to epileptic pathology and is a potential antiepileptic drug target.

In the fast lane: Receptor trafficking during status epilepticus

Status epilepticus (SE) remains a significant cause of morbidity and mortality and often is refractory to standard first-line treatments. A rapid loss of synaptic inhibition and development of pharmacoresistance to benzodiazepines (BZDs) occurs early during SE, while NMDA and AMPA receptor antagonists remain effective treatments after BZDs have failed. Multimodal and subunit-selective receptor trafficking within minutes to an hour of SE involves GABA-A, NMDA, and AMPA receptors and contributes to shifts in the number and subunit composition of surface receptors with differential impacts on the physiology, pharmacology, and strength of GABAergic and glutamatergic currents at synaptic and extrasynaptic sites. During the first hour of SE, synaptic GABA-A receptors containing γ2 subunits move to the cell interior while extrasynaptic GABA-A receptors with δ subunits are preserved. Conversely, NMDA receptors containing N2B subunits are increased at synaptic and extrasynaptic sites, and homomeric GluA1 ("GluA2-lacking") calcium permeant AMPA receptor surface expression also is increased. Molecular mechanisms, largely driven by NMDA receptor or calcium permeant AMPA receptor activation early during circuit hyperactivity, regulate subunit-specific interactions with proteins involved with synaptic scaffolding, adaptin-AP2/clathrin-dependent endocytosis, endoplasmic reticulum (ER) retention, and endosomal recycling. Reviewed here is how SE-induced shifts in receptor subunit composition and surface representation increase the excitatory to inhibitory imbalance that sustains seizures and fuels excitotoxicity contributing to chronic sequela such as "spontaneous recurrent seizures" (SRS). A role for early multimodal therapy is suggested both for treatment of SE and for prevention of long-term comorbidities.

Chronically altered NMDAR signaling in epilepsy mediates comorbid depression

Depression is the most common psychiatric comorbidity of epilepsy. However, the molecular pathways underlying this association remain unclear. The NMDA receptor (NMDAR) may play a role in this association, as its downstream signaling has been shown to undergo long-term changes following excitotoxic neuronal damage. To study this pathway, we used an animal model of fluoxetine-resistant epilepsy-associated depression (EAD). We determined the molecular changes associated with the development of depressive symptoms and examined their response to various combinations of fluoxetine and a selective neuronal nitric oxide synthase inhibitor, 7-nitroindazole (NI). Depressive symptoms were determined using the forced swim test. Furthermore, expression and phosphorylation levels of markers in the ERK/CREB/ELK1/BDNF/cFOS pathway were measured to determine the molecular changes associated with these symptoms. Finally, oxidative stress markers were measured to more clearly determine the individual contributions of each treatment. While chronic fluoxetine (Flxc) and NI were ineffective alone, their combination had a statistically significant synergistic effect in reducing depressive symptoms. The development of depressive symptoms in epileptic rats was associated with the downregulation of ERK2 expression and ELK1 and CREB phosphorylation. These changes were exactly reversed upon Flxc + NI treatment, which led to increased BDNF and cFOS expression as well. Interestingly, ERK1 did not seem to play a role in these experiments. NI seemed to have augmented Flxc’s antidepressant activity by reducing oxidative stress. Our findings suggest NMDAR signaling alterations are a major contributor to EAD development and a potential target for treating conditions associated with underlying excitotoxic neuronal damage.

Role of calcium/calmodulin-dependent kinase 2 in neurodevelopmental disorders

Neurodevelopmental disorders are a complex and heterogeneous group of neurological disorders characterized by their early-onset and estimated to affect more than 3% of children worldwide. The rapid advancement of sequencing technologies in the past years allowed the identification of hundreds of variants in several different genes causing neurodevelopmental disorders. Between those, new variants in the Calcium/calmodulin dependent protein kinase II (CAMK2) genes were recently linked to intellectual disability. Despite many years of research on CAMK2, this proves for the first time that this well-known and highly conserved molecule plays an important role in the human brain. In this review, we give an overview of the identified CAMK2 variants, and we speculate on potential mechanisms through which dysfunctions in CAMK2 result in neurodevelopmental disorders. Additionally, we discuss how the identification of CAMK2 variants might result in new exciting discoveries regarding the function of CAMK2 in the human brain.

Phosphorylation of the HCN channel auxiliary subunit TRIP8b is altered in an animal model of temporal lobe epilepsy and modulates channel function

Temporal lobe epilepsy (TLE) is a prevalent neurological disorder with many patients experiencing poor seizure control with existing anti-epileptic drugs. Thus, novel insights into the mechanisms of epileptogenesis and identification of new drug targets can be transformative. Changes in ion channel function have been shown to play a role in generating the aberrant neuronal activity observed in TLE. Previous work demonstrates that hyperpolarization-activated cyclic nucleotide-gated (HCN) channels regulate neuronal excitability and are mislocalized within CA1 pyramidal cells in a rodent model of TLE. The subcellular distribution of HCN channels is regulated by an auxiliary subunit, tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b), and disruption of this interaction correlates with channel mislocalization. However, the molecular mechanisms responsible for HCN channel dysregulation in TLE are unclear. Here we investigated whether changes in TRIP8b phosphorylation are sufficient to alter HCN channel function. We identified a phosphorylation site at residue Ser²³⁷ of TRIP8b that enhances binding to HCN channels and influences channel gating by altering the affinity of TRIP8b for the HCN cytoplasmic domain. Using a phosphospecific antibody, we demonstrate that TRIP8b phosphorylated at Ser²³⁷ is enriched in CA1 distal dendrites and that phosphorylation is reduced in the kainic acid model of TLE. Overall, our findings indicate that the TRIP8b-HCN interaction can be modulated by changes in phosphorylation and suggest that loss of TRIP8b phosphorylation may affect HCN channel properties during epileptogenesis. These results highlight the potential of drugs targeting posttranslational modifications to restore TRIP8b phosphorylation to reduce excitability in TLE.

Epilepsy-associated alterations in hippocampal excitability

The hippocampus exhibits a wide range of epilepsy-related abnormalities and is situated in the mesial temporal lobe, where limbic seizures begin. These abnormalities could affect membrane excitability and lead to overstimulation of neurons. Multiple overlapping processes refer to neural homeostatic responses develop in neurons that work together to restore neuronal firing rates to control levels. Nevertheless, homeostatic mechanisms are unable to restore normal neuronal excitability, and the epileptic hippocampus becomes hyperexcitable or hypoexcitable. Studies show that there is hyperexcitability even before starting recurrent spontaneous seizures, suggesting although hippocampal hyperexcitability may contribute to epileptogenesis, it alone is insufficient to produce epileptic seizures. This supports the concept that the hippocampus is not the only substrate for limbic seizure onset, and a broader hyperexcitable limbic structure may contribute to temporal lobe epilepsy (TLE) seizures. Nevertheless, seizures also occur in conditions where the hippocampus shows a hypoexcitable phenotype. Since TLE seizures most often originate in the hippocampus, it could therefore be assumed that both hippocampal hypoexcitability and hyperexcitability are undesirable states that make the epileptic hippocampal network less stable and may, under certain conditions, trigger seizures.

Identifying and Analyzing Novel Epilepsy-Related Genes Using Random Walk with Restart Algorithm

As a pathological condition, epilepsy is caused by abnormal neuronal discharge in brain which will temporarily disrupt the cerebral functions. Epilepsy is a chronic disease which occurs in all ages and would seriously affect patients' personal lives. Thus, it is highly required to develop effective medicines or instruments to treat the disease. Identifying epilepsy-related genes is essential in order to understand and treat the disease because the corresponding proteins encoded by the epilepsy-related genes are candidates of the potential drug targets. In this study, a pioneering computational workflow was proposed to predict novel epilepsy-related genes using the random walk with restart (RWR) algorithm. As reported in the literature RWR algorithm often produces a number of false positive genes, and in this study a permutation test and functional association tests were implemented to filter the genes identified by RWR algorithm, which greatly reduce the number of suspected genes and result in only thirty-three novel epilepsy genes. Finally, these novel genes were analyzed based upon some recently published literatures. Our findings implicate that all novel genes were closely related to epilepsy. It is believed that the proposed workflow can also be applied to identify genes related to other diseases and deepen our understanding of the mechanisms of these diseases.

The role of Ca2+-calmodulin stimulated protein kinase II in ischaemic stroke - A potential target for neuroprotective therapies

Studies in multiple experimental systems show that Ca²⁺-calmodulin stimulated protein kinase II (CaMKII) is a major mediator of ischaemia-induced cell death and suggest that CaMKII would be a good target for neuroprotective therapies in acute treatment of stroke. However, as CaMKII regulates many cellular processes in many tissues any clinical treatment involving the inhibition of CaMKII would need to be able to specifically target the functions of ischaemia-activated CaMKII. In this review we summarise new developments in our understanding of the molecular mechanisms involved in ischaemia-induced CaMKII-mediated cell death that have identified ways in which such specificity of CaMKII inhibition after stroke could be achieved. We also review the mechanisms and phases of tissue damage in ischaemic stroke to identify where and when CaMKII-mediated mechanisms may be involved.

Metabotropic Glutamate Receptors and Interacting Proteins in Epileptogenesis

Neurotransmitter and receptor systems are involved in different neurological and neuropsychological disorders such as Parkinson's disease, depression, Alzheimer’s disease and epilepsy. Recent advances in studies of signal transduction pathways or interacting proteins of neurotransmitter receptor systems suggest that different receptor systems may share the common signal transduction pathways or interacting proteins which may be better therapeutic targets for development of drugs to effectively control brain diseases. In this paper, we reviewed metabotropic glutamate receptors (mGluRs) and their related signal transduction pathways or interacting proteins in status epilepticus and temporal lobe epilepsy, and proposed some novel therapeutical drug targets for controlling epilepsy and epileptogenesis.

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.

Changes in microRNA expression in the whole hippocampus and hippocampal synaptoneurosome fraction following pilocarpine induced status epilepticus

MicroRNAs regulate protein synthesis by binding non-translated regions of mRNAs and suppressing translation and/or increasing mRNA degradation. MicroRNAs play an important role in the nervous system including controlling synaptic plasticity. Their expression is altered in disease states including stroke, head injury and epilepsy. To better understand microRNA expression changes that might contribute to the development of epilepsy, microRNA arrays were performed on rat hippocampus 4 hours, 48 hours and 3 weeks following an episode of pilocarpine induced status epilepticus. Eighty microRNAs increased at one or more of the time points. No microRNAs decreased at 4 hours, and only a few decreased at 3 weeks, but 188 decreased 48 hours after status epilepticus. The large number of microRNAs with altered expression following status epilepticus suggests that microRNA regulation of translation has the potential to contribute to changes in protein expression during epileptogenesis. We carried out a second set of array's comparing microRNA expression at 48 hours in synaptoneurosome and nuclear fractions of the hippocampus. In control rat hippocampi multiple microRNAs were enriched in the synaptoneurosomal fraction as compared to the nuclear fraction. In contrast, 48 hours after status epilepticus only one microRNA was enriched in the synaptoneurosome fraction. The loss of microRNAs enriched in the synaptoneurosomal fraction implies a dramatic change in translational regulation in synapses 48 hours after status epilepticus.

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.

Statistical parametric mapping reveals regional alterations in cannabinoid CB1 receptor distribution and G-protein activation in the 3D reconstructed epileptic rat brain

PURPOSE

  The endocannabinoid system is known to modulate seizure activity in several in vivo and in vitro models, and CB(1) -receptor activation is anticonvulsant in the rat pilocarpine model of acquired epilepsy (AE). In these epileptic rats, a unique redistribution of the CB(1) receptor occurs within the hippocampus; however, an anatomically inclusive analysis of the effect of status epilepticus (SE)-induced AE on CB(1) receptors has not been thoroughly evaluated. Therefore, statistical parametric mapping (SPM), a whole-brain unbiased approach, was used to study the long-term effect of pilocarpine-induced SE on CB(1) -receptor binding and G-protein activation in rats with AE.

METHODS

  Serial coronal sections from control and epileptic rats were cut at equal intervals throughout the neuraxis and processed for [(3) H]WIN55,212-2 (WIN) autoradiography, WIN-stimulated [(35) S]GTPγS autoradiography, and CB(1) -receptor immunohistochemistry (IHC). The autoradiographic techniques were evaluated with both region of interest (ROI) and SPM analyses.

KEY FINDINGS

  In rats with AE, regionally specific increases in CB(1) -receptor binding and activity were detected in cortex, discrete thalamic nuclei, and other regions including caudate-putamen and septum, and confirmed by IHC. However, CB(1) receptors were unaltered in several brain regions, including substantia nigra and cerebellum, and did not exhibit regional decreases in rats with AE.

SIGNIFICANCE

  This study provides the first comprehensive evaluation of the regional distribution of changes in CB(1) -receptor expression, binding, and G-protein activation in the rat pilocarpine model of AE. These regions may ultimately serve as targets for cannabinomimetic compounds or manipulation of the endocannabinoid system in epileptic brain.

Auditory impairment in infants at risk for bilirubin-induced neurologic dysfunction

Classical and subtypes of kernicterus associated with bilirubin toxicity can be differentiated in part with physiological auditory measures that include auditory-evoked potentials and measures of cochlear integrity. The combination of these auditory measures suggests that bilirubin exposure results in auditory system damage initially at the level of the brainstem, progressing to the level of the VIII cranial nerve and then to greater neural centers. There is no evidence of neural damage at the level of the cochlea. Auditory neural damage from bilirubin toxicity ranges from neural timing deficits, including neural firing delays and dyssynchrony, to neural response reduction and even elimination of auditory neural responses. This condition is comprehensively described as auditory neuropathy spectrum disorder. Independent measures of cochlear function and auditory neural function up to the level of the brainstem can effectively diagnose auditory neural damage resulting from bilirubin neurotoxicity. Intervention, including cochlear implants can be effective.

Strain-related differences after experimental traumatic brain injury in rats

The present study directly compares the effects of experimental brain injury in two commonly used rat strains: Fisher 344 and Sprague-Dawley. We previously found that Fisher rats have a higher mortality rate and more frequent seizure attacks at the same injury level than Sprague-Dawley rats. Although strain differences in rats are commonly accepted as contributing to variability among studies, there is a paucity of literature addressing strain influence in experimental neurotrauma. Therefore this study compares outcome measures in two rat strains following lateral fluid percussion injury. Fisher 344 and Sprague-Dawley rats were monitored for changes in physiological measurements, intracranial pressure, and electroencephalographic activity. We further analyzed neuronal degeneration and cell death in the injured brain using Fluoro-Jade-B (FJB) histochemistry and caspase-3 immunostaining. Behavioral studies using the beam walk and Morris water maze were conducted to characterize strain differences in both motor and cognitive functional recovery following injury. We found that Fisher rats had significantly higher intracranial pressure, prolonged seizure activity, increased FJB-positive staining in the injured cortex and thalamus, and increased caspase-3 expression than Sprague-Dawley rats. On average, Fisher rats displayed a greater amount of total recording time in seizure activity and had longer ictal durations. The Fisher rats also had increased motor deficits, correlating with the above results. In spite of these results, Fisher rats performed better on cognitive tests following injury. The results demonstrate that different rat strains respond to injury differently, and thus in preclinical neurotrauma studies strain influence is an important consideration when evaluating outcomes.

Polymorphisms in CACNA1E and Camk2d are associated with seizure susceptibility of Sprague-Dawley rats

Seizures are associated with high intracellular calcium levels. However, conditions characterized by high intracellular calcium levels, such as stroke or traumatic brain injury, do not always evoke epilepsy. We hypothesized that polymorphisms in calcium-related genes CACNA1E and Camk2d contribute to the individual variability in seizure susceptibility. The distribution of one single nucleotide polymorphism (SNP) in the CACNA1E and one in the Camk2d gene was determined in Sprague-Dawley rats that were subjected to amygdala kindling or hyperthermia-induced seizures. The pre-kindling afterdischarge threshold was significantly lower in rats with the CACNA1E GG genotype (45.2+/-6.7microA) than in the GT genotyped animals (79.3+/-53.7microA). Among hyperthermia treated rats, the Camk2d G allele was more frequent among rats that did not display behavioral seizures during hyperthermia (67%) than in animals that did show behavioral seizures during hyperthermia (52%, chi(2)(1)=3.847, p=0.05). SNPs in CACNA1E and Camk2d genes are associated with the individual variability in seizure susceptibility in two experimental seizure models.

Downregulation of dendritic HCN channel gating in epilepsy is mediated by altered phosphorylation signaling

The onset of spontaneous seizures in the pilocarpine model of epilepsy causes a hyperpolarized shift in the voltage-dependent activation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channel-mediated current (Ih) in CA1 hippocampal pyramidal neuron dendrites, contributing to neuronal hyperexcitability and possibly to epileptogenesis. However, the specific mechanisms by which spontaneous seizures cause downregulation of HCN channel gating are yet unknown. We asked whether the seizure-dependent downregulation of HCN channel gating was due to altered phosphorylation signaling mediated by the phosphatase calcineurin (CaN) or the kinase p38 mitogen-activated protein kinase (p38 MAPK). We first found that CaN inhibition upregulated HCN channel gating and reduced neuronal excitability under normal conditions, showing that CaN is a strong modulator of HCN channels. We then found that an in vitro model of seizures (1 h in 0 Mg2+ and 50 microM bicuculline at 35-37 degrees C) reproduced the HCN channel gating change seen in vivo. Pharmacological inhibition of CaN or activation of p38 MAPK partially reversed the in vitro seizure-induced hyperpolarized shift in HCN channel gating, and the shift was fully reversed by the combination of CaN inhibition and p38 MAPK activation. We then demonstrated enhanced CaN activity as well as reduced p38 MAPK activity in vivo in the CA1 hippocampal area of chronically epileptic animals. Pharmacological reversal of these phosphorylation changes restored HCN channel gating downregulation and neuronal hyperexcitability in epileptic tissue to control levels. Together, these results suggest that alteration of two different phosphorylation pathways in epilepsy contributes to the downregulation of HCN channel gating, which consequently produces neuronal hyperexcitability and thus may be a target for novel antiepileptic therapies.

Intrinsic plasticity in acquired epilepsy: too much of a good thing?

Mechanisms of plasticity are important to the astounding capacity of the brain to adapt and learn. Ion channels are significant contributors to neuronal plasticity, but their dysfunction has been implicated in several nervous system diseases from movement disorders to epilepsy. Although many inherited ion channel mutations have been associated with these disorders, it has been recently recognized that channelopathies can also include aberrant ion channel function that is acquired after an insult or injury to the brain. These acquired alterations are being investigated in animal models of temporal lobe epilepsy, where studies have shown functional changes in voltage-gated ion channels that lead to increases in excitability. Studies of these hyperexcitable neurons have included recordings in the hippocampus, entorhinal cortex, and thalamus and support the existence of an extended seizure network with several nodes of altered activity that are established during epileptogenesis. A better understanding of the key ion channels and brain regions that are responsible for the development of this hyperexcitability, along with the molecular mechanisms involved, may provide novel treatment strategies for epilepsy.

Role of Ca2+/calmodulin-dependent protein kinase II in dendritic spine remodeling during epileptiform activity in vitro

Epileptiform activity (EA) in vivo and in vitro induces a loss of dendritic spines and synapses. Because CaMKII has been implicated in synaptogenesis and synaptic plasticity, we investigated the role of CaMKII in the effects of EA on spines, using rat hippocampal slice cultures. To visualize dendrites and postsynaptic densities (PSDs) in pyramidal neurons in the slices, we used biolistic transfection to express either free GFP or a PSD95-YFP construct that specifically labels PSDs. This allowed us to distinguish two classes of dendritic protrusions: spines that contain PSDs, and filopodia that lack PSDs and that are, on average, longer than spines. By these criteria, 48 hr of EA caused a decrease specifically in the number of spines. Immunoblots showed that EA increased CaMKII activity in the slices. Inhibition of CaMKII by expression of AIP, a specific peptide inhibitor of CaMKII, reduced spine number under basal conditions and failed to prevent EA-induced spine loss. However, under EA conditions, AIP increased the number of filopodia and the number of PSDs on the dendritic shaft. These data show at least two roles for CaMKII activity in maintenance and remodeling of dendritic spines under basal or EA conditions. First, CaMKII activity promotes the maintenance of spines and spine PSDs. Second, CaMKII activity suppresses EA-induced formation of filopodia and suppresses an increase in shaft PSDs, apparently by promoting translocation of PSDs from dendritic shafts to spines and/or selectively stabilizing spine rather than shaft PSDs.

Calcineurin-mediated GABA(A) receptor dephosphorylation in rats after kainic acid-induced status epilepticus

Calcineurin (CaN) is a neuronally enriched, calcium-dependent phosphatase, which plays an important role in a number of neuronal processes including development of learning and memory, and modulation of receptor's function and neuronal excitability as well as induction of apoptosis. It has been established in kindling model that the status epilepticus (SE)-induced increase in CaN activity is involved in the development of seizures through down-regulation of gamma-aminobutyric acid A receptor (GABA(A)R) activation. However, the mechanism by which CaN mediates GABA(A) receptor dephosphorylation in SE is not fully understood. Here, using a model of kainic acid (KA)-induced SE and CaN inhibitor FK506, we observed the behaviors induced by KA and levels of CaN activity and CaN expression in hippocampus by immunobloting. The results showed that the SE-induced CaN activity was time-dependent, with a peak at 2h and a return to basal level at 24h, whereas a significant increase in CaN expression was seen at 24h after SE. It is proposed that the rapid elevation in CaN activity after KA-induced SE is not likely due to an increase in CaN expression but rather an increase in CaN activation state or kinetics. In addition, we also demonstrated that pre-treatment with FK506 remarkably suppressed the SE-induced CaN activity and its expression, and reversed the SE-induced dephosphorylation of GABA(A)R 2/3 subunits. Taken together, our data suggest that down-regulation in inhibition of GABA(A)R 2/3 by CaN activity contributes to an elevation in neuronal excitability of hippocampus, which may be involved in development of chronic processes of seizures.

Ischemia and status epilepitcus result in enhanced phosphorylation of calcium and calmodulin-stimulated protein kinase II on threonine 253

Ca2+-stimulated protein kinase II (CaMKII) is critically involved in the regulation of synaptic function and is implicated in the neuropathology associated with ischemia and status epilepticus (SE). The activity and localization of CaMKII is regulated by multi-site phosphorylation. In the present study we investigated the effects of global ischemia followed by reperfusion and of SE on the phosphorylation of CaMKII on T253 in rat forebrains and compared this to the phosphorylation of T286. Both ischemia and SE resulted in marked increases in the phosphorylation of T253, and this was particularly marked in the postsynaptic density (PSD). Phosphorylation of T286 decreased rapidly towards basal levels following ischemia whereas phosphorylation of T253 remained elevated for between 1 and 6 h before decreasing to control values. Following SE, phosphorylation of T253 remained elevated for between 1 and 3 h before decreasing to control levels. In contrast, phosphorylation of T286 remained elevated for at least 24 h following the termination of SE. Total CaMKII associated with PSDs transiently increased 10 min following ischemia, but only several hours following SE. The results demonstrate that phoshorylation of CaMKII on T253 is enhanced following both ischemia/reperfusion and SE and indicate that the phosphorylation of T253 and T286 are differentially regulated.

Epileptogenesis causes an N-methyl-d-aspartate receptor/Ca2+-dependent decrease in Ca2+/calmodulin-dependent protein kinase II activity in a hippocampal neuronal culture model of spontaneous recurrent epileptiform discharges

Alterations in the function of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) have been observed in both in vivo and in vitro models of epileptogenesis; however the molecular mechanism mediating the effects of epileptogenesis on CaM kinase II has not been elucidated. This study was initiated to evaluate the molecular pathways involved in causing the long-lasting decrease in CaM kinase II activity in the hippocampal neuronal culture model of low Mg2+-induced spontaneous recurrent epileptiform discharges (SREDs). We show here that the decrease in CaM kinase II activity associated with SREDs in hippocampal cultures involves a Ca2+/N-methyl-d-aspartate (NMDA) receptor-dependent mechanism. Low Mg2+-induced SREDs result in a significant decrease in Ca2+/calmodulin-dependent substrate phosphorylation of the synthetic peptide autocamtide-2. Reduction of extracellular Ca2+ levels (0.2 mM in treatment solution) or the addition of dl-2-amino-5-phosphonovaleric acid (APV) 25 microM blocked the low Mg2+-induced decrease in CaM kinase II-dependent substrate phosphorylation. Antagonists of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainic acid receptor or L-type voltage sensitive Ca2+ channel had no effect on the low Mg2+-induced decrease in CaM kinase II-dependent substrate phosphorylation. The results of this study demonstrate that the decrease in CaM kinase II activity associated with this model of epileptogenesis involves a selective Ca2+/NMDA receptor-dependent mechanism and may contribute to the production and maintenance of SREDs in this model.

An in vitro model of Stroke‐Induced Epilepsy: Elucidation of The roles of Glutamate and Calcium in The induction and Maintenance of Stroke‐Induced Epileptogenesis

Stroke is a major risk factor for developing acquired epilepsy (AE). Although the underlying mechanisms of ischemia-induced epileptogenesis are not well understood, glutamate has been found to be associated with both epileptogenesis and ischemia-induced injury in several research models. This chapter discusses the development of an in vitro model of epileptogenesis induced by glutamate injury in hippocampal neurons, as found in a clinical stroke, and the implementation of this model of stroke-induced AE to evaluate calcium's role in the induction and maintenance of epileptogenesis. To monitor the acute effects of glutamate on neurons and chronic alterations in neuronal excitability up to 8 days after glutamate exposure, whole-cell current-clamp electrophysiology was employed. Various durations and concentrations of glutamate were applied to primary hippocampal cultures. A single 30-min, 5-microM glutamate exposure produced a subset of neurons that died or had a stroke-like injury, and a larger population of injured neurons that survived. Neurons that survived the injury manifested spontaneous, recurrent, epileptiform discharges (SREDs) in neural networks characterized by paroxysmal depolarizing shifts (PDSs) and high-frequency spike firing that persisted for the life of the culture. The neuronal injury produced in this model was evaluated by determining the magnitude of the prolonged, reversible membrane depolarization, loss of synaptic activity, and neuronal swelling. The permanent epileptiform phenotype expressed as SREDs that resulted from glutamate injury was found to be dependent on the presence of extracellular calcium. The "epileptic" neurons manifested elevated intracellular calcium levels when compared to control neurons, independent of neuronal activity and seizure discharge, demonstrating that alterations in calcium homeostatic mechanisms occur in association with stroke-induced epilepsy. Findings from this investigation present the first in vitro model of glutamate injury-induced epileptogenesis that may help elucidate some of the mechanisms that underlie stroke-induced epilepsy.

Potential new antiepileptogenic targets indicated by microarray analysis in a rat model for temporal lobe epilepsy

To get insight into the mechanisms that may lead to progression of temporal lobe epilepsy, we investigated gene expression during epileptogenesis in the rat. RNA was obtained from three different brain regions [CA3, entorhinal cortex (EC), and cerebellum (CB)] at three different time points after electrically induced status epilepticus (SE): acute phase [group D (1 d)], latent period [group W (1 week)], and chronic epileptic period [group M (3-4 months)]. A group that was stimulated but that had not experienced SE and later epilepsy was also included (group nS). Gene expression analysis was performed using the Affymetrix Gene Chip System (RAE230A). We used GENMAPP and Gene Ontology to identify global biological trends in gene expression data. The immune response was the most prominent process changed during all three phases of epileptogenesis. Synaptic transmission was a downregulated process during the acute and latent phases. GABA receptor subunits involved in tonic inhibition were persistently downregulated. These changes were observed mostly in both CA3 and EC but not in CB. Rats that were stimulated but that did not develop spontaneous seizures later on had also some changes in gene expression, but this was not reflected in a significant change of a biological process. These data suggest that the targeting of specific genes that are involved in these biological processes may be a promising strategy to slow down or prevent the progression of epilepsy. Especially genes related to the immune response, such as complement factors, interleukins, and genes related to prostaglandin synthesis and coagulation pathway may be interesting targets.

Erratum to "Cellular mechanisms underlying acquired epilepsy: the calcium hypothesis of the induction and maintenance of epilepsy." [Pharmacol. Ther. 105(3) (2005) 229-266]

Epilepsy is one of the most common neurological disorders. Although epilepsy can be idiopathic, it is estimated that up to 50% of all epilepsy cases are initiated by neurological insults and are called acquired epilepsy (AE). AE develops in 3 phases: (1) the injury [central nervous system (CNS) insult]. (2) epileptogenesis (latency), and (3) the chronic epileptic (spontaneous recurrent seizure) phases. Status epilepticus (SE), stroke, and traumatic brain injury (TBI) are 3 major examples of common brain injuries that can lead to the development of AE. It is especially important to understand the molecular mechanisms that cause AE because it may lead to innovative strategies to prevent or cure this common condition. Recent studies have offered new insights into the cause of AE and indicate that injury-induced alterations in intracellular calcium concentration levels ([Ca(2+)](i)) and calcium homeostatic mechanisms play a role in the development and maintenance of AE. The injuries that cause AE are different, but the share a common molecular mechanism for producing brain damage--an increase in extracellular glutamate and are exposed to increased [Ca(2+)](i) are the cellular substrates to develop epilepsy because dead cells do not seize. The neurons that survive injury sustain permanent long-term plasticity changes in [Ca(2+)](i) and calcium homeostatic mechanisms that are permanent and are a prominent feature of the epileptic phenotype. In the last several years, evidence has accumulated indicating that the prolonged alteration in neuronal calcium dynamics plays an important role in the induction and maintenance of the prolonged neuroplasticity changes underlying the epileptic phenotype. Understanding the role of calcium as a second messenger in the induction and maintenance of epilepsy may provide novel insights into therapeutic advances that will prevent and even cure AE.

Altered calcium/calmodulin kinase II activity changes calcium homeostasis that underlies epileptiform activity in hippocampal neurons in culture

Epilepsy is characterized by the occurrence of spontaneous recurrent epileptiform discharges (SREDs) in neurons. A decrease in calcium/calmodulin-dependent protein kinase II (CaMK-II) activity has been shown to occur with the development of SREDs in a hippocampal neuronal culture model of acquired epilepsy, and altered calcium (Ca(2+)) homeostasis has been implicated in the development of SREDs. Using antisense oligonucleotides, this study was conducted to determine whether selective suppression of CaMK-II activity, with subsequent induction of SREDs, was associated with altered Ca(2+) homeostasis in hippocampal neurons in culture. Antisense knockdown resulted in the development of SREDs and a decrease in both immunocytochemical staining and enzyme activity of CaMK-II. Evaluation of [Ca(2+)](i) using Fura indicators revealed that antisense-treated neurons manifested increased basal [Ca(2+)](i), whereas missense-treated neurons showed no change in basal [Ca(2+)](i). Antisense suppression of CaMK-II was also associated with an inability of neurons to restore a Ca(2+) load. Upon removal of oligonucleotide treatment, CaMK-II suppression and Ca(2+) homeostasis recovered to control levels and SREDs were abolished. To our knowledge, the results demonstrate the first evidence that selective suppression of CaMK-II activity results in alterations in Ca(2+) homeostasis and the development of SREDs in hippocampal neurons and suggest that CaMK-II suppression may be causing epileptogenesis by altering Ca(2+) homeostatic mechanisms.

Hyperbilirubinemia and kernicterus

This article describes new findings concerning the basic science of bilirubin neurotoxicity, new considerations of the definition of clinical kernicterus, and new and useful tools to diagnose kernicterus in older children, and discusses treatments for kernicterus beyond the newborn period and why proper diagnosis is important.

AMPA/kainate receptor-mediated downregulation of GABAergic synaptic transmission by calcineurin after seizures in the developing rat brain

Hypoxia is the most common cause of perinatal seizures and can be refractory to conventional anticonvulsant drugs, suggesting an age-specific form of epileptogenesis. A model of hypoxia-induced seizures in immature rats reveals that seizures result in immediate activation of the phosphatase calcineurin (CaN) in area CA1 of hippocampus. After seizures, CA1 pyramidal neurons exhibit a downregulation of GABA(A) receptor (GABA(A)R)-mediated inhibition that was reversed by CaN inhibitors. CaN activation appears to be dependent on seizure-induced activation of Ca2+-permeable AMPA receptors (AMPARs), because the upregulation of CaN activation and GABA(A)R inhibition were attenuated by GYKI 52466 [1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride] or Joro spider toxin. GABA(A)R beta2/3 subunit protein was dephosphorylated at 1 h after seizures, suggesting this subunit as a possible substrate of CaN in this model. Finally, in vivo administration of the CaN inhibitor FK-506 significantly suppressed hypoxic seizures, and posttreatment with NBQX (2,3-dihydroxy-6-nitro-7-sulfonyl-benzo[f]quinoxaline) or FK-506 blocked the hypoxic seizure-induced increase in CaN expression. These data suggest that Ca2+-permeable AMPARs and CaN regulate inhibitory synaptic transmission in a novel plasticity pathway that may play a role in epileptogenesis in the immature brain.

Serial analysis of gene expression in the hippocampus of patients with mesial temporal lobe epilepsy

Hippocampal sclerosis constitutes the most frequent neuropathological finding in patients with medically intractable mesial temporal lobe epilepsy. Serial analysis of gene expression was used to get a global view of the gene profile in human hippocampus in control condition and in epileptic condition associated with hippocampal sclerosis. Libraries were generated from control hippocampus, obtained by rapid autopsy, and from hippocampal surgical specimens of patients with mesial temporal lobe epilepsy and the classical pattern of hippocampal sclerosis. More than 50,000 tags were analyzed (28,282, control hippocampus; 25,953, hippocampal sclerosis) resulting in 9206 (control hippocampus) and 9599 (hippocampal sclerosis) unique tags (genes), each representing a specific mRNA transcript. Comparison of the two libraries resulted in the identification of 143 transcripts that were differentially expressed. These genes belong to a variety of functional classes, including basic metabolism, transcription regulation, protein synthesis and degradation, signal transduction, structural proteins, regeneration and synaptic plasticity and genes of unknown identity of function. The database generated by this study provides an extensive inventory of genes expressed in human control hippocampus, identifies new high-abundant genes associated with altered hippocampal morphology in patients with mesial temporal lobe epilepsy and serves as a reference for future studies aimed at detecting hippocampal transcriptional responses under various pathological conditions.

A mechanism for the inactivation of Ca2+/calmodulin-dependent protein kinase II during prolonged seizure activity and its consequence after the recovery from seizure activity in rats in vivo

Seizure is a form of excessive neuronal excitation and seizure-induced neuronal damage has profound effects on the prognosis of epilepsy. In various seizure models, the inactivation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) occurs during seizure activity preceding neuronal cell death. CaMKII is a multifunctional protein kinase enriched in the brain and involved in various ways the regulation of neuronal activity. CaMKII inactivation during seizure activity may modify neuronal cell survival after seizure. However, the mechanism for CaMKII inactivation and its consequence after seizure recovery remain to be elucidated yet. In the present study, we employed a prolonged seizure model by systemic injection of kainic acid into rats and biochemically examined the activity state of CaMKII. In status epilepticus induced by kainic acid, not only the inactivation of CaMKII in brain homogenate, but also a shift in the distribution of CaMKII protein from the soluble to particulate fraction occurred in both hippocampus and parietal cortex. The particulate CaMKII showed a large decrease in the specific activity and a concurrent large increase in the autophosphorylation ratio at Thr-286 (alpha) and at Thr-287 (beta). In contrast, the soluble CaMKII showed normal or rather decreased specific activity and autophosphorylation ratio. After 24 h of recovery from kainic acid-induced status epilepticus, all such changes had disappeared. On the other hand, the total amount of CaMKII was decreased by 35% in hippocampus and 20% in parietal cortex, but the existing CaMKII was indistinguishable from those of controls in terms of the autonomous activity ratio, specific activity and autophosphorylation ratio. Thus, CaMKII inactivation in kainic acid-induced status epilepticus seems to be derived not from simple degradation of the enzyme, but from the formation of the autophosphorylated, inactivated and sedimentable CaMKII. Such a form of CaMKII may be important during pathological conditions in vivo in preventing excessive CaMKII activation due to Ca2+ overload.

Activity-driven postsynaptic translocation of CaMKII

Ca2+ influx through the NMDA receptor and subsequent activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) are crucial for learning and one of its physiological correlates, long-term potentiation (LTP). Ca2+/calmodulin promotes CaMKII binding to several postsynaptic proteins, including the NMDA receptor. These interactions strategically place CaMKII at locations where Ca2+ influx through the NMDA receptor is highest for further activation of CaMKII and for phosphorylation of nearby AMPA receptors and of other proteins that are important for LTP. Ca2+-dependent postsynaptic CaMKII clustering is of specific interest because LTP is synapse specific: only synapses that experience LTP-inducing high-frequency activity exhibit LTP. Ca2+-driven protein binding ensures that CaMKII accumulates only at those synapses undergoing LTP. This selectivity is economical and could contribute to the synapse specificity of LTP because downstream effects of CaMKII will occur mainly at synapses that accumulate CaMKII. In this article, we provide an overview of recent progress in postsynaptic CaMKII anchoring and discuss its implication in synaptic plasticity and the etiology and potential treatments of neurological diseases.

Analysis of pThr286-CaMKII and CaMKII immunohistochemistry in the hippocampus of patients with temporal lobe epilepsy

Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylates a variety of neuronal proteins, thereby, coordinating responses to changes of intracellular Ca2+ concentrations. Autophosphorylation at threonine286 generates an autonomously active form of CaMKII (pThr286-CaMKII), thus prolonging responses to transient increases in Ca2+. Our previous studies in hippocampi of temporal lobe epilepsy (TLE) patients revealed a significant up-regulation of CaMKII in dentate granule cells (DGCs) of specimens with Ammon's horn sclerosis (AHS). However, the functional status of the up-regulated enzyme remained unclear. Therefore, we performed double immunofluorescence staining for CaMKII and pThr286-CaMKII in hippocampi of TLE patients and controls. Furthermore, we analyzed the ratio of the relative fluorescence intensities pThr286-CaMKII: CaMKII in DGCs. CaMKII immunoreactivity was significantly increased in DGC bodies and their proximal dendrites in AHS. In contrast, immunostaining for pThr286-CaMKII was localized to the DGC bodies, revealing similar labeling intensities in all TLE and control specimens, and was not observed in the dendritic compartment of DGCs. Analysis of the ratio of the relative fluorescence intensities pThr286-CaMKII:CaMKII in DGC bodies revealed a significantly reduced ratio in AHS compared to lesion-associated TLE and controls. Thus, up-regulation of total CaMKII in DGCs of AHS specimens is not paralleled by an increase of its autonomously active form.

Modulation of CaM Kinase II Activity Is Coincident with Induction of Status Epilepticus in the Rat Pilocarpine Model

PURPOSE

This study was conducted to characterize the early cellular changes in CaM kinase II activity that occur during the induction of status epilepticus (SE).

METHODS

The pilocarpine model of SE was characterized both behaviorally and electrographically. At specific time points after the first discrete seizure, specific brain regions were isolated for biochemical study. Phosphate incorporation into a CaM kinase II-specific substrate, autocamtide III, was used to determine kinase activity.

RESULTS

After the development of SE, the data show an immediate inhibition of both cortical and hippocampal CaM kinase II activity in homogenate, but a delayed inhibition in synaptic kinase activity. The maintenance of synaptic kinase activity was due to a translocation of CaM kinase II protein to the synapse. However, despite the translocation of functional kinase, CaM kinase II activity was not maintained, membrane potential was not restored, and the newly translocated CaM kinase II did not terminate the SE event. Unlike the homogenate samples, in the crude synaptoplasmic membrane (SPM) subcellular fractions, a positive correlation is found between the duration of SE and the inhibition of CaM kinase II activity in both the cortex and hippocampus.

CONCLUSIONS

The data support the hypothesis that alterations of CaM kinase II activity are involved in the early events of SE pathology.

Pilocarpine-induced status epilepticus: Monoamine level, muscarinic and dopaminergic receptors alterations in striatum of young rats

Behavioural changes, muscarinic and dopaminergic receptors density and levels of monoamines were measured in striatum of rats after pilocarpine-induced status epilepticus (SE). Wistar rats at the age of 21 days were treated with pilocarpine (400mg/kg; subcutaneously) whilst the control group was treated with 0.9% saline (s.c.). Both groups were sacrificed 1h following the treatment. SE induced a muscarinic receptor downregulation of 64% in pilocarpine group. This effect was also observed to be 57% in D(1) and 32% in D(2). In the dissociation constant (K(d)) values in muscarinic and D(1) receptor no alterations were verified. On the other hand, the K(d) value for D(2) was observed to increase 41%. High performance liquid chromatography determinations showed 63, 35, 77 and 64% decreases in dopamine, 3-methoxy-phenylacetic acid, serotonin and 5-hydroxyindoleacetic acid contents, respectively. The homovanilic acid level was verified to increase 119%. The noradrenaline content was unaltered. A direct evidence of monoamine levels alterations can be verified during seizure activity and receptor density changes appear to occur in an accentuated way in immature brain during the estabilishment of SE induced by pilocarpine.

Age dependence of pilocarpine-induced status epilepticus and inhibition of CaM kinase II activity in the rat

This study was conducted to characterize the post-pubertal developmental aspects on seizure susceptibility and severity as well as calcium/calmodulin protein kinase type II (CaM kinase II) activity in status epilepticus (SE). Thirty- to ninety-day-old rats, in 10-day increments, were studied. This corresponds to a developmental age group that has not received thorough attention. The pilocarpine model of SE was characterized both behaviorally and electrographically. Seven criteria were analyzed for electrographical characterization: seizure severity, SE susceptibility, the average number of discrete seizures, average time until first seizure, average time to SE, average time from first discrete seizure to SE, and death. After 1 h of SE, specific brain regions were isolated for biochemical study. Phosphate incorporation into a CaM kinase II-specific substrate, autocamtide III, was used to determine kinase activity. There was no developmental effect on the average number of discrete seizures, average time until first seizure, average time to SE, average time from first discrete seizure to SE, and death; however, there was a significant effect on SE probability and seizure severity. Once SE was expressed, all animals showed a decrease in both cortical and hippocampal CaM kinase II activities. Conversely, seizure activity in the absence of SE did not result in a decrease in CaM kinase II activity. The data suggest that there is a gradual age-dependent modulation of SE susceptibility and seizure severity within the developmental stages studied. Additionally, once status epilepticus is observed at any age, there is a corresponding SE-induced inhibition of CaM kinase II.

Cellular mechanisms underlying acquired epilepsy: the calcium hypothesis of the induction and maintainance of epilepsy

Epilepsy is one of the most common neurological disorders. Although epilepsy can be idiopathic, it is estimated that up to 50% of all epilepsy cases are initiated by neurological insults and are called acquired epilepsy (AE). AE develops in 3 phases: (1) the injury (central nervous system [CNS] insult), (2) epileptogenesis (latency), and (3) the chronic epileptic (spontaneous recurrent seizure) phases. Status epilepticus (SE), stroke, and traumatic brain injury (TBI) are 3 major examples of common brain injuries that can lead to the development of AE. It is especially important to understand the molecular mechanisms that cause AE because it may lead to innovative strategies to prevent or cure this common condition. Recent studies have offered new insights into the cause of AE and indicate that injury-induced alterations in intracellular calcium concentration levels [Ca(2+)](i) and calcium homeostatic mechanisms play a role in the development and maintenance of AE. The injuries that cause AE are different, but they share a common molecular mechanism for producing brain damage-an increase in extracellular glutamate concentration that causes increased intracellular neuronal calcium, leading to neuronal injury and/or death. Neurons that survive the injury induced by glutamate and are exposed to increased [Ca(2+)](i) are the cellular substrates to develop epilepsy because dead cells do not seize. The neurons that survive injury sustain permanent long-term plasticity changes in [Ca(2+)](i) and calcium homeostatic mechanisms that are permanent and are a prominent feature of the epileptic phenotype. In the last several years, evidence has accumulated indicating that the prolonged alteration in neuronal calcium dynamics plays an important role in the induction and maintenance of the prolonged neuroplasticity changes underlying the epileptic phenotype. Understanding the role of calcium as a second messenger in the induction and maintenance of epilepsy may provide novel insights into therapeutic advances that will prevent and even cure AE.

Long-lasting alterations in neuronal calcium homeostasis in an in vitro model of stroke-induced epilepsy

Altered calcium homeostatic mechanisms have been implicated in the development of acquired epilepsy in numerous models. Stroke is one of the leading brain injuries that cause acquired epilepsy, yet little is known concerning the molecular mechanisms underlying stroke-induced epileptogenesis. Recently an in vitro model of stroke-induced epilepsy was developed and characterized as a powerful tool to study the pathophysiology of injury and stroke-induced epileptogenesis. Using this glutamate injury-induced epileptogenesis model, we have investigated the role of altered calcium homeostatic mechanisms in the development and maintenance of stroke-induced epilepsy. Epileptic neurons manifested elevated intracellular calcium levels compared to control neurons independent of neuronal activity and seizure discharge for the remainder of the life of the neurons in culture. In addition, epileptic neurons were found to have alterations in the ability to reduce intracellular calcium levels following a calcium load. These long-term epileptic changes in calcium homeostasis were dependent on calcium during the initial glutamate injury. The data demonstrate that significant alterations in calcium homeostatic mechanisms occur in association with stroke-induced epilepsy and suggest that these changes may play a role in both the induction and maintenance of the epileptic phenotype in this model.

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.

DNA microarray analysis of cortical gene expression during early recirculation after focal brain ischemia in rat

Focal brain ischemia is followed by changes in gene expression as reflected by altered mRNA levels. DNA microarray analysis can be used to survey thousands of genes for differential expression triggered by ischemic metabolic stress. In this study, Sprague-Dawley rats were subjected to 2 h of middle cerebral artery occlusion (MCAO) using an intravascular poly-L-lysine-coated filament, and brains were removed after 3 h of recirculation for mRNA isolation. A differential measurement of mRNAs from post-ischemic and sham control animals was performed using the Mouse UniGene 1 microarray. Established values for differential expression were used (> or =1.7 or < or =-1.7 fold), and hits (n=2-3 arrays) divided into known 'ischemia-hypoxia response' genes and 'newly connected' annotated genes. n=28 ischemia-hypoxia response genes were up-regulated and n=6 were down-regulated. Regulated genes comprised immediate early genes, heat shock proteins, anti-oxidative enzymes, trophic factors, and genes involved in RNA metabolism, inflammation and cell signaling. Based on the ability of the microarray to replicate known changes in gene expression, n=35 newly connected genes were found up-regulated and n=41 down-regulated. DNA microarray analysis allows one to develop novel working hypotheses for responses to brain ischemia based on the regulation of annotated genes.

Chronic inhibition of cortex microsomal Mg(2+)/Ca(2+) ATPase-mediated Ca(2+) uptake in the rat pilocarpine model following epileptogenesis

In the rat pilocarpine model, 1 h of status epilepticus caused significant inhibition of Mg(2+)/Ca(2+) ATPase-mediated Ca(2+) uptake in cortex endoplasmic reticulum (microsomes) isolated immediately after the status episode. The rat pilocarpine model is also an established model of acquired epilepsy. Several weeks after the initial status epilepticus episode, the rats develop spontaneous recurrent seizures, or epilepsy. To determine whether inhibition of Ca(2+) uptake persists after the establishment of epilepsy, Ca(2+) uptake was studied in cortical microsomes isolated from rats displaying spontaneous recurrent seizures for 1 year. The initial rate and total Ca(2+) uptake in microsomes from epileptic animals remained significantly inhibited 1 year after the expression of epilepsy compared to age-matched controls. The inhibition of Ca(2+) uptake was not due to individual seizures nor an artifact of increased Ca(2+) release from epileptic microsomes. In addition, the decreased Ca(2+) uptake was not due to either selective isolation of damaged epileptic microsomes from the homogenate or decreased Mg(2+)/Ca(2+) ATPase protein in the epileptic microsomes. The data demonstrate that inhibition of microsomal Mg(2+)/Ca(2+) ATPase-mediated Ca(2+) uptake in the pilocarpine model may underlie some of the long-term plasticity changes associated with epileptogenesis.

A significant increase in both basal and maximal calcineurin activity in the rat pilocarpine model of status epilepticus

This study focused on the effects of status epilepticus on the activity of calcineurin, a neuronally enriched, calcium-dependent phosphatase. Calcineurin is an important modulator of many neuronal processes, including learning and memory, induction of apoptosis, receptor function and neuronal excitability. Therefore, a status epilepticus-induced alteration of the activity of this important phosphatase would have significant physiological implications. Status epilepticus was induced by pilocarpine injection and allowed to continue for 60 min. Brain region homogenates were then assayed for calcineurin activity by dephosphorylation of p-nitrophenol phosphate. A significant status epilepticus-dependent increase in both basal and Mn(2+)-dependent calcineurin activity was observed in homogenates isolated from the cortex and hippocampus, but not the cerebellum. This increase was resistant to 150 nM okadaic acid, but sensitive to 50 microM okadaic acid. The increase in basal activity was also resistant to 100 microM sodium orthovanadate. Both maximal dephosphorylation rate and substrate affinity were increased following status epilepticus. However, the increase in calcineurin activity was not found to be due to an increase in calcineurin enzyme levels. Finally, increase in calcineurin activity was found to be NMDA-receptor activation dependent. The data demonstrate that status epilepticus resulted in a significant increase in both basal and maximal calcineurin activity.