Kindling alters the calcium/calmodulin-dependent phosphorylation of synaptic plasma membrane proteins in rat hippocampus

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.

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.

■ REVIEW : Long-Term Modulation of Gene Expression in Epilepsy

Molecular genetics has led to major advances in the study of neurological disease over the last 2 decades. Initial advances were made in understanding specific mutations that were associated with disease, such as epilepsy and other neurological conditions. In addition to specific mutations, recent research has focused on long-lasting or permanent changes in genetic expression as an underlying substrate of acquired diseases such as epilepsy. In symptomatic epilepsy, normal brain tissue is permanently altered and develops spon taneous recurrent seizures. Evidence indicates that long-lasting changes in gene expression at both tran scriptional and post-transcriptional levels are associated with epileptogenesis. The expression of transcription factors and other regulatory proteins represent a molecular mechanism for mediating these changes. Understanding the effects of severe environmental stresses on the multiple sites of transcriptional and post-transcriptional regulation of gene expression is likely to provide important insights into the devel opment of altered neuronal function in a number of important disease states, including epilepsy. NEURO SCIENTIST 5:86-99, 1999

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.

Influences of hyperthermia-induced seizures on learning, memory and phosphorylative state of CaMKIIα in rat hippocampus

Febrile seizure (FS) remains the most common childhood neurological emergency. Although many studies have been done, controversy exists as to whether these seizures are associated with a significant risk for cognitive impairment. The aim of our study is to check whether there is a spatial learning and memory deficit in the experimental FS rats using a heated-air FS paradigm and to determine the possible molecular mechanism of cognitive impairment. On days 10 to 12 postpartum, the male rat pups were subjected to one, three, or nine episodes of brief hyperthermia-induced seizures (HS). At adolescence and adulthood, the rats subjected to three, or nine episodes of HS had significant deficits in spatial learning and memory tested by Morris water maze. At adulthood, no apparent hippocampal neuronal loss was found in any HS group, but the seizure threshold to flurothyl was decreased significantly in the rats subjected to nine episodes of HS. In the rats subjected to three, or nine episodes of HS, the Western immunoblotting showed that there was a significant translocation of Ca(2+)-calmodulin stimulated protein kinase II (CaMKII) from the postsynaptic density to the cytosol. In the postsynaptic density the phosphorylation of CaMKIIα Thr(286) was reduced significantly, but the phosphorylation of CaMKIIα Thr(305) was increased significantly. Our study showed early-life brief but recurrent HS caused long-term cognitive impairment and CaMKIIα was involved in carrying forward the signal resulting from HS. The change of the phosphorylative level in Thr(286) and Thr(305) sites of CaMKIIα may underlie the molecular mechanism for the HS related cognitive impairment.

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.

Development of the calcium plateau following status epilepticus: role of calcium in epileptogenesis

Status epilepticus is a clinical emergency defined as continuous seizure activity or rapid, recurrent seizures without regaining consciousness and can lead to the development of acquired epilepsy, characterized by spontaneous, recurrent seizures. Understanding epileptogenesis--the transformation of healthy brain tissue into hyperexcitable neuronal networks--is an important challenge and the elucidation of molecular mechanisms can lend insight into new therapeutic targets to halt this progression. It has been demonstrated that intracellular calcium increases during status epilepticus and that these elevations are maintained past the duration of the injury (Ca(2+) plateau). As an important second messenger, Ca(2+) elevations can lead to changes in gene expression, neurotransmitter release and plasticity. Thus, characterization of the post-injury Ca(2+) plateau may be important in eventually understanding the pathophysiology of epileptogenesis and preventing the progression to chronic epilepsy after brain injury.

Alterations of GABAA-Receptor Function and Allosteric Modulation During Development of Status Epilepticus

Partial limbic seizures in rodents induced by pilocarpine progress from stages I–II (mouth and facial movements; head nodding) to stage III (forelimb clonus) and then progress rapidly to stages IV–V (generalized limbic seizures; rearing, and rearing with falling) followed by status epilepticus (SE). Although limbic seizures in rodents are terminated by benzodiazepines, a group of γ-aminobutyric acid type A (GABAA)–receptor positive modulators, significant pharmacoresistance to benzodiazepines develops within minutes during SE. The alterations of GABAA-receptor function and allosteric modulation during development of SE are poorly understood. We induced seizures in juvenile rats by administration of lithium followed by pilocarpine, and whole cell recordings of miniature inhibitory postsynaptic currents (mIPSCs) were obtained from hippocampal dentate granule cells in brain slices. Compared with a sham-treated group, mIPSC amplitude was reduced and decay was accelerated at onset of the first occurrence of stage III (S3) seizures [S3(0)], resulting in a reduction in the total charge transfer at S3(0). Recovery of mIPSC amplitude and prolongation of mIPSC decay occurred 30 min after onset of S3 seizures [S3(30)]. The mIPSC frequency was not altered for S3(0) and S3(30) neurons compared with sham neurons. The net enhancement of total charge transfer by diazepam was smaller for S3(30) than that for sham and S3(0) neurons; however, the net reduction of total charge transfer by zinc was greater for S3(30) than that for sham and S3(0) neurons. These findings suggest that substantial plastic changes of GABAA-receptor function and allosteric modulation occur rapidly in neurons from juvenile animals during development of SE.

Molecular signaling mechanisms underlying epileptogenesis

Epilepsy, a disorder of recurrent seizures, is a common and frequently devastating neurological condition. Available therapy is only symptomatic and often ineffective. Understanding epileptogenesis, the process by which a normal brain becomes epileptic, may help identify molecular targets for drugs that could prevent epilepsy. A number of acquired and genetic causes of this disorder have been identified, and various in vivo and in vitro models of epileptogenesis have been established. Here, we review current insights into the molecular signaling mechanisms underlying epileptogenesis, focusing on limbic epileptogenesis. Study of different models reveals that activation of various receptors on the surface of neurons can promote epileptogenesis; these receptors include ionotropic and metabotropic glutamate receptors as well as the TrkB neurotrophin receptor. These receptors are all found in the membrane of a discrete signaling domain within a particular type of cortical neuron--the dendritic spine of principal neurons. Activation of any of these receptors results in an increase Ca2+ concentration within the spine. Various Ca2+-regulated enzymes found in spines have been implicated in epileptogenesis; these include the nonreceptor protein tyrosine kinases Src and Fyn and a serine-threonine kinase [Ca2+-calmodulin-dependent protein kinase II (CaMKII)] and phosphatase (calcineurin). Cross-talk between astrocytes and neurons promotes increased dendritic Ca2+ and synchronous firing of neurons, a hallmark of epileptiform activity. The hypothesis is proposed that limbic epilepsy is a maladaptive consequence of homeostatic responses to increases of Ca2+ concentration within dendritic spines induced by abnormal neuronal activity.

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.

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.

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.

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.

Genes differentially expressed in the kindled mouse brain

Kindling involves long-term changes in brain excitability and is considered a model of epilepsy and neuroplasticity. Differentially expressed genes in the kindled mouse brain were screened using an reverse transcription-polymerase chain reaction (RT-PCR) differential display (DD) method. C3H male mice were kindled with 40 stimuli in the hippocampus at 5-min intervals. Hippocampal RNA was isolated for DD from mice at 0.5 h, 1 day, 1 week, and 1 month after kindling and from sham-operated controls. About 30,000 bands were screened and of these, 50 were displayed differentially. Northern blot analysis confirmed that 26 of the 50 bands were differentially expressed following rapid kindling. Further sequence analysis revealed that 14 of the genes were previously identified and 12 were novel. The novel genes are referred to as King (1-12) genes because of their association with kindling. According to their temporal and quantitative pattern of expression in forebrain, the 26 genes were grouped into five types. Expression of five of the DD genes, one from each expression type, was further analyzed in hippocampus, forebrain, brainstem, and cerebellum of the kindled mice. Differential expression of these genes was observed in hippocampus and forebrain, but not in brainstem or cerebellum. Only one gene, a regulator of G-protein signaling 4 (RGS4), showed prolonged changes in expression in response to kindling. Our results show that rapid kindling produces spatial and temporal changes in gene expression that may influence kindling-associated neuroplasticity.

Involvement of cAMP- and Ca(2+)/calmodulin-dependent neuronal protein phosphorylation in mechanisms underlying genetic predisposition to audiogenic seizures in rats

It was shown that increased excitability in neurons underlying epilepsies would be maintained by abnormalities in protein phosphorylation systems. This study was initiated to compare the functioning of Ca(2+)/calmodulin- and cAMP-dependent systems of protein phosphorylation in homogenates of neocortex and hippocampus in three animal groups: genetically prone to audiogenic seizures (GPAS) rats, GPAS rats exposed to daily repeated audiogenic seizures (AGPAS rats) and nonepileptic Wistar ones. We found significant differences in phosphorylation of 270, 58, 54 and 42 kDa proteins in neocortex and hippocampus of GPAS rats in comparison with Wistar ones. Daily repeated seizures induced further modifications of phosphorylation of these proteins in only hippocampus of AGPAS rats as compared with GPAS ones. Ca(2+)-independent, functional CAMKII activity was considerably increased in hippocampus but decreased in neocortex of GPAS rats in comparison with Wistar ones. The activity of PKA was increased both in neocortex and hippocampus of GPAS rats. Daily repeated audiogenic seizures induced the decrease of Ca(2+)-independent CAMKII activity in hippocampus and the increase of PKA activity in neocortex of AGPAS rats in comparison with GPAS ones. The present results indicate that modification of 270, 58, 54, and 42 kDa proteins phosphorylation as well as altered CAMKII and PKA activities might be involved in mechanisms of genetic predisposition to audiogenic seizures.

Epileptiform activity and EPSP-spike potentiation induced in rat hippocampal CA1 slices by repeated high-K(+): involvement of ionotropic glutamate receptors and Ca(2+)/calmodulin-dependent protein kinase II

We have previously demonstrated that repeated brief increases in extracellular K(+) (K(+)(o)) induce a hyperexcitability in CA1 pyramidal cells that persists for a long time after the final application of K(+) [Neurosci. Lett. 223 (1997) 177; Epilepsy Research (2000) 75]. This epileptiform activity, which was associated with a lasting excitatory postsynaptic potential (EPSP)-spike potentiation, presented some of the characteristic features of traditional in vivo kindling. We have also found that Ca(2+) influx through L-type voltage-sensitive Ca(2+) channels is essential for the development of both in vitro kindling and EPSP-spike potentiation. The aims of this study were to investigate the involvement of ionotropic glutamate receptors, especially those of the NMDA subtype, and the requirement for Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in these phenomena. Field EPSPs with presynaptic fibre volleys from the stratum radiatum, and population spikes from the stratum pyramidale, were recorded in the CA1 area of rat hippocampal slices in response to electrical stimulation of the Schaffer collateral/commissural fibres. Repeated (three episodes) brief (30 s) increases in extracellular K(+) induced a sustained decrease in the threshold for development of evoked epileptiform discharges (i.e. an in vitro kindling-like state) and a lasting potentiation of the EPSP-spike transfer in CA1 pyramidal neurons (EPSP-spike potentiation). The selective antagonist of NMDA receptors, APV (50 microM), blocked the EPSP-spike potentiation, depressed the induction phase of the in vitro kindling-like state, and blocked the maintenance phase of this state. In contrast to APV, the blockade of AMPA/kainate receptors by CNQX (10 microM) had no effect. Like APV, KN62 (3 microM), a selective membrane permeable inhibitor of CaMKII, blocked the EPSP-spike potentiation and the maintenance phase of the in vitro kindling-like state. Our previous and present results therefore demonstrate that Ca(2+) influxes through L-type voltage-dependent-and NMDA receptor-dependent-Ca(2+) channels contribute differentially to the development of an in vitro kindling-like state, and both induce EPSP-spike potentiation in CA1 hippocampal pyramidal cells in response to repeated brief increases in K(+)(o). It is suggested that these effects of intracellular Ca(2+) on the maintenance phase of the in vitro kindling-like state and EPSP-spike potentiation are mediated by CaMKII-dependent mechanisms.

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

The development of symptomatic epilepsy is a model of long-term plasticity changes in the central nervous system. The rat pilocarpine model of epilepsy was utilized to study persistent alterations in calcium/calmodulin-dependent kinase II (CaM kinase II) activity associated with epileptogenesis. CaM kinase II-dependent substrate phosphorylation and autophosphorylation were significantly inhibited for up to 6 weeks following epileptogenesis in both the cortex and hippocampus, but not in the cerebellum. The net decrease in CaM kinase II autophosphorylation and substrate phosphorylation was shown to be due to decreased kinase activity and not due to increased phosphatase activity. The inhibition in CaM kinase II activity and the development of epilepsy were blocked by pretreating seizure rats with MK-801 indicating that the long-lasting decrease in CaM kinase II activity was dependent on N-methyl-D-aspartate receptor activation. In addition, the inhibition of CaM kinase II activity was associated in time and regional localization with the development of spontaneous recurrent seizure activity. The decrease in enzyme activity was not attributed to a decrease in the alpha or beta kinase subunit protein expression level. Thus, the significant inhibition of the enzyme occurred without changes in kinase protein expression, suggesting a long-lasting, post-translational modification of the enzyme. This is the first published report of a persistent, post-translational alteration of CaM kinase II activity in a model of epilepsy characterized by spontaneous recurrent seizure activity.

Inhibition of calcium/calmodulin kinase II alpha subunit expression results in epileptiform activity in cultured hippocampal neurons

Several models that develop epileptiform discharges and epilepsy have been associated with a decrease in the activity of calmodulin-dependent kinase II. However, none of these studies has demonstrated a causal relationship between a decrease in calcium/calmodulin kinase II activity and the development of seizure activity. The present study was conducted to determine the effect of directly reducing calcium/calmodulin-dependent kinase activity on the development of epileptiform discharges in hippocampal neurons in culture. Complimentary oligonucleotides specific for the alpha subunit of the calcium/calmodulin kinase were used to decrease the expression of the enzyme. Reduction in kinase expression was confirmed by Western analysis, immunocytochemistry, and exogenous substrate phosphorylation. Increased neuronal excitability and frank epileptiform discharges were observed after a significant reduction in calmodulin kinase II expression. The epileptiform activity was a synchronous event and was not caused by random neuronal firing. Furthermore, the magnitude of decreased kinase expression correlated with the increased neuronal excitability. The data suggest that decreased calmodulin kinase II activity may play a role in epileptogenesis and the long-term plasticity changes associated with the development of pathological seizure activity and epilepsy.

Long-lasting decrease in neuronal Ca2+/calmodulin-dependent protein kinase II activity in a hippocampal neuronal culture model of spontaneous recurrent seizures

Ca2+/calmodulin-dependent protein kinase II (CaM Kinase II) activity was evaluated in a well-characterized in vitro model of epileptiform activity. Long-lasting spontaneous recurrent seizure (SRS) activity was induced in hippocampal neuronal cultures by exposure to low Mg2+ media for 3 h. Analysis of endogenous Ca2+/calmodulin-dependent phosphorylation revealed a significant long-lasting decrease in 32P incorporation into the alpha (50 kDa) and beta (60 kDa) subunits of CaM kinase II in association with the induction of SRS activity in this preparation. Ca2+/calmodulin-dependent substrate phosphorylation of the synthetic peptides, Autocamtide-2 and Syntide II, was also significantly reduced following the induction of SRSs and persisted for the life of the neurons in culture. The decrement in CaM kinase II activity associated with low Mg2+ treatment remained significantly decreased when values were corrected for changes in levels of alpha subunit immunoreactivity and neuronal cell loss. Addition of the protein phosphatase inhibitors, okadaic acid and cyclosporin A, to the phosphorylation reaction did not block the SRS-associated decrease in substrate phosphorylation, indicating that enhanced phosphatase activity was not a contributing factor to the observed decrease in phosphate incorporation. The findings of this study demonstrate that CaM kinase II activity is decreased in association with epileptogenesis observed in these hippocampal cultures and may contribute to the production and maintenance of SRSs in this model.

Variations of rat brain calmodulin content in dark and light phases: effect of pentylenetetrazol-induced kindling

Calmodulin (CaM) through activation of CaM-kinase II may be involved in the molecular mechanisms underlying the epileptogenic processes. Some evidence suggests that kindling responses change across the day-night cycle. In order to test if kindling stimulation modifies CaM content, we measured CaM concentrations in amygdala, hippocampus and hypothalamus obtained from control and kindled rats during light and darkness. Male Wistar rats (250-300 g), were injected i.p. with Pentylenetetrazol (PTZ) (35 mg/kg/24 h). Once chemical kindling was established, rats were sacrificed by decapitation at 10:30 a.m. and 01:30 a.m. The brains were obtained, and the amygdala, hippocampus and hypothalamus dissected. CaM content was measured in the cytosol and membrane fractions by radioimmunoassay. We found a significant increase in CaM content in cytosol and membrane fractions of both control and kindled rats during the dark phase. No significant differences in CaM concentrations were observed between control and experimental rats, whether during the light or the dark phase. The data suggest a well defined photoperiodic variation in CaM concentrations in limbic structures, despite the neuronal excitability produced by kindling. In addition, the observed CaM increases during the dark time may be related to a protective mechanism against enhanced sensitivity to seizures observed during the night.

Post-ictal depression transiently inhibits induction of LTP in area CA1 of the rat hippocampal slice

We tested the effects of electrographic seizures (EGSs) elicited in a remote site (area CA3) on the induction of long-term potentiation (LTP) in area CA1 of the rat hippocampal slice. Induction of LTP was inhibited only when the LTP-inducing stimulus was delivered during the period of post-ictal depression (5-10 min period of field response depression) following an evoked EGS. It was not inhibited during the tonic firing phase of the EGS. The time course for the recovery of the ability to induce LTP after an EGS matched the recovery of field responses from post-ictal depression. Moreover, the magnitude of LTP was inversely proportional to the duration of post-ictal depression. Delaying the onset of depression with the adenosine A1 receptor antagonist 8-cyclopentyltheophylline (CPT) permitted LTP induction at a time point when it would normally be suppressed. Finally, the inhibitory effects of post-ictal depression on LTP induction were not restricted to electrically evoked EGSs, as LTP could not be induced during the depressed phase following a spontaneous EGS elicited in 10 mM K+ medium. These results demonstrate that the inhibition of LTP induction following epileptiform activity in vitro is in part a consequence of post-ictal depression of responses.

The effects of focal N-methyl-D-aspartate pretreatment on the parameters of amygdaloid electrical kindling

Evidence is accumulating for a role of glutamate in both the development (epileptogenesis) and spread of epileptic neuronal hyperactivity in the brain. In the present investigation we examined the influence of daily focal pretreatment with the selective glutamate receptor agonist N-methyl-D-aspartate (NMDA) on the parameters of amygdaloid electrical kindling, an animal model of human complex partial and secondary generalised focal seizures. Pretreatment with NMDA significantly increased the electrical afterdischarge threshold in this model. With subsequent daily suprathreshold electrical stimulation, however, NMDA pretreatment enhanced the kindling process as shown by both electroencephalographic and motor seizure responses. Marked reductions in the number of stimulations required to reach each distinct stage of kindling development were evident. The number of stimulations required to achieve the fully kindled state was approximately halved by pretreatment with NMDA (6.8 +/- 1.6 stimulations) compared with control, buffer-pretreated animals (11.6 +/- 1.4 stimulations; mean +/- S.E.M.; P < 0.05). Consistent with this, the mean durations of the electrically-evoked afterdischarges on most NMDA pretreatment days were significantly increased compared to those recorded in control animals. Importantly, fully kindled animals showed a markedly enhanced sensitivity to focally applied NMDA. The results of the present experiments provide strong in vivo evidence to support the concept that ion fluxes through NMDA receptor-linked cation channels play a major role in the mechanisms of kindling epileptogenesis. Extracellular glutamate at abnormally raised levels, acting at least in part via NMDA receptors, may be the principal agent triggering many forms of epilepsy.

Increased levels of mRNA for beta- but not alpha-subunit of calmodulin kinase II following kindled seizures

We studied levels of mRNA for the alpha- and beta-subunits of calmodulin (CaM) kinase II using the amygdaloid kindling model of epilepsy. There were significant increases in mRNA for the beta-subunit of CaM kinase II in the hippocampus 4-24 h after stage 5-kindled seizures. Moreover, this mRNA was significantly increased by 20.0-26.5% in the bilateral dentate gyrus 8 to 24 h after kindled seizures. The beta-subunit mRNA was also significantly increased by 13.5-19.0% in the CA3 on the side ipsilateral to the stimulation, 4 to 8 h after kindled seizures. mRNA for the alpha-subunit of CaM kinase II was not significantly changed in the regions examined for up to 24 h after the kindled seizures. These results suggest that CaM kinase II mediates the molecular processes that follow kindled seizures. It is possible that increases in CaM kinase II-dependent protein phosphorylation are associated with the plastic changes in kindling.

Vascular malformations and epilepsy: clinical considerations and basic mechanisms

Vascular malformations (VMs) are associated with epilepsy. The natural history of the various VMs, clinical presentation, and tendency to provoke epilepsy determine treatment strategies. Investigations have probed the mechanisms of epileptogenesis associated with these lesions. Electrophysiologic changes are associated with epileptogenic cortex adjacent to VMs. Putative pathophysiologic mechanisms of epileptogenesis include neuronal cell loss, glial proliferation and abnormal glial physiology, altered neurotransmitter levels, free radical formation, and aberrant second messenger physiology.

The molecular basis of kindling

Kindling is an experimental model of epilepsy that involves activity-dependent changes in neuronal structure and function. During kindling, pathological changes may occur at several organizational levels of the nervous system, from alterations in gene-expression in individual neurons to the loss of specific neuronal populations and rearrangement of synaptic connectivity resulting from sustained stimulation of major excitatory pathways. This review summarizes recent developments in alterations at single neuronal and molecular levels that may be responsible for kindling epileptogenesis.

Rapid dephosphorylation of microtubule-associated protein 2 in the rat brain hippocampus after pentylenetetrazole-induced seizures

We have studied the effect of Pentylenetetrazole (PTZ)-induced seizures on the state of phosphorylation of microtubule-associated protein 2 (MAP-2) from rat hippocampus. A method for the in vivo 32P-labeling of hippocampal proteins has been established, consisting of intracerebro-ventricular injection of 32PO4 of high specific activity. The results obtained indicate that PTZ induces a rapid and transient dephosphorylation of high-molecular-mass MAP-2, which is prevented when the N-methyl-D-aspartate receptor antagonist MK-801 is previously administered. Phosphopeptide mapping of 32P-labeled MAP-2 obtained from hippocampi of PTZ-treated rats reveals a pattern of phosphorylation distinct from that obtained from control saline-treated rats or MK-801 plus PTZ treated rats. We discuss the possible implications of N-methyl-D-aspartate-receptor activation and MAP-2 dephosphorylation on the plastic changes induced in rat brain hippocampus after induced epileptiform activity.

Comparison of Ca2+/calmodulin-dependent protein kinase II purified from control and diisopropyl phosphorofluoridate (DFP)-treated hens

Diisopropyl phosphorofluoridate (DFP) produces type I organophosphorus ester-induced delayed neurotoxicity in humans and sensitive animal species. This is accompanied by enhanced Ca2+/CaM-dependent protein kinase II (CaM-kinase II) activity, and [125I]calmodulin binding to CaM-kinase II in DFP-treated hen brain supernatant without increase in the enzyme quantity. We have purified CaM-kinase II from control and DFP-treated hen whole brains and compared various physical and biochemical properties. The two enzymes exhibited similar properties in many respects. However, there was a decrease in calcium-independent protein kinase II activity after autophosphorylation, and an increase in K0.5 for free calcium and calmodulin of enzyme purified from DFP-treated hen brains. This change in kinetic parameters may result in greater percentage of total CaM-kinase II present in unphosphorylated form, which is consistent with the increased autophosphorylation of CaM-kinase II and [125I]calmodulin binding in the brain supernatant of DFP-treated hens.

Excitotoxicity affects membrane potential and calmodulin kinase II activity in cultured rat cortical neurons

BACKGROUND AND PURPOSE

Glutamate-induced excitotoxicity has been implicated as a causative factor for selective neuronal loss in ischemia and hypoxia. Toxic exposure of neurons to glutamate results in an extended neuronal depolarization that precedes delayed neuronal death. Because both delayed neuronal death and extended neuronal depolarization are dependent on calcium, we examined the effect of glutamate exposure on extended neuronal depolarization and calcium/calmodulin-dependent protein kinase II (CaM kinase II) activity.

METHODS

Three-week-old cortical cell cultures from embryonic rats were exposed to 500 microM glutamate and 10 microM glycine or to control medium for 10 minutes. Cells were examined for neuronal toxicity, electrophysiology, and biochemical alterations. In one set of experiments, whole-cell current clamp recording was performed throughout the experiment. In a parallel experiment, cortical cultures were allowed to recover from glutamate exposure for 1 hour, at which time the cells were homogenized and CaM kinase II activity was assayed using standard techniques.

RESULTS

Excitotoxic exposure to glutamate resulted in extended neuronal depolarization, which remained after removal of the glutamate. Glutamate exposure also resulted in delayed neuronal death, which was preceded by significant inhibition of CaM kinase II activity. The excitotoxic inhibition of CaM kinase II correlated with neuronal loss, was N-methyl-D-aspartate receptor-mediated, and was not due to autophosphorylation of the enzyme.

CONCLUSIONS

Glutamate-induced delayed neuronal toxicity correlates with extended neuronal depolarization and inhibition of CaM kinase II activity. Because inhibition of CaM kinase II activity significantly preceded the histological loss of neurons, the data suggest that modulation of CaM kinase II activity may be involved in the cascade of events resulting in loss of calcium homeostasis and delayed neuronal death.

Amygdala kindling alters protein kinase C activity in dentate gyrus

Kindling is a use-dependent form of synaptic plasticity and a widely used model of epilepsy. Although kindling has been widely studied, the molecular mechanisms underlying induction of this phenomenon are not well understood. We determined the effect of amygdala kindling on protein kinase C (PKC) activity in various regions of rat brain. Kindling stimulation markedly elevated basal (Ca(2+)-independent) and Ca(2+)-stimulated phosphorylation of an endogenous PKC substrate (which we have termed P17) in homogenates of dentate gyrus, assayed 2 h after kindling stimulation. The increase in P17 phosphorylation appeared to be due at least in part to persistent PKC activation, as basal PKC activity assayed in vitro using an exogenous peptide substrate was increased in kindled dentate gyrus 2 h after the last kindling stimulation. A similar increase in basal PKC activity was observed in dentate gyrus 2 h after the first kindling stimulation. These results document a kindling-associated persistent PKC activation and suggest that the increased activity of PKC could play a role in the induction of the kindling effect.

Increases in cerebral blood flow in rat hippocampus after medial septal injection of naloxone

BACKGROUND AND PURPOSE

In a previous study, we occasionally found that the rat given naloxone in the preoptic region develops behavioral seizures. In view of knowledge that the forebrain including the medial septal nucleus provides cholinergic projections to the hippocampal formation, the present study examined the effects of naloxone injected into the medial septal nucleus on the local blood flow in the hippocampus.

METHODS

A polyurethane-coated platinum electrode with a 1-mm bare tip for measurement of blood flow and a guide cannula made of stainless steel tube for naloxone injection were implanted chronically into the brain. The cerebral blood flow was measured by the hydrogen clearance method in freely moving rats.

RESULTS

The injection of 50 micrograms naloxone caused a significant increase in hippocampal blood flow, with its peak at 20 minutes. Twenty micrograms naloxone caused a similar increase, but 10 micrograms caused only a slight increase that peaked at 30 minutes, suggesting a dose-response of naloxone effect. Hippocampal blood flow was not changed after the injection of saline into the medial septal nucleus and after the injection of naloxone into the caudate nucleus.

CONCLUSIONS

Taken together with previous findings, the results suggest that endogenous opioids exert a decreasing effect on the local blood flow in the hippocampus, probably mediated by the magnocellular cholinergic neurons projecting to the hippocampus.

Effect of septal kindling on glutamate binding and calcium/calmodulin-dependent phosphorylation in a postsynaptic density fraction isolated from rat cerebral cortex

Postsynaptic density (PSD) fractions were isolated from the cerebral cortices of control and kindled rats and assayed for glutamate and gamma-aminobutyric acid-binding capacities and for the Ca2+/calmodulin-dependent protein kinase. Glutamate binding was found to be increased by approximately 50% in the PSDs isolated from kindled rats as compared to controls; this increase was almost completely from an increase in Bmax; Kd decreased only slightly. Studies with inhibitors indicate that the receptors involved were of the N-methyl-D-aspartate and quisqualate types. PSDs isolated from control and kindled rats did not differ in gamma-aminobutyric acid or flunitrazepam binding. The in vitro autophosphorylation of the Ca2+/calmodulin-dependent protein kinase was depressed by 45-76% in PSDs isolated from kindled rats as compared to controls, with little change in amount of the kinase. Therefore, we infer that (i) the kindled state is associated with an increase in glutamate activation of postsynaptic sites, allowing Ca2+ to enter dendritic spines, (ii) a change has occurred in activity of the protein kinase, which is the major cerebral cortex PSD protein, and (iii) perhaps major alterations in the PSD are a concomitant to the long-lasting nature of the kindled state.

Calcium/calmodulin-dependent protein kinase II

There is a great deal known about the in vitro properties of CaM kinase II, both in terms of its substrate specificity and its regulation by calmodulin and autophosphorylation. Much of this characterization is based on experiments performed with the rat brain isozyme of CaM kinase II, although in the aspects examined to date isozymes of the kinase from other tissues appear to behave in a broadly similar manner in vitro. However, relatively little is known about the functions of the kinase in vivo. The proteins phosphorylated by the kinase (with the probable exception of synapsin I and tyrosine hydroxylase) and the role of kinase autophosphorylation in vivo remain largely unknown. Investigation of the physiological role of the kinase in brain and other tissues will be a particularly exciting area for future work. The current knowledge of the in vitro properties and the availability of cDNA clones will hopefully expedite this research.

Regulatory properties of calcium/calmodulin-dependent protein kinase II in rat brain postsynaptic densities

Calcium/calmodulin (CaM)-dependent protein kinase II (CaM-kinase II) contained within the postsynaptic density (PSD) was shown to become partially Ca2+-independent following initial activation by Ca2+/CaM. Generation of this Ca2+-independent species was dependent upon autophosphorylation of both subunits of the enzyme in the presence of Mg2+/ATP/Ca2+/CaM and attained a maximal value of 74 +/- 5% of the total activity within 1-2 min. Subsequent to the generation of this partially Ca2+-independent form of PSD CaM-kinase II, addition of EGTA to the autophosphorylation reaction resulted in further stimulation of 32PO4 incorporation into both kinase subunits and a loss of stimulation of the kinase by Ca2+/CaM. Examination of the sites of Ca2+-dependent autophosphorylation by phosphoamino acid analysis and peptide mapping of both kinase subunits suggested that phosphorylation of Thr286/287 of the alpha- and beta-subunits, respectively, may be responsible for the transition of PSD CaM-kinase II to the Ca2+-independent species. A synthetic peptide 281-309 corresponding to a portion of the regulatory domain (residues 281-314) of the soluble kinase inhibited syntide-2 phosphorylation by the Ca2+-independent form of PSD CaM-kinase II (IC50 = 3.6 +/- 0.8 microM). Binding of Ca2+/CaM to peptide 281-309 abolished its inhibitory property. Phosphorylation of Thr286 in peptide 281-309 also decreased its inhibitory potency. These data suggest that CaM-kinase II in the PSD possesses regulatory properties and mechanisms of activation similar to the cytosolic form of CaM-kinase II.

Calcium/calmodulin-dependent protein kinase II

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Synaptic protein tyrosine kinase: partial characterization and identification of endogenous substrates

The subcellular distribution of protein tyrosine kinase in rat forebrain was determined using [Val5]-angiotensin II as exogenous substrate. Enzyme activity was present in each of the fractions analyzed and was enriched in synaptic membranes (SMs) and the synaptosomal soluble fraction (2.2- and 2.5-fold over the homogenate, respectively). SMs also phosphorylated polyglutamyltyrosine (pGT; molar ratio of 4:1), the Vmax for angiotensin and pGT phosphorylation being 26.3 +/- 1.6 and 142 +/- 4 pmol/min/mg, respectively. Extraction of SMs with several different detergents resulted in enhanced enzyme activity and the solubilization of 33-37% of the angiotensin and 43-70% of the pGT-phosphorylating activity. Isolated postsynaptic densities (PSDs) contained tyrosine kinase and phosphorylated angiotensin and pGT. The Vmax values for angiotensin and pGT phosphorylation by PSDs were 17 +/- 5 and 23 +/- 1 pmol/min/mg, respectively. Six putative endogenous substrates for SM tyrosine kinase, with molecular weights of 205K, 180K, 76K, 60K, 50K, and 45K, were identified. Each of these proteins, except p76, was phosphorylated in the detergent-insoluble residue obtained following the extraction of SMs with Triton X-100 as well as in PSDs, indicating that the postsynaptic apparatus is an active site of tyrosine phosphorylation. The phosphorylation of p76 was localized to the Triton X-100 extract and also occurred in the synaptosomal soluble fraction. The results indicate that tyrosine kinase and its substrates are located in both pre- and postsynaptic compartments and suggest a role for this enzyme in synaptic function.

A retinal calmodulin-dependent kinase: calcium/calmodulin-stimulated and -inhibited states

A calcium/calmodulin-dependent protein kinase was isolated from retina. The retinal enzyme is composed exclusively of 50-kilodalton (kD) subunits and has a molecular mass of approximately 275 kD, in contrast to forebrain calmodulin kinase II, which is composed of 50-kD and 60-kD subunits in a 3:1 ratio and has a molecular mass of approximately 520 kD. Similar substrate specificities, kinetic properties, capacity to bind calmodulin, and immunoreactivity suggest that the retinal kinase is an isoenzyme of forebrain calmodulin kinase II. Both kinases autophosphorylate in an intramolecular manner; however, autophosphorylation has different effects on the activities of the two enzymes. Autophosphorylation of retinal calmodulin kinase converts the enzyme from a calcium/calmodulin-dependent to a calcium/calmodulin-inhibited kinase, with high activity in the absence of calcium, whereas autophosphorylation of the forebrain kinase results in a less active, calcium/calmodulin-independent enzyme. These properties of calmodulin kinase may play an important role in retinal function.

Phosphorylation of synaptic proteins in chick forebrain: changes with development and passive avoidance training

We have used synaptic plasma membranes (SPMs) and postsynaptic densities (PSDs) to study protein phosphorylation at the synapse in the developing chick forebrain and in 1-day-old chick forebrain following training on a passive avoidance task. Endogenous phosphorylation patterns in SPMs and PSDs prepared by extraction with n-octylglucoside isolated from chick forebrain were investigated by labelling with [32P]ATP. The phosphoprotein components of the SPM and PSD fractions were separated using sodium dodecyl sulphate gradient polyacrylamide gel electrophoresis. Autoradiography and densitometry of the Coomassie Blue protein staining pattern revealed phosphate incorporation into several SPM components including those of molecular mass 52, 37, and 29 kilodaltons (kDa). Bands of similar molecular mass were not phosphorylated in PSD fractions. This difference in phosphorylation between SPMs and PSDs was not due to the detergent n-octylglucoside. In a developmental study in which SPM and PSD fractions were prepared from 1-day-old, 14-day-old, and 21-day-old chickens, the phosphorylation patterns of SPMs were similar throughout, but striking differences occurred in PSDs, both in the level of phosphorylation and in the components phosphorylated. A time-course study was carried out in which phosphorylation of SPMs and PSDs from 1-day-old chicks trained on a passive avoidance task was compared with patterns from control chicks trained on a water-coated bead and untrained chicks. In SPMs prepared from forebrains removed 10 mins following training, a consistent but nonsignificant decrease (-21%) in phosphorylation of a 52 kDa band occurred in chicks with passive avoidance training compared with water-trained and untrained chicks.(ABSTRACT TRUNCATED AT 250 WORDS)

Calmodulin kinase II in pure cultured astrocytes

Calcium- and calmodulin-dependent protein kinase activity was studied in pure neuronal and glial cultures. The addition of calcium and calmodulin stimulated 32P incorporation into several neuronal proteins including two in the 50- and 60-kilodalton (kD) region which comigrated with purified forebrain calmodulin kinase II subunits (CaM kinase II). In mature astrocytes, CaM kinase activity was also present, and was inhibited by trifluoroperazine and diazepam. Again in homogenates of these cells, two phosphoproteins of apparent molecular masses of 50 and 60 kD comigrated with purified CaM kinase. CaM kinase activity was absent in immature mixed glia and oligodendrocytes. The presence of CaM kinase in neurons and mature astrocytes was confirmed using monoclonal antibodies specific for the 50-kD subunit of the enzyme. No immunoreactivity was observed in oligodendrocytes. The presence of CaM kinase in astrocytes suggests a more ubiquitous role of this enzyme in regulating cellular processes than was previously recognized.

Molecular mechanisms of neuronal excitability: possible involvement of CaM kinase II in seizure activity

A type II calmodulin-dependent protein kinase (CaM kinase II) has been characterized in the synaptic region and may mediate some of the effects of Ca2+ on neuronal excitability. The activity of CaM kinase II is inhibited by anticonvulsant compounds and may be the molecular basis of their neuro-modulatory effects. The direct injection of purified CaM kinase II into invertebrate neurons has demonstrated that this kinase can directly alter specific ion conductances and neuronal activity. A long-lasting decrease in CaM kinase II activity is associated with septal kindling, an experimental model of epilepsy and long-term memory. In summary, CaM kinase II appears to be a central mediator of the effects of Ca2+ on neuronal function. Further investigation of this enzyme and its effects on neuronal activity may provide a molecular insight into an endogenous mechanism for modulating some of the effects of Ca2+ on neuronal excitability and may increase our understanding of the complex regulatory mechanisms that underlie the pathogenesis of seizure discharge and its regulation by anticonvulsant compounds.

Ganglioside changes associated with temporal lobe epilepsy in the human hippocampus

To understand better the molecular and cellular events associated with status epilepticus, a multifaceted analysis has begun on hippocampal tissues therapeutically removed from patients with temporal lobe epilepsy. In this first study, quantitative changes in major ganglioside species are reported, as well as the immunocytochemical localization on the ganglioside GD3 in epileptic human hippocampus. Although significant variations were found between patients, the pattern of change was consistent when compared to normal values obtained from an autopsied specimen and the literature. Total ganglioside content was reduced in epileptic hippocampi, which was attributable, in part, to pyramidal cell loss found in CA1 and CA3. In each case, the percentage of ganglioside GD3 was increased significantly, while ganglioside GD1a decreased. The former change is probably associated with reactive astrocytosis and the latter with loss of neuronal dendrites. Immunocytochemical localization revealed GD3 in the stratum radiatum and the subgranular layer of the dentate gyrus. In these areas, GD3 was present in punctate structures and astrocytes. These findings indicate that GD3 increases in selected areas of the sclerotic hippocampus and is presumably related to localized accumulation of reactive glial cells. Since gangliosides have a high affinity for calcium and localized increase in extracellular calcium could disrupt normal neuronal function, the localized increase in GD3 may not only denote reactive glial cells but may contribute directly to the altered, hyperexcitable condition of epilepsy.

Modulation of calcium-mediated inactivation of ionic currents by Ca2+/calmodulin-dependent protein kinase II

Iontophoretic injection of Ca2+ causes reduction of I0A (an early rapidly activating and inactivating K+ current) and I0C (a late Ca2+-dependent K+ current) measured across the isolated type B soma membrane (Alkon et al., 1984, 1985; Alkon and Sakakibara, 1984, 1985). Similarly, voltage-clamp conditions which cause elevation of [Ca2+]i are followed by reduction of I0A and I0C lasting 1-3 min. Iontophoretic injection of highly purified Ca2+/CaM-dependent protein kinase II (CaM kinase II) isolated from brain tissue (Goldenring et al., 1983) enhanced and prolonged this Ca2+-mediated reduction of I0A and I0C. ICa2+, a voltage-dependent Ca2+ current, also showed some persistent reduction under these conditions. Iontophoretic injection of heat-inactivated enzyme had no effect. Agents that inhibit or block Ca2+/CaM-dependent phosphorylation produced increased I0A and I0C amplitudes and prevented the effects of CaM kinase II injection. The results reported here and in other studies implicate Ca2+-stimulated phosphorylation in the regulation of type B soma ionic currents.

Cyclic nucleotide response of the hippocampal formation to septal stimulation in naive and kindled rats

Rats were kindled through nonmagnetic electrodes stereotaxically implanted into the medial septum. Concentrations of cyclic AMP and cyclic GMP were measured by radioimmunoassay in seven brain regions after microwave fixation during the development and expression of kindled seizures. Hippocampal concentrations were similar to untreated controls (cyclic GMP level in the left and right hippocampus, 0.66 +/- 0.04 and 0.68 +/- 0.07 pmol/mg of protein, respectively; cyclic AMP, 9.4 +/- 0.9 and 9.6 +/- 0.8 pmol/mg of protein, respectively), in kindled animals that were not stimulated, and in naive animals in response to septal stimulation, in spite of the presence in the latter group of bilateral hippocampal afterdischarges. Animals that failed to develop kindling and kindled animals that failed to have a seizure in response to stimulation also showed no change in cyclic nucleotide concentrations in any brain region. Kindled animals that developed a seizure following stimulation showed significant elevations in levels of both cyclic GMP and cyclic AMP in hippocampus and in several other brain regions. A single naive animal that had a seizure in response to its first stimulation also appeared to have elevated concentrations of both cyclic nucleotides in hippocampus. These data suggest that the elevation in levels of both cyclic GMP and cyclic AMP during kindled seizures is associated with seizure development rather than with the generation of afterdischarges or with the kindling engram.