Mechanism of epilepsy

Gadd45 in Neuronal Development, Function, and Injury

The growth arrest and DNA damage-inducible (Gadd) 45 proteins have been associated with numerous cellular mechanisms including cell cycle control, DNA damage sensation and repair, genotoxic stress, neoplasia, and molecular epigenetics. The genes were originally identified in in vitro screens of irradiation- and interleukin-induced transcription and have since been implicated in a host of normal and aberrant central nervous system processes. These include early and postnatal development, injury, cancer, memory, aging, and neurodegenerative and psychiatric disease states. The proteins act through a variety of molecular signaling cascades including the MAPK cascade, cell cycle control mechanisms, histone regulation, and epigenetic DNA demethylation. In this review, we provide a comprehensive discussion of the literature implicating each of the three members of the Gadd45 family in these processes.

Bee venom acupuncture therapy ameliorates neuroinflammatory alterations in a pilocarpine-induced epilepticus model

Bee venom (BV) is applied in different traditional medicinal therapies and is used worldwide to prevent and treat many acute and chronic diseases. Epilepsy has various neurological effects, e.g., epileptogenic insults; thus, it is considered a life-threatening condition. Seizures and their effects add to the burden of epilepsy because they can have health effects including residual disability and even premature mortality. The use of antiinflammatory drugs to treat epilepsy is controversial; therefore, the alternative nonchemical apitherapy benefits of BV were evaluated in the present study by assessing neuroinflammatory changes in a pilocarpine-induced epilepticus model. Levels of electrolytes, neurotransmitters, and mRNA expression for some gate channels were determined. Moreover, ELISA assays were conducted to detect pro- and anti-inflammatory cytokines, whereas RT-PCR was performed to assess mRNA expression of Foxp3 and CTLA-4. BV ameliorated the interruption in electrolytes and ions through voltage- and ligand-gated ion channels, and it limited neuronal excitability via rapid repolarization of action potentials. In addition, BV inhibited the high expression of proinflammatory cytokines. Acupuncture with BV was effective in preventing some of the deleterious consequences of epileptogenesis associated with high levels of glutamate and DOPA in the hippocampus. BV ameliorates changes in the expression of voltage-gated channels, rebalances blood electrolytes and neurotransmitters, and modulates the levels of pro- and anti-inflammatory cytokines. Thus, BV could reduce the progression of epileptogenesis as a cotherapy with other antiepileptic drugs.

Semaphorins in Adult Nervous System Plasticity and Disease

Semaphorins, originally discovered as guidance cues for developing axons, are involved in many processes that shape the nervous system during development, from neuronal proliferation and migration to neuritogenesis and synapse formation. Interestingly, the expression of many Semaphorins persists after development. For instance, Semaphorin 3A is a component of perineuronal nets, the extracellular matrix structures enwrapping certain types of neurons in the adult CNS, which contribute to the closure of the critical period for plasticity. Semaphorin 3G and 4C play a crucial role in the control of adult hippocampal connectivity and memory processes, and Semaphorin 5A and 7A regulate adult neurogenesis. This evidence points to a role of Semaphorins in the regulation of adult neuronal plasticity. In this review, we address the distribution of Semaphorins in the adult nervous system and we discuss their function in physiological and pathological processes.

Preparation of Nanocrystals for Insoluble Drugs by Top-Down Nanotechnology with Improved Solubility and Bioavailability

Midazolam is a rapidly effective benzodiazepine drug that is widely used as a sedative worldwide. Due to its poor solubility in a neutral aqueous solution, the clinical use of midazolam is significantly limited. As one of the most promising formulations for poorly water-soluble drugs, nanocrystals have drawn worldwide attention. We prepared a stable nanosuspension system that causes little muscle irritation. The particle size of the midazolam nanocrystals (MDZ/NCs) was 286.6 ± 2.19 nm, and the crystalline state of midazolam did not change in the size reduction process. The dissolution velocity of midazolam was accelerated by the nanocrystals. The pharmacokinetics study showed that the AUC0–t of the MDZ/NCs was 2.72-fold (p < 0.05) higher than that of the midazolam solution (MDZ/S), demonstrating that the bioavailability of the MDZ/NC injection was greater than that of MDZ/S. When midazolam was given immediately after the onset of convulsions, the ED₅₀ for MDZ/NCs was significantly more potent than that for MDZ/S and DZP/S. The MDZ/NCs significantly reduced the malondialdehyde content in the hippocampus of the seizures model rats and significantly increased the glutathione and superoxide dismutase levels. These results suggest that nanocrystals significantly influenced the dissolution behavior, pharmacokinetic properties, anticonvulsant effects, and neuroprotective effects of midazolam and ultimately enhanced their efficacy in vitro and in vivo.

Advantages of Structure-Based Drug Design Approaches in Neurological Disorders

OBJECTIVE

The purpose of the review is to portray the theoretical concept on neurological disorders from research data.

BACKGROUND

The freak changes in chemical response of nerve impulse causes neurological disorders. The research evidence of the effort done in the older history suggests that the biological drug targets and their effective feature with responsive drugs could be valuable in promoting the future development of health statistics structure for improved treatment for curing the nervous disorders.

METHODS

In this review, we summarized the most iterative theoretical concept of structure based drug design approaches in various neurological disorders to unfathomable understanding of reported information for future drug design and development.

RESULTS

On the premise of reported information we analyzed the model of theoretical drug designing process for understanding the mechanism and pathology of the neurological diseases which covers the development of potentially effective inhibitors against the biological drug targets. Finally, it also suggests the management and implementation of the current treatment in improving the human health system behaviors.

CONCLUSION

With the survey of reported information we concluded the development strategies of diagnosis and treatment against neurological diseases which leads to supportive progress in the drug discovery.

Neuroinformatics analyses reveal GABAt and SSADH as major proteins involved in anticonvulsant activity of valproic acid

The unequivocal hypotheses about anticonvulsant activity of valproic acid (VPA) have always been a basic hurdle in designing next generation neurotherapeutics, particularly the anti-epileptic drugs. The present study reports about a comprehensive in-silico investigation into qualitative and quantitative binding of VPA and corresponding natural ligands of four major enzymes involved in neurotransmissions, namely-GABA transaminase (GABAt), α-keto glutarate dehydrogenase (α-KGDH), Succinate Semialdehyde dehydrogenase (SSADH) and Glutamate Decarboxylase (GAD), respectively. The molecular docking analyses revealed that VPA inhibits GABAt and α-KGDH through allosteric while SSADH through competitive mode of binding. There is an observed elevation in binding of glutamate over GAD in the presence of VPA. The docking inhibition constant (Ki) of VPA to all the studied enzymatic receptors were observed to be well below the therapeutic concentration of VPA in blood, except for α-KGDH, thus favouring GABAergic over glutamatergic mode of anticonvulsant activity of VPA. The report is probably the first comprehensive in-silico molecular study about VPA action.

Effects of phenytoin and lamotrigine treatment on serum BDNF levels in offsprings of epileptic rats

The role of brain-derived neurotrophic factor (BDNF) is to promote and modulate neuronal responses across neurotransmitter systems in the brain. Therefore, abnormal BDNF signaling may be associated with the pathophysiology of schizophrenia. Low BDNF levels have been reported in brains and serums of patients with psychotic disorders. In the present study, we investigated the effects of antiepileptic drugs on BDNF in developing rats. Pregnant rats were treated with phenytoin (PHT), lamotrigine (LTG) and folic acid for long-term, all through their gestational periods. Experimental epilepsy (EE) model was applied in pregnant rats. Epileptic seizures were determined with electroencephalography. After birth, serum BDNF levels were measured in 136 newborn rats on postnatal day (PND) 21 and postnatal day 38. In postnatal day 21, serum BDNF levels of experimental epilepsy group were significantly lower compared with PHT group. This decrease is statistically significant. Serum BDNF levels increased in the group LTG. This increase compared with LTG+EE group was statistically significant. In the folic acid (FA) group, levels of serum BDNF decreased statistically significantly compared to the PHT group. On postnatal day 38, no significant differences were found among the groups for serum BDNF levels. We concluded that, the passed seizures during pregnancy adversely affect fetal brain development, lowering of serum BDNF levels. PHT use during pregnancy prevents seizure-induced injury by increasing the levels of BDNF. About the increase level of BDNF, LTG is much less effective than PHT, the positive effect of folic acid on serum BDNF levels was not observed. LTG increase in BDNF is much less effective than PHT, folic acid did not show a positive effect on serum BDNF levels. Epilepsy affects fetal brain development during gestation in pregnant rats, therefore anti-epileptic therapy should be continued during pregnancy.

Anticonvulsant effects of structurally diverse GABA(B) positive allosteric modulators in the DBA/2J audiogenic seizure test: Comparison to baclofen and utility as a pharmacodynamic screening model

The GABA(B) receptor has been indicated as a promising target for multiple CNS-related disorders. Baclofen, a prototypical orthosteric agonist, is used clinically for the treatment of spastic movement disorders, but is associated with unwanted side-effects, such as sedation and motor impairment. Positive allosteric modulators (PAM), which bind to a topographically-distinct site apart from the orthosteric binding pocket, may provide an improved side-effect profile while maintaining baclofen-like efficacy. GABA, the major inhibitory neurotransmitter in the CNS, plays an important role in the etiology and treatment of seizure disorders. Baclofen is known to produce anticonvulsant effects in the DBA/2J mouse audiogenic seizure test (AGS), suggesting it may be a suitable assay for assessing pharmacodynamic effects. Little is known about the effects of GABA(B) PAMs, however. The studies presented here sought to investigate the AGS test as a pharmacodynamic (PD) screening model for GABA(B) PAMs by comparing the profile of structurally diverse PAMs to baclofen. GS39783, rac-BHFF, CMPPE, A-1295120 (N-(3-(4-(4-chloro-3-fluorobenzyl)-6-methoxy-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)phenyl)acetamide), and A-1474713 (N-(3-(4-(4-chlorobenzyl)-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)phenyl)acetamide) all produced robust, dose-dependent anticonvulsant effects; a similar profile was observed with baclofen. Pre-treatment with the GABA(B) antagonist SCH50911 completely blocked the anticonvulsant effects of baclofen and CMPPE in the AGS test, indicating such effects are likely mediated by the GABA(B) receptor. In addition to the standard anticonvulsant endpoint of the AGS test, video tracking software was employed to assess potential drug-induced motor side-effects during the acclimation period of the test. This analysis was sensitive to detecting drug-induced changes in total distance traveled, which was used to establish a therapeutic index (TI = hypoactivity/anticonvulsant effects). Calculated TIs for A-1295120, CMPPE, rac-BHFF, GS39783, and A-1474713 were 5.31x, 5.00x, 4.74x, 3.41x, and 1.83x, respectively, whereas baclofen was <1. The results presented here suggest the DBA/2J mouse AGS test is a potentially useful screening model for detecting PD effects of GABA(B) PAMs and can provide an initial read-out on target-related motor side-effects. Furthermore, an improved TI was observed for PAMs compared to baclofen, indicating the PAM approach may be a viable therapeutic alternative to baclofen.

The role of reactive species in epileptogenesis and influence of antiepileptic drug therapy on oxidative stress

Epilepsy is considered one of the most common neurological disorders. The focus of this review is the acquired form of epilepsy, with the development process consisting of three major phases, the acute injury phase, the latency epileptogenesis phase, and the phase of spontaneous recurrent seizures. Nowadays, an increasing attention is paid to the possible interrelationship between oxidative stress resulting in disturbance of physiological signalling roles of calcium and free radicals in neuronal cells and mitochondrial dysfunction, cell damage, and epilepsy. The positive stimulation of mitochondrial calcium signals by reactive oxygen species and increased reactive oxygen species generation resulting from increased mitochondrial calcium can lead to a positive feedback loop. We propose that calcium can pose both, physiological and pathological effects of mitochondrial function, which can lead in neuronal cell death and consequent epileptic seizures. Various antiepileptic drugs may impair the endogenous antioxidative ability to prevent oxidative stress. Therefore, some antiepileptic drugs, especially from the older generation, may trigger oxygen-dependent tissue injury. The prooxidative effects of these antiepileptic drugs might lead to enhancement of seizure activity, resulting in loss of their efficacy or apparent functional tolerance and undesired adverse effects. Additionally, various reactive metabolites of antiepileptic drugs are capable of covalent binding to macromolecules which may lead to deterioration of the epileptic seizures and systemic toxicity. Since neuronal loss seems to be one of the major neurobiological abnormalities in the epileptic brain, the ability of antioxidants to attenuate seizure generation and the accompanying changes in oxidative burden, further support an important role of antioxidants as having a putative antiepileptic potential.

Manganese-enhanced magnetic resonance imaging detects mossy fiber sprouting in the pilocarpine model of epilepsy

PURPOSE

Mossy fiber sprouting (MFS) is a frequent finding following status epilepticus (SE). The present study aimed to test the feasibility of using manganese-enhanced magnetic resonance imaging (MEMRI) to detect MFS in the chronic phase of the well-established pilocarpine (Pilo) rat model of temporal lobe epilepsy (TLE).

METHODS

To modulate MFS, cycloheximide (CHX), a protein synthesis inhibitor, was coadministered with Pilo in a subgroup of animals. In vivo MEMRI was performed 3 months after induction of SE and compared to the neo-Timm histologic labeling of zinc mossy fiber terminals in the dentate gyrus (DG).

KEY FINDINGS

Chronically epileptic rats displaying MFS as detected by neo-Timm histology had a hyperintense MEMRI signal in the DG, whereas chronically epileptic animals that did not display MFS had minimal MEMRI signal enhancement compared to nonepileptic control animals. A strong correlation (r = 0.81, p < 0.001) was found between MEMRI signal enhancement and MFS.

SIGNIFICANCE

This study shows that MEMRI is an attractive noninvasive method for detection of mossy fiber sprouting in vivo and can be used as an evaluation tool in testing therapeutic approaches to manage chronic epilepsy.

Wavelet-based Gaussian-mixture hidden Markov model for the detection of multistage seizure dynamics: a proof-of-concept study

Background

Epilepsy is a common neurological disorder characterized by recurrent electrophysiological activities, known as seizures. Without the appropriate detection strategies, these seizure episodes can dramatically affect the quality of life for those afflicted. The rationale of this study is to develop an unsupervised algorithm for the detection of seizure states so that it may be implemented along with potential intervention strategies.

Methods

Hidden Markov model (HMM) was developed to interpret the state transitions of the in vitro rat hippocampal slice local field potentials (LFPs) during seizure episodes. It can be used to estimate the probability of state transitions and the corresponding characteristics of each state. Wavelet features were clustered and used to differentiate the electrophysiological characteristics at each corresponding HMM states. Using unsupervised training method, the HMM and the clustering parameters were obtained simultaneously. The HMM states were then assigned to the electrophysiological data using expert guided technique. Minimum redundancy maximum relevance (mRMR) analysis and Akaike Information Criterion (AICc) were applied to reduce the effect of over-fitting. The sensitivity, specificity and optimality index of chronic seizure detection were compared for various HMM topologies. The ability of distinguishing early and late tonic firing patterns prior to chronic seizures were also evaluated.

Results

Significant improvement in state detection performance was achieved when additional wavelet coefficient rates of change information were used as features. The final HMM topology obtained using mRMR and AICc was able to detect non-ictal (interictal), early and late tonic firing, chronic seizures and postictal activities. A mean sensitivity of 95.7%, mean specificity of 98.9% and optimality index of 0.995 in the detection of chronic seizures was achieved. The detection of early and late tonic firing was validated with experimental intracellular electrical recordings of seizures.

Conclusions

The HMM implementation of a seizure dynamics detector is an improvement over existing approaches using visual detection and complexity measures. The subjectivity involved in partitioning the observed data prior to training can be eliminated. It can also decipher the probabilities of seizure state transitions using the magnitude and rate of change wavelet information of the LFPs.

Network-level analysis of cortical thickness of the epileptic brain

Temporal lobe epilepsy (TLE) characterized by an epileptogenic focus in the medial temporal lobe is the most common form of focal epilepsy. However, the seizures are not confined to the temporal lobe but can spread to other, anatomically connected brain regions where they can cause similar structural abnormalities as observed in the focus. The aim of this study was to derive whole-brain networks from volumetric data and obtain network-centric measures, which can capture cortical thinning characteristic of TLE and can be used for classifying a given MRI into TLE or normal, and to obtain additional summary statistics that relate to the extent and spread of the disease. T1-weighted whole-brain images were acquired on a 4-T magnet in 13 patients with TLE with mesial temporal lobe sclerosis (TLE-MTS), 14 patients with TLE with normal MRI (TLE-no), and 30 controls. Mean cortical thickness and curvature measurements were obtained using the FreeSurfer software. These values were used to derive a graph, or network, for each subject. The nodes of the graph are brain regions, and edges represent disease progression paths. We show how to obtain summary statistics like mean, median, and variance defined for these networks and to perform exploratory analyses like correlation and classification. Our results indicate that the proposed network approach can improve accuracy of classifying subjects into two groups (control and TLE) from 78% for non-network classifiers to 93% using the proposed approach. We also obtain network "peakiness" values using statistical measures like entropy and complexity-this appears to be a good characterizer of the disease and may have utility in surgical planning.

Continuous blockade of GABA-ergic inhibition induces novel forms of long-lasting plastic changes in apical dendrites of the hippocampal cornu ammonis 1 (CA1) in vitro

Hippocampal long-term potentiation (LTP) is considered as a fundamental mechanism for learning and memory formation. A role for GABA was reported for the induction and early but not late maintenance of LTP. We have now investigated whether GABA-receptor function is involved in the prolonged maintenance of LTP (>4 h) at afferent synapses at apical dendrites of cornu ammonis 1 (CA1)-pyramidal neurons in hippocampal slices in vitro. Our data demonstrate that GABA-receptor mediated events are not required for conventional, tetanically-induced early- or late-LTP in the hippocampal CA1-region in vitro. Inhibition of GABA-ergic transmission did not negatively influence either early- or late-LTP. In contrast, an additional facilitation was observed at time points corresponding to the establishment of late-LTP (after 3-4 h). Investigation of a second, non-tetanized control input to the same neuronal population revealed that the elevated potentiation of late-LTP in the tetanized input was not LTP-specific. Therefore, we have examined, whether continuous application of GABA-receptor inhibitors also affected the time course of the recorded potentials when a low-frequency stimulation protocol was used. Under these conditions two distinct forms of a late-onset potentiation occurred 5-6 h after drug application. Investigation of mechanisms responsible for this prolonged enhancement of potentials revealed that the higher form of potentiation (potentiation levels above 200%) was dependent on presynaptic activity and N-methyl-d-aspartate (NMDA)-receptor activation, whereas the lower form (potentiation less than 200%) did not require these mechanisms. However, the latter potentiation was prevented by nifedipine, an L-type voltage-dependent calcium channel inhibitor.

Ethnopharmacology of Q'eqchi' Maya antiepileptic and anxiolytic plants: effects on the GABAergic system

ETHNOPHARMACOLOGICAL RELEVANCE

The Q'eqchi' Maya possess a large selection of plants to treat neurological disorders, including epilepsy and susto (fright), a culture-bound illness related to anxiety disorders.

AIM OF THE STUDY

To investigate the activity of antiepileptic and anxiolytic plants in the GABAergic system, and determine if there is a pharmacological basis for plant selection.

MATERIALS AND METHODS

Ethanol extracts of 34 plants were tested in vitro for their ability to inhibit GABA-transaminase (GABA-T) or bind to the GABA(A)-benzodiazepine (BZD) receptor, two principal drug targets in epilepsy and anxiety. Pharmacological activity was correlated with relative frequency of use, based on informant consensus.

RESULTS

Ten plants showed greater than 50% GABA-T inhibition at 1mg/ml, while 23 showed greater than 50% binding to the GABA(A)-BZD receptor at 250 microg/ml. Piperaceae, Adiantaceae and Acanthaceae families were highly represented and active in both assays. There was a significant positive correlation between GABA-T inhibition and relative frequency of use for epilepsy, and an even stronger correlation between GABA(A) binding and relative frequency of use for susto (fright).

CONCLUSIONS

Clearly, Q'eqchi' traditional knowledge of antiepileptic and anxiolytic plants is associated with the use of pharmacologically active plants. Based on the evidence, it is suggested that the mechanism of action for some traditionally used plants may be mediated through the GABAergic system.

Navigating their way to the clinic: emerging roles for axon guidance molecules in neurological disorders and injury

The mechanisms underlying formation of the basic network of the nervous system are of fundamental interest in developmental neurobiology. During the wiring of the nervous system, newborn neurons send axons that travel long distances to their targets. These axons are directed by environmental cues, known as guidance cues, to their correct destinations. Through extensive studies in vertebrates and invertebrates many of the guidance cues and their receptors have been identified. Recently, guidance molecules have been suggested to have important roles in pathological conditions of the nervous system. Mutations in guidance receptors have been associated with hereditary neurological disorders, and deregulation of guidance cues might be associated with predisposition to epilepsy. In addition, it was suggested that guidance molecules play roles in the ability of the adult nervous system to recover and repair after injury. Thus, molecules that were first discovered as "developmental cues" are now emerging as important factors in neurological disease and injury in the adult.

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.

Repeated 4-aminopyridine seizures reduce parvalbumin content in the medial mammillary nucleus of the rat brain

Parvalbumin (Pv) containing fast spiking neurons play a crucial role in synchronizing the activity of excitatory neuronal circuits in the brain. Alterations of parvalbumin content in these neurons can affect their spike characteristics and, ultimately, may increase the susceptibility of neuronal circuits to epileptic seizures. In the present study, we examined whether repeated 4-aminopyridine (4-AP)-induced seizures modify the regional parvalbumin contents in the rat brain. 4-Aminopyridine was injected intraperitoneally in adult rats, controls received the solvent. Animals were sacrificed at 3 h after a single acute treatment, or following repeated, daily treatments of 12 days. In situ hybridization (ISH) indicated significantly decreased parvalbumin mRNA level in the medial mammillary nucleus (MM) at 12 days. Western blotting revealed 20.1% significant decrease of parvalbumin content in the medial mammillary area, while parvalbumin immunohistochemistry indicated no change of the number of immunoreactive cells in the medial mammillary nucleus. The results reveal the downregulation of the transcription of the parvalbumin gene and the decrease of parvalbumin synthesis in medial mammillary nucleus neurons in response to experimental seizures.

Epileptogenesis Causes Acute and Chronic Increases in GABAA Receptor Endocytosis That Contributes to the Induction and Maintenance of Seizures in the Hippocampal Culture Model of Acquired Epilepsy

Altered GABAergic inhibitory tone has been observed in association with a number of both acute and chronic models of epilepsy and is believed to be the result, in part, of a decrease in function of the postsynaptic GABAA receptor (GABAAR). This study was carried out to investigate if alterations in receptor internalization contribute to the decrease in GABAAR function observed with epilepsy, utilizing the hippocampal neuronal culture model of low-Mg2+-induced spontaneous recurrent epileptiform discharges (SREDs). Analysis of GABAAR function in "epileptic" cultures showed a 62% reduction in [3H]flunitrazepam binding to the GABAA alpha receptor subunit and a 50% decrease in GABA currents when compared with controls. Confocal microscopy analysis of immunohistochemical staining of GABAAR beta2/beta3 subunit expression revealed approximately a 30% decrease of membrane staining in hippocampal cultures displaying SREDs immediately after low-Mg2+ treatment and in the chronic epileptic state. Low-Mg2+-treated cultures internalized antibody labeled GABAA receptor with an increase in rate of 68% from control. Inhibition of GABAAR endocytosis in epileptic cultures resulted in both a recovery to control levels of membrane GABAA beta2/beta3 immunostaining and a total blockade of SREDs. These results indicate that altered GABAAR endocytosis contributes to the decrease in GABAAR expression and function observed in this in vitro model of epilepsy and plays a role in causing and maintaining SREDs. Understanding the mechanisms underlying altered GABAA R recycling may offer new insights into the pathophysiology of epilepsy and provide novel therapeutic strategies to treat this major neurological condition.

Consequences of Multiple Withdrawals From Alcohol

This article represents the proceedings of a symposium at the 2003 annual meeting of the Research Society on Alcoholism in Fort Lauderdale, FL, organized by Theodora Duka and chaired by Dai Stephens. The purpose of the symposium was to examine the effects of multiple experiences of withdrawal from alcohol in animals made dependent on alcohol and in humans who are alcohol dependent. Parallels were drawn to the effects of repeated short-lived high-content alcohol exposures in animals and in humans who are social drinkers but indulge in binge drinking. The presentations were (1) Multiple detoxifications and risk of relapse in abstinent alcoholics, by John Gentry and Robert Malcolm; (2) Emotional and cognitive impairments after long-term use of alcohol: relationship to multiple detoxifications and binge drinking, by Theodora Duka; (3) The effect of repeated withdrawal from ethanol on conditioning to appetitive stimuli, by Tamzin Ripley, Gilyanna Borlikova, and Dai Stephens; (4) Alcohol withdrawal kindling: electrographic measures in a murine model of behavioral seizure sensitization, by Lynn Veatch and Howard Becker; and (5) Binge drinking induced changes in CNS, by Fulton Crews.

Molecular basis of an inherited epilepsy

Epilepsy is a common neurological condition that reflects neuronal hyperexcitability arising from largely unknown cellular and molecular mechanisms. In generalized epilepsy with febrile seizures plus, an autosomal dominant epilepsy syndrome, mutations in three genes coding for voltage-gated sodium channel alpha or beta1 subunits (SCN1A, SCN2A, SCN1B) and one GABA receptor subunit gene (GABRG2) have been identified. Here, we characterize the functional effects of three mutations in the human neuronal sodium channel alpha subunit SCN1A by heterologous expression with its known accessory subunits, beta1 and beta2, in cultured mammalian cells. SCN1A mutations alter channel inactivation, resulting in persistent inward sodium current. This gain-of-function abnormality will likely enhance excitability of neuronal membranes by causing prolonged membrane depolarization, a plausible underlying biophysical mechanism responsible for this inherited human epilepsy.

Dynamics of gene expression for immediate early- and late genes after seizure activity in aged rats

The ability of the rodent brain to support plasticity-related phenomena declines with increasing age. A decreased coordination of genes implicated in brain plasticity may be one factor contributing to this decline. Synaptic rearrangement that occurs after seizure activity is regarded as a model of brain plasticity. In a rat model of seizure-related brain plasticity, we found that the induction of immediate-early genes, as exemplified by c-fos and tissue plasminogen activator ( tPA), is not impaired in the aged rat brain. However, the aged rat brain responded more slowly to chemically induced seizure, and the levels of c-fos and tPA mRNAs induction are decreased in the cortex and in the hippocampus of 30 month old rats, as compared to the levels expressed by 3 month old rats. In addition, at the peak induction, the TPA transcripts were restricted to certain cortical layers of the older rats. Surprisingly, in applying the same experimental paradigm to late genes, we found that there was a shift toward earlier times in the maximum expression of growth-related molecules, the microtubule-associated protein 1B (MAP1B) mRNA, which was very evident in 18 month old rats. Aberrant immunolabeling of MAP1B occurred in cortical layer VI of the aged rats where, unlike in young rats, there was heavy staining of neuronal somata. These results suggest that (1) one consequence of aging, besides decreases in the levels of mRNA, is a progressive loss of coordination in gene activity following the administration of a stimulus; (2) since c-fos, TPA and MAP1B have been implicated in neuronal plasticity, these findings could explain, in part, the limited plasticity of the aging brain.

Histamine and selective H3-receptor ligands: a possible role in the mechanism and management of epilepsy

The interaction of selective histamine H3-receptor agonist R(alpha)-methyl-histamine (RAMH) and antagonist thioperamide (THP) with some antiepileptic drugs [AED; phenytoin (PHT), carbamazepine (CBZ), sodium valproate (SVP), and gabapentin (GBP)] was studied on seizures induced by maximal electroshock (MES) and pentylenetetrazole (PTZ) in mice. It was found that subeffective dose of THP in combination with the subeffective doses of PHT and GBP provided protection against MES and/or PTZ-induced seizures. Further, RAMH reversed the protection afforded by either PHT or GBP on MES and/or PTZ seizures. In another set of experiments, the histamine content was measured in the whole brain and in different brain regions including cerebral cortex, hypothalamus, brain stem and cerebellum following convulsant (MES and PTZ) and AED treatment. It was seen that while MES exhibited a tendency to enhance brain histamine levels, PTZ showed the opposite effect. AEDs either increased (PHT and GBP) or decreased (SVP) brain histamine content in different regions to varying degrees. The results indicate a role for histamine in seizures and in the action of AEDs and suggest that selective H3-receptor antagonists may prove to be of value as adjuncts to conventional AEDs.

Brain plasticity: to what extent do aged animals retain the capacity to coordinate gene activity in response to acute challenges

The ability of the rodent brain to support plasticity-related phenomena declines with increasing age. A decreased coordination of genes implicated in brain plasticity may be one factor contributing to this decline. Synaptic rearrangement that occurs after seizure activity is regarded as a model of brain plasticity. In a rat model of seizure-related brain plasticity, we found that the induction of immediate-early genes, as exemplified by c-fos and tissue plasminogen activator (TPA) is not impaired in the aged rat brain. However, the aged rat brain responded more slowly to chemically induced seizure and the levels of c-fos and TPA mRNAs induction are decreased in the cortex and in the hippocampus of 30-month-old rats, as compared to the levels expressed by 3-month-old rats. In addition, at the peak induction the TPA transcripts were restricted to certain cortical layers of the older rats. Surprisingly, in applying the same experimental paradigm to late genes we found that there was a shift toward earlier times in the maximum expression of growth-related molecule, the microtubule-associated protein 1B (MAP1B) mRNA, which was very evident in 18-month-old rats. Aberrant immunolabeling of MAP1B occurred in cortical layer VI of the aged rats where, unlike in young rats, there was heavy staining of neuronal somata. These results suggest that (i) one consequence of aging, besides decreases in the levels of mRNA, is a progressive loss of coordination in gene activity following the administration of a stimulus; (ii) since c-fos, TPA and MAP1B have been implicated in neuronal plasticity, these findings could explain, in part, the limited plasticity of the aging brain.

Developmental and genetic audiogenic seizure models: behavior and biological substrates

Audiogenic seizure (AGS) models of developmental or genetic origin manifest characteristic indices of generalized seizures such as clonus or tonus in rodents. Studies of seizure-resistant strains in which AGS is induced by intense sound exposure during postnatal development provide models in which other neural abnormalities are not introduced along with AGS susceptibility. A critical feature of all AGS models is the reduction of neural activity in the auditory pathways from deafness during development. The initiation and propagation of AGS activity relies upon hyperexcitability in the auditory system, particularly the inferior colliculus (IC) where bilateral lesions abolish AGS. GABAergic and glutaminergic mechanisms play crucial roles in AGS, as in temporal lobe models of epilepsy, and participate in AGS modulatory and efferent systems including the superior colliculus, substantia nigra, basal ganglia and structures of the reticular formation. Catecholamine and indolamine systems also influence AGS severity. AGS models are useful for elucidating the underlying mechanisms for formation and expression of generalized epileptic behaviors, and evaluating the efficacy of modern treatment strategies such as anticonvulsant medication and neural grafting.

Use of a reverse transcriptase-polymerase chain reaction assay to analyze allele-specific expression in individual hippocampal neurons

We report here a single-cell RT-PCR assay for allele-specific gene expression that can be used to probe for somatic variability within the CNS. Such variability, arising from epigenetic (nonmutational) events or somatic mutation early in development, may give clues as to clonal origin and may also affect the inheritance pattern of some CNS disorders. As a model system, we used reciprocal F1 hybrids of the cross Mus musculus C57BL/6J x Mus musculus castaneus. RNA was isolated from individual dissociated pyramidal neurons from hippocampi of F1 pups. For each gene of interest, single base polymorphisms were identified between the two parental strains by automated sequencing of RT-PCR products. Allele-specific expression was then analyzed by means of the previously described quantitative RT-PCR single nucleotide primer extension (SNuPE) assay (Singer-Sam et al., PCR Methods Appl. 1:160-163, 1992). Individual neurons showed monoallelic expression of the two control genes, X-linked Rps4, and the imprinted gene Snrpn; in contrast expression of Ncam and F3cam, coding for neural cell adhesion molecules, was found to be biallelic.

Hereditary epilepsy syndromes

This paper reviews the present knowledge on the genetics of the epilepsies. Main clinical features, gene localization and pattern of inheritance of the idiopathic epilepsies, the progressive myoclonus epilepsies, and some other genetic disorders often associated with epilepsy, are described.

Synaptic plasticity is preserved in the temporal cortex of 20-month-old rats

The molecular mechanisms associated with age-related alterations in the plasticity of the cortical neurons in response to chemically-induced seizure are largely unknown. Administration of pentylenetetrazole (PTZ) (50 mg/kg body weight) to rats of various ages evoked tonic-clonic seizures. Using immunoblotting and in situ hybridization analysis we found that 72 h after the onset of seizure, the mRNA for microtubule-associated protein 1B (MAP1B), a marker of synaptic plasticity, was increased in the cortex of 3-month-old rats. The levels of MAP1B mRNA in the cortex of 3-month-old rats returned to control levels by 10 days after PTZ administration. The levels of MAP1B mRNA in the hippocampus and cortex of 20 months at later times (10 days) and returned nearly to basal levels by 20 days following PTZ treatment. Immunohistochemical analysis revealed that MAP1B-like immunoreactivity was confined to layer II and neuronal processes extending into layer I. In contrast, the staining of MAP1B in the temporal cortex of 20-month-old animals was restricted to neuronal cell bodies of layer II. Since synaptic plasticity is associated mainly with neuronal processes we conclude that synaptic plasticity is reduced in the temporal cortex of 20-month-old rats. Remarkably, the induction of MAP1B in neuronal extensions was not impaired in the temporal cortex of older animals following intense neuronal activity. However, the aged rat brain responded more slowly to chemically-induced seizure although the levels of MAP1B induction are not decreased as compared to the levels expressed by 3-month-old rats.

Reduced cortical ecto-ATPase activity in rat brains during prolonged status epilepticus induced by sequential administration of lithium and pilocarpine

Considerable evidence indicates that ATP, acting intracellularly of as a neurotransmitter, can influence nerve cell physiology in a variety of ways. Defects in the functioning of ATP-metabolizing enzymes could therefore lead to disturbances in neurotransmission and creation of sustained neuronal discharges characteristic of status epilepticus. In this study we investigated synaptosomal ATPase changes in rat brains during lithium/pilocarpine-induced status epilepticus. After 2 h of continuous electroencephalographic spiking, both Mg(2+)- and Ca(2+)-dependent ecto-ATPases were significantly decreased in freshly prepared synaptosomal preparations from the status rats. The intracellularly acting Ca2+Mg(2+)-ATPase (Ca-pump) was also decreased, but no changes occurred in synaptosomal Na+K(+)-ATPase activity. The difference between ecto-ATPase activities of the control and status rat brains was not affected by repeated freezing-thawing and lengthy storage. Possible involvement of reduced synaptosomal divalent cation-dependent ATPases in the pathophysiology of status epilepticus is discussed.

Magnetohydrodynamic wave resonance and the evocation of epileptiform activity by millitesla DC magnetic fields

DC magnetic fields of low- to medium-flux density (nTesla to mTesla) affect a variety of brain activities. The cellular mechanism underlying these effects is unknown. A model involving magnetohydrodynamic waves and corresponding resonance phenomena is offered here as a solution. The model is discussed in relation to the evocation of epileptiform activity due to external DC magnetic fields in the mTesla range. The assumed existence of a resonance wave makes it possible to calculate the size of the involved area.

Calmodulin in ischemic neurotoxicity of rat hippocampus in vitro

To determine whether calmodulin plays a role in neurodegeneration after ischemia, effects of the selective calmodulin inhibitors calmidazolium and W7 were studied in organotypic cultures of rat hippocampus. Protection of pyramidal cells in the CA1 region of the hippocampus by calmidazolium and W7 against hypoxia/hypoglycemia suggests that activation of intracellular calmodulin plays a significant role in ischemic neuronal injury. Both ryanodine and TMB-8, inhibitors of intracellular Ca2+ release, failed to prevent ischemic neuronal injury. These results indicate that calmodulin, a major intracellular Ca2+ binding protein, plays a significant role in experimental ischemia-induced hippocampal neuronal injury in vitro.

Calcium in suramin-induced rat sensory neuron toxicity in vitro

Suramin is an experimental chemotherapeutic agent and a neurotoxin which causes a dose-dependent peripheral neuropathy in vivo and inhibits dorsal root ganglion (DRG) neurite outgrowth in vitro. The mechanism of suramin-induced cyto- and neurotoxicity remains unclear. Calcium is a key signal transducer in cellular responses to a variety of physiological and pathogenic stimuli. In the present study, we have determined the role of calcium in suramin-induced neurotoxicity in dorsal root ganglion neurons in vitro. Suramin-induced inhibition of neurite outgrowth and induction of neuronal cell death were dose-related phenomena. A low level of extracellular calcium significantly reduced suramin-induced inhibition of neurite outgrowth and delayed neuronal cell death in vitro. Nimodipine (100 microM), an L-type voltage-sensitive calcium channel (VSCC) inhibitor, mimicked low calcium medium and protected neurite outgrowth in regular calcium medium supplemented with 300 microM suramin. TMB-8 (100 microM), an inhibitor of intracellular calcium release, failed to protect neurite outgrowth against the toxin. Calmidazolium (10 microM), a potent calmodulin inhibitor, and calpain inhibitor peptide (CIP, 10 microM) protected neurite outgrowth against suramin. The results support the hypothesis that the calcium signaling system is important in suramin-induced neurotoxicity. Influx of extracellular calcium is more important than release of intracellular calcium in causing cell injury in vitro.

Seizure induced C-Fos mRNA in the rat brain: comparison between young and aging animals

The molecular mechanisms associated with age-related alterations in the pharmacological and physiological properties of hippocampal and cortical neurons in response to chemically induced seizure are largely unknown. Administration of pentylenetetrazole (PTZ) (50 mg/kg body weight) to rats of various ages evoked tonic-colonic seizures. Using RNA gel blot analysis we found that 1 h after the onset of seizure, the mRNA for the protooncogene c-fos was increased in the hippocampus and cortex of 3-month-old rats. The levels of c-fos mRNA in the hippocampus and cortex of 3-month-old rats returned to control levels by 3 h after PTZ administration. The levels of c-fos mRNA in the hippocampus and cortex of 20-month-old and 30-month-old rats peaked at 3 h and returned to basal levels by 15 h following PTZ treatment. These results suggest that the induction of immediate-early gene expression, as exemplified by c-fos, is not impaired in the aged rat brain. However, the aged rat brain responded more slowly to chemically induced seizure and the levels of c-fos mRNA induction are decreased by about 49% in the cortex and by 27% in the hippocampus of 30-month-old rats, as compared to the levels expressed by 3-month-old rats.

N-methyl-D-aspartate and kainate receptor gene expression in hippocampal pyramidal and granular neurons in the kindling model of epileptogenesis

To investigate the changes underlying kindling epileptogenesis in the rat hippocampus, the levels of the messenger RNAs encoding for the subunits of the N-methyl-D-aspartate-receptor (1, 2A-D) and the kainate-receptor (1, -2, GluR-5, -6, -7) were determined in hippocampal principal neurons using in situ hybridization techniques and semi-quantitative analysis of the autoradiograms. Schaffer collateral-commissural pathway kindled rats were investigated at three different stages of kindling acquisition, always 24 h after the last stimulation. Furthermore, fully kindled rats were studied at long-term (28 days) after termination of kindling stimulations. NR1 messenger RNA levels were slightly decreased in CA1 area of fully kindled animals. In the fascia dentata region, a minor increase of NR2A and NR2B transcripts was found at all stages of kindling acquisition. KA-2 messenger RNA was enhanced in all hippocampal subfields during kindling development. However, none of these changes persisted at long-term after the last seizure and only the low-abundant GluR-7 expression was slightly depressed in the fascia dentata. From our observations we conclude that it is unlikely that alterations in N-methyl-Daspartate or kainate receptor gene expression play an important role in kindling acquisition or maintenance.