Plasticity, synaptic strength, and epilepsy: what can we learn from ultrastructural data?

Epileptogenic insult alters endogenous adenosine control on long-term changes in synaptic strength by theta pattern stimulation in hippocampus area CA1

The impact of theta patterning of the stimulation on the kindling effects of pentylenetetrazol (PTZ) was studied in rat hippocampus area CA1 in vitro. A potential involvement of adenosine A1 receptors was also examined. Primed-bursts stimulation (PBs) and theta pulse stimulation (TPS) were used as patterned activities. Stimulus patterns were applied to the Schaffer collateral afferents of hippocampal slices from both control and PTZ-kindled rats, the field excitatory postsynaptic potentials (fEPSP) and population spikes (PS) were simultaneously recorded from stratum radiatum and stratum pyramidale, respectively. Experiments were carried out in the presence or absence of the adenosine A1 receptor antagonist CPX. The following changes in kindled vs. control slices were observed. PBs was unable to produce both fEPSP LTP and PS LTP in untreated slices. When A1 receptor antagonist CPX was applied before PBs, both fEPSP LTP and PS LTP were elicited. PS LTP was selectively depressed by TPS (applied at 60 min after LTP induction) exclusively when A1 receptors were blocked, while TPS failed to depress PS LTP in untreated PBs-exposed slices. These findings suggest that seizing entails lasting changes in hippocampus area CA1 so that LTP induction by PBs is masked due to intensive adenosine release which in turn prevents TPS to induce PS LTD in epileptic CA1 network.

Altered expression of Dscam in temporal lobe tissue from human and experimental animals

Down syndrome cell adhesion molecule (Dscam) is a neural adhesion molecule that plays an essential role in the establishment of neural circuits. Considerable evidence suggests that Dscam is required for axon guidance and dendritic arborization. Our aim was to investigate the expression of Dscam in the temporal lobes of patients with intractable epilepsy (IE) and of experimental animals. In this study, we used immunohistochemistry, immunofluorescence, and western blotting to examine Dscam expression in thirty-five surgical samples from brains of IE patients and 15 control brain samples. We also measured the levels of Dscam during the entire epileptic process in a rat model of temporal lobe epilepsy. Dscam expression in IE patients was significantly higher compared with that in the controls. In addition, Dscam was also highly expressed in the rat brain during the different phases of the epileptic process. It is the first time to find abnormal expression of Dscam in the brain tissues in patients with IE. And this finding provides an experimental evidence for the study of neuronal circuit remodeling and synaptic plasticity in IE, furthermore, our results also suggest that Dscam may be involved in the generation and the development of IE.

NCAM/spectrin complex disassembly results in PSD perforation and postsynaptic endocytic zone formation

Mechanisms inducing perforation of the postsynaptic density (PSD) are poorly understood. We show that neural cell adhesion molecule- deficient (NCAM-/-) hippocampal neurons have an abnormally high percentage of synapses with perforated PSDs. The percentage of synapses with perforated PSDs is also increased in wild-type (NCAM+/+) neurons after the disruption of the NCAM/spectrin complex indicating that the NCAM-assembled spectrin cytoskeleton maintains the structural integrity of PSDs. We demonstrate that PSD perforations contain endocytic zones involved in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) internalization. Induction of long-term potentiation in NCAM+/+ neurons accompanied by insertion of AMPAR into the neuronal cell surface is subsequently followed by formation of perforated synapses and AMPAR endocytosis suggesting that perforation of PSDs is important for membrane homeostasis in activated synapses. In NCAM-/- or NCAM+/+ neurons with dissociated spectrin meshwork, AMPAR endocytosis is enhanced under conditions of basal activity. An abnormally high rate of postsynaptic membrane endocytosis may thus contribute to brain pathologies associated with mutations in NCAM or spectrin.

Epilepsy secondary to tuberous sclerosis: lessons learned and current challenges

BACKGROUND

In tuberous sclerosis complex (TSC), a substantially increased risk of developing epilepsy is present as a result of a disruption of a TSC gene expression in the brain and secondary abnormal cellular differentiation, migration, and proliferation. Dysregulated excitation probably has its roots in the disruption of GABAergic interneuron development. There is an age-dependent electroclinical expression of seizures, and epilepsy is often quite severe and unremitting.

DISCUSSION

The majority of patients (>60%) who are candidates for surgery remain seizure-free after tuberectomy. During the recent years technical advances in the localization of the epileptogenic zone during the recent years have lead to a 63% of Engel class I status after surgery compared with a previous 52%. In medically refractory patients not suitable for surgery, vagus nerve stimulation has proved efficacy in significantly reducing seizure frequency in more than 50% of cases. New evidence suggests that mTOR inhibitors may be helpful in the management of intractable epilepsy for individuals with TSC.

The h current is a candidate mechanism for regulating the sliding modification threshold in a BCM-like synaptic learning rule

Hebbian synaptic plasticity acts as a positive feedback mechanism and can destabilize a neuronal network unless concomitant homeostatic processes that counterbalance this instability are activated. Within a Bienenstock-Cooper-Munro (BCM)-like plasticity framework, such compensation is achieved through a modification threshold that slides in an activity-dependent fashion. Although the BCM-like plasticity framework has been a useful formulation to understand synaptic plasticity and metaplasticity, a mechanism for the activity-dependent regulation of this modification threshold has remained an open question. In this simulation study based on CA1 pyramidal cells, we use a modification of the calcium-dependent hypothesis proposed elsewhere and show that a change in the hyperpolarization-activated, nonspecific-cation h current is capable of shifting the modification threshold. Based on the direction of such a shift in relation to changes in the h current, and supported by previous experimental results, we argue that the h current fits the requirements for an activity-dependent regulator of this modification threshold. Additionally, using the same framework, we show that multiple voltage- and ligand-gated ion channels present in a neuronal compartment can regulate the modification threshold through complex interactions among themselves. Our results underscore the heavy mutual interdependence of synaptic and intrinsic properties/plasticity in regulating learning and homeostasis in single neurons and their networks under both physiological and pathological brain states.

Prenatal morphine exposure alters the layer II/III pyramidal neurons morphology in lateral secondary visual cortex of juvenile rats

Altered cortical neuronal morphology and juvenile behavior manifestation by prenatal morphine exposure were well documented. However, this developmental morphine exposure affect the lateral secondary visual area (V2L), which may be critically involved in the multisensory of auditory and visual stimulus, remained poorly understood. To clarify the neuronal architecture changes possibly occurring in the V2L, Golgi-Cox staining was used in this study to count dendritic length and the spine density of the layer II/III pyramidal neurons in the V2L of the juvenile rats (postnatal day 25, PND25) prenatally exposed to morphine (gestation days 11-18). Quantitative analysis showed that prenatal morphine exposure decreased the total length, branch number, and spine density of the layer II/III pyramidal neurons in the V2L, and selectively altered the total length of the basal dendrites but not of the apical dendrites. The findings may provide the mechanistic understanding of the behavioral changes in the children whose mothers abuse opiates during pregnancy.

Abnormal expression and spatiotemporal change of Slit2 in neurons and astrocytes in temporal lobe epileptic foci: A study of epileptic patients and experimental animals

Repellent guidance molecules provide targeting information to outgrowing axons along predetermined pathways during development. These molecules may also play a role in synaptic reorganization in the adult brain and thereby promote epileptogenesis. Our aim was to investigate the expression of Slit2, one of repellent guidance molecules, in temporal lobe epileptic foci from epileptic patients and experimental animals. Thirty-five temporal neocortex tissue samples from patients with intractable temporal lobe epilepsy (TLE) and fifteen histological normal temporal lobes from controls were selected. Fifty-four Sprague-Dawley rats were divided randomly into six groups, including five groups with epilepsy induced by lithium-pilocarpine administration and one control group. Temporal lobe tissue samples were taken from rats at 1, 7, 14, 30, and 60 days post-seizure and from controls. Expression of Slit2 was assessed by immunohistochemistry, immunofluorescence, and Western blot analysis. Slit2 was mainly expressed in neurons in human controls and in both neurons and astrocytes in TLE patients. Slit2 expression was significantly higher in TLE patients as compared with the controls. Slit2-positive cells were mainly neurons in the rat temporal lobe tissues of the control group, the acute period group, and the latent period group, while the Slit2-positive cells were mainly astrocytes in chronic phase. Compared with controls, Slit2 expression in animals in the TLE group gradually decreased from days 1 to 14 post-seizure, but then increased over the levels seen in controls, to peak levels at days 30 and 60. These results suggest that Slit2 may play an important role in the pathogenesis of TLE.

Timed changes of synaptic zinc, synaptophysin and MAP2 in medial extended amygdala of epileptic animals are suggestive of reactive neuroplasticity

Repeated seizures induce permanent alterations of the brain in experimental models and patients with intractable temporal lobe epilepsy (TLE), which is a common form of epilepsy in humans. Together with cell loss and gliosis in many brain regions, synaptic reorganization is observed principally in the hippocampus. However, in the amygdala this synaptic reorganization has been not studied. The changes in Zn density, synaptophysin and MAP(2) as markers of reactive synaptogenesis in medial extended amygdala induced by kainic acid (KA) as a model of TLE was studied. Adult male rats (n=6) were perfused at 10 days, 1, 2, 3 and 4 months after KA i.p. injection (9 mg/kg). Controls were injected with saline. The brains were processed by the Timm's method to reveal synaptic Zn and analyzed by densitometry. Immunohistochemistry was used to reveal synaptophysin and MAP(2) expression. A two-way ANOVA was used for statistics, with a P<0.05 as a significance limit. Normal dark staining was seen in all medial extended amygdala subdivisions of control animals. At 10 days post KA injection a dramatic loss of staining was observed. A slow but steady recovery of Zn density can be followed in the 4 month period studied. Parallel, from 10 days to 2 months stronger synaptophysin expression could be observed, whereas MAP(2) expression increased from 1 month with peak levels at 3-4 months. The results suggest that a process of sprouting exists in surviving neurons of medial extended amygdala after status epilepticus and that these neurons might be an evidence of a reactive synaptogenesis process.

Neurotrofinas na epilepsia do lobo temporal

INTRODUÇÃO: A neurotrofinas NGF, BDNF, NT-3 e NT-4 são os principais representantes da família das neurotrofinas no sistema nervoso central de mamíferos. Estão presentes em estágios específicos do crescimento e sobrevivência neuronal como a divisão celular, diferenciação e axogênese e também nos processos naturais de morte celular neuronal. A atividade biológica das neurotrofinas é mediada pelos receptores de tropomiosina quinase Trk. NGF ativa principalmente os receptores TrkA, BDNF e NT-4 interagem com os receptores TrkB e NT-3 com TrkC. Todas as NTs também podem se ligar, com menor afinidade, ao receptor p75NTR. Nesta breve revisão serão levantadas as principais evidências sobre o papel e expressão das principais neurotrofinas no hipocampo, com ênfase nas alterações que ocorrem em modelos animais de epilepsia. RESULTADOS: As neurotrofinas parecem ter um papel chave na plasticidade sináptica relacionada à epilepsia, onde elas poderiam agir tanto como fatores promotores da epileptogênese quanto como substâncias anti-epiléptogênicas endógenas. Além disso a expressão dos genes que codificam os fatores neurotróficos e seus receptores pode ser alterada pela atividade de crises em diversos modelos de epilepsia. CONCLUSÃO: Vários estudos têm demonstrado a relação entre a expressão das neurotrofinas e as alterações na plasticidade dos circuitos neuronais que ocorrem após danos cerebrais, tais como a epilepsia. O conhecimento das alterações na expressão das neurotrofinas na plasticidade neuronal pode nos auxiliar a entender como estas moléculas participam dos mecanismos epileptogênicos e dessa forma, dar início ao estudo de novas terapias e ao desenvolvimento de novas drogas que auxiliem no tratamento da epilepsia.

Ultrastructure of hippocampal field CA1 in rats after status epilepticus induced by systemic administration of kainic acid

The ultrastructure of hippocampal field CA1 in rats was studied 14 days after status epilepticus induced by administration of kainic acid. Structural changes were seen in 40% of cells, predominantly interneurons, which showed both reversible changes (mitochondria with an electron-dense matrix or small numbers of short cristae, moderate dilation of rough endoplasmic reticulum (RER) cisterns, and small numbers of ribosomes) and more significant abnormalities: swollen mitochondria with very small numbers of cristae, which were partially degraded, some with damaged mitochondrial membranes, along with pathologically damaged RER components and focal or peripheral chromatolysis. Chromatolyzed areas sometimes contained membrane-like includes and vacuoles. In addition, the neuropil contained occasional large osmiophilic formations surrounded by astrocyte processes with accumulations of glycogen or gliofibrils. Synaptoarchitectonics were also altered. Asymmetrical synapses were often seen on small dendrites and spines, with highly osmiophilic postsynaptic zones, their synaptic terminals containing numerous synaptic vesicles and large vesicles with electron-dense cores. Some presynaptic endings showed clear signs of classical dark-type degeneration. As the nucleus remained intact in all types of altered neurons, it appears that most cells underwent pathological changes of the necrotic type.

Partial kindling induces neurogenesis, activates astrocytes and alters synaptic morphology in the dentate gyrus of freely moving adult rats

A partial kindling procedure was used to investigate the correlation between focal seizure development and changes in dendritic spine morphology, ongoing neurogenesis and reactive astrogliosis in the adult rat dentate gyrus (DG). The processes of neurogenesis and astrogliosis were investigated using markers for doublecortin (DCX), 5-bromo-2-deoxyuridine (BrdU) and glial fibrillary acidic protein (GFAP). Our data demonstrate that mild focal seizures induce a complex series of cellular events in the DG one day after cessation of partial rapid kindling stimulation consisting (in comparison to control animals that were electrode implanted but unkindled), firstly, of an increase in the number of postmitotic BrdU labeled cells, and secondly, an increase in the number of DCX labeled cells, mainly in subgranular zone. Ultrastructural changes were examined using qualitative electron microscope analysis and 3-D reconstructions of both dendritic spines and postsynaptic densities. Typical features of kindling in comparison to control tissue included translocation of mitochondria to the base of the dendritic spine stalks; a migration of multivesicular bodies into mushroom dendritic spines, and most notably formation of "giant" spinules originating from the head of the spines of DG neurons. These morphological alterations arise at seizure stages 2-3 (focal seizures) in the absence of signs of the severe generalized seizures that are generally recognized as potentially harmful for neuronal cells. We suggest that an increase in ongoing neurogenesis, reactive astrogliosis and dendritic spine reorganization in the DG is the crucial step in the chain of events leading to the progressive development of seizure susceptibility in hippocampal circuits.

TRPV1: a potential target for antiepileptogenesis

Epilepsy is one of the most common diseases in neurology department. It is caused by many different kinds of perturbances of normal balance of excitation and inhibition within the central nervous system. Current clinical antiepileptic drugs (AEDs) targets include ion channels, neurotransmitter transporters and neurotransmitter metabolic enzymes. They could control about 70-80% of the patients' symptoms; 20-30% patients develop to be intractable epilepsy sufferers. Moreover, antiepileptic drugs could not prevent formation of foci and disease process, but only alleviate symptoms of seizures at risk of different adverse effects as the consequences of large doses. Recently, impressive data on the actions of transient receptor potential vanilloid receptor 1 (TRPV1) prove it to be an inspiring antiepileptogenic target. TRPV1 activation modulates activity-dependent synaptic efficacy: (i) facilitating long-term potentiation (LTP) and suppressing long-term depression (LTD) of hippocampal neurons (ii) selectively inhibiting excitatory synapses onto hippocampal interneurons, which is expected to increase the excitability of innervated pyramidal cells. Nerve growth factor (NGF) can acutely and chronically upregulates TRPV1 expression, suggesting that TRPV1 channels would play an important role in the course of NGF regulated epileptogenesis. Endocannabinoid anandamide (AEA) is one of the TRPV1 endogenous agonists. It has been proved that, in the course of epilepsy, AEA levels increases due to enhanced formation and both exogenously administered and endogenously produced AEA display proconvulsant activity. Moreover, TRPV1 activation triggers apoptotic neuronal death of rat cortical cultures, which may be responsible, at least in part, for the volume loss of neocortex in chronic epilepsy. Our hypothesis may broaden the drug screening and designing for clinical strategies for epilepsy treatment.

Synaptic plasticity along the sleep-wake cycle: implications for epilepsy

Activity-dependent changes in synaptic efficacy (i.e., synaptic plasticity) can alter the way neurons communicate and process information as a result of experience. Synaptic plasticity mechanisms involve both molecular and structural modifications that affect synaptic functioning, either enhancing or depressing neuronal transmission. They include redistribution of postsynaptic receptors, activation of intracellular signaling cascades, and formation/retraction of dendritic spines, among others. During the sleep-wake cycle, as the result of particular neurochemical and neuronal firing modes, distinct oscillatory patterns organize the activity of neuronal populations, modulating synaptic plasticity. Such modulation, for example, has been shown in the visual cortex following sleep deprivation and in the ability to induce hippocampal long-term potentiation during sleep. In epilepsy, synchronized behavioral states tend to contribute to the initiation of paroxystic discharges and are considered more epileptogenic than desynchronized states. Here, we review some of the current understandings of synaptic plasticity changes in wake and sleep states and how sleep may affect epileptic seizures.

The extracellular matrix protein SC1/hevin localizes to excitatory synapses following status epilepticus in the rat lithium-pilocarpine seizure model

The epileptic brain is characterized by increased susceptibility to neuronal hyperexcitability. The rat lithium-pilocarpine model, which mimics many features of temporal lobe epilepsy, has been used to study processes leading to the development of recurrent seizures. After a prolonged seizure episode, termed status epilepticus (SE), neural changes occur during a period known as epileptogenesis and include neuronal cell death, reactive gliosis, axonal sprouting, and synaptogenesis. Extracellular matrix adhesion molecules are important regulators of synaptogenesis and axonal sprouting resulting from SE. SC1, also known as hevin, is an antiadhesive extracellular matrix molecule that localizes to synapses in the mammalian brain. In this study, the distribution of SC1 protein in neurons following SE was examined using the lithium-pilocarpine model. SC1 protein levels in neuronal cell bodies showed a transient decrease at 1 day post-SE, which coincided with an increase of SC1 in the synapse-rich neuropil that was identified with the synaptic marker synaptophysin. Immunoelectron microscopy confirmed the decrease of SC1 signal in neurons at 1 day post-SE and showed that SC1 remained localized to postsynaptic elements throughout the seizure time course. Increased colocalization of SC1 was detected with the excitatory synaptic markers vesicular glutamate transporter 1 (VGLUT1), AMPA receptor subunit GluR1, and N-methyl-D-aspartate receptor subunit NR1, but not with the inhibitory synaptic markers vesicular gamma-aminobutyric acid (GABA) transporter (VGAT) and GABA(A) receptor subunit beta2 (GABA(A) beta2), which could reflect enhanced association of SC1 with excitatory synapses. These findings suggest that SC1 may be involved in synaptic modifications underlying epileptogenesis.

Overexpression of N-WASP in the brain of human epilepsy

Neuronal circuit remodeling is the most critical pathological characteristic closely associated with the initiation and maintenance of epilepsy; however, the exact mechanisms of neuronal remodeling need further elucidation. Neuronal Wiskott-Aldrich syndrome protein (N-WASP) is a key regulator of the actin cytoskeleton that causes actin polymerization and thus neurite extension. Our previous research demonstrated that the upstream regulator of N-WASP, cell division cycle 42 GTP-binding protein (Cdc42), is significantly upregulated in the brains of patients with intractable epilepsy (IE). In addition, cDNA microarray analysis has shown that gene expression of N-WASP is notably enhanced in the epileptic brain, suggesting a possible role for N-WASP in epileptogenesis. Here, we investigated the expression of N-WASP and its downstream effector, actin-related protein 2/3 (Arp2/3), at the protein level in the temporal lobe of IE patient brains to explore its possible role in the genesis of IE. Forty surgical samples from brains of patients with IE and 20 control brain tissues were obtained for this study. The expression of N-WASP in the anterior temporal neocortex was detected using immunohistochemistry, immunofluorescence and western blotting; Arp2/3 expression was detected by western blotting. Compared with controls, N-WASP expression in brains of IE patients was significantly higher; similarly, Arp2/3 level was markedly increased in the IE patient group. These results suggest that increased expression of N-WASP in the human brain may be associated with human IE.

Repeated seizures lead to altered skilled behaviour and are associated with more highly efficacious excitatory synapses

People with epilepsy have a high incidence of interictal behavioural problems that appear to be related to the location of their seizure focus. This study investigated a novel test of the hypotheses that repeated seizures result in behavioural deficits and altered performance during the interictal state, and that those behaviours are related to the presence of more highly efficacious excitatory synapses. We tested these hypotheses by first repeatedly eliciting seizures with electric current through indwelling electrodes in the corpus callosum at the level of the caudal forelimb area of sensorimotor neocortex in the rat. We then assessed learned skilled behaviours that primarily utilize the forelimbs on tasks that are sensitive to the functional integrity of that structure. We observed both behavioural deficits and altered kinematic performance in rats that experienced repeated neocortical seizures relative to an electrode-implanted control group. From a separate set of rats, tissue was prepared for quantification of thickness and excitatory synaptic subtypes from neocortical layer V. We observed significantly increased numbers of perforated synapses that make their connections directly onto the dendritic shaft at 3 weeks following the last seizure. Altered reaching behaviours are likely due to neural reorganization in the neocortex including more efficacious synapses.

Bilateral diffusion tensor abnormalities of temporal lobe and cingulate gyrus white matter in children with temporal lobe epilepsy

PURPOSE

Bilateral diffusion tensor imaging (DTI) abnormalities have been reported in the white matter associated to the hippocampus in adults with mesial temporal lobe epilepsy (TLE). In children with a shorter duration of epilepsy, such changes may not have yet emerged. The aim of this study was to investigate interictal changes in the temporal lobe white matter (TLWM) and cingulate gyrus white matter (CGWM) of children with TLE using DTI.

METHODS

DTI was performed in eight children with TLE and 10 healthy, age-matched controls. Fractional anisotropy (FA), trace, parallel (lambda(||)) and perpendicular (lambda( perpendicular)) diffusivity were calculated for a volume of interest in the TLWM and CGWM on the seizure focus side and the contralateral side. Data were compared for differences between sides for patients and between patients and controls.

RESULTS

There was no significant difference in FA, trace, lambda(||) and lambda( perpendicular) between TLWM and CGWM on the seizure focus side versus the contralateral side in TLE patients. Increased diffusivity, lambda(||) and lambda( perpendicular) within the TLWM and CGWM were found in TLE patients compared to controls, but no significant difference in FA was seen.

CONCLUSIONS

Bilaterally increased diffusivity, lambda(||) and lambda( perpendicular) in the white matter in children with TLE may be related to seizure induced functional or structural changes. The preserved FA in our pediatric cohort is in contrast to the reduced FA in the white matter of adults with TLE and may relate to differences in the duration of epilepsy or in the vulnerability of white matter to seizures.

Dendritic excitability and synaptic plasticity

Most synaptic inputs are made onto the dendritic tree. Recent work has shown that dendrites play an active role in transforming synaptic input into neuronal output and in defining the relationships between active synapses. In this review, we discuss how these dendritic properties influence the rules governing the induction of synaptic plasticity. We argue that the location of synapses in the dendritic tree, and the type of dendritic excitability associated with each synapse, play decisive roles in determining the plastic properties of that synapse. Furthermore, since the electrical properties of the dendritic tree are not static, but can be altered by neuromodulators and by synaptic activity itself, we discuss how learning rules may be dynamically shaped by tuning dendritic function. We conclude by describing how this reciprocal relationship between plasticity of dendritic excitability and synaptic plasticity has changed our view of information processing and memory storage in neuronal networks.

ATP signalling in epilepsy

This paper focuses on a role for ATP neurotransmission and gliotransmission in the pathophysiology of epileptic seizures. ATP along with gap junctions propagates the glial calcium wave, which is an extraneuronal signalling pathway in the central nervous system. Recently astrocyte intercellular calcium waves have been shown to underlie seizures, and conventional antiepileptic drugs have been shown to attenuate these calcium waves. Blocking ATP-mediated gliotransmission, therefore, represents a potential target for antiepileptic drugs. Furthermore, while knowledge of an antiepileptic role for adenosine is not new, a recent study showed that adenosine accumulates from the hydrolysis of accumulated ATP released by astrocytes and is believed to inhibit distant synapses by acting on adenosine receptors. Such a mechanism is consistent with a surround-inhibitory mechanism whose failure would predispose to seizures. Other potential roles for ATP signalling in the initiation and spread of epileptiform discharges may involve synaptic plasticity and coordination of synaptic networks. We conclude by making speculations about future developments.

Loss of astrocytic domain organization in the epileptic brain

Gliosis is a pathological hallmark of posttraumatic epileptic foci, but little is known about these reactive astrocytes beyond their high glial fibrillary acidic protein (GFAP) expression. Using diolistic labeling, we show that cortical astrocytes lost their nonoverlapping domain organization in three mouse models of epilepsy: posttraumatic injury, genetic susceptibility, and systemic kainate exposure. Neighboring astrocytes in epileptic mice showed a 10-fold increase in overlap of processes. Concurrently, spine density was increased on dendrites of excitatory neurons. Suppression of seizures by the common antiepileptic, valproate, reduced the overlap of astrocytic processes. Astrocytic domain organization was also preserved in APP transgenic mice expressing a mutant variant of human amyloid precursor protein despite a marked upregulation of GFAP. Our data suggest that loss of astrocytic domains was not universally associated with gliosis, but restricted to seizure pathologies. Reorganization of astrocytes may, in concert with dendritic sprouting and new synapse formation, form the structural basis for recurrent excitation in the epileptic brain.

Long-term potentiation of high-frequency oscillation and synaptic transmission characterize in vitro NMDA receptor-dependent epileptogenesis in the hippocampus

The implication of high-frequency network oscillations (HFOs) in brain pathology resides in as yet unclear mechanisms. Employing field recordings from ventral hippocampal slices and two models of epileptogenesis (i.e. establishment of interictal-like persistent bursts), we found that HFOs associated with epileptiform bursts and excitatory synaptic transmission were co-modulated during epileptogenesis. NMDA receptor-dependent epileptogenesis in CA3 was consistently accompanied by long-lasting strengthening in synaptic transmission (by 94+/-17%, n=5) and HFOs (frequency, power and duration increased by 24+/-8%, 57+/-18% and 33+/-10%, respectively). Co-modulation of synaptic transmission and HFOs was also observed in NMDA receptor-independent epileptogenesis, although in individual experiments either enhancement or depression of both phenomena was observed. Pathological HFOs >200 Hz were unequivocally present in persistent bursts induced by NMDA receptor-dependent but not NMDA receptor-independent mechanisms. The duration of pathological HFOs associated with persistent bursts but not of HFOs associated with bursts before the establishment of epileptogenesis was linearly and strongly correlated with the duration of bursts (r=0.58, P<0.0001). We propose that interplay between spontaneous synchronous bursting and long-lasting synaptic potentiation accompanying certain forms of epileptogenesis may underlie long-lasting potentiation of HFOs, whose quantitative aspects may reliably signal the degree of network changes involved in epileptogenesis.

Protein synthesis inhibitors, gene superinduction and memory: too little or too much protein?

To date, the effects of protein synthesis inhibitors (PSI) in learning and memory processes have been attributed to translational arrest and consequent inhibition of de novo protein synthesis. Here we argue that amnesia produced by PSI can be the direct result of their abnormal induction of mRNA-a process termed gene superinduction. This action exerted by PSI involves an abundant and prolonged accumulation of mRNA transcripts of genes that are normally transiently induced. We summarize experimental evidence for the multiple mechanisms and signaling pathways mediating gene superinduction and consider its relevance for PSI-induced amnesia. This mechanistic alternative to protein synthesis inhibition is compared to models of electroconvulsive seizures and fragilexsyndrome associated with enhanced mRNA/protein levels and cognitive deficits.

Test-retest reliability of pressure pain threshold measurements of the upper limb and torso in young healthy women

The goal of this study was to determine the intra- and interday reliability of pressure pain thresholds (PPT) in the upper extremity and torso of asymptomatic women. Nineteen healthy women (20-39 years) with no underlying musculoskeletal problems had 3 PPT trials performed on 8 different locations in the upper extremity and torso over 4 consecutive days. The test-retest reliability of PPT values was robust and highly consistent over the 4 days. The PPT intraclass correlations (ICC) were highly consistent and repeatable over the 4 days of testing (day 1: ICC = 0.94; day 2: ICC = 0.96; day 3: ICC = 0.97 and day 4: ICC = 0.96). When compared with baseline measurements obtained on day 1, the PPT values were significantly lower (P < .05) on days 2, 3, and 4 at all 8 locations. Although the PPT test-retest reliability is robust and consistent throughout the 4 days, there appears to be a similar overall decline in the magnitude of the absolute PPT response at each of the 8 locations. A specific explanation for this greater overall sensitivity in PPTs at all 8 locations is lacking; however, a centrally mediated alteration in pressure/pain sensation could contribute to the overall trend observed in this study.

PERSPECTIVE

PPT measurements of the upper limb and torso will be significantly lower with repeated measures over a short period time. A standardized evaluation grid should be included in baseline so as to accurately evaluate the progression in shoulder rehabilitation in women with shoulder dysfunction.

Status epilepticus induces region-specific changes in dendritic spines, dendritic length and TrkB protein content of rat brain cortex

Induction of status epilepticus (SE) with kainic acid results in a large reorganization of neuronal brain circuits, a phenomenon that has been studied primarily in the hippocampus. The neurotrophin BDNF, by acting through its receptor TrkB, has been implicated in such reorganization. In the present work we investigated, by Western blot and immunohistochemistry, whether regional changes of TrkB expression within the rat brain cortex are correlated with altered neuronal morphology and/or with apoptotic cell death. We found that the full-length TrkB protein decreased within the cortex when measured 24 h to 1 week after induction of SE. Analysis by immunohistochemistry revealed that TrkB staining diminished within layer V of the retrosplenial granular b (RSGb) and motor cortices, but not within the auditory cortex. In layer II/III, differential changes were also observed: TrkB decreased in the motor cortex, did not change within the RSGb but increased within the auditory cortex. Reduced TrkB was associated with dendritic atrophy and decreased spine density in pyramidal neurons within layer V of the RSGb. No correlation was observed between regional and cellular changes of TrkB protein and apoptosis, measured by the TdT-mediated dUTP nick end labeling (TUNEL) method. The global decrease of TrkB within the neocortex and the associated dendritic atrophy may counteract seizure propagation in the epileptic brain but may also underlie cognitive impairment after seizures.

Angels and demons: neurotrophic factors and epilepsy

Several lines of evidence indicate that neurotrophic factors (NTFs) could be key causal mediators in the development of acquired epileptic syndromes. Yet the trophic properties of NTFs indicate that they might be used to treat epilepsy-associated damage. Accordingly, different NTFs, or even the same NTF, could produce functionally contrasting effects in the context of epilepsy. Recent experimental evidence begins to shed light on the mechanisms underlying these contrasting effects. Understanding these mechanisms will be instrumental for the development of effective therapies, which must be based on a careful consideration of the biological properties of NTFs. Here, we critically evaluate new information emerging in this area and discuss its implications for clinical treatment.

Effect of eugenol on spreading depression and epileptiform discharges in rat neocortical and hippocampal tissues

Eugenol, an aromatic molecule derived from several plants, has been receiving examination for clinical relevance in epilepsy and headache. To investigate the neurophysiologic properties of the action of eugenol, its effects on epileptiform field potentials elicited by omission of extracellular Mg2+, spreading depression induced by KCl microinjection, electrically evoked field potentials, and long-term potentiation were tested in rat neocortical and hippocampal tissues. Eugenol (10-100 micromol/l) dose-dependently and reversibly suppressed both epileptiform field potentials and spreading depression Eugenol also reversibly decreased the amplitude of the field postsynaptic potentials evoked in CA1 area of hippocampus and the third layer of neocortex. Eugenol significantly reduced the long-term potentiation by approximately 30% compared with controls. Thus, eugenol can suppress epileptiform field potentials and spreading depression, likely via inhibition of synaptic plasticity. The results indicate the potential for eugenol to use in the treatment of epilepsy and cephalic pain.

Effects of Lamotrigine on field potentials, propagation, and long-term potentiation in rat prefrontal cortex in multi-electrode recording

Lamotrigine (LTG) is an anti-epileptic drug that is widely used clinically in various neuropsychiatric disorders. Although consensus is found on the general mode of action by LTG on voltage-gated sodium current, its effect on field potential, neuropropagation, and long-term potentiation, especially in prefrontal cortex (PFC), is still not understood completely. We investigated LTG effects on synaptic response in rat prefrontal cortical slice with the aid of a novel multi-electrode dish (MED64) system. The amplitude and propagation of field excitatory postsynaptic potentials (fEPSP), presynaptic fiber volleys (PrV) were expressed dimensionally in the MED64 system. Lamotrigine (3-100 microM) inhibited the amplitude and propagation of fEPSP and PrV in a concentration dependent manner. It exerted a predominant presynaptic action, as indicated by the increment in paired-pulse facilitation. Stimulating dependency with reduction fEPSP was seen in the presence of LTG at clinically relevant concentrations as well as with PrV, both in amplitude and propagation. In addition, the depression of PrV amplitudes in the presence of LTG showed a use-dependent fashion. As to LTP in PFC, it was not fEPSP amplitude but propagation reduced by LTG. In PFC, LTG exerts its use- and concentration-dependent inhibitory effect on presynaptic action and depresses fEPSP amplitude and propagation in a clinically relevant concentration. LTP was preserved in its fEPSP amplitude but not propagation in PFC in the presence of LTG.