Self-sustaining status epilepticus after a brief electrical stimulation of the perforant path: a 2-deoxyglucose study

Compartmental neuronal degeneration in the ventral striatum induced by status epilepticus in young rats' brain in comparison with adults

According to experimental and clinical studies, status epilepticus (SE) causes neurodegenerative morphological changes not only in the hippocampus and other limbic structures, it also affects the thalamus and the neocortex. In addition, several studies reported atrophy, metabolic changes, and neuronal degeneration in the dorsal striatum. The literature lacks studies investigating potential neuronal damage in the ventral component of the striatopallidal complex (ventral striatum [VS] and ventral pallidum) in SE experimentations. To better understand the development of neuronal damage in the striatopallidal complex associated with SE, the detected neuronal degeneration in the compartments of the VS, namely, the nucleus accumbens (NAc) and the olfactory tubercle (OT), was analyzed. The experiments were performed on Wistar rats at age of 25-day-old pups and 3-month-old adult animals. Lithium-pilocarpine model of SE was used. Lithium chloride (3 mmol/kg, ip) was injected 24 h before administering pilocarpine (40 mg/kg, ip). This presented study demonstrates the variability of post SE neuronal damage in 25-day-old pups in comparison with 3-month-old adult rats. The NAc exhibited small to moderate number of Fluoro-Jade B (FJB)-positive neurons detected 4 and 8 h post SE intervals. The number of degenerated neurons in the shell subdivision of the NAc significantly increased at survival interval of 12 h after the SE. FJB-positive neurons were evidently more prominent occupying the whole anteroposterior and mediolateral extent of the nucleus at longer survival intervals of 24 and 48 h after the SE. This was also the case in the bordering vicinity between the shell and the core compartments but with clusters of degenerating cells. The severity of damage of the shell subdivision of the NAc reached its peak at an interval of 24 h post SE. Isolated FJB-positive neurons were detected in the ventral peripheral part of the core compartment. Degenerated neurons persisted in the shell subdivision of the NAc 1 week after SE. However, the quantity of cell damage had significantly reduced in comparison with the aforementioned shorter intervals. The third layer of the OT exhibited more degenerated neurons than the second layer. The FJB-positive cells in the young animals were higher than in the adult animals. The morphology of those cells was identical in the two age groups except in the OT.

Parvalbumin neurons in the nucleus accumbens shell modulate seizure in temporal lobe epilepsy

A growing number of clinical and animal studies suggest that the nucleus accumbens (NAc), especially the shell, is involved in the pathogenesis of temporal lobe epilepsy (TLE). However, the role of parvalbumin (PV) GABAergic neurons in the NAc shell involved in TLE is still unclear. In this study, we induced a spontaneous TLE model by intrahippocampal administration of kainic acid (KA), which generally induce acute seizures in first 2 h (acute phase) and then lead to spontaneous recurrent seizures after two months (chronic phase). We found that chemogenetic activation of NAc shell PV neurons could alleviate TLE seizures by reducing the number and period of focal seizures (FSs) and secondary generalized seizures (sGSs), while selective inhibition of PV exacerbated seizure activity. Ruby-virus mapping results identified that the hippocampus (ventral and dorsal) is one of the projection targets of NAc shell PV neurons. Chemogenetic activation of the NAc-Hip PV projection fibers can mitigate seizures while inhibition has no effect on seizure ictogenesis. In summary, our findings reveal that PV neurons in the NAc shell could modulate the seizures in TLE via a long-range NAc-Hip circuit. All of these results enriched the investigation between NAc and epilepsy, offering new targets for future epileptogenesis research and precision therapy.

Increased Susceptibility to Pilocarpine-Induced Status Epilepticus and Reduced Latency in TRPC1/4 Double Knockout Mice

Canonical transient receptor potential channels (TRPCs) are a family of calcium-permeable cation channels. Previous studies have shown that heteromeric channels comprising TRPC1 and TRPC4 mediate epileptiform bursting in lateral septal neurons and hippocampal CA1 pyramidal neurons, suggesting that TRPC1/4 channels play a pro-seizure role. In this study, we utilized electroencephalography (EEG) recording and spectral analysis to assess the role of TRPC1/4 channels in the pilocarpine model of status epilepticus (SE). We found that, surprisingly, TRPC1/4 double knockout (DKO) mice exhibited an increased susceptibility to pilocarpine-induced SE. Furthermore, SE latency was also significantly reduced in TRPC1/4 DKO mice. Further studies are needed to reveal the underlying mechanisms of our unexpected results.

Nucleus accumbens shell modulates seizure propagation in a mouse temporal lobe epilepsy model

Temporal lobe epilepsy (TLE) is the most common form of epilepsy with focal seizures which in some conditions can develop into secondarily generalized tonic-clonic seizures by the propagation of epileptic activities in the temporal lobe to other brain areas. The nucleus accumbens (NAc) has been suggested as a treatment target for TLE as accumulating evidence indicates that the NAc, especially its shell, participates in the process of epileptic seizures of patients and animal models with TLE. The majority of neurons in the NAc are GABAergic medium spiny neurons (MSNs) expressing dopamine receptor D1 (D1R) or dopamine receptor D2 (D2R). However, the direct evidence of the NAc shell participating in the propagation of TLE seizures is missing, and its cell type-specific modulatory roles in TLE seizures are unknown. In this study, we microinjected kainic acid into basolateral amygdala (BLA) to make a mouse model of TLE with initial focal seizures and secondarily generalized seizures (SGSs). We found that TLE seizures caused robust c-fos expression in the NAc shell and increased neuronal excitability of D1R-expressing MSN (D1R-MSN) and D2R-expressing MSN (D2R-MSN). Pharmacological inhibition of the NAc shell alleviated TLE seizures by reducing the number of SGSs and seizure stages. Cell-type-specific chemogenetic inhibition of either D1R-MSN or D2R-MSN showed similar effects with pharmacological inhibition of the NAc shell. Both pharmacological and cell-type-specific chemogenetic inhibition of the NAc shell did not alter the onset time of focal seizures. Collectively, these findings indicate that the NAc shell and its D1R-MSN or D2R-MSN mainly participate in the propagation and generalization of the TLE seizures.

Functional connectivity changes of nucleus Accumbens Shell portion in left mesial temporal lobe epilepsy patients

Growing evidence has supported that the nucleus accumbens (NAc), especially its shell portion, has been involved in epileptogenesis. However, relevant studies on vivo human brain are quite limited. In this study, we investigated left mesial temporal lobe epilepsy (MTLE) related function connectivity (FC) changes of NAc subregions using resting-state functional magnetic resonance imaging. We calculated functional connectivity from two NAc subregions to both whole brain and 16 related targets. Two-sample t-test (Alphasim multiple comparisons corrected) was performed to identify the effect of the disease on each seed's whole brain network. Repeated-measures ANOVA and Post hoc pairwise t test (Bonferroni corrections) were performed to visualize the seed to target FC group differences in each subdivision. In whole brain FC networks, neither the left or right core show different FC changes. The left shell showed decreased FC with a cluster located around the right inferior frontal gyrus. The right shell portion showed increased FC with a cluster located around the left inferior temporal gyrus. The seed to targets results showed that the left shell of LTLE group exhibited lower FC with left posterior-parahippocampal gyrus and right caudate, putamen, thalamus, paracingulate gyrus but higher FC with right subcallosal cortex. The right core of LTLE group exhibited higher FC with right frontal pole and the right shell exhibited lower FC with left thalamus and left anterior-parahippocampal gyrus. This is the first study to investigate the functional connectivity changes of NAc subdivisions of epilepsy in vivo human brain. Our results showed that the left MTLE related FC changes on NAc are mainly on shell portion rather than core. The decrease FC between the left shell and right frontal area and the decrease FC between the right shell and left temporal area suggested they serve vital roles for MTLE.

Changes in the Blood-Brain Barrier Function Are Associated With Hippocampal Neuron Death in a Kainic Acid Mouse Model of Epilepsy

The kainic acid (KA)-induced epilepsy experimental model is widely used to study the mechanisms underlying this disorder. Recently, the blood-brain barrier (BBB) has become an innovative alternative treatment target for epilepsy patients. KA causes neuronal injury and BBB damage in this experimental epilepsy model but the mechanisms underlying epilepsy-related neuronal injury, autophagy, and BBB damage remain unclear. Therefore, the present study investigated the relationships among neuronal injury, the expressions of autophagy-related proteins, and changes in BBB-related proteins during the acute phase of epilepsy to further understand the mechanisms and pharmacotherapy of epilepsy. NeuN immunohistochemistry and Fluoro-Jade B (FJ-B) staining in the hippocampal CA3 region revealed that neuronal death induced by intraventricular injections of 10 μg/kg KA was greater than that induced by 3 μg/kg KA. In addition, there were transient increases in the levels of microtubule-associated protein light chain 3-II (LC3I/II) and Beclin-1, which are autophagy-related proteins involved in neuronal death, in this region 24 h after the administration of 10 μg/kg KA. There were also morphological changes in BBB-related cells such as astrocytes, endothelial cells (ECs), and tight junctions (TJs). More specifically, there was a significant increase in the activation of astrocytes 72 h after the administration of 10 μg/kg KA as well as continuous increases in the expressions of platelet endothelial cell adhesion molecule-1 (PECAM-1) and BBB-related TJ proteins (Zonula occludens-1 and Claudin-5) until 72 h after KA treatment. These results suggest that the overexpression of autophagy-related proteins and astrocytes and transient increases in the expressions of BBB-related TJ proteins may be closely related to autophagic neuronal injury. These findings provide a basis for the identification of novel therapeutic targets for patients with epilepsy.

Connectivity-based parcellation of the nucleus accumbens into core and shell portions for stereotactic target localization and alterations in each NAc subdivision in mTLE patients

The nucleus accumbens (NAc), an important target of deep brain stimulation for some neuropsychiatric disorders, is thought to be involved in epileptogenesis, especially the shell portion. However, little is known about the exact parcellation within the NAc, and its structural abnormalities or connections alterations of each NAc subdivision in temporal lobe epilepsy (TLE) patients. Here, we used diffusion probabilistic tractography to subdivide the NAc into core and shell portions in individual TLE patients to guide stereotactic localization of NAc shell. The structural and connection abnormalities in each NAc subdivision in the groups were then estimated. We successfully segmented the NAc in 24 of 25 controls, 14 of 16 left TLE patients, and 14 of 18 right TLE patients. Both left and right TLE patients exhibited significantly decreased fractional anisotropy (FA) and increased radial diffusivity (RD) in the shell, while there was no significant alteration in the core. Moreover, relatively distinct structural connectivity of each NAc subdivision was demonstrated. More extensive connection abnormalities were detected in the NAc shell in TLE patients. Our results indicate that neuronal degeneration and damage caused by seizure mainly exists in NAc shell and provide anatomical evidence to support the role of NAc shell in epileptogenesis. Remarkably, those NAc shell tracts with increased connectivities in TLE patients were found decreased in FA, which indicates disruption of fiber integrity. This finding suggests the regeneration of aberrant connections, a compensatory and repair process ascribed to recurrent seizures that constitutes part of the characteristic changes in the epileptic network.

Safety and feasibility of nucleus accumbens stimulation in five patients with epilepsy

In five adult patients with intractable partial epilepsy, safety and feasibility of chronic bilateral electrical stimulation of the nucleus accumbens (NAC) were assessed, also providing initial indications of therapeutic efficacy. Concurrent medication remained unchanged. In this phase 1 trial, clinical outcome parameters of interest were Quality of Life in Epilepsy questionnaire (QOLIE-31-P), Beck Depression Inventory, Mini International Neuropsychiatric Interview, neuropsychological testing, and Liverpool Seizure Severity Scale. Those data were obtained after 6 months of NAC stimulation and compared to the equivalent assessments made directly before implantation of electrodes. Additionally, monthly frequencies of simple partial seizures, complex partial seizures (CPS), and generalised tonic–clonic seizures (GTCS) were assessed during 3 months before electrode implantation and at the end of 6-month NAC stimulation. Proportion of responders, i.e. ≥50 % reduction in frequency of disabling seizures (sum of CPS and GTCS), was calculated. Main findings were unchanged psychiatric and neuropsychological assessment and a significant decrease in seizure severity (p = 0.043). QOLIE-31-P total score trended towards improvement (p = 0.068). Two out of five participants were responders. The median reduction in frequency of disabling seizures was 37.5 %. In summary, we provide initial evidence for safety and feasibility of chronic electrical stimulation of the NAC in patients with intractable partial epilepsy, as indicated by largely unchanged neurocognitive function and psychiatric comorbidity. Even though our data are underpowered to reliably assess efficacy, the significant decrease in seizure severity provides an initial indication of antiictal efficacy of NAC stimulation. This calls for larger and at best randomised trials to further elucidate efficacy of NAC stimulation in patients with pharmacologically intractable epilepsy.

Galanin and epilepsy

Neuroanatomical localization and physiological properties of galanin suggest that the peptide may be involved in the regulation of seizures. Indeed, administration of galanin receptor agonists into brain areas pertinent to the initiation and propagation of epileptic activity attenuated seizure responses under conditions of animal models of epilepsy; pharmacological blocking of galanin receptors exerted proconvulsant effects. Functional deletion of both galanin and galanin type 1 receptor genes produced transgenic mice with either spontaneous seizure phenotype, or with enhanced susceptibility to seizure stimuli. At the same time, overexpression of galanin in seizure pathways, using both transgenic and virus vector transfection techniques, hindered the epileptic process. Galanin exerts anticonvulsant effects through both type 1 and type 2 receptors, with distinct downstream signaling cascades. Several synthetic agonists of galanin receptors with optimized bioavailability have been synthesized and inhibited experimental seizures upon systemic administration, thus opening an opportunity for the development of galanin-based antiepileptic drugs.

Iron-induced experimental cortical seizures: Electroencephalographic mapping of seizure spread in the subcortical brain areas

The iron-induced model of post-traumatic chronic focal epilepsy in rats was studied by depth-electrode mapping to investigate the spread of epileptiform activity into subcortical brain structures after its onset in the cortical epileptic focus. Electrical seizure activity was recorded in the hippocampal CA1 and CA3 areas, amygdala and caudate-putamen, in rats with iron-induced chronic cortical focal epilepsy. These experiments showed that the epileptiform activity with its onset in the cortical focus synchronously propagated into the studied subcortical brain areas. Seizure behaviours seemed to increase in correspondence with the spread of the epileptic electrographic activity in subcortical areas. Comparison of the cortical focus electroencephalographic and associated multiple-unit action potential recordings with those from the subcortical structures showed that the occurrence and evolution of the epileptiform activity in the subcortical structures were in parallel with that in the cortical focus. The intracerebral anatomic progression and delineation of seizure spread (mapped by field potential (EEG) and multiple-unit action potentials (MUA) recordings) indicated participation of these regions in the generalization of seizure activity in this model of epilepsy. The seizure-induced activation of the hippocampus appeared to evolve into an epileptic focus independent of the cortical focus. The present study demonstrates the propagation of epileptic activity from the cortical focus into the limbic and basal ganglia regions. Treatment of iron-induced epileptic rats with ethosuximide, an anti-absence drug, resulted in suppression of the epileptiform activity in the cortical focus as well as in the subcortical brain areas.

DNA damage and nonhomologous end joining in excitotoxicity: neuroprotective role of DNA-PKcs in kainic acid-induced seizures

DNA repair plays a critical, but imprecisely defined role in excitotoxic injury and neuronal survival throughout adulthood. We utilized an excitotoxic injury model to compare the location and phenotype of degenerating neurons in mice (strain 129-C57BL) deficient in the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs), an enzyme required for nonhomologous end joining (NHEJ). Brains from untreated adult heterozygous and DNA-PKcs null mice displayed comparable cytoarchitecture and undetectable levels of cell death. By day 1, and extending through 4 days following kainic acid-induced seizures, brains from DNA-PKcs null mice showed widespread neurodegeneration that encompassed the entire hippocampal CA1-CA3 pyramidal cell layer, entorhinal cortex, and lateral septum, with relative sparing of the dentate gyrus granule cell layer and hilus, as judged by toluidine blue, Fluoro-Jade B, and terminal dUTP nick end labeling staining. In contrast, seizure-related neurodegeneration in heterozygous littermates was limited to the CA3 region of the hippocampus. NeuN and calbindin staining revealed a selective decrease in the number and density of NeuN-positive neurons in the pyramidal layers of degenerating regions in both heterozygous and DNA-PKcs null mice. To elucidate the mechanisms leading to cell death, we examined an involvement of the p53 pathway, known to be induced by DNA damage. Addition of pifithrin-alpha, a p53 inhibitor, or expression of a dominant-negative p53 rescued neurons from kainate-induced excitotoxic cell death in primary cortical cultures derived from wildtype, DNA-PKcs heterozygous, or DNA-PKcs null neonatal mice. Moreover, pifithrin-alpha prevented kainate-induced loss of mitochondrial membrane potential, dendrite degeneration, and cell death. Results suggest that NHEJ plays a neuroprotective role in excitotoxicity, within the perforant, Schaffer collateral, hippocampal-septal, and temperoammonic pathways, in part by repairing DNA damage that would otherwise result in activation of a p53-dependent apoptotic cascade.

Different types of status epilepticus lead to different levels of brain damage in rats

We investigated a possible correlation between behavior during status epilepticus (SE) and underlying brain damage. Adult rats were electrically stimulated in the left amygdala to induce SE, which was stopped 2 hours later. We observed two different types of SE: (1) typical SE (TSE), with facial automatisms, neck and forelimb myoclonus, rearing and falling, and tonic-clonic seizures; (2) ambulatory SE (ASE), with facial automatisms, neck myoclonus, and concomitant ambulatory behavior. TSE was behaviorally more severe than ASE (P<0.05). Histology revealed neuronal loss in several brain areas. There was a positive correlation between SE type and amount of injured areas 24 hours and 14 days after SE (P<0.01). The areas more affected were piriform cortex and hippocampal formation. We suggest quality of seizures during SE may be considered in further SE studies, as our results indicate its influence on the severity of brain damage following this paradigm.

Galanin and galanin receptors in epilepsy

The shift in the balance between the inhibition and the excitation in favor of the latter is a major mechanism of the evolvement of epileptic seizures. On the neurotransmitter level two major players contribute to such misbalance: an inhibitory transmitter gamma-aminobutyric acid, and an excitatory amino acid glutamate. Neuropeptides are powerful modulators of classical neurotransmitters, and thus represent an intriguing tool for restoring the balance between the inhibition and the excitation, through either blocking or activating peptide receptors depending on whether a peptide is pro- or anticonvulsant. Galanin, a 29-amino acid residues neuropeptide which inhibits glutamate release in the hippocampus, is a likely member of the anticonvulsant peptide family. During the past decade growing evidence has been suggesting that galanin is in fact a powerful inhibitor of seizure activity. This review summarizes the state of research of galanin in epilepsy, beginning with the first simple experiments which showed that central injection of galanin agonists inhibited seizures, and that seizures themselves affected galanin signaling in the hippocampus; exploring the impact of active manipulation with the expression of galanin and galanin receptors on seizures, using transgenic animals, antisense and peptide-expressing vector approaches; and concluding with the recent advances in pharmacology, which led to the synthesis of non-peptide galanin receptor agonists with anticonvulsant properties. We also address recently established functions of galanin in seizure-associated neuronal degeneration and neuronal plasticity.

Galanin type 2 receptors regulate neuronal survival, susceptibility to seizures and seizure-induced neurogenesis in the dentate gyrus

The neuropeptide galanin has been implicated in inhibiting seizures and protecting hippocampal neurons from excitotoxic injury. In the hippocampus galanin acts through two receptor subtypes, GalR1, expressed in CA1, and GalR2, abundant in dentate gyrus. We developed an approach to induce and to study selective semichronic knockdown of GalR2 in the rat hippocampus. A 50% reduction of GalR2 binding was achieved by continuous infusion of complementary peptide nucleic acid antisense oligonucleotide into the dentate gyrus. This resulted in an increase in the severity of self-sustaining status epilepticus induced by electrical stimulation of the perforant path, induced mild neuronal injury in the dentate hilus, augmented seizure-induced hilar injury and inhibited seizure-induced neurogenesis in the subgranular zone of the dentate gyrus. Our data suggest that in the dentate gyrus, galanin, acting through GalR2, inhibits seizures, promotes viability of hilar interneurons and stimulates seizure-induced neurogenesis. These results are important for understanding the role of galanin and galanin receptor subtypes in the hippocampus both under normal conditions and in excitotoxic injury.

Electrophysiologic changes in the lateral and basal amygdaloid nuclei in temporal lobe epilepsy: an in vitro study in epileptic rats

The functional consequences of neuronal loss during epileptogenesis in the lateral and basal amygdaloid nuclei are poorly understood. The present study tested the hypothesis that electrical responsiveness varies in different amygdaloid nuclei in the chronically epileptic amygdala. Further, we examined the amygdaloid region most prone to seizure initiation. Epileptogenesis was triggered in 20 rats by inducing status epilepticus (SE) with electrical stimulation of the lateral nucleus of the amygdala. Electrode-implanted non-stimulated rats served as controls. The occurrence and duration of spontaneous seizures were monitored with video-electroencephalography (EEG) at 8-9 weeks after SE. Thereafter, animals were killed and extracellular recordings were made from slices of both amygdalas. In the lateral nucleus of epileptic animals, the frequency of spontaneous responses was reduced compared with controls (P < 0.05). The amplitudes of evoked field responses were reduced (P < 0.01), whereas paired pulse (PP) facilitation was enhanced (P < or = 0.05). In the basal nucleus of the epileptic animals, PP facilitation was enhanced (P < 0.05) and sensitivity to 4-aminopyridine (4-AP)-induced epileptiform activity was increased compared with controls (P < 0.05). In the epileptic animals, the basal nucleus was also more sensitive than the lateral nucleus to 4-AP-induced epileptiform activity (P < 0.05). Correlation analysis indicated that longer SE duration was associated with longer half widths (P = 0.001) and smaller slopes (P < 0.05) of evoked responses as well as with attenuated PP facilitation (P<0.01). Moreover, a higher frequency of spontaneous seizures was associated with longer half widths (P < 0.05) and smaller slopes (P < 0.05) of evoked responses as well as with enhanced PP facilitation (P < 0.05). These data suggest that there is a reduced release of glutamate and reduced inhibition in the lateral and basal amygdaloid nuclei in epileptic animals. Further, the basal nucleus is more prone to epileptic activity than the lateral nucleus. Finally, the severity of SE and spontaneous seizures in vivo is associated with electrophysiologic alterations in vitro.

Tracing the Neuroanatomical Profiles of Reward Pathways with Markers of Neuronal Activation

Functional neuroanatomical tools have played an important role in proposing which structures underlie brain stimulation reward circuitry. This review focuses on studies employing metabolic markers of neuronal and glial activation, including 2-deoxyglucose, cytochrome oxidase, and glycogen phosphorylase, and a marker of cellular activation, the immediate early gene c-fos. The principles underlying each method, their application to the study of brain stimulation reward, and their strengths and limitations are described. The usefulness of this strategy in identifying candidate structures, and the degree of overlap in the patterns of activation arising from different markers is addressed in detail. How these data have contributed to an understanding of the organization of reward circuitry and directed our thinking towards an alternative framework of neuronal arrangement is discussed in the final section.

Short-term plasticity of hippocampal neuropeptides and neuronal circuitry in experimental status epilepticus

PURPOSE

We used a model of self-staining status epilepticus (SSSE), induced by brief intermittent stimulation of the perforant path in unanesthetized rats, to study the mechanism of initiation and of maintenance of SSSE and the role of neuropeptides in those processes.

METHODS

The perforant path was stimulated intermittently for 7 min (ineffective stimulation) or 30 min (generating SSSE). Peptides and their agonists and antagonists were delivered either intraperitoneally, or directly into the hippocampus through a implanted cannula. Behavior and electroencephalogram (EEG) were recorded through a videotape-telemetry system with automatic spike and seizures detection programs, which were supplemented by manual review of the records to confirm the diagnosis. Immunocytochemistry and enzyme-linked immunosorbent assay followed published methods.

RESULTS

Initiation of SSSE was blocked by many agonists of inhibitory neurotransmitters or neuromodulators, and by many antagonists of excitatory synapses, and was facilitated by agents with the opposite action, suggesting the activation of a complex circuit with multiple potential entry points. Once SSSE was established, however, only N-methyl-d-aspartate (NMDA)-receptor ligands and a few neuropeptides had major effects on its maintenance. Galanin and dynorphin had powerful anticonvulsant roles in the maintenance phase of SSSE, whereas somatostatin and neuropeptide Y suppressed seizures only transiently. SSSE seemed to induce maladaptive changes in neuropeptides: it depleted the hippocampus of the galanin- and dynorphin-immunoreactive (IR) fibers, which normally function as endogenous anticonvulsants; whereas it induced overexpression of the proconvulsant neuropeptides substance P and neurokinin B; however, late in the course of SSSE, galanin-IR interneurons appeared in the dentate hilus.

CONCLUSIONS

Initiation of SSSE seems to involve a circuit with many points of entry, and blockage of any point along this circuit inhibits the development of SSSE. Far fewer agents alter the maintenance phase of SSSE. Galanin, dynorphin, somatostatin, and neuropeptide Y have anticonvulsant roles, matching the previous described convulsant role of substance P and neurokinin B. Galanin and dynorphin seem to undergo maladaptive changes, which appear to play an important role of the maintenance phase of SSSE. Later, the de novo expression of inhibitory neuropeptides in novel cells in hippocampus coincides with the waning of seizures and may play a role in their termination.

Epileptogenesis after self-sustaining status epilepticus

PURPOSE

To describe the natural history of chronic epilepsy after experimental self-sustaining status epilepticus (SSSE) and to correlate patterns of SSSE with ictal, interictal, and plastic changes that characterize chronic epilepsy.

METHODS

SSSE was induced in adult Wistar rats by 30-min intermittent electrical stimulation of the perforant path. In some animals, SSSE was treated by short-term administration of antiepileptic drugs (AEDs). After SSSE, EEG and animal behavior were monitored for </=1 year. Some animals were killed to study mossy fiber sprouting in the dentate gyrus.

RESULTS

Despite the high reproducibility of the electrographic and behavioral manifestations of SSSE, patterns of chronic epilepsy varied considerably among animals in terms of seizure frequency, initial seizure pattern at the onset of chronic epilepsy, and frequency of interictal spikes. Statistically significant correlations were found between spike frequency during SSSE and interictal spike frequency, as well as between the frequency of spontaneous seizures and degree of mossy fiber sprouting. Early treatment of SSSE prevented the occurrence of spontaneous seizures and significantly decreased frequency of interictal spikes. Late treatment of SSSE did not prevent spontaneous seizures, but significantly decreased their frequency, and eventually may lead to remission of epilepsy.

CONCLUSIONS

SSSE leads after a "silent" period to chronic epilepsy, which is maintained for > or =1 year in the rat. The silence is only behavioral, because EEG paroxysmal activity is seen in every animal. In this model of SSSE, the timing of treatment is a major determinant of outcome. Early treatment reduces the incidence of chronic epilepsy, whereas late treatment only reduces its severity. The possibility that this reduction of the severity of epilepsy may led to spontaneous remissions merits further study.

Pallidal administrations of gabazine and 5-AVA affect pressure-induced behavioral disorders in rats

The aim of this work was to study the role of pallidal GABAa and GABAb neurotransmission in the behavioral disorders induced by pressure. The effects of GABAb antagonist 5-aminovalleric acid (5-AVA) or GABAa antagonist gabazine administrations in the globus pallidus (GP) on locomotor and motor hyperactivity (LMA) and myoclonia expressions in the model of the rat submitted to 8 MPa of helium-oxygen breathing mixture were analyzed. The administration of GABAa antagonist gabazine enhances the occurrence of the epileptic seizures, slightly increases LMA but decreases myoclonia. In contrast, the administration of GABAb antagonist 5-AVA decreases both LMA and myoclonia during the compression and the beginning of the holding time at 8 MPa. These data indicate that some behavioral disorders induced by pressure are in relation with GABAergic neurotransmission and establish clearly that GABAa and GABAb receptor mediations have distinct functions in the GP of the rat.

Self-sustaining status epilepticus: a condition maintained by potentiation of glutamate receptors and by plastic changes in substance P and other peptide neuromodulators

We describe a model of self-sustaining status epilepticus (SSSE) induced by stimulation of the perforant path in free-running rats. In this model, seizures can be transiently suppressed by intrahippocampal injection of a blocker of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid/ kainate synapses but return in the absence of further stimulation when the drug ceases to act. However, seizures are irreversibly abolished by blockers of N-methyl-D-aspartate receptors given locally or systemically. SSSE is enhanced by substance P and its agonists and blocked by its antagonists. SSSE induces novel expression of substance P-like immunoreactivity in hippocampal principal cells. These changes and those in other limbic peptides may contribute to the maintenance of SSSE and to the modulation of hippocampal excitability during epileptic seizures. NMDA