Subtle alterations in memory systems and normal visual attention in the GAERS model of absence epilepsy.

OBJECTIVE: Even if considered benign, absence epilepsy may alter memory and attention, sometimes subtly. Very little is known on behavior and cognitive functions in the Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model of absence epilepsy. We focused on different memory systems and sustained visual attention, using Non Epileptic Controls (NECs) and Wistars as controls. METHODS: A battery of cognitive/behavioral tests was used. The functionality of reference, working, and procedural memory was assessed in the Morris water maze (MWM), 8-arm radial maze, T-maze and/or double-H maze. Sustained visual attention was evaluated in the 5-choice serial reaction time task. RESULTS: In the MWM, GAERS showed delayed learning and less efficient working memory. In the 8-arm radial maze and T-maze tests, working memory performance was normal in GAERS, although most GAERS preferred an egocentric strategy (based on proprioceptive/kinesthetic information) to solve the task, but could efficiently shift to an allocentric strategy (based on spatial cues) after protocol alteration. Procedural memory and visual attention were mostly unimpaired. SIGNIFICANCE: Absence epilepsy has been associated with some learning problems in children. In GAERS, the differences in water maze performance (slower learning of the reference memory task and weak impairment of working memory) and in radial arm maze strategies suggest that cognitive alterations may be subtle, task-specific, and that normal performance can be a matter of strategy adaptation. Altogether, these results strengthen the "face validity" of the GAERS model: in humans with absence epilepsy, cognitive alterations are not easily detectable, which is compatible with subtle deficits.

Intact neurobehavioral development and dramatic impairments of procedural-like memory following neonatal ventral hippocampal lesion in rats.

Neonatal ventral hippocampal lesions (NVHL) in rats are considered a potent developmental model of schizophrenia. After NVHL, rats appear normal during their preadolescent time, whereas in early adulthood, they develop behavioral deficits paralleling symptomatic aspects of schizophrenia, including hyperactivity, hypersensitivity to amphetamine (AMPH), prepulse and latent inhibition deficits, reduced social interactions, and spatial working and reference memory alterations. Surprisingly, the question of the consequences of NVHL on postnatal neurobehavioral development has not been addressed. This is of particular importance, as a defective neurobehavioral development could contribute to impairments seen in adult rats. Therefore, at several time points of the early postsurgical life of NVHL rats, we assessed behaviors accounting for neurobehavioral development, including negative geotaxis and grip strength (PD11), locomotor coordination (PD21), and open-field (PD25). At adulthood, the rats were tested for anxiety levels, locomotor activity, as well as spatial reference memory performance. Using a novel task, we also investigated the consequences of the lesions on procedural-like memory, which had never been tested following NVHL. Our results point to preserved neurobehavioral development. They also confirm the already documented locomotor hyperactivity, spatial reference memory impairment, and hyperresponsiveness to AMPH. Finally, our rseults show for the first time that NVHL disabled the development of behavioral routines, suggesting dramatic procedural memory deficits. The presence of procedural memory deficits in adult rats subjected to NHVL suggests that the lesions lead to a wider range of cognitive deficits than previously shown. Interestingly, procedural or implicit memory impairments have also been reported in schizophrenic patients.

Ultrafast in vivo microwave irradiation for enhanced metabolic stability of brain biopsy samples during HRMAS NMR analysis.

High resolution magic-angle spinning (HRMAS) NMR spectroscopy is a well established technique for ex vivo metabolite investigations but experimental factors such as ischemic delay or mechanical stress due to continuous spinning deserve further investigations. Cortical brain samples from rats that underwent ultrafast in vivo microwave irradiation (MWp group) were compared to similar samples that underwent standard nitrogen freezing with and without exposure to domestic microwaves (FN and FN+MWd groups). One dimensional (1)H HRMAS NMR spectra were acquired and 16 metabolites of interest were quantified. Within each group 3 samples underwent long lasting acquisition (up to 15 h). Statistically significant differences in metabolite concentrations were observed between groups for metabolites associated to post mortem biochemical changes and/or anaerobic glycolysis including several neurotransmitters. Spectral assessment over time showed a drastic reduction of biochemical variations in both MW groups. Only 2/16 metabolites exhibited significant signal variations after 15 h of continuous spinning and acquisition in the MWp group. This number increased to 10 in the FN group. We confirmed limited anaerobic metabolism and post mortem degradation after ultra fast in vivo MW irradiation. Furthermore, spectra obtained after MWp and MWd irradiation exhibited an extremely stable spectral pattern over extended periods of continuous acquisition.

SPM analysis of ictal-interictal SPECT in mesial temporal lobe epilepsy: relationships between ictal semiology and perfusion changes.

A combination of temporo-limbic hyperperfusion and extratemporal hypoperfusion was observed during complex partial seizures (CPS) in temporal lobe epilepsy (TLE). To investigate the clinical correlate of perfusion changes in TLE, we analyzed focal seizures of increasing severity using voxel-based analysis of ictal SPECT. We selected 26 pre-operative pairs of ictal-interictal SPECTs from adult mesial TLE patients, seizure-free after surgery. Ictal SPECTs were classified in three groups: motionless seizures (group ML, n=8), seizures with motor automatisms (MA) without dystonic posturing (DP) (group MA, n=8), and seizures with DP with or without MA (DP, n=10). Patients of group ML had simple partial seizures (SPS), while others had CPS. Groups of ictal-interictal SPECT were compared to a control group using statistical parametric mapping (SPM). In ML group, SPM analysis failed to show significant changes. Hyperperfusion involved the anteromesial temporal region in MA group, and also the insula, posterior putamen and thalamus in DP group. Hypoperfusion was restricted to the posterior cingulate and prefrontal regions in MA group, and involved more widespread associative anterior and posterior regions in DP group. Temporal lobe seizures with DP show the most complex pattern of combined hyper-hypoperfusion, possibly related both to a larger spread and the recruitment of more powerful inhibitory processes.

[Epileptogenic and non-epileptogenic zones: blood flow studies of temporo-limbic seizures]. / Zones épileptogènes et non-épileptogènes: imagerie de perfusion des crises temporo-limbiques.

To assess the contribution of ictal SPECT to the definition of the epileptogenic zone (EZ) prior to surgery in focal drug-resistant epilepsies, we investigated the effect of the timing of injection and seizure semiology on patterns of perfusion and cerebral blood flow changes (CBF) beyond the EZ. In the rat model of amygdala-kindled seizures, we measured CBF changes with the quantitative [(14)C]-iodoantipyrine autoradiographic method during secondary generalized (SGS, n=26 fully-kindled rats) and focal seizures (FS, n=19 partially kindled rats), according to sequential timing of injection with respect to seizure onset. During SGS, the correct lateralization and rough localization of the focus within limbic structures was only possible at the early ictal and post-ictal times, in between we observed widespread rCBF increases. The switch from hyper to hypoperfusion occurred at the time of late ictal injection. The accurate localization of the EZ was obtained in the study of the more subtle FS (stage 0). At stage 1 of the kindling, there was already a remote widespread spreading of hyperperfusion. In patients surgically cured from a mesio-temporal lobe epilepsy (mean post-operative follow-up: 66 months), we retrospectively studied 26 pairs of ictal and interictal pre-operative SPECTs, classified in 3 groups according to the progression of ictal semiology. Using visual analysis of subtracted SPECTs (SISCOM) and group comparisons with a control group (using SPM), we observed more widespread combined hyper and hypoperfusion with the increasing complexity of seizures. In simple partial seizures, the SISCOM analysis allowed a correct localization of the focus in 4/8 patients, whereas the SPM analysis failed to detect significant changes, due to individual variation, spatial normalization and small magnitude of CBF changes. In complex partial seizures with automatisms, SISCOM and SPM analysis showed antero-mesial temporal hyperperfusion (overlapping the EZ), extending to the insula, basal ganglia, and thalamus in the group of patients having dystonic posturing (DP group) in addition to automatisms. Ictal hypoperfusion involved pre-frontal and parietal regions, the anterior and posterior cingulate gyri, to a greater extent in the DP group. In both human and animals studies, we observed a correlation between the extent of composite patterns of hyper/hypoperfusion and the severity of seizures, and the recruitment of remote sub-cortical structures. Hypoperfused areas belong to neural networks involved in perceptual decision making and motor planning, whose transient disruption could support purposeless actions, i.e. motor automatisms.

Modifications of local cerebral glucose utilization in thalamic structures following injection of a dopaminergic agonist in the nucleus accumbens--involvement in antiepileptic effects?

Dopaminergic transmission in the nucleus accumbens (NAcc) is implicated in different aspects of reward and motivational mechanisms. More recently, it has been suggested that this nucleus could also be involved in the modulation of generalized epileptic seizures. In particular, microinjection of dopaminergic agonists in the NAcc suppresses the occurrence of epileptic seizures in a model of absence seizures, the GAERS (generalized absence epileptic rats from Strasbourg). The aim of this study was to identify the structures involved in this effect. Local cerebral metabolic rates for glucose utilization (LCMRglc) were measured in different parts of the basal ganglia and output structures after apomorphine injection in the NAcc in GAERS and in the inbred non-epileptic rats (NE), concomitantly with seizure suppression. Apomorphine injection in the NAcc induced a significant increase of glucose intake in the anteromedial, mediodorsal and ventrolateral nuclei of the thalamus in NE rats, while no significant changes were observed in the basal ganglia structures (globus pallidus, subthalamic nucleus, substantia nigra). Furthermore, microinjections of muscimol (100 and 200 pmol/side) in the mediodorsal nucleus of the thalamus in GAERS rats suppressed seizures. These results suggest that the mediodorsal nucleus of the thalamus could be involved in absence seizures modulation. Along with data from the literature, our data suggest that this nucleus could participate in the control of the basal ganglia over generalized epileptic seizures.

Neuroprotective properties of topiramate in the lithium-pilocarpine model of epilepsy.

The lithium-pilocarpine model reproduces the main characteristics of human temporal lobe epilepsy. After status epilepticus (SE), rats exhibit a latent seizure-free phase characterized by development of extensive damage in limbic areas and occurrence of spontaneous recurrent seizures. Neuroprotective and antiepileptogenic effects of topiramate were investigated in this model. SE was induced in adult male rats by LiCl (3 mEq/kg) followed 20 h later by pilocarpine (25 mg/kg). Topiramate (10, 30, or 60 mg/kg) was injected at 1 and 10 h of SE. Injections were repeated twice a day for six additional days. Another group received two injections of diazepam on the day of SE and of vehicle for 6 days. Neuronal damage was assessed at 14 days after SE by cell counting on thionin-stained sections. Occurrence of spontaneous recurrent seizures (SRS) was videorecorded for 10 h per day in other groups of rats. In diazepam-treated rats, the number of neurons was dramatically reduced after SE in all subregions of hippocampus and layers II-IV of ventral cortices. At all doses, topiramate induced a 24 to 30% neuroprotection in layer CA1 of hippocampus (p < 0.05). In CA3b, the 30-mg/kg dose prevented neuronal death. All rats subjected to SE became epileptic. The latency (14-17 days) to and frequency of SRS were similar in topiramate- and diazepam-treated rats. The high mortality in the 30 mg/kg topiramate group (84%) was possibly the result of interaction between lithium and topiramate. In conclusion, topiramate displayed neuroprotective properties only in CA1 and CA3 that were not sufficient to prevent epileptogenesis.

Metabolic approach of absence seizures in a genetic model of absence epilepsy, the GAERS: study of the leucine-glutamate cycle.

We suggest that a dysregulation of energy metabolism in the brain of genetic absence epilepsy rats from Strasbourg (GAERS) could create a specific cerebral environment that would favor the expression of spike-and-wave discharges (SWD) in the thalamocortical loop, largely dependent on glutamatergic and gamma-aminobutyric acid (GABA)-ergic neurotransmissions. We tested several aspects of metabolic activity in the brain of GAERS compared to a genetic strain of nonepileptic (NE) rats. Glucose metabolism was higher in all brain regions of GAERS compared to those of NE rats along the whole glycolytic and aerobic pathways, as assessed by regional histochemical measurement of lactate dehydrogenase and cytochrome oxidase activities. Branched-chain amino acids (BCAA) and alpha-ketoisocaproate (alpha-KIC), the ketoacid of leucine, when injected intraperitoneally, increased the number of SWD in GAERS but had only a slight effect on their duration. These data speak in favor of a BCAA- or alpha-KIC-induced change in neuronal excitability. Leucine and alpha-KIC decreased the concentration of glutamate in thalamus and cortex without affecting GABA concentrations. Thus, BCAA and alpha-KIC, by decreasing glutamatergic neurotransmission, could favor GABAergic neurotransmission, which is known to increase the occurrence of seizures in GAERS. Finally, the transport of [1-(14)C]alpha-KIC in freshly isolated cortical neurons was lower in GAERS than in NE rats, and this difference was shown to be of metabolic origin. The addition of gabapentin, a specific inhibitor of BCAA transaminase (BCAT), reduced the transport of [1-(14)C]alpha-KIC in GAERS and NE rats to a level that became identical in both strains. This strain-dependent change was not related to a difference in the activity of BCAT, which was identical in GAERS and NE rats. The exact origin of this apparent metabolic dysregulation of energy metabolism in GAERS that could underlie the origin of seizures in that strain remains to be explored further.

Caffeine does not affect excitotoxic brain lesions in newborn mice.

Caffeine is frequently administered to human pre-term newborns although its neurological impact has not been fully evaluated. In the present study performed in mice, we examined the effects of caffeine administration on neonatal excitotoxic lesions of the periventricular white matter, which mimics several aspects of human periventricular leukomalacia. In this model, caffeine exposure did not worsen white matter lesions. These data suggest that neonatal caffeine administration might not affect clastic lesions in pre-term infants.

Vigabatrin protects against hippocampal damage but is not antiepileptogenic in the lithium-pilocarpine model of temporal lobe epilepsy.

In temporal lobe epilepsy (TLE), the nature of the structures involved in the development of the epileptogenic circuit is still not clearly identified. In the lithium-pilocarpine model, neuronal damage occurs both in the structures belonging to the circuit of initiation and maintenance of the seizures (forebrain limbic system) as well as in the propagation areas (cortex and thalamus) and in the circuit of remote control of seizures (substantia nigra pars reticulata). In order to determine whether protection of some brain areas could prevent the epileptogenesis induced by status epilepticus (SE) and to identify the cerebral structures involved in the genesis of TLE, we studied the effects of the chronic exposure to Vigabatrin (gamma-vinyl-GABA, GVG) on neuronal damage and epileptogenesis induced by lithium-pilocarpine SE. The animals were subjected to SE and GVG treatment (250 mg/kg) was initiated at 10 min after pilocarpine injection and maintained daily for 45 days. These pilo-GVG rats were compared with rats subjected to SE followed by a daily saline treatment (pilo-saline) and to control rats not subjected to SE (saline-saline). GVG treatment induced a marked, almost total neuroprotection in CA3, an efficient protection in CA1 and a moderate one in the hilus of the dentate gyrus while damage in the entorhinal cortex was slightly worsened by the treatment. All pilo-GVG and pilo-saline rats became epileptic after the same latency. Glutamic acid decarboxylase (GAD67) immunoreactivity was restored in pilo-GVG rats compared with pilo-saline rats in all areas of the hippocampus, while it was increased over control levels in the optical layer of the superior colliculus and the substantia nigra pars reticulata. Thus, the present data indicate that neuroprotection of principal cells in the Ammon's horn of the hippocampus is not sufficient to prevent epileptogenesis, suggesting that the hilus and extra-hippocampal structures, that were not protected in this study, may play a role in the genesis of spontaneous recurrent seizures in this model. Furthermore, the study performed in non-epileptic rats indicates that chronic treatment with a GABAmimetic drug upregulates the expression of the protein GAD67 in specific areas of the brain, independently from the seizures.

Age-dependent consequences of seizures and the development of temporal lobe epilepsy in the rat.

The age-related functional changes underlying epileptogenesis remain to be clarified. In the present study, we explored the correlation between metabolic changes, neuronal damage and epileptogenesis during the acute, silent and chronic phases following status epilepticus (SE) induced by lithium-pilocarpine (Li-Pilo) in 10- (P10), 21-day-old (P21) and adult rats. Local cerebral metabolic rates for glucose (LCMRglcs) were measured by the [14C]2-deoxyglucose method during SE, the silent period and the interictal phase of the chronic period. Neurodegeneration was assessed by cresyl violet staining. During SE, LCMRglcs dramatically increased at all ages mainly in forebrain vulnerable regions. During the silent phase, in P21 and adult rats, metabolic decreases were recorded in damaged forebrain regions involved in the genesis and propagation of seizures 14 days after SE. At the end of the silent phase, P21 and adult rats exhibited metabolic increases in intact brainstem areas involved in the remote control of epilepsy. During the interictal phase of the chronic period, LCMRglcs decreased in damaged forebrain areas of adult and P21 rats that were not spontaneously epileptic, while LCMRglcs were similar to control levels in epileptic P21 rats. In P10 rats, there was no damage and no metabolic consequences at any time after SE. In conclusion, the process of epileptogenesis and its functional consequences differ in P21 and adult rats. The factors underlying these age-related differences remain to be explored.

Alterations of hippocampal GAbaergic system contribute to development of spontaneous recurrent seizures in the rat lithium-pilocarpine model of temporal lobe epilepsy.

Reorganization of excitatory and inhibitory circuits in the hippocampal formation following seizure-induced neuronal loss has been proposed to underlie the development of chronic seizures in temporal lobe epilepsy (TLE). Here, we investigated whether specific morphological alterations of the GABAergic system can be related to the onset of spontaneous recurrent seizures (SRS) in the rat lithium-pilocarpine model of TLE. Immunohistochemical staining for markers of interneurons and their projections, including parvalbumin (PV), calretinin (CR), calbindin (CB), glutamic acid decarboxylase (GAD), and type 1 GABA transporter (GAT1), was performed in brain sections of rats treated with lithium-pilocarpine and sacrificed after 24 h, during the silent phase (6 and 12 days), or after the onset of SRS (10-18 days after treatment). Semiquantitative analysis revealed a selective loss of interneurons in the stratum oriens of CA1, associated with a reduction of GAT1 staining in the stratum radiatum and stratum oriens. In contrast, interneurons in CA3 were largely preserved, although GAT1 staining was also reduced. These changes occurred within 6 days after treatment and were therefore insufficient to cause SRS. In the dentate gyrus, extensive cell loss occurred in the hilus. The pericellular innervation of granule cells by PV-positive axons was markedly reduced, although the loss of PV-interneurons was only partial. Most strikingly, the density of GABAergic axons, positive for both GAD and GAT1, was dramatically increased in the inner molecular layer. This change emerged during the silent period, but was most marked in animals with SRS. Finally, supernumerary CB-positive neurons were detected in the hilus, selectively in rats with SRS. These findings suggest that alterations of GABAergic circuits occur early after lithium-pilocarpine-induced status epilepticus and contribute to epileptogenesis. In particular, the reorganization of GABAergic axons in the dentate gyrus might contribute to synchronize hyperexcitability induced by the interneuron loss during the silent period, leading to the onset of chronic seizures.

Modulation of absence seizures by branched-chain amino acids: correlation with brain amino acid concentrations.

The occurrence of absence seizures might be due to a disturbance of the balance between excitatory and inhibitory neurotransmissions in the thalamo-cortical loop. In this study, we explored the consequences of buffering the glutamate content of brain cells on the occurrence and duration of seizures in Genetic Absence Epilepsy Rats from Strasbourg (GAERS), a genetic model of generalized non-convulsive epilepsy. Branched-chain amino acids (BCAAs) and alpha-ketoisocaproate (alpha-KIC), the ketoacid of leucine were repeatedly shown to have a critical role in brain glutamate metabolism. Thus, GAERS were injected by intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) route with these compounds, then the effects on seizures were evaluated on the electroencephalographic recording. We also measured the concentration of amino acids in thalamus and cortex after an i.p. injection of leucine or alpha-KIC. Intracerebroventricular injections of leucine or alpha-KIC did not influence the occurrence of seizures, possibly because the substances reached only the cortex. BCAAs and alpha-KIC, injected intraperitoneally, increased the number of seizures whereas they had only a slight effect on their duration. Leucine and alpha-KIC decreased the concentration of glutamate in thalamus and cortex without affecting GABA concentrations. Thus, BCAAs and alpha-KIC, by decreasing the effects of glutamatergic neurotransmission could facilitate those of GABAergic neurotransmission, which is known to increase the occurrence of seizures in GAERS.

Relationship between neuronal loss and interictal glucose metabolism during the chronic phase of the lithium-pilocarpine model of epilepsy in the immature and adult rat.

The lithium-pilocarpine (Li-Pilo) model of epilepsy reproduces most of the features of human temporal lobe epilepsy. After having studied the metabolic changes occurring during the silent phase, in the present study, we explored the relationship between interictal metabolic changes and neuronal loss during the chronic phase following status epilepticus (SE) induced by Li-Pilo in 10-day-old (P10), 21-day-old (P21), and adult rats. Rats were observed and their EEG was recorded to detect the occurrence of spontaneous recurrent seizures (SRS). Local cerebral glucose utilization was measured during the interictal period of the chronic phase, between 2 and 7 months after SE, by the [(14)C]2-deoxyglucose method in rats subjected to SE at P10, P21, or as adults. Neuronal damage was assessed by cell counting on adjacent cresyl violet stained sections. When SE was induced at P10, rats did not become epileptic, did not develop lesions and cerebral glucose utilization was in the normal range 7 months later. When SE was induced in adult rats, they all became epileptic after a mean duration of 25 days and developed lesions in the forebrain limbic areas, which were hypometabolic during the interictal period of the chronic phase, 2 months after SE. When SE was induced in P21 rats, 24% developed SRS, and in 43% seizures could be triggered (TS) by handling, after a mean delay of 74 days in both cases. The remaining 33% did not become epileptic (NS). The three groups of P21 rats developed quite comparable lesions mainly in the hilus of the dentate gyrus, lateral thalamus, and entorhinal cortex; at 6 months after SE, the forebrain was hypometabolic in NS and TS rats while it was normo- to slightly hypermetabolic in SRS rats. These data show that interictal metabolic changes are age-dependent. Moreover, there is no obvious correlation, in this model, between interictal hypometabolism and neuronal loss, as reported previously in human temporal lobe epilepsy.

Activation of specific neuronal circuits by corticotropin releasing hormone as indicated by c-fos expression and glucose metabolism.

The neuropeptide corticotropin releasing hormone (CRH) is the central nervous system (CNS) transducer of stressful stimuli. Endogenous CRH is released from neuronal terminals in several central nervous system regions-for example, amygdala and hypothalamus-during stress, and exogenous CRH administration mimics stress-related behaviors and hormonal patterns. However, whereas the role of endogenous CRH as a stress neuromodulator has been established, recent findings suggest that the peptide also functions to influence cognitive, emotional, and neuroimmune functions by modulating neuronal communication in a number of circuits. Although anatomic and pharmacologic approaches have provided evidence for this wider spectrum of CRH actions, the discrete regions and specific circuits activated by CRH have not been fully elucidated. In this article, the authors report on the use of two complementary methods to discern specific regions and cell groups activated by the administration of CRH. Glucose metabolism analysis provided quantitative measures of CRH-induced activation, but at a regional resolution; expression of the immediate early gene c-fos permitted a single cell resolution, but underestimated the neuroanatomic extent of CRH-induced activation. Overlapping regions activated using both methods delineated discrete cortical, limbic. and motor pathways. Importantly, cell groups activated by CRH included those possessing either or both members of the CRH receptor family, suggesting that both receptors may mediate the effects of the endogenous ligand. In summary, CRH activates a broad but selective array of neuronal structures belonging to cortical, limbic, and motor circuits. These findings indicate that stress-related release of this peptide may contribute to a spectrum of important modulations of CNS function.

The lesional and epileptogenic consequences of lithium-pilocarpine-induced status epilepticus are affected by previous exposure to isolated seizures: effects of amygdala kindling and maximal electroshocks.

In temporal lobe epilepsy, the occurrence of seizures seems to correlate with the presence of lesions underlying the establishment of a hyperexcitable circuit. However, in the lithium-pilocarpine model of epilepsy, neuronal damage occurs both in the structures belonging to the circuit of initiation and maintenance of the seizures (forebrain limbic system) as in the propagation areas (cortex and thalamus) and in the circuit of remote control of seizures (substantia nigra pars reticulata). To determine whether or not we could protect the brain from lesions and epileptogenesis induced by status epilepticus and identify cerebral structures involved in the genesis of epilepsy, we studied the effects of the chronic exposure to non-deleterious seizures, either focalized with secondary generalization (amygdala kindling, kindled-pilocarpine rats), or primary generalized (ear-clip electroshocks, electroshock-pilocarpine rats) on neuronal damage and epileptogenesis induced by lithium-pilocarpine status epilepticus. These animals were compared to rats subjected to status epilepticus but not pretreated with seizures (sham-kindled-pilocarpine or sham-electroshock-pilocarpine rats). Compared to sham-pilocarpine rats, neuronal damage was prevented in the limbic system of the kindled-pilocarpine rats, except in the hilus of the dentate gyrus and the entorhinal cortex, while it was enhanced in rats pretreated with electroshocks, mainly in the entorhinal and perirhinal cortices. Most sham-kindled- and sham-electroshock-pilocarpine rats (92-100%) developed recurrent seizures after a silent period of 40-54days. Likewise, all kindled-pilocarpine rats developed spontaneous seizures after the same latency as their sham controls, while only two of 10 electroshock-pilocarpine rats became epileptic after a delay of 106-151days. The present data show that the apparent antiepileptic properties of electroshocks correlate with extensive damage in midbrain cortical regions, which may prevent the propagation of seizures from the hippocampus and inhibit their motor expression. Conversely, the extensive neuroprotection of the limbic system but not the hilus and entorhinal cortex provided by amygdala kindling does not prevent epileptogenesis. Thus, the hilus, the entorhinal and/or perirhinal cortex may be key structure(s) for the establishment of epilepsy.

Electroshocks delay seizures and subsequent epileptogenesis but do not prevent neuronal damage in the lithium-pilocarpine model of epilepsy.

Electroconvulsive therapy, which is used to treat refractory major depression in humans increases seizure threshold and decreases seizure duration. Moreover, the expression of brain derived neurotrophic factor induced by electroshocks (ECS) might protect hippocampal cells from death in patients suffering from depression. As temporal lobe epilepsy is linked to neuronal damage in the hippocampus, we tested the effect of repeated ECS on subsequent status epilepticus (SE) induced by lithium-pilocarpine and leading to cell death and temporal epilepsy in the rat. Eleven maximal ECS were applied via ear-clips to adult rats. The last one was applied 2 days before the induction of SE by lithium-pilocarpine. The rats were electroencephalographically recorded to study the SE characteristics. The rats treated with ECS before pilocarpine (ECS-pilo) developed partial limbic (score 2) and propagated seizures (score 5) with a longer latency than the rats that underwent SE alone (sham-pilo). Despite this delay in the initiation and propagation of the seizures, the same number of ECS- and sham-pilo rats developed SE with a similar characteristic pattern. The expression of c-Fos protein was down-regulated by repeated ECS in the amygdala and the cortex. In ECS-pilo rats, c-Fos expression was decreased in the piriform and entorhinal cortex and increased in the hilus of the dentate gyrus. Neuronal damage was identical in the forebrain areas of both groups, while it was worsened by ECS treatment in the substantia nigra pars reticulata, entorhinal and perirhinal cortices compared to sham-pilo rats. Finally, while 11 out of the 12 sham-pilo rats developed spontaneous recurrent seizures after a silent period of 40+/-27 days, only two out of the 10 ECS-pilo rats became epileptic, but after a prolonged latency of 106 and 151 days. One ECS-pilo rat developed electrographic infraclinical seizures and seven did not exhibit any seizures. Thus, the extensive neuronal damage occurring in the entorhinal and perirhinal cortices of the ECS-pilo rats seems to prevent the establishment of the hyperexcitable epileptic circuit.

A metabolic and neuropathological approach to the understanding of plastic changes that occur in the immature and adult rat brain during lithium-pilocarpine-induced epileptogenesis.

PURPOSE: The age-related functional changes that underlie epileptogenesis remain to be clarified. In the present study, we explored the correlation between metabolic changes, neuronal damage, and epileptogenesis during the silent and chronic phases after status epilepticus (SE) induced by lithium-pilocarpine in 10-day-old (P10), 21-day-old (P21), and adult rats. METHODS: Local cerebral metabolic rates for glucose (LCMRglcs) were measured by the [14C]2-deoxyglucose method during the silent period (14 and 60 days after SE in P10 and P21 rats and only at 14 days after SE in adult rats because the silent phase lasts for about 14 days in adults and 60 days in P21 rats) and the interictal phase of the chronic period (2 months after spontaneous seizures or 6 to 7 months after SE in P10 and P21 rats that do not become epileptic). Neurodegeneration was assessed by the silver staining and cresyl violet techniques. RESULTS: In P10 rats, there was no damage and no metabolic consequences at any time after SE. During the silent phase in P21 rats, metabolic decreases were recorded at 14 days after SE, mainly in damaged forebrain regions. At 60 days after SE, P21 rats exhibited metabolic increases in both damaged forebrain and intact brainstem areas. In adult rats studied at 14 days after SE, LCMRglcs decreased in damaged forebrain areas involved in the genesis and propagation of seizures and increased in brainstem areas involved in the remote control of epilepsy. During the interictal phase of the chronic period, LCMRglcs decreased in damaged forebrain areas of adult epileptic rats and P21 rats that were not spontaneously epileptic, whereas it was similar to control levels in epileptic P21 rats. CONCLUSIONS: The process of epileptogenesis and its effects differ in duration and functional consequences in P21 and adult rats. The factors that underlie these age-related differences remain to be explored.

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

Hypervascularization in the magnocellular nuclei of the rat hypothalamus: relationship with the distribution of aquaporin-4 and markers of energy metabolism.

In the magnocellular nuclei of the hypothalamus, there is a rich vascular network for which the function remains to be established. In the supraoptic nucleus, the high vascular density may be one element, which together with the water channel aquaporin-4 expressed in the astrocytes, is related to a role in osmoreception. We tested the osmoreception hypothesis by studying the correlation between vascular and cellular densities in the paraventricular nucleus and the supraoptic nucleus. Whether aquaporin-4 is likely to contribute to osmoreception was tested by studying the distribution in the magnocellular nuclei of the hypothalamus. The high vascular density may also reflect a high metabolic activity due to the synthesis of vasopressin and oxytocin. This metabolic hypothesis was tested by studying the regional cytochrome oxidase histochemistry, the local cerebral blood flow, and the density of glucose transporter type-1 in the supraoptic and paraventricular nuclei. All the magnocellular nuclei were characterized by an extended and intense aquaporin-4 labelling and a weak cytochrome oxidase histochemistry. The highest vascular density was found in the supraoptic nucleus and the magnocellular regions of the paraventricular nucleus. The local cerebral blood flow rates were surprisingly low in the paraventricular nucleus and the supraoptic nucleus in comparison to the cerebral cortex. Furthermore in these nuclei, the antibody for glucose transporter type-1 revealed two populations of vessels differing by their labelling intensity. The similarities observed between the different nuclei suggest that, in the hypothalamus, all magnocellular regions sense the plasma osmolarity. The low local cerebral blood flow, and the patterns of glucose transporter type-1 labelling and cytochrome oxidase histochemistry suggest that the high vascularization of these hypothalamic nuclei is not related to a high metabolic capacity in basal conditions.