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La mort soudaine inattendue (SUDEP) est fréquemment rapportée chez les patients qui souffrent d'épilepsie et compte pour près de 17% des décès dans cette population. Bien que son étiologie soit restée longtemps incertaine, des études menées sur des cas de victimes de SUDEP suggèrent fortement l'implication de l'apnée post-ictale dans la survenue de ce type de décès. Afin d'élucider les mécanismes physiopathologique de la SUDEP, il était nécessaire de mettre en place un modèle animal qui présente à la fois des crise spontanées récurrentes comme dans le syndrome épileptique et des altérations respiratoires. Dans une première partie, nous mettons en évidence la présence d'altérations respiratoires (RAs) chez 30 à 50% des rats qui présentent une épilepsie suite à un état de mal épileptique (SE) induit par l'administration de pilocarpine. Ces RAs, que nous avons assimilées à des apnées, ont été mises en évidence par thermochimie respiratoire et se traduisent par une diminution de la consommation en oxygène, dont la durée peut varier entre 20 secondes et 13 minutes. La présence des RAs est associée à des altérations du système sérotoninergique au niveau du tronc cérébral, où sont concentrés la majorité des groupes de neurones impliqués dans la régulation et dans la modulation de la fonction respiratoire. Nous montrons que de nombreux gènes du système sérotoninergique sont dérégulés lors de la mise en évidence des RAs ; toutefois, seules les altérations touchant le récepteur 5-HT2c semblent être associées au maintien des RAs. Ce résultat est d'autant plus important qu'il avait été montré que la délétion de ce récepteur chez les souris peut conduire à un arrêt respiratoire fatal suite à une crise épileptique, provoquée ou spontanée. Dans une seconde partie, nous montrons que la surface de la zone présentant un hypersignal T2 dans le système limbique ventral des rats épileptiques est prédictive de la présence de RAs. En outre, des différences d'expression du récepteur 5-HT2c similaires à celles qui avaient été observées dans le tronc cérébral sont retrouvées entre les rats épileptiques selon qu'ils présentent ou pas des RAs. Les résultats de cette thèse impliquent donc le récepteur 5-HT2c dans la survenue et/ou le maintien des altérations respiratoires associées à l'épilepsie. Dans le contexte de la SUDEP, nos résultats ouvrent comme première perspective clinique celle de développer des traitements permettant de cibler spécifiquement le récepteur 5-HT2c chez les patients qui présenteraient un risque de survenue de la SUDEP. La seconde perspective clinique serait de pouvoir identifier ces patients à risque à partir de biomarqueurs tels que les anomalies de signal T2 que nous avons identifiées dans la région limbique ventrale qui inclut notamment l'insula, dont il a été montré qu'elle contribue à la modulation de la fonction respiratoirePas de résumé anglai

Respiratory dysfunctions in two rodent models of chronic epilepsy and acute seizures and their link with brainstem serotonin system

Abstract Patients with drug-resistant epilepsy can experience respiratory alterations notably during seizures. The mechanisms underlying this long-term alteration of respiratory function remain unclear. This study aimed at determining in rats whether epilepsy is associated with alterations of both the respiratory function and brainstem serotonin (5-HT) system. Epilepsy was triggered by pilocarpine-induced status epilepticus in rats. 30-50% of epileptic (EPI) rats exhibited sharp decrease of oxygen consumption (SDOC), low metabolic rate of oxygen and slow regular ventilation; these rats were called EPI/SDOC+ rats. These alterations were only detected in rats with chronic epilepsy, independent of behavioral seizures, persisted over the time, and were not associated with death. In these rats, 5-HT fiber density in the nucleus tractus solitarius was below that of control and EPI/SDOC-rats. Both EPI/SDOC+ rats and DBA/2 mice presenting with fatal respiratory arrest following an audiogenic-induced seizure, a model of sudden and expected death in epilepsy, had increased transcript levels of tryptophan hydroxylase 2 (p<0.001 for both strains) and 5-HT presynaptic transporter (rats: p=0.003; mice: p=0.001). Thus, our data support that 5-HT alterations are associated with chronic and acute epilepsy-related respiratory dysfunctions

Respiratory dysfunction in two rodent models of chronic epilepsy and acute seizures and its link with the brainstem serotonin system

International audiencePatients with drug-resistant epilepsy can experience respiratory alterations, notably during seizures. The mechanisms underlying long-term alterations in respiratory function remain unclear. As the brainstem 5-HT system is a prominent modulator of respiratory function, this study aimed at determining whether epilepsy is associated with alterations in both the respiratory function and brainstem serotonin (5-HT) system in rats. Epilepsy was triggered by pilocarpine-induced status epilepticus in rats. Our results showed that 30-50% of epileptic (EPI) rats exhibited a sharp decrease in oxygen consumption (SDOC), low metabolic rate of oxygen, and slow regular ventilation (EPI/SDOC + rats). These alterations were detected only in rats with chronic epilepsy, independent of behavioral seizures, were persistent over time, and not associated with death. In these rats, 5-HT fiber density in the nucleus tractus solitarius was lower than that in the control and EPI/SDOC- rats. Both EPI/SDOC + rats and DBA/2 mice that present with audiogenic-induced seizure followed by fatal respiratory arrest-a model of sudden and expected death in epilepsy-had increased transcript levels of tryptophan hydroxylase 2 and 5-HT presynaptic transporter. Thus, our data support that 5-HT alterations are associated with chronic and acute epilepsy-related respiratory dysfunction

Standardized environmental enrichment supports enhanced brain plasticity in healthy rats and prevents cognitive impairment in epileptic rats.

Environmental enrichment of laboratory animals influences brain plasticity, stimulates neurogenesis, increases neurotrophic factor expression, and protects against the effects of brain insult. However, these positive effects are not constantly observed, probably because standardized procedures of environmental enrichment are lacking. Therefore, we engineered an enriched cage (the Marlau™ cage), which offers: (1) minimally stressful social interactions; (2) increased voluntary exercise; (3) multiple entertaining activities; (4) cognitive stimulation (maze exploration), and (5) novelty (maze configuration changed three times a week). The maze, which separates food pellet and water bottle compartments, guarantees cognitive stimulation for all animals. Compared to rats raised in groups in conventional cages, rats housed in Marlau™ cages exhibited increased cortical thickness, hippocampal neurogenesis and hippocampal levels of transcripts encoding various genes involved in tissue plasticity and remodeling. In addition, rats housed in Marlau™ cages exhibited better performances in learning and memory, decreased anxiety-associated behaviors, and better recovery of basal plasma corticosterone level after acute restraint stress. Marlau™ cages also insure inter-experiment reproducibility in spatial learning and brain gene expression assays. Finally, housing rats in Marlau™ cages after severe status epilepticus at weaning prevents the cognitive impairment observed in rats subjected to the same insult and then housed in conventional cages. By providing a standardized enriched environment for rodents during housing, the Marlau™ cage should facilitate the uniformity of environmental enrichment across laboratories

EE in Marlau™ cages immediately after Li-Pilo-SE at weaning improves LTP in CA1 pyramidal neurons observed 1–2 weeks later after SE.

<p><b>A.</b> Induction of LTP in CA1 neurons was significantly (p = 0.0003) impaired in slices of rats housed in conventional cages following Li-Pilo-SE (n = 14) compared with healthy rats housed in the same cages (n = 13). <b>B.</b> Induction of LTP in CA1 neurons was significantly decreased (p = 0.0006) in slices of rats housed in Marlau™ cages following Li-Pilo-SE (n = 11) compared with healthy rats housed in the same cages (n = 12). <b>C.</b> LTP in CA1 pyramidal neurons of rats subjected to Li-Pilo-SE at weaning was significantly higher (p = 0.0003) when rats were housed in Marlau™ cages (n = 11) compared to those housed in conventional cages (n = 14). <b>D.</b> Induction of LTP in rats subjected to Li-Pilo-SE and then housed in Marlau™ cages (n = 11) was statistically similar (p = 0.98) to that of healthy rats housed in conventional cages (n = 13). The top traces show EPSPs before and after LTP induction. Arrow marks the starting point of tetanus stimulation. Results are presented as the mean ± SEM (n = number of cells; 1–2 cell(s) per rat). Abbreviations: Cv and En as in Fig. 1.</p

Rats raised in Marlau™ cages after excitotoxic brain injury displayed decreased cognitive impairments.

<p>Rats underwent pilocarpine-induced <i>status epilepticus</i> (Pilo-SE) at 3 week-old, and were raised, on the following day, either in conventional or Marlau™ cages. Rats developing spontaneous recurrent seizures (SRS, or “epileptic”) were then subjected at 15- and 16-week old to the WET and to the MWM, respectively. In these results, 10 rats not subjected to Pilo-SE were included in each Cv and En groups. The number of rats subjected to Pilo-SE that developed SRS was not identical in each Cv (n = 16/18) and En (n = 9/18) groups. <b>A.</b> WET. While rats undergoing SRS displayed marked anxiety-like behavior, the positive effect of enrichment in control rats was observed in epileptic rats, as demonstrated by the increased time spent floating in the central zone. Cv-E vs. Cv and En-E vs. En: ** p<0.01, *** p<0.01; En-E vs. Cv-E: p<0.01, ANOVA 2. <b>B.</b> MWM. Enriched housing prevented the deterioration of learning and memory observed in conventional housing, as indicated by the latency to find the platform and the proportion of rats finding the platform. Cv-E vs. Cv: * p<0.05, ** p<0.01, *** p<0.01; En-E vs. Cv-E: p<0.01, two-way repeated measures ANOVA. Abbreviations: Cv and En as in Fig. 1; En-E, epileptic rats housed in enriched Marlau™ cages; Cv-E, epileptic rats housed in conventional cages.</p

Rat weight, but not total body fat, is increased after housing in the Marlau™ cage. A.

<p>After 4 weeks in the Marlau™ cage, “enriched” rats had an increase in body weight that was significantly greater than that of rats raised in conventional conditions (n = 12 in each group). <b>B.</b> Total body fat percentage measured at termination time was not altered by housing conditions (n = 8 in each group). All results are expressed as the mean ± SEM. Abbreviations: Cv, rats in conventional cages; En, rats in Marlau™ cages.</p

Effect of FG-7142 (25 mg/kg, i.p.) and diazepam (3 mg/kg; i.p.) treatments, administered 30 min prior to WET in Sprague-Dawley rats at 9 weeks of age, raised in conventional cages.

<p>Differences between controls and FG-7142 or diazepam-treated rats:</p>*<p>p<0.05;</p>**<p>p<0.01;</p>***<p>p<0.001 (ANOVA 1).</p

Marlau™ cages meet the criterion of enrichment-induced cortical thickness.

<p>Six weeks after housing in Marlau™ cages, averaged cortical thickness measured as shown by colored arrows on Nissl-stained sections was increased compared to conventional conditions, especially in M1 and S1 subregions. En vs. Cv: * p<0.05, ** p<0.01, two-way ANOVA, factor 1: rat group, factor 2: subregion. Each bar represents the mean ± SEM (<i>n = 4</i> in each group). Abbreviations: Cv and En as in Fig. 1; Cg1/2, cingular cortex 1 and 2; M1, primary motor cortex; M2, secondary motor cortex; RSGb, retrosplenial granular b cortex; S1BF, primary somatosensory cortex, barrel field; S1ULp, primary somatosensory cortex, upper lip region.</p

Marlau™ cages meet the criterion of enrichment-induced hippocampal neurogenesis.

<p>Fourteen days after BrdU injections, the averaged number of cells having incorporated BrdU (counted in 3 sections, 300 µm apart) nearly doubled in the hippocampus of rats raised in Marlau™ cages. While BrdU could be detected in both neurons and astrocytes, respectively identified by NeuN and GFAP, BrdU was primarily found in neurons. En vs. Cv: *** p<0.001, two-way ANOVA, factor 1: rat group, factor 2: anatomical plane. Each bar represents the mean ± SEM (<i>n = 4</i> in each group). Abbreviations: Cv and En as in Fig. 1.</p