Epileptic seizure clustering and accumulation at transition from activity to rest in GAERS rats

Knowing when seizures occur may help patients and can also provide insight into epileptogenesis mechanisms. We recorded seizures over periods of several days in the Genetic Absence Epileptic Rat from Strasbourg (GAERS) model of absence epilepsy, while we monitored behavioral activity with a combined head accelerometer (ACCEL), neck electromyogram (EMG), and electrooculogram (EOG). The three markers consistently discriminated between states of behavioral activity and rest. Both GAERS and control Wistar rats spent more time in rest (55–66%) than in activity (34–45%), yet GAERS showed prolonged continuous episodes of activity (23 vs. 18 min) and rest (34 vs. 30 min). On average, seizures lasted 13 s and were separated by 3.2 min. Isolated seizures were associated with a decrease in the power of the activity markers from steep for ACCEL to moderate for EMG and weak for EOG, with ACCEL and EMG power changes starting before seizure onset. Seizures tended to occur in bursts, with the probability of seizing significantly increasing around a seizure in a window of ±4 min. Furthermore, the seizure rate was strongly increased for several minutes when transitioning from activity to rest. These results point to mechanisms that control behavioral states as determining factors of seizure occurrence

Disrupted Co-activation of Interneurons and Hippocampal Network after Focal Kainate Lesion

GABAergic interneurons are known to control activity balance in physiological conditions and to coordinate hippocampal networks during cognitive tasks. In temporal lobe epilepsy interneuron loss and consecutive network imbalance could favor pathological hypersynchronous epileptic discharges. We tested this hypothesis in mice by in vivo unilateral epileptogenic hippocampal kainate lesion followed by in vitro recording of extracellular potentials and patch-clamp from GFP-expressing interneurons in CA3, in an optimized recording chamber. Slices from lesioned mice displayed, in addition to control synchronous events, larger epileptiform discharges. Despite some ipsi/contralateral and layer variation, interneuron density tended to decrease, average soma size to increase. Their membrane resistance decreased, capacitance increased and contralateral interneuron required higher current intensity to fire action potentials. Examination of synchronous discharges of control and larger amplitudes, revealed that interneurons were biased to fire predominantly with the largest population discharges. Altogether, these observations suggest that the overall effect of reactive cell loss, hypertrophy and reduced contralateral excitability corresponds to interneuron activity tuning to fire with larger population discharges. Such cellular and network mechanisms may contribute to a runaway path toward epilepsy

Complémentarité des photographies aériennes et des images sonar pour l'analyse des structures bio-morpho-sédimentaires du littoral.

International audienceLes images acoustiques des unités morpho-sédimentaires identifiées sur les photographies aériennes d'une flèche sableuse littorale permettent d'analyser précisément: i) les herbiers de zostères situés au niveau des plus basses mers et dans les petits fonds de l'avant côte, ii) le système de rides sableuses de la basse et moyenne plage et du delta de flot s'étendant à l'extrémité interne de la flèche littorale, iii) enfin les vasières internes de la lagune, colonisées par la végétation halophile. La combinaison des images sonar et des photographies aériennes - validée par des observations de terrain - permet d'améliorer la description qualitative et quantitative des différentes structures bio-morpho-sédimentaires du littoral

Complémentarité des photographies aériennes et des images sonar pour l'analyse des structures bio-morpho-sédimentaires du littoral.

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The Mont St Michel Bay : an exceptional megatidal eenvironment influenced by natural evolution and man-made modifications.

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The Mont-Saint-Michel Bay : an exceptional megatidal environment influenced by natural evolution and man-made modifications

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Réponses acoustiques de différents faciès morpho-sédimentaires d’une lagune côtière et d’une flèche littorale.

International audienceThis study presents a combinated approach of the coastal area of the "Sables-d'Or" with acoustic and optical data. A sand spit, covered by dunes, which isolates a lagunal system behind it, constitutes this coastal portion. The acoustic imageries of the sedimentary structures, identified on the aerial photographs (optical imageries), show: seagrasses meadows which grow in shallow waters on sandy substratum near lowest tide sea level; a sandy ridges system of large extension from the middle to the lower beach; a flood delat developed at the internal extremity of the sand spit and, eventually, the internal mud flats colonized by the halophile vegetation (salt marsh) with external edges invaded by sands. Thus, the combination of sonar data, aerial pictures and field work observation allows a very precise description of the different morpho-sedimentary structures. This double approach constitutes a fast and relliable survey method, perfectly adapted to follow the evolution of the coastal area.Etudié selon une double approche, acoustique et optique, le littoral de Sables d’Or est formé d’une longue flèche sableuse surmontée d’un massif dunaire, qui isole en arrière d’elle une lagune côtière. Les images acoustiques des unités morpho-sédimentaires identifiées sur les photographies aériennes (images optiques) révèlent : * les herbiers de zostères qui se développent au niveau des plus basses mers sur les petits fonds sableux de l’avant-côte ; * le système de rides sableuses de grande extension qui occupent la basse et la moyenne plage; le delta de flot qui s’étend à l’extrémité interne de la flèche littorale; * et enfin les vasières internes de la lagune, colonisées par la végétation halophile (le schorre) dont la bordure externe est envahie par les sables. Ainsi, la combinaison des images sonar et des photographies aériennes – validée par des observations de terrain - permet une description qualitative et quantitative (amplitudes et longueurs d’onde) des différentes unités morpho-sédimentaires. Cette double approche permet une reconnaissance rapide et fiable, donc parfaitement adaptée, pour un suivi d’évolution du littora