Contribution of protease-activated receptor 1 in status epilepticus-induced epileptogenesis.

Clinical observations and studies on different animal models of acquired epilepsy consistently demonstrate that blood-brain barrier (BBB) leakage can be an important risk factor for developing recurrent seizures. However, the involved signaling pathways remain largely unclear. Given the important role of thrombin and its major receptor in the brain, protease-activated receptor 1 (PAR1), in the pathophysiology of neurological injury, we hypothesized that PAR1 may contribute to status epilepticus (SE)-induced epileptogenesis and that its inhibition shortly after SE will have neuroprotective and antiepileptogenic effects. Adult rats subjected to lithium-pilocarpine SE were administrated with SCH79797 (a PAR1 selective antagonist) after SE termination. Thrombin and PAR1 levels and neuronal cell survival were evaluated 48h following SE. The effect of PAR1 inhibition on animal survival, interictal spikes (IIS) and electrographic seizures during the first two weeks after SE and behavioral seizures during the chronic period was evaluated. SE resulted in a high mortality rate and incidence of IIS and seizures in the surviving animals. There was a marked increase in thrombin, decrease in PAR1 immunoreactivity and hippocampal cell loss in the SE-treated rats. Inhibition of PAR1 following SE resulted in a decrease in mortality and morbidity, increase in neuronal cell survival in the hippocampus and suppression of IIS, electrographic and behavioral seizures following SE. These data suggest that the PAR1 signaling pathway contributes to epileptogenesis following SE. Because breakdown of the BBB occurs frequently in brain injuries, PAR1 inhibition may have beneficial effects in a variety of acquired injuries leading to epilepsy.

Modulation of the hippocampal propensity to non- synaptic epileptiform synchronization in low-calcium model of epilepsy.

The CA3 and CAI regions are the main stages of the "three-synaptic pathway", which plays a role in the generation of hyper-synchronous events in the hippocampus. Under certain experimental conditions, this brain structure might support pathological epileptiform synchronization that is independent of active chemical synaptic transmission. In present work, we estimated the conditions that would facilitate non- synaptic synchronization of the hippocampus. Non-synaptic epileptiform activity was induced in hippocampal slices by the omission calcium ions from the extracellular milieu. The propensity of hippocampal regions to nonsynaptic interactions was estimated by measuring the delay time neededfor the development of low-Ca²âº discharges in the CA3 and CAI. Next, an increase of neuronal excitability was induced by the pre- incubation ofhippocampal slices in 4-aminopyridine (4-AP) and by the reduction ofextracellular osmolarity. Pre-incubation of hippbcampal slices with 4-AP under normal osmotic conditions resulted in decreased latency for non-synaptic discharges in the CA3, but not in the CAl. However hypo-osmotic conditions caused increased excitability of the CA3 region, which resulted in decreased delay time for nonsynaptic discharges and this level of cellular excitability was not further enhanced by the pre-incubation with 4-AR.

Surface charge impact in nonsynaptic model of epilepsy in rat hippocampus.

Decreasing of surface charge screening near voltage-gated ion channels via reduction of extracellular cation divalent ions provide potent mechanism of altering cellular excitability and seizure threshold. Spontaneous field potentials were recorded from horizontal brain slices of young Wistar rats (postnatal day 10-12). Extracellular registrations wereobtained from CA1 and CA3 area of hippocampus. For induction of nonsynaptic epileptiform activity slices were perfused with artificial cerebrospinal fluid with omitted Ca2+and Mg2+ ions. Effect of different Mg2+ concentration (1, 2, and 3mmol/l) on initial stage of nonsynaptic epileptiform discharges was studied. Our results suggest that the change in Mg2+ concentration dramatically affects the probability of induction of low-Ca2+seizure-like activity (SLA), providing evidence that Mg2+ can alter cerebral excitability by affecting the surface charge and supporting the idea that surface charge could be a pharmacological target for anti-epileptic treatment.