Dantrolene inhibits the calcium plateau and prevents the development of spontaneous recurrent epileptiform discharges following in vitro status epilepticus

Abstract

Status epilepticus is a clinical emergency that can lead to the development of acquired epilepsy following neuronal injury. Understanding the pathophysiological changes that occur between the injury itself and the expression of epilepsy is important in the development of new therapeutics to prevent epileptogenesis. Currently, no anti-epileptogenic agents exist; thus, the ability to treat an individual immediately after status epilepticus to prevent the ultimate development of epilepsy remains an important clinical challenge. In the Sprague–Dawley rat pilocarpine model of status epilepticus-induced acquired epilepsy, intracellular calcium has been shown to increase in hippocampal neurons during status epilepticus and remain elevated well past the duration of the injury in those animals that develop epilepsy. This study aimed to determine if such changes in calcium dynamics exist in the hippocampal culture model of status epilepticus-induced acquired epilepsy and, if so, to study whether manipulating the calcium plateau after status epilepticus would prevent epileptogenesis. The in vitro status epilepticus model resembled the in vivo model in terms of elevations in neuronal calcium concentrations that were maintained well past the duration of the injury. When used following in vitro status epilepticus, dantrolene, a ryanodine receptor inhibitor, but not the N-methyl-d-aspartic acid channel blocker MK-801 inhibited the elevations in intracellular calcium, decreased neuronal death and prevented the expression of spontaneous recurrent epileptiform discharges, the in vitro correlate of epilepsy. These findings offer potential for a novel treatment to prevent the development of epileptiform discharges following brain injuries.

Development of status epilepticus, sustained calcium elevations and neuronal injury in a rat survival model of lethal paraoxon intoxication

“…We have demonstrated that SE leads to development of Ca 2+ plateau (Raza et al , 2004; Deshpande et al , 2010) that has its origins in Ca 2+ release from intracellular stores (Nagarkatti et al , 2010). To investigate contribution of intracellular CICR receptors in the development of POX Ca 2+ plateau, [Ca 2+ ] i were measured in neurons obtained from POX SE rats in the presence of RyR blocker dantrolene (Nagarkatti et al , 2010).…”

“…To investigate contribution of intracellular CICR receptors in the development of POX Ca 2+ plateau, [Ca 2+ ] i were measured in neurons obtained from POX SE rats in the presence of RyR blocker dantrolene (Nagarkatti et al , 2010). As shown in Fig.…”

“…These elevations were sustained and lasted for up to one-month following the termination of SE. This Ca 2+ plateau had its origin in Ca 2+ release from intracellular stores, since intervention with CICR receptor inhibitors dantrolene (Nagarkatti et al , 2010) or levetiracetam (Nagarkatti et al , 2008) abolished the Ca 2+ plateau when administered in vitro or in vivo. The Ca 2+ plateau following SE is thought to trigger plasticity changes during the period of epileptogenesis that ultimately results in the development of acquired epilepsy (DeLorenzo et al , 2005).…”

“…Thus, MK-801 administered 1-h after SE cannot prevent the development of Ca 2+ plateau and does not afford neuroprotection (Raza et al , 2004; DeLorenzo et al , 2005). However, CICR from intracellular stores contributes to the maintenance of the Ca 2+ plateau such that inhibition of RyRs not only abolishes Ca 2+ plateau, but it also prevents the development of SE-like injury induced spontaneous epileptiform discharges in hippocampal neurons in vitro (Nagarkatti et al , 2010). We hypothesize that it is this Ca 2+ entry occurring during SE and not the Ca 2+ plateau generated after one-hour of SE that contributes to neuronal death.…”

“…This study will evaluate the effects of POX induced SE on the development of the Ca 2+ plateau and neuronal damage to determine if the POX SE model produces similar effects on these processes as seen with pilocarpine and DFP SE. We will also investigate the contribution of ryanodine receptor (RyR) or inositol trisphosphate receptor (IP 3 R)-dependent regulation of [Ca2+] i towards the maintenance of the Ca2+ plateau utilizing select inhibitors that have been shown to lower elevated Ca 2+ levels following SE (Nagarkatti et al , 2008; Nagarkatti et al , 2010). Being able to reverse the Ca 2+ plateau after survival of POX SE with the Ca 2+ induced Ca 2+ release (CICR) inhibitors could provide new targets for the development of agents to reverse the Ca 2+ plateau and offer a unique insight into the pathophysiology of POX toxicity.…”