Cannabinoid CB1 receptor antagonists cause status epilepticus-like activity in the hippocampal neuronal culture model of acquired epilepsy

Status epilepticus (SE) is a major medical emergency associated with a significant morbidity and mortality. Little is known about the mechanisms that terminate seizure activity and prevent the development of status epilepticus. Cannabinoids possess anticonvulsant properties and the enclocannabinoid system has been implicated in regulating seizure duration and frequency. Enclocannabinoids regulate synaptic transmission and dampen seizure activity via activation of the presynaptic cannabinoid receptor 1 (CB1). This study was initiated to evaluate the role of CBI receptor-dependent enclocannabinoid synaptic transmission towards preventing the development of status epilepticus-like activity in the well-characterized hippocampal neuronal culture model of acquired epilepsy using patch clamp electrophysiology. Application of the CBI receptor antagonists SR141716A (1 mu M) or AM251 (1 mu M) to "epileptic" neurons caused the development of continuous epileptiform activity, resembling electrographic status epilepticus. The induction of status epilepticus-like activity by CBI receptor antagonists was reversible and could be overcome by maximal concentrations of CBI agonists. Similar treatment of control neurons with CBI receptor antagonists did not produce status epilepticus or hyperexcitability. These findings suggest that CBI receptor-dependent endocannabinoid endogenous tone plays an important role in modulating seizure frequency and duration and preventing the development of status epilepticus-like activity in populations of epileptic neurons. The regulation of seizure activity and prevention of status epilepticus by the endocannabinoid system offers an important insight into understanding the basic mechanisms that control the development of continuous epileptiform discharaes. (c) 2006 Elsevier Ireland Ltd. All rights reserved.