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

Abstract

Status epilepticus 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 endocannabinoid system has been implicated in regulating seizure duration and frequency. Endocannabinoids 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 CB1 receptor-dependent endocannabinoid synaptic transmission towards preventing the development of status epilepticuslike activity in the well-characterized hippocampal neuronal culture model of acquired epilepsy using patch clamp electrophysiology. Application of the CB1 receptor antagonists SR141716A (1 μM) or AM251 (1 μM) to "epileptic" neurons caused the development of continuous epileptiform activity, resembling electrographic status epilepticus. The induction of status epilepticus-like activity by CB1 receptor antagonists was reversible and could be overcome by maximal concentrations of CB1 agonists. Similar treatment of control neurons with CB1 receptor antagonists did not produce status epilepticus or hyperexcitability. These findings suggest that CB1 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 discharges. KeywordsCB1 receptor; status epilepticus; cannabinoid; epilepsy; endocannabinoid tone Epilepsy is one of the most common neurological disorders affecting approximately 1-2% of the world population [5]. It is characterized by the occurrence of spontaneous recurrent epileptiform discharges (SREDs) or seizures [9,16]. Status epilepticus (SE) is a majorTo whom correspondence should be addressed: Robert J. DeLorenzo, M.D., Ph.D., M.P.H., Virginia Commonwealth University, School of Medicine, PO Box 980599, Richmond, VA 23298, Phone: 804-828-8969, Fax: 804-828-6432, E-mail: rdeloren@hsc.vcu.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. [2,12,18,19]. The CB1 receptor has been shown to mediate many of the anticonvulsant effects of cannabinoids [20] and to play an important role in regulating synaptic transmissio...

In vitro status epilepticus but not spontaneous recurrent seizures cause cell death in cultured hippocampal neurons

“…Age-matched control neurons revealed ''normal'' baseline activity consisting of intermittent action potentials. SREDs were never observed in control neurons and there were no significant differences in membrane potential and input resistance between control and epileptic neurons (Deshpande et al, 2007c).…”

“…SREDs were induced in the neuronal cultures by exposing them for 3 h to a solution containing no added MgCl 2 (low Mg 2+ ) using procedures described previously (Blair et al, 2006;Deshpande et al, 2007c;Sombati and DeLorenzo, 1995). Briefly, after the removal of maintenance media, neurons were gently washed with 3× 1.5 ml of pBRS (±1mM MgCl 2 ) and then allowed to incubate in this solution at 37 °C under 5% CO 2 /95% air atmosphere.…”

The novel antiepileptic drug carisbamate (RWJ 333369) is effective in inhibiting spontaneous recurrent seizure discharges and blocking sustained repetitive firing in cultured hippocampal neurons

“…This study was initiated to investigate mechanisms underlying the antiepileptic effects of carisbamate using the hippocampal neuronal culture models of status epilepticus and spontaneous epileptiform discharges (SREDs) (Delorenzo et al, 2005;Deshpande et al, 2007c;Sombati and DeLorenzo, 1995). In addition, we also investigated effects of carisbamate on depolarization-induced sustained repetitive firing in cultured hippocampal neurons.…”

“…The low Mg 2+ model utilizes an episode of continuous seizure activity (in vitro status epilepticus) for 3 h. Upon return to normal Mg 2+ solutions, networks of neurons manifest synchronized SREDs for their life in culture (in vitro model of SREDs). The low Mg 2+ models of status epilepticus and SREDs in hippocampal neuronal cultures have been routinely used to characterize biochemical, electrophysiological and molecular mechanisms underlying epilepsy in an in vitro setting (Churn et al, 2000;Delorenzo et al, 2005;Deshpande et al, 2007c;Pal et al, 2001). These in vitro models also allow for careful control of the neuronal environment and are ideally suited to evaluate the effects of various investigational compounds on electrographic seizure activity.…”

The Pharmacological Basis of Cannabis Therapy for Epilepsy

“…Akin to phytocannabinoids, the endogenous cannabinoid anandamide produced an anticonvulsant effect (Wallace et al, 2002). Moreover, certain cannabinoid-receptor antagonists cause status epilepticus-like proseizure activity (Deshpande et al, 2007). Experimental studies linked the cannabinoid receptors type 1 (CB 1 ) to the anticonvulsant activity of THC but did not mention the mechanistic aspects of CBD.…”