Activation of the Cannabinoid Type-1 Receptor Mediates the Anticonvulsant Properties of Cannabinoids in the Hippocampal Neuronal Culture Models of Acquired Epilepsy and Status Epilepticus

Abstract

Cannabinoids have been shown to have anticonvulsant properties, but no studies have evaluated the effects of cannabinoids in the hippocampal neuronal culture models of acquired epilepsy (AE) and status epilepticus (SE). This study investigated the anticonvulsant properties of the cannabinoid receptor agonist R(ϩ)- [2,3-dihydro-5-methyl-3-[(morpholinyl) (WIN 55, in primary hippocampal neuronal culture models of both AE and SE. WIN 55,212-2 produced dose-dependent anticonvulsant effects against both spontaneous recurrent epileptiform discharges (SRED) (EC 50 ϭ 0.85 M) and SE (EC 50 ϭ 1.51 M), with total suppression of seizure activity at 3 M and of SE activity at 5 M. The anticonvulsant properties of WIN 55,212-2 in these preparations were both stereospecific and blocked by the cannabinoid type-1 (CB1) receptor antagonist N-(piperi-, showing a CB1 receptor-dependent pathway. The inhibitory effect of WIN 55,212-2 against low Mg 2ϩ -induced SE is the first observation in this model of total suppression of SE by a selective pharmacological agent. The clinically used anticonvulsants phenytoin and phenobarbital were not able to abolish low Mg 2ϩ -induced SE at concentrations up to 150 M. The results from this study show CB1 receptor-mediated anticonvulsant effects of the cannabimimetic WIN 55,212-2 against both SRED and low Mg 2ϩ -induced SE in primary hippocampal neuronal cultures and show that these in vitro models of AE and SE may represent powerful tools to investigate the molecular mechanisms mediating the effects of cannabinoids on neuronal excitability.Since the isolation and purification of the psychotropically active constituent ⌬ 9 -tetrahydrocannabinol from Cannabis in the 1960s (reviewed in Mechoulam, 2000), a number of studies have shown the anticonvulsant effects of cannabinoids in a variety of experimentally induced seizure models that include maximal electroshock-induced convulsions, electrical kindling, chemoconvulsants, and audiogenic and photogenic seizures (Corcoran et al., 1973;Karler et al., 1974;Wada et al., 1975;Consroe and Wolkin, 1977;Chiu et al., 1979;Wallace et al., 2001Wallace et al., , 2002Shafaroodi et al., 2004). In addition, several reports have been published on the clinical use of cannabinoids as antiepileptic agents in humans (reviewed in Consroe, 1998). Thus, it is important to elucidate the molecular mechanisms mediating the anticonvulsant effects of cannabinoids. Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.105.100354.ABBREVIATIONS: CB1, cannabinoid type 1; MES, maximal electroshock; WIN 55, N-(piperidin-1-yl-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamidehydrochloride; pBRS, physiological bath recording solution; PDS, paroxysmal depolarization shift(s); AEA, arachidonylethanolamine; DSI, depolarization-induced suppression of inhibition; DSE, depolarization-induced suppression of excitation.

Inhibition of endocannabinoid metabolism attenuates enhanced hippocampal neuronal activity induced by kainic acid

“…Previous in vitro and in vivo studies have shown that exogenously applied CB receptor agonists, such as D 9 THC and WIN 55, 212-2 are antiepileptic in a number of animal seizure models. This includes in vivo models of maximal electroshock in mice (Wallace et al, 2001) and the pilocarpine model in rats (Wallace et al, 2003), and in vitro, in hippocampal neuronal culture models of acquired epilepsy and status epilepticus (Blair et al, 2006). Moreover, endocannabinoids such as AEA and 2-AG have been shown to exhibit neuroprotective effects (Marsicano et al, 2003) and antiepileptic effects when applied exogenously (Wallace et al, 2002).…”

“…Cannabinoid compounds have been reported to exhibit both antiepileptic (Blair et al, 2006;Wallace et al, 2001; and neuroprotective properties (Marsicano et al, 2003) via cannabinoid receptors. The endogenous cannabinoid (endocannabinoid) system is integral in controlling neuronal excitability and synaptic plasticity.…”

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

“…Studies were conducted on primary mixed hippocampal neuronal cultures prepared as described previously with slight modifications (Blair et al, 2006;Deshpande et al, 2007b;Sombati and DeLorenzo, 1995). In brief, hippocampal cells were obtained from 2-day postnatal Sprague-Dawley rats (Harlan, Frederick, MD) and plated at a density of 1 × 10 5 cells/cm 2 onto 35-mm Falcon cell culture dishes (Becton Dickinson and Co., Franklin Lakes, NJ) previously coated with poly-L-lysine (0.05 mg/ml).…”

Cannabinoid-mediated short-term plasticity in hippocampus

“…This has possible implications in pathological manifestations of inhibition and excitation imbalance such as epilepsy (Blair, 2006). Interestingly, CBs have been found to exert both convulsant and anticonvulsant effects (Monory and Lutz, 2008).…”

“…Indeed, an upregulation of CB 1 receptors on GABAergic terminals but not on glutamatergic terminals has been observed due to febrile seizures, suggesting a pathological enhancement of DSI (Chen et al, 2007). Also, it has been hypothesised that suppression of excitation is the mode of action of the anti-convulsant effects of CBs (Blair, 2006;Hajos and Freund, 2002). This hypothesis has been supported in a study by Monory et al (Monory et al, 2006) where deletion of CB 1 receptors from glutamatergic terminals was shown to be pro-convulsant whereas the deletion of CB 1 receptors from GABAergic cells did not change seizure behaviour.…”