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.

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(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolol[1,2,3 de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone (WIN 55,212-2) 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) (EC50 = 0.85 microM) and SE (EC50 = 1.51 microM), with total suppression of seizure activity at 3 microM and of SE activity at 5 microM. 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-(piperidin-1-yl-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamidehydrochloride (SR141716A; 1 microM), showing a CB1 receptor-dependent pathway. The inhibitory effect of WIN 55,212-2 against low Mg2+-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 Mg2+-induced SE at concentrations up to 150 microM. The results from this study show CB1 receptor-mediated anticonvulsant effects of the cannabimimetic WIN 55,212-2 against both SRED and low Mg2+-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.