Abstracts

RATIONALE: Cannabinoids are compounds originally isolated from marijuana ([italic]Cannabis sativum[/italic]). [DELTA]9-THC is a cannabinoid compound that was shown to be anticonvulsant in the Maximal Electroshock (MES) model of seizures. This anticonvulsant effect recently was shown to be mediated via the CB1 receptor due to the ability of SR141716A, the selective CB1 antagonist, to completely abolish the cannabinoid anticonvulsant effect. The compound arachidonyl ethanolamine, more commonly known as anandamide, is an endogenous cannabinoid found abundantly in brain. It produces many cannabinoid-like effects, such as analgesia, hypothermia, catalepsy and decreased locomotor activity, which are mediated via the CB1 receptor. The present studies were conducted to determine if this endogenous cannabinoid is anticonvulsant in the MES model. We hypothesize that anandamide is an endogenous modulator of neuronal hyperexcitability that functions via activation of the CB1 receptor.
METHODS: All drugs were dissolved in 1:1:18 (emulphor: ethanol: 0.9% saline) vehicle. Male CF-1 mice (age 20-28 days) were injected with phenymethylsulfonylfluoride (PMSF) 30 mg/kg i.p. 10 minutes prior to anandamide injection to inhibit amidohydrolase activity. For evaluation of CB1 mediated activity, animals were injected with SR141716A (10 mg/kg i.p.) 5 minutes prior to PMSF injection. Animals received MES via corneal electrodes (50 mA, 110 V, 60 Hz, 0.2 sec) 20 minutes following the final injection. Animals were considered protected if the hind limb extension phase of seizure was absent.
RESULTS: Anandamide is a well characterized endogenous cannabinoid. A dose response curve for inhibition of hind limb extension in the MES model was generated. Anandamide was shown to be a potent anticonvulsant in the MES model (ED50 = 50mg/kg i.p.). Anandamide was as effective as [DELTA]9-THC in preventing hind limb extension. The anticonvulsant effect of anandamide was completely blocked by pretreatment with the CB1 receptor antagonist SR141716A (10 mg/kg i.p.). Vehicle alone conferred no anticonvulsant effects.
CONCLUSIONS: These data further implicate the CB1 receptor as a site that modulates the anticonvulsant effects of cannabinoids. Anandamide is an endogenous effector molecule for the CB1 receptor. Its potent anticonvulsant activity shown in this study provides the first direct evidence demonstrating the effects of endogenous cannabinoids as anticonvulsant molecules. The results suggest a role for the endogenous cannabinoid system in seizure termination.
Support: R01-NS23350, P50-NS25630 to R.J. DeLorenzo, P50-DA05274 to B.R. Martin, T13-DA07027 to M.J. Wallace.