Systemic or intra-amygdala infusion of an endocannabinoid CB1 receptor antagonist AM251 blocked propofol-induced anterograde amnesia.

Propofol is well-known for its anterograde amnesic actions. However, a recent experiment showed that propofol can also produce retrograde memory enhancement effects via an interaction with the endocannabinoid CB1 system. Therefore, the authors hypothesized that the regulating effect of propofol on the endocannabinoid CB1 system might also decrease the anterograde amnesic effect of propofol under some conditions, which might be a risk factor for intraoperative awareness. Since, the basolateral amygdala (BLA) has been confirmed to mediate propofol-induced anterograde amnesia and the BLA contains a high concentration of CB1 receptors, the authors investigated whether and how the endocannabinoid system, particularly the CB1 receptor within BLA, influences propofol-induced anterograde amnesia. Male Sprague-Dawley rats trained with inhibitory avoidance (IA) were systematically pre-trained using a memory-impairing dose of propofol (25 mg/kg). Before propofol administration, rats received an intraperitoneal injection of a CB1 receptor antagonist AM251 (1 mg/kg or 2 mg/kg) or a bilateral intra-BLA injection of AM251 (0.6 ng or 6 ng per 0.5 μl). Twenty-four hours after IA training, the IA retention latency was tested. It was found that systemic or intra-BLA injection of a non-regulating dose of AM251 (2 mg/kg or 6 ng per 0.5 μl, respectively) blocked the memory-impairing effect of propofol. These results indicate that the anterograde amnesic effect of propofol is mediated, in part, by activation of the CB1 cannabinoid receptors in the BLA.