The results from the present study are unique in that they are the first to demonstrate that microinjection of a CB1 receptor antagonist into the hippocampus blocked spatial memory deficits caused by systemic administration of Δ9-THC, the primary active constituent of marijuana, as well as CP55-940, a potent cannabinoid analogue. Moreover, the effects of intrahippocampal infusion of rimonabant on radial arm choice accuracy were behaviorally selective. Intrahippocampal rimonabant administration did not attenuate non-mnemonic effects of cannabinoids, including behaviors assessed in the tetrad test and decreased radial arm running speeds in the radial arm maze. Finally, the effects of rimonabant were regionally selective, as its administration to sites just dorsal or ventral to the borders of the hippocampus did not antagonize the memory disruptive effects of systemically administered cannabinoids. These finding support the contention that hippocampal CB1 receptors are necessary for the memory disruptive effects of marijuana.
