Because of the possibility that intracerebral rimonabant may prevent the disruptive effects of cannabinoids because of diffusion to sites distal to the injection site, we next evaluated whether its infusion just dorsal (Figure 3) or ventral (Figure 4) to the borders of the hippocampus would also block Δ9-THC-induced memory impairment. As shown in Figure 3A, i.p. administration of Δ9-THC led to a significant increase in the number of re-entry errors (main effect of Δ9-THC treatment, F (1,14) = 53.98, p < 0.0001). However, microinjection of rimonabant dorsal to the hippocampus failed to block these memory disruptive effects, as indicated by no significant interaction between rimonabant and Δ9-THC (p = 0.24) and no significant main effect of rimonabant (p = 0.24). Systemically administered Δ9-THC decreased entry rate into each arm (main effect of Δ9-THC: F (1,14) = 7.39, p < 0.05; Figure 3B). Rimonabant infused into the region dorsal to the hippocampus did not block this effect, as indicated by a lack of interaction between the two drug (p = 0.17) and no main effect of rimonabant (p = 0.15). All cannulae were placed dorsal to the hippocampus in the prefrontal cortex or corpus callosum (Figure 3C).
