In the present study we examined the effect of the cannabinoid receptor agonist, [[1 a,2-(R)-5-(1,1-dimethylheptyl)-2-[5-hydroxy-2-(3-hydroxypropyl)cyc lohexyl]-phenol; CP 55,940] on [14C]acetylcholine and [3H]norepinephrine release from hippocampal slices and on [14C]acetylcholine release from striatal slices. CP 55,940 potently inhibited electrically evoked [14C]acetylcholine release from hippocampal slices, with an EC50 of 0.02 microM and a maximal inhibition of 61% at 1 microM. The inhibition of acetylcholine release by CP 55,940 was partially antagonized (60%) by the cannabinoid receptor antagonist, [[N-piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1H-pyrazole-3-carboxamide hydrochloride; SR 141716A]. Alone, SR 141716A significantly enhanced stimulated [14C]acetylcholine release. In contrast to the effects of CP 55,940 on [14C]acetylcholine release, electrically evoked [3H]norepinephrine release from hippocampal slices and [14C]acetylcholine release from striatal slices were both unaffected by this compound. Similarly, hippocampal [3H]norepinephrine release and striatal [14C]acetylcholine release were not affected by SR 141716A. In conclusion, the results of this study extend our previous data indicating that cannabinoid receptors modulate acetylcholine release in the hippocampus. The effects of cannabinoid receptor activation on [3H]acetylcholine release in the hippocampus does not appear to extend to [3H]norepinephrine release from this region or to acetylcholine release from the striatum.