Effects of chronic Δ9-tetrahydrocannabinol treatment on hippocampal extracellular acetylcholine concentration and alternation performance in the T-maze

Delta (9)-Tetrahydrocannabinol (Delta (9)-THC), the psychoactive ingredient of cannabis sativa, reduces both extracellular hippocampal acetylcholine concentration and correct alternation tasks in the T-maze. The principal aim of this study was to determine whether a chronic Delta (9)-THC treatment would induce tolerance both to the reduction of extracellular hippocampal acetylcholine concentration and memory deficit produced by the drug. Our results show that a chronic Delta (9)-THC treatment (5 mg/kg, i.p., twice daily for two weeks) did not produce tolerance to the inhibitory effects induced by the drug. Moreover, no strict temporal correlation between the two Delta (9)-THC effects was observed: the inhibition in extracellular acetylcholine concentration appeared only 80 min after treatment, while the reduction of correct alternation tasks in the T-maze began after 20 min. The cognitive and cholinergic effects induced by a chronic Delta (9)-THC treatment were completely blocked by the CB1 cannabinoid receptor antagonist SR 141716A, indicating an involvement of CB1 cannabinoid receptors in the persistent negative effects induced by the drug. These findings confirm the proposition that CB1 cannabinoid receptors mediate the negative effects induced by Delta (9)-THC both on hippocampal extracellular acetylcholine concentration and correct alternation tasks in the T-maze, and they indicate that these effects may be differentiated. However, the major outcome of this work is the demonstration that no tolerance to the two inhibitory effects develops after a chronic Delta (9)-THC treatment. (C) 2001 Published by Elsevier Science Ltd.