INHIBITION OF HIPPOCAMPAL ACETYLCHOLINE-RELEASE AFTER ACUTE AND REPEATED DELTA(9)-TETRAHYDROCANNABINOL IN RATS

The effects of acute and repeated administration of Delta(9)-tetrahydr ocannabinol (Delta(9)-THC), the psychoactive principle of marijuana, o n acetylcholine release in the hippocampus was studied in freely movin g rats by microdialysis. The acute intraperitoneal (i.p.) administrati on of Delta(9)-THC at the doses of 2.5 and 5 mg/kg reduced acetylcholi ne release by about 25% and 45%, respectively. A dose of 7.5 mg/kg pro duced no further reduction. Delta(9)-THC effects were antagonized by t he cannabinoid CB1 antagonist SR141716A at the i.p. dose of 1 mg/kg, p er se ineffective in modifying acetylcholine concentrations. After a r epeated exposure (twice daily for up to seven days) to Delta(9)-THC (7 .5 mg/kg, i.p.) or vehicle (0.3 ml/kg, i.p.), the inhibitory effect of Delta(9)-THC (2.5 and 5 mg/kg, i.p) on acetylcholine release was not reduced. The results confirm previous observations that cannabinoids i nhibit acetylcholine release through cannabinoid CB1 receptors, and in dicate that no tolerance to this effects develops after a repeated Del ta(9)-THC administration. (C) 1998 Elsevier Science B.V. All rights re served.