Cannabinoid receptor-mediated inhibition of acetylcholine release from hippocampal and cortical synaptosomes.
In previous studies cannabinoid agonists have been found to inhibit and cannabinoid antagonists to enhance electrically-evoked [(3)H]-acetycholine (ACh) release in hippocampal slices. The present study was undertaken to determine if similar cannabinoid effects could be observed in synaptosomes. [(3)H]-ACh release was evoked by two methods, both sensitive to presynaptic receptor effects. The first involved the addition of 1.3 mM calcium following perfusion with calcium-free Krebs and the second the addition of 11 mM potassium following perfusion with normal Krebs. In hippocampal synaptosomes the 1.3 mM calcium-evoked release and the high potassium-evoked [(3)H]-ACh release were inhibited by the cannabinoid agonist, WIN 55212-2, by 59 and 39%, respectively, and with an EC(50) of approximately 1 nM. WIN 55212-2 produced a similar, although less potent, inhibition of [(3)H]-ACh release in cortical synaptosomes. No inhibitory effect of WIN 55212-2 on [(3)H]-ACh release in striatal synaptosomes was observed, supporting previous data collected in this area with brain slices. The cannabinoid antagonist, SR 141716A, produced a robust enhancement of 1.3 mM calcium-evoked [(3)H]-ACh release in hippocampal synaptosomes (EC(50)<0.3 nM) but had no effect on potassium-evoked release or on [(3)H]-ACh release in the cortex or striatum. In conclusion our data demonstrates the inhibitory effects of WIN 55212-2 observed on ACh release in brain slices can be observed in hippocampal and cortex synaptosomes, suggesting a direct action of these compounds on the synaptic terminals. The SR 141716A-induced enhancement of ACh release can similarly be observed in hippocampal synaptosomes and is probably due to an inverse agonist action at constitutively active receptors.
Gifford
A N
AN
Medical Department, Brookhaven National Laboratory, Upton, New York, NY 11973, USA. gifforda@bnl.gov
Bruneus
M
M
Gatley
S J
SJ
Volkow
N D
ND
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D048588:Benzoxazines; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002186:Cannabinoids / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D006624:Hippocampus / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D000077285:Rimonabant; D013574:Synaptosomes / Q000378:metabolism*
D048588:Benzoxazines; D002121:Calcium Channel Blockers; D002186:Cannabinoids; D009025:Morpholines; D009281:Naphthalenes; D010880:Piperidines; D011720:Pyrazoles; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D000109:Acetylcholine; D000077285:Rimonabant