The effects of cannabinoids on synaptic transmission were measured optically in rat hippocampal cultures. Synaptic release sites were labeled with the fluorescent dye FM1-43 in a stimulus-dependent manner. Action potential-induced release of FM1-43 required extracellular Ca2+ and was inhibited 65±3% by blockade of high-threshold voltage-gated Ca2+ channels with ω-grammotoxin SIA (300 nM). The cannabimimetic drug, Win 55212-2 (300 nM), inhibited FM1-43 release by 51±3%. The inhibition produced by Win55212-2 was blocked by the CB1 cannabinoid receptor antagonist, SR141716 (1 μM). The intensity of FM1-43 labeled puncta ranged 4-fold, although the inhibition produced by Win55212-2 was distributed normally across synaptic sites of various labeling intensities. The FM1-43-based optical method appears promising for the study of the effects of cannabinoids and other drugs on synaptic networks. These results indicate that cannabimimetics act presynaptically to inhibit the release of neurotransmitter and that this inhibition is observed uniformly at boutons of varied activity levels. Copyright (C) 2000 Elsevier Science B.V.
Bibliographical noteFunding Information:
This work was supported by grants from the National Institute on Drug Abuse (DA07304, DA09293, DA11806) and the National Science Foundation (IBN9723796).
- Glutamate neurotransmission
- Neurotransmitter release
- Presynaptic inhibition