Pharmacological evidence for the involvement of diacylglycerol lipase in depolarization-induced endocanabinoid release

• Published in: Neuropharmacology 2008-01, Vol.54 (1), p.58-67
• Main Authors: Hashimotodani, Yuki, Ohno-Shosaku, Takako, Maejima, Takashi, Fukami, Kiyoko, Kano, Masanobu
• Format: Article
• Language: English
• Subjects: 2-Arachidonoylglycerol; Adrenergic beta-Antagonists - pharmacology; Animals; Animals, Newborn; Arachidonic Acids - metabolism; Calcium - metabolism; Cannabinoid Receptor Modulators - metabolism; CB1 cannabinoid receptor; Cells, Cultured; Depolarization-induced suppression of inhibition; Diacylglycerol lipase; Electric Stimulation; Endocannabinoids; Enzyme Inhibitors - pharmacology; Glycerides - metabolism; Hippocampus - cytology; Inhibitory Postsynaptic Potentials - drug effects; Inhibitory Postsynaptic Potentials - physiology; Lipoprotein Lipase - metabolism; Membrane Potentials - drug effects; Membrane Potentials - physiology; Membrane Potentials - radiation effects; Mice; Mice, Knockout; Neurons - drug effects; Neurons - metabolism; Neurons - radiation effects; Patch-Clamp Techniques; Phospholipase C delta - deficiency; Propranolol - pharmacology; Rats; Rats, Sprague-Dawley; Tetrahydrolipstatin
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/j.neuropharm.2007.06.002

Depolarization-induced suppression of inhibition (DSI) or excitation (DSE) is a well-known form of endocannabinoid-mediated short-term plasticity that is induced by postsynaptic depolarization. It is generally accepted that DSI/DSE is triggered by Ca2+ influx through voltage-gated Ca2+ channels. It is also demonstrated that DSI/DSE is mediated by 2-arachidonoylglycerol (2-AG). However, how Ca2+ induces 2-AG production is still unclear. In the present study, we investigated molecular mechanisms underlying the Ca2+-driven 2-AG production. Using cannabinoid-sensitive inhibitory synapses of cultured hippocampal neurons, we tested several inhibitors for enzymes that are supposed to be involved in 2-AG metabolism. The chemicals we tested include inhibitors for phospholipase C (U73122 and ET-18), diacylglycerol kinase (DGK inhibitor 1), phosphatidic acid phosphohydrolase (propranolol), and diacylglycerol lipase (DGL; RHC-80267 and tetrahydrolipstatin (THL)). However, unfavorable side effects were observed with these inhibitors, except for THL. Furthermore, we found that RHC-80267 hardly inhibited the endocannabinoid release driven by Gq/11-coupled receptors, which is thought to be DGL-dependent. By contrast, THL exhibited no side effects as long as we tested, and was confirmed to inhibit the DGL-dependent process. Using THL as a DGL inhibitor, we demonstrated that DGL is involved in both hippocampal DSI and cerebellar DSE. To test a possible involvement of PLCδ in DSI, we examined hippocampal DSI in PLCδ1, δ3 and δ4-knockout mice. However, there was no significant difference in the DSI magnitude between these knockout mice and wild-type mice. The present study clearly shows that DGL is a prerequisite for DSI/DSE. The enzymes yielding DG remain to be determined.