The initiation of synaptic 2-AG mobilization requires both an increased supply of diacylglycerol precursor and increased postsynaptic calcium. (April 2015)

• Record Type: Journal Article
• Authors: Shonesy, Brian C.; Winder, Danny G.; Patel, Sachin; Colbran, Roger J.
• Is Part Of: Neuropharmacology. Volume 91(2015)
• Page Start: 57
• Page End: 62
• Publication Date: 2015-04
• Subjects: Endocannabinoids -- Diacylglycerol lipase -- 2-arachidonoylglycerol; Neuropsychopharmacology -- Periodicals; Autonomic Agents -- Periodicals; Neuropsychopharmacologie -- Périodiques; Neuropsychopharmacology; Periodicals; Electronic journals; 615.78
• DOI: 10.1016/j.neuropharm.2014.11.026
• Languages: English
• ISSNs: 0028-3908

Abstract

Abstract: On-demand postsynaptic synthesis and release of endocannabinoid lipids and subsequent binding to presynaptic CB1 receptors (CB1Rs) mediates short and long-term depression (LTD) of excitatory transmission in many brain regions. However, mechanisms involved in the synthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG) by diacylglycerol lipase α (DGLα) are poorly understood. Since Gq -coupled receptor activation can stimulate production of a major DGL substrate 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG) by PLCβ, we sought to determine if 2-AG biosynthesis was limited only by a lack of substrate availability, or if other pathways, such as Ca 2+ signaling, also need to be simultaneously engaged. To address this question, we loaded medium spiny neurons of the dorsolateral striatum with SAG while monitoring excitatory synaptic inputs. SAG-loading had no significant effect on evoked excitatory synaptic currents when cells were voltage-clamped at −80 mV. However, depolarization of MSNs to −50 mV revealed a SAG-loading dependent decrease in the amplitude of excitatory currents that was accompanied by an increase in paired pulse ratio, consistent with decreased glutamate release. Both effects of loading SAG at −50 mV were blocked by chelation of postsynaptic Ca 2+ using BAPTA or by bath application of tetrahydrolipstatin (THL), a DGL inhibitor. Loading of SAG into glutamatergic pyramidal neurons of the amygdala similarly inhibited excitatory synaptic inputs and increased the PPR. SAG-induced depression was absent in both regions from mice lacking CB1Rs. These data show that increasing substrate availability alone is insufficient to drive 2-AG mobilization and that DGL-dependent synaptic depression via CB1R activation requires postsynaptic Ca 2+ signals. Highlights: Neurons were loaded with a diacylglycerol precursor of 2-AG, a major endocannabinoid. This caused retrograde depression of excitatory inputs at −50 mV but not −80 mV. Synaptic depression at −50 mV was prevented by chelating postsynaptic calcium. Synaptic depression required diacylglycerol lipase (DGL) activity and CB1 receptors.