Localization of Diacylglycerol Lipase-α around Postsynaptic Spine Suggests Close Proximity between Production Site of an Endocannabinoid, 2-Arachidonoyl-glycerol, and Presynaptic Cannabinoid CB1 Receptor

Abstract

2-Arachidonoyl-glycerol (2-AG) is an endocannabinoid that is released from postsynaptic neurons, acts retrogradely on presynaptic cannabinoid receptor CB1, and induces short-and long-term suppression of transmitter release. To understand the mechanisms of the 2-AG-mediated retrograde modulation, we investigated subcellular localization of a major 2-AG biosynthetic enzyme, diacylglycerol lipase-␣ (DAGL␣), by using immunofluorescence and immunoelectron microscopy in the mouse brain. In the cerebellum, DAGL␣ was predominantly expressed in Purkinje cells. DAGL␣ was detected on the dendritic surface and occasionally on the somatic surface, with a distal-to-proximal gradient from spiny branchlets toward somata. DAGL␣ was highly concentrated at the base of spine neck and also accumulated with much lower density on somatodendritic membrane around the spine neck. However, DAGL␣ was excluded from the main body of spine neck and head. In hippocampal pyramidal cells, DAGL␣ was also accumulated in spines. In contrast to the distribution in Purkinje cells, DAGL␣ was distributed in the spine head, neck, or both, whereas somatodendritic membrane was labeled very weakly. These results indicate that DAGL␣ is essentially targeted to postsynaptic spines in cerebellar and hippocampal neurons, but its fine distribution within and around spines is differently regulated between the two neurons. The preferential spine targeting should enable efficient 2-AG production on excitatory synaptic activity and its swift retrograde modulation onto nearby presynaptic terminals expressing CB1. Furthermore, different fine localization within and around spines suggests that the distance between postsynaptic 2-AG production site and presynaptic CB1 is differentially controlled depending on neuron types.

The evolution and comparative neurobiology of endocannabinoid signalling

“…DSE and DSI are not observed in DAGLa-knockout mice, indicating that 2-AG mediates these mechanisms of synaptic plasticity [18,19]. DAGLa is concentrated postsynaptically in dendritic spines that are apposed to CB 1 -expressing axon terminals [62], which is consistent with the notion that 2-AG is synthesized postsynaptically but acts presynaptically. The 2-AG degrading enzyme MAGL is localized presynaptically in the axons of neurons, most notably in glutamatergic neurons [20,63] and the duration of DSI and DSE in MAGL-knockout mice is prolonged when compared with wild-type mice, indicating that MAGL controls the temporal dynamics of 2-AG/CB 1 -mediated retrograde synaptic signalling [64,65].…”

A neuroscientist's guide to lipidomics

“…4). Type I mGluR, PLC-β and DGL-α are localized at the perisynapse (light red), a region of the dendritic spine that borders the postsynaptic density (purple) [63][64][65][66] . 2-AG crosses the synaptic cleft and activates presynaptic CB 1 cannabinoid receptors (CB 1 R), which suppress glutamate release.…”

“…Immunogold electron-microscopy studies of hippocampal and cerebellar neurons have shown that this lipid hydrolase is primarily localized in a subdivision of the dendritic spine, called the perisynapse, which forms a thin border (100-200 nm thick) around the postsynaptic density 63,64 . Along with DAG lipase α, this same area also contains type I mGlurs 65 and phospholipase C-β 66 , and might, thus, be viewed as a stable perisynaptic site for the receptor-operated release of 2-AG.…”

Protein purification and cloning of diacylglycerol lipase from rat brain

“…CB1 is expressed in the neurons of hippocampal CA1 and the molecular layer in the cerebellum (27). In addition, DGLa is distributed in hippocampal neurons and dendrites of Purkinje cells in the molecular layer of the cerebellum (14,28). In the hippocampal neurons and the Purkinje cells of cerebellum, endocannabinoids have been shown to participate in DSI (8,29).…”