Depolarization-induced suppression of excitation (DSE) is a major form of cannabinoid-mediated short-term retrograde neuronal plasticity and is found in numerous brain regions. Autaptically cultured murine hippocampal neurons are an architecturally simple model for the study of cannabinoid signaling, including DSE. The transient nature of DSE-tens of seconds-is probably determined by the regulated hydrolysis of the endocannabinoid 2-arachidonoyl glycerol (2-AG). No less than five candidate enzymes have been considered to serve this role: fatty acid amide hydrolase (FAAH), cyclooxygenase-2 (COX-2), monoacylglycerol lipase (MGL), and ␣/␤-hydrolase domain (ABHD) 6 and 12. We previously found that FAAH and COX-2 do not have a role in determining the duration of autaptic DSE. In the current study, we found that two structurally distinct inhibitors of MGL [N-arachidonoyl maleimide and 4-nitrophenyl 4-(dibenzo [d][1,3]dioxol-5-yl(hydroxy)methyl)piperidine-1-carboxylate (JZL184)] prolong DSE in autaptic hippocampal neurons, whereas inhibition of ABHD6 by N-methyl-N-[[3-(4-pyridinyl) phenyl]methyl]-4Ј-(aminocarbonyl)[1,1Јbiphenyl]-4-yl ester, carbamic acid (WWL70) had no effect. In addition, we developed antibodies against MGL and ABHD6 and determined their expression in autaptic cultures. MGL is chiefly expressed at presynaptic terminals, optimally positioned to break down 2-AG that has engaged presynaptic CB 1 receptors. ABHD6 is expressed in two distinct locations on autaptic islands, including a prominent localization in some dendrites. In summary, we provide strong pharmacological and anatomical evidence that MGL regulates DSE in autaptic hippocampal neurons and, taken together with other studies, emphasizes that endocannabinoid signaling is terminated in temporally diverse ways.

Cannabinoid receptors and their ligands constitute an endogenous signaling system that is found throughout the body, including the eye. This system can be activated by Δ 9 -tetrahydrocannabinol, a major drug of abuse. Cannabinoids offer considerable therapeutic potential in modulating ocular immune and inflammatory responses and in regulating intraocular pressure. The location of cannabinoid receptors 1 (CB 1 ) in the retina is known, but recently a constellation of proteins has been identified that produce and break down endocannabinoids (eCBs) and modulate CB 1 function. Localization of these proteins is critical to defining specific cannabinoid signaling circuitry in the retina.Here we show the localization of diacylglycerol lipase α and β (DGLα/β), implicated in the production of the eCB 2-arachidonoyl glycerol (2-AG); monoacylglycerol lipase (MGL) and α/β-hydrolase domain 6 (ABHD6), both implicated in the breakdown of 2-AG; cannabinoid receptor interacting protein 1a (CRIP1a), a protein that may modulate CB 1 function; Fatty acid amide hydrolase (FAAH) and N-acylethanolamine-hydrolyzing acid amidase (NAAA) which have been shown to break down the eCB anandamide and related acyl amides. In our most prominent finding, DGLα is present in post-synaptic Type 1 OFF cone bipolar cells juxtaposed to CB 1 -containing cone photoreceptor terminals. Interestingly, CRIP1a is reliably presynaptic to DGLα, consistent with a possible role in cannabinoid signaling, NAAA is restricted to retinal pigment epithelium (RPE), while DGLβ is limited to retinal blood vessels. These results taken together with previous anatomic and functional studies define specific cannabinoid circuitry likely to modulate eCB signaling at the first synapse of the retina as well as in the inner plexiform layer (IPL).

About 18.8 million American adults suffer depressive disorders that may occur with anxiety and substance abuse. Tetrahydrocannabinol (THC), a compound in marijuana, is a cannabinoid chemical that binds to and activates cannabinoid receptors (CB1) in the pre‐synaptic cell membrane as part of neuron‐to‐neuron transmission in the endocannabinoid system (ECS). Glutamate in the pre‐synaptic cell is released and binds to the post‐synaptic cell triggering the synthesis and release of 2‐arachidonoylglycerol (2‐AG). 2‐AG returns to the pre‐synaptic cell binding to and activating CB1 receptors. THC mimics 2‐AG action, and is used to study the ECS retrograde signaling system and its effect on appetite and mood. A protein from the pre‐synaptic cell, monoacylglycerol lipase (MAGL), hydrolyzes 2‐AG into arachidonic acid (AA) and glycerol controlling 2‐AG levels. When MAGL is hyperactive, too much 2‐AG degrades, which is hypothesized to contribute to depression and anxiety. Hypoactive MAGL activity creates an excess of 2‐AG. It is hypothesized that this can contribute to obesity and addictive behaviors. The Brown Deer Students Modeling a Research Topic Team, in alliance with MSOE, built a MAGL model using a 3D printer. Study of MAGL crystal structure may provide the key to regulating MAGL's enzymatic activity leading to therapies that will prevent neurodegenerative disorders. Supported by a grant from NIH‐NCRR‐SEPA