Depolarization‐induced retrograde synaptic inhibition in the mouse cerebellar cortex is mediated by 2‐arachidonoylglycerol

Abstract

Endocannabinoids acting on CB 1 cannabinoid receptors are involved in short-and long-term depression of synaptic transmission. The aim of the present study was to determine which endocannabinoid, anandamide or 2-arachidonoylglycerol (2-AG), is involved in depolarization-induced suppression of inhibition (DSI) in the cerebellar cortex, which is the most widely studied form of short-term depression. Depolarization of Purkinje cells in the mouse cerebellum led to an increase in intracellular calcium concentration and to suppression of the inhibitory input to these neurons (i.e. DSI occurred). Orlistat and RHC80267, two blockers of sn-1-diacylglycerol lipase, the enzyme catalysing 2-AG formation, abolished DSI by acting downstream of calcium influx. In contrast, DSI occurred also in the presence of a phospholipase C inhibitor. Intact operation of the calcium-dependent messengers calmodulin and Ca 2+ -calmodulin-dependent protein kinase II were necessary for DSI. DSI was potentiated by an inhibitor of the main 2-AG-degrading enzyme, monoacylglycerol lipase. Interference with the anandamide metabolizing enzyme, fatty acid amide hydrolase, did not modify DSI. Thus, three kinds of observations identified 2-AG as the endocannabinoid involved in DSI in the mouse cerebellum: DSI was abolished by diacylglycerol lipase inhibitors; DSI was potentiated by a monoglyceride lipase inhibitor; and DSI was not changed by an inhibitor of fatty acid amide hydrolase. Further experiments indicated that 2-AG is the endocannabinoid mediating short-term retrograde signalling also at other synapses: orlistat abolished DSI in the rat cerebellum, DSI in the mouse substantia nigra pars reticulata and depolarization-induced suppression of excitation in the mouse cerebellum.

The Endocannabinoid 2-Arachidonoyl-Glycerol Controls Odor Sensitivity in Larvae of Xenopus laevis

“…As to the autocrine pathway, we did not find any particular modulation of DAG lipases in ORNs, but nevertheless the odorinduced increase of [Ca 2ϩ ] i might cause 2-AG release [as reported in other neurons (Szabo et al, 2006;Hashimotodani et al, 2007)]. [Ca 2ϩ ] i transients during odorant stimulation would thus induce, via 2-AG release, a subsequent increase of sensitivity and signal-to-noise ratio.…”

Input-specific plasticity at excitatory synapses mediated by endocannabinoids in the dentate gyrus

“…However, DSE remained normal with this manipulation (44.7 ± 4 % depression, n = 4, p>0.05; Figure 6A). We also tested another chemically unrelated DGL inhibitor, Orlistat (Bisogno et al, 2003;Szabo et al, 2006). Loading 4 μM Orlistat in the postsynaptic cell also failed to block DSE (46 ± 6 % depression, n = 4, p>0.05; Figure 6B), strongly suggesting that DSE at the MCF-DGC synapse is independent of DGL activity.…”

“…Among the several eCBs that have been identified in the brain, 2-arachidonoyl glycerol (2-AG), is one of the most abundant Kogan and Mechoulam, 2006;Piomelli, 2003), and reportedly mediates DSI in cerebellum, striatum (Szabo et al, 2006) and presumably in hippocampus as well (Hashimotodani et al, 2007;Kim and Alger, 2004;Makara et al, 2005). The main enzyme responsible for 2-AG production, diacylglycerol lipase (DGL), is highly expressed in the SGL (Katona et al, 2006), suggesting that 2-AG may also be involved in DSE at the MCF-DGC synapse.…”

Exogenous and Endogenous Cannabinoids Suppress Inhibitory Neurotransmission in the Human Neocortex

“…Depolarization of postsynaptic neurons activates voltage-gated calcium channels and the increase in intracellular calcium concentration is a trigger of endocannabinoid production (Ohno-Shosaku et al, 2001;Wilson and Nicoll, 2001;Wallmichrath and Szabo, 2002;Kim and Alger, 2004;Szabo et al, 2006). Endocannabinoid production can also be triggered by activation of certain Ga q/11 protein-coupled receptors on postsynaptic neurons Galante and Diana, 2004;Straiker and Mackie, 2007).…”