Keimpema_2013_Sci.Rep_3_2093

Endocannabinoids are small signaling lipids, with 2-arachidonoylglycerol (2-AG) implicated in modulating axonal growth and synaptic plasticity. The concept of short-range extracellular signaling by endocannabinoids is supported by the lack of trans-synaptic 2-AG signaling in mice lacking sn-1-diacylglycerol lipases (DAGLs), synthesizing 2-AG. Nevertheless, how far endocannabinoids can spread extracellularly to evoke physiological responses at CB(1) cannabinoid receptors (CB(1)Rs) remains poorly understood. Here, we first show that cholinergic innervation of CA1 pyramidal cells of the hippocampus is sensitive to the genetic disruption of 2-AG signaling in DAGLalpha null mice. Next, we exploit a hybrid COS-7-cholinergic neuron co-culture system to demonstrate that heterologous DAGLalpha overexpression spherically excludes cholinergic growth cones from 2-AG-rich extracellular environments, and minimizes cell-cell contact in vitro. CB(1)R-mediated exclusion responses lasted 3 days, indicating sustained spherical 2-AG availability. Overall, these data suggest that extracellular 2-AG concentrations can be sufficient to activate CB(1)Rs along discrete spherical boundaries to modulate neuronal responsiveness.