| First Author | Tong J | Year | 2017 |
| Journal | J Neurosci | Volume | 37 |
| Issue | 11 | Pages | 3030-3044 |
| PubMed ID | 28209735 | Mgi Jnum | J:239811 |
| Mgi Id | MGI:5881830 | Doi | 10.1523/JNEUROSCI.2810-16.2017 |
| Citation | Tong J, et al. (2017) The Epac-Phospholipase Cepsilon Pathway Regulates Endocannabinoid Signaling and Cocaine-Induced Disinhibition of Ventral Tegmental Area Dopamine Neurons. J Neurosci 37(11):3030-3044 |
| abstractText | Exchange protein directly activated by cAMP (Epac) is a direct effector for the ubiquitous second messenger cAMP. Epac activates the phospholipase Cepsilon (PLCepsilon) pathway. PLCbeta has been linked to the synthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG). Here, we report that Epac facilitates endocannabinoid-mediated retrograde synaptic depression through activation of PLCepsilon. Intracellular loading of a selective Epac agonist 8-CPT-2Me-cAMP into ventral tegmental area (VTA) dopamine neurons enabled previously ineffective stimuli to induce depolarization-induced suppression of inhibition (DSI) and long-term depression of IPSCs (I-LTD) in the VTA. DSI and I-LTD are mediated by 2-AG since they were blocked by a diacylglycerol lipase inhibitor. The effects of 8-CPT-2Me-cAMP on DSI and I-LTD were absent in Epac2 and PLCepsilon knock-out mice, but remained intact in Epac1 knock-out mice. These results identify a novel mechanism for on-demand synthesis of retrograde signaling 2-AG by the Epac2-PLCepsilon pathway. We investigated the functional significance of Epac2-PLCepsilon-2-AG signaling in regulating inhibitory synaptic plasticity in VTA dopamine neurons induced by in vivo cocaine exposure. We showed that cocaine place conditioning led to a decrease in the frequency and amplitude of spontaneous IPSCs and an increase in action potential firing in wild-type mice, but not in Epac2 or PLCepsilon knock-out mice. Together, these results indicate that the Epac2-PLCepsilon-2-AG signaling cascade contributes to cocaine-induced disinhibition of VTA dopamine neurons.SIGNIFICANCE STATEMENT 2-arachidonoylglycerol (2-AG) is an endogenous cannabinoid that depresses synaptic transmission through stimulation of CB1 receptors. Among the six isoforms of phospholipase C (PLC; PLCbeta, PLCgamma, PLCdelta, PLCepsilon, PLCzeta, PLCeta), only PLCbeta has been linked to 2-AG synthesis. Here we demonstrate that 8-CPT-2Me-cAMP, a selective agonist of the cAMP sensor protein Epac, enhances 2-AG-mediated synaptic depression in ventral tegmental area (VTA) dopamine neurons via activation of PLCepsilon. These results identify a novel mechanism for 2-AG synthesis via activation of the Epac-PLCepsilon pathway. Furthermore, we show that cocaine-induced conditioned place preference and disinhibition of VTA dopamine neurons were impaired in mice lacking Epac or PLCepsilon. Thus, the Epac-PLCepsilon signaling pathway contributes to cocaine-induced disinhibition of VTA dopamine neurons and formation of drug-associated memories. |
