Mechanisms of cannabinoid CB2 receptor-mediated reduction of dopamine neuronal excitability in mouse ventral tegmental areaResearch in context
Zegang Ma,
Fenfei Gao,
Brett Larsen,
Ming Gao,
Zhihua Luo,
Dejie Chen,
Xiaokuang Ma,
Shenfeng Qiu,
Yu Zhou,
Junxia Xie,
Zheng-Xiong Xi,
Jie Wu
Affiliations
Zegang Ma
Department of Physiology, Shandong Provincial Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders and State Key Disciplines: Physiology, Medical College of Qingdao University, Qingdao 266071, China; Department of Neurobiology, St. Joseph's Hospital and Medical Center, Barrow Neurological Institute, Phoenix, AZ 85013, USA
Fenfei Gao
Department of Pharmacology, Shantou University Medical College, Shantou, Guangdong 210854, China; Department of Neurobiology, St. Joseph's Hospital and Medical Center, Barrow Neurological Institute, Phoenix, AZ 85013, USA
Brett Larsen
Department of Neurobiology, St. Joseph's Hospital and Medical Center, Barrow Neurological Institute, Phoenix, AZ 85013, USA; Department of Basic Medical Sciences, University of Arizona College of Medicine, Phoenix, AZ 85004, USA
Ming Gao
Department of Neurobiology, St. Joseph's Hospital and Medical Center, Barrow Neurological Institute, Phoenix, AZ 85013, USA
Zhihua Luo
Department of Pharmacology, Shantou University Medical College, Shantou, Guangdong 210854, China
Dejie Chen
Department of Neurobiology, St. Joseph's Hospital and Medical Center, Barrow Neurological Institute, Phoenix, AZ 85013, USA; Department of Neurology, Yunfu People's Hospital, Yunfu, Guangdong 527300, China
Xiaokuang Ma
Department of Neurobiology, St. Joseph's Hospital and Medical Center, Barrow Neurological Institute, Phoenix, AZ 85013, USA; Department of Pharmacology, Shantou University Medical College, Shantou, Guangdong 210854, China; Department of Basic Medical Sciences, University of Arizona College of Medicine, Phoenix, AZ 85004, USA
Shenfeng Qiu
Department of Basic Medical Sciences, University of Arizona College of Medicine, Phoenix, AZ 85004, USA
Yu Zhou
Department of Physiology, Shandong Provincial Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders and State Key Disciplines: Physiology, Medical College of Qingdao University, Qingdao 266071, China
Junxia Xie
Department of Physiology, Shandong Provincial Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders and State Key Disciplines: Physiology, Medical College of Qingdao University, Qingdao 266071, China
Zheng-Xiong Xi
Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD 21224, USA
Jie Wu
Department of Physiology, Shandong Provincial Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders and State Key Disciplines: Physiology, Medical College of Qingdao University, Qingdao 266071, China; Department of Neurobiology, St. Joseph's Hospital and Medical Center, Barrow Neurological Institute, Phoenix, AZ 85013, USA; Department of Pharmacology, Shantou University Medical College, Shantou, Guangdong 210854, China; Department of Neurology, Yunfu People's Hospital, Yunfu, Guangdong 527300, China; Corresponding author at: Divisions of Neurology and Neurobiology, St. Joseph's Hospital and Medical Center, Barrow Neurological Institute, 350 W Thomas Road, Phoenix, AZ, USA.
Background: We have recently reported that activation of cannabinoid type 2 receptors (CB2Rs) reduces dopamine (DA) neuron excitability in mouse ventral tegmental area (VTA). Here, we elucidate the underlying mechanisms. Methods: Patch-clamp recordings were performed in mouse VTA slices and dissociated single VTA DA neurons. Findings: Using cell-attached recording in VTA slices, bath-application of CB2R agonists (JWH133 or five other CB2R agonists) significantly reduced VTA DA neuron action potential (AP) firing rate. Under the patch-clamp whole-cell recording model, JWH133 (10 μM) mildly reduced the frequency of miniature excitatory postsynaptic currents (mEPSCs) but not miniature inhibitory postsynaptic currents (mIPSCs). JWH133 also did not alter evoked EPSCs or IPSCs. In freshly dissociated VTA DA neurons, JWH133 reduced AP firing rate, delayed AP initiation and enhanced AP after-hyperpolarization. In voltage-clamp recordings, JWH133 (1 μM) enhanced M-type K+ currents and this effect was absent in CB2−/− mice and abolished by co-administration of a selective CB2R antagonist (10 μM, AM630). CB2R-mediated inhibition in VTA DA neuron firing can be mimicked by M-current opener (10 μM retigabine) and blocked by M-current blocker (30 μM XE991). In addition, enhancement of neuronal cAMP by forskolin (10 μM) reduced M-current and increased DA neuron firing rate. Finally, pharmacological block of synaptic transmission by NBQX (10 μM), D-APV (50 μM) and picrotoxin (100 μM) in VTA slices failed to prevent CB2R-mediated inhibition, while intracellular infusion of guanosine 5'-O-2-thiodiphosphate (600 μM, GDP-β-S) through recording electrode to block postsynaptic G-protein function prevented JWH133-induced reduction in AP firing. Interpretation: Our results suggest that CB2Rs modulate VTA DA neuron excitability mainly through an intrinsic mechanism, including a CB2R-mediated reduction of intracellular cAMP, and in turn enhancement of M-type K+ currents. Fund: This research was supported by the Barrow Neuroscience Foundation, the BNI-BMS Seed Fund, and CNSF (81771437). Keywords: Cannabinoid, CB2 receptor, Ventral tegmental area, Dopamine neuron
