Tuttle, Jared; Payne, Andrew; Obray, J Daniel; Steffensen, Scott (Brigham Young University)
Faculty Advisor: Steffensen, Scott (Family, Home, and Social Sciences; Psychology)
A subpopulation of ventral tegmental area (VTA) GABA neurons express connexin-36 (Cx36) gap junctions (GJs). Activation of GJ-mediated electrical coupling between VTA GABA neurons supports brain stimulation reward and alcohol reward is lowered in Cx36 KO mice due to a hyper-dopamine (DA) state. The aim of this study was to further evaluate the role of a subpopulation of Cx36+ VTA GABA neurons in alcohol reward and dependence. To accomplish this study, we customized a Gq-coupled Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) viral vector to only express in Cx36+ neurons (AAV8.hCx36.hM3D(Gq)-mCherry.WPRE.rBG) in the VTA. The hM3Dq viral vector was infused into male CD-1 GAD GFP mice and male Wistar rats. The animals were then given 10-14 days to recover prior to experimentation. A control virus (AAV9.CB7.CI.mCherry.WPRE.rBG) was used for comparison. We implemented standard cell-attached mode electrophysiology to evaluate the effects of clozapine-n-oxide (CNO; the ligand for DREADDs) on VTA GABA and DA neuronal activity. We found a robust enhancement of VTA GABA neuron firing rate in hM3Dq+ neurons with 20 _M CNO ex vivo. Surprisingly, while investigating CNO effects on VTA DA neuron firing rate, we found that CNO activation of hM3Dq+ VTA GABA neurons increased DA neuron activity, suggesting that Cx36+ VTA GABA neurons indirectly modulate local VTA DA neurons. Intraperitoneal CNO (3 mg/kg) also enhanced the firing rate of VTA GABA neurons in vivo. Administration of CNO reduced ethanol consumption (drink-in-the-dark paradigm) in both ethanol naïve and ethanol dependent hM3Dq-injected mice as compared to controls, suggesting that activation of Cx36+ neurons in the VTA is enough to block ethanol consumption in both naïve and dependent animals. Taken together, these findings support previous studies indicating that enhanced electrical coupling between VTA GABA neurons is rewarding and promotes reward and lowers the hedonic value of ethanol.