Neuroimmune mechanisms of alcohol reward

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PROJECT SUMMARY/ABSTRACT The prevailing dogma in the alcohol field is that the rewarding properties of ethanol (EtOH) result from enhancement of ventral tegmental area (VTA) dopamine (DA) neural activity and accompanying DA release in the mesolimbic reward system. In preliminary studies, we will demonstrate that some of EtOH’s effects on midbrain neurons and NAc DA release are mediated by peripheral substrates including DA D2-subtype 2 receptor (D2R) expressing monocyte-derived macrophages (MDMs). These findings suggest a neuroimmune interaction for acute EtOH use and challenge the dogma that EtOH has exclusively central effects on DA neuronal activity, release, and reward. Our proposed studies constitute a focused investigation into the role of neuroimmune interactions in EtOH effects on VTA neurons, DA transmission, and EtOH reward and consumption. The core thesis is that acute EtOH enhancement of mesolimbic DA transmission and EtOH reward is mediated by EtOH enhancement of blood DA, subsequent activation of D2R-expressing MDMs, and subsequent cytokine modulation of VTA neurons, that are responsible for chronic adaptations in VTA GABA neurons and DA release. Prior and preliminary evidence supporting our hypothesis include: 1) Peripheral DA increases the activity of DA neurons and NAc DA release, reduces locomotor activity, and promotes reward via peripheral D2Rs; 2) EtOH enhances blood DA, inhibits VTA GABA neurons, enhances brain DA, and reduces intoxication via peripheral D2Rs; 3) EtOH induces microglia activation and enhances D2 receptor expression on monocytes, neurons, and microglia; 4) Depletion of MDMs reduces EtOH effects on VTA GABA neurons and DA release; 5) Select cytokines enhance VTA neuron excitability and DA release; 6) Last, we show preliminary evidence of DA and ATP co-release from DA terminals, and motility effects of EtOH on microglia, which indicate further study for potential NAc EtOH immune interactions in vivo. These data will provide new, fundamental knowledge on the neurobiology of EtOH reward and dependence and the role of peripheral substrates that may help improve drug development efforts. To test the hypotheses, we propose two Specific Aims: 1) Define the role of peripheral neuroimmune interactions in EtOH effects on VTA GABA neurons and NAc DA release, and related behaviors; 2) Describe effects of EtOH on NAc DA terminals and microglia, co-release of DA and ATP. We will use wild-type and transgenic mouse models (GAD67-GFP knock-in; VGAT-Chr2, VGAT-Cre/GAD67-GFP; and MaFIA mice) and MDM depletion to study neurochemical and electrochemical recordings of DA release. Cytometry techniques will be used to determine cytokine factors involved in mesolimbic alterations. Multiphoton microscopy approaches to study microglia chemotaxis in the context of DA and ATP as measured by fast scan cyclic voltammetry. Multiphoton microscopy will be used in vivo through endoscopic relay gradient index lenses to study GFP labeled satellite microglia surveillance while measured dopamine release using a red shifted optical sensor for detecting DA release, which will be performed on mice undergoing chronic intermittent EtOH (CIE) induction, thus describing neuroimmune activity from first exposure to EtOH, through to dependence. Scientific rigor is high considering the use of conventional behavioral, pharmacological, electrochemical, microscopy and molecular tools.