Excessive alcohol drinking is an enormous public health burden in need of more radical therapy. Most health problems associated with excessive drinking are due to two types of drinking: (i) binge (BALs >0.08 grams % in a 2-hour period) and (ii) relapse (sustained heavy drinking for at least 2 days following a single or multiple abstinence periods). Previously, we showed that alcohol- preferring (P) rats express elevated levels of the GABAA subunits for alpha1, alpha2 and toll-like receptor 4 (TLR4) innate immunity receptors, and using specific siRNA vectors infused into the central amygdala (CeA), demonstrated that regulation of binge drinking at this site is mediated by GABAA a2 regulated TLR4 (a2/TLR4 axis). While the alpha1 subunit was also shown to regulate binge drinking, it was associated with the ventral pallidum (VP) and was independent of TLR4 (Liu et al., PNAS, 2011). In the current grant, we propose to better elucidate the mechanism responsible for the TLR4 effect, focusing on the chemokine monocyte chemotactic protein-1 (MCP-1) and the dopamine rate- limiting enzyme tyrosine hydroxylase (TH)--implicated by data obtained after the application was last submitted--and on brain sites that regulate different domains of the alcohol addiction cycle. The working hypothesis is that neuronal TLR4 induces MCP-1 expression via activation of cell type- specific transcription factors and it, in turn, functions as a neurotransmitter to stimulate dopamine release and excitability (inferred by TH) in select reward loci.
The specific aims are:
Aim I. Define the expression of GABAA a2/a1, TLR4, MCP-1 and/or TH at alcohol reward loci from P vs NP rats.
Aim II. Define the role played by the a2/TLR4 axis that encompasses MCP-1 and/TH at alcohol reward loci in impulsive binge drinking.
Aim III. Define the contribution of a1, a2, TLR4 and its downstream targets (MCP-1 and/or TH) at alcohol reward loci in compulsive relapse drinking.
Aim I V. Define the mechanism of TLR4-mediated regulation of binge drinking by focusing on downstream signals that upregulate MCP-1 and TH expression, through the use of the pHSVsiMCP-1 amplicon. Better understanding of the role of chemokines in neurotransmission and the regulation of distinct (viz. dopaminergic) neurons will help broaden current concepts of neuroimmune communication and their roles in excessive drinking. This highly innovative proposal will create a paradigm shift in understanding the relationship between innate immunity signals and neuronal responses that impact alcohol addiction. Use of non-toxic herpes simplex virus (HSV)- siRNA constructs to inhibit relevant genes at specific brain loci will define therapeutic gene targets and test the potential of gene therapy approaches for binge and relapse drinking.
The goal of the proposed research is to investigate the role played by interactive responses between signals induced by GABA and TLR4 receptors in mediating binge and relapse drinking. Successful completion of the proposed studies will create a paradigm shift in neuroscience.