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J Neurosci. 2017 Feb 1;37(5):1139-1155. doi: 10.1523/JNEUROSCI.2002-16.2016. Epub 2016 Dec 16.

Genetic and Pharmacologic Manipulation of TLR4 Has Minimal Impact on Ethanol Consumption in Rodents.

Author information

1
Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, Texas 78712, harris@austin.utexas.edu.
2
Committee on the Neurobiology of Addictive Disorders, The Scripps Research Institute, La Jolla, California 92037.
3
Department of Psychiatry, Institute of Psychiatric Research, Indiana University School of Medicine, Indianapolis, Indiana 46202.
4
Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, Texas 78712.
5
Department of Psychiatry, University of Illinois, Chicago, Illinois 60612.
6
Molecular and Cellular Neuroscience Department and Mouse Behavioral Assessment Core, The Scripps Research Institute, La Jolla, California 92037.
7
Deparment of Chemistry, The Scripps Research Institute, La Jolla, California 92037.
8
Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, and.
9
Departments of Anesthesiology and Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.

Abstract

Toll-like receptor 4 (TLR4) is a critical component of innate immune signaling and has been implicated in alcohol responses in preclinical and clinical models. Members of the Integrative Neuroscience Initiative on Alcoholism (INIA-Neuroimmune) consortium tested the hypothesis that TLR4 mediates excessive ethanol drinking using the following models: (1) Tlr4 knock-out (KO) rats, (2) selective knockdown of Tlr4 mRNA in mouse nucleus accumbens (NAc), and (3) injection of the TLR4 antagonist (+)-naloxone in mice. Lipopolysaccharide (LPS) decreased food/water intake and body weight in ethanol-naive and ethanol-trained wild-type (WT), but not Tlr4 KO rats. There were no consistent genotypic differences in two-bottle choice chronic ethanol intake or operant self-administration in rats before or after dependence. In mice, (+)-naloxone did not decrease drinking-in-the-dark and only modestly inhibited dependence-driven consumption at the highest dose. Tlr4 knockdown in mouse NAc did not decrease drinking in the two-bottle choice continuous or intermittent access tests. However, the latency to ethanol-induced loss of righting reflex increased and the duration decreased in KO versus WT rats. In rat central amygdala neurons, deletion of Tlr4 altered GABAA receptor function, but not GABA release. Although there were no genotype differences in acute ethanol effects before or after chronic intermittent ethanol exposure, genotype differences were observed after LPS exposure. Using different species and sexes, different methods to inhibit TLR4 signaling, and different ethanol consumption tests, our comprehensive studies indicate that TLR4 may play a role in ethanol-induced sedation and GABAA receptor function, but does not regulate excessive drinking directly and would not be an effective therapeutic target.

SIGNIFICANCE STATEMENT:

Toll-like receptor 4 (TLR4) is a key mediator of innate immune signaling and has been implicated in alcohol responses in animal models and human alcoholics. Members of the Integrative Neuroscience Initiative on Alcoholism (INIA-Neuroimmune) consortium participated in the first comprehensive study across multiple laboratories to test the hypothesis that TLR4 regulates excessive alcohol consumption in different species and different models of chronic, dependence-driven, and binge-like drinking. Although TLR4 was not a critical determinant of excessive drinking, it was important in the acute sedative effects of alcohol. Current research efforts are directed at determining which neuroimmune pathways mediate excessive alcohol drinking and these findings will help to prioritize relevant pathways and potential therapeutic targets.

KEYWORDS:

(+)-naloxone; Toll-like receptor 4 knock-out; chronic intermittent ethanol vapor; drinking-in-the-dark; lipopolysaccharide; operant self-administration

PMID:
27986929
PMCID:
PMC5296793
DOI:
10.1523/JNEUROSCI.2002-16.2016
[Indexed for MEDLINE]
Free PMC Article

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