1. ¹Department of Psychiatry, UNC School of Medicine, Chapel Hill, NC, USA
2. ²Department of Pharmacology, UNC School of Medicine, Chapel Hill, NC, USA
3. ³Bowles Center for Alcohol Studies, UNC School of Medicine, Chapel Hill, NC, USA
4. ⁴UNC Neuroscience Center, UNC School of Medicine, Chapel Hill, NC, USA
5. ⁵Neurobiology Curriculum, UNC School of Medicine, Chapel Hill, NC, USA

Correspondence: Dr GR Breese, Bowles Center for Alcohol Studies, UNC School of Medicine, Thurston-Bowles Building, CB 7178, Chapel Hill, NC 27599-7178, USA. Tel: +1 919 966 3081; Fax: +1 919 966 5679; E-mail: george_breese@med.unc.edu

Received 8 November 2006; Revised 16 April 2007; Accepted 1 May 2007; Published online 6 June 2007.

Abstract

Previous investigations demonstrated that repeated stresses before an ethanol exposure sensitize ethanol withdrawal-induced anxiety-like behavior ('anxiety'). In addition to activating the hypothalamic–pituitary–adrenal axis, acute stress also elevates cytokines in brain. Initially, to test possible cytokine involvement in this stress/withdrawal protocol, cytokines were increased in brain with 2 weekly repeated lipopolysaccharide (LPS) administrations (1000 /kg) (LPS/withdrawal protocol) or with twice weekly intracerebroventricular (i.c.v.) administrations of the cytokines IL-1, CCL2 (MCP-1) or TNF (cytokine/withdrawal protocol) before exposure and withdrawal from a 5-day cycle of chronic ethanol diet. Both protocols sensitized withdrawal-induced anxiety and confirm cytokine involvement in the sensitized anxiety response. Testing of various doses of LPS (16–1000 g/kg) and TNF (3–100 ng, i.c.v.) demonstrated the dose-related nature of these protocols to sensitize withdrawal-induced anxiety. The sensitized anxiety was not produced by a single 5-day ethanol diet cycle or by repeated LPS or cytokine treatments alone. Likewise, sensitized anxiety in these protocols could not be attributed to differences in ethanol ingestion. When challenged with a subsequent re-exposure to a 5-day ethanol diet cycle 16 days after completion of the LPS/withdrawal or cytokine/withdrawal protocols, an increase in withdrawal-induced anxiety was observed—an indication of induction of an underlying persistent adaptive change. Finally, just as found previously with the stress/withdrawal protocol, administration of the benzodiazepine receptor antagonist flumazenil before the LPS or TNF treatments prevented anxiety sensitization. Together, these findings indicate that increased cytokine activity induces adaptive change that supports sensitization of ethanol withdrawal-induced anxiety that may be linked to GABA_A-receptor function.