Alcohol-Preferring Rats Show Decreased Corticotropin-Releasing Hormone-2 Receptor Expression and Differences in HPA Activation Compared to Alcohol-Nonpreferring Rats

Authors

  • Weidong Yong,

    1. Institute of Laboratory Animal Science , Chinese Academy of Medical Sciences (CAMS) & Peking Union Medical College (PUMC), Beijing, China
    2. Department of Pediatrics , Indiana University School of Medicine, Indianapolis, Indiana
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    • The authors contributed equally to this study.
  • John Paul Spence,

    1. Department of Psychiatry , Indiana University School of Medicine, Indianapolis, Indiana
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    • The authors contributed equally to this study.
  • Robert Eskay,

    1. Laboratory of Clinical and Translational Studies , National Institute on Alcohol Abuse and Alcoholism/National Institute of Health, Bethesda, Maryland
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  • Stephanie D. Fitz,

    1. Department of Psychiatry , Indiana University School of Medicine, Indianapolis, Indiana
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  • Ruslan Damadzic,

    1. Laboratory of Clinical and Translational Studies , National Institute on Alcohol Abuse and Alcoholism/National Institute of Health, Bethesda, Maryland
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  • Dongbing Lai,

    1. Department of Medical and Molecular Genetics , Indiana University School of Medicine, Indianapolis, Indiana
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  • Tatiana Foroud,

    1. Department of Medical and Molecular Genetics , Indiana University School of Medicine, Indianapolis, Indiana
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  • Lucinda G. Carr,

    1. Department of Medicine , Indiana University School of Medicine, Indianapolis, Indiana
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  • Anantha Shekhar,

    1. Department of Psychiatry , Indiana University School of Medicine, Indianapolis, Indiana
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  • Julia A. Chester,

    1. Department of Psychological Sciences , Purdue University, West Lafayette, Indiana
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  • Markus Heilig,

    1. Laboratory of Clinical and Translational Studies , National Institute on Alcohol Abuse and Alcoholism/National Institute of Health, Bethesda, Maryland
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  • Tiebing Liang

    Corresponding author
    1. Department of Medicine , Indiana University School of Medicine, Indianapolis, Indiana
    • Reprint requests: Tiebing Liang, PhD, Department of Medicine, Indiana University School of Medicine, Clinical Building, Room 500A, 541 Clinical Drive, Indianapolis, IN 46202; Tel.: 317-274-7813; Fax: 317-274-2695; E-mail: tliang@iu.edu

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Abstract

Background

Corticotropin-releasing hormone (CRH) and urocortins (UCNs) bind to corticotropin-releasing hormone type 2 receptor (CRF2 receptor), a Gs protein-coupled receptor that plays an important role in modulation of anxiety and stress responses. The Crhr2 gene maps to a quantitative trait locus (QTL) for alcohol preference on chromosome 4 previously identified in inbred alcohol-preferring (iP) and-nonpreferring (iNP) F2 rats.

Methods

Real-time polymerase chain reaction was utilized to screen for differences in Crhr2 mRNA expression in the central nervous system (CNS) of male iP and iNP rats. DNA sequence analysis was then performed to screen for polymorphism in Crhr2 in order to identify genetic variation, and luciferase reporter assays were then applied to test their functional significance. Next, binding assays were used to determine whether this polymorphism affected CRF2 receptor binding affinity as well as CRF2 receptor density in the CNS. Finally, social interaction and corticosterone levels were measured in the P and NP rats before and after 30-minute restraint stress.

Results

Crhr2 mRNA expression studies found lower levels of Crhr2 mRNA in iP rats compared to iNP rats. In addition, DNA sequencing identified polymorphisms in the promoter region, coding region, and 3′-untranslated region between the iP and iNP rats. A 7 bp insertion in the Crhr2 promoter of iP rats altered expression in vitro as measured by reporter assays, and we found that CRF2 receptor density was lower in the amygdala of iP as compared to iNP rats. Male P rats displayed decreased social interaction and significantly higher corticosterone levels directly following 30-minute restraint when compared to male NP rats.

Conclusions

This study identified Crhr2 as a candidate gene of interest underlying the chromosome 4 QTL for alcohol consumption that was previously identified in the P and NP model. Crhr2 promoter polymorphism is associated with reduced mRNA expression in certain brain regions, particularly the amygdala, and lowered the density of CRF2 receptor in the amygdala of iP compared to iNP rats. Together, these differences between the animals may contribute to the drinking disparity as well as the anxiety differences of the P and NP rats.

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