CRF System and Methamphetamine Extinction

DESCRIPTION (provided by applicant): Methamphetamine (METH) is an addictive psychostimulant with extremely high relapse rates. Effective pharmacotherapies to treat METH addiction, and in particular to counter relapse have not yet been developed. Research in animal models implicates the corticotropin releasing factor (CRF) peptide system in the mechanisms of extinction and reinstatement of psychostimulant self- administration (SA). These studies suggest CRF receptors could be an important target for therapeutic development. The CRF peptide system is complex, consisting of two main types of receptors, CRF1 and CRF2, and four endogenous ligands, CRF, urocortin 1 (Ucn1), urocortin 2 (Ucn2) and urocortin 3 (Ucn3). Since many brain regions are innervated by several of these endogenous ligands and often contain both receptors, the contribution of individual components of the CRF system to extinction and relapse is difficult to resolve using pharmacological approaches. Recently developed knockout (KO) mice, deficient in components of the CRF system, provide a novel approach that can complement pharmacological studies and clarify the role of components of the CRF system in behaviors such as reinstatement of drug-seeking. Here we propose using CRF1KO, CRF2 KO and Ucn1 KO to study the role of components of the CRF system in extinction from, and reinstatement of SA of METH. We hypothesize that different components of the CRF system will be differentially involved in drug- versus stress-induced reinstatement of METH SA. The project will include 3 Specific Aims: (1) to compare rates of METH SA in CRF1, CRF2 and Ucn1 KO mice using operant intravenous procedures. We hypothesize that CRF1 KO will show slightly slower acquisition rates of METH SA than other genotypes, but that all three genotypes will ultimately reach a similar level of METH SA. (2) To compare rates of extinction from METH SA in CRF1, CRF2 and Ucn1 KO mice. We hypothesize that CRF2 KO mice will show faster rates of extinction from METH SA compared to other genotypes. (3) To compare reinstatement of METH SA in CRF1, CRF2 and Ucn1 KO mice following a priming dose of METH or exposure to stress (metabolic and physical). We hypothesize that drug-induced reinstatement will be attenuated in CRF1 KO, but not in CRF2 or Ucn1 KO mice, and that stress-induced reinstatement will be attenuated in CRF2 KO mice suggesting that it involves endogenous urocortins. Analysis of stress- induced reinstatement in Ucn1 KO mice will further delineate whether this behavior is mediated by Ucn1 versus Ucn2 or Ucn3 peptides. PUBLIC HEALTH RELEVANCE: Methamphetamine (METH) is an addictive psychostimulant with extremely high relapse rates. Effective pharmacotherapies to treat METH addiction, and in particular to counter relapse, have not yet been developed. This research will use an animal model of METH self-administration to examine the involvement of the corticotropin releasing factor (CRF) peptide system in the mechanisms of extinction and reinstatement of METH-seeking behavior. These studies will determine if CRF receptors could be an important target for therapeutic development.