1. ¹Specialized Neuroscience Research Program 2, John A Burns School of Medicine, University of Hawaii, Honolulu, HI, USA
2. ²Molecular Neuroendocrinology Laboratory, Max Planck Institute of Experimental Medicine, John A Burns School of Medicine, University of Hawaii, Honolulu, HI, USA
3. ³Department of Pharmacology, Faculty of Medicine, National University of Singapore, Singapore
4. ⁴Department of Pharmacology, School of Pharmacy, Fudan University, Shanghai, China

Correspondence: Dr C Todorovic, Specialized Neuroscience Research Project 2, John A Burns School of Medicine, 651, Ilalo Street, Honolulu, HI 96813, USA. E-mail: cedomir@hawaii.edu; Dr Y-Z Zhu, School of Pharmacy and Institute of Biomedical Sciences, Fudan University, 138 Yi Xue Yuan Rd, Shanghai 200032, China. E-mail: zhuyz@fudan.edu.cn

⁵These authors share equal contribution to this work.

Received 1 January 2007; Revised 17 October 2007; Accepted 26 November 2007; Published online 15 January 2008.

Abstract

Corticotropin-releasing factor (CRF) and cholecystokinin (CCK), two highly colocalized neuropeptides, have been linked to the etiology of stress-related anxiety disorders. Recent evidence points to the possibility that some of the anxiogenic effects of the central CCK system take place through interplay with the CRF system. The aim of the present study was to examine the effects of chronic, mild activation of CRF receptor 1 (CRF₁) on the central CCK system of the C57BL/6J mouse. As shown by in situ hybridization, real-Time PCR and immunohistochemistry, 5 days of intracerebroventricular (i.c.v.) injections of a subeffective dose (2.3 pmol) of cortagine, a CRF₁-selective agonist, resulted in an increase in CCK mRNA levels and CCK₂ receptor immunoreactivity in several brain regions, such as amygdala and hippocampus, known to be involved in the regulation of anxiety. Mice with elevated endogenous central CCK tone exhibited significantly higher anxiety-like behaviors in the open-field task and elevated plus maze, and enhanced conditioned fear. These behavioral changes were reversed by i.c.v. administration of the CCK₂-selective antagonist LY225910, after 5 days of priming with cortagine. Under the same conditions, the intraperitoneal administration of the CRF₁ antagonist antalarmin was ineffective. This result indicated that once the CCK system was sensitized by prior CRF₁ activation, it exhibited its anxiogenic effects, without influence by CRF₁, possibly because of its observed downregulation. In sum, our results provide a novel model for the interaction of the CRF and CCK systems contributing to the development of hypersensitive emotional circuitry.