We describe here the cloning and characterization of a rat homolog of the chemokine receptor CXCR3. The predicted amino acid sequence of rat CXCR3 contains 367 amino acid residues, sharing 96 and 87% amino acid sequence identity to the murine and human CXCR3, respectively. Among a large panel of chemokines tested, only interferon-inducible protein-10 (IP-10), interferon-gamma-induced monokine, and interferon-inducible T cell alpha-chemoattractant demonstrated specific abilities to induce an intracellular calcium mobilization response in human embryonic kidney 293 cells transfected with rat CXCR3 expression vector. (125)I-IP-10 competition binding studies to the CXCR3-transfected human embryonic kidney 293 cells demonstrated that human IP-10 and interferon-inducible T cell alpha-chemoattractant are more potent ligands than human interferon-gamma-induced monokine. Following our previous observation for the induced expression of IP-10 in focal stroke, we demonstrate here the time-dependent up-regulation of CXCR3 mRNA in the rat ischemic cortex after permanent occlusion of the middle cerebral artery. A significant increase in (125)I-IP-10-specific binding to ischemic cerebral cortical samples was obtained and paralleled the increase in CXCR3 mRNA expression. The changes in receptor expression and ligand binding correlate highly with known changes in leukocyte accumulation, and gliosis occurred after focal stroke. These data suggest that CXCR3/IP-10 may be a potential novel therapeutic target in focal stroke. In addition, the cloning of rat CXCR3 provides an important tool for the investigation of the pathophysiological role of CXCR3 in other rodent disease models.