Distribution, cellular localization and functional role of CCR2 chemokine receptors in adult rat brain

Recent studies demonstrated that the chemokine monocyte chemoattractant protein-1 (MCP-1)/CCL2 and its receptor, CCR2, play important roles in various brain diseases. In this study, using quantitative autoradiography, we studied the pharmacological properties of [I-125]MCP-1/CCL2 binding in rat brain and we clearly showed the distribution of CCR2 receptors in cerebral cortex, nucleus accumbens, striatum, amygdala, thalamus, hypothalamus, hippocampus, substantia nigra, mammillary bodies and raphe nuclei. Moreover, using double fluorescent immunohistochemistry, we showed that CCR2 receptors were constitutively expressed on neurons and astrocytes. Using RT-PCR methods, we demonstrated that CCR2 mRNA is present in various brain areas described above. Four hours after an acute intraperitoneal lipopolysaccharide injection, we showed that MCP-1/CCL2 binding was up-regulated in several brain structures; this effect took place on both CCR2B labelled neurons and astrocytes and to a lesser extent on activated microglia. To explore neurobiological function of CCR2, actimetric study was carried out. After intracerebroventricular injections of MCP-1/CCL2, we showed that motor activity was markedly decreased. Our results provide the first evidence for constitutive CCR2 receptor expression with precise neuroanatomical and cellular localizations in the brain, and its regulation during an inflammatory process, suggesting that MCP-1/CCL2 and CCR2 play important physiological and pathophysiological role(s) in the CNS.