Macrophage migration inhibitory factor modulates formalin induced behaviors in rats

Cytokine proteins are involved in different signaling pathways throughout the central nervous system. To study the efficacy of an inflammatory cytokine, the macrophage migration inhibitory factor (MIF), which acts via several receptor molecules including the receptor CXCR2, male rats' behaviors were determined after intracerebroventricular (ICY) administration of MIF. There were three treatments: One group received only the cytokine, a second group received MIF and an CXCR2 antagonist (SB265610), and a third, control group received only the carrier medium saline. All rats were subjected to a subcutaneous injection of formalin in the hind paw after the ICV administration. Pain behaviors induced after formalin injection showed increased values in the MIF group of licking in the first phase and increased values of flexing, licking and paw-jerk in the second phase. On the contrary, spontaneous behaviors induced by formalin injection changed alternatively between the two groups compared with saline. These results suggest a possible effect of cytokine MIF on central nervous processes implicated in pain modulation mediated by the receptor CXCR2.