To examine the role of leptin in the immune function of the brain, we examined the effect of leptin on interleukin-1 beta (IL-1 beta) expression in mouse primary cultured glial cells. The expression of leptin receptor isoforms Ob-Ra and Ob-Rb mRNA was detected by RT-PCR analysis of total RNA from primary cultured glial cells. Protein of leptin receptor was also expressed in mouse primary cultured glial cells as evaluated by Western blotting analysis. Leptin increased the expression of IL-1 beta mRNA evaluated by RT-PCR. The expression of IL-1 beta transcript peaked 2 to 6 h after leptin application. These results indicate that leptin could induce IL-1 beta transcript in the brain and that one of the target cells of the leptin-induced IL-1 beta transcript may be a glial cell.