Electrical stimulation of afferent vagus nerve induces IL-1β expression in the brain and activates HPA axis

Possible roles of the afferent vagus nerve in regulation of interleukin (IL)-1 beta expression in the brain and hypothalamic-pituitary-adrenal (HPA) axis were examined in anesthetized rats. Levels of IL-1 beta mRNA and protein in the brain were measured by comparative RT-PCR and ELISA. Direct electrical stimulation of the central end of the vagus nerve was performed continuously for 2 h. The afferent stimulation of the vagus nerve induced increases in the expression of mRNA and protein levels of IL-1 beta in the hypothalamus and the hippocampus. Furthermore, expression of corticotropin-releasing factor mRNA was increased in the hypothalamus 2 h after vagal stimulation. Plasma levels of ACTH and corticosterone were also increased by this stimulation. The present results indicate that activation of the afferent vagus nerves itself can induce production of IL-1 beta in the brain and activate the HPA axis. Therefore, the afferent vagus nerve may play an important role in transmitting peripheral signals to the brain in the infection and inflammation.