Cyclooxygenase in the vagal afferents: is it involved in the brain prostaglandin response evoked by lipopolysaccharide?

The vagal afferents are proposed to transmit abdominal immune signals to th e brain. In this immune-brain communication, prostaglandins might play a me diator role. In fact, prostaglandin receptors are abundant in the vagal aff erents. We examined here the presence of cyclooxygenase, an enzyme necessar y for prostaglandin biosynthesis, in the vagal afferents of rats. We also t ested whether the vagal afferents contribute to the elevation of prostaglan din E-2 in the brain after intraperitoneal injection of lipopolysaccharide. Under normal conditions, cyclooxygenase-1-like immunoreactivity was consti tutively expressed in the vagal afferents at their central terminals and in their cell bodies. Cyclooxygenase-2-like immunoreactivity was absent in th e vagal afferents under normal as well as lipopolysaccharide-challenged con ditions. Instead, cyclooxygenase-2-like immunoreactivity was induced in bra in endothelial cells by the lipopolysaccharide challenge. The elevation of prostaglandin E-2 in the cerebrospinal fluid after lipopolysaccharide chall enge was not inhibited, but was rather enhanced, by the bilateral vagotomy. These results suggest that the vagal afferents potentially generate prosta glandins, which may locally modulate the vagal signal transmission, but tha t the vagal efferents are not essential to the elevation of prostaglandin E -2 in the brain after intraperitoneal challenge with LPS. (C) 2000 Elsevier Science B.V. All rights reserved.