SIGNALING THE BRAIN IN SYSTEMIC INFLAMMATION - WHICH VAGAL BRANCH IS INVOLVED IN FEVER GENESIS

Recent evidence has suggested a role of abdominal vagal afferents in t he pathogenesis of the febrile response. The abdominal vagus consists of five main branches (viz., the anterior and posterior celiac branche s, anterior and posterior gastric branches, and hepatic branch). The b ranch responsible for transducing a pyrogenic signal from the peripher y to the brain has not as yet been identified. In the present study, w e address this issue by testing the febrile responsiveness of male Wis tar rats subjected to one of four selective vagotomies: celiac (CBV), gastric (GBV), hepatic (HBV), or sham (SV). In the case of CBV, GBV, a nd HBV, only the particular vagal branch(es) was cut; for SV, all bran ches were left intact. After the postsurgical recovery (26-29 days), t he rats had a catheter implanted into the jugular vein. On days 29-32, their colonic temperature (T-c) responses to a low dose (1 mu g/kg) o f Escherichia coli lipopolysaccharide (LPS) were studied. Three days l ater, the animals were subjected to a 24-h food and water deprivation, and the effectiveness of the four vagotomies to induce gastric food r etention, pancreatic hypertrophy, and impairment of the portorenal osm otic reflex was assessed by weighing the stomach and pancreas and meas uring the specific gravity of bladder urine, respectively. Stomach mas s, pancreas mass, and urine density successfully separated the four ex perimental groups into four distinct clusters, thus confirming that ea ch type of vagotomy had a different effect on the indexes measured. Th e T-c responses of SV, CBV, and GBV rats to LPS did not differ and wer e characterized by a latency of similar to 40 min and a maximal rise o f 0.7 +/- 0.1, 0.6 +/- 0.1, and 0.9 +/- 0.2 degrees C, respectively. T he fever response of the HBV rats was different; practically no T-c ri se occurred (0.1 +/- 0.2 degrees C). The HBV appeared to be the only s elective abdominal vagotomy affecting the febrile responsiveness. We c onclude, therefore, that the hepatic vagus plays an important role in the transduction ofa pyrogenic signal from the periphery to the brain.