Role of vagal afferent innervation in feeding and brain Fos expression produced by metabolic inhibitors

Hepatic vagal afferent fibers have been implicated in the feeding responses initiated by administration of 2,5-anhydro-D-mannitol (2,5-AM; an inhibito r of hepatic metabolism) and methyl palmoxirate (MP; an inhibitor of fat me tabolism). 2.5-AM and MP also increase brain Fos expression, an indicator o f neural activity, which suggests that Fos expression can reveal the centra l neural pathways involved in the stimulation of feeding by these agents. T o more closely test the hypothesis that brain Fos expression is related to the effects of 2,5-AM and MP on feeding, the vagus was lesioned by applicat ion of capsaicin, which destroys afferent fibers, directly to the cervical vagi. Perivagal capsaicin treatment blocked 2,5-AM-induced eating and atten uated MP-induced eating. Although perivagal capsaicin treatment attenuated MP-induced Fos expression, capsaicin treatment did not affect brain Fos exp ression produced by 2,5-AM. It is concluded that (1) brain Fos expression i s not always related to the effects of 2,5-AM on feeding, (2) capsaicin-sen sitive hepatic vagal afferent fibers carry the signal that stimulates feedi ng following 2,5-AM treatment, and (3) MP-induced feeding and brain Fos exp ression is mediated in part by capsaicin-sensitive fibers. (C) 2001 Elsevie r Science B.V. All rights reserved.