RESUMO
Intraperitoneal (IP) or intraportal epinephrine (E) administration produces strong hypophagia in rats whereas intravenous or intramuscular (IM) injection does not. These results suggest that E acts on liver to control food intake through vagal afferents to the brain. In the present work, immediate-early gene c-fos expression was used as an index of neuronal activity, comparing the respective effects of IP and IM E on food intake and on activation of brain areas that receive vagal information. Male Wistar rats were IP or IM injected with saline or E (100 micrograms/kg). In a first experiment, food intake was measured. In a second experiment, c-fos expression in different brain areas was assessed immunohistochemically. IP E administration reduced food intake by 75% (p < 0.01) whereas IM E had no effect. C-fos expression results showed that those solitary tract nucleus/area postrema regions receiving gastrointestinal and hepatic vagal afferents were specifically activated by IP E administration. These results support the possibility that E decreases food intake through a hepatic action involving vagal sensory neurons. However, higher integration levels of vagal information, such as lateral parabrachial nucleus or paraventricular nucleus, do not seem to be implicated in IP E effect on food intake.