Increased c-Fos expression in nodose ganglion in rats with electrical vagus nerve stimulation.

BACKGROUND: Central nervous system receives information from the gut and modifies food intake mainly by vagus nerves. Some our data show that long-term electrical vagus nerve stimulation (VNS), which "mimics" satiety signal from gut, may cause reduction of body mass and decrease in food intake. OBJECTIVE: The purpose of this study was to assess the effects of chronic vagal stimulation on neurons in the nodose ganglions of vagus nerves, analyzed by c-Fos expression and image analysis. METHODS: Male Wistar rats (n = 24) were implanted with microstimulator (MS) and kept during the whole study (3 months) on high calorie diet. Sub-diaphragmatic left vagal nerve was stimulated by electrical rectangular pulses duration 10 ms, amplitude 200 mV, frequency 0.05 Hz generated by MS. Twelve rats (6--control and 6--MS implanted) were used for 3-week and 3-month experiments respectively. At the end of experiments the nodose ganglions of both vagus nerves (left and right) were taken, formalin fixed and paraffin-embedded specimens were made. The nodose ganglions neurons were identified by immunochemistry (PGP 9.5 as a marker) and the percentage of c-Fos positive neurons (anti c-Fos as a marker) were evaluated. RESULTS: Assessment of c-Fos positive neurons in nodose ganglia of vagal nerve showed significant increase in percentage of positive cells in the left nodose ganglion (4.19%) and non significant in the right nodose ganglion (2.64 %) compared to control (1.44%) in 3-week experiment. Data obtained from 3-month experiment were similar: (4.97%; 2.66% and 1.68%) for left, right and control respectively. In both experiments number of c-Fos positive neurons was higher in left vagal ganglion compared to the right ganglion and control. There were no significant differences between 3-week and 3-month experimental groups. CONCLUSIONS: Increase in c-Fos expression in left nodose ganglion neurons confirms the afferent transmission of the signal (generated by MS) from periphery to the brain by the vagal nerves.