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

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.

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.

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.

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.

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.