Effects of chronic abdominal vagal stimulation of small-diameter neurons on brain metabolism and food intake

- Very high-frequency stimulation of the abdominal vagus was able to trigger action potentials.
- Two weeks of very high-frequency stimulation applied bilaterally at the abdominal vagus reduced daily food intake.
- This was associated with brainstem activation and, subsequently, to several higher order brain areas.
- Very high frequency stimulation was not associated with deleterious histological changes within the investigated time frame.

BackgroundAbdominal bilateral vagal stimulation reduces food intake in animals. However, the classical square wave, mA range current generator is poorly effective to evoke action potentials on A∂ and C neurons that represent the majority of vagal neurons at the abdominal level.Objective/Hypothesis(i)To ascertain the capability of very high-frequency stimulation schemes (pulsons) to trigger action potentials in abdominal vagal neurons in anaesthetized pigs. (ii) To compare these stimulation schemes with classical ones using PET imaging of brain metabolism and food intake behaviour in conscious pigs.MethodsThe current thresholds for pulsons (S2 & S3) and millisecond pulses (S1) required to trigger action potentials were calculated in 5 anaesthetized pigs using single fibre recording. Similar stimulation protocols were compared chronically to sham stimulation in 24 pigs. After two weeks of chronic stimulation, food intake and brain metabolism were investigated. The electrical characteristics and histology of the vagus nerve were also studied.ResultsS3 stimulation required a lower amount of charges to trigger an action potential. Chronically applied S2 & S3 activated the dorsal vagal complex and increased the metabolism of its afferent cortical structures. They also reduced energy intake together with a reduced ingestion of high fat and high sugar diets. All these effects were not observed for the S1 group. The vagal histology for the S1, S2 and S3 groups was not different from that of the sham.ConclusionsThese findings demonstrate that pulsons applied bilaterally on the abdominal vagus reduced food intake as a consequence of the activation of the brainstem and higher-order brain areas.