Brain processing of duodenal and portal glucose sensing

Peripheral and central glucose sensing play a major role in the regulation of food intake. Peripheral sensing occurs at duodenal and portal levels, although the importance of these sensing sites is still controversial. The present study aimed to compare the respective influence of these sensing pathways on the eating patterns; plasma concentrations of glucose, insulin and glucagon-like peptide-1 (GLP-1); and brain activity in juvenile pigs. In Experiment 1, we characterised the changes in the microstructure as a result of a 30-min meal in eight conscious animals after duodenal or portal glucose infusion in comparison with saline infusion. In Experiment 2, glucose, insulin and GLP-1 plasma concentrations were measured during 2 h after duodenal or portal glucose infusions in four anaesthetised animals. In Experiment 3, single photon emission computed tomography brain imaging was performed in five anaesthetised animals receiving duodenal or portal glucose or saline infusions. Both duodenal and portal glucose decreased the amount of food consumed, as well as the ingestion speed, although this effect appeared earlier with the portal infusion. Significant differences of glucose and GLP-1 plasma concentrations between treatments were found at the moment of brain imaging. Both duodenal and portal glucose infusions activated the dorsolateral prefrontal cortex and primary somatosensory cortex. Only duodenal glucose infusion was able to induce activation of the prepyriform area, orbitofrontal cortex, caudate and putamen, as well as deactivation of the anterior prefrontal cortex and anterior entorhinal cortex, whereas only portal glucose infusion induced a significant activation of the insular cortex. We demonstrated that duodenal and portal glucose infusions led to the modulation of brain areas that are known to regulate eating behaviour, which probably explains the decrease of food intake after both stimulations. These stimulation pathways induced specific systemic and central responses, suggesting that different brain processing matrices are involved.