DUODENAL NUTRIENT INFUSIONS DIFFERENTIALLY AFFECT SHAM-FEEDING AND FOS EXPRESSION IN RAT-BRAIN STEM

Duodenal infusions of macronutrients inhibit sham and normal feeding. Neural substrates of this response were studied by infusing glucose, l inoleic acid, an amino acid mixture, saline, or water into the duodenu m of unanesthetized rats and then measuring sham feeding of 30% sucros e or Fos expression in the dorsal vagal complex. Linoleic acid and ami no acids (both 1.5 kcal) and glucose (4.5 kcal) suppressed sham feedin g relative to control infusions, and all three macronutrients triggere d Fos expression in the nucleus of the solitary tract and area postrem a. Although there were significant quantitative differences, the subnu clear distribution pattern of Fos-expressing neurons was not different for the three macronutrients and was largely localized to the medial, dorsomedial, and commissural subnuclei of the nucleus of the solitary tract and the area postrema. Linoleic acid suppressed intake and stim ulated Fos expression similarly to glucose infusions of three times th e caloric value. Amino acids strongly suppressed sham feeding but trig gered relatively little Fos expression. These results indicate that th e intake-suppressing potency of duodenal macronutrients is dependent o n nutrient type, rather than simply caloric value, and that amino acid s, although potent inducers of satiety, affect ingestion by processes different from those subserving lipids and carbohydrates. Furthermore, the similar patterns of neuronal activation after different duodenal infusions may indicate a large degree of convergence at the level of p rimary and second-order sensory neurons, whereas the distinctly differ ent pattern obtained earlier with gastric distension indicates partial ly separate neural pathways for satiety signals generated by duodenal nutrients and gastric mechanoreceptors.