Reduced hindbrain and enteric neuronal response to intestinal oleate in rats maintained on high-fat diet

Rats maintained on a high-fat diet (HF) reduce their food intake less in re sponse to intestinal infusion of oleic acid than rats maintained on a low-f at diet (LF). Inhibition of gastric emptying by intestinal infusion of olea te also is attenuated in rats fed a high-fat diet. It is well documented th at intestinal oleate reduces food intake and inhibits gastric emptying via vagal sensory neurons. In addition, activation of intrinsic myenteric neuro ns participates in oleate-induced changes in gastrointestinal motility. To determine whether diminished behavioral and gastric reflex responses to int estinal oleate infusion is accompanied by reduced vagal sensory and myenter ic neuronal activation, we examined expression of Fos-like immunoreactivity (Fos-li) in the dorsal hindbrains and the small intestinal enteric plexuse s of rats maintained on HF or LF, following, intraintestinal infusion of ol eate (0.06 kcal/ml) or the oligosaccharide, maltotriose (0.26 kcal/ml). Fol lowing oleate infusion there was a dramatic increase in the number of Fos-l i nuclei in the NTS and AP of LF rats but not in HF rats. There also were s ignificantly more Fos-Li neuronal nuclei in the upper small intestinal subm ucosal and myenteric plexuses of the LF rats than the HF rats. In contrast to the effects of oleate infusion, maltotriose infusion significantly and s imilarly increased Fos-li nuclei in the hindbrains of both LF and HF rats. The results indicate that adaptation to high-fat diet selectively reduces v agal and enteric neuronal sensitivity to intestinal oleate and suggests tha t reduced sensitivity to the satiation and gastric inhibitory effects of ol eate in high-fat fed rats may be mediated by a selective reduction in the n euronal response to intestinal stimulation by fatty acid. (C) 2000 Elsevier Science B.V. All rights reserved.