Opposite influence of carbohydrates and fat on hypothalamic neurotensin in Long-Evans rats

Neurotensin inhibits food intake when injected in the central nervous system and is released after fat ingestion. The aim of the present study was to measure it in different brain areas and to determine if it is involved in the long-term variations in food intake induced by the ingestion of a high-fat (HF) diet. We compared the results with those obtained with 2 low-fat [high-carbohydrates (HC)] diets and a well-balanced diet. For this purpose, weanling male Long-Evans rats were fed ad libitum for 14 weeks either on a control diet, a HF diet or a HC diet. The rats with the HC (high-starch) diet were divided into 2 subgroups: the first (HC) drank water and the second (HCS) drank a 25% sucrose solution. During the last week of the experiment, energy intake of the HCS rats was significantly greater than that of the 3 other groups of rats (+17.2%; p < 0.01; +27.1%; p < 0.001 and +34.6%; P < 0.001 vs the control, HC and HF rats respectively). NT did not vary in the midbrain and particularly in the ventral tegmental area. Its concentrations were significantly higher in the 2 HC groups than in the HF rats both in the paraventricular (PVN; p < 0.02) and dorsomedial nuclei (DMN; p < 0.03). In the DMN, they were positively correlated with energy intake (r = 0.39; p = 0.027). These results indicate that hypothalamic neurotensin is indeed involved in the long-term modulation of feeding behavior by diet composition and that fat is the more potent macronutrient for its regulation.