Acute third ventricular administration of leptin decreases protein and fat in self-selecting rats

The peripheral administration of leptin reduces food intake (FI) body weight gain (BWG) and modifies food choice. The aim of this study was to examine the effect of acute cerebral injections of leptin on food selection in rats. Male rats were first adapted to the food choice paradigm (protein, carbohydrate, fat) for 3 weeks. They were then implanted with a cannula in the third ventricle. Leptin (leptin group=L) or saline (control group=C) injections were performed at either the beginning or the end of the night at 4-day intervals. FI was recorded continuously, 3 days before, during and then after injections. Rats were sacrificed 86 h after the second injection. After both injections, BWG and FI were reduced. The reduction in FI concerned only nocturnal intake, whatever the timing of the injection. When the injection was given at the beginning of the night, the reductions after a 1-h latency period were -45% and -27.5% during the first and second days, respectively. Following the second injection, the same effects were observed immediately (-16% and -41%, respectively). Only the fat and protein intakes were significantly reduced. This lower FI was due to a reduction in meal size and duration. The reduction resulted in a lower BWG and total white adipose tissue mass. At the time of sacrifice, 6 h after food deprivation, leptinemia and insulinemia were reduced in leptin-treated rats. Glycemia values were identical. It was thus demonstrated that central leptin was a satiation factor rather than a satiety factor.