Central leptin signaling transmits positive valence

Hunger resulting from food deprivation is associated with negative affect. This is supported by recent evidence showing that hunger-sensitive neurons drive feeding through a negative valence teaching signal. However, the complementary hypothesis that hormonal signals of energy surfeit counteract this negative valence, or even transmit positive valence, has received less attention. The adipose-derived hormone leptin signals in proportion to fat mass, is an indicator of energy surplus, and reduces food intake. Here, we showed that centrally-delivered leptin reduced food intake and conditioned a place preference in food-restricted as well as ad libitum fed rats. In contrast, leptin did not reduce food intake nor condition a place preference in obese rats, likely due to leptin resistance. Despite a well-known role for hindbrain leptin receptor signaling in energy balance control, hindbrain leptin delivery did not condition a place preference in food-restricted rats, suggesting that leptin acting in midbrain or forebrain sites mediates place preference conditioning. Supporting the hypothesis that leptin signaling induces a positive affective state, leptin also decreased the threshold for ventral tegmental area brain stimulation reward. Together, these data suggest that leptin signaling is intrinsically preferred, and support the view that signals of energy surfeit are associated with positive affect. Harnessing the positive valence of signals such as leptin may attenuate the negative affect associated with hunger, providing a compelling new approach for weight loss maintenance.