Satiety assessment in neonatally handled rats.

Eating more sweet food did not mean an inability to feel full

If animals eat more of a sweet food, one explanation is that signals of fullness are not working normally. This study tested that explanation for the increased sweet-food consumption previously observed in rats handled briefly after birth.

Examining satiety rather than intake alone. Rats were handled for ten minutes a day during their first ten days or left undisturbed. In adulthood, researchers tested sweet-food intake in the home cage and after exposure to a sucrose solution intended to produce satiety. They also compared the response to a palatable food containing complex carbohydrates and measured body fat, blood glucose and appetite-related hormones.

Testing in the familiar home cage helped assess whether the earlier feeding difference depended on the novelty of the testing environment. Comparing foods and measuring the pattern of intake helped distinguish a selective response to sweetness from a general inability to stop eating.

Handled rats retained a measurable response to fullness. They ate more sweet food, including in the home cage, but their intake declined in a pattern consistent with satiety. After the sucrose solution, they reduced sweet-food intake; control animals did not show the same reduction. The group difference disappeared with the complex-carbohydrate food.

Body weight, abdominal fat, glucose, insulin and leptin did not differ. Ghrelin, a hormone involved in appetite signaling, was lower in handled animals. This combination does not fit a simple account of generalized hunger or absent satiety.

The experiment narrows the explanation for the feeding effect. Early experience was associated with a selective change in sweet-food consumption while responses that limit intake remained detectable. The hormone result identifies another feature of the model, but the study did not prove that lower ghrelin caused the behavior.