Early life handling decreases serotonin turnover in the nucleus accumbens and affects feeding behavior of adult rats.

Serotonin-related signaling contributes to an early-experience effect on eating

Earlier experiments showed that brief neonatal handling changed adult rats’ consumption of sweet food. This study investigated serotonin as one possible part of that developmental effect, focusing on the nucleus accumbens, a brain region involved in reward and motivated behavior.

Measuring a candidate pathway and then perturbing it. Rat litters were handled for ten minutes a day during the first ten days after birth or left undisturbed. In one experiment, researchers measured serotonin metabolism in the adult nucleus accumbens. In another, handled and control animals received either imipramine in their drinking water or water alone, followed by measurements of feeding and weight gain.

Serotonin turnover reflects how the messenger is metabolized and is used as an indicator of aspects of its activity. Imipramine alters monoamine reuptake, including serotonin, allowing the team to test whether changing this signaling environment modified the feeding difference.

The biochemical and behavioral findings pointed in the same general direction. Handled animals had lower serotonin metabolism in the nucleus accumbens. Chronic imipramine treatment reversed their increased sweet-food consumption. Handled animals also weighed less than controls, and imipramine reduced weight gain across groups after longer treatment.

The drug result strengthens the case that the feeding pattern is responsive to monoamine signaling rather than being an unchangeable consequence of early experience. However, imipramine acts on more than one transmitter system and throughout the body and brain. Its effect does not isolate serotonin in the nucleus accumbens as the sole cause.

The study identifies a modifiable neurochemical component of the relationship between early experience and later food preference. It also shows why greater sweet-food intake should not automatically be equated with greater body weight: these measures differed in their relationship to handling and treatment.