Microinjection of ghrelin in the nucleus accumbens core enhances locomotor activity induced by cocaine.

Ghrelin has a regulatory role not only in the rewarding aspect for feeding but also in drug addiction by interaction with mesolimbic dopaminergic pathways in the brain. Previously it has been shown that systemic ghrelin enhances cocaine-induced hyper-locomotor activity. However, it has not been determined yet what effects ghrelin may produce on cocaine-induced locomotor behavior when microinjected into the nucleus accumbens core, where cocaine actually produces its locomotor activating effects. In the present study, when rats were administered cocaine (15 mg/kg, i.p.) following a bilateral microinjection of ghrelin (0.1 or 0.5 µg/side) into the NAcc core, their locomotor activity was significantly enhanced, while these effects were inhibited by co-microinjection of ghrelin receptor antagonist (0.5 µg/side) into this site. When ghrelin alone microinjected, basal locomotor activity was unchanged. These results expand previous similar findings obtained by systemic ghrelin to more specific neuronal site, the nucleus accumbens core, and further suggest that it may work in this site to positively contribute to the expression of locomotor sensitization.