THE ASSOCIATION BETWEEN NOVELTY AND MORPHINE ADMINISTRATION ON THE EXPRESSION OF A CONDITIONED LOCOMOTOR RESPONSE: EFFECTS ON ERK ACTIVATION IN THE NUCLEUS ACCUMBENS AND VENTRAL TEGMENTAL AREA.

Opioid drugs increase dopamine release in the reward pathways, which in turn induces an increase in the locomotor response in rodents. The locomotor response to opioid drugs is also modulated by environmental factors. Novelty directly activates the dopamine system increasing dopamine levels in brain areas involved in the reward system. Dopamine neurons play a key role in associative learning.