Researchers at Kanazawa University have identified dopamine-dependent neural mechanisms that regulate motivation in a mouse model of behavioral addiction. The study, published in the journal Neuropsychopharmacology, provides new insights into how pathological forms of motivation develop in psychiatric and behavioral disorders.

The scientists investigated mouse behavior using a running-wheel paradigm, in which access to a running wheel served as a natural reward. To gain access to the wheel, the animals had to perform a specific action—nose-poking into a designated hole. The number of nose-pokes reflected “reward-seeking” behavior, while the amount of time spent running represented “reward consumption.”

The results showed that dopamine and its D1 and D2 receptors within a brain region known as the medial nucleus accumbens play a critical role in initiating motivation. D1 receptors, in particular, appeared to be essential both for pursuing a reward and for experiencing it once obtained.

By monitoring neural activity, the researchers found that neuronal firing decreased before the onset of reward-seeking behavior and increased after the reward was received. At the same time, dopamine levels rose both before the animals initiated the action and after they achieved the desired outcome, suggesting a two-phase motivational signal.

Pharmacological experiments further demonstrated that blocking D1 receptors eliminated the reduction in neural activity that normally occurs before reward-seeking behavior begins, effectively disrupting the mechanism that triggers motivation.

The authors conclude that the dopamine system, acting through D1 and D2 receptors, forms a central circuit underlying motivated behavior. The findings may help improve understanding not only of addiction but also of disorders characterized by impaired motivation, including depression and behavioral addictions.