Repeated intermittent administration of psychostimulants (cocaine, d-amphetamine, etc.) in rodents causes a progressive increase in drug-induced locomotor activity that is higher in magnitude compared to that induced by a single injection. This phenomenon is known as locomotor sensitization. This enhanced locomotor activity is long-lasting and can be seen after a drug-free ('washout') period in response to a sub-threshold dose of the compound. The emergence of locomotor sensitization in rodents treated with a novel compound indicates potential abuse liability of the compound.

(A) Mice were trained with a chronic dosing regime of cocaine (15 mg/kg). (B) Mice were then challenged with a lower dose of cocaine (10 mg/kg) after training and a washout period of one week and showed greater locomotion in the chronic cocaine-treated group compared to the chronic vehicle-treated group.