In contrast to the key roles of THC and D1 in the above behaviors, no role has been observed in discrimination or withdrawal effects. For example, Solinas et al. ( ) used rats to demonstrate that D1 receptors did not augment THC discrimination, which is a type of experiment that tests an animal's ability to distinguish between THC and control substances. The D1 receptor's antagonist, SCH-23390, did not play a role in reducing the THC discrimination effect. Additionally, D1 receptor's antagonist did not counteract THC discrimination yielded by cocaine and amphetamine augmentation. The D1 receptor antagonist also did not show a discriminative effect at low doses of THC . In other work, Sañudo-Peña et al. (1999) treated rats with THC or vehicle and then subsequently SCH23390 sulpiride was administered. Then, their behaviors were investigated for 1 hour after getting injected with SR141716A, a selective CB1 antagonist, or vehicle. The study revealed that the cannabinoid triggered a withdrawal syndrome that was not weakened by treatment with dopamine antagonists in THC tolerant animals. However, syndromes were increased by agonists .