In any case, there is nonetheless a good deal of evidence to indicate that modafinil is producing at least a portion of its wakefulness-promoting effects by acting as a DRI, or at least via activation of the dopaminergic system. In support of modafinil acting as a dopaminergic agent, its wakefulness-promoting effects are abolished in DAT knockout mice (although it is important to note that DAT knockout mice show D1 and D2 receptor and norepinephrine compensatory abnormalities, which might confound this finding), reduced by both D1 and D2 receptor antagonists (although conflicting reports exist), and completely blocked by simultaneous inactivation of both D1 and D2 receptors. In accordance, modafinil shows full stimulus generalization to other DAT inhibitors including cocaine, methylphenidate, and vanoxerine, and discrimination is blocked by administration of both ecopipam (SCH-39166), a D1 receptor antagonist, and haloperidol, a D2 receptor antagonist. Partial substitution was seen with the DRA dextroamphetamine and the D2 receptor agonist PNU-91356A, as well as with nicotine (which indirectly elevates dopamine levels through activation of nicotinic acetylcholine receptors).