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For example, a concomitant block of dopamine Dl and 02 receptors is needed to block stress-induced reinstatement", whereas selective antagonists of either receptors suffice to decrease positive reinforcing effects of drugs16•17• In parallel, although the sole injection of glucocorticoids can induce reinstatement53, blocking the secretion of these hormones does not prevent stressinduced reinstatement of heroin self-administration, which is, in contrast, attenuated by corticotropinreleasing factor (CRF) receptor antagonists59•

However, it should also be noted that the differences between self-administration and reinstatement could simply reflect the fact that different mechanisms mediate the behavioural response to different drugs of abuse. Thus, the majority of the studies investigating the role of glucocorticoids and dopamine in the mediation of the effects of stress on self-administration concern psychostimulant drugs. In contrast, studies on reinstatement have been performed principally in animals trained to self-administer heroin.