Selective dopamine D-4 receptor agonist (A-412997) improves cognitive performance and stimulates motor activity without influencing reward-related behaviour in rat

Current therapies for attention deficit hyperactivity disorder comprise psychostimulants, which block the dopamine transporter and/or stimulate the release of dopamine, leading to a global elevation in extrasynaptic dopamine. These drugs are, however, associated with a series of unwanted side effects such as insomnia, anorexia, headache, stomach problems and potential drug abuse. Recent evidence suggests that the dopamine D-4 receptor may represent a selective dopamine target that could mediate cognitive as well as striatal motor processes. In this study we compare the effects of a selective D-4 receptor agonist, A-412997, with methylphenidate or amphetamine in preclinical models of efficacy versus abuse liability. Both methylphenidate and A-412997 improved a temporally induced deficit in the rat novel object recognition task at doses 10-fold lower than those stimulating activity. In both cases, procognitive doses were associated with elevated extracellular levels of dopamine and acetylcholine in the medial prefrontal cortex. In contrast to amphetamine, A-412997 did not mediate reward-related behaviour in the conditioned place preference paradigm, a preclinical rodent test used to assess potential abuse liability. Collectively, these data suggest that selective activation of the D-4 receptor may represent a target for the treatment of attention deficit hyperactivity disorder without the potential drug abuse liability associated with current psychostimulant therapies. Behavioural Pharmacology 19:765-776 (C) 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins.