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    Pharmacological targeting of dopamine D3 receptors: Possible clinical applications of selective drugs.

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    Dopamine D3 receptors have been pharmacologically engaged in humans since the development of the first antipsychotics and ergot-derivative dopamine (DA) agonists, even without knowing it. These agents were generally non-selective, developed primarily to target D2 receptors. In the last 10 years the understanding of the clinical implication of D3 receptors has been progressing also due to the identification of D3 gene polymorphisms, the use of more selective PET ligands such as [(11)C]-(+)-PHNO and the learning regarding the clinical use of the D3-preferential D2/D3 agonists ropinirole and pramipexole. A new specific neuroplasticity role of D3 receptor regarding dendrite arborisation outgrowth in dopaminergic neurons was also proposed to support, at least in part, the slowing of disease observed in subjects with Parkinson׳s Disease treated with DA agonists. Similar mechanisms could be at the basis of the antidepressant-like effects observed with DA agonists when co-administered with standard of care. Severe adverse event occurring with the use of anti-parkinsonian DA agonists in predisposed subjects, i.e., impulse control disorders, are now suggested to be putatively related to overactive D3 receptors. Not surprisingly, blockade of D3 receptors was proposed as treatment for addictive disorders, a goal that could be potentially achieved by repositioning buspirone, an anxiolytic drug with D3-preferential antagonistic features, or with novel selective D3 antagonists or partial agonists currently in development for schizophrenia. At the moment ABT-925 is the only selective D3 antagonist tested in schizophrenic patients in Phase II, showing an intriguing cognitive enhancing effects supported by preclinical data. Finally, exploratory pharmacogenetic analysis suggested that ABT-925 could be effective in a subpopulation of patients with a polymorphism on the D3 receptor, opening to a possible personalised medicine approach

    Plasma nociceptin/orphanin FQ levels in response to the hyperventilation test in healthy subjects.

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    In vitro and in vivo studies demonstrated that nociceptin/orphanin FQ inhibits norepinephrine release, while the effects of norepinephrine on nociceptin/orphanin FQ release remain unknown. Previous studies in healthy and hypertensive subjects showed that prolonged and forced hyperventilation induces different blood pressure (BP) responses depending on changes in plasma catecholamine levels. We investigated whether the effects of hyperventilation on the sympatho-adrenergic system involve nociceptin/orphanin FQ release. Fifty-six healthy subjects (26 females, mean age 63 2 and 30 males, mean age 63 3) underwent the hyperventilation test. A hierarchical cluster analysis based on BP response to hyperventilation identified three groups of subjects: group 1 (n = 20) with a decrease in BP, norepinephrine (1311.1 45.5 fmol/ ml versus 900.0 55.3 fmol/ml, P < 0.01) and nociceptin/orphanin FQ (13.0 0.7 pg/ml versus 7.9 0.8 pg/ ml, P < 0.01), group 2 (n = 18) without any change in BP and norepinephrine (1133.0 31.5 fmol/ml versus 1176.0 44.6 fmol/ml), with a decrease in nociceptin/orphanin FQ (12.5 3.2 pg/ml versus 7.4 0.6 pg/ml, P < 0.01) and group 3 (n = 18) with an increase in BP, norepinephrine (1216.7 50.9 fmol/ml versus 1666.7 44.9 fmol/ml, P < 0.01) and nociceptin/orphanin FQ values (11.5 1.6 pg/ml versus 19.9 1.5 pg/ ml,P < 0.01). Norepinephrine changes in response tohyperventilationingroups 1and3weredirectly (P < 0.01) correlated with those of nociceptin/orphanin FQ. Our results showed that vigorous and prolonged hyperventilation changes plasma nociceptin/orphanin FQ levels due to the direct effects of hypocapnic alkalosis or to different sympatho-adrenergic system responses
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