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    Safety, tolerability, pharmacokinetics, and pharmacodynamics of the oral Dopamine D1/D5 agonist PF-06649751 in Parkinson’s disease: A multiple ascending dose study
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    • Dopamine agonist, with high affinity for the D2 receptor (less potent than pergolide or cabergoline). This action is the reason for effectiveness. Also has weak α agonist and 5-HT1A/1D agonist activity. In the treatment of hormone-secreting pituitary adenomas, bromocriptine works as a dopamine agonist, which inhibits prolactin-secreting cells in the anterior pituitary, reducing tumor size
    Pergolide
    Cabergoline
    Serotonin Agonist
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    Abstract The suppression of spontaneous motor impulses is an essential facet of cognitive control that is linked to frontal-BG circuitry. BG dysfunction caused by Parkinson disease (PD) disrupts the proficiency of action suppression, but how pharmacotherapy for PD impacts impulsive motor control is poorly understood. Dopamine agonists improve motor symptoms of PD but can also provoke impulsive–compulsive behaviors (ICB). We investigated whether dopamine agonist medication has a beneficial or detrimental effect on impulsive action control in 38 PD patients, half of whom had current ICB. Participants performed the Simon conflict task, which measures susceptibility to acting on spontaneous action impulses as well as the proficiency of suppressing these impulses. Compared with an off-agonist state, patients on their agonists were no more susceptible to reacting impulsively but were less proficient at suppressing the interference from the activation of impulsive actions. Importantly, agonist effects depended on baseline performance in the off-agonist state; more proficient suppressors off agonist experienced a reduction in suppression on agonist, whereas less-proficient suppressors off agonist showed improved suppression on agonist. Patients with active ICB were actually less susceptible to making fast, impulsive response errors than patients without ICB, suggesting that behavioral problems in this subset of patients may be less related to impulsivity in motor control. Our findings provide further evidence that dopamine agonist medication impacts specific cognitive control processes and that the direction of its effects depends on individual differences in performance off medication.
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    The evidence supporting initial dopamine agonist treatment of PD is reviewed. The two rationales for initial agonist treatment are reduced frequency of motor complications and possible relative neuroprotection by dopamine agonists. The basic science supporting these rationales is equivocal. The clinical evidence for advantages of initial agonist treatment is incomplete. More data are required to determine the optimal initial treatment for PD.