The graph below represents the relationship between the dose of a new drug and the severity of Parkinson-like motor symptoms, a suspected side effect. This drug is most likely a:

Question

The graph below represents the relationship between the dose of a new drug and the severity of Parkinson-like motor symptoms, a suspected side effect.  This drug is most likely a:

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11ecba2d_0c7f_cf09_a3bf_ab6e0c725d75_MD0008_00 Dopamine is a neurotransmitter with widespread targets throughout the brain, specifically in the basal ganglia (motor function), mesolimbic pathway (pleasure, reward), and prefrontal cortex (motivation, emotion regulation). Parkinson disease is associated with the loss of dopaminergic neurons in the substantia nigra (a structure in the basal ganglia that inhibits excess movement). A dopamine deficit in the basal ganglia causes motor symptoms such as resting tremors (eg, shaky hands), muscle rigidity, and shuffling gait. Many antipsychotic drugs are dopamine antagonists that work in part by blocking the action of dopamine, an excess of which in certain areas of the brain has been linked to psychotic symptoms (eg, hallucinations), such as those seen in schizophrenia. These medications can have side effects that resemble the motor symptoms of Parkinson disease (eg, tremors, muscle rigidity). A positive correlation between the dose of a drug and the severity of Parkinson-like motor symptoms (ie, severity of side effect symptoms increases as drug dose increases) suggests that this drug is most likely a dopamine antagonist, which blocks or reduces the effects of dopamine. (Choice B) Some medications used to treat Parkinson disease are dopamine agonists, which mimic or enhance the effects of dopamine. These medications can include adverse side effects such as hallucinations or delusions (ie, psychotic symptoms). (Choices C and D) Serotonin is a neurotransmitter involved in the experience of mood, sleep/wake regulation, social dominance/aggression, and appetite, among others. Neither a serotonin agonist nor antagonist would produce Parkinson-like motor symptoms. Educational objective: Dopamine is a neurotransmitter involved in movement, reward, pleasure, motivation, and emotion regulation. The loss of dopaminergic neurons in the substantia nigra associated with Parkinson disease causes motor symptoms such as resting tremors (eg, shaky hands), muscle rigidity, and shuffling gait.

The Graph Below Represents the Relationship Between the Dose of a New