The mechanism of carbidopa′s action is:

Correct Answer: B

Rationale: The correct answer is B because carbidopa inhibits dopa decarboxylase enzyme, preventing the conversion of levodopa into dopamine outside the brain. This allows more levodopa to reach the brain and be converted into dopamine, improving its efficacy in treating Parkinson's disease. Choice A is incorrect as carbidopa does not directly affect the synthesis, release, or reuptake of dopamine. Choice C is incorrect because carbidopa does not stimulate dopamine receptors but rather works on the enzymatic conversion of levodopa to dopamine. Choice D is incorrect as carbidopa does not inhibit catechol-O-methyltransferase (COMT), which is another enzyme involved in dopamine metabolism.

Correct Answer: C

Rationale: The correct answer is C, the mesolimbic and mesofrontal systems, as they are directly involved in regulating behaviors related to motivation, reward, and decision-making. The mesolimbic system projects from the ventral tegmental area to the limbic system, influencing emotions and reinforcement. The mesofrontal system connects the prefrontal cortex to the ventral tegmental area, modulating executive functions and cognitive control of behavior. A: The hypothalamic-pituitary system primarily regulates hormone production and homeostasis, not behavior. B: The extrapyramidal system is involved in motor control and not directly linked to behavior. D: The chemoreceptor trigger zone of the medulla is related to vomiting reflex and not behavior.

Correct Answer: D

Rationale: The correct answer is D: All of the above. MAO inhibitors can lead to dangerous interactions with selective serotonin reuptake inhibitors, tricyclics, and sympathomimetics due to the risk of serotonin syndrome or hypertensive crisis. The inhibition of monoamine oxidase enzyme by MAO inhibitors can increase the levels of serotonin, norepinephrine, and dopamine, resulting in potentially life-threatening effects when combined with these medications. It is crucial to avoid this combination to prevent serious adverse reactions.

Correct Answer: C

Rationale: The correct answer is C because nootropics are known for enhancing cognitive functions such as memory, focus, and creativity, not causing a decline in integrative brain functions. A: Selective influence is true as nootropics target specific brain areas. B: Improving communication aligns with nootropics enhancing cognitive abilities. D: Increased energetic exchange is a common effect of nootropics, boosting brain cell function.

Correct Answer: C

Rationale: Cocaine exerts its central action by inhibiting dopamine and norepinephrine reuptake. This leads to an accumulation of these neurotransmitters in the synaptic cleft, enhancing their effects. This mechanism results in increased stimulation of the central nervous system, leading to the characteristic effects of cocaine such as increased alertness and euphoria. Choices A and D are incorrect as cocaine does not directly affect phosphodiesterase or serotonin turnover. Choice B is incorrect as while cocaine does increase the release of neurotransmitters, its primary mechanism of action is through reuptake inhibition.