The therapeutic effect of aripiprazole in the 28-year-old man with paranoid schizophrenia is most likely mediated by decreased dopaminergic transmission in which of the following brain structures?

Correct Answer: C

Rationale: The correct answer is C, the mesolimbic mesocortical pathway. Aripiprazole is an atypical antipsychotic that works by blocking dopamine receptors in this pathway, reducing dopaminergic transmission. This helps alleviate positive symptoms of schizophrenia like hallucinations and delusions. The other choices are incorrect because: A: Tuberoinfundibular pathway is involved in regulating prolactin secretion, not related to schizophrenia. B: Locus ceruleus is primarily involved in noradrenergic neurotransmission, not the main target for antipsychotics. D: N/A is not a valid answer and does not provide any relevant information.

Correct Answer: A

Rationale: The correct answer is A: Blockade of M receptors. The enteric nervous system predominantly utilizes muscarinic receptors to regulate gastrointestinal motility. Blocking these receptors can lead to adverse effects such as constipation, as it disrupts normal peristalsis. Increased serotonergic activity (B) would typically enhance gastrointestinal motility. Activation of β receptors (C) would enhance smooth muscle relaxation, potentially improving motility. Increased adrenergic activity (D) could also enhance motility due to the role of adrenergic receptors in promoting smooth muscle contraction. However, the adverse effect described in the question is more likely to be caused by the blockade of M receptors, making choice A the correct answer.

Correct Answer: B

Rationale: The correct answer is B: Clonidine. Clonidine is an alpha-2 adrenergic agonist, which means it acts by stimulating presynaptic alpha-2 receptors, leading to a decrease in norepinephrine release. This matches the drug described in the question that blocks presynaptic alphareceptors. Amitriptyline (A) is a tricyclic antidepressant that primarily acts by blocking the reuptake of serotonin and norepinephrine. Bupropion (C) is an atypical antidepressant that inhibits the reuptake of dopamine and norepinephrine. Mirtazapine (D) is a noradrenergic and specific serotonergic antidepressant that enhances serotonin and norepinephrine activity through different mechanisms. Therefore, Clonidine is the most likely drug given due to its action on presynaptic alphareceptors, while the other choices have different mechanisms

Correct Answer: B

Rationale: The correct answer is B: Decreased renal elimination of lithium. Thiazides reduce lithium excretion leading to lithium accumulation and toxicity. Thiazide-induced dilutional hypernatremia (A) is unlikely as thiazides generally cause hyponatremia. Decreased hepatic metabolism of lithium (C) is not a major factor in lithium toxicity. Thiazide-induced hypokalemia (D) is a possible side effect but not the primary reason for lithium toxicity in this scenario.

Correct Answer: C

Rationale: The correct answer is C: Lamotrigine. This drug is commonly prescribed for patients with past episodes of depression and mania as it is a mood stabilizer effective in treating bipolar disorder. It helps in regulating mood swings and preventing both manic and depressive episodes. Valproic acid (A) is also a mood stabilizer, but Lamotrigine is more commonly used in this context. Aripiprazole (B) is an atypical antipsychotic often used for bipolar disorder but is not as specific for treating past episodes of depression and mania. Imipramine (D) is a tricyclic antidepressant used for major depressive disorder and not typically prescribed for bipolar disorder.