Which of the following molecular actions in the enteric nervous system most likely mediated the adverse effect of the drug in the patient?

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: 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.

Correct Answer: B

Rationale: The correct answer is B: Mesolimbic pathway. In ADHD, dysfunction in the mesolimbic pathway, involved in reward and motivation, is often implicated. Stimulant medications like those used to treat ADHD act on this pathway to improve focus and impulse control. The other pathways listed do not play as significant of a role in ADHD symptomatology. A: Tuberoinfundibular is involved in hormonal regulation, not ADHD. C: Corticostriatal is more associated with movement control. D: Mesocortical is related to cognitive functions, but not the main site of therapeutic action for ADHD.

Correct Answer: B

Rationale: The correct answer is B: Dextroamphetamine. This drug is a stimulant commonly prescribed for attention deficit hyperactivity disorder (ADHD) in children. It helps improve focus and control impulsivity, addressing symptoms like inability to sit still in school. Cocaine (A) is a highly addictive illegal drug with no therapeutic use in this context. Methylphenidate (C) is another stimulant used for ADHD. Guanfacine (D) is a non-stimulant medication that is typically used as an alternative treatment for ADHD-related symptoms, but it is less likely to be prescribed for a child unable to sit still in school compared to stimulant medications like Dextroamphetamine.