The principal mechanism of action of adrenoreceptor antagonists is:

Correct Answer: A

Rationale: Rationale: A: Adrenoreceptor antagonists work by reversible or irreversible interaction with adrenoreceptors, blocking the action of catecholamines. This directly affects the sympathetic nervous system. B: Depletion of catecholamines is not the primary mechanism of action of adrenoreceptor antagonists. C: Blockade of amine reuptake pumps is not the primary mechanism of action of adrenoreceptor antagonists. D: Nonselective MAO inhibition is not the mechanism of action of adrenoreceptor antagonists.

Correct Answer: A

Rationale: The correct answer is A. Carbamazepine is an antiepileptic drug known to cause dose-related adverse effects such as diplopia (double vision), ataxia (lack of coordination), and nausea. Diplopia and ataxia are common neurological side effects, while nausea is a gastrointestinal side effect. This is due to the drug's mechanism of action on sodium channels in the nervous system. Choices B, C, and D are incorrect. Gingival hyperplasia and hirsutism are not common adverse effects of carbamazepine. Sedation and dependence are more associated with benzodiazepines, and hemeralopia and myasthenic syndrome are not typically linked to carbamazepine use.

Correct Answer: D

Rationale: The correct answer is D because all three drugs (Reserpine, Haloperidol, Chlorpromazine) antagonize the effects of levodopa by different mechanisms, leading to a junctional blockade of dopamine action. Reserpine depletes dopamine stores, Haloperidol blocks dopamine receptors, and Chlorpromazine inhibits dopamine release. Therefore, all of these drugs can reduce the effectiveness of levodopa in treating Parkinson's disease by interfering with dopamine function. Choices A, B, and C are incorrect because each of them individually, not collectively, antagonizes the effects of levodopa and leads to a junctional blockade of dopamine action.

Correct Answer: C

Rationale: Rationale: 1. Nalbuphine is a strong kappa receptor agonist: It primarily activates kappa receptors, providing analgesia. 2. Nalbuphine is a mu receptor antagonist: It blocks mu receptors, reducing the risk of mu receptor-associated side effects. 3. Naltrexone (A) is a mu receptor antagonist but not a kappa agonist. 4. Methadone (B) is a mu receptor agonist and NMDA receptor antagonist. 5. Buprenorphine (D) is a partial mu receptor agonist and kappa receptor agonist, not a mu antagonist like nalbuphine.

Correct Answer: B

Rationale: Rationale for Choice B (Hyperactive dopaminergic state in the presence of dopamine blockers): 1. Dopamine blockers disrupt the balance of dopamine in the brain. 2. Dopamine blockers lead to an increase in dopamine receptor activity. 3. Hyperactive dopaminergic state causes abnormal movements seen in tardive dyskinesia. 4. This choice directly correlates with the pathophysiology of tardive dyskinesia. Summary of why other choices are incorrect: A: Degeneration of dopaminergic and cholinergic fibers - Tardive dyskinesia is not primarily caused by degeneration of these fibers. C: Degeneration of histaminergic fibers - Histaminergic fibers are not implicated in the development of tardive dyskinesia. D: Supersensitivity of cholinergic receptors in the caudate-putamen - While cholinergic dysfunction is involved, it is not the primary cause of tardive dyskinesia.