Which of the following antimuscarinic drugs is often effective in preventing or reversing vestibular disturbances, especially motion sickness?

Correct Answer: C

Rationale: Rationale: Scopolamine is effective for vestibular disturbances due to its central anticholinergic effects. It crosses the blood-brain barrier and blocks muscarinic receptors in the vestibular nuclei, helping to alleviate motion sickness. Atropine (A) mainly affects peripheral muscarinic receptors, not as effective. Ipratropium (B) is a bronchodilator, not used for motion sickness. Homatropine (D) is primarily used for ophthalmic purposes, not vestibular issues. Therefore, C is the correct choice.

Correct Answer: B

Rationale: Rationale: 1. Xylometazoline is an alpha2-selective agonist, which means it selectively activates alpha2 adrenergic receptors. 2. This action leads to vasoconstriction and reduces nasal congestion without affecting blood pressure. 3. Phenylephrine (choice A) is an alpha1-selective agonist, causing increased blood pressure. 4. Ephedrine (choice C) is a mixed agonist affecting both alpha and beta receptors. 5. Epinephrine (choice D) is a non-selective agonist acting on both alpha and beta receptors.

Correct Answer: C

Rationale: The correct answer is C because reserpine actually causes a sympatholytic effect, not a sympathomimetic effect. Reserpine depletes norepinephrine and serotonin stores in the brain, leading to decreased sympathetic activity. Choices A, B, and D are incorrect because reserpine does inhibit the uptake of norepinephrine, decrease cardiac output and peripheral resistance, and deplete catecholamines and serotonin stores in the brain, respectively.

Correct Answer: C

Rationale: The correct answer is C: Phenobarbital. Phenobarbital enhances GABA-mediated inhibition by increasing the duration of GABA-A receptor channel opening, leading to increased chloride ion influx. This enhances inhibitory neurotransmission, reducing neuronal excitability and seizure activity. Ethosuximide (A) works by blocking T-type calcium channels, Carbamazepine (B) by blocking voltage-gated sodium channels, and Lamotrigine (D) by inhibiting sodium channels and reducing glutamate release, none of which directly enhance GABA-mediated inhibition.

Correct Answer: A

Rationale: The correct answer is A: TRUE. In Parkinson's disease, there is a reduction in dopamine levels in the basal ganglia, leading to the characteristic motor symptoms. This is due to the degeneration of dopamine-producing neurons in the substantia nigra. Choice B is incorrect because the statement is true. Choice C (None) and D (All) are incorrect as they do not provide any meaningful explanation.