A 33-year-old woman becomes poisoned after receiving an injection of concentrated botulinum toxin. Which of the following is the main neurochemical mechanism by which this Clostridium toxin causes its effects?

Correct Answer: B

Rationale: The correct answer is B: Inhibits ACh release from all cholinergic nerves. Botulinum toxin blocks the release of acetylcholine (ACh) from cholinergic nerve terminals, leading to muscle paralysis. This occurs through the cleavage of SNARE proteins, preventing vesicle fusion and neurotransmitter release. Choice A is incorrect because botulinum toxin does not directly activate receptors. Choice C is incorrect as botulinum toxin does not affect neuronal norepinephrine reuptake. Choice D is incorrect because botulinum toxin does not release norepinephrine via a nonexocytotic process.

Correct Answer: C

Rationale: Monoamine oxidase enzyme (MAO) is responsible for the degradation of neurotransmitters like adrenaline. MAO breaks down adrenaline into inactive metabolites, regulating its levels in the body. This process is crucial for maintaining neurotransmitter balance. Choice A is incorrect because MAO does not activate adrenaline. Choice B is incorrect as MAO is not involved in adrenaline synthesis. Choice D is incorrect as MAO does not degrade acetylcholine, but rather neurotransmitters like serotonin, dopamine, and adrenaline.

Correct Answer: D

Rationale: The correct answer is D: Atropine does not produce bronchoconstriction. Atropine is an anticholinergic drug that blocks the action of acetylcholine, leading to increased heart rate (A), stimulation of the respiratory center (B), and mydriatic effect (C). Bronchoconstriction is not a pharmacological effect of atropine because it actually helps dilate the bronchi, making it a useful treatment in cases of bronchospasm.

Correct Answer: D

Rationale: The correct answer is D because acidification of urine actually increases the excretion of amphetamine. Step 1: Amphetamine is an indirect acting sympathomimetic, which means it stimulates the release of norepinephrine. Step 2: It has prominent CNS action by increasing the release of dopamine and norepinephrine, leading to effects like increased alertness and euphoria. Step 3: Chronic use of amphetamine can indeed lead to addiction due to its reinforcing properties and impact on the brain's reward system. Therefore, D is incorrect as acidification of urine does not decrease amphetamine excretion; instead, it can enhance excretion by increasing its solubility in urine.

Correct Answer: A

Rationale: Sumatriptan is the correct answer for treating acute migraine attacks as it is a specific serotonin receptor agonist that helps constrict blood vessels in the brain. Ergometrine and dihydroergometrine are ergot alkaloids used for other conditions, not migraine. Propranolol is a beta-blocker used for migraine prevention, not acute attacks.