**Core Concept**
Ergotamine is a medication used to treat migraines, which are severe headaches often accompanied by nausea, vomiting, and sensitivity to light and sound. Ergotamine acts by causing vasoconstriction of the blood vessels in the brain, which in turn reduces inflammation and pain.

**Why the Correct Answer is Right**
Ergotamine is a selective 5-HT1 receptor agonist, which means it binds to specific serotonin receptors in the brain to induce vasoconstriction. This action is crucial in terminating a migraine attack. Ergotamine also has a mild analgesic effect, which helps to reduce pain. The vasoconstrictive effect of ergotamine is achieved through the activation of 5-HT1B receptors, which are found on the blood vessels of the brain. This results in the constriction of these blood vessels, thereby reducing the inflammation and pain associated with a migraine.

**Why Each Wrong Option is Incorrect**
**Option A:** Acetylcholine is a neurotransmitter involved in various physiological processes, including muscle contraction and the regulation of the autonomic nervous system. However, it does not have a direct role in terminating a migraine attack and may even exacerbate symptoms in some cases.

**Option C:** Morphine is an opioid analgesic used to treat moderate to severe pain. While it may provide relief from the pain associated with a migraine, it is not specifically indicated for the treatment of migraines and can have side effects such as nausea and vomiting, which may worsen migraine symptoms.

**Option D:** Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) used to treat pain, inflammation, and fever. While it may provide some relief from the pain associated with a migraine, it is not as effective as ergotamine in terminating a migraine attack and may not address the underlying mechanisms of the condition.

**Clinical Pearl / High-Yield Fact**
Ergotamine is a high-yield fact in the treatment of migraines, and students should remember that it is specifically indicated for the termination of a migraine attack due to its vasoconstrictive effects.

**✓ Correct Answer: B. Ergotamine**