<prompt> Olcegepant, mechanism of action is:5HT1d1b agonistInhibits the release of vasodilating peptidesCGRP antagonistDecreases the excessive firing of vasoconstrictor nerve fibers  <response>: Ans. C. CGRP antagonistRef: Katzungs Basic and Clinical Pharmacology 13thed, p308Explanation Calcitonin family of peptides includes: Calcitonin Calcitonin gene-related peptide CGRP Adrenomedullin Amylin CGRP Widely distributed: Largely in the C-cells of the thyroid gland, also found in CNS central nervous system, PNS peripheral nervous system, CVS cardiovascular system, RS respiratory system and GIT gastrointestinal tract. CGRP-containing neuronal fibers are more abundant around arteries than around veins and in atria than in ventricles. This peptide has vasodilatory property, in fact CGRP is the most potent vasodilator yet discovered. When injected in systemic circulation, it causes hypotension and tachycardia. When injected into CNS, it causes hypertension and suppression of feeding. Release of CGRP from trigeminal nerves plays a central role in the pathophysiology of migraine. Selective serotonin agonist triptans normalizes CGRP levels. CGRP antagonists though have not yet received FDA approval have shown promising results in trials for migraine. Antagonists developed are:- Olcegepant- Telcagepant Note the name olcegepant: Calcitonin gene-related peptide antagonist. These drugs are non-peptide antagonist. Two primary hypotheses to explain the actions of antimigraine drugs are: First, The triptans, ergot alkaloids, and antidepressants may activate 5-HT1D1B receptors on presynaptic trigeminal nerve endings, thereby inhibiting the release of vasodilating peptides, option b and antiseizure agents may suppress excessive firing of these nerve endings option d. Second, the vasoconstrictor actions of direct 5-HT agonists the triptans and ergot may prevent vasodilation and stretching of the pain endings. It is possible that both mechanisms contribute in the case of some drugs. Option a: Triptans sumatriptan is 5 HT agonist. Option b: CGRP itself is vasodilating peptide and olcegepant is CGRP antagonist. The triptans, ergot alkaloids, and antidepressants act by inhibiting the release of vasodilating peptides. Option d: Antiseizure drugs like valproic acid and topiramate are useful in treatment of migraine, they reduce the excessive firing by trigeminal neurons. 