Neurotransmitters – Serotonin MCQs With Answer

Neurotransmitters – Serotonin MCQs With Answer

This concise, exam-focused introduction clarifies serotonin (5-HT) biology, pharmacology, and clinical relevance for B. Pharm students. Topics include serotonin synthesis from tryptophan, rate-limiting enzyme TPH, vesicular storage, SERT-mediated reuptake, MAO-A metabolism, major receptor families (5-HT1–7), and physiological roles in mood, sleep, appetite, GI motility, and platelet function. Drug classes such as SSRIs, SNRIs, MAO inhibitors, triptans, and receptor-specific agonists/antagonists are emphasized along with adverse effects like serotonin syndrome and important drug interactions. Keywords: neurotransmitters, serotonin, 5-HT, TPH, SERT, MAO-A, SSRI, receptors, pharmacology, B. Pharm. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which enzyme is the rate-limiting step in neuronal serotonin biosynthesis?

• Tryptophan hydroxylase
• Aromatic L-amino acid decarboxylase
• Monoamine oxidase A
• Tyrosine hydroxylase

Correct Answer: Tryptophan hydroxylase

Q2. What is the immediate precursor of serotonin (5-HT) in its biosynthetic pathway?

• 5-Hydroxytryptophan (5-HTP)
• Tryptamine
• L-DOPA
• Tyrosine

Correct Answer: 5-Hydroxytryptophan (5-HTP)

Q3. Which enzyme converts 5-hydroxytryptophan to serotonin?

• Aromatic L-amino acid decarboxylase
• Monoamine oxidase B
• Phenylethanolamine N-methyltransferase
• Glutamic acid decarboxylase

Correct Answer: Aromatic L-amino acid decarboxylase

Q4. Which transporter is primarily responsible for reuptake of serotonin into presynaptic terminals?

• Serotonin transporter (SERT)
• Noradrenaline transporter (NET)
• Vesicular monoamine transporter 2 (VMAT2)
• Choline transporter (CHT)

Correct Answer: Serotonin transporter (SERT)

Q5. Which monoamine oxidase isoform mainly metabolizes serotonin in the brain?

• MAO-A
• MAO-B
• Both equally
• MAO-C

Correct Answer: MAO-A

Q6. Where is most peripheral serotonin produced and stored?

• Enterochromaffin cells of the gut
• Adrenal medulla
• Platelets synthesize and store it
• Pancreatic β-cells

Correct Answer: Enterochromaffin cells of the gut

Q7. Platelets acquire serotonin by which mechanism?

• Uptake from plasma via SERT
• De novo synthesis using TPH
• Endocytosis of enterochromaffin cells
• Conversion from dopamine

Correct Answer: Uptake from plasma via SERT

Q8. Activation of 5-HT1A receptors in the raphe nuclei primarily produces which effect?

• Autoreceptor-mediated inhibition of serotonin release
• Stimulation of serotonin synthesis
• Increased platelet aggregation
• Intestinal smooth muscle contraction

Correct Answer: Autoreceptor-mediated inhibition of serotonin release

Q9. Which 5-HT receptor is a ligand-gated ion channel rather than G-protein coupled?

• 5-HT3 receptor
• 5-HT1B receptor
• 5-HT2A receptor
• 5-HT4 receptor

Correct Answer: 5-HT3 receptor

Q10. Triptans used for migraine act primarily as agonists at which receptor subtype?

• 5-HT1B/1D receptors
• 5-HT2A receptors
• 5-HT3 receptors
• 5-HT4 receptors

Correct Answer: 5-HT1B/1D receptors

Q11. Which antidepressant class selectively inhibits the serotonin transporter?

• Selective serotonin reuptake inhibitors (SSRIs)
• Tricyclic antidepressants (TCAs)
• Monoamine oxidase inhibitors (MAOIs)
• Beta-blockers

Correct Answer: Selective serotonin reuptake inhibitors (SSRIs)

Q12. A dangerous interaction causing serotonin syndrome is most likely when combining:

• An SSRI with an MAO inhibitor
• An SSRI with a benzodiazepine
• A triptan with a beta-blocker
• An SSRI with aspirin

Correct Answer: An SSRI with an MAO inhibitor

Q13. Common clinical features of serotonin syndrome include all EXCEPT:

• Muscle rigidity and hyperreflexia
• Autonomic instability (hyperthermia, tachycardia)
• Hyporeflexia and flaccid paralysis
• Agitation and confusion

Correct Answer: Hyporeflexia and flaccid paralysis

Q14. Which drug is a partial agonist at 5-HT1A receptors used as an anxiolytic?

• Buspirone
• Ondansetron
• Sumatriptan
• Fluoxetine

Correct Answer: Buspirone

Q15. Ondansetron is an antiemetic that blocks which serotonin receptor?

• 5-HT3 receptor antagonist
• 5-HT1A receptor agonist
• 5-HT2C receptor antagonist
• 5-HT4 receptor agonist

Correct Answer: 5-HT3 receptor antagonist

Q16. Which 5-HT receptor subtype is most associated with platelet aggregation and vasoconstriction?

• 5-HT2A
• 5-HT1A
• 5-HT3
• 5-HT7

Correct Answer: 5-HT2A

Q17. Which statement about SSRIs is correct regarding pharmacodynamics?

• They inhibit SERT, increasing synaptic 5-HT levels
• They irreversibly inhibit MAO-A
• They directly agonize 5-HT2A receptors
• They block vesicular storage of serotonin

Correct Answer: They inhibit SERT, increasing synaptic 5-HT levels

Q18. Which metabolite is produced during oxidative deamination of serotonin by MAO?

• 5-HIAA (5-hydroxyindoleacetic acid)
• HVA (homovanillic acid)
• DOPAC (3,4-dihydroxyphenylacetic acid)
• Metanephrine

Correct Answer: 5-HIAA (5-hydroxyindoleacetic acid)

Q19. Measurement of 5-HIAA in urine is clinically useful for diagnosing:

• Carcinoid syndrome
• Parkinson’s disease
• Schizophrenia
• Myasthenia gravis

Correct Answer: Carcinoid syndrome

Q20. Which pharmacological action best explains why SSRIs may take weeks to show clinical antidepressant effects?

• Adaptive downregulation of autoreceptors and receptor remodeling
• Immediate increase in monoamine synthesis
• Rapid desensitization of postsynaptic receptors within hours
• Direct agonism at synaptic 5-HT receptors

Correct Answer: Adaptive downregulation of autoreceptors and receptor remodeling

Q21. Which receptor subtype is implicated in modulation of circadian rhythm and sleep?

• 5-HT7 receptors
• 5-HT3 receptors
• 5-HT1B receptors
• 5-HT2B receptors

Correct Answer: 5-HT7 receptors

Q22. Which class of drugs increases synaptic serotonin by inhibiting vesicular monoamine transporter VMAT?

• Reserpine depletes vesicular stores and reduces serotonin
• SSRIs increase synaptic serotonin by VMAT inhibition
• MAOIs inhibit VMAT directly
• Triptans inhibit VMAT to release serotonin

Correct Answer: Reserpine depletes vesicular stores and reduces serotonin

Q23. A selective 5-HT2A antagonist is likely to have which clinical effect?

• Antipsychotic and improved negative symptoms when part of atypical antipsychotics
• Pro-emetic action causing nausea
• Direct stimulation of platelet aggregation
• Induction of migraine

Correct Answer: Antipsychotic and improved negative symptoms when part of atypical antipsychotics

Q24. Which of the following is a side effect commonly associated with SSRIs due to increased serotonergic activity?

• Sexual dysfunction
• Bradycardia with heart block
• Severe hypertension in all patients
• Renal failure

Correct Answer: Sexual dysfunction

Q25. In pharmacology, ‘serotonin syndrome’ results from excess serotonergic activity at which receptor types primarily?

• Multiple 5-HT receptor subtypes including 5-HT1A and 5-HT2A
• Only 5-HT3 receptors
• Only peripheral 5-HT2B receptors
• Exclusively 5-HT7 receptors

Correct Answer: Multiple 5-HT receptor subtypes including 5-HT1A and 5-HT2A

Q26. Which laboratory method is commonly used to measure serotonin or its metabolites in biological samples?

• High-performance liquid chromatography (HPLC)
• Western blotting
• Flow cytometry
• Magnetic resonance imaging

Correct Answer: High-performance liquid chromatography (HPLC)

Q27. Which genetic variant can influence SSRI response by altering SERT function?

• Polymorphism in the SLC6A4 promoter (5-HTTLPR)
• COMT Val158Met polymorphism
• MAO-A promoter VNTR has no influence
• DRD2 Taq1A polymorphism

Correct Answer: Polymorphism in the SLC6A4 promoter (5-HTTLPR)

Q28. Which statement about 5-HT4 receptor agonists is correct?

• They enhance gastrointestinal motility and can be prokinetic
• They are primary treatments for migraine via vasoconstriction
• They are potent platelet aggregation inhibitors
• They antagonize 5-HT3-mediated nausea

Correct Answer: They enhance gastrointestinal motility and can be prokinetic

Q29. Buspirone’s clinical anxiolytic effect is mainly through partial agonism at which receptor?

• 5-HT1A autoreceptors and postsynaptic 5-HT1A
• 5-HT3 receptors in the area postrema
• 5-HT2A receptors in cortex
• Histamine H1 receptors

Correct Answer: 5-HT1A autoreceptors and postsynaptic 5-HT1A

Q30. Which of the following best describes enterochromaffin cell serotonin physiology relevant to pharmacology?

• Gut-derived serotonin modulates motility and is largely separate from central 5-HT pools
• Enterochromaffin cells synthesize central serotonin used by brain neurons
• Platelets synthesize serotonin in the gut and transport it to CNS
• All peripheral serotonin freely crosses the blood-brain barrier to affect mood

Correct Answer: Gut-derived serotonin modulates motility and is largely separate from central 5-HT pools

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com