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
