Neurotransmitters – Glycine MCQs With Answer

Neurotransmitters – Glycine MCQs With Answer
Glycine is a major inhibitory neurotransmitter in the spinal cord and brainstem and an essential neuromodulator in the CNS. This concise set of Neurotransmitters – Glycine MCQs With Answer is tailored for B. Pharm students to reinforce core concepts: glycine synthesis and degradation, glycine receptors (alpha/beta subunits), GlyT1/GlyT2 transporters, co-agonist role at NMDA receptors, vesicular loading (VIAAT/VGAT), clinical disorders (hyperekplexia, non‑ketotic hyperglycinemia), pharmacology (strychnine antagonism, GlyT inhibitors), and laboratory measurement techniques. Questions emphasize receptor pharmacodynamics, synaptic physiology, and therapeutic implications to prepare you for exams and practical applications. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which enzyme primarily synthesizes glycine from serine in neurons?

• Serine hydroxymethyltransferase
• Glycine decarboxylase
• Glutamic acid decarboxylase
• Tyrosine hydroxylase

Correct Answer: Serine hydroxymethyltransferase

Q2. The glycine receptor is best described as which type of receptor?

• Ligand-gated chloride channel
• G-protein coupled receptor
• Ligand-gated sodium channel
• Tyrosine kinase receptor

Correct Answer: Ligand-gated chloride channel

Q3. Which compound is a classical competitive antagonist of the glycine receptor causing convulsions?

• Strychnine
• Ketamine
• CNQX

Correct Answer: Strychnine

Q4. GlyT1 and GlyT2 differ primarily in their localization and function. Which statement is correct?

• GlyT1 is mainly glial and regulates NMDA co-agonist levels; GlyT2 is neuronal and involved in vesicular refill.
• GlyT1 is neuronal and refills vesicles; GlyT2 is glial and degrades glycine.
• Both GlyT1 and GlyT2 are exclusively presynaptic and function identically.
• GlyT1 transports glycine into mitochondria; GlyT2 exports glycine from cells.

Correct Answer: GlyT1 is mainly glial and regulates NMDA co-agonist levels; GlyT2 is neuronal and involved in vesicular refill.

Q5. The vesicular transporter that packages glycine into synaptic vesicles (shared with GABA) is called:

• VIAAT (VGAT)
• VMAT2
• VGLUT1
• EAAT2

Correct Answer: VIAAT (VGAT)

Q6. Glycine acts as a co-agonist at which receptor to facilitate excitatory neurotransmission?

• NMDA receptor
• AMPA receptor
• GABAB receptor
• kainate receptor

Correct Answer: NMDA receptor

Q7. Non-ketotic hyperglycinemia is caused by defects in which system?

• Glycine cleavage system
• Serotonin synthesis pathway
• Monoamine oxidase system
• Choline acetyltransferase complex

Correct Answer: Glycine cleavage system

Q8. Which gene mutation is commonly associated with hereditary hyperekplexia (startle disease)?

• GLRA1 (glycine receptor alpha1 subunit)
• GLT1 (glutamate transporter)
• GAD1 (glutamic acid decarboxylase)
• SLC6A4 (serotonin transporter)

Correct Answer: GLRA1 (glycine receptor alpha1 subunit)

Q9. Positive allosteric modulation of glycine receptors can be produced by which of the following?

• Alcohols and volatile anesthetics
• Strychnine
• NMDA receptor antagonists like MK-801
• Glycine dehydrogenase inhibitors

Correct Answer: Alcohols and volatile anesthetics

Q10. Which metabolite or amino acid also serves as an endogenous co-agonist at the NMDA glycine site?

• D-serine
• L-glutamine
• Taurine
• Gamma-aminobutyric acid

Correct Answer: D-serine

Q11. In spinal inhibitory synapses, activation of glycine receptors typically produces which ionic flux?

• Chloride influx leading to hyperpolarization
• Sodium influx leading to depolarization
• Calcium efflux leading to inhibition
• Potassium influx leading to hyperpolarization

Correct Answer: Chloride influx leading to hyperpolarization

Q12. A selective inhibitor of GlyT1 is being investigated for schizophrenia because it:

• Increases synaptic glycine to enhance NMDA receptor function
• Prevents glycine synthesis reducing NMDA activity
• Blocks glycine receptors decreasing inhibition
• Enhances glycine cleavage lowering CNS glycine levels

Correct Answer: Increases synaptic glycine to enhance NMDA receptor function

Q13. Which measurement technique is commonly used to quantify extracellular glycine in research microdialysates?

• HPLC with fluorescence or mass spectrometry detection
• Western blotting
• ELISA for glycine protein complexes
• Patch-clamp electrophysiology

Correct Answer: HPLC with fluorescence or mass spectrometry detection

Q14. The glycine binding site on the NMDA receptor is located on which subunit?

• GluN1 (formerly NR1)
• GluN2A (formerly NR2A)
• GluN3B
• GluA1

Correct Answer: GluN1 (formerly NR1)

Q15. Which clinical sign is most characteristic of strychnine poisoning due to glycine receptor blockade?

• Generalized rigidity and severe spasms
• Bradycardia and hypotension
• Profound sedation and coma
• Peripheral neuropathy without motor signs

Correct Answer: Generalized rigidity and severe spasms

Q16. The glycine cleavage system functions primarily in which cellular compartment?

• Mitochondrial matrix
• Endoplasmic reticulum
• Cytosol
• Golgi apparatus

Correct Answer: Mitochondrial matrix

Q17. Which subunit composition confers strychnine sensitivity to glycine receptors?

• Alpha subunits (e.g., α1 homomeric or α1β heteromeric receptors)
• Only beta subunit homomers
• NMDA receptor subunits
• Metabotropic glutamate receptor complexes

Correct Answer: Alpha subunits (e.g., α1 homomeric or α1β heteromeric receptors)

Q18. Inhibition of GlyT2 would be expected to cause which immediate synaptic effect?

• Reduced presynaptic glycine refill and decreased glycinergic transmission over time
• Increased glycine synthesis from serine
• Direct blockade of postsynaptic glycine receptors
• Increased vesicular storage of glycine

Correct Answer: Reduced presynaptic glycine refill and decreased glycinergic transmission over time

Q19. Which of the following is NOT a recognized physiological role of glycine in the CNS?

• Primary direct activation of muscarinic acetylcholine receptors
• Inhibitory neurotransmission in spinal cord
• Co-agonist for NMDA receptors facilitating excitatory transmission
• Modulation of pain pathways

Correct Answer: Primary direct activation of muscarinic acetylcholine receptors

Q20. Mutations in which transporter are most directly associated with autosomal recessive hyperekplexia?

• GLYT2 (SLC6A5)
• GlyT1 (SLC6A9)
• EAAT1 (SLC1A3)
• DAT (SLC6A3)

Correct Answer: GLYT2 (SLC6A5)

Q21. Which pharmacological agent would enhance glycinergic inhibitory currents by acting as a positive allosteric modulator of the glycine receptor?

• Ivermectin (in certain receptor isoforms)
• Strychnine
• Phencyclidine (PCP)
• NBQX

Correct Answer: Ivermectin (in certain receptor isoforms)

Q22. Which clinical laboratory finding is characteristic of non-ketotic hyperglycinemia?

• Markedly elevated glycine in CSF and plasma with high CSF:plasma ratio
• Low plasma glycine and high CSF glutamate
• Elevated urinary ketones with normal glycine
• Low CSF glycine with elevated serine

Correct Answer: Markedly elevated glycine in CSF and plasma with high CSF:plasma ratio

Q23. Which experimental approach directly detects glycine receptor-mediated currents in neurons?

• Whole-cell patch-clamp electrophysiology
• Western blotting of receptor subunits
• qPCR for GLRA1 mRNA
• Immunohistochemistry for glycine

Correct Answer: Whole-cell patch-clamp electrophysiology

Q24. Glycine’s inhibitory effect is reduced if the neuronal chloride equilibrium potential becomes more positive. This phenomenon is called:

• Depolarizing shift of inhibitory postsynaptic potential
• Long-term potentiation
• Presynaptic facilitation
• Metaplasticity

Correct Answer: Depolarizing shift of inhibitory postsynaptic potential

Q25. Which molecule donates one-carbon units during the conversion of serine to glycine by serine hydroxymethyltransferase?

• Tetrahydrofolate (THF)
• S-adenosylmethionine (SAM)
• ATP
• Biotin

Correct Answer: Tetrahydrofolate (THF)

Q26. Co-release of glycine with GABA at some inhibitory synapses results in:

• Mixed inhibitory postsynaptic currents with contributions from GABAA and glycine receptors
• Enhanced excitatory transmission via AMPA receptors
• Exclusive activation of metabotropic receptors
• Blockade of NMDA receptors

Correct Answer: Mixed inhibitory postsynaptic currents with contributions from GABAA and glycine receptors

Q27. A GlyT1 inhibitor would most likely have which short-term effect on NMDA receptor-mediated synaptic currents?

• Increase NMDA-mediated currents by raising glycine at synaptic/extrasynaptic sites
• Decrease NMDA currents by blocking glutamate binding
• Directly open glycine receptor chloride channels
• Cause rapid degradation of NMDA receptors

Correct Answer: Increase NMDA-mediated currents by raising glycine at synaptic/extrasynaptic sites

Q28. Which subunit composition is commonly found in adult spinal glycine receptors mediating fast inhibition?

• α1β heteromeric receptors
• α3 homomeric receptors only
• β homomeric receptors only
• NMDA-GluN2 heteromers

Correct Answer: α1β heteromeric receptors

Q29. Which therapeutic agent is commonly used to reduce exaggerated startle and muscle stiffness in hyperekplexia?

• Clonazepam
• Propranolol
• Levodopa
• Phenytoin

Correct Answer: Clonazepam

Q30. Which statement best describes glycine’s dual role in the CNS?

• Glycine is both an inhibitory synaptic neurotransmitter (via glycine receptors) and an excitatory NMDA co‑agonist modulating glutamatergic signaling.
• Glycine only serves as an inhibitory neurotransmitter and has no excitatory functions.
• Glycine acts primarily as a neuromodulator of acetylcholine receptors.
• Glycine exclusively functions in peripheral neurotransmission, not in the CNS.

Correct Answer: Glycine is both an inhibitory synaptic neurotransmitter (via glycine receptors) and an excitatory NMDA co‑agonist modulating glutamatergic signaling.

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