Neurotransmitters – GABA MCQs With Answer

Neurotransmitters – GABA MCQs With Answer

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Neurotransmitters – GABA MCQs With Answer

Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the mammalian central nervous system. This concise, student-focused review highlights GABA synthesis, metabolism, receptors (GABAA and GABAB), transporters, pharmacological modulators such as benzodiazepines, barbiturates, baclofen, vigabatrin, and clinical implications in epilepsy, anxiety, sleep disorders, and muscle spasm. Emphasis is given to GABAergic pharmacology, receptor subunit composition, mode of action (ionotropic vs metabotropic), and drug targets relevant to B. Pharm students preparing for exams and therapeutics. Clear understanding of GAD enzymes, GABA-T, VGAT, and GAT transporters is essential for rational drug design and safe pharmacotherapy. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which enzyme catalyzes the conversion of glutamate to GABA?

  • Glutamic acid decarboxylase (GAD)
  • GABA transaminase (GABA-T)
  • Glutamine synthetase
  • Monoamine oxidase

Correct Answer: Glutamic acid decarboxylase (GAD)

Q2. Which cofactor is essential for the activity of glutamic acid decarboxylase (GAD)?

  • Pyridoxal phosphate (PLP)
  • Flavin adenine dinucleotide (FAD)
  • Nicotinamide adenine dinucleotide (NAD+)
  • Biotin

Correct Answer: Pyridoxal phosphate (PLP)

Q3. GABA-A receptors are best described as which type of receptor?

  • Ionotropic chloride channel
  • Metabotropic G protein-coupled receptor
  • Tyrosine kinase receptor
  • Nicotinic acetylcholine receptor family member

Correct Answer: Ionotropic chloride channel

Q4. GABA-B receptors primarily signal through which mechanism?

  • Gi/Go protein-mediated inhibition of adenylate cyclase
  • Opening of ligand-gated sodium channels
  • Activation of receptor tyrosine kinases
  • Direct gating of chloride channels

Correct Answer: Gi/Go protein-mediated inhibition of adenylate cyclase

Q5. Which drug is a selective GABA-B receptor agonist used as a muscle relaxant?

  • Baclofen
  • Diazepam
  • Phenobarbital
  • Vigabatrin

Correct Answer: Baclofen

Q6. Which drug irreversibly inhibits GABA transaminase (GABA-T), increasing brain GABA levels?

  • Vigabatrin
  • Tiagabine
  • Gabapentin
  • Flumazenil

Correct Answer: Vigabatrin

Q7. Which agent blocks GABA reuptake by inhibiting the GAT-1 transporter?

  • Tiagabine
  • Baclofen
  • Picrotoxin
  • Pregabalin

Correct Answer: Tiagabine

Q8. The vesicular transporter responsible for packaging GABA into synaptic vesicles is known as:

  • Vesicular GABA transporter (VGAT/VIAAT)
  • Vesicular monoamine transporter (VMAT)
  • Glutamate transporter EAAT
  • Choline acetyltransferase (ChAT)

Correct Answer: Vesicular GABA transporter (VGAT/VIAAT)

Q9. Which class of drugs acts as positive allosteric modulators at the benzodiazepine binding site on GABA-A receptors?

  • Benzodiazepines
  • SSRIs
  • MAO inhibitors
  • Opioids

Correct Answer: Benzodiazepines

Q10. Barbiturates potentiate GABA-A receptor function primarily by:

  • Prolonging the duration of chloride channel opening
  • Blocking GABA binding competitively
  • Inhibiting GABA synthesis
  • Acting as GABA-B agonists

Correct Answer: Prolonging the duration of chloride channel opening

Q11. Which compound is a competitive antagonist at the GABA-A receptor?

  • Bicuculline
  • Picrotoxin
  • Flumazenil
  • Phenobarbital

Correct Answer: Bicuculline

Q12. Picrotoxin inhibits GABA-A receptor-mediated inhibition by:

  • Blocking the chloride channel pore noncompetitively
  • Competing with GABA at the orthosteric site
  • Enhancing benzodiazepine binding
  • Inhibiting GABA synthesis

Correct Answer: Blocking the chloride channel pore noncompetitively

Q13. Which GAD isoform is primarily associated with synaptic GABA synthesis and is membrane-associated?

  • GAD65
  • GAD67
  • GAD100
  • GAD1

Correct Answer: GAD65

Q14. Which GAD isoform is constitutively active and distributed throughout the neuron cytosol?

  • GAD67
  • GAD65
  • GAD2
  • GAD3

Correct Answer: GAD67

Q15. Benzodiazepine efficacy depends on the presence of which GABA-A receptor subunit in addition to α and β?

  • γ subunit
  • δ subunit
  • ε subunit
  • π subunit

Correct Answer: γ subunit

Q16. Which GABA-A receptor subunit composition is most associated with sedative effects of benzodiazepines?

  • α1-containing receptors
  • α2-containing receptors
  • α3-containing receptors
  • α5-containing receptors

Correct Answer: α1-containing receptors

Q17. Flumazenil is used clinically to:

  • Reverse benzodiazepine effects by antagonizing the benzodiazepine site
  • Inhibit GABA transaminase
  • Enhance barbiturate activity
  • Act as a GABA-B agonist

Correct Answer: Reverse benzodiazepine effects by antagonizing the benzodiazepine site

Q18. Which adverse effect is commonly associated with excessive GABAergic activity from sedative-hypnotics?

  • Respiratory depression and sedation
  • Hypertension and tachycardia
  • Hyperreflexia and agitation
  • Severe cholinergic crisis

Correct Answer: Respiratory depression and sedation

Q19. Vigabatrin’s major clinical use is in the treatment of:

  • Refractory epilepsyIncluding infantile spasms and complex partial seizures
  • Essential hypertension
  • Parkinson’s disease tremor
  • Major depressive disorder

Correct Answer: Refractory epilepsyIncluding infantile spasms and complex partial seizures

Q20. Gabapentin and pregabalin increase GABAergic tone indirectly by:

  • Binding to the α2δ subunit of voltage-gated calcium channels to reduce excitatory neurotransmitter release
  • Directly agonizing GABA-A receptors
  • Inhibiting GABA-T irreversibly
  • Blocking benzodiazepine binding

Correct Answer: Binding to the α2δ subunit of voltage-gated calcium channels to reduce excitatory neurotransmitter release

Q21. Which transporter mediates reuptake of GABA into presynaptic neurons and glia?

  • GAT-1 (GABA transporter 1)
  • DAT (dopamine transporter)
  • SERT (serotonin transporter)
  • EAAT2 (glutamate transporter)

Correct Answer: GAT-1 (GABA transporter 1)

Q22. Tolerance to the sedative effects of benzodiazepines is primarily due to:

  • Receptor desensitization and adaptive changes in GABA-A receptor expression
  • Increased GABA synthesis
  • Permanent loss of GABAergic neurons
  • Upregulation of GABA transporters

Correct Answer: Receptor desensitization and adaptive changes in GABA-A receptor expression

Q23. Which clinical condition is most directly related to reduced GABAergic inhibition?

  • Epilepsy
  • Hyperthyroidism
  • Parkinson’s disease
  • Myasthenia gravis

Correct Answer: Epilepsy

Q24. The inhibitory postsynaptic potential (IPSP) produced by GABA-A receptor activation is primarily due to:

  • Increased chloride conductance causing hyperpolarization
  • Increased sodium influx causing depolarization
  • Activation of adenylate cyclase
  • Opening of voltage-gated calcium channels

Correct Answer: Increased chloride conductance causing hyperpolarization

Q25. Which drug is an inverse agonist at the benzodiazepine site and can provoke anxiety and seizures?

  • β-carboline inverse agonists (e.g., FG-7142)
  • Diazepam
  • Flunitrazepam
  • Baclofen

Correct Answer: β-carboline inverse agonists (e.g., FG-7142)

Q26. Which statement about GABA metabolism is correct?

  • GABA is catabolized by GABA transaminase to succinic semialdehyde
  • GABA is methylated by COMT to inactive metabolites
  • GABA is converted back to glutamate by monoamine oxidase
  • GABA is degraded by acetylcholinesterase

Correct Answer: GABA is catabolized by GABA transaminase to succinic semialdehyde

Q27. Which therapeutic strategy increases synaptic GABA concentration acutely?

  • Enhancing GABA release or blocking GABA reuptake
  • Inhibiting GAD activity
  • Increasing GABA-T activity
  • Blocking VGAT

Correct Answer: Enhancing GABA release or blocking GABA reuptake

Q28. The term “GABAergic interneurons” primarily refers to neurons that:

  • Release GABA and mediate local inhibitory control within circuits
  • Project long distances to peripheral organs
  • Release glutamate and excite pyramidal cells
  • Are exclusively found in the peripheral nervous system

Correct Answer: Release GABA and mediate local inhibitory control within circuits

Q29. Which drug interaction is of major concern with GABAergic sedative-hypnotics?

  • Additive respiratory depression with opioids and alcohol
  • Reduced effect when combined with SSRIs
  • Hypertensive crisis with MAO inhibitors
  • Serotonin syndrome with tricyclics

Correct Answer: Additive respiratory depression with opioids and alcohol

Q30. For rational drug design targeting GABA-A receptors, which feature is most relevant?

  • Subunit composition (α, β, γ, δ) determines pharmacology and drug selectivity
  • Only the α subunit exists and determines all receptor properties
  • GABA-A receptors are identical in all brain regions
  • Drugs cannot differentiate between receptor subtypes

Correct Answer: Subunit composition (α, β, γ, δ) determines pharmacology and drug selectivity

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