Central Nervous System Pharmacology Practice Questions

Q: Which of the following is true about barbiturates?

Shows GABA facilitatory action. ***Shows GABA facilitatory action*** - Barbiturates enhance the effect of **GABA** (gamma-aminobutyric acid), the primary inhibitory neurotransmitter in the central nervous system, by increasing the **duration** of chloride channel opening. - This facilitatory action leads to **hyperpolarization** of neurons, making them less excitable and resulting in CNS depression. - This is the **primary mechanism** of action of barbiturates at therapeutic doses. *Enhances GABAergic activity by mimicking GABA's effects* - While barbiturates enhance GABAergic activity, they do not **mimic GABA's effects** in the same direct way that full agonists do. - Instead of acting as direct agonists, barbiturates **allosterically modulate** the GABA A receptor, increasing the receptor's affinity for GABA and prolonging the opening time of the associated chloride channel. *Limbic system is most sensitive to the depressive action of barbiturates to CNS* - The **reticular activating system (RAS)** in the brainstem, which plays a crucial role in regulating wakefulness and arousal, is generally considered the most sensitive area to the depressive effects of barbiturates. - While the limbic system is affected, its sensitivity is not uniquely highest compared to other CNS regions like the RAS, which is critical for the sedative and hypnotic effects observed. *Primarily acts by blocking voltage gated Na+ and K+ channels* - This is **incorrect**. The primary mechanism of barbiturates is through **GABA A receptor modulation**, not by blocking voltage-gated ion channels. - While barbiturates can have non-specific membrane effects on voltage-gated channels at very high (toxic) concentrations, this is not their primary or therapeutic mechanism of action.

Q: Which of the following is not true about benzodiazepines?

REM, and Stage 3 and 4 sleep is increased. **REM, and Stage 3 and 4 sleep is increased** - Benzodiazepines actually **decrease REM sleep** and **slow-wave sleep** (Stages 3 and 4) while increasing Stage 2 sleep. - This alteration in sleep architecture contributes to less restorative sleep despite inducing sedation. *Can produce ataxia* - Benzodiazepines can cause **ataxia**, especially at higher doses, due to their depressant effects on the **cerebellum** and motor coordination centers. - This side effect is a common concern, particularly in older adults, increasing the risk of falls. *Has GABA facilitatory but no GABA mimetic action* - Benzodiazepines **facilitate the action of GABA** by increasing the *frequency* of chloride channel opening, leading to enhanced inhibitory neurotransmission. - They do not directly activate GABA receptors in the absence of GABA, meaning they have no direct **GABA mimetic action**. *Produces muscle relaxation by action on spinal cord* - Benzodiazepines exert their **muscle relaxant effects** primarily by enhancing *GABAergic inhibition* in the **spinal cord** and **brainstem**. - This leads to a reduction in skeletal muscle tone and can be beneficial in treating muscle spasms.

Q: Which drug is contraindicated in the treatment of absence seizures?

Tiagabine. ***Tiagabine*** - **Tiagabine** is an antiepileptic drug that selectively inhibits the reuptake of **GABA** (gamma-aminobutyric acid) in the brain, thereby increasing GABAergic transmission [1, 2, 3]. This mechanism is primarily effective in **focal seizures** and sometimes in **generalized tonic-clonic seizures** [2, 3]. - While tiagabine is used for other seizure types, it is known to **exacerbate absence seizures**, making it contraindicated in their treatment [1]. This paradoxical effect is thought to be due to its complex influence on thalamocortical networks involved in absence seizure generation [1, 2].*Ethosuximide* - **Ethosuximide** is a first-line agent specifically for **absence seizures**. It acts by blocking **T-type calcium channels** in the thalamic neurons, which are crucial for the generation of the characteristic 3-Hz spike-and-wave discharges of absence seizures. - It is highly effective in reducing or eliminating absence seizures with a favorable side effect profile, making it a preferred choice for this specific seizure type.*Clonazepam* - **Clonazepam** is a **benzodiazepine** that enhances the effect of GABA at GABA-A receptors, leading to increased neuronal inhibition. It is effective in various seizure types, including **absence seizures** and **myoclonic seizures**. - While not a first-line treatment due to its sedative side effects and potential for tolerance, it can be used as an adjunct or alternative when other medications are ineffective or not tolerated.*Valproate* - **Valproate** (valproic acid) is a broad-spectrum antiepileptic drug effective against a wide range of seizure types, including **absence seizures**, myoclonic seizures, and **generalized tonic-clonic seizures**. - Its mechanism of action is multifaceted, involving increased GABA synthesis and decreased degradation, voltage-gated sodium channel blockade, and modulation of T-type calcium channels, making it a highly versatile agent.

Q: What is the drug of choice for aborting the acute attack of migraine?

Triptans such as sumatriptan. ***Triptans such as sumatriptan*** - **Triptans** are **serotonin 5-HT1B/1D receptor agonists** that cause **vasoconstriction** of intracranial blood vessels and inhibit pronociceptive neuropeptide release, making them highly effective for acute migraine attacks. - They are considered the **first-line specific treatment** for moderate to severe migraine pain or when NSAIDs are ineffective. *NSAIDs such as indomethacin* - **NSAIDs** are effective for mild to moderate migraine attacks but are generally **less effective** than triptans for severe attacks. - While they can reduce inflammation and pain, their mechanism of action is **non-specific** compared to triptans in targeting migraine pathology. *Opioids such as morphine* - **Opioids** are generally **not recommended** for acute migraine treatment due to their potential for **abuse, dependence**, and lack of specific anti-migraine effects. - They can also worsen migraine outcomes over time and contribute to **medication overuse headache**. *Glucocorticoids* - **Glucocorticoids** like dexamethasone may be used as **adjunctive therapy** to prevent migraine recurrence, particularly in status migrainosus. - However, they are **not the primary drug of choice** for aborting an acute attack due to their slower onset of action and broad side effect profile.

Q: Which of the following drug pairs is correctly matched?

Peripheral decarboxylase inhibitor - Benserazide. ***Peripheral decarboxylase inhibitor - Benserazide*** - **Benserazide** is a **peripheral decarboxylase inhibitor** that is commonly co-administered with **levodopa** to prevent its metabolism in the periphery. - By inhibiting the breakdown of levodopa outside the brain, **more levodopa can cross the blood-brain barrier**, where it is then converted to dopamine. *MAO-A inhibitor - Selegiline* - **Selegiline** is an **MAO-B inhibitor**, not an MAO-A inhibitor. It selectively inhibits the enzyme **monoamine oxidase B**, which is responsible for dopamine breakdown in the brain. - **MAO-A inhibitors** (like moclobemide) are primarily used as antidepressants, as they inhibit the breakdown of serotonin and norepinephrine. *COMT inhibitor - Rasagiline* - **Rasagiline** is an **MAO-B inhibitor**, similar to selegiline, used in the treatment of **Parkinson's disease** to reduce the breakdown of dopamine. - **COMT inhibitors** (like entacapone and tolcapone) block the enzyme **catechol-O-methyltransferase**, another enzyme involved in the peripheral and central metabolism of levodopa and dopamine. *Dopamine agonist - Amantadine* - **Amantadine** is an **antiviral drug** that also has **anti-Parkinsonian effects**, primarily through its influence on dopamine release and reuptake, as well as NMDA receptor antagonism. - While it modulates dopamine, it is not classified as a direct **dopamine agonist**; true dopamine agonists (like pramipexole and ropinirole) directly stimulate dopamine receptors.

Q: Which of the following is the most commonly prescribed first-line medication for ADHD?

Methylphenidate. ***Methylphenidate*** - **Methylphenidate** is a central nervous system stimulant and is widely considered a **first-line treatment** for ADHD in both children and adults. - It works by increasing the levels of **dopamine** and **norepinephrine** in the brain, improving attention and reducing impulsivity. - Most commonly prescribed due to extensive clinical experience, proven efficacy, and favorable safety profile. *Atomoxetine* - **Atomoxetine** is a **non-stimulant** medication used for ADHD, but it is typically considered second-line due to slower onset of action compared to stimulants. - It selectively inhibits the reuptake of **norepinephrine**, taking several weeks to show full therapeutic effect. - Preferred when stimulants are contraindicated or not tolerated. *Dextroamphetamine* - **Dextroamphetamine** is an effective **stimulant** medication for ADHD, but it is often reserved as an alternative if methylphenidate is not well-tolerated or effective. - It also increases **dopamine** and **norepinephrine** but has a slightly different pharmacological profile and duration of action. *Guanfacine* - **Guanfacine** is an **alpha-2 adrenergic agonist** used as adjunctive or alternative therapy for ADHD. - It is **not a first-line medication** and is typically used when stimulants are ineffective, contraindicated, or for specific symptom management (especially hyperactivity/impulsivity). - Has a different mechanism of action focusing on prefrontal cortex modulation.

Q: Withdrawal of which of the following substances is most commonly associated with piloerection?

Morphine. ***Morphine*** - **Piloerection**, or "goosebumps," is a classic symptom of **opioid withdrawal**, particularly from strong opioids like morphine, due to sympathetic nervous system overactivity. - This sympathetic hyperactivity also manifests as **dilated pupils**, rhinorrhea, lacrimation, and sweating during opioid withdrawal. *Cannabis* - Withdrawal symptoms from **cannabis** typically include irritability, anxiety, sleep disturbances, and decreased appetite, but not prominent piloerection. - The sympathetic activation seen with opioid withdrawal is generally absent in cannabis withdrawal. *Smoking* - **Nicotine withdrawal** is characterized by irritability, anxiety, difficulty concentrating, and increased appetite, but **piloerection** is not a common or prominent symptom. - Nicotine withdrawal primarily affects neuropsychological functions and cravings, rather than leading to significant sympathetic overdrive causing skin manifestations. *Alcohol* - **Alcohol withdrawal** can be severe, including tremors, hallucinations, and seizures (delirium tremens), but **piloerection** is not a hallmark symptom. - Alcohol withdrawal primarily involves central nervous system hyperexcitability and autonomic dysfunction, but "goosebumps" are not typically reported as a key feature.

Q: All of the following about thiopentone are true except which one?

IV injection is painless. ***IV injection is painless*** - Thiopentone is a **barbiturate anesthetic** that is known to cause **pain on injection** due to its **alkaline pH** and propensity to cause local irritation. - This characteristic makes the statement that its IV injection is painless incorrect, as pain and venous irritation are common side effects. *It decreases ICP* - Thiopentone, like other barbiturates, causes **cerebral vasoconstriction**, leading to a decrease in **cerebral blood flow** and **intracranial pressure (ICP)**, making it useful in neurosurgical settings. - This effect is due to a reduction in **cerebral metabolic rate for oxygen (CMRO2)**, which couples with cerebral blood flow. *It has anticonvulsant action* - Thiopentone is a potent **anticonvulsant** because it enhances the inhibitory effects of **GABA** in the central nervous system, which helps to suppress seizure activity. - It is used to terminate **status epilepticus** that is refractory to other treatments. *It can cause reflex tachycardia* - Thiopentone can cause **peripheral vasodilation** and a decrease in **blood pressure**, which may trigger a **reflex tachycardia** as the body attempts to compensate for the reduced systemic vascular resistance. - This effect is generally mild but can be more pronounced in hypovolemic patients or at higher doses.

Q: Which of the following serotonin receptors is classified as an ionotropic receptor?

5-HT3. ***5-HT3*** - The 5-HT3 receptor is unique among serotonin receptors as it is the **only ionotropic receptor**, meaning it directly gates an ion channel upon ligand binding. - Activation of 5-HT3 receptors leads to rapid **depolarization** of the neuronal membrane through the influx of **sodium and potassium ions**, mediating fast excitatory neurotransmission. *5-HT1A* - The 5-HT1A receptor is a **G-protein coupled receptor (GPCR)** and is inhibitory, primarily located pre- and post-synaptically in the brain. - Activation leads to a decrease in **cAMP** levels and opening of **potassium channels**, resulting in hyperpolarization. *5-HT1B* - The 5-HT1B receptor is also a **GPCR**, primarily found on presynaptic terminals where it acts as an **autoreceptor** to inhibit serotonin release. - Similar to 5-HT1A, its activation inhibits adenylyl cyclase activity, leading to reduced **cAMP** levels. *5-HT2A* - The 5-HT2A receptor is a **GPCR** that couples to the Gq protein, leading to increased **inositol triphosphate (IP3)** and **diacylglycerol (DAG)**. - This pathway activates protein kinase C and mobilizes intracellular calcium, typically leading to **excitatory effects** in various brain regions.

Question 1

Which of the following is true about barbiturates?

Accepted Answer

Shows GABA facilitatory action

Answer

Limbic system is most sensitive to the depressive action of barbiturates to CNS

Answer

Enhances GABAergic activity by mimicking GABA's effects

Answer

Primarily acts by blocking voltage gated Na+ and K+ channels

Question 2

Which of the following is not true about benzodiazepines?

Accepted Answer

REM, and Stage 3 and 4 sleep is increased

Answer

Can produce ataxia

Answer

Has GABA facilitatory but no GABA mimetic action

Answer

Produces muscle relaxation by action on spinal cord

Question 3

Which drug is contraindicated in the treatment of absence seizures?

Accepted Answer

Tiagabine

Answer

Clonazepam

Answer

Ethosuximide

Answer

Valproate

Question 4

Which of the following statements about the anti-Parkinson drug levodopa is true?

Accepted Answer

Only a small percentage of administered levodopa crosses the blood-brain barrier (approximately 2%).

Answer

Levodopa is an active metabolite of dopamine.

Answer

About 50% of administered levodopa is peripherally converted to dopamine.

Answer

Levodopa is not used in the management of hepatic coma.

Question 5

What is the drug of choice for aborting the acute attack of migraine?

Accepted Answer

Triptans such as sumatriptan

Answer

NSAIDs such as indomethacin

Answer

Opioids such as morphine

Answer

Glucocorticoids

Question 6

Which of the following drug pairs is correctly matched?

Accepted Answer

Peripheral decarboxylase inhibitor - Benserazide

Answer

Dopamine agonist - Amantadine

Answer

COMT inhibitor - Rasagiline

Answer

MAO-A inhibitor - Selegiline

Question 7

Which of the following is the most commonly prescribed first-line medication for ADHD?

Accepted Answer

Methylphenidate

Answer

Atomoxetine

Answer

Dextroamphetamine

Answer

Guanfacine

Question 8

Withdrawal of which of the following substances is most commonly associated with piloerection?

Accepted Answer

Morphine

Answer

Cannabis

Answer

Smoking

Answer

Alcohol

Question 9

All of the following about thiopentone are true except which one?

Accepted Answer

IV injection is painless

Answer

It has anticonvulsant action

Answer

It can cause reflex tachycardia

Answer

It decreases ICP

Question 10

Which of the following serotonin receptors is classified as an ionotropic receptor?

Accepted Answer

5-HT3

Answer

5-HT1A

Answer

5-HT1B

Answer

5-HT2A

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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