In patients with chronic obstructive pulmonary disease, stimulation of muscarinic acetylcholine receptors results in an increase in mucus secretion, smooth muscle contraction and bronchoconstriction. The end result is an increase in airway resistance. Which of the following pharmacologic agents interferes directly with this pathway?
Q222
A 43-year-old man is brought to the emergency department by his wife because of a 1-hour history of confusion and strange behavior. She reports that he started behaving in an agitated manner shortly after eating some wild berries that they had picked during their camping trip. His temperature is 38.7°C (101.7°F). Physical examination shows warm, dry skin and dry mucous membranes. His pupils are dilated and minimally reactive to light. His bowel sounds are decreased. The patient is admitted and pharmacotherapy is initiated with a drug that eventually results in complete resolution of all of his symptoms. This patient was most likely administered which of the following drugs?
Q223
A 24-year-old man is brought to the emergency department by his roommates for aggressive and unusual behavior. His roommates state that he has been under a lot of stress lately from his final exams and has been more reclusive. They state that this evening he was very irritable and was yelling at his computer prior to breaking it, followed by him spending several hours at the gym. His temperature is 101°F (38.3°C), blood pressure is 137/98 mmHg, pulse is 120/min, respirations are 23/min, and oxygen saturation is 99% on room air. Physical exam is notable for an irritable young man. Cardiopulmonary exam is notable for tachycardia and bilateral clear breath sounds. Neurological exam reveals dilated pupils. The patient is notably diaphoretic and speaks very rapidly during the physical exam and is aggressive. He is given haloperidol, diphenhydramine, and diazepam for sedation and placed in soft restraints. His symptoms resolved over the next 10 hours in the emergency department. Which of the following is the most likely diagnosis?
Q224
A 65-year-old man presents to the emergency department with confusion and a change in his behavior. The patient was in his usual state of health 3 days ago. He became more confused and agitated this morning thus prompting his presentation. The patient has a past medical history of depression, hypertension, diabetes, and Parkinson disease and is currently taking fluoxetine, lisinopril, insulin, metformin, and selegiline (recently added to his medication regimen for worsening Parkinson symptoms). He also takes oxycodone and clonazepam for pain and anxiety; however, he ran out of these medications last night. His temperature is 101°F (38.3°C), blood pressure is 111/78 mmHg, pulse is 117/min, respirations are 22/min, and oxygen saturation is 99% on room air. Physical exam is notable for an irritable, sweaty, and confused elderly man. Neurological exam reveals hyperreflexia of the lower extremities and clonus. Which of the following is the most likely etiology of this patient’s symptoms?
Q225
A 50-year-old woman presents with altered taste and a gritty sensation in her eyes for the last month. She mentions that she needs to drink water frequently and often feels that her mouth and throat are dry. On physical examination, she has bilateral enlargement of the parotid glands and dry conjunctivae. Her physical examination and laboratory findings suggest a diagnosis of sicca syndrome. In addition to non-pharmacological measures, a drug is prescribed to improve symptoms related to dryness of mouth by increasing salivation. Which of the following is the mechanism of action of the drug that most likely is being prescribed to this patient?
Q226
A 19-year-old male presents to the ER with generalized tonic-clonic seizures. He does not have a prior history of seizures and has not taken any drugs except for his daily asthma medication. Which of the following is associated with seizures?
Q227
A 36-year-old man is admitted to the hospital for treatment of burn wounds on his upper extremities. Analgesic therapy with an opioid drug is begun. Shortly after, the patient develops chills, diaphoresis, nausea, and abdominal pain. On further questioning, the patient reports that he has been smoking opium at home to help him ""deal with the depression and pain.” This patient was most likely given which of the following opioid drugs?
Q228
A 16 year-old female is being evaluated for shortness of breath. For the last year she has had shortness of breath and subjective wheezing with exercise and intermittent coughing at night. She reports waking up from sleep coughing 1-2 times per month. She now skips gym class because of her symptoms. She denies any coughing, chest tightness, or shortness of breath on the day of her visit. On exam, her lungs are clear to auscultation bilaterally, with normal inspiratory to expiratory duration ratio. Her pulmonary function tests (PFTs) show normal FEV1 and FVC based on her age, gender, and height. She is told to inhale a medication, and her PFTs are repeated, now showing a FEV1 79% of her previous reading. The patient is diagnosed with asthma. Which of the following medications was used to diagnose the patient?
Q229
A 32-year-old man with a history of major depressive disorder is brought to the emergency department by his wife because of a sudden onset of restlessness and disorientation that developed 3 hours ago. The patient’s wife says that he suddenly started sweating, having tremors, and mumbling to himself. Yesterday, the patient visited his psychiatrist with worsening depression who added phenelzine to his current treatment regimen. No other significant past medical history. His temperature is 39.7°C (103.5°F), blood pressure is 145/90 mm Hg, and pulse is 115/min. On physical examination, the skin is flushed. Mucous membranes are dry, and pupils are dilated. There is pronounced clonus in the extremities bilaterally. Babinski sign is present bilaterally. All the patient’s medications are discontinued, and intravenous fluids are started. Which of the following drugs most likely interacted with phenelzine to cause this patient’s condition?
Q230
A neurophysiologist describes the mechanism of a specific type of synaptic transmission to his students. While illustrating this, he points out that when the action potential reaches the presynaptic terminal of a chemical synapse, the voltage-gated Ca2+ channels open. Ca2+ ions trigger the release of neurotransmitters from vesicles in the presynaptic terminal. In this type of synaptic transmission, increased cytosolic Ca2+ levels cause the release of a neurotransmitter from small vesicles with dense cores. Which of the following neurotransmitters is most likely to be the one that is released into the synaptic cleft in this type of synapse?
Cholinergic/Adrenergic drugs US Medical PG Practice Questions and MCQs
Question 221: In patients with chronic obstructive pulmonary disease, stimulation of muscarinic acetylcholine receptors results in an increase in mucus secretion, smooth muscle contraction and bronchoconstriction. The end result is an increase in airway resistance. Which of the following pharmacologic agents interferes directly with this pathway?
A. Epinephrine
B. Albuterol
C. Theophylline
D. Ipratropium (Correct Answer)
E. Metoprolol
Explanation: ***Ipratropium***
- **Ipratropium** is an **anticholinergic** agent that blocks muscarinic acetylcholine receptors.
- By blocking these receptors, it **reduces bronchoconstriction**, mucus secretion, and smooth muscle contraction, thus decreasing airway resistance.
*Epinephrine*
- **Epinephrine** is a non-selective **adrenergic agonist** that stimulates both alpha and beta receptors.
- Its effects in the airways are primarily mediated through **beta-2 agonism**, leading to bronchodilation, but it does not directly interfere with muscarinic pathways.
*Albuterol*
- **Albuterol** is a **short-acting beta-2 adrenergic agonist (SABA)**.
- It primarily causes bronchodilation by stimulating beta-2 receptors on airway smooth muscle, independent of the muscarinic pathway.
*Theophylline*
- **Theophylline** is a **methylxanthine** that primarily acts as a non-selective phosphodiesterase inhibitor.
- This leads to increased intracellular **cAMP** and bronchodilation, but it does not directly block muscarinic acetylcholine receptors.
*Metoprolol*
- **Metoprolol** is a **selective beta-1 adrenergic blocker** (beta-blocker).
- Its primary action is on the heart; it has minimal effect on airway beta-2 receptors at therapeutic doses due to its selectivity, and it does not interfere with the muscarinic pathway.
Question 222: A 43-year-old man is brought to the emergency department by his wife because of a 1-hour history of confusion and strange behavior. She reports that he started behaving in an agitated manner shortly after eating some wild berries that they had picked during their camping trip. His temperature is 38.7°C (101.7°F). Physical examination shows warm, dry skin and dry mucous membranes. His pupils are dilated and minimally reactive to light. His bowel sounds are decreased. The patient is admitted and pharmacotherapy is initiated with a drug that eventually results in complete resolution of all of his symptoms. This patient was most likely administered which of the following drugs?
A. Rivastigmine
B. Atropine
C. Scopolamine
D. Physostigmine (Correct Answer)
E. Neostigmine
Explanation: ***Physostigmine***
- The patient's symptoms (confusion, agitation, dilated pupils, warm/dry skin, decreased bowel sounds, fever) are characteristic of **anticholinergic toxicity**, often caused by ingestion of plants like Jimson weed or deadly nightshade (containing atropine-like alkaloids).
- **Physostigmine** is a **reversible acetylcholinesterase inhibitor** that can cross the **blood-brain barrier** and reverse both central (confusion, agitation) and peripheral (dilated pupils, dry skin, decreased bowel sounds) anticholinergic effects.
*Rivastigmine*
- **Rivastigmine** is an acetylcholinesterase inhibitor primarily used to treat **Alzheimer's disease** and Parkinson's disease dementia.
- While it inhibits acetylcholinesterase, its primary clinical use and efficacy profile do not align with rapid reversal of acute, severe anticholinergic poisoning.
*Atropine*
- **Atropine** is a **muscarinic anticholinergic agent** that would *exacerbate* the patient's symptoms, as the presentation is consistent with anticholinergic poisoning.
- It works by blocking acetylcholine receptors, leading to effects like dilated pupils, dry mouth, and decreased gastrointestinal motility.
*Scopolamine*
- **Scopolamine** is another potent **muscarinic anticholinergic agent** that causes similar symptoms to atropine, particularly confusion and delirium due to its central nervous system effects.
- Administering scopolamine would worsen the patient's existing anticholinergic toxidrome.
*Neostigmine*
- **Neostigmine** is a **reversible acetylcholinesterase inhibitor** used for conditions like myasthenia gravis and reversal of neuromuscular blockade.
- However, **neostigmine does not cross the blood-brain barrier** effectively, meaning it would not reverse the central nervous system symptoms (confusion, agitation) prominent in this anticholinergic poisoning case.
Question 223: A 24-year-old man is brought to the emergency department by his roommates for aggressive and unusual behavior. His roommates state that he has been under a lot of stress lately from his final exams and has been more reclusive. They state that this evening he was very irritable and was yelling at his computer prior to breaking it, followed by him spending several hours at the gym. His temperature is 101°F (38.3°C), blood pressure is 137/98 mmHg, pulse is 120/min, respirations are 23/min, and oxygen saturation is 99% on room air. Physical exam is notable for an irritable young man. Cardiopulmonary exam is notable for tachycardia and bilateral clear breath sounds. Neurological exam reveals dilated pupils. The patient is notably diaphoretic and speaks very rapidly during the physical exam and is aggressive. He is given haloperidol, diphenhydramine, and diazepam for sedation and placed in soft restraints. His symptoms resolved over the next 10 hours in the emergency department. Which of the following is the most likely diagnosis?
A. Cocaine intoxication (Correct Answer)
B. Phencyclidine intoxication
C. Schizophrenia
D. Caffeine intoxication
E. Lisdexamfetamine intoxication
Explanation: ***Cocaine intoxication***
- The patient's presentation with **agitation, aggression, dilated pupils, tachycardia, hypertension, diaphoresis, and rapid speech** is highly consistent with stimulant intoxication, especially **cocaine**.
- The **rapid resolution of symptoms over 10 hours** supports cocaine intoxication, as cocaine has a short half-life (~1 hour) with effects typically resolving within a few hours after cessation.
*Phencyclidine intoxication*
- While PCP can cause aggression, agitation, and dilated pupils, it is classically associated with **nystagmus (horizontal or vertical)**, which is not mentioned here.
- PCP intoxication often presents with **dissociative symptoms** and a severe level of unpredictable violence or bizarre behavior not fully described.
*Schizophrenia*
- The **acute onset of symptoms** in a previously functioning individual, particularly with a clear trigger (stress), is less typical for schizophrenia, which usually has a more insidious prodromal phase.
- The **rapid and complete resolution** of symptoms within hours strongly argues against a primary psychotic disorder like schizophrenia, which requires longer-term treatment.
*Caffeine intoxication*
- While high doses of caffeine can cause **tachycardia, anxiety, and agitation**, it rarely leads to the severe **aggression and property damage** described in this case.
- The degree of physical symptoms like **dilated pupils, hypertension, and significant diaphoresis** would be unusually severe for typical caffeine intoxication.
*Lisdexamfetamine intoxication*
- Lisdexamfetamine (Vyvanse) is an amphetamine prodrug that shares many symptoms with cocaine intoxication, including **agitation, aggression, dilated pupils, and sympathetic overdrive**.
- However, amphetamines have a **much longer duration of action (8-12+ hours)** compared to cocaine, so complete symptom resolution within 10 hours would be less typical for amphetamine intoxication, which often requires longer observation periods.
Question 224: A 65-year-old man presents to the emergency department with confusion and a change in his behavior. The patient was in his usual state of health 3 days ago. He became more confused and agitated this morning thus prompting his presentation. The patient has a past medical history of depression, hypertension, diabetes, and Parkinson disease and is currently taking fluoxetine, lisinopril, insulin, metformin, and selegiline (recently added to his medication regimen for worsening Parkinson symptoms). He also takes oxycodone and clonazepam for pain and anxiety; however, he ran out of these medications last night. His temperature is 101°F (38.3°C), blood pressure is 111/78 mmHg, pulse is 117/min, respirations are 22/min, and oxygen saturation is 99% on room air. Physical exam is notable for an irritable, sweaty, and confused elderly man. Neurological exam reveals hyperreflexia of the lower extremities and clonus. Which of the following is the most likely etiology of this patient’s symptoms?
A. Electrolyte abnormality
B. Medication complication (Correct Answer)
C. Viral infection
D. Substance withdrawal
E. Bacterial infection
Explanation: ***Medication complication***
- The combination of **fluoxetine** and **selegiline** can precipitate **serotonin syndrome**, characterized by altered mental status, autonomic dysfunction (fever, tachycardia, sweating), and neuromuscular hyperactivity (hyperreflexia, clonus).
- Both medications increase serotonin levels in the central nervous system; fluoxetine is a selective serotonin reuptake inhibitor (SSRI), and selegiline is a monoamine oxidase type B (MAO-B) inhibitor that, at higher doses, can also inhibit MAO-A, leading to increased serotonin.
*Electrolyte abnormality*
- While electrolyte imbalances can cause confusion and altered mental status, they typically do not present with the specific constellation of fever, tachycardia, sweating, hyperreflexia, and clonus seen here.
- There is no specific information in the clinical presentation to suggest an electrolyte imbalance is the primary cause over a medication-induced syndrome.
*Viral infection*
- Viral infections can cause fever and confusion, but the rapid onset and the specific neurological findings of marked **hyperreflexia** and **clonus** are more indicative of a central nervous system (CNS) disturbance like serotonin syndrome rather than a typical viral encephalopathy or infection.
- The absence of other common viral symptoms (e.g., cough, sore throat, GI symptoms) makes it less likely.
*Substance withdrawal*
- Withdrawal from **oxycodone** (opioid) or **clonazepam** (benzodiazepine) could cause agitation and autonomic symptoms. However, opioid withdrawal typically causes diarrhea, nausea, vomiting, and muscle aches, not hyperreflexia or fever, and benzodiazepine withdrawal usually presents with seizures, anxiety, and tremors, but the hyperreflexia and clonus point more strongly to serotonin syndrome, especially given the medication history.
- The patient ran out of these medications the previous night, which could contribute to some symptoms but doesn't fully explain the specific neurological signs in the context of the recent medication change.
*Bacterial infection*
- A bacterial infection could cause fever and confusion, but typically less specific neurological signs like **hyperreflexia** and **clonus** are not characteristic.
- While a CNS infection like meningitis could present with altered mental status and fever, it would usually involve neck stiffness and specific CSF findings, which are not mentioned.
Question 225: A 50-year-old woman presents with altered taste and a gritty sensation in her eyes for the last month. She mentions that she needs to drink water frequently and often feels that her mouth and throat are dry. On physical examination, she has bilateral enlargement of the parotid glands and dry conjunctivae. Her physical examination and laboratory findings suggest a diagnosis of sicca syndrome. In addition to non-pharmacological measures, a drug is prescribed to improve symptoms related to dryness of mouth by increasing salivation. Which of the following is the mechanism of action of the drug that most likely is being prescribed to this patient?
A. Selective M2 muscarinic receptor agonist
B. Selective M3 muscarinic receptor agonist (Correct Answer)
C. Selective M2 muscarinic receptor antagonist
D. Selective M3 muscarinic receptor antagonist
E. Selective M1 muscarinic receptor antagonist
Explanation: ***Selective M3 muscarinic receptor agonist***
- **Pilocarpine** or **cevimeline**, M3 muscarinic receptor agonists, are commonly used for **sicca symptoms** in Sjögren's syndrome.
- Activation of **M3 receptors** on salivary and lacrimal glands directly stimulates increased **saliva** and **tear production**.
*Selective M2 muscarinic receptor agonist*
- **M2 receptors** are primarily found in the **heart**, and their activation would primarily affect **cardiac function** (e.g., bradycardia), not salivary secretion.
- While M2 receptors are G protein-coupled, their role in exocrine gland secretion is minimal compared to M3.
*Selective M2 muscarinic receptor antagonist*
- An **M2 antagonist** would primarily cause an **increase in heart rate** by blocking parasympathetic input to the heart.
- Such a drug would have no direct positive effect on saliva production and could worsen dry mouth by its indirect effects.
*Selective M3 muscarinic receptor antagonist*
- An **M3 antagonist** would **block salivary and tear production**, exacerbating the patient's dry mouth and gritty eyes.
- These drugs are typically used to treat conditions like overactive bladder (e.g., darifenacin) or chronic obstructive pulmonary disease (e.g., tiotropium).
*Selective M1 muscarinic receptor antagonist*
- **M1 receptors** are predominantly found in the **cerebral cortex** and **gastric glands**.
- An M1 antagonist would primarily affect cognitive function or gastric acid secretion, which is not the therapeutic goal here.
Question 226: A 19-year-old male presents to the ER with generalized tonic-clonic seizures. He does not have a prior history of seizures and has not taken any drugs except for his daily asthma medication. Which of the following is associated with seizures?
A. Albuterol
B. Prednisone
C. Cromolyn
D. Theophylline (Correct Answer)
E. Ipratropium
Explanation: ***Theophylline***
- **Theophylline** has a narrow therapeutic index, and its toxicity can manifest as **seizures** and cardiac arrhythmias, especially in a patient with no prior seizure history.
- While used for asthma, uncontrolled or high doses can lead to systemic effects including neurological complications like **seizures**.
*Albuterol*
- **Albuterol** is a beta-2 agonist and is generally well-tolerated at therapeutic doses, with common side effects being **tremor** and **tachycardia**.
- While overdose can cause cardiotoxicity, it is less commonly associated with **seizures** as a primary side effect compared to theophylline.
*Prednisone*
- **Prednisone**, a corticosteroid, can have psychiatric side effects like mood changes and psychosis, but **generalized tonic-clonic seizures** are a rare complication.
- Seizures are more likely to be associated with steroid withdrawal or very high doses in susceptible individuals, which is not clearly indicated here.
*Cromolyn*
- **Cromolyn** is a mast cell stabilizer used for asthma prevention and is known for its excellent safety profile, with very few systemic side effects.
- It is not associated with **seizures** or other severe neurological complications.
*Ipratropium*
- **Ipratropium** is an anticholinergic bronchodilator primarily used for asthma and COPD. Systemic absorption is minimal, so systemic side effects are rare.
- While high doses can cause anticholinergic effects, **seizures** are not a typical or common adverse event associated with its use.
Question 227: A 36-year-old man is admitted to the hospital for treatment of burn wounds on his upper extremities. Analgesic therapy with an opioid drug is begun. Shortly after, the patient develops chills, diaphoresis, nausea, and abdominal pain. On further questioning, the patient reports that he has been smoking opium at home to help him ""deal with the depression and pain.” This patient was most likely given which of the following opioid drugs?
A. Butorphanol (Correct Answer)
B. Oxycodone
C. Morphine
D. Fentanyl
E. Hydrocodone
Explanation: ***Butorphanol***
- **Butorphanol** is a **mixed opioid agonist-antagonist** that acts as a **kappa (κ) receptor agonist** and **mu (μ) receptor antagonist/partial agonist**.
- In opioid-dependent patients who use **mu receptor agonists** (like opium), butorphanol can precipitate **acute opioid withdrawal** by displacing full agonists from mu receptors and blocking their effects.
- The patient's symptoms of chills, diaphoresis, nausea, and abdominal pain are classic signs of **acute opioid withdrawal syndrome**.
*Oxycodone*
- **Oxycodone** is a **full mu opioid receptor agonist** and would not precipitate withdrawal in an opioid-dependent patient.
- Administering oxycodone would provide continued mu receptor stimulation, potentially alleviating withdrawal symptoms or maintaining the patient's opioid dependence.
*Morphine*
- **Morphine** is a **full mu opioid receptor agonist** and would not cause withdrawal in an opioid-dependent individual.
- It would continue to stimulate mu opioid receptors, providing analgesia and preventing withdrawal symptoms.
*Fentanyl*
- **Fentanyl** is a potent **full mu opioid receptor agonist** and would provide continued opioid receptor stimulation.
- Its administration would prevent withdrawal and provide effective analgesia in an opioid-tolerant patient.
*Hydrocodone*
- **Hydrocodone** is a **full mu opioid receptor agonist** and would not induce withdrawal symptoms.
- Like other full agonists, it would continue mu receptor activation, providing analgesia without precipitating withdrawal.
Question 228: A 16 year-old female is being evaluated for shortness of breath. For the last year she has had shortness of breath and subjective wheezing with exercise and intermittent coughing at night. She reports waking up from sleep coughing 1-2 times per month. She now skips gym class because of her symptoms. She denies any coughing, chest tightness, or shortness of breath on the day of her visit. On exam, her lungs are clear to auscultation bilaterally, with normal inspiratory to expiratory duration ratio. Her pulmonary function tests (PFTs) show normal FEV1 and FVC based on her age, gender, and height. She is told to inhale a medication, and her PFTs are repeated, now showing a FEV1 79% of her previous reading. The patient is diagnosed with asthma. Which of the following medications was used to diagnose the patient?
A. Pilocarpine
B. Carbachol
C. Methacholine (Correct Answer)
D. Bethanechol
E. Physostigmine
Explanation: ***Methacholine***
- **Methacholine** is a muscarinic cholinergic agonist that, when inhaled, causes **bronchoconstriction** in susceptible individuals, leading to a decrease in FEV1.
- A significant drop in FEV1 (typically 20% or more) after methacholine challenge is diagnostic for **asthma**, especially when baseline PFTs are normal.
*Pilocarpine*
- **Pilocarpine** is a muscarinic agonist primarily used to treat **glaucoma** (by causing miosis and reducing intraocular pressure) and **dry mouth/eyes**.
- It is not used for the diagnosis of asthma through bronchial challenge testing.
*Carbachol*
- **Carbachol** is a cholinergic agonist with both muscarinic and nicotinic activity, used mainly in ophthalmology to induce **miosis** during surgery.
- It is not a standard agent for bronchial provocation testing in asthma diagnosis.
*Bethanechol*
- **Bethanechol** is a muscarinic agonist used to treat **urinary retention** and reduce symptoms of **gastroesophageal reflux disease (GERD)**.
- It is not used for asthma diagnosis.
*Physostigmine*
- **Physostigmine** is an acetylcholinesterase inhibitor that indirectly increases acetylcholine levels, used as an **antidote for anticholinergic poisoning**.
- It is not used as a direct broncho-constrictor for asthma diagnosis.
Question 229: A 32-year-old man with a history of major depressive disorder is brought to the emergency department by his wife because of a sudden onset of restlessness and disorientation that developed 3 hours ago. The patient’s wife says that he suddenly started sweating, having tremors, and mumbling to himself. Yesterday, the patient visited his psychiatrist with worsening depression who added phenelzine to his current treatment regimen. No other significant past medical history. His temperature is 39.7°C (103.5°F), blood pressure is 145/90 mm Hg, and pulse is 115/min. On physical examination, the skin is flushed. Mucous membranes are dry, and pupils are dilated. There is pronounced clonus in the extremities bilaterally. Babinski sign is present bilaterally. All the patient’s medications are discontinued, and intravenous fluids are started. Which of the following drugs most likely interacted with phenelzine to cause this patient’s condition?
A. Sertraline (Correct Answer)
B. Olanzapine
C. Mirtazapine
D. Bupropion
E. Lithium
Explanation: ***Sertraline***
- The patient exhibits classic symptoms of **serotonin syndrome**, including **mental status changes (disorientation, mumbling), autonomic hyperactivity (sweating, fever, flushed skin, tachycardia, hypertension, dry mucous membranes, dilated pupils)**, and **neuromuscular abnormalities (tremors, clonus, Babinski sign)**.
- **Sertraline** is an **SSRI** (selective serotonin reuptake inhibitor). The concurrent use of an **SSRI** with **phenelzine**, a **MAOI** (monoamine oxidase inhibitor), can lead to a dangerous overabundance of serotonin in the central nervous system, predictably causing **serotonin syndrome**.
- This is a **classic, high-risk drug interaction** that is absolutely contraindicated.
*Olanzapine*
- **Olanzapine** is an **atypical antipsychotic** primarily used to treat schizophrenia and bipolar disorder, and it does not significantly impact serotonin levels in a way that would precipitate serotonin syndrome when combined with a MAOI.
- Its main mechanisms involve antagonism at **dopamine D2 and serotonin 5-HT2A receptors**, and it generally does not elevate serotonin to toxic levels.
*Mirtazapine*
- **Mirtazapine** is an **alpha-2 adrenergic antagonist** and specific **serotonin receptor antagonist** (5-HT2 and 5-HT3). While it can theoretically interact with MAOIs, it enhances serotonergic transmission indirectly through increased norepinephrine release rather than directly blocking serotonin reuptake.
- The risk of serotonin syndrome with mirtazapine + MAOI is **significantly lower than with SSRIs + MAOI**, though caution is still warranted. It would not be the **most likely** cause in this scenario.
*Bupropion*
- **Bupropion** is a **norepinephrine-dopamine reuptake inhibitor (NDRI)**; it does not significantly affect serotonin levels.
- Therefore, it would not interact with **phenelzine** to cause serotonin syndrome.
*Lithium*
- **Lithium** is a **mood stabilizer** primarily used for bipolar disorder. It has no direct serotonergic mechanism that would interact with a **MAOI** to cause serotonin syndrome.
- Its therapeutic effects are thought to be mediated through various intracellular signaling pathways.
Question 230: A neurophysiologist describes the mechanism of a specific type of synaptic transmission to his students. While illustrating this, he points out that when the action potential reaches the presynaptic terminal of a chemical synapse, the voltage-gated Ca2+ channels open. Ca2+ ions trigger the release of neurotransmitters from vesicles in the presynaptic terminal. In this type of synaptic transmission, increased cytosolic Ca2+ levels cause the release of a neurotransmitter from small vesicles with dense cores. Which of the following neurotransmitters is most likely to be the one that is released into the synaptic cleft in this type of synapse?
A. Epinephrine
B. Glutamate
C. Glycine
D. GABA (γ-amino butyric acid)
E. Norepinephrine (Correct Answer)
Explanation: ***Norepinephrine***
- **Norepinephrine** is the primary catecholamine neurotransmitter stored in **small vesicles with dense cores** (dense-core vesicles).
- It is released from **sympathetic postganglionic neurons** and central nervous system neurons, particularly from the **locus coeruleus**.
- Dense-core vesicles are the hallmark of catecholaminergic neurons, and norepinephrine is the most abundant neuronal catecholamine.
- The description perfectly matches noradrenergic synaptic transmission.
*Epinephrine*
- While epinephrine is also a catecholamine stored in dense-core vesicles, it functions primarily as a **hormone** released from the **adrenal medulla** (not a neurotransmitter).
- Only a **very small number** of CNS neurons use epinephrine as a neurotransmitter (mainly in medullary regions).
- In the context of synaptic transmission, norepinephrine is far more common.
*Glutamate*
- **Glutamate** is the primary excitatory neurotransmitter in the CNS but is stored in **small, clear synaptic vesicles**, not dense-core vesicles.
- It does not fit the description of dense-core vesicle storage.
*Glycine*
- **Glycine** is an inhibitory neurotransmitter stored in **small, clear synaptic vesicles**.
- Found predominantly in the **spinal cord** and brainstem, not in dense-core vesicles.
*GABA (γ-amino butyric acid)*
- **GABA** is the main inhibitory neurotransmitter stored in **small, clear synaptic vesicles**.
- Not associated with dense-core vesicle storage.
