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Questions and Answers
What is the susceptibility of Carbachol to cholinesterases?
What is the susceptibility of Carbachol to cholinesterases?
- +
- ++
- − (correct)
- +++
Which pharmacological property does Carbachol exhibit with respect to gastrointestinal activity?
Which pharmacological property does Carbachol exhibit with respect to gastrointestinal activity?
- ++
- ±
- +
- +++ (correct)
How does Carbachol compare to Acetylcholine in terms of nicotinic activity?
How does Carbachol compare to Acetylcholine in terms of nicotinic activity?
- Not different
- Equal
- Higher
- Lower (correct)
What is the antagonism of Carbachol by Atropine?
What is the antagonism of Carbachol by Atropine?
In which aspect does Carbachol show a higher effect compared to Bethanechol?
In which aspect does Carbachol show a higher effect compared to Bethanechol?
What type of receptors does acetylcholine (ACh) mediate neurotransmission at ganglia?
What type of receptors does acetylcholine (ACh) mediate neurotransmission at ganglia?
Which of the following muscarinic receptors are coupled with Gq proteins?
Which of the following muscarinic receptors are coupled with Gq proteins?
Which structure forms the inner surface of the nicotinic ACh receptor channel?
Which structure forms the inner surface of the nicotinic ACh receptor channel?
What feature of muscular nicotinic receptors allows for binding and gating in response to ligand binding?
What feature of muscular nicotinic receptors allows for binding and gating in response to ligand binding?
Which sub-type of muscarinic receptors is primarily located peripherally?
Which sub-type of muscarinic receptors is primarily located peripherally?
Which of the following is characteristic of nicotinic receptors compared to muscarinic receptors?
Which of the following is characteristic of nicotinic receptors compared to muscarinic receptors?
How are the five homologous transmembrane protein subunits organized in muscular nicotinic receptors?
How are the five homologous transmembrane protein subunits organized in muscular nicotinic receptors?
Which statement is true about muscarinic ACh receptors?
Which statement is true about muscarinic ACh receptors?
Which drug is specifically used to treat xerostomia related to head and neck radiation?
Which drug is specifically used to treat xerostomia related to head and neck radiation?
What effect do cholinergic agonists have on glaucoma treatment?
What effect do cholinergic agonists have on glaucoma treatment?
Which is NOT a contraindication for methacholine testing?
Which is NOT a contraindication for methacholine testing?
Bethanechol is indicated for which condition?
Bethanechol is indicated for which condition?
What is the primary effect of methacholine in asthmatic patients?
What is the primary effect of methacholine in asthmatic patients?
Carbachol is primarily used to treat which of the following?
Carbachol is primarily used to treat which of the following?
What is a common side effect of the cholinergic agonists used in glaucoma treatment?
What is a common side effect of the cholinergic agonists used in glaucoma treatment?
Which of the following drugs is NOT contraindicated for use in patients with uncontrolled hypertension?
Which of the following drugs is NOT contraindicated for use in patients with uncontrolled hypertension?
What primary function is associated with M3 receptors in smooth muscle?
What primary function is associated with M3 receptors in smooth muscle?
Which pathway do M3 receptors couple through to stimulate smooth muscle contraction?
Which pathway do M3 receptors couple through to stimulate smooth muscle contraction?
In which region of the CNS are M4 receptors predominantly expressed?
In which region of the CNS are M4 receptors predominantly expressed?
What is the primary effect of M4 receptor activation on neurotransmitter release?
What is the primary effect of M4 receptor activation on neurotransmitter release?
What disease is associated with M4 receptor dysfunction?
What disease is associated with M4 receptor dysfunction?
Which mechanism is primarily used by M5 receptors to facilitate the release of dopamine?
Which mechanism is primarily used by M5 receptors to facilitate the release of dopamine?
What is one of the roles of M3 receptors in glands?
What is one of the roles of M3 receptors in glands?
What specific cellular response is mediated by M4 receptors upon activation?
What specific cellular response is mediated by M4 receptors upon activation?
Which of the following effects is associated with M5 receptors?
Which of the following effects is associated with M5 receptors?
Which condition is linked to dysfunction in M3 receptors?
Which condition is linked to dysfunction in M3 receptors?
What key neurotransmitter release is inhibited by M4 receptors?
What key neurotransmitter release is inhibited by M4 receptors?
What cellular mechanism do M4 receptors utilize to hyperpolarize cells?
What cellular mechanism do M4 receptors utilize to hyperpolarize cells?
What pathway do M5 receptors couple through to affect neural activity?
What pathway do M5 receptors couple through to affect neural activity?
What outcome is observed with the activation of M3 receptors in the urinary system?
What outcome is observed with the activation of M3 receptors in the urinary system?
What is the primary cellular location of M1 muscarinic acetylcholine receptors?
What is the primary cellular location of M1 muscarinic acetylcholine receptors?
What is the functional consequence of M2 muscarinic receptor activation in the heart?
What is the functional consequence of M2 muscarinic receptor activation in the heart?
Which of the following diseases is associated with M1 muscarinic receptor dysfunction?
Which of the following diseases is associated with M1 muscarinic receptor dysfunction?
What signaling pathway is primarily associated with M1 muscarinic receptors?
What signaling pathway is primarily associated with M1 muscarinic receptors?
What effect does M2 receptor activation have on the secretion of neurotransmitters?
What effect does M2 receptor activation have on the secretion of neurotransmitters?
Which of the following receptor types is an antagonist for M2 muscarinic receptors?
Which of the following receptor types is an antagonist for M2 muscarinic receptors?
Which additional function is attributed to the M1 muscarinic receptors in relation to cognitive function?
Which additional function is attributed to the M1 muscarinic receptors in relation to cognitive function?
In which part of the body would you expect to find a high density of M2 receptors?
In which part of the body would you expect to find a high density of M2 receptors?
What is a known effect of M1 receptor activation in the gastric glands?
What is a known effect of M1 receptor activation in the gastric glands?
How does M2 receptor activation affect the atrioventricular (AV) node?
How does M2 receptor activation affect the atrioventricular (AV) node?
What cellular response is triggered by the M2 receptor pathway?
What cellular response is triggered by the M2 receptor pathway?
What is a common effect experienced due to the activation of M1 muscarinic receptors on cognitive function?
What is a common effect experienced due to the activation of M1 muscarinic receptors on cognitive function?
Which of the following is NOT a characteristic feature of M2 receptor activation?
Which of the following is NOT a characteristic feature of M2 receptor activation?
What pathway does M2 muscarinic receptor activation employ to exert its effects?
What pathway does M2 muscarinic receptor activation employ to exert its effects?
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Study Notes
Cholinergic Transmission
- Acetylcholine (ACh) mediates neurotransmission in the autonomic nervous system at two locations:
- Ganglia: Neuronal nicotinic receptors (NN)
- Parasympathetic nerve endings: Muscarinic receptors (M1-5)
- Presynaptic receptors regulate ACh release through auto- and cross-regulation.
Nicotinic ACh receptors
- Ligand-gated cation channels permeable to sodium and calcium.
- Activation causes rapid depolarization.
- Classified into two categories:
- Neuronal nicotinic receptors (NN)
- Muscular nicotinic receptors (NM)
- First isolated from the electric organ of the Pacific electric ray (Torpedo spp.).
- Each receptor is composed of five homologous transmembrane protein subunits surrounding a central ion pore (α, β, γ, and δ in the ratio 2:1:1:1 in muscle).
- Ligand binding sites in muscular nicotinic receptors exist at the αγ and αδ interface.
Muscarinic ACh Receptors
- Five distinct subtypes exist.
- Different subtypes exist in the same organ.
- M3 is predominantly present peripherally.
- All muscarinic receptors are G protein-coupled receptors (GPCRs).
- M1, M3, and M5 are Gq-coupled.
- M2 and M4 are Gi/o coupled.
- No highly selective agonists or antagonists exist.
Receptor Subtypes and Therapeutic Relevance
- M1:
- Abundant in the CNS: Cerebral cortex, hippocampus, striatum, thalamus and autonomic ganglia.
- Plays a role in cognitive function, learning, and memory.
- Potential therapeutic target for Alzheimer's disease, cognitive dysfunction, and schizophrenia.
- M2:
- Widely expressed in the CNS, heart, and smooth muscle.
- Functions as an autoreceptor and heteroreceptor affecting neurotransmitter release.
- Potential therapeutic target for Alzheimer's disease, cognitive dysfunction, pain, and tremor.
- M3:
- Abundant in smooth muscle, glands, and the heart.
- Responsible for smooth muscle contraction and glandular secretion.
- Potential therapeutic target for chronic obstructive pulmonary disease (COPD), urinary incontinence, and irritable bowel disease.
- M4:
- Predominantly expressed in the CNS.
- Functions in the regulation of transmitter release, primarily acting as an autoreceptor.
- Potential therapeutic target for Parkinson's disease, schizophrenia, and neuropathic pain.
- M5:
- Expressed in low levels in the CNS and periphery.
- Plays a role in dopamine release and reward pathways.
- Potential therapeutic target for drug dependence, Parkinson's disease, and schizophrenia.
Cholinergic Agonists
- Acetylcholine (ACh):
- Highly susceptible to cholinesterases.
- Methacholine:
- Used for the diagnosis of bronchial hyperreactivity.
- Patients with asthma experience intense bronchoconstriction.
- Contraindicated in patients with: severe airflow limitation, recent myocardial infarction, stroke, uncontrolled hypertension, and pregnancy.
- Its effect is exaggerated in patients using β-blockers.
- Bethanechol:
- Treatment of urine retention in the absence of organic obstruction (postoperative urinary retention, diabetic autonomic neuropathy, chronic hypotonic bladder).
- Given orally 3-4 times/day on an empty stomach.
- Previously used to treat postoperative abdominal distention, gastric atony, gastroparesis, adynamic ileus, and gastroesophageal reflux.
- Carbachol:
- Used topically to treat glaucoma and to induce miosis during surgery.
- Pilocarpine:
- Treatment of xerostomia following head and neck radiation or associated with Sjögren's syndrome.
- Lower doses are recommended for patients with hepatic impairment.
- Topical treatment for glaucoma.
Therapeutic Uses
- Urinary bladder disorders:
- Agonists can treat urine retention.
- Paralytic ileus:
- Agonists can stimulate peristalsis and increase motility.
- Xerostomia:
- Agonists can alleviate dry mouth.
- Glaucoma:
- Agonists produce miosis (pupil constriction) and increase aqueous humor drainage.
- Diagnosis of bronchial hyperreactivity:
- Methacholine challenge test.
M1 and M4 Receptor Stimulation
- Potential therapeutic interest for Alzheimer's dementia and schizophrenia.
Glaucoma
- Cholinergic agonists produce miosis and increase aqueous humor drainage.
- Adverse effects include: decreased peripheral and dark visual acuity, poor far vision.
- Currently, they are increasingly replaced with agents with better side-effect profiles.
Contra-indications and Side Effects
- Consequences of receptor stimulation.
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