Cholinergic Drugs (Exam 1) Flashcards
What is a neuron made up of?
- Cell body or soma
- Dendrites
- Axon
Dendrites
Receive signals from other neurons
Axon
Sends out signal to surrounding neurons through axon terminal
Action Potential
Electrical signal that travels down axon
Created using Na+, Inhibited by K+
Depolarization
Voltage gated Na+ channels open
Na+ influx
Repolarization
Voltage gated Na+ channels close and K+ channels open
K+ efflux
Hyperpolarization
Voltage gated K+ channels close
Increased signaling occurs from drugs that…?
- Increase concentration of neurotransmitter at synapse
- Activate postsynaptic receptors
Decreased signaling occurs from drugs that…?
- Decrease concentration of neurotransmitter at synapse
- Decrease activation of postsynaptic receptors
Relationship between cholinergic signaling and heart rate
Inverse relationship
Increase cholinergic signaling, decrease heart rate
Relationship between adrenergic signaling and heart rate
Direct relationship
Increase adrenergic signaling, increase heart rate
Cholinergic
Acetylcholine (Ach) neurotransmitter
Cholinergic Receptors
Nicotinic (N1, N2)
Muscarinic (M1-M5)
Cholinomimetics
Enhance cholinergic signaling
Anticholinergics
Reduce cholinergic signaling
Synthesis of Ach
Synthesized from Acetyl-S-CoA and Choline by choline acetyltransferase (ChAT)
Sympathetic Nervous System
Fight or flight
Parasympathetic Nervous System
Rest and digest
Nicotinic Receptors (N)
Nn and Nm
Nn Receptor
Ganglia
Adrenal medulla
Nm Receptor
Neuromuscular
Muscarinic Receptor (M)
M1, M2, M3, M4, M5
M1 Receptor
Gastric
Ganglia
CNS
M2 Receptor
Heart
CNS
M3 Receptor
Eye
GIT
Bladder
Bronchus
Glands
CNS
M4 Receptor
CNS
M5 Receptor
CNS
Nicotinic Ach Receptor Properties
- 5 subunits , 2 bind Ach
- Opens ion channels, K+ out Na+ in
- Acetylcholinesterase stops signal
Acetylcholinesterase (AChE)
Primary enzyme responsible for synaptic acetylcholine breakdown
Butyrylcholinesterase (BChE)
Enzyme that can break down acetylcholine mainly found in bloodstream
Breakdown of ACh by AChE
Rapidly broken down via ester hydrolysis into acetate and choline
Choline Acetyltransferase (ChAT)
Enzyme responsible for acetylcholine synthesis
Vesicular ACh Transporter (VAT or VAChT)
Responsible for ACh uptake in storage vesicles
Presynaptic M2 Receptors
Function as autoreceptors
Can be located postsynaptically
Cholinergic signaling in the eye
M3 Receptor
Contraction of iris circular muscle causing miosis; increase outflow of aqueous humor
Cholinergic signaling in the heart
M2 Receptor
Reduction in heart rate and contractility
Cholinergic signaling in the blood vessels
M3 Receptor
Can cause vasodilation
Cholinergic signaling in the lungs
M3 Receptor
Contraction of bronchiolar smooth muscle leading to bronchoconstriction
Cholinergic signaling in the GI tract
M3 Receptor
Increases digestion and digestive secretions
Cholinergic signaling in the bladder
M3 Receptor
Detrusor muscle contraction
Urinary sphincter relaxation
Facilitation of urination
Spastic paralysis
Caused by drugs that enhance cholinergic signaling at NMJ
Flaccid paralysis
Caused by drugs that block cholinergic signaling at NMJ
Cholinergic signaling affect on learning and memory
Activation of receptors in hippocampus enhances learning and memory
Cholinergic signaling affect on reward pathways
Activation of nicotinic receptors in VTA activates dopaminergic neurons and stimulates dopamine release
Cholinergic signaling affect on regulating sleep-wake cycles
Cholinergic signaling increases REM sleep but also wakefulness; important in establishing circadian rhythms
Cholinergic signaling affect on motor control and normal movement
Cholinergic - dopaminergic balance in striatum is important for normal movement
Cholinergic signaling affect on appetite suppression
Activation of nicotinic receptors in brain can reduce appetite
Acetylcholinesterase inhibitors
Increase cholinergic signaling in brain
Used to treat Alzheimer’s
Muscarinic receptor antagonists
Decrease bronchoconstriction - used to treat asthma and COPD
Decrease urination - used to treat overactive bladder
Nicotine receptor agonist at Nn
Enhance alertness, reduces appetite, causes addiction - recreational drug
Nicotinic receptor blockers at NMJ Nm
Cause muscle paralysis - used during surgery to facilitate endotracheal intubation, treats painful muscle spasms
Direct Acting Cholinomimetics
Act as agonists at muscarinic and/or nicotinic receptors
Indirect Acting Cholinomimetics
Increase cholinergic signaling without directly activating receptors
Inhibitors of acetylecholinesterase
Antimuscarinic drugs
Act as antagonists at muscarinic receptors
Antinicotinic drugs
Act as antagonists at nicotinic receptors
Cholinesterase regenerator drugs
Used in organophosphate poisoning which remove covalently bound phosphate group from acetylcholinesterase enzyme
Choline Esters
Highly hydrophilic due to quaternary amine
Poor oral absorption, low ability to cross BBB
Beta-methyl group
Provides steric hinderance against cholinesterase hydrolysis but reduces potency at nicotinic receptors
Choline Esters with Beta-methyl Group
Selective for muscarinic receptors and less susceptible to cholinesterase hydrolysis
Longer half life
Alkaloids
Naturally occurring compounds containing at least one nitrogen and having alkaline properties
Not susceptible to hydrolysis because of the ester
Drugs that contain a tertiary amine…
- Cross biological membranes easily
- Urinary excretion is increased if urine becomes acidic
Indirectly Acting Reversible Cholinergic Drugs
- Carbamates
- Acridine
Indirectly Acting Irreversible Cholinergic Drugs
- Organophosphates
- Carbamates
Atropine
Prototypical muscarinic antagonist
Nonselective
Can treat acetylcholinesterase inhibitor poisoning
Ganglion Blocking Drugs
Treatment of hypertension
Block Nn receptors
Reduce sympathetic outflow
Neuromuscular-blocking drugs
Producing skeletal muscle relaxation
Block Nm receptors
Direct Acting Cholinergic Agonist Indications
Urinary retention after surgery or postpartum
Glaucoma
Direct Acting Cholinergic Agonist Adverse Effects Muscarinic
Salvation, flushing, bronchospasm, sweating, nausea, abdominal pain
Direct Acting Cholinergic Agonist Adverse Effects Nicotinic
Fasciculations, respiratory arrest
Direct Acting Nicotinic Agonist Adverse Effects
Vomiting, convulsions, hypertension, cardiac arrhythmias
Muscarinic Receptor Antagonist Adverse Effects
PNS- dry mouth, blurred vision, tachycardia, urinary retention, constipated
SAS- Inhibition of sweating
CNS- restlessness, confusion, hallucinations