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Neuropharmacology > ACh 1 > Flashcards

ACh 1 Flashcards

1
Q

Acetylcholine

A

An ester of acetic acid and choline functions as a neurotransmitter

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2
Q

Structure of acetylcholine

A

Diagram

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3
Q

Different between acetylcholine and other small neurotransmitters such as GABA and glutamate

A

Not involved in metabolic pathways

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4
Q

Behavioural processes involving acetylcholine

A

Arousal and attention

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5
Q

Where is ACh used in the body?

A

Neuromuscular junction (paralysis, convulsions)
Autonomic nervous system (autonomic ganglia,
parasympathetic nervous system)
Central nervous system (arousal, attention, motivation)

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6
Q

History of ACh

A

First neurotransmitters to be discovered

Otto Loewi confirmed ACh as neurotransmitter in 1921

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7
Q

ACh and Henry Dale

A

In 1936, Henry Dale went on to demonstrate that
ACh is released when the motor nerve is
stimulated, activating voluntary, striated muscle
Dale used isolated leech muscles for his
experiments
Dale and Loewi won Nobel Prize in 1936

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8
Q

function of ACh

A

Chemical synaptic transmission at the neuromuscular junctions of humans, mammals and some invertebrates
Chemical synaptic transmission in the human, mammalian and invertebrate brains
Chemical transmission in the human and mammalian
autonomic nervous systems
Non-neuronal signalling roles (skin, bone, immune cells)

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9
Q

location of ACh

A

Diagram

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10
Q

ACh synthesis

A

Diagram

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11
Q

choline

A

is an essential nutrient

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12
Q

acetylcoenzyme A

A

Is synthesised in the mitochondria

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13
Q

Choline acetyltransferase

A

is the diagnostic marker for cholinergic neurons

no drugs target directly

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14
Q

Vesicular Acetylcholine

Transporter (VAChT)

A

loads

acetylcholine into vesicles

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15
Q

Botulinum toxin

A

Produced by Clostridium botulinum ( gram-negative)

inhibits release of ACh, causing muscle paralysis and death

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16
Q

latrotoxin

A

Black widow spider venom; increases ACh release, leading to pain, cramps, sweating and fast pulse

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17
Q

ACh catabolism

A

Diagram

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18
Q

AChE

A

AChE is widely distributed in nerve
(synaptic cleft) and muscle but is also present in other tissues such
as red blood cells
AChE has very high catalytic activity: each molecule degrades
25,000 molecules of ACh per second!!

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19
Q

ACh synapses

A

Short, fast bursts

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20
Q

BChE

A 
Butyrylcholinesterase (BChE)
is also known as
pseudocholinesterase
BChE is a nonspecific
cholinesterase enzyme 
BChE is mainly found in
blood (but also brain)
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21
Q

Cholinergic receptors

A

Two families, nicotinic and muscarinic

22
Q

Langley 1905

A

1st to talk about receptors as mediators to cell responses

23
Q

Dale 1914

A

muscarine and
nicotine only partially
mimicked ACh effects

24
Q

Muscarine

A

Muscarine is a drug extracted from the fly agaric mushroom Amanita muscaria (hallucinogenic); Muscarine is a non-selective agonist of the muscarinic acetylcholine receptor (mAChR);
Muscarine poisoning causes miosis, increased salivation, lacrimation, excessive sweating,
abdominal cramping, diarrhoea, bradycardia, bronchconstriction

25
Q

CNS mAChRs

A

regulate many important functions such as cognitive, behavioural, sensory, motor and autonomic processes

26
Q

Peripheral mAChRs

A

mediate Ach effects in parasympathetic nervous system (e.g. decrease heart rate, increase smooth-muscle contractility and glandular secretion)

27
Q

Muscarinic receptors

A

G-protein-coupled receptors;
metabotropic, and affect neurons and other cells
over a longer time frame;
M1-M5

28
Q

Where are M1,4,5 mainly expressed?

A

mainly expressed in the

CNS

29
Q

Where are M1,4,5 mainly expressed?

A

widely
distributed in the
CNS and peripheral
tissues

30
Q

Mechanism of action of muscarinic receptors

A

Diagram

31
Q

Specific function of different muscarinic receptors

A

Table

32
Q

Agonists of muscarinic receptors are

A

Parasympathomimetic

33
Q

Antagonists of muscarinic receptors are

A

Parasympatholytic

tend to be non-selective for subtype

34
Q

Examples of muscarinic receptor antagonists

A

Oxybutynin for overactive bladder and
incontinence (M1-3)
Ipratropium for asthma and COPD (derivative of atropine, entirely non-selective but only works locally due to ROA)

35
Q

Atropine

A

Competitive, reversible antagonist of muscarinic receptors (non-selective)
Atropa belladonna
causes mydriasis, tachycardia, urinary, retention, constipation, dry mouth
used in surgery as an antidote to nerve agent and pesticide poisoning

36
Q

Muscarinic receptors as drug targets

A

Table

37
Q

Nicotine

A

Non-selective agonist of nicotinic ACh receptor
Nicotine binds muscle and
neuronal nAChRs in the peripheral and central nervous systems
agonism/antagonism is dose-dependent

38
Q

Nicotinic receptors

A 
The nAChRs function as acetylcholine-gated cation channels;
nAChRs are ionotropic receptors permeable to sodium, potassium and
calcium ions.
Two types: muscular and neuronal
Expressed in the central and peripheral
nervous systems, both presynaptically
and postsynaptically
Selectively blocked by hexamethonium
39
Q

which ion are nicotinic receptors most permeable to at the neuromuscular junction?

A

Potassium

40
Q

Neuronal nicotinic receptors

A

Neuronal nAChRs are comprised
of combinations of the α2-α10 and β2-β4 subunits
Can form homomeric or
heteromeric receptors
The different receptor
stoichiometry configurations confer differences in calcium
permeability and agonist and antagonist sensitivity between different receptors

41
Q

Homomeric neuronal nAChRs

A

Homomeric neuronal nAChRs • All five subunits are the same (α7,
α9) • The α7 subunit is widely expressed
throughout the mammalian CNS (higher level control) • In the CNS, the α9 subunit has
been primarily identified in the inner ear cells

42
Q

Nicotinic receptors antagonists

A 
Ganglionic blocking agents: act on
the autonomic nervous system (e.g.
TEA, used only in lab work now). • Neuromuscular (competitive)
blocking agents: act on
neuromuscular junction (e.g.
tubocurarine). • Centrally-acting compounds (e.g.
bupropion, mecamylamine) to help
people stop smoking
43
Q

combined nicotinic and muscarinic responses in the ganglia, and CNS?

A

Look up

44
Q

Changing ACh levels

A

unable to modulate ChAT or VAChT
No evidence that increase dietary Choline changes
ACh levels
Increase levels of synaptically available Ach by preventing breakdown –> Cholinesterase Inhibitors

45
Q

Acetylcholinesterase inhibitors

A

3 main groups:
– Short-acting – edrophonium: reversible, brief action (10 min), used to diagnose myasthenia gravis.
– Medium-acting (1-2h) – neostigmine, physostigmine; reversible, broken down more slowly, used to treat
myasthenia gravis and glaucoma.
– Irreversible – used as pesticides (organophosphates
- malathion) or chemical weapons (VX, Novichok).
Centrally acting- AD

46
Q

Acetylcholinesterase inhibitors

A

Side effects: Actions on parasympathetic nervous
system (bradycardia, hypotension,
hypersecretion, bronchoconstriction,
GI tract hypermotility, decrease
intraocular pressure); SLUDGE syndrome (Salivation,
Lacrimation, Urination, Diaphoresis,
Gastrointestinal upset and Emesis); Prolonged muscle contraction.

47
Q

Snake venom

A

Fasciculins are toxic proteins found in mamba snake venom; They bind to AChE, blocking its
activity; They cause intense muscle
fasciculation thus paralysing and/or killing prey

48
Q

Physostigmine

A

Eserine (physostigmine) from the Calabar bean was originally used
as a test for witchcraft;
Reversible cholinesterase inhibitor • Now used to treat glaucoma,
(myasthenia gravis, Alzheimer’s
disease, delayed gastric emptying now with neostigmine); Antidote for anticholinergic drug
overdoses (e.g. atropine)

49
Q

Irreversible AChE inhibitors

A

Sarin gas (chemical weapon) is an
inhibitor of AChE • Commonly used insecticides
(malathion, organophosphates)
have a similar effect • Cause SLUDGE – then death by
cardiac failure • Reactivators of the irreversibly
blocked enzyme (e.g.
pralidoxime) developed as snake
bite antidotes and protection
against nerve agents

50
Q

Pralidoxime action

A

1) Organophosphate is bound to “esteric site” of AchE
2) Pralidoxime binds to “anionic site” of AchE and to organophosphate
3) Organophosphatedetaches from AchE

Neuropharmacology (20 decks)

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