Synaptic Transmission + Cellular Signalling

Question 1

Acetylcholine locations/function in CNS + PNS (3)

Answer 1

• Neurotransmitter in CNS and PNS

PNS:
* Cardiac function
* NMJ

CNS:
* Cognition
* Movement
* Conserved across various species
(evolutionary)

Question 2

Allergic toxicity and Ach (2)

Answer 2

• allergic toxicity can result from various diff things (eg insecticides, nerve agents, medications, mushrooms etc.)
• common form of cholinergic toxicity is exposure to organic phosphates or carbonation insecticides

Question 3

nature -> drug egs (2)

Answer 3

belladonna: get atripine from it (overdoses = PNS symptoms - tremors, tachycardia etc)

tubocurarine: non-depolarising neuromuscular blocking agent - reduces amount of anaesthesia needed in surgery to elicit same effects

Question 4

Ach in synapse steps (6)

Answer 4

1) packaged into vescicles (VAChT)
2) fuses w/membrane + released into synaptic cleft
3) ACh –> Choline + acetyl (by ACh esterase)
4) re-uptake via Acetyl transferase
5) converted back into ACh
6) packaged into vescicles (VAChT)

Question 5

What is the rate limiting step in ACh synthesis? (1)

Answer 5

the uptake of choline from synaptic cleft into pre-synaptic membrane via NACh r

Question 6

Main cholinergic pathways (3)

Answer 6

• Basal forebrain complex innervates
• Hippocampus
• Frontal cortex
• Olfactory bulb
• Medial habenula
• Pedunculopontine
• VTA
• Thalamus
• Cerebellum
• Laterodorsal tegmental areas
• Medial habenula

Question 7

Cholinergic receptors classification (5)

Answer 7

1)Nicotinic:
—> Neuronal (Nn) -> Adrenal, Immune cells, CNS, Ganglia
—-> Non-neuronal/skeletal (Nm)

2)Muscarinic:
—> M1, M3, M5
—>M2, M4

Question 8

Nicotine info (6)

Answer 8

• The psychoactive ingredient of tobacco
• Naturally produced alkaloid
• Present in the seeds of theNicotiana tabacum plant
• It binds to nAChRs in the brain
• Acts as an stimulant and anxiolytic
• It is highly addictive

Question 9

Nicotinic acetylcholine receptors (nAChRs) info (5)

Answer 9

• found through the CNS and play an important role in many functions
• nAChRs are ligand-gated cation channels permeable to Na+, K+ and Ca 2+ ions
• Pentamers formed as homomeric or heteromeric combinations of α (α2–7)and β (β2–4) subunits
• Subunit combinations affect things such as drug affinity
• After activation by an agonist, nAChRs enter a desensitized state, which limits the duration of nicotine’s acute effect

Question 10

nAChRs locations (6)

Answer 10

nAChRs are distributed widely throughout the brain

• Are located pre- and postsynaptically
• Presynaptic nAChRs usually facilitate the release of other
  neurotransmitters(glutamate, dopamine and GABA)
• Postsynaptic nAChRs (on NMJ in Somatic NS) mediate fast excitatory transmission
• also located in the ganglia of the autonomic nervous system (sympathetic and parasympathetic).

locations:
* Cerebral cortex
* Hippocampus (memory + learning)
* Basal ganglia (addiction)
* Substantia nigra (addiction)
* Ventral tegmental area (VTA) (addiction)
* Nucleus accumbens(NAC

Question 11

Pharmacological effects of nicotine (4)

Answer 11

• Nicotine acts as an agonist of nAChRs
• Produces physiological, behavioural, and subjective effects
• The acute effects of nicotine differ from the chronic effects of nicotine
• The effects of nicotine in the brain derive from the widespread distribution of the cholinergic system

Question 12

Effects of nicotine on psychomotor function (4)

Answer 12

• Nicotine’s behavioural effects include alterations in movement and cognitive function
• Nicotine effects on psychomotor function differ between acute and chronic administration
• Acute administration of nicotine induces a decrease in psychomotor activity
• Chronic administration of nicotine results in an increase in psychomotor function

Question 13

Effects of nicotine on cognitive function (5)

Answer 13

• Nicotine shows some benefits for cognitive function
• The effect of nicotine in alertness is circumstance- and dose- dependent
• Nicotine has also been described to wake people up when they are drowsy and calms them down when they are tense
• Small doses of nicotine tend to cause arousal, whereas large doses do the reverse
• The effects on memory are unclear (placebo + not placebo results are similar)

Question 14

Cholinergic signalling: Drug targets (3)

Answer 14

-Vesamicol: drug targeting ACh v packaging

• botulin (toxin): inhibits exocytosis
• ACh esterase inhibitors: Alzheimer’s treatment

Question 15

Muscarinic receptors signalling (2)

Answer 15

M1, M3, M5 = GQ/11 (excitatory)

M2, M4 = Gi/Go (inhibitory)

Question 16

Muscarinic receptor locations (5)

Answer 16

M1: Neural (= CNS excitation, gastric secretion)

M2: Cardiac (= cardiac + neural inhib (tremors, hypothermia)

M3: Glandular/smooth muscle (= gastric/ salivary secretion, GI smooth muscle contraction, vasodilation)

M4: CNS (= enhanced locomotion)

M5: CNS but localised in SN, salivary glands, iris/ciliary muscle (=unknown)

Question 17

Catecholamines synthesis (5)

Answer 17

1) L-Tyrosine
—Tyrosine Hydrolase—
2) L-dopa (parkinsons treatment)
— Dopa decarboxylase—
3) Dopamine
—Dopamine beta-hydroxylase—
4) Noradrenaline
—Phenylethanolamine N-methyltransferase—
5) Adrenaline

Question 18

Dopamine pathways (4)

Answer 18

1) Nigrostriatal (SN -> striatum)
2) Mesolimbic (VTA -> NAcc)
3) Mesocortical (VTA -> DL, VM PF)
4)Tuberoinfundibular ( Hypo -> AP)

Question 19

Dopamine receptors classification (6)

Answer 19

D1- like :
- D1, D5
- Large C-terminal domain
- Gs signalling

D2-like :
- D2, D4, D6
- large intracellular loop
- Gi signalling

= ST responses + gene transcription

Question 20

Adrenal medulla info (4)

Answer 20

• Composed of modified postganglionic
  neurons
• Stimulated by preganglionic fibres
• Release 80% adrenaline, 20%
  noradrenaline (small amounts
  dopamine, neuropeptides and ATP)
• Release their transmitters directly into the bloodstream

Question 21

Adrenoceptors subtypes + potency (3)

Answer 21

• subtypes are α (a1 type + a2 type) and β
• Potency at α receptors is noradrenaline > adrenaline > isoprenaline
• Potency at β receptors is isoprenaline > adrenaline > noradrenaline

(NαI βrIAN)

Question 22

Adrenoceptor subtype signalling + response (3)

Answer 22

α1: Gq = smooth muscle
contraction (GI, Bladder, Skin vasocons.)

α2: Gi/o = smooth muscle
contraction - mixed effects, platelet activation

β1: Gs = Heart muscle contraction, smooth muscle relaxation, glycogenolysis
β2: Smooth muscle relaxation
β3: Enhance lipolysis, Relaxation of
detrusor muscle in the bladder

Question 23

Presynaptic agents/drugs (5)

Answer 23

• alpha-methyldopa NA: hypertension treatment - specifically in pregnancy (acts as a false neurotransmitter = reduces adrenaline effects)
• carbidopa alpha-methyldopa: prevents Dopa D carboxylase = no dopamine –> parkinsons so dopamine doesn’t cross BBB
• cocaine, imipranine: works by building up in cleft
• amphetamines, ephedrine: re-uptake + displace noradrenaline, build up = leaked in cleft

-clonidine, yohimbine:

Question 24

Catecholamine metabolism (2)

Answer 24

2 main enzymes:
- Monoamine oxidase => bound to mito
-Catecholemethyl transferase => adrenal medulla: regs signal of adrenaline

Question 25

Opioids def (1)

Answer 25

naturally occurring, synthetic or semi-synthetic compounds which act at opioid receptors

Question 26

Naturally occurring compounds (also known as opiates) def (1)

Answer 26

usually derived from the resin of the opium poppy. Main egs alkaloids such as morphine, codeine and thebaine

Question 27

Morphine esters (1)

Answer 27

derived from opium- include morphine prodrugs such as diacetylmorphine (heroin)

Question 28

Semi-synthetic opioids (1)

Answer 28

derived from opium or morphine esters - include buprenorphine and oxycodone

Question 29

Synthetic opioids (1)

Answer 29

include fentanyl, pethidine, methadone and tramadol

Question 30

Endogenous opioids (1)

Answer 30

include enkephalins and endorphins

Question 31

Diacetylmorphine - heroin (2)

Answer 31

- not an active drug but is rapidly metabolised into active drugs: 1) heroin 2) 6-monoacetylmorphine (active)/ 3-monoacetylmorphine (inactive) 3) morphine (active) - 2 acetyl groups make the compound more lipid soluble = cross BBB much easier

Question 32

Opioid receptors (4)

Answer 32

mu - main kappa delta NOP all Gi/o

Question 33

opioids in pain pathway (5)

Answer 33

ascending pathway: 1) noxious stimulus 2) C-fibre activity 3) excitation of transmission neuron 4) output from brain = pain opioids work on descending pathway (5-HT, NA --> reduce transmission of pain) and Ascending pathway (reduce activation of C-fibres

Question 34

Opioid abuse effects (8)

Answer 34

-have a very high abuse potential -have been used and abused since antiquity – evidence suggests the opium poppy was cultivated as far back as 3400 B.C. * Surge of pleasurable sensation (“rush”) * Reduced stress and anxiety * Reduced pain (physical and psychological) * Sedation * Impaired mental function * Cardiac and respiratory function slows (can be life threatening)

Question 35

What reverses opioid overdose + how? (2)

Answer 35

naxolone reverses opioid overdose by works as an opioid antagonist => higher affinity = decreases/reverses effects

Question 36

Why is fentanyl ~100 times more potent than morphine? (3)

Answer 36

Fentanyl is much more potent in vivo, but has similar binding and potency in vitro fentanyl is much more lipophilic it can cross the BBB much easier than morphine So, for an equivalent dose, much more fentanyl gets into the CNS - More drug in the brain = more mu-opioid receptor activated = greater CNS effects (e.g. respiratory depression via mu-opioid receptors in respiratory areas in the brain stem)

Question 37

β-arrestin 2 knockout mice do not develop anti-nociceptive morphine tolerance - experiment (3)

Answer 37

- testing latency of rodent retracting tail from heat stimuli - more morphine = longer to retract tail - morphine for 9 days = tolerance -KO didnt develop tolerance

Question 38

Multiple molecular mechanisms may contribute to opioid tolerance (6)

Answer 38

1) Loss of MOR signalling 2) Accumulation of desensitised MOR 3) No change in endocytosis 3) Persistent PKC activity 4) GRK or arrestin increases desensitised MOR 5) Recycling is impaired

Question 39

Modulation of inhibitory synaptic transmission-experiment results - CB1 agonist + GABA (3)

Answer 39

CB1 agonists inhibit GABA-mediated synaptic transmission 1) CB1 agonist reduces postsynaptic sensitivity to GABA (postsynaptic effect) 2) CB1 agonist reduces presynaptic release probability (presynaptic effect) * Reduces probability of action potential firing * Inhibits release mechanisms * Inhibits action-potential dependent Ca2+channel activity * Inhibits action-potential independent Ca2+ channel activity

Question 40

Using miniature synaptic currents to determine synaptic locus of drug effect (3)

Answer 40

* If amplitude (A) of events reduced → postsynaptic effect * If frequency (F) of events reduced → presynaptic effect * If no effect → presynaptic, action potential dependant effect

Question 41

Effect of CB1 agonists on miniature inhibitory postsynaptic currents (ISPC's) (3)

Answer 41

CB1 agonists do NOT affect: * mIPSC frequency * mIPSC amplitude But DO reduce evoked IPSCs Therefore, they reduce AP dependant GABA release (via inhibition of Ca2+ channels)

Question 42

Depolarisation induced suppression of inhibition (DSI) experiment (2)

Answer 42

* Depolarisation of postsynaptic cell results in a transient reduction in GABAergic transmission * Observed in cellebellar Purkinje cells, medium spiny neurones of the striatum and hippocampal pyramidal cells etc.

Question 43

1) Evidence that DSI is mediated via a retrograde messenger (5)

Answer 43

1) Increase in postsynaptic [Ca2+]i is necessary and sufficient for the induction of DSI * Blockers of Ca2+ entry block DSI * Postsynaptic Ca2+ chelating agents prevent DSI * Artificially raising [Ca2+] (uncaging) induces DSI 2. The frequency (number) of spontaneous inhibitory synaptic events is reduced – fewer vesicles released presynaptically 3. Postsynaptic sensitivity to exogenously applied GABA is not affected by depolarisation

Question 44

2) Evidence that DSI is mediated via a retrograde messenger (2)

Answer 44

4. DSI is not blocked by classical neurotransmitter receptor antagonists 5. DSI is not synapse or cell-specific

Question 45

DSI is mediated by endocannabinoids (6)

Answer 45

1.Synthesis and release of endocannabinoids dependent on Ca2+ 2.CB1 agonists depress GABAergic transmission 3.DSI is blocked by the CB1 antagonists 4.DSI is mimicked by blocking endocannabinoid uptake 5.DSI is absent in the CB1 knockout mouse Endocannabinoids are released in response to postsynaptic depolarisation/action potentials → suppression of GABA release