Opioids and Pain Processing

Question 1

Where are opioids extracted from?

Answer 1

Poppy juice, contain alkaloids

Question 2

What are the general uses of opioids?

Answer 2

Socially for euphoria, medically for analgesic sleep

Question 3

What are endogenous or synthetic opioids?

Answer 3

Endogenous- enkephalins, synthetic-drug

They prod similar effects to morphine

Question 4

How do you block the effects of opioids?

Answer 4

Use NALOXONE

prevent dangerous side effects eg resp depression

Question 5

How long does IV opioid take to cause an effect?

Answer 5

2 minutes

Question 6

How long does intramuscular opioid take to cause an effect?

Answer 6

20 minutes

Question 7

How long does oral opioid take to cause an effect?

Answer 7

1 hour

Question 8

At which receptors do opoids act?

Answer 8

μ Mu

7TMR coupled to G proteins

Question 9

Describe μ receptors?

Answer 9

7TMR receptors coupled to G proteins- Gi/Go

Inhibit adenylate cyclase, decrease cAMP, open K+ channels, close Ca2+ channels

Question 10

What is the effect of opioids binding to receptors?

Answer 10

Calcium channels close,
Potassium ions efflux
Membrane potential of cell decreases- hyperpolarised
Less excitable
Opioid binding activates Gi protein, decreases AC, decrease cAMP

Question 11

What is the name of the main pain pathway?

Answer 11

Spinothalamic tract

Question 12

What are the spinal effects of opioids?

Answer 12

STT synapses in dorsal horn
A fibres- touch, tickle, brush
C fibres- pain- superficial laminae
Opioid receptors are in superficial laminae so opioids only affect nociception (pain)

Question 13

Describe the descending inhibitory control of pain

Answer 13

2 neurone network
GABA and glutamate
Morphine blocks GABA release, increase glutamate, excitation.
More dopamine released-- pleasure
Receptor on interneurone

Question 14

Describe how morphine works

Answer 14

Acts at Mu receptors- analgesic
Causes euphoria, dysphoria
Anti tussive, dependence not an issue
tolerance is an issue and constipation

Question 15

Describe the use of diamorphine (heroin)

Answer 15

Higher lipophilicity- rapid brain penetration
Broken down into morphine in CNS
More potent and addictive

Question 16

Describe the use of codeine

Answer 16

less addictive, weak, less resp depression, good for cough

Question 17

Describe the use of pethidine

Answer 17

Used in labour

Orally active, less potent, short duration

Question 18

Describe the use of fentanyl

Answer 18

Used in anaesthesia
Orally active
High potency
Short duration

Question 19

Describe the use of methadone

Answer 19

Half like of more than 24 hours
Reduce opioid use
Similar dependence, pain relief

Question 20

What are the main side effects of opioids

Answer 20

Constipation, euphoria, dysphoria, resp depression, tolerance

Question 21

Are opioids useful for neuropathic pain?

Answer 21

NO
Allodynia relayed by A fibres
Need a neuropathic analgesic eg Amitryptyline, Gabapentin, Pregbalin