Opioids and Pain Processing Flashcards
Where are opioids extracted from?
Poppy juice, contain alkaloids
What are the general uses of opioids?
Socially for euphoria, medically for analgesic sleep
What are endogenous or synthetic opioids?
Endogenous- enkephalins, synthetic-drug
They prod similar effects to morphine
How do you block the effects of opioids?
Use NALOXONE
prevent dangerous side effects eg resp depression
How long does IV opioid take to cause an effect?
2 minutes
How long does intramuscular opioid take to cause an effect?
20 minutes
How long does oral opioid take to cause an effect?
1 hour
At which receptors do opoids act?
μ Mu
7TMR coupled to G proteins
Describe μ receptors?
7TMR receptors coupled to G proteins- Gi/Go
Inhibit adenylate cyclase, decrease cAMP, open K+ channels, close Ca2+ channels
What is the effect of opioids binding to receptors?
Calcium channels close,
Potassium ions efflux
Membrane potential of cell decreases- hyperpolarised
Less excitable
Opioid binding activates Gi protein, decreases AC, decrease cAMP
What is the name of the main pain pathway?
Spinothalamic tract
What are the spinal effects of opioids?
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)
Describe the descending inhibitory control of pain
2 neurone network GABA and glutamate Morphine blocks GABA release, increase glutamate, excitation. More dopamine released-- pleasure Receptor on interneurone
Describe how morphine works
Acts at Mu receptors- analgesic
Causes euphoria, dysphoria
Anti tussive, dependence not an issue
tolerance is an issue and constipation
Describe the use of diamorphine (heroin)
Higher lipophilicity- rapid brain penetration
Broken down into morphine in CNS
More potent and addictive
Describe the use of codeine
less addictive, weak, less resp depression, good for cough
Describe the use of pethidine
Used in labour
Orally active, less potent, short duration
Describe the use of fentanyl
Used in anaesthesia
Orally active
High potency
Short duration
Describe the use of methadone
Half like of more than 24 hours
Reduce opioid use
Similar dependence, pain relief
What are the main side effects of opioids
Constipation, euphoria, dysphoria, resp depression, tolerance
Are opioids useful for neuropathic pain?
NO
Allodynia relayed by A fibres
Need a neuropathic analgesic eg Amitryptyline, Gabapentin, Pregbalin
