pain and opioid analgesics

Question 1

What are peptide neuromodulators?

Answer 1

Neuropeptides

• small protein/polypeptide that acts as a neurotransmitter in the nervous system
• found on the CNS and PNS
• some neuropeptides also act as hormones
• AA join together by bonds
• > 100 known neuropeptides

Question 2

What are the opioid peptides

Answer 2

• B-Endorphin
  
  • Met-enkephalins
  • Leu-enkephalins
  • Dynorphins

Question 3

Describe the mechanism of action of opioids on neutrons and receptors involved:

Answer 3

• binds to receptor and changes conformation interaction with G-proteins (agonist)
• GDP protein bound at rest is exchanged for GTP activates G-protein receptors which signal to things inside cell
• overall, all actions will be inhibitory on the cell
  • activate K+ channel, so K+ leaves cell which reduces excitation
  • inhibit Ca2+ channels inhibit neurotransmitter release
• when antagonist is taken (eg. naloxone), it blocks the agonist from binding to receptor but doesn’t cause the cascade of events above

Question 4

How does noxious stimulus activate the pain circuits in the CNS:

Answer 4

• primary afferent sensory neutrons detect changes in the local environment and provide us with information about temp, touch and our chemical surroundings
• noxious stimulates activates nociceptors

Question 5

What are the sites of action of opioids in the CNS?

Answer 5

1. Analgesia: activation of descending pain pathway
2. Euphoria/reward
   • opioids act in ventral tegumental area to reduce GABAergic inhibition - promote dopamine release
     = euphoric response
   • compromises reward circuit = addiction

Question 6

What are the main side effects/actions of opioids?

Answer 6

• analgesia
• euphoria
• impaired cough reflux
• constipation
• respiratory depression - in medulla
• N/V
• Dependence
• Miosis - pupillary constriction
• pruritis - itching at side of admin

Question 7

Examples of opioids

Answer 7

• Morphine
  
  • Oxycodone
  • Fentanyl
  • Tramadol
  • Codeine