Wk10 Opioid

Question 1

What are the neuropeptides and how they work?

Answer 1

Neuropeptides:

• a small protein/polypeptide that acts as a neurotransmitter in the nervous system
• some neuropeptides also act as hormones

Neuromodulator:
- substances that do not directly act on ion-channel receptors, but act with other neurotransmitters to enhance or inhibitory the responses/excitatory of the receptors

Opioid peptide
- Act as a neuromodulator to inhibit the action of other neurotransmitters, making neurons more difficult to excite

Question 2

How does a noxious stimulus activate the pain circuits in the CNS?

Answer 2

• Environmental stimuli, ie burns, activate specialised proteins, which stimulate the nociceptors to convert the stimuli into electrical potentials.
• The nociceptors then allow Ca+ into the cell and release ‘glutamate’ at the synapse joining to the spinal cord
• The glutamate binds to the specific receptors on the spinal cord neuron, and let Na+ into the cell to fire action potentials up into the brain
• the action potential is encoded into detailed information about the pain by the brain cortex

Note:

• thalamus is an important relay station for the pain circuit along the spinal cord neuron.
• stroke in thalamus may cause possible chronic pain sensation

Question 3

What is the mechanism of action of opioids on neurons and the receptors?

Answer 3

• direct inhibits primary afferents:
  opioids bind to the opioid receptors on the neurons to produce an inhibitory effect on the excitation of the neurons
• activates the descending analgesic pathway
  opioids can also active the DAP which releases some potent inhibitory neurotransmitters to produce less painful experience
• μ-opioid receptor, is the most common opioid receptor
  > it produces ‘analgesia’, ‘nausea’, ‘constipation’, and ‘respiratory depression’

Question 4

What are the sites of action of opioids in the CNS and how this results in the main side effects?

Answer 4

Analgesia - SOA: spinal cord, PAG
Euphoria/rash - SOA: nucleus accumbens
Respiratory depression - SOA: medulla

Question 5

What are some common types of opioids?

Answer 5

mu-receptor agonists:

• morphine
• codeine (constipation)
• oxycodone (nausea …)
• tramadol (nausea …)

mu-receptor antagonists:

• naloxone: reverse opioid overdose (take with the opioid), low bioavailability
• naltrexone: ↓ opioid dependency, long bioavailability