Placebo effects in analgesia Flashcards
(21 cards)
Placebo effect
psycho-sociobiological phenomenon activated when the patients believes in an effective therapy and so expects a reduction of symptoms.
The placebo effect is the outcome following a “dummy” treatment or the administration of an inert medical treatment, which can be pharmacological or not.
Which is the key pathway that is important here?
Descending inhibitory
What component of opium is reponsible for the analgesic effect?
Morphine
What are the 3 opiate receptors?
Opiate receptors: µ δ, κ.
What were the first identified opiods?
first endogenous opioids, small peptide molecules called Met-enkephalin and Leuenkephalin.
Since then, several other endogenous opiates have been discovered. These include the endorphins and dynorphins.
What do most placebo studies show a link between?
Expectancy and pain
What does reducing anxiety do?
Reduce pain
Expectations of clinical benefit
Has a role in placebo-induced analgesia
- Expectation of reward (less pain) results in enhanced release of dopamine in nucleus accumbens
- Increased mu opioid activity and descending pain inhibition (PAG)
- Anxiety modulation (orbitofrontal region): expect less pain and anxiety decreases
What is classical conditioning? (unconscious mechanism)
- After repeated associations between a conditioned stimulus (CS), the environment around the patient (e.g. color of pill or the injection) and an unconditioned stimulus (the active drug, e.g.morphine) the CS alone is able to elicit a conditioned response (CR) similar to that induced by the drug.
what area of the brain may be involved in classical conditioning?
› Dorsolateral prefrontal cortex might be involved
What are the areas in the brain involved in the PLacebo response?
-
conditioning response
- (dorsolateral prefrontal cortex)
-
reward and anxiety response
- (nucleus accumbens and orbitofrontal cortex, respectively
What does expectation trigger and what does conditioning trigger?
- Expectation triggers endogenous opioids,
- conditioning activates specific subsystems.
What dictates whether the placebo is with opiod or non-opiod receptor/mechanism?
Depends whether the conditioning was done with opiod receptors or if it was done with a non-opiod mechanism
What is the Non-opioid analgesia mediated by?
Cannabinoid receptors
CB1 cannabinoid receptor antagonist rimonabant blocks non-opioid placebo analgesia.
Open vs hidden treatment
Hidden treatment:
- Computer controlled by dr delivers the treatment, pt won’t know when it is administered.
When hidden some drugs are less effective in pain reduction
TREATMENT= ALWAYS active treatment PLUS the placebo effect
How is the placebo component affected by the difference between the open and hidden administration?
- larger the difference between the open and hidden administration, the larger the placebo component
- Conversely, the smaller the difference, the greater the specific effects of the treatment
- slower decrease of pain in the hidden patient group compared with the open one, which indicates that most of the initial benefit in the open group was due to a placebo effect
Does brain imaging support the opiod hypothesis?
fMRI study showed a decrease in activity in pain pathways areas after a placebo treatment and a cognitive-evaluative network is activated before the placebo response
same areas activated administering a placebo and an opioid drug (PET)
What circuit is involved in placebo analgesia?
descending rACC-PAG-pons-medulla painmodulating circuit involved in placebo analgesia
WHat happens if there is a high expectation of pain?
there will be a high brain activity in pain
also works vice-versa, low expectations = low activity
Who doesn’t benefit from the Placebo effect mainly?
disease group
Alzheimer’s patients
