Lecture 24- Opiates Flashcards
What do endorphins do?
- brain’s own natural pain-relief system
- mimic opiates effects: pain relief, pleasure, stress-relief
When are endorphins released?
following exercise and certain injuries
What does acupunture do?
- may relieve pain by releasing endorphins
- naloxone blocks acupuncture-induced analgesia
Placebos
may release endorphins as Naloxone blocks placebo-induced analgesia
Opiate effects on the brain- neurobio
- mimic action of endogenous opiod peptides (endorphins) at opiod receptors (are agonists)
- directly affects neuronal activity, intrinsic pain-modulating circuitry, additional therapeutic effects
Opiod system is prominent in…
sensory role
inhibiting responses to painful stimuli
Opiod system is prominent in…
modulatory role
gastrointestinal, endocrine and autonomic functions
Opiod system is prominent in…
emotional role
rewarding and addicting properties of opiods
Opiod system is prominent in…
cognitive role
modulating learning and memory
Opiod major receptor subtypes
mu (u)
endorphin (agonist)
Opiod major receptor subtypes
delta (δ)
enkephalin (agonist)
opiod major receptor subtypes
kappa
dynorphin (agonist)
What type of receptors are opiod receptors?
metabotropic (g-coupled)
What do opiod receptors do in terms of neuronal action potentials?
- inhibits excitability
- activation of K+ channels
- inhibits voltage-activated Ca2+ channels
- inhibits NT release
Opiates pharmacological effects
- euphoria- drowsiness, body warmth, “heavy” limbs
- analgesia (pain relief)
- sedation (including mental clouding)
- reduced anxiety
- depression of respiration
- cough suppression
- pupillary constriction (miosis)
- nausea/vomiting
- constipation
- impotence (loss of desire)
- vivid dreams
Opiates actions on pain signaing
- possible direct actions of opioids on peripheral tissue
- inhibition occurs at spinal cord
- possible site of action in diencephalon
binds to gaba-tropic interneuron at MOR receptor in spinal cord
Opiates’ actions on the reward pathway
- inhibit gaba and NAc
Opiate tolerance -why?
- more drug is needed to achieve the same effects due to decreased receptors, increased liver enzymes, and conditioned tolerance
Opiates withdrawal
- appear after 1-2 weeks of chronic use
- depression, crying
- high anxiety, irritability
- panting
- diarrhea
Why is the relapse rate for opiates so high?
- environmental factors and Pavlovian effects
- Vietnam veterans: 21% addiction rate by end of war, but low relapse rate due to different environment at home
reinforcement opiates
there is a switch from positive to negative reinforcement- avoiding withdrawal effects
When can negative symptoms arise?
- around 6-12 hours after last dose
- almost flu-like symptoms
