Lecture 17: Opioid Analgesics Flashcards
two types of chronic pain
- nociceptive
2. neuropathic
nociceptive pain
caused by tissue damage
processes that increase or decrease nociception are __ or ___
pronociceptive or antinociceptive
neuropathic pain
caused by a lesion or dysfunction of NS; characterized by increased sensitivity (hyperalgesia) to pain-producing or innocuous stimuli
laudanum
opium + alcohol; used to relieve diarrhea, cough, pain, produce sleep
rate of abusing prescription pain drugs is ___
second only to marijuana abuse
opium
dried exudate of opium poppy
opiate
drug extracted from opium, mainly morphine and codeine (+thebaine)
opioid
any exogenous drug that binds to an opiate receptor, produces agonistic morphine-like effects, and is blocked by opiate antagonists
semisynthetic opioids
come from opiates (e.g. heroin from morphine)
synthetic opioids
come from precursor compounds (e.g. methadone)
4 naturally occuring alkaloids from poppy
- morphine
- codeine
- thebaine
- papaverine
3 main opiate receptors
- mu
- kappa
- delta
what activates mu?
endorphin
what activates delta?
enkephalin
what activates kappa?
dynorphin
three endogenous opiates
- endorphin
- enkephalin
- dynorphin
how many membrane spanning regions and amino acids in a GPCR?
- 7
2. 400
what channel does cAMP activate? what is the effect?
HCN channel (non selective cation channel, opened by hyperpolarization)
what do opioids do to adenylyl cyclase? what is the effect?
inhibit it; causes the cell to hyperpolarize. net inhibition
what is the main location of mu receptors?
periaqueductal gray
7 areas mu receptors are
- periaqueductal gray
- spinal trigeminal nucleus
- caudate
- thalamus
- dorsal horn of spinal cord
- brain stem nuclei that control respiration
- nucleus accumbens
prototypical mu receptor agonist
morphine
what receptors does morphine act on?
agonizes mu, kappa, and delta
what receptors does naloxone act on?
antagonist at mu, kappa, and delta
what receptors does fentanyl act on?
agonist at mu, kappa, and delta
7 areas kappa receptors are in
- basal ganglia
- nucleus accumbens
- VTA
- cerebral cortex
- hypothalamus
- periaqueductal gray
- dorsal horn of spinal cord
5 effects of kappa receptors
- modest analgesia
- respiratory depression
- dysphoria
- disorientation
- depersonalization
kappa receptors may antagonize ___
mu receptor activity
bremazocine
kappa receptor agonist; more analgesic than morphine w/o euphoria, dependence, and respiratory depression. limited by perceptual side fx
2 effects of delta receptor stimulation; why?
- antidepressant
- anxiolytic
increase levels of brain-derived neurotrophic factor (BDNF) which are reduced during high stress or depression
3 synthetic opioids
- methadone
- meperdine
- fentanyl
morphine is __ more potent than codeine
10x
heroin is ___ as potent as morphine
4-5x
codeine is converted to ___
morphine
when is endorphin released? (5)
- exercise
- excitement
- pain
- sex
- spicy food
where are nociceptors located?
dorsal root ganglia of spinal cord
nociceptors have ___ axons
bidirectional
where do bidirectional nociceptors relay pain impulses?
to synapse in dorsal horn of spinal cord, and then to brain
activation of opioid receptors causes ___ of neurotransmission due to ___
- reduction/inhibition
2. presynaptic inhibition of NT release
what NT is inhibited in spinal cord?
substance P
what NT is inhibited in VTA?
GABA (disinhibits DA release)
4 methods of mediation of analgesic effects
- activation of inhibitory endorphine-secreting or GABA-secreting neurons in dorsal horn of spinal cord
- activation of descending inhibitory neurons from brain to spinal cord
- modulation of central processing of pain stimuli (reduces sensory and affective aspects of pain)
- presynaptic inhibition of nociceptive afferent sensory neurons (inhib release of subst P in dorsal horn)
mixed agonist-antagonist
binds to opioid receptors esp kappa; causes analgesia in non-opioid-dependent people, but may precipitate withdrawal in opioid-dependent persons
4 pure agonists
morphine
heroin
demerol (meperidine)
methadone (dolophine)
2 pure antagonists
naloxone (narcan)
naltrexone (vivitrol)
3 partial agonists
- buprenorphene (suboxone)
- tramadol (ultram)
- tapentadol (nucynta)
3 medical uses of opiates
- analgesia
- suppression of cough
- GI symptoms
6 other effects of opiates
- euphoria
- resp depression
- nausea
- sedation/anxiolysis
- pupillary constriction
- endocrine effects
how is morphine put into spinal fluid?
delivered directly via implanted subcutaneous pump and intrathecal catheter
cause of morphine euphoria
activation of NAc
cause of drive to resume morphine use
cannabinoid system
___ can block compulsion for drug use
cannabinoid receptor antagonist
how does morphine suppress cough?
suppression of cough center in brain system
why does morphine cause nausea?
stimulation of medulla’s chemoreceptor trigger zone
how does morphine reduce GI symptoms?
acts directly on intestine
endocrine effects of morphine
reduce sex hormone releasing agents from hypothalamus
what pathway is necessary for initiation of opioid psychological dependence?
mesolimbic dopaminergic pathway (VTA to NAc)
the way morphine increases dopamine to NAc
binds to mu in VTA, inhibiting GABA
disinhibits DA neurons in VTA
codeine is usually combined with ___
aspirin or acetaminophen
codeine duration of action
three-four hours
___ or 6 SSRI antidepressants can block ___. why?
4
pain relief of codeine
block conversion of codeine to morphine
why does heroin have more psychoactive effects than morphine?
more lipid soluble; quickly passes BBB
3 metabolites of heroin
- monoacetylmorphine
- morphine
- codeine
what is heroin derived from?
morphine
demerol
synthetic opioid structurally different from morphine, prescribed as subst drug for heroin addicts
demerol potency
1/10 of morphine
4 excitatory side effects of demerol. why?
- tremors
- delirium
- hyperreflexia
- convulsions
metabolite of meperdine causes CNS excitation
2 benefits of methadone
- oral absorption
2. long half life
two uses of methadone
- prevention of w/d in opioid dependent persons
2. long acting analgesic for chronic pain
5 uses of naloxone
- opioid reversal
- treatment of alcoholism to reduce craving
- may reduce opioid craving
- treatment of autism, self-injurious behaviors, BPD
- chronically block opioid euphoria
tolerance to opioids dont have cross tolerance to ___
sedative-hypnotics
2 reasons withdrawal occurs
- reduced DA in nucleus accumbens
2. increased NE release from locus coeruleus
4 treatments for opioid dependence
- agonist maintenance therapy (methadone)
- agonist-antagonist therapy (suboxone)
- antagonist therapy (naltrexone)
- treatment of comorbid disorders