Opiates Flashcards
Dynorphin
A NT that binds to opiate receptors.
Protein.
Synthesized in cell body of neuron, packaged into vesicles. Metabolized in synaptic gap by peptidases. No evidence for reuptake.
3 endogenous ligans for opioid receptors
Dynorphins, enkephalins and endorphins
Activation of opioid receptors leads to
Inhibition of adenylyl cyclase and a decrease in the concentration of cAMP.
This results in an increase in K conductance and a decrease in Ca conductance. (depends on which receptor is activated)
3 types of opioid receptors
Mu, Kappa, Delta.
Mu and Delta. Activation causes what
Leads to opening of K channels.
Produces hyper polarization, decreases frequency of action potentials.
Greatest effect of opioid analgesics are here !
Kappa. Activation causes what
Causes less Ca influx into pre-synaptic nerve terminal, resulting in a decreased NT release.
Decreases the number of vesicles that release excitatory NT.
Difference between analgesia and anesthesia
Analgesia- lack of feeling of pain. All other sensory function is unaffected
Anesthesia- all sensory info is affected so that the perception of any sensory stimulus is reduced
Where are opiate receptors located
- What do the surrounding dynorphin neurons do?
- How do serotonin releasing neurons affect dynorphin neurons?
Brain, spinal cord and many peripheral tissues/organs.
**Analgesia mediated by receptors in spinal cord
At the synapse between the sensory neuron and the ascending neuron that goes to the brain. on membranes of both neurons. activation counters excitatory effect.
Dynorphin surround the synapse. Activation= physiologic analgesia.
Serotonin releasing neurons activate dynorphin neurons, which is why SSRIs can be used to tx chronic pain
*Sedation and euphoria mediated by receptors in brain
Why can SSRIs be used to tx chronic pain
Serotonin releasing neurons activate dynorphin neurons, which when activated, cause physiologic analgesia.
CNS effects of opiates
Analgesia Drowsy Euphoria- seen even when analgesia is not required aka when person is not in pain. Dysphoria/confusion Pupillary constriction Nausea/vomiting Respiratory depression Cough suppression Decreased BP
PNS effects of opiates
Lowered activity of GI
Urine retention
Uterine relaxation
Clinical use of opioid agonist
Antidiarrheal- especially loperamide
Antitussive- anti cough.
Dyspnea- shortness of breath. Use in situations of respiratory difficulty.
Tx of opiate addiction by methadone
Loperamide when to rx
Antidiarrheal
Efficacious orally
Low potential for abuse
Admin of opiate agonists
Some effect orally, some degraded in GI
All effected IV
Epidural injection helpful because does not have undesired effects and does not prolong labor.
Meperidine compared to other opiate agonists
Less strong
No miotic effect
Slower development of tolerance and dependence than morphine.
