addictions Flashcards
define tolerance
Reduced responsiveness to a drug caused by previous administration
how does tolerance develop?
in response to many types of drug
eg opioids, ethanol, barbiturates, benzodiazepines
what are the 2 mechanisms of tolerance?
- dispositional tolerance
- pharmacodynamic tolerance
describe dispositional tolerance?
Less drug reaches the active site!!!
- less drug absorbed
- drug metabolised faster
- more drug excreted
- decreased rate of absorption
- increased rate of metabolism to inactive metabolites
- decreased rate of metabolism to active metabolites
- increased rate of excretion
describe pharmacodynamic tolerance
site of action is less affected by the drug!!!
- fewer drug receptors
- less efficient drug receptors
- down-regulation or internalisation of drug receptors
- reduced signalling down stream of drug receptors
- some other compensatory mechanism
Development of tolerance may also lead to withdrawal symptoms.
For example—
taking the drug- reduces transmitter release
->
results in increased sensitivity to transmitter
but when u take away the drug- the increased sensitivity to transmitter remains
acute affect of opiod
constipation
withdrawal affect of opiod
diarrhoea
barbiturate acute affect
anticonvulsant
withdrawal affect of barbiturate
convulsions
cocaine acute affect
elevate mood
cocaine withdrawal effect
depressed mood
describe the reward pathway?
Neurones project from the ventral tegmental area to the nucleus accumbens & prefrontal cortex
When VTA neurones are stimulated they release dopamine is released
This causes a sensation of pleasure/reward
how has the reward pathway evolved?
The reward pathway is normally activated by eating, drinking and sex
It therefore encourages those “healthy” behaviours that lead to propagation of your genes
how does heroin affect reward pathways and dopamine levels?
heroin increases firing rate of dopaminergic neurones
