introduction to addiction and the brain Flashcards
define neuropharmacology
branch of pharmacology that deals with the action of drugs on the nervous system
what is a neurotransmitter?
naturally occurring chemical that carry chemical signals (messages) from one neuron (nerve cell) to the next target cell
define psychotropic
drugs that affect a person’s mental state
identify 4 classic neurotransmitters involved in addiction
- dopamine
- noradrenaline
- serotonin
- acetylcholine
what is another name for serotonin?
5-hydroxytryptamine, 5-HT
what drugs release neurotransmitter dopamine?
amphetamines
cocaine
what drugs release neurotransmitter noradrenaline?
amphetamines
cocaine
what drugs increase serotonin?
ecstasy (MDMA)
what drug activates acetylcholine receptors?
nicotine
what is chemical transmission?
the way a signal gets from one neuron/brain cell to the next
chemical transmission relies on number of different signalling pathways and chemical systems
why do we have neurotransmitters?
due to the need for communication within the brain and the rest of nervous system
neuron and nerve cells need to communicate with eac hother
describe the nerve transmission process
dendrites -> cell body (soma) -> axon -> axon terminal
- neural signals travel electrically along nerve fibres
- neurotransmitters cross a synaptic gap/cleft between nerve cells to reach next neuron
- crosses synaptic cleft through process of diffusion
what are neurotransmitters stored in?
synaptic vesicles
how are neurotransmitters received at end of axon terminal?
- receptors
- these are specially configured to receive and be activated by the neurotransmitter that is released
- this unlocks a postsynaptic response as an ‘agonist’
what is similar about psychotropic drugs and neurotransmitters and how does this affect receptors?
- psychotropic drugs and neurotransmitters have similar chemical structures
- meaning they can activate or block receptors that are intended to recognise brain’s own neurotransmitters
what is it meant by ‘AGONIST’ with regards to neurotransmitters?
- AGONISTS are substances that bind to synaptic receptors
- these INCREASE the effect of neurotransmitter
- has the net effect to increase neurotransmission (as a direct or indirect agonist)
what is it meant by ‘ANTAGONIST’ with regards to neurotransmitters?
- ANTAGONISTS are substances that bind to synaptic receptors
- these DECREASE the effect of a neurotransmitter (these block receptor)
- has the net effect to decrease neurotransmission (as a direct or indirect antagonist)
what do ‘autoreceptors’ do?
- found presynaptically
- act like thermostats
- regulate neurotransmitter release and neuronal firing at neuron terminal and cell body
- neurotransmitters/drugs acting here can reduce further release at the termal so further neurotransmission is reduced
what effect can drugs have on synaptic transmission?
- can have a net positive effect (as direct or indirect agonist)
- can have a net negative effect (as direct or indirect antagonist)
give an example of drug action that acts as an agonist
amphetamines
stimulate release of dopamine and noradrenaline
give an example of drug action that acts as an antagonist
cocaine
blocks the reuptake of dopamine and noradrenaline
What are the short term effects of MDMA/Ecstasy?
Gerra et al. (2000) study looking at the effects of MDMA/ecstasy
- drug increases serotonergic (5-HT)
- serotonergic = affecting serotonin neurotransmitter
- drug increases levels of serotonin
What is the suggested long term effect of MDMA/Ecstasy?
Gerra et al. (2000) study looking at the effects of MDMA/ecstasy
- evidence that serotonin can become depleted
- indicating neurotoxicity (altering of normal activity of nervous system)
- results in cell death in serotonergic pathways
Outline Gerra et al. (2000) study looking at the effects of MDMA/ecstasy
- uses an indirect measure to look at effect
- looks at measuring serotonergic function indirectly
- done by issuing challenge test
- fenfluramine is a drug that increases serotonin release
- increased serotonin has effect on pituitary gland –> this is shown as hormonal change (specifically prolactin response
- plasma prolactin is looked at to measure the effect of fenfluramine
- a normal response should show that an increase of fenfluramine would results in an increase in plasma prolactin as fenfluramine increases serotonin which increases hormonal response of prolactin
Outline findings of Gerra et al. (2000) study looking at the effects of MDMA/ecstasy
‘normal’ volunteers
- show an increased prolactin response to fenfluramine
- consistent with what was expected of normal response
‘MDMA’ users
- showed a reduced prolactin response to fenfluramine
- suggests that MDMA users serotonergic function is depressed
- additionally, reduced response to prolactin persists in ppts who previously used MDMA but do not presently
- suggests long term effects of long term use of MDMA
- evidence consistent with neurotoxicity and death of pathways –> if change was functional, some recovery would be expected when drug use stops but this is not the case
Outline findings of Gerra et al. (2000) study looking at the effects of MDMA/ecstasy
‘normal’ volunteers
- show an increased prolactin response to fenfluramine
- consistent with what was expected of normal response
‘MDMA’ users
- showed a reduced prolactin response to fenfluramine
- suggests that MDMA users serotonergic function is depressed
- additionally, reduced response to prolactin persists in ppts who previously used MDMA but do not presently
- suggests long term effects of long term use of MDMA
- evidence consistent with neurotoxicity and death of pathways –> if change was functional, some recovery would be expected when drug use stops but this is not the case
Outline Miczek & Mutschler (1996) study looking at the effects of social stress in lab animals
- lab animals used
- social stress brings about physiological response
- rats trained to respond by pressing level for cocaine or food reward
- before social stress introduced, rats responded more for lever
- social stress introduced
- social stress manufactured by placing an ‘intruder’ which was another male rat
- intruder would attack (wire mesh placed to prevent injury)
- lasted 60 minutes
- after social stress, rats showed increase response for cocaine but not for food reward
- shows selective effect of social stress on cocaine-reinforced responding
- shows drug as very powerful reward
How does Miczek & Mutschler (1996) rat study apply to addiction in humans?
- suggests role of stressful life events in relapse of human drug users
