Lecture Verhij Flashcards
What are the key elements in animal models to study addiction?
- Reward
- Escalation
- Drug use despite negative consequences
- Difficulty in restricting drug use
- Withdrawal
- Relapse
How does reward conditioning take place in addiction
there is 2 compartments, one has circles and one has squares. in the middle there is a door.
Habituation: (mouse gets familiar with apparatus to reduce effect of novelty seeking at testing. both control and conditioning groups experience this step.
single 5 minutes trial
Conditioning: unconditioned stimulus is repeatedly presented in a single compartment (cocaine injection)
every day, for 5 minutes over 1-2 weeks
Control: The mouse is presented with a control stimulus (usually saline solution
every day, for 5 minutes over 1-2 weeks
Preference testing: The time spent in each compartment is measured by the experimentor. The conditioning group is compared with the control group and statistical tests are done to determine if conditioning was successful.
ca 30 minutes
What happens if you experience reward in the brain?
Natural behavior (e.g. sex or food intake) that stimulates the release of dopamine in the nucleus accumbens is associated with the sensation of pleasure
drugs of abuse lead to excessive increase of dopamine in the nucleus accumbens
How is the drug introduced in rats brain
A guide canula is implanted in the brain, and then a sample is taken from nucleus accumbens to analyse the amounts of dopamine inside (MICRODIALYSIS)
What is the effect of cocaine in nucleus accumbens?
1 mg/kg
5 mg/kg
10 mg/kg
15 mg/kg
Cocaine is a reuptake inhibitor. The measurement of dopamine is the microdialisis
Setup for animal to receive cocaine
suspending elastic band connected with brain and stimulator which is also connected with lever. when lever is pressed cocaine is released.
Electrical stimulation nucleus acumbens dopamine neurons
What happens if the rat is given cocaine in terms of its behavior?
behaviour regulated by dopamine in the nucleus accumbens
if cocaine is given, the animal gets much more active. the more cocaine (between 5 and 20 mg/kg) the higher the instance travelled in 5 minutes.
How is escalation researched?
Self administration. Cocaine goes directly into the brain (into jugular vein)
learning takes
How is the self administration done? what is the surgery done?
- Gas anesthesia: little mask.
- isophlorine gas mixed with oxygen
- surgery lasts 20-3 min
- eye lubricant
- incision is made where tube is on the back of the animal
- connective tissue is removed and right jugular vein is visible
- diagonal cut t
self administration
Learning takes about 2 weeks and then in an hour they press 10 to 15 times for cocaine
Division between:
- short access (SA or ShA), daily 1 hour session
animal model for non-compulsive drug use
- long access (LA or LgA), daily 6 hours sessions
animal model for compulsive drug use
Number of infusions grows leading to escalation in LA access not in SA access.
experimental setup
2 levers:
one active lever
one inactive lever (control)
chamber with electric shock on ground (metal grid)
single 2h session for habituation
canula can also be inserted from head
each training session (5 min acclimatisation (no cocaine)
light is on (cocaine is there)
after every infusion there is a time out period (between 30 s and a minute) to prevent an overdose
also max number of infusions is set in to prevent overdose
How is progressive motivation tested?
progressive ration (PR) responding. animal must press more often to receive the cocaine.
LA have more motivation, i.e. num of infusion for a break point (animal has to press 800 900 times).
motivation is really high to get cocaine.
escalation in other drugs of abuse
SA vs LA is present for cocaine, heroin, Nicotine, and Methamphetamine. For alcohol it does not work, cause animals do not like the alcohol. But alcohol vapor is done and prime them to use the alcohol. after a while it works.
Self administration induced down-regulation of the dopamine system
- continuous activation of the dopamine pathway alters the availability of dopamine (compensation)
- the reduction of down-regulation in dopamine availability has blunting effecton the natural reward circuit, leading to tolerance
- basically, dopamine system is shut down
Drug use despite negative consequences
alcohol + kinine (bitter/does not like it) or with foot shock
There is a negative consequence, but animal still takes the drug.
food shocks do not prevent the animal to take cocaine
difficulty in restricting drug use
continuation of cocaine seeking behaviour in the absence of the drug. Saline intake during extinction. For LgA animals, extinction is slower ( not 2/3 days, but almost 10 compared to ShA
How can research on relapse be done?
Drug addiction, extinction and then relapse can be studied
what happens during withdrawal? What are symptoms in animals?
They experience stress and anxiety
Research: maze open arm entries
reduction in open arm behaviour on elevated plus-maze (increase in anxiety-like behaviour
CRF (corticotroping releasing factor) are higher during withdrawal.
What is the relapse behaviour
relapse causes higher num of lever pressing in relapse compared to before
reinstatement after long access is stronger than after short access
Increase in stress and stress hormone levels enhance the intake of cocaine
Foot shock in animals or with corticosterone increases their lever pressing.
extinction lever pressing is very low but increases under stress
Summary
- addiction is a chronic brain disease, that starts with experimental/social drug use, where after rug use escalates
- most drugs of abuse initially increase dopamine levels in the reward system (e.g. nucleus accumbens)
- During the course of addiction, dopamine levels in the reward system decreases and stress hormone levels in the stress system increase
- The increase in, for instance, the levels of CRF during withdrawal may drive relapse behaviour
- intravenous drug self administration is the most commonly used animal model for measuring compulsive drug taking behaviour
- Long access exposure to the drug is used to mimic escalation of the drug intake
- Progressive ratio responding is used to mimic motivation to self administer the drug
- continuation of drug self administration espite negative consequences can be measured using foot shocks
- an extinction paradigm can be used to measure failure to stop drug seeking in the absence of the drug
Example ongoing study
Humans: reduction of serotonin transporter (SERT) activity predicts an increase in axiety-related behaviour and psychostimulant intake
Question: What drives this increased negative emotional state and psychostimulant intake?
WEIRD because: if you lack the serotonin transporter you’d expect cocaine to have no effect
study SERT knock-out (KO) rats
SERT knock-out(KO) rats are the result ENU-induced mutagenesis (premature stop codon in exon 3 of the SERT gene)
in one rat No SERT mRNA id protein expression (tested in raphe nuclein and other areas)
If microdialysis is done and serotonine is measured you find i8-9 times of serotonine release because there is no transporter (there is no reuptake)
KO rats (higher motivation to get cocaine)
in self-administration KO have higher num of intake both in 1 and 6 h –> link with serotonine transporter and cocaine intake
Also under pr this trend is confirmed
Why?
dopamine levels where not diferent in KO rats NO EFFECT IN DOPAMINE SYSTEM
CRF levels in KO rats:
CRF-containing brain regions are innervated by serotonergic brain regions. Serotonergic agents may change CRF release. Changes in CRF may drive cocaine intake
To test if SERT KO rats differ from their control rats in CRF immunoreactivity (IR) levels CRF staining is done
SERT KO leads to reduction of CRF in PNV, but not CeA, after short access intake of cocaine.
Long access : Leads to reduction of CRF in CeA, but not PVN (opposite effect of short access) after long access intake of cocaine
Increase of anxiety related behavior after long access intake of cocaine in SERT KO rats
Summary part 2
- variation in serotonin transporter (SERT) availability is accompanied by cariation in the intake of cocaine
- Accumbal dopamine does not play an important role in the increased intake of cocaine observed in individuals marked by a reduction of SERT
- short, but not long, access to cocaine changes CRF levels in the PVN, but not CeA
- Long, but not short, access to cocaine changes CRF levels in the CeA, but not PVN
- Changes in CRF lead to changes in emotional behavior, which, in turn, may drive the additional intake of cocaine
Hypotesis:
Switch from CRF release from paraventricular Nucleus to CRF release from central Amygdala, if there is switch from short to long term access (from non-compulsive to compulsive drug use).
the switch from the non-compulsive to compulsive intake of cocaine in individuals with a reduction of SERT may be mediated by a shift in CRF release from the PVN to the CeA
