Lecture Verhij

Question 1

What are the key elements in animal models to study addiction?

Answer 1

• Reward
• Escalation
• Drug use despite negative consequences
• Difficulty in restricting drug use
• Withdrawal
• Relapse

Question 2

How does reward conditioning take place in addiction

Answer 2

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

Question 2

What happens if you experience reward in the brain?

Answer 2

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

Question 3

How is the drug introduced in rats brain

Answer 3

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)

Question 4

What is the effect of cocaine in nucleus accumbens?

Answer 4

1 mg/kg
5 mg/kg
10 mg/kg
15 mg/kg

Cocaine is a reuptake inhibitor. The measurement of dopamine is the microdialisis

Question 5

Setup for animal to receive cocaine

Answer 5

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

Question 6

What happens if the rat is given cocaine in terms of its behavior?

Answer 6

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.

Question 7

How is escalation researched?

Answer 7

Self administration. Cocaine goes directly into the brain (into jugular vein)

learning takes

Question 8

How is the self administration done? what is the surgery done?

Answer 8

• 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

Question 9

self administration

Answer 9

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.

Question 10

experimental setup

Answer 10

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

Question 11

How is progressive motivation tested?

Answer 11

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.

Question 12

escalation in other drugs of abuse

Answer 12

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.

Question 13

Self administration induced down-regulation of the dopamine system

Answer 13

• 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

Question 14

Drug use despite negative consequences

Answer 14

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

Question 15

difficulty in restricting drug use

Answer 15

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

Question 16

How can research on relapse be done?

Answer 16

Drug addiction, extinction and then relapse can be studied

Question 17

what happens during withdrawal? What are symptoms in animals?

Answer 17

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.

Question 18

What is the relapse behaviour

Answer 18

relapse causes higher num of lever pressing in relapse compared to before
reinstatement after long access is stronger than after short access

Question 19

Increase in stress and stress hormone levels enhance the intake of cocaine

Answer 19

Foot shock in animals or with corticosterone increases their lever pressing.
extinction lever pressing is very low but increases under stress

Question 20

Summary

Answer 20

• 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

Question 21

Example ongoing study

Answer 21

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

Question 22

SERT KO leads to reduction of CRF in PNV, but not CeA, after short access intake of cocaine.

Answer 22

Long access : Leads to reduction of CRF in CeA, but not PVN (opposite effect of short access) after long access intake of cocaine

Question 23

Increase of anxiety related behavior after long access intake of cocaine in SERT KO rats

Question 24

Summary part 2

Answer 24

• 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