Flashcards
07. Addiction
Cards in this deck (24)
- 1What is meant by 'addiction'?Addiction involves the compulsive seeking of substance despite any negative consequences. Addiction is a primary, chronic and neurobiological disease.
- 2Why do people become addicted?1. Positive reinforcement
2. Tolerance
3. Physical dependence / withdrawal effect - 3Briefly mention the consequences of addiction• Addiction causes long-lasting changes at a cellular and molecular level.
• The drug enters the bloodstream and is carried to the CNS. - 4Concentration of the drug in the brain / time after drug administration
- 5What is the role of dopamine?Dopamine is a neurotransmitter that helps control the brain’s reward and pleasure centres. It also helps regulate movement and emotional responses, and it enables us not only to see rewards, but to take action to move toward them.
- 6The connection between dopamine and addiction• Neural mechanisms of drug addiction (including natural rewards) often focus on the mesolimbic pathway. The release of dopamine from the mesolimbic pathway into the nucleus accumbens regulates incentive salience (i.e. motivation and desire for rewarding stimuli) and facilitates reinforcement and reward-related motor functioning learning; it may also play a role in the subjective perception of pleasure. The dysregulation of the mesolimbic pathway and its output neurons in the nucleus accumbens plays a significant role in the development and maintenance of addiction.
• The ventral tegmental area (VTA) is part of the mesolimbic pathway, and located by the amygdala and hippocampus, responsible for part of our memory / learning and motivation. - 7Studying the effects of drugs: Animal paradigms - Single cell recording of mesolimbic pathway cells (Procedure)⎝ In this study by Mirenowicz and Schultz (1994), monkeys learned to respond to a sound to receive a reward. Neurons in the NAcc are active when the reward is given! After training, neurons in the NAcc are active when the stimuli (here: sound) is presented. This is called instrumental conditioning and involves strengthening neural connections:
1. Discriminative stimulus: Sound
2. Response: Animal responding
3. Reinforcing stimulus: Food - 8Studying the effects of drugs: Animal paradigms - Single cell recording of mesolimbic pathway cells (Results)Neurotransmitter (dopamine) is released. Thus, the connections between neurons that detect the stimulus and neurons producing the instrumental response were strengthened using positive reinforcement. This can be seen in the aftermath:
1. Discriminative stimulus: Sound
Neurotransmitter (dopamine) release
2. Response: Animal responding
3. Reinforcing stimulus: Food
Synapse strengthened - 9NAcc - what is it?The nucleus accumbens s a region in the basal forebrain rostral to the preoptic area of the hypothalamus.
The nucleus accumbens is a primary site mediating reward behavior, and it is thought to be directly involved in reinforcing and addictive behaviors in response to drug use (as demonstrated above). - 10Studying the effects of drugs: Animal paradigms Explain the conditioned place-preference paradigmConditioned place preference is a form of Pavlovian conditioning used to measure the motivational effects of objects or experiences. Here, microinjections of drugs are placed into the NAcc to produce conditioned place preference
- 11Studying the effects of drugs: Animal paradigms How to study the conditioned place-preference paradigm• There are different methods of conducting this kind of experiment: The biased method allows the animal to explore the apparatus, and the compartment they least prefer is the one that the drug is administered in and the one they most prefer is the one where the vehicle is injected. The unbiased method does not allow the animal to choose what compartment they get the drug and vehicle in and instead the researcher chooses the compartments.
• Humans have also shown to develop conditioned place preferences; for examples, individuals taking therapeutic doses of amphetamine develop CPP for where they consumed the drug. - 12Studying the effects of drugs: Animal paradigms Explain the drug self-administration / stimulation paradigmThis involves the self-administration of weak electrical stimulation or microinjection (e.g. of cocaine) directly into the NAcc (the “pleasure centre” for natural rewards).
- 13Studying the effects of drugs: Animal paradigms How to study the drug self-administration / stimulation paradigm• Intracranial self-stimulation (ICSS) is the operant conditioning method used to produce a brain stimulation reward (BRSR – a pleasurable phenomenon elicited via direct stimulation of specific brain regions) in an experimental setting.
• ICSS typically involves subjects with permanent electrode implants in one of several regions in the brain known to produce BSR when stimulated. Subjects are trained to continuously respond to electrical stimulation of that brain region, which produces BSR.
• ICSS studies have been particularly useful for examining the effects of various pharmacological manipulations on reward sensitivity. It has also been utilized as a means to gauge addiction liability for drugs of many classes. These data correlate well with findings from self-administration studies on the addictive properties of drugs. - 14Explain self administration• Self-administration is the process of a subject administering a pharmacological substance to themselves. In animal experimentation, self-administration is a form of operant conditioning where the reward is a drug. This drug can be administered remotely through an implanted intravenous line or an intracerebroventricular injection. Self-administration of putatively addictive drugs is considered one of the most valid experimental models to investigate drug-seeking and drug-taking behaviour. The higher the frequency with which a test animal emits the operant behaviour, the more rewarding (and addictive) the test substance is considered.
- 15A prominent model of self-administration⎝ In a prominent model of self-administration developed by George Koob, rats are allowed to self-administer cocaine for either 1 hour each day (short access) or 6 hours each day (long access). Those animals who are allowed to self-administer for 6 hours a day show behaviour that is thought to resemble cocaine dependence, such as an escalation of the total dose taken during each session and an increase in the dose taken when cocaine is first made available.
- 16What is the reward circuit?The reward circuit is a group of neural structures responsible for incentive salience (i.e. motivation and “wanting”, desire…), associative learning (e.g. positive reinforcement and classical conditioning), and positive emotions, particularly ones which involve pleasure as a core component.
(see lecture notes on p 31 for reward circuits for different drugs) - 17The involvement of dopamine and the mesolimbic pathway (i.e. nucleus accumbens) in drug addiction--> Natural reinforcers or (self-) administration of addictive drugs cause higher levels of dopamine in NAcc
--> Lesions to NAcc or VTA blocks self-administration of drugs or conditioned place preference - 18The effect of drugs on neurotransmitterDrugs can alter the way people think, feel and behave by disrupting neurotransmission, the process of communication between neurons (nerve celles) in the brain.
- 19Explain antagonists1. Antagonists (inhibit neurotransmitter effect): These drugs prevent a neurotransmitter from binding to its receptor. For example, drugs used to treat patients with schizophrenia are antagonists at receptors in the brain for dopamine.
- 20Explain agonists1. Agonists (facilitate neurotransmitter effect): These drugs act by binding to a receptor and mimicking the normal neurotransmitter. An example of this is morphine, an opiate that mimics effects of the endogenous neurotransmitter B-endorphin to relieve pain. Other drugs interfere with the deactivation of neurotransmitter after it has been released, thereby prolonging the action of a neurotransmitter. This can be accomplished by blocking re-uptake or inhibiting degradative enzymes.
- 21The effect of cocaine on neurotransmitter⎝ Cocaine, for example, blocks the reuptake of dopamine back into the presynaptic neuron, leaving the neurotransmitter molecules in the synaptic gap for an extended period of time. Since the dopamine remains in the synapse longer, the neurotransmitter continues to bind to the receptors on the postsynaptic neuron, eliciting a pleasurable emotional response. Physical addiction to cocaine may result from prolonged exposure to excess dopamine in the synapses, which leads to the downregulation of some post-synaptic receptors. After the effects of the drug wear off, an individual can become depressed due to decreased probability of the neurotransmitter binding to a receptor.
- 22The connection between drugs, dopamine and toleranceAddictive drugs tend to increase the dopamine release in the mesolimbic pathway and flood the circuit with dopamine.
• If the ‘reward circuit’ is continuously overstimulated, the brain adapts to the overwhelming surges in dopamine. This reduces the sensitivity of receptors and reduces the number of receptors in the reward circuit.
• The drug’s impact is lessened, increasing tolerance.
- 23Drugs and individual differences: Human studies in risk for addictionRisks for addiction is associated by a combination of factors:
--> Biological: The genes that people are born with – in combination with environmental influences
--> Environmental: Social environment, socio-economical, status quality of life
--> Developmental: Can develop at any age but is more likely to start during adolescence
• Young people report less effect of stimulant than adults: Feeling tired or different instead of euphoria
• Less hallucination with ketamine than adults - 24What have we learnt about addiction? Summary• Addiction is a primary, chronic and neurobiological disease
• Memory and learning is involved in addiction
• Neurotransmitter activity (e.g. dopamine) is affected by drugs, potentially causing alteration of the reward system (e.g. NAcc, VTA)
• Animal studies support the effect of drugs
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- Psychology 2A (Psychobiology) Flashcards on 07. Addiction, created by Nina Olsson on 26/07/2018.
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