Reward and Drug Addiction Flashcards
Psychoactive Drugs
- Drugs: Chemical substances which interact with the biochemistry of the body
- Psychoactive drugs: Any chemicals that influence the way we feel or act
Agonists vs Antagonists
- Agonist: mimics the action of the neurotransmitter
- Antagonist: blocks the action of the neurotransmitter
- Synapse Level: effect on the post-synaptic neuron
- Receptor Level: effect on the receptor
Pre-synaptic Receptors
Post-synaptic Receptors
Autoreceptors
- inhibiting the exocytosis of their own neurotransmitters, noradrenaline or adrenaline, as part of a negative feedback loop
Reuptake
- after a signal has been transmitted
- reabsorbed by the nerve cells
- allows neurotransmitters to be reused and helps regulate neurotransmitter levels present in the synapse
Pharmacokinetics
The study of how the body interacts with administered substances for the entire duration of exposure
Intake
Routes include:
- Digestive tract: desired but slow
- Respiratory tract: faster
- Through skin: ex. ibuprofen gel, nicotine patch; fairly quick
- Through mucous membranes: ex. snorting cocaine
- Intravenous injection (directly into blood)
- Intramuscular injection (into the muscles)
- Subcutaneous injection (under the skin)
Distribution
- distribution can be different depending on whether its water-soluble or lipid-soluble
- blood stream (capillaries) to tissues (capillaries reach all organs and all parts of it)
- only difference in the blood-barrier of capillaries in the brain
Elimination
- all drugs are eventually eliminated from the body (by chemical breakdown (enzymes) or excretion (urine)
- drugs can be stored in the body for varying lengths of time (depending on their biological half-life)
Physical Dependence
- A side effect of the tolerance that your body has built up to the drug; Body maintaining homeostasis
- Will develop even with therapeutic doses
Psychological Dependence
- That association of “this is good i enjoy it” to the drug
- When drug directly interacts with the brain’s reward system
- Addicts will crave the drug, even while disliking the effects
Tolerance (Metabolic and Functional)
Metabolic Tolerance:
- Your body gets better at clearing the drug
- Better elimination of the drug
Functional Tolerance:
- Exposure to the drug makes changes to structures over time
- Change in receptor numbers; Change in receptor sensitivity; Change in intra-cellular cascades
Withdrawal
Person will start to feel the body’s counteraction/response to the drug that they have stopped taking (the counteraction that have built up the body’s tolerance towards the drug)
Mesotelencephalic Dopamine System
Opiate Addictiveness
- In Ventral Tegmental Area (VTA), opiates inhibit GABA-nergic interneurons
- This releases inhibition from neurons which project to Nucleus Accumbens
- More dopamine release WHICH is what makes you want it again and again
- In Nucleus Accumbens, effects are independent from but similar to Dopamine from VTA
Intravenous Injection
directly into the blood
Intramuscular Injection
into the muscle
Subcutaneous Injection
under the skin
Water-soluble Molecules
- Can be directly dissolved in the blood, but do not pass through cell membranes
- Water-soluble molecules can be directly dissolved in the blood but do not pass through membranes
- Easier to dissolve in the blood but harder to pass through membranes
Lipid-soluble Molecules
- Need carriers to transport them through the blood, but can pass directly through cell membranes
- Can pass through membranes and cross the blood-brain barrier
- Needs carriers to circulate in the blood but can easily cross tissues
Blood-brain Barrier
- Protecting the brain
Biological Half-Life
- The time required for the concentration of agents in the body or plasma to clear from the body (FROM FULL TO HALF)
- Can vary very differently from drug to drug (minutes to weeks)
- Depends on how fat-soluble they are, how easily they are broken down by enzymes, etc.
Classical Conditioning
- Unconditioned Stimulus, Unconditioned response
- Could be the environment of taking the drugs (US) and the withdrawal symptoms (UR)
- Possible reason for relapse
Context Dependence
- Taking drugs in a novel environment could trigger greater drug effects compared to taking it where you usually would, because novel environments do not trigger the body’s preparatory response to taking the drug (the counteraction that allows you higher tolerance)
- Classical conditioning
Operant Conditioning (= Instrumental Conditioning)
- More to consequences
- Reward makes you more likely to do the behaviour again
- Performing behaviours based on previous consequences that followed it
Reinforcement System
- Part of operant conditioning
- Reinforces this connection between the detection of the stimulus and the doing of the behaviour
Intracranial Self-stimulation
Medial Forebrain Bundle
All the axons from the VTA to the Nucleus Accumbens
Nucleus Accumbens
- in the telencephalon (forebrain)
- one of the brain areas where it is easiest to get reward (requires least electrical stimulation)
Ventral Tegmental Area
- in the mesencephalon (midbrain)
- one of the brain areas where it is easiest to get reward (requires least electrical stimulation)
Mesencephalon
midbrain
Telencephalon
forebrain
Micro-dialysis
Intracranial Drug Self-administration
