Neuroscience and Clinical Semester 1 Week 8: Drug Addiction and the brain’s reward circuits Flashcards
What is addiction?
A state resulting from the interaction between an organism and a drug, characterised by a compulsion to take the drug periodically for its psychic effects. Tolerance may or may not be present.
Routes of drug administration
o Ingestion: oral route
- Easy and relatively safe
- Absorption via digestive tract is unpredictable
o Injection: bypasses digestive tract
- Subcutaneously (SC) -> under the skin
- Intramuscularly (IM) -> into large muscles
- Intravenously -> into veins – drug delivered directly to brain
o Inhalation – tobacco and marijuana
- Absorbed through capillaries in lungs
o Absorption through mucous membranes
- Nose, mouth
Tolerance
- The body adapts to the presence of the drug over time, diminishing its effects at the original dose.
- A person needs increasingly larger doses of a drug to achieve the same effect that they initially experienced
Withdrawal
The physical and psychological symptoms that occur when a person who has become dependent on a substance suddenly reduces or stops using it
Sensitisation
- repeated use of a drug leads to an increased response to its effects
- the opposite of tolerance
What is contingent tolerance?
- Tolerance only develops to drug effects that are experienced e.g. if it reduces pain it may eventually stop having this effect if it is taken in the same way every time.
What is conditioned tolerance?
- Maximal tolerance effects are seen in the environment in which the drug is usually taken
- Can cause overdose if you give yourself the typical dose in a different environment
Methods to investigate neural and behavioural basis of drug use
Self-report - questions about drug use and dependence
Animal models:
- Behavioural preference tests
- Intracranial self-stimulation
- Self administration paradigm
Behavioural preference test
Rat receives drug in one compartment and a placebo in another. When the drugs are removed, the rat shows a preference for the drug compartment.
Intracranial self-stimulation
Electrodes placed in rat’s brain in reward area. Rat presses lever for stimulation to that area. The rat is given drugs. Measures taken of how often the rat continues to press the lever, therefore measuring effect of drug on brain.
Self administration paradigm
Rat presses lever to receive drug, observe which drugs the rat presses the lever for.
Pharmacological action of commonly used drugs
- interferes with synaptic transmission
- bind to receptors to block reuptake
- Drugs elicit effect in the area of the brain called the nucleus accumbens
Cocaine and amphetamine
block reuptake of dopamine leading to increased levels of it
Ecstasy and SSRIs
- blocks reuptake of serotonin leading to increased levels of it
- also reduces activity of limbic system
LSD
Caffeine
Cannabis/marijuana
Heroine/morphine
LSD - doesn’t inhibit reuptake but binds to serotonin receptors
Caffeine - adenosine receptors
Cannabis/marijuana - THC, binds to cannabinoid receptors
Heroine/morphine - opiates, pain killers
