Topic 3 - drug addiction

What is a drug?

A chemical substance that interacts with the biochemistry of the body:

• inhibits or reinforces enzyme activity

• blocks or activates receptors

• interacts with neurotransmitters or hormones in other ways

• attacks invaders (e.g. antibiotics)

psychoactive is

any chemical that changes the way we feel, interacting with the nervous system and/or the endocrine

Auto receptor

Receptors in the synaptic cleft which neurotransmitters bind to, acting as a negative feedback loop to stop/start the release of neurotransmitters.

Drugs on the receptor being an agonist

Attaches to the presynaptic receptor and stimulates the release of neurotransmitters

Drugs on the synapse being an antagonist

It binds to the auto receptor to stop neurotransmitters

Drugs as an antagonist on the receptor but agonist at the synapse

It blocks the presynaptic receptors so neurotransmitters can't bind to it, acting as an antagonist. However, this increases the amount of neurotransmitters as feedback loop is stopped, making the presynaptic vesicle release more neurotransmitters

Drugs as an agonist at the receptor but antagonist at the synapse

It stimulates the release of more neurotransmitters at the receptor, but through the auto receptor, stops the production of neurotransmitters for the synapse as a whole

Ways to take drugs?

Through digestive tract (swallow pill)

Respiratory tract (smoking)

Through skin (a patch, cream)

Through mucus membrane (cocaine being snorted)

Intravenous injection (directly into the blood)

Intramuscular injection (into the muscle)

Subcutaneous injection (under the skin)

How does the drug travel through the body?

Through the blood stream

Water-soluble molecule drugs

Can be directly dissolved into the bloodstream but cant travel through the cell membrane

Lipid-soluble molecule drugs

Is made of fat, requiring transport to get them through the blood but can directly pass through the cell membrane

Blood brain barrier

the lack of gaps found in the capillaries in the brain makes sure that only specific parts of the blood goes to the brain

How to get through the blood-brain barrier

Fat-lipid drugs can get through the blood brain barrier as they dissolve straight through the capillaries

What type of soluble molecules are psychoactive drugs made of?

Lipid-soluble

How are drugs eliminated from the body?

Through chemical breakdown (by enzyme) or excretion (in urine)

What types of frugs stay in the body for long time?

Lipid-soluble drugs as they are stored in fat tissue

Half-life in drugs

Is the easiest way to predict how long the drug will stay in the body, and can be artificially changed to serve the need of the drug (e.g. sleeping pills do not need to last more than a few hours)

What is the result of drug tolerance?

The same does of the drug is less effective and more of the drug is needed for that original effect

Homeostasis

Maintaining a stable internal environment despite changes in the external environment. This is a form of negative feedback and results in drug tolerance developing

The two mechanisms of drug tolerance

Metabolic tolerance and functional tolerance

Metabolic tolerance

Allows for a quicker elimination of the drug

Functional tolerance

• change in the receptor number

• change in the receptor sensitivity

• change in intra-cellular cascades

What is the withdrawal effect?

The effect of stopping the drug due to the tolerance mechanism still being present. This will result in whatever the drug was stopping (e.g. insomnia drug withdrawal will result in insomnia)

Physical dependency

The physical result of stopping a drug

Classical conditioning and drugs

By taking drugs in a particular area, the body associates the environment with taking the drug. This results in the body triggering the tolerance response for the drug, potentially causing withdrawal symptoms if in that environment.

Operant conditionings evolutionary reason

It is good for helping you achieve the rewards needed for survival, causing positive responses to stimuli. (e.g. repeating a positive behaviour that gets food)

Olds and Millners rat study 1

There was an idea that a rat can be controlled by using electrodes in its mind; however, they were worried of causing harm. To test if harm was caused they stimulated the rat in a particular part of the maze. It was hypothesised that the rat would avoid this area of the maze; however, the rat ended up going to the area more so. It was found that this part of the brain reinforced the behaviour of going to the area through dopamine release.

Olds and Millners rat study 2

The rat was placed in a Skinner box with intracranial drug self-administration electrodes in the brain. The rat could press a lever to stimulate the brain and release dopamine. It was found that a rat would reportedly pull the lever, showing it to be operantly conditioned.

Two parts of forebrain

Telencephalon and diecephalon

Parts of midbrain

Mescenphalon

Parts of hind brain

Metencephalon and myelncephalon

Two major parts of brain for dopamine release

Nucleus accumbens and ventral tegmental area

What makes a brain area majour for dopamine release?

It is stimulated quickly with little current

What brain system are the nucleus accumbens and ventral tegmental area in?

The mesotelecephalic dopamine system

Medial forebrain bundle

Contains alot of action potentials in the mesotelecephalic dopamine area

How to test for a causal effect of dopamine?

Give a dopamine receptor blocker to stop dopamine release

What is dopamine used for

It is for exploring the environment, finding information and creating a compulsion to repeat something even if that thing is not good for you.

Psychological dependancy

When drugs directly interact with the brain reward system

Dopamine of a rat that self-injects a drug

Initially, it is high to create a link, then it decreases once the link has been made. However, the rat keeps pressing the button.

Placing drug directly into nucleus accumbens

Animals still learn to press the lever as dopamine is still created