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Summary Hoorcolleges (1 tm 6) Behaviour and the Brain
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Hoorcolleges (1 tm 6) Behaviour and the Brain
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Hoorcollege 1, addictionWhat do we mean if we talk about drugs? Definition: a chemical substance, when absorbed
in the body, alters the function of the body, with exception of nutrients which are related to
normal functions.
Mostly interested in psychoactive drugs: A drug which alters mood, thought processes, or
behaviour or that is used to manage neuropsychological illness, as a result of an effect on the
central nervous system.
Drug medications have 3 names:
- Chemical systemic name: describes how the molecule looks like. For instance: 1,2
dichloorpropaan.
- Generic name: Diazepam
- Trade or brand name: bijv. Valium.
Drug use is a choice. The first time of a person using drugs is predominantly determined bij
environmental factors. But nobody chooses to be addicted.
Both the ICD-10 and the DSM-5 mention certain characteristics:
- No control of the drug intake behaviour
- Time needed for drug-related activities is at expense of their activities
- Continuing with drug intake despite negative consequences
- Tolerance
- Withdrawal
Tolerance: A state of progressively decreasing responsiveness to a drug. So you need more of
the drug for the same effect.
Withdrawal: The occurrence of abstinence symptoms
in case of drug cessation. This can be physiological
and psychological problems when the drug has not
been taken for a while.
Here on the left a study focussing on withdrawal
symptoms in forms of headache with coffee.
,Then how does addiction develop?
First theories:
- Possession by demons
- Lack of moral/will power (18th and 19th century)
Modern theories:
- Disease model - result of biomedical proces.
- Personality predisposition theories - drug to deal with emotions
- Reinforcement theory - Behaviour with pleasurable outcome is reinforced.
- Final common pathway theory - outcome of combination of genetic, social,
psychological and spiritual factors.
How do drugs have their effect on the body?
ADME: The 4 phases of the drug entering the body and being absorbed by it.
- Absorption
- Distribution
- Metabolism
- Elimination
Elimination is the same as
excretion.
Absorption: Process by which the drug passes from the external world into the bloodstream.
The degree of the absorption is dependent on the type of drug and the way of administration.
So where does this absorption begin?
,Oral administration: Swallowing a drug, either by eating or drinking. Example: alcohol XTC.
Advantage:
- slow absorption time
- possibility to respond in the case of toxicity and overdose.
Disadvantages:
- Medicijn/drug must be protected against the acids in the belly.
- slow adsorption time
- no immediate effect
- less control over the dose
Injection - Intravenous: By a needle in a vein. For example: heroin or morphine.
Advantage:
- Very quick adsorption time
- immediate effect.
Disadvantage:
- It cannot be reversed
- Risk of allergic reaction.
Injection - Intramuscular: By a needle in a muscle. For
example many inoculations.
Advantage:
- Quicker to administer than intravenous injection.
(Don't need to take in account veins).
Disadvantage:
- Risk of hitting a vein
- somewhat slower absorption than intravenous
injection.
Injection - subcutaneous: By a needle under the skin.
Example: Heroin.
Advantage:
- easiest injection technique
Disadvantage:
- Slower absorption time than intramuscular injection
- Risk of skin irritation and degradation
Special dangers of injecting: Many viruses and diseases can be shared by using the same
needle. Also called needle sharing.
Inhalation - Smoking: Burning a drug and inhaling the smoke-carried particles into the
lungs. Example: nicotine and marihuana.
Advantage:
- Extreme rapid absorption (faster than injection)
Disadvantages:
- Risk of emphysema, asthma, lung cancer and lung and throat irritations.
, Inhalation - vapour inhalation: Inhaling the vapours of a drug: example: sniffing of
solvents.
Advantage:
- Extreme rapid absorption
Disadvantages:
- lung and throat irritations
Absorption through skin or membranes:
- Placing drug to skin
- Placing drug to rectal membrane
- Sniffing drug towards mucosal membranes of nose
- Placing drug under the tongue or cheek.
Examples: cocaine, nicotine.
Advantage:
- Rapid absorption
Disadvantage:
- Irritation and destruction of skin and membranes.
Then the Distribution of the drug: The drug is being distributed through the body via the
bloodstream. A drug is transported via blood to tissues. How the drug is distributed is
dependent on the size and shape of the drug molecule itself. The effects of Psychoactive
drugs are mostly generated in the brain.
But to reach the brain the drug has to pass some membranes. Cell membranes consist of a
layer of fats and proteins. Small lipid-soluble molecules (moleculen die kunnen oplossen in
vet) can permeate these membranes.
When in the bloodstream drugs are continuously
exchanged between blood capillaries (haarvaten)
and body tissues. If the pores are very large:
passage of drug is easy and not dependent on being
lipid-soluble. Red blood cells and proteins are too
large to go through the membrane pores. Like too
big protein-bound drugs.
The speed of the drug exchange is dependent on the
speed of the bloodstream through the tissues and
the ease of the capillary passage.
In the brain the capillary membranes have no pores. That's why the drug has to pass through
the Blood Brain Barrier. The drug has to pass the capillary wall and the membrane of
astrocyte cells (glia sheath) to reach the brain cell. The passage is determined by the drug
being lipid-soluble. So if the drug isn’t lipid soluble it cannot pass.
In the distribution process there is a risk of Depot Binding. This is the phenomenon that the
drug binds with albumin (proteins in the blood) or body tissues (fat, muscle and liver). If this
is the case they can't pass the blood brain barrier anymore and won't reach the brain.
Because of the high fat percentage of the body and other body tissues only a small amount of
the drug will reach the brain. This temporarily captures the drug.
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