Topic 3 HC 3 Drugs & Hormones
Chapter 6
The study of drugs and how they effect your brain is called
psychopharmacology. We will talk about psychopharmacology
first a bit in general so how is drugs entered in our body, how does
it enter our brain, that kind of questions. And then in the part of
grouping psychoactive drugs I will show you and explain quite
some different kind of drugs and which neurotransmitting systems
they effect. I will shortly touch on individual responses to drugs.
Not everyone responds to drugs in the same way. And we will
shortly talk about substance use and addiction which is my own expertise but is also quite indept
explained in the book. And we will end with hormones. As you know by know, hormones are
different type of molecules that are used for communication between neurons, but also between in
the case of neurons, between the brain and the autonomic nervous system.
Principles of Psychopharmacology
To start with, what is psychopharmacology?
Psycho refers to effects on the brain and the
nervous system. Pharmacology refers to the
science of drug action on biological systems.
So if you combine that it logically suggest
that psychopharmacology is the study of
how drugs effect the nervous system and
behavior. So that’s what we are talking
about today, how can different kind of drugs
effect our nervous system and how does that influence our behavior. If we talk about psychoactive
drugs that means that those substances have an effect on the brain and on the nervous system. And
most often then they alter our mood, thoughts or behavior. So there are also many drugs for
example that are changing your blood pressure that are not psychoactive drugs. Psychoactive drugs
are only those drugs that do effect our brain and nervous system and by doing so our mood and
behavior.
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, So usually
when drugs
are orally
taken, they
enter the
brain via the
stomach,
intestines,
liver, heart
and lungs. A
very long
route and
therefore it
takes
relatively long
before the
drug can have
its effect. So if you take a certain pill that will have an effect on your mood, it will take some time if
you do it orally.
There are other ways that a drug can enter the brain much quicker and that’s when drugs are
injected or inhaled. The reason why that’s much quicker is if you inhale it for example it is already
there in your lungs immediately, it only has to pass through the heart and then immediately to the
brain. And if you inject certain drugs its there in the bloodstream so again it goes to the heart, lungs,
heart again and brain. So that’s much quicker than when you orally take drugs because then it has to
go the whole way through the intestines and to the liver and then it comes in the blood and then the
heart, lungs, heart and brain. So that’s a very long route if you take it orally. So that’s why substances
that are injected or inhaled are much more addictive than drugs that are taken orally. Because what
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,a brain does, is it forms associations with for example smoking. It forms associations with the
smoking act and the quick effects on the brain. So nicotine patches for example that goes even
slower because it has to be absorbed by the skin and that’s much slower. So people wont become
addicted to nicotine patches but they will become addicted to nicotine cigarettes because when you
smoke a cigarette there is an immediate effect on your mood. So that association can be formed very
quickly and easily. Whereas if it takes a long time for certain drugs to have an effect, you don’t
associate it easily with all kind of ques so its not so addictive.
Of course drugs also have to be
eliminated from the body so it wont
have there action continuously. That’s
most often done by the liver called
catabolization. So sorts of enzymes
are broken down by the liver. And
that’s also why people who use a lot
of alcohol have liver problems,
because their liver has to work much
harder.
People also excrete drugs through
their face, sweat, breath and milk for example in breast feeding woman. And again if we take the
example of alcohol, I once gave a lecture here in this lecture hall during introduction week and I
entered the lecture hall and I smelled the alcohol so then people are excreting the alcohol through
their breath.
So there is this specific system in the brain that prevents the brain from all kinds of substances to
enter the brain. Its very dangerous if all substances that we eat for example or that we can be
exposed to in the environment could enter the brain easily. So only certain molecules can enter the
brain and that is because it has to pass the blood brain barrier. So if we have a normal vein in our
body, lets say in our leg, there are certain junctions through which materials can easily move in and
out of the blood vessel. So all kind of things that we eat for example come into our body and they
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, can enter the blood through those junctions. In the brain however, the junctions are covered by
astrocytes. So that means that the junctions are not so easily open for all kinds of substances to cross
into the blood vessels in the brain and thereby into the brain. So there are certain specific
mechanisms of actions so that certain specific molecules can cross the blood brain barrier. That’s
oxygen because that’s very important that our brain has oxygen. Also CO2 and glucose because
glucose is the energy supply of the brain. So there are specific way in which those substances can
enter the brain by crossing the blood brain barrier. And then in our brain there are three more sides
where certain substances can enter the brain and they are listed here (on the right around the brain).
So that’s the pineal gland and that’s a lot of chemicals that effect day and night cycles so that is
involved in your day and night rhythm. And this is the pituitary gland that is involved in passing of
chemicals that influence hormones. And then there is a small spot here in the brain where
substances can enter the brain that induce vomiting if they are toxic. So that’s kind of a safety spot if
you have a toxin in our body that is very dangerous, this part of the brain will notice that and let you
start vomiting. So there are certain ways in which substances can enter the brain but generally its
quite difficult. So if certain medicine is developed and it is developed to have an impact on the brain
it has to be developed in such a way that it can cross the blood brain barrier, otherwise it won’t
effect the brain.
So if the substances are in our brain,
how can they then have an effect on
the communication between neurons.
So if a certain is in our brain, in order to
have an effect on our behavior or on
our mood, it has the be able to
influence the signaling of the neurons,
so the communication between neurons. And there are two ways in which substances of drugs can
actually influence the neurotransmission. It can either enhance neurotransmission and then they are
called an agonist. And it can block or decrease the function of neurotransmitters so the
communication between neurons and then its called antagonist. And those terms you have to know
very well, agonist and antagonist. It will be in this lecture multiple times and its very important to
remember. Something that is agonizing that is enhancing the function of certain neurotransmitters.
Something that is an antagonist it blocks or decreases the function. You will get many examples in
this lecture of antagonist are for example at the dopamine receptors. Out of the dopamine system
are cocaine and amphetamine. Cocaine and amphetamine are antagonists for dopamine so they
mimic the effects of dopamine itself and they increase the effect of dopamine.
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