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Neurons and neurtransmitters

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Stacey Coufal

on 20 September 2018

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Transcript of Neurons and neurtransmitters

Neurons
Neurons are cells that receive information and transmit it to other cells.
Depression
A relationship appears to exist between the 3 main monoamine neurotransmitters in the brain (i.e., dopamine, norepinephrine, and serotonin) and specific symptoms of major depressive disorder.
Biological Approach
The D2 (a type of Dopamine receptor) has been found to increase the probability of a variety of pleasure seeking behaviors (alcoholism, recreational drug use, overeating, and habitual gambling)
Variations in D4 receptor found that these people have a "novelty-seeking" personality - consisting of being impulsive, exploratory, and quick-tempered...
A drug that
blocks
the effects of a
neurotransmitter
is called an
antagonist
.

A drug that
mimics
or increases
the effects of a
neurotransmitter
is called an
agonist
.

How drugs affect synapses

So what is depression?
What does it feel like?

Video: The Truth about Depression
read article;
Depression's Evolutionary Roots
Nurnberger and Gershon (1982)

Link to Genetics and Behavior
Informed consent for genetic research

It is important, especially for genetic research that the individual must be specifically informed about the true aims of the experiment and must require consent from the person involved and or from the parent/family guardians responsible for them before commencement of research.

Uninformed consent may lead to serious a problem if the study proves to be controversial, which, for example, is demonstrated by...
This study shows revelations of carrying genes linked to depression is a study by Nurnberger and Gershon (1982).
Method:Reviewed the results of seven twin studies.
Results:

Concordance rate – correlation – for major depressive disorder was consistently higher for monozygotic twins (MZ) than dizygotic twins (DZ).
This study supports that there are genetic predispositions to depression.
Knowledge of a genetic predisposition to depression
may cause people
undue stress
as they may fear the onset of the disorder
.

Ethical considerations:
Self-fulfilling prophecy
:
If one MZT has depression, their twin may express the self-fulfilling prophecy and demonstrate symptoms of depression as well.
Stigmatization
:

Twins may be stigmatized – social discrimination of an individual with characteristics that distinguish them in society

People may be stigmatized because their twin has a disorder, even if they themselves do not
Informed consent with
GENETICS RESEARCH
:

The potential harm of participants due to knowledge of genetic predispositions is why genetic testing requires informed consent from the individual involved or from family members responsible for them.

Participants should be informed of the risk that they may experience revelations of a genetic predisposition.

They must give informed consent to show that they have a clear understanding of true aims and nature of the study they are participating in, and the implications, including potential harm.
THREE MAJOR AREAS TO CONSIDER (IN GENERAL)
(These are known as the Belmont Principles)

Beneficence

Justice

Respect for persons
Because psychologists must rely on others' help to pursue knowledge, we are ethically obligated to conduct a
cost-benefit analysis
to ensure that the study's potential outcomes exceed potential negative experiences or risks to participants.
Beneficience
- acting with the purpose of benefiting others.

Participants
AND
humanity!
DO NO HARM!
confidentiality

and

anonymity
protecting the privacy of individuals
a guarantee that individual responses cannot be linked back to the participant
physical
or
psychological
and of course the cost of
NOT
doing research
Choose particpants equitably so as to avoid targeting a weak or vulnerable group
Ex: Tuskagee 1932-1972 ='(
Ethical standards dictate that we avoid* targeting vulnerable individuals, such as children, prisoners, and other institutions like mental hospitals, who may be at risk for coercion.

They have an inability to refuse participion.

*there are exceptions
AUTONOMY!

participants must freely make an
informed
decision about their participation in research
voluntary

no adverse consequences if they decline

informed consent

right to withdraw without penalty

18 years old*
Neuron Knowledge

The structure of a neuron

The nature of information transmission in the nervous system is partly electrical and partly chemical

Electrical processes: threshold of excitation, action potential

Chemical processes: neurotransmitters and how they function

Excitatory and inhibitory neurotransmitters

Agonists and antagonists
Limitations in neurotransmitter research
(increasing levels of neurotransmitter X results in a change in behavior Z)

X may function as an agonist or antagonist for Y, which affects Z (indirect effect)

X may serve as a trigger for a long-lasting process of change (postponed effect)

X is usually not the only factor affecting Z(multi-determination)

X is never the only factor that changes (side effects)
Excitatory neurotransmitters
- allow the impulse to cross the synapses. They stimulate the brain.
Inhibitory neurtransmitters
-
stop the impulse in the brain by preventing it from crossing the synapse. This calms the brain
Most are located in the brain - but not all.
Serotonin
The serotonin (5-HT) hypothesis of depression dates from the 1960s. It originally postulated that a deficit in brain serotonin, corrected by antidepressant drugs, was the origin of the illness(Albert et.al 2012).

The serotonin hypothesis: low levels of serotonin in the brain play a
causal role
in developing depression.
Serotonin does lots of things (although many are not yet understood), like;
mood regulation
sleep regulation
sexual desire and function
appetite
sleep
memory and learning
temperature regulation
some social behavior
In terms of our body function, serotonin can also affect the functioning of our cardiovascular system, muscles,and various elements in the endocrine system. (https://www.healthline.com/health/mental-health/serotonin)
Although the variables seem distant; researchers attempt to link these variables.

Effects of neurotransmission on something such as mood or fatigue are believable because these are rooted in biological processes, but prosocial behavior seems to be a person's own choice or free will.

How can a person's free will be affected by a biological factor?
Crockett et al (2010) investigated the effect serotonin on prosocial behavior.


partcipants 30 healthy subjects (x̅ = 26 years old).
repeated measures design
two conditions

condition 1 - participants/citalopram.

This drug is a highly selective serotonin reuptake inhibitor (SSRI): a chemical that blocks reuptake of serotonin from the synapse, in this way boosting its concentration and prolonging its effects.

condition 2 (the control) participants/placebo (a harmless substance with no active effect).

The design was counter-balanced and it was a double-blind.
After taking the drug, participants were given a series of moral dilemmas that involved choosing between a utilitarian outcome (saving five lives) and aversive harmful actions (such as killing an innocent person).

Aversive harmful actions in the scenarios were two types: personal (for example, pushing a man off a bridge to stop a train and prevent it from hitting five people) and impersonal (for example, pressing a lever to divert a train off a track where it will hit five people to a track where it will hit one).
This kind of dilemma is known as "the trolley problem", and it is a popular discussion in relation to ethics.

In the impersonal version of the problem there is a runaway trolley moving along the tracks, and you see that there five people on the tracks ahead and the trolley is about to hit them. You have a choice to press the lever and divert the trolley onto another track where it will hit and kill one person, or do nothing.
Results showed
responses in the impersonal version were unaffected by citalopram

citalopram participants were less likely to push the man off the bridge in the personal scenario

Would you push a man off the bridge to stop the train and prevent it from hitting five other people?
If you were an average participant in this study, you would probably say no, but after receiving a dose of citalopram you would be opposed to the idea even more strongly. Note that your judgment on the impersonal version (pressing a lever) would be unaffected.
Researchers concluded
serotonin reduces acceptability of personal harm
promotes prosocial behavior
modulates reactions of the brain to emotionally salient situations
inflicting harm on other people is judged as less acceptable
A limitation of the study that the authors recognized is that citalopram intake induced slight nausea.

This
might
mean that participants could work out what condition they were in on that trial. However, it is not possible to estimate the extent to which this might have influenced the results.
DOPAMINE
Dopamine and romantic love ...dawwwww

Fisher, Aron and Brown (2005) conducted a study of the neural mechanisms of romantic love,suggesting that the central role of dopamine in the brain response to loved ones.
Dopamine is an excitatory neurotransmitter that is involved in our desire to get things done (motivation), in controlling the brain's reward and pleasure centers and in regulating emotional responses.
participants
10 men & 7 women
currently "intensely in love"
not with each other
by word of mouth & through flyers
mean age was 21 years
mean reported duration in love = 7mo.
functional magnetic resonance imaging (FMRi) scanner
engaged in a standardized procedure of looking at photographs
their brains were being scanned
Four stages
l. For 30 seconds each participant viewed a pic of his or her love.

2. Then there was a 40-second filler activity, which was to count back from a given random number.
3. For 30 more seconds participants viewed a pic of an emotionally neutral acquaintance.

4. Last stage was 20 seconds of counting backwards from a random number.
A: ventral tegmental area
B: caudate nucleus
Pattern of activation in participant's brains in response to pic of the person they love
Results showed a specific pattern of activation in response to their loved ones:

activation was observed in dopamine-rich neural systems

primarily the ventral tegmental area (VTA) and caudate nucleus
Both regions
rich in dopamine
form the key part of the so-called dopaminergic pathway

(a system that generates and transmits dopamine and increases dopamine-related activity in the brain)

It is a reward system because dopaminergic activity is associated with
motivation and feelings of pleasure
.

In this way, dopamine activity in the brain plays a role in romantic love
From this the researchers inferred the role of dopamine in romantic love. To what extent do you think it is a substantiated conclusion? Or is it far-fetched?
Parkinson's Disease
Freed
et al
. (2001)
studied the role of dopamine Parkinson's disease

Parkinson's disease --> degenerative disorder
affects the motor functions of the nervous system.

The early symptoms:
shaking
rigidity
difficulty with movement & talking

Later symptoms:
thinking
behavioral problems

There is no cure for Parkinson's disease & exact causes are unknown.
Freed
et al
.
sample --> 40 patients
34-75 years old
severe Parkinson's disease
mean duration of 14 years
The sample was randomly divided into two groups:

experimental group received a transplant of nerve cells

control group got the sham surgery
In the transplant group, nerve tissue containing dopamine-producing neurons was taken from embryos aborted 7—8 weeks after conception and transplanted into the patients' putamen—a structure of the limbic system involved in movement regulation.
All surgeries were performed with the patient awake. Local anesthesia was administered to the skin of the forehead and four holes were drilled through the frontal bone, after which the tissue was transplanted through long needles.
In the sham surgery group, holes were drilled in the skull but the dura (a thick membrane that surrounds the brain) was not penetrated. Otherwise, the procedure was identical.
What's a sham surgery?
Why have a sham surgery?
The protocol of the study and the consent form describing the risks and potential benefits were approved by the ethics committee.

A separate written informed consent form was used for the women who donated fetal tissue from abortions.
Wait what?
We are dealing with an ethically sensitive study.

It involved aborted embryos, nerve tissue transplants and a sham surgery.

To what extent are these procedures ethically justified by the anticipated benefits of the study?
A number of measures were taken both before and after the surgery:

clinical observations
brain scans— positron emission tomography (PET)
followed up longitudinally for one year
Results of Freed
et al.
(2001)

Irrespective of the age group, PET scans revealed increased growth of dopamine producing cells in the putamen.

A reduction of symptoms by 28% was found in the patients in the transplant group, but only the younger ones (aged 60 or younger). No improvement was registered in the older subgroup of patients (aged over 60).
The overall conclusion was that transplantation of dopamine-producing neurons in the putamen of patients with severe Parkinson's disease results in some clinical benefit in younger but not older patients. Less response to treatment in the older patients despite successful growth of dopamine neurons may be attributed to lower
neuroplasticity
of the brain.
Neurotransmission can explain drug addiction. Some scientists say that the mechanism of drug addiction is that a synthetic drug replaces the naturally produced neurotransmitter and the organism starts to depend on the intake of the drug to keep the neurotransmitter at its natural levels.
Serotonin has been shown to be involved in the symptoms of major depressive disorder (MDD).
The
serotonin hypothesis
states that low levels of serotonin in the brain play a
causal
role in developing depression.
Studies have mainly involved clinical trials
two groups

experimental group --> drug that affects levels of serotonin
control group --> placebo (a harmless substance that the patient believes to be a drug)

symptoms of depression would be compared
However, this logic has a number of limitations:

1. drugs affect neurotransmitters within minutes
2. behavioral effects do not manifest immediately
3. sometimes weeks

Universal or not...direct or indirect, there is a link between serotonin and depression.
Recently, depression was also linked to a particular gene the serotonin transporter gene - the 5-HTT gene. Serveral studies show certain ones added to chilkdhood trauma greatly increase your chances of getting depression (Caspi
et al
. 2003)
influence may be indirect
perhaps a longer path where changing levels of serotonin is just one stage

For example, one theory suggests that increased stress damage neurons in the hippocampus and so lead to depression, whereas, SSRIs restore the damaged naurons gradually, alleviating the symptoms. (Taupin 2006).
https://www.ted.com/talks/andres_lozano_parkinson_s_depression_and_the_switch_that_might_turn_them_off
Sherwin Nuland
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