MAOA gene, Serotonin and Aggression - AQA Psychology A Level

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Moogann
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Hi guys,

Me and multiple of my teachers have been stuck on this point that's come up in the aggression section of AQA A level psychology.

In neural and hormonal influences it states that low levels of serotonin leads to an increase in aggressive behaviour due to lack of inhibition. This makes sense, until it begins talking about the MAOA gene in genetic influences. It states the MAOA gene is responsible for the metabolism of serotonin, and low activity levels of the gene are implicated in having more aggression.

I may be misinterpreting but I am assuming metabolism of serotonin means breakdown, therefore surely low activity MAOA would increase serotonin levels and subsequently based on what the previous topic said, decrease aggression?

I also found on Illuminates online textbook there was an AO3 on mice that seemed to be supporting MAOA influence, showing that when the MAOA producing gene was removed, mice serotonin levels increased leading to hyper-aggression. This seems to be massively contradicting the neural explanations pages. Not sure if it's suggesting animals react differently though?

Please can someone elaborate on this, because me and many others are confused! I'm probably misinterpreting so help would be much appreciated!
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Claisen
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Hi,

MAOA is responsible for breaking down multiple neurotransmitters that are also linked to aggression. This is why it is confusing in the book. Also, it might be worth noting that the gene itself does not directly break down / lead to reuptake of the neurotransmitter but rather than protein that is produced from the genetic code of the gene.
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Afterlife?
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(Original post by Moogann)
I may be misinterpreting but I am assuming metabolism of serotonin means breakdown, therefore surely low activity MAOA would increase serotonin levels and subsequently based on what the previous topic said, decrease aggression?

I also found on Illuminates online textbook there was an AO3 on mice that seemed to be supporting MAOA influence, showing that when the MAOA producing gene was removed, mice serotonin levels increased leading to hyper-aggression. This seems to be massively contradicting the neural explanations pages. Not sure if it's suggesting animals react differently though?
MAO-A is an Enzyme that breaks down serotonin - in other words removing it from synapses. Low activity MAO-A gene means brain doesn't break down these serotonin so they are left in the synapse. This leads to a low level of serotonin in ur neurons.

Its like how if ur Digestive system isn't digesting Protein you will have no protein even tho u ate loads of protein, it remains in your gut and ur just gonna poo it out.

Those Mice have their MAO-A gene cut out, and therefore, serotonin isn't removed from synapses so they have high serotonin in brain. They are highly aggressive because they have no serotonin in the actual brain, its just left been in between the neurons. i.e the gut example: the protein is still in the gut, not been digested.

LOL I actually don't know if that's right
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anonymoussse
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so glad im not the only 1 confused! did u find an answer?
im just gonna think of it like this: because the MAO enzyme breaks down serotonin, if there's less MAO, then that indicates less serotonin was there to begin with.

therefore, if the individual has the low variant MAO gene, that's because the natural serotonin level was low to begin with, so the body compensates by activating the low variant MAO gene, which will ensure that less serotonin is broken down so that the little serotonin there isn't broken down even more! (this means that although less serotonin is broken down, the individual still OVERALL has less serotonin compared to a non aggressive person)

so the MAO gene doesn't CAUSE the low serotonin, it just comes AFTER and is CORRELATED with less serotonin. the whole MAO thing just strengthens the idea that Aggression has genetic roots.

to recap: an individual with low serotonin -----> the low MAO gene is activated so that the already little serotonin isn't broken down even more (culd u imagine if the high mao activity gene was activated? the person is left with NO serotonin. so this actually strengthens the idea that low serotonin is linked with aggression) ----> the individual has some serotonin left lol

hope u got what i'm saying
Last edited by anonymoussse; 1 year ago
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xxrachelsxx
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anyone have any studies of the MAOA gene?
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revisionniblet12
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Hi everyone sorry for the late reply but still might be helpful for future students, the MAOA enzyme breaks down, or catabolises, excess serotonin in the synapse that hasn't bound to postsynaptic binding sites, allowing for its reuptake by the reuptake pump, so it can CONTINUE to be released by the presynaptic neurone (once remanufactured) , and hence exert inhibitory effect on the limbic system (responsible for aggression). With a mutation of this MAOA gene, the enzyme it produces isn't as effective in breaking down serotonin, and therefore less reuptake into the presynaptic neurone occurs so less inhibition of the limbic system occurs, producing a more violent/aggressive indiviual. Brunner-Case Study on Dutch Family, Moffitt- found in his longitudinal study of 442 of males from NZ, that individuals who had 'warrior' MAOA gene and had early childhood abuse, were 9 times more likely to be aggressive and antisocial than those who didn't share these two characteristics.
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