Author Archives: Kenzo Le Vaillant

Emotions from serotonin

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Introduction

This page is the third part of a study of the article

Serotonin and emotion, learning and memory by Alfredo Meneses and Gustavo Liy

Tryptophan

Serotonin is synthesised in the raphe nuclei. These neurons need ingredients to create it.

The ingredient for serotonin production is tryptophan. It is an essential amino acid that comes from the food that we eat. There are large amounts in beans and high protein foods.

Tryptophan

An essential amino acid that is used to make proteins such as serotonin.

Essential amino acid

An amino acid, the ingredient of proteins, that cannot be created by the body. Thus, it needs to be taken through food.

The only way tryptophan can be taken is from food. However, this makes a type of research called acute tryptophan depletion possible.

Acute tryptophan depletion

A research method where the participants ( animals ) are given a diet without or with little tryptophan.

As a result of acute tryptophan depletion, the production of serotonin is reduced or even blocked.

This has been found to cause an influence on several areas. For example, the activity in the prefrontal areas, which regulate mood, mnemonic functions and executive functions are varied.

This happens for the orbitofrontal, cingulate and subcortical regions which are said to be involved in emotional processing.

Alzheimers disease, whose main symptoms are impaired memory and emotional or behavioural changes, is also said to reduce serotonin levels.

Serotonin and mood

Serotonin has effects on many other neurotransmitters. These include dopamine , GABA and acetylcholine.

Dopamine

A neurotransmitter involved in reward behaviour

Acetylcholine

The main neurotransmitter of the parasympathetic nervous system. It is also involved in other functions such as memory or emotions.

Acetylcholine

The acetylcholine networks are strongly involved in memory processes. But they are also involved in emotional ones.

It has been found that the 5HT6 receptor antagonists were able to reverse the effects of aging on novel object discrimination, working memory and emotional responses.

Working memory

A part of short term memory that keeps the information relevant to the current situation available.

The α7 nicotinic acetylcholine receptor receives input from serotonin and is involved in anxiety and cognitive functions. However, its numbers seem to be regulated by serotonin as the cutting off of the serotonin inputs reduced the numbers of the receptor.

Dopamine

The mesolimbic dopaminergic pathway is responsible for cognitive processes ad the reward, addiction response to drugs.

The firing of this pathways is regulated by 5HT1A receptors like wise many serotonin receptors control the addictions.

The activation of 5HT1B&2C and the blockage of 5HT1A, 2A,2C and 6 decrease the self administration of addictive drugs.

This is done by controlling emotional processes, like the effects of 5HT6 receptor and the effects of the 5HT3A receptors on the amygdala and the hippocampus , mesolimbic pathway activation, like the influence of the 5HT2B and C receptors, and addiction related memories, regulated by 5HT2A receptors.

GABA

The GABAergic involvement in mood is mainly indirect.

For example, GABAergic interneurons to the PFC inhibit an overreaction of dopamine to drugs.

Some serotonin receptors such as 5HT3A are found on GABA neurons.

The activation of the 5HT3 receptor also refgulates GABA receptor activities. This suggests that the GABAergic system may regulate the effects of certain serotonergic transmissions.

For example, working memory.

The opposite may be possible too as the 5HT6 receptor agonist increased the extracellular GABA to inhibit current in the CA1 region.

CA1

A region of the hippocampus from which output goes to the entorhinal cortex. It has many pyramidal cells and is involved in memory recall.

Part 1 : The Serotonin system

Part 2 : The memory functions of the serotonergic system

Definition : Autoshaping task

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Autoshaping task

A task in which a lever ( for rats) or a light ( for pigeons ) is presented (Conditioned Stimulus) and food is given right after.

This leads to the animals learning to respond to the CS.

Related

Classical conditionning

Conditioned stimulus

Unconditioned stimulus