Author Archives: Kenzo Le Vaillant

The memory functions of the serotonergic system

Accessible Science

Introduction

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

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

The numerous receptor types and projections of the serotonergic system show the variety of the effects it has on the human brain, including learning ad memory, depression and stress.

Learning and memory

The simplest finding yet is that a decrease in serotonin caused an impairment in memory.

In addition, with the inhibition of serotonin uptakers, which prevent serotonin from being used, memory consolidation was improved.

Studies on specific receptors or neurotransmitters are usually done by injecting an agonist or antagonist of it to see its effects. Several types of agonists were seen in this article.

Agonist

A chemical that enhances the function of its target

Antagonist

A chemical that inhibits the function of its target

5HT7 and 5HT1A

8-OH-DPAT is a 5HT1A and 5HT7 receptor agonist.

The 5HT7 receptor has been found to be important in allocentric representation processes and instrumental learning tasks.

Allocentric representation

Seeing or sensing things from another persons perspective.

Instrumental learning task

A task that requires the subjects ( usually animals ) to learn to use an object.

This agonist was able to enhance rats learning in both short term memory and long term memory. These rats were preinjected with saline.

Saline

Salt water. It prevents the death of tissues surrounding the area which was opened for research purposes.

The activation of the presynaptic 5HT1A receptor by it also enhanced memory. this receptor when blocked leads to increased new learning but impaired long term memory.

This agonist, in high doses had negative effects on learning and long term memory.

Another was the AS19 which is a 5HT7 receptor agonist.

This agonist improved the memory consolidation process and changed the levels of expression of the 5HT7 and 5HT1A receptors.

5HT6

This receptor was the opposite to the two above. Its antagonist was found to improve cognitive dysfunction.

This is said to be done through a pathway related to pERK1/2 expression.

pERK1/2

Phospho extracellular signal regulated kinase

It activates signal cascades that regulate cell proliferation, differentiation and survival

Others

A study looked at the brain during memory formation in a pavlovian / instrumental autoshaping task.

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.

They found many transporters to be involved in it from many different brain regions.

For example, it was associated with

in the prefrontal cortex, the increase of GABA and glutamate transporters.

In the striatum, the increase of SERT, dopamine transporters, EAAC1

EAAC1

Essential amino acid carrier 1

A protein that carries essential amino acid neurotransmitters such as glutamate and GABA.

In the hippocampus, the decrease of EACC1, GABA transporters, SERT.

Amino acid transporters were also found to be involved in factual memory registration while the neurotransmitters noradrenaline and serotonin were involved in emotional memory encoding.

Part 1 : The Serotonin system

Next Part : Serotonin, stress and tryptophan