Serotonin and purines

Question 1

Where can serotonin be found?

Answer 1

In the periphery

In the CNS

Question 2

What is the main source of serotonin in the periphery?

Answer 2

Enterochromaffin cells in the mucosa of the stomach and intestine

Question 3

What is the main source of serotonin in the CNS?

Answer 3

Midbrain Raphe nucleus

Question 4

What peripheral organs do serotonin affect?

Answer 4

Blood

GI tract

Platelets

Question 5

What is the effect of serotonin on the GI tract?

Answer 5

Increases secretion and motility

Question 6

What is the effect of serotonin in the blood?

Answer 6

Controls microvasculature

Question 7

What is the effect of serotonin in platelets?

Answer 7

Mediates aggregation and inflammation

Question 8

What functions of the CNS is serotonin implicated in?

Answer 8

Appetite

Sleep

Vomiting

Mood

Descending control of pain inputs

Question 9

In which conditions is serotonin dysfunctional?

Answer 9

Affective disorders

Anxiety

Enterochromaffin tumours

Question 10

Where is serotonin synthesised from?

Answer 10

Dietary tryptophan

Question 11

What is another name for serotonin?

Answer 11

5-HT

Question 12

How does 5-HT go to the neurons?

Answer 12

Through reuptake transporters

Important targets of SSRIs

Question 13

What is the main way of terminating 5-HT action in the CNS?

Answer 13

Through reuptake

Question 14

How does 5-HT go to platelets?

Answer 14

Platelets lack enzyme required for 5-HT synthesis

So they actively take up the neurotransmitter

Question 15

How is 5-HT degraded in the GI?

Answer 15

Most of it will be deaminated in the liver by MAO

The 5-HT that survives first-pass liver metabolism is taken up by endothelial cells lung blood vessels with MAO

Question 16

How many families of 5-HT receptors exist?

Answer 16

7 families

14 receptors in total

Question 17

What type of receptors are 5-HT receptors?

Answer 17

G-protein coupled

Question 18

Where are most 5-HT receptors found?

Answer 18

In the brain

Question 19

Neuronal characteristics of migraines

Answer 19

Abnormal neuronal discharge

Changes in cerebral blood flow

Question 20

Why is it thought that serotonin is involved with migraines?

Answer 20

There is increased urinary excretion of 5-HIAA (degradation product) during a migraine attack

Useful clinical benefits obtained by modification of 5-HT mechanisms

Question 21

How is serotonin involved in migraine?

Answer 21

Causes visual effects through vasoconstriction

Causes inflammatory dilation

Question 22

Therapies for migraine

Answer 22

5-HT2 antagonists - inhibits early vasoconstriction

5HT-1 agonists have been useful through constricting cranial blood vessels

Question 23

Example of purines

Answer 23

ATP

Adenosine

Question 24

How are purines synthesised?

Answer 24

Through breakdown of ATP in the extracellular space using ATPases

Question 25

What type of receptors bind to ATP/Adenosine?

Answer 25

G-protein coupled recepors Except one ATP receptor - ligand-gated

Question 26

Drugs used to treat migraines

Answer 26

Beta-blockers NSAIDs Calcium channel blockers Antiepileptics Antidepressants

Question 27

Receptors of Adenosine

Answer 27

A1 - Gi A2A - Gs A2B A3 - Gi

Question 28

Receptors of ATP

Answer 28

Ligand-gated ion channel G-protein channel