Serotonin - Receptors

Question 1

What advantage is it for us to have discovered so many serotonin receptors (16)?

Answer 1

Allows us to develop drugs to target each

Question 2

Where are 5HT-1 receptors found?

Answer 2

Predominantly in the brain where they function as inhibitory presynaptic receptors. Inhibits adenylyl cyclase (decrease cAMP)

Question 3

Which are the two serotonin auto receptors and where are they located?

Answer 3

On the Soma it is the 5HT-1A

On the terminal it is the 5HT-1D

Question 4

What does the 5HT-1A receptor do to the neuron?

Answer 4

It opens up the potassium channel so that it hyper- polarizes the neuron

Question 5

What do the 5HT-1D and 1B receptors do to the neuron?

Answer 5

They prevents the release of the neurotransmitter.

Question 6

Can you have an inhibitory post synaptic 5HT-1A neuron and if so what does it do?

Answer 6

Yes, it opens a potassium channel and hyper polarizes whatever is at the end of the neuron

Question 7

What is the second messenger system of 5HT-2?

Answer 7

Phosphatidyl Inosotol triphosphate, which means they increase DAG (activates protein kinase C) and IP3 (releases stored calcium from cells)

Question 8

What drug is an agonist at the 5HT-1A receptors?

Answer 8

Busipirone (Buspar), and anxiolytic (anti anxiety) agent. It is the only one in the market.

Question 9

Which drugs are combined 5HT-1B and 1D agonists?

Answer 9

The triptans

Question 10

What does 5HT stimulation cause in arterial smooth muscle?

Answer 10

Contraction, especially in the carotid circulation.

Question 11

What is unusual about cerebral blood vessels with respect to serotonin receptors?

Answer 11

Vasoconstriction is mediated by 5HT1 receptors. In most vessels 5HT2 receptors are responsible.

Question 12

What causes the vasoconstriction which counteracts migrainous vasodilation?

Answer 12

Agonist action at the 5HT-1B receptor.

Question 13

Are 5HT-1B and 1D receptors auto or hetero receptors?

Answer 13

Both

Question 14

What does stimulation of 5HT-2 receptors cause?

Answer 14

Constriction of vascular and intestinal smooth muscle. In humans, serotonin is a powerful vasoconstrictor, except in skeletal muscle in the heart, where it dilates vessels and increases microcirculation and vascular permeability.

Question 15

What does activation of 5HT-2 receptors on endothelial cells cause?

Answer 15

Stimulates the release of nitric oxide in prostaglandins which act locally on smooth muscle cells to cause relaxation.

Question 16

What does activation of 5HT-2A receptors on platelet membranes cause?

Answer 16

Platelet aggregation

Question 17

In the CNS, activation of 5HT-2 receptors causes what?

Answer 17

Neuronal excitation in the cerebral cortex

Question 18

What does activation of 5HT-2B receptors cause?

Answer 18

Stomach fundus contraction

Question 19

What is the 5HT-3 receptor?

Answer 19

A serotonin gated sodium channel. The binding of serotonin to this receptor opens the channel leading to rapid depolarization of neurons.

Question 20

Where are 5HT-3 receptors found?

Answer 20

Afferent nerves of baroreceptors and chemo receptors. Also in the coronary bed where they initiate the coronary reflects (inhibit sympathetic outflow) -> profound bradycardia and hypotension (reflex)
- They are found at the vomiting center and the CTZ

Question 21

What does the stimulation of 5HT-3 receptors in the G.I. tract or brain chemo receptor trigger zone and vomiting center induce?

Answer 21

Nausea and vomiting

Question 22

What does activation of the 5HT-4 receptor lead to?

Answer 22

An increase in adenylyl cyclase activity and therefore an increase in intracellular cAMP levels

Question 23

What does activation of the 5HT-4 receptor in the G.I. tract produce?

Answer 23

It produces secretion and facilitates peristalsis