Neuropeptides

Question 1

Describe properties of neuropeptides.

Answer 1

1. 2-40 aa’s long
2. larger than neurotransmitters
3. can act as NT’s and also as co transmitters. e.g. adenosine
4. bind to cell surface receptors

Question 2

How are NT different from NPs

Answer 2

potent
present in small quantities
synthesis and inactivation different

similarity
release calcium dependent

Question 3

How is neuropeptide synthesised?

Answer 3

occurs in cell body directed by Ribosomal RNA
The prepropeptide enters the ER - transported to Golgi where the pre-sequence is removed. The propeptide is then packaged into granules for transport to the nerve terminal via microtubules. The peptides then go through enzymatic cleavage becoming neuromodulators.

Question 4

Where are np’s stored?

Answer 4

large vesicles

Question 5

How are NP’s released?

Answer 5

calcium dependent exocytosis

Question 6

How is NP’s inactivated?

Answer 6

enzymatic metabolism via metallo peptidases. So precursor proteins are required to maintain adequate NP levels.

Question 7

Where do NP’s work?

Answer 7

NPs are found in many regions of the brain and spinal cord

Question 8

What are the functions of NPs?

Answer 8

1. modulate effects of classical NT by altering release or post synaptic effects. These are co-transmitters that are stored together with classical NT’s
2. They can act as primary NTs e.g. substance P in spine
3. NPs act more slowly than classican NTs. They diffuse away to act at a distance on other neurons with NP receptors.

NPs therefore are modulatory and for communication of synapses.

Question 9

What are the two types of NPs?

Answer 9

1. Tachykinins

2. Opioid peptides

Question 10

What is an example of a NP tachykinins?

Answer 10

Substance P. relays pain information

Question 11

How are tachykinins distributed?

Answer 11

1. primary afferents for pain to dorsal horn of spinal cord which releases substance P.
2. Goes to STriato-nigral projection (co-localised with GABA)
3. Goes to hypothalamus

Question 12

What are the three types of opioid peptides?

Answer 12

a) enkephalins
b) endorphins - precursor POMC
c) Dynorphin - precurson proenkephalin B

Question 13

How are enkephalins distributed?

Answer 13

basal ganglia to motor input

Thalamus, Dorsal horn of spinal cord, Perlacqueductal grey to pain sensation

Question 14

How are beta endorphins distributed?

Answer 14

To Pituitary or hypothalamus for neuroendocrine control

Question 15

Where are dynorphins distributed and why?

Answer 15

To spine for pain and inflammation
To hippocampus for learning and memory
and to basal ganglia

Question 16

How opioid peptides released?

Answer 16

calcium dependent

Question 17

What are the functions of opioid peptides?

Answer 17

pain - analgesia
motor control
excitatory and inhibitory
Brain reward and drug addiction (nucleus accumbens)

Question 18

What are the three types of opioid receptors?

Answer 18

mu, delta and kappa

Question 19

Describe opioid mu receptor

Answer 19

beta endorphins
for brain reward and drug abuse, pain control with morphine and respiratory depression.
decreases cAMP and increases Potassium

G-protein couples receptor

Question 20

Describe opioid delta

Answer 20

leuenkephaline

works by decreasing camp

Question 21

Describe opioid kappa

Answer 21

dynophin

Naloxone which is a competitive agonist to all 3 receptors. antagonises morphine and heroin effects in the brain

Question 22

Morphine function

Answer 22

control pain
increased selectivity decreases drug abuses and brain reward so it only affects pain.
It mimics endogenous opioids and causes the release of dopamine in nucleus accumbens.