L9 - Neuropeptides - 5 IRL made flash cards
Similarities between NP (neuropeptides) and NT
1) Release via Ca2+ dependent exocytosis
2) Stored in vesicles
3) Diverse roles - sleep, reward, pain, memory
4) CNS or PNS
5) Bind to GPCR (exceptions e.g. insulin - TKR)
Differences between NP (neuropeptides) and NT
1) Can be secreted into blood by neurones and act as hormones e.g. oxytocin and vasopressin OR luteinizing hormone secreted by endocrine gland OR act within peripheral organ such as GIT e.g. Cholecystokinin
2) NP - stored in large dense core vesicles (LDCV) rather than the small clear synaptic vesicles BUT NT is stored in both types
3) Synthesis - NP (cell body) NT (some in cell body, MOST in nerve terminal)
4) Release trigger - NT: large transient increase in Ca2+ from AP. NP: requires numerous high freq AP, causes an increase in Ca2+ (lesser magnitude but longer duration compared to NT) - this is because LDCV are located further away from synaptic membrane and hence need a longer increase in Ca2+ so that the machinery can get them to the membrane
5) Diffusion - diffuses relatively large distances compared to NT as NP are not subjected to reuptake and NP are degraded by endopeptidase or exopeptidase cleavage
There are overlaps in NP such as:
a) alpha-Melanocyte stimulating hormone (a-MSH)
b) Corticotropin Releasing Factor (CRF)
a) a-MSH is released from pituitary (endocrine-like function) but in hypothalamus (neuropeptide-like function - inhibits appetite)
b) CRF is a hypothalamic RF and also found in CNS (neuropeptide-like function)
Are exons or introns spliced out?
Introns
Why is there so much peptide diversity? (3)
- Alternative splicing of DNA into mRNA
- Tissue specific proteolytic cleavage at dibasic residues (PC1 and PC2 and Exopeptidases)
- Post-translational modifications: C/N-terminal acetylation, acetylation, sulfation, carboxylation, alpha-amidation
Which cell organelle forms LDCV? What happens after NP are stored in LDCV?
Golgi apparatus forms LDCV where NP is stored. Next vesicles are transported along axon to synapse
Difficulties in designing peptide drugs
1) Size means they interact with multiple sites on their receptor
2) Poorly absorbed orally or metabolised in the gut (hence taken nasally or injected)
3) Short duration of action due to rapid degradation (hydrolysis by peptidases in plasma)
4) Ability to cross BBB unpredictable
5) Expensive to manufacture
6) Immunogenic - cause immune response
7) Lack of pharmacological tools - not sure what is happening in the brain
8) Redundancy - lots of NP with similar function, multiple receptors, if we target one receptor - it may activate other ones with affects the effect of the receptor we are targeting
* Very few peptide drugs exist
Tachykinin family of NP (3)
Substance P (1930s), Neurokinin A (1980s), Neurokinin B (1980s)
How many Tachykinin (Tac) genes are there?
1 - Has 4 splice variants where Sub P is found in all but Neurokinin A only found in 2 (beta and gamma)
3 - Has 2 splice variants - both Neurokinin B
4 - Has 4 splice variants
*No 2 because it contained Neurokinin A and Substance P so they got rid of it
!There is a homology within all the Tachykinin-derived peptides’ amino acid sequence- which allows binding to neurokinin receptors.
EXCEPTION: Endokinin C and D don’t have that homologous sequence. They have very little tachykinin function and little affinity for neurokinin receptors. Aka tachykinin related peptides
There is a homology within all the Tachykinin-derived peptides’ amino acid sequence- which allows binding to neurokinin receptors.
EXCEPTION: Endokinin C and D don’t have that homologous sequence. They have very little tachykinin function and little affinity for neurokinin receptors. Aka tachykinin related peptides
Why were NK1R antagonist clinical trial results disappointing?
There are more factors such as CGRP, glutamate, opioids that are involved with the transmission of pain. Although NK1 antagonists did attenuate neurogenic inflammation to a degree.
!Actions of substance P
a) Retrograde release leads to
b) Unmyelinated sensory C fibres in lung release Sub P, NKA, NKB which act on
c) High conc of NK1 receptors in vomiting centre in medulla (NTS) and in the chemoreceptor trigger zone for vomiting. - what does this mean for NK1 antagonists?
a) Vasodilation and extravasation of plasma proteinss from capillaries, there is edema which causes additional release of bradykinin and it also triggers release of histamine from mast cells that activate noiceceptors
b) Smooth muscles, secretory and inflammatory cells
c) NK1 antagonist is effective in chemotherapy and post-operative induced nausea.
Opioid Receptors are found?
In the dorsal horn
!In regards to the mechanisms of vomiting, where are NK1 receptors found?
`1) Vomiting centre (NTS)
2) Chemoreceptor trigger zone (Area postrema)
