Lecture 24: Neuropeptides and Gaseous Neurotransmitters

Type 1 and 2 Neurotransmitters:

* Precursor Molecules: in presynaptic neuron and terminal of presynaptic neuron
* Synthesis: occurring in cytoplasm of presynaptic terminal
* Vesicles: docked and released via exocytosis

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Neuropeptides:

* Precursor Molecules: “prepropeptides” synthesized in soma
* Synthesis: final step- taking place in vesicle itself
* Vesicles: dense core vesicles in terminal

Compare Type 1 and 2 Neurotransmitters vs. Neuropeptides with the following topics:

* Precursor Molecules
* Synthesis
* Vesicles

Small clear synaptic vesicles:

* Contain: “classical” and amino acid neurotransmitters
* Electron: light
* Released: from the active zonr

Large dense core vesicles:

* Contain: neuropeptides
* Electron: dense
* Released: extrasynaptically

Compare and contrast small clear synaptic vesicles and large dense core vesicles with the following:

* What do they contain?
* Electron light or electron dense?
* Where are they released from?

1. Protein synthesis (ribosomes on the ER)
2. Prepropeptides packaged into vesicles in the Golgi Apparatus
3. Vesicles bud off and trafficked by microtubule pathways that go down the axon terminal
4. Synthesis occurs in vesicles: prepropeptide-→Neuropeptide
5. Neuropeptide released from large dense-core vesicle to act postsynaptically

Describe Neuropeptide synthesis

pre- precursor molecule

pro- still needs to be processed (needs to be cleaved, spliced, or enzymatically activated)

What is a prepropeptide?

POMC precursor peptide---→ ACTH and B-LPH (anterior lobe)

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ACTH-→ a-MSH and CLIP (intermediate lobe)

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B-LPH-→ y-LPH and B-ENDO (intermediate lobe)

Explain post-translational processing of neuropeptides

thyroid: Calcitonin

sensory neurons: CGRP

With alternative splicing of neuropeptides:

CALC1 mRNA has two exons:

* name the exon that CALC1 mRNA produced in the thyroid
* name the exon that CALC1 mRNA is produced in sensory neurons

calcium

Neuropeptide release and regulation is considered ________ dependent

extrasynaptically

Neuropeptides are released ______________

increase

if there is an increase in calcium levels, there is an __________ in neuropeptide production

Types I and II Neurotransmitters:

* Concentrations and binding affinities: packing is efficient; concentration of 100 mM
* Sites of release: active zone; working on synaptic receptors
* Sites of action: active zone
* Termination and recycling: AA are subject to reuptake, monoamines: enzymatic degradation and reuptake
* Half life: 5 ms

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Neuropeptides:

* Concentrations and binding affinities: 3-5 mM
* Sites of release: outside of active zone, act on extrasynaptic receptor
* Sites of action: active zone
* Termination and recycling: no recycling, done after synthesis. Breakdown: enzymatic degradation
* Half life: 20 minutes

Compare and contrast types I and II neurotransmitters vs. neuropeptides for the following topics:

* Concentrations and binding affinities
* Sites of release
* Sites of action
* Termination and recycling

* NPY can have pre and postsynaptic effects
* Are G-Protein-Coupled receptors

Affect functions such as:

* Feeding behavior
* Homeostasis
* Circadian Rhythm
* Stress and Anxiety
* Increased genetic alcoholism

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Exemplifies signaling pathways are NOT specific to a neurotransmitter

Taking the neuropeptide Y (NPY) as an example, this example exemplifies what?

Arginine---→Citrulline

Enzyme: Nitric Oxide Synthetase

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Co-Factors: FAD, FMN, BH4

Describe Nitric oxide synthesis

dependent.

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Uses calmodulin for reaction

Nitric Oxide Synthetase is calcium ____________

Neuronal NOS: found in neurons

Endothelial NOS: found in blood vessel endothelium

Inducible NOS: found after inflammation

Name the four types of Nitric Oxide Synthetase (NOS)

* Cannot be stored in the body
* Not inactivated by normal mechanisms such as reuptake
* Can damage cells at high concentrations
* May contribute to neuronal damage after other injury

Why must NO synthesis be tightly controlled?

1. Intracellular calcium (calcium dependent)
2. Gene expression (upregulate or downregulate expression)

What are the two mechanisms where NO synthesis is regulated?

* Reaction with amino acids
* Activity of phosphodiesterases

Explain the termination of action for NO synthesis

1. Calcium entry
2. Calmodulin (CaM) activated
3. Neuronal Nitric Oxide Synthetase (nNOS) is activated

Explain the mechanism for what happens within a Non-Adernergic, Non-Citurelenic (NANC) myenteric neuron

Against:

* Not released from vesicles
* No transmembrane receptors

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For:

can affect neuronal signaling by:

* Activation of guanylyl cyclase
* s-nitrosylation of proteins
* Might not need a transmembrane receptor

Is Nitric Oxide a Neurotransmitter? Explain

1. Calcium entry
2. Calmodulin (CaM) activated
3. Neuronal Nitric Oxide Synthetase (nNOS) is activated
4. Diffusion into smooth muscle in intestine
5. GTP is converted into cGMP by s guanylyl cyclase (sGC)
6. cGMP allows Postassium efflux
7. Vasorelaxation occurs

With Nitric Oxide as a neurotransmitter in the PNS, how does this affect smooth muscle within the intestine?

* Neurotransmitter release
* Synaptogenesis (creation of new synapses)
* Apoptosis
* Synaptic plasticity

Name four ideas that NOS affects

Heme-----→CO + Fe2+

Enzyme: Heme Oxygenase

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Heme: non-protein part of hemoglobin

Describe carbon monoxide synthesis

1. Phosphorylation of HO2
2. End products of heme catabolism

Describe the two types of regulation of Carbon Monoxide synthesis

1. Calcium enters NANC myenteric neuron
2. Calcium binds to PKC and activates PKC
3. PKC activates HO2
4. HO2 activates CO
5. CO diffuses into smooth muscle
6. CO activates Guanylyl Cyclase through ATP Hydrolysis
7. cGMP activates potassium channel for potassium efflux
8. Potassium efflux causes vasorelaxation

With Carbon Monoxide as a neurotransmitter within the PNS, describe its role on the smooth muscle in the intestine

* Enhances NMDA receptors
* Increases LTP induction

\*\*\*\*NOTE: can be neuroprotective and neurodegenerative at increased concentrations

Name the two ways that Hydrogen sulfide assists NMBA receptors and LTP induction

1. More than one transmitter at each synapse in different vesicles
2. More than one transmitter at each synapse in the same vesicles
3. A different transmitter at each synapse
4. A different mix of transmitters at each synapse

Name four different theoretical situations where multiple transmitters can be released from a single neuron

1. ATP is released from the vesicle
2. ATP acts on:


1. EctoATPase
2. P2X Receptor
3. P2Y Receptor
3. EctoATPase converts ATP to AMP
4. Ectonucleotidase converts AMP to Adenosine
5. Adenosine acts on P1 Receptor

What is the synthesis/mechanism for use of ATP and adenosine as transmitters?

Overall: look at mIPSC

* mIPSC has faster hyperpolarization period
* Within the mIPSC, there are two neurotransmitters:
* Strychnine (blocks glycine receptors)
* Biccuculine (activates GABA)

Explain the evidence that GABA and Glycine are in the same synaptic vesicle

Nerve terminals in the spinal cord can release both GABA and Glycine by expressing the required pre and postsynaptic proteins for both

Nerve terminals in the spinal cord can release both ________ and ________ by expressing the required pre and postsynaptic _______ for both

two different transmitter, different synapses

Using the sorting of vesicles in the Golgi, neurons can send ______________________ containing vesicles to different axon collaterals for use at ___________________

dendrites

Not all synapses are at the ends of axons- some can be on ____________