Neuropeptides and gaseous neurotransmitters

What are the seven categories that differentiate type 1 and type 2 signaling molecules versus neuropeptids

1. precurser molecules (neuropeptides are synthesiszed in the soma)
2. synthesis (neuropeptides change once in packaged in the vesicles)
3. vesicles (class one=small clear vesicles and class two=dense core vesicles)
4. concentration and binding affinities (type 1 and 2 have 100mM concnetrations and half life of only 5 milliseconds. Neuropeptides need a concentration of only 3-5 mM and half-life is on order of 20 minutes and can bind inthe nanamolar range)
5. sites of release (type one and two release from active zone and neuropeptides release extra-synaptically)
6. sites of action
7. termination/recycling (type one and two can have reuptake or enzymatic degredation and be recycled while neuropeptides are comepletely broken down and unusable after neuropeptide was released.)

what are small clear synaptic vesicles?

* contain “classical” and amino acid neurotransmitters
* released from the active zone

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what are the large, dense core vesicles?

* contain neuropeptides
* electron-dense
* released extrasynaptically

What is the neuropeptide synthesis (in short)?

* gene is taken adn synthesized into the ER and packaged inside the golgi (regular protein synthesis)
* then the vesicles bid off of the golgi and then take the microtubule pathways down the axons to the end of the axon to be eventually released extrasynaptically.
* the vesicles that are released from the golgi are prepropeptides: pre=precurser molecule and thus needs to be acted on to become the actual neurotransmitter (this occurs in the vesicle while traveling down the axon)

How is there post-translational processing of neuropeptides? What does it show?

* it shows that there can be great diversity of neuropeptide products from one gene product
* POMC precurser peptide can be broken down into ACTH and beta-LPH (these both can project to the anterior lobe of the pituitary gland)
* ACTH and beta-LPH can be broken down further to project to the intermediate lobe of the pituitary gland)
* ACTH can be broken doesn into alpha-MSH and CLIP
* beta-LPH can be broken down into gamma-LPH and beta-ENDO

What is another mechanism for diversrity for propetitdes to become neuropeptides?

* alternative splicing
* CALC1 mRNA after transcription can be seen as CALC1 mRNA in thyroid or CALC1 mRNA is sensory neurons
* CALC1 mRNA in thyroid→ spliced into calcitonin mRNA→ calcitonin prepropeptide
* CALC1 mRNA in sensory neurons→ spliced into CGRP mRNA→ CGRP prepropeptide

What is a part of neuro peptide release and regulation of synthesis?

* Affinity of release machinery (synaptotagmin) is really low compared to the affinity of the desne core vesicles
* large dense core vesicles see lesser concentration of clacium so they require a higher rate of activity of firing rates to see release
* dense core vesicles are not docked at the active zone, so the calcium that comes in has to diffuse a long way to get to the dense core vesicles (however Ca++ gets buffered quickly so this is hwy calcium is in very low concentration in the cytoplasm and requires a high enough AP activity to and high affinity in order for large dense core vesicles to be released after a period of high activity)
* regulation of synthesis is actually CALCIUM DEPENDENT
* more complicated than regular calcium regulation
* calcium feedback information to feedback to the soma stop synthesis in the ER (increase calcium levels can also increase neuropeptide production)

Neuropeptide effects: Neuropeptide Y (NPY)

* NPY can have pre- and post-synaptic effects
* NPY receptors are G-protein-coupled receptors
* NPY can affect functions such as: feeding behavior, homeostasis, circadian rhythm, stress and anxiety
* NPY actually works more at times of alertness adn depressed at times of sleeping

Effects of NPY on stress/anxiety/depression

* regulates HPA axis
* regulated by corticosterone (rodent equivalent of cortisone)
* intranasal or central administration can reverse anxiety/dpression-like behaviors in rodents
* Anti-anxiety effect seems to depend on Y1R or Y5R; activation of Y2Rs CAUSES anxiety
* 5-HT receptors are associated with cortical, amygdala, and other NPY-producing neurons, and NPY generally increases 5-HT signaling

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What is the effects of Prozax admisistration in rodents?

* can increase NPY production, including in the arcuate and anterior cingulate cortex, dentate gyrus
* caused decreased NPY in the hypothalamus
* may be able to reduce dperession-like symptoms (studies are limited)

What are the three caseous transmitters?

* nitric oxide (NO)
* carbon monoxide (CO)
* Hydrogen sulfide (H2S)

What is the synthesis of nitric oxide synthesis?

arginine +(NADPH, 2O2, (FAD, FMN, BH4), Calcium, Camodulin, and NOS)= citrulline

* NO is a product of the reaction
* synthesis is calcium and calmoduline dependent
* neuronal nitric oxide synthetase (nNOS): from of NOS normall found in neurons
* endothelial NOS: form found in blood vessel endothelium
* inducible NOS: found after inflammation

Why must NO synthesis be so tightly controlled?

* NO cannot be stored in the body (it is lipid solub;e so it can not be stored in vesicles and it is a free radical so it can and will interact with anything it runs into
* it is not inactivated by normal mechanisms like reuptake
* NO can damamge cells at high concentrations
* may contribute neuronal damage after other injury

How is NO sythesis regulated?

* intracellular calcium
* gene epression

How termination of action of NO occurs?

* reaction with amino acids
* activity of phosphodiesterases

Is nitric oxide a neurotransmitter? Pros/cons:

* Against: not released from vesicles, and no transmembrane receptors
* For: can affect neuronal signaling by:
* activation of guanylyl cyclase (turns GTP to cGMP)
* s-nitrosylation of proteins (results in conformational change in proteins and sometines acts on ion channels)

How does nitric oxide act as a neurotransmitter in the PNS?

* this influences the enteric nervous system (smooth muscle in the intestine)
* calcium enters Ca++ channel and binds to nNOS to make NO→ NO enters the smooth muscle in the intenstin and interacts with sGC (soluble guanylyl cyclase)_> NO production results in potassium channels in the smooth muscle opening and thus causes hyperpolarization and therefore causes muscle relaxation

Nitric oxide as a neurotransmitter in the CNS?

* onlt 1-2% of CNS neurons have NOS
* NOS affects: NT release, synaptogenesis, apoptosis, synaptic plasticity
* post-synaptic neurons= calcium entry is a little different, it wnters through NMDA receptors
* NO in CNS can act on postsynaptic, presynaptic, and glial cells can be acted on
* NO has a relaly short half-life (reacts quickly with target)
* note: bc NO does not have vesicles→ not quantal release

What is teh synthesis of carbon monoxide in the body?

Heme + (O2, NADPH and *Heme oxygenase*) = CO and Fe++

* catalysis of heme (the non-protein part of hemoglobine) and gets broken down into iron atoms and carbon monoxide
* Heme oxygenase in the unique synthetic enzyme or producing carbon monoxide

How is CO synthesis regulated?

* phosphorylation of HO2
* end products of heme catabolism
* regulated by end-product inhibition and ensymatic degradation

How does carbon monoxide act as a neurotransmitter in the PNS?

Calcium enters the cell thorugh a Ca++ channel and attached to PKC→ this induces HO2 to make CO→ CO enters the smoothe muslce in the intenstine and approachees guanylyl cyclase→ this opens the potassium ion channels that result in hyperpolarization and vasorelaxation

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What does Nydrogen sulfide do?

* enhances NMDA receptors (increases conduction)
* increases LTP induction (though enhancing NMDA recptors)

How cna multiple NT be released from a single neuron? (4 theoretical situations)

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

(Corelease, differential release, spatial segregation)

What are purine transmitters? (how are they made)

* ATP+ (ectoATPase+ectonucleotidease)= adenosine
* ATP and adenosine are both transmitters
* how do we know if ATP has an effect on a target? ATP receptors!

How to identify if GABA and glycine are in the same synaptic vesicle?

* since the IPSC for both glycine and GABA would look very similar if packaged together, look at the mIPSC
* Glycine mIPSC is much quicker gated and GABA is much longer and shorter

Nerve terminal in the spinal cord can release both…….. (what components to looks for)

* both GABA and Glycine by expressing the required pre- and postsynaptic proteins for both
* glycine synapse only has VIAAT, GLYT2, and Glycine receptors
* GABA syanpse only has GAD (to become GABA), VIAAT and GABA receptors
* mixed synapse has GAD, VIAAT, GLYT2, and GABA and Gylcine receptors

Using the sorting of vesicles in teh Golgi, neurons…..

can send two different transmitter containing vesicles to different acon collaterals for use at different synapses

* can have different NT on different sides of the axon
* different NT @ different axon terminals and different mixes of NT

Not all synapses are at the ends of axons:

* some are on dendrites→ dendritic synapse 9ex granule cell to mitral cell
* pre to post= granule cell releases GABA onto mitral cell
* post to pre synaptic= mitral cell can release glutamate onto the granule cell (dendrite is releasing NT to work in backwards direction)
* this is a feedback look with dendrite cells.