Key Difference – Neuropeptides vs Neurotransmitters
Neurotransmitters and neuropeptides are chemical molecules involved in the transmission of signals through neurones in the nervous system. Neurotransmitters are different types of low molecular weight molecules including amino acids and smaller peptides. The neuropeptides are one type of neurotransmitters, and they are composed only of peptides [proteins] with larger molecular weights. This is the key difference between neuropeptides and neurotransmitters. There are various other differences between the neuropeptides and neurotransmitters in the production, action, and release processes. Following descriptions will help you to understand those differences.
CONTENTS
1. Overview and Key Difference
2. What are Neuropeptides
3. What are Neurotransmitters
4. Side by Side Comparison – Neuropeptides vs Neurotransmitters
5. Summary
What are Neuropeptides?
Neuropeptides are small protein molecules consisting mainly of peptides and are used by the neurones to pass signals from one neurone to the next neurone. These are the neurone signalling molecules, influencing the brain and the body functions. There are different types of neuropeptides. Approximately 100 of neuropeptide encoding genes are found in the mammalian genome. Neuropeptides are more potent than the other conventional neurotransmitters. These peptides are stored in dense core vesicles and are released with small neurotransmitters to regulate the signal transmission.
The release of neuropeptides can happen from any part of the neurone, not only from the synapse end like other neurotransmitters. The production of neuropeptides follows the normal gene expression process. Neuropeptides bind with the specific receptor or receptors located on the surface of the target cell. The neuropeptide receptors are mainly G-protein coupled receptors. One neuropeptide can bind to different types of neuropeptide receptors and do different functions.
Common neuropeptides include hypocretin/orexin, vasopressin, cholecystokinin, neuropeptide Y, and Norepinephrine.
Figure_1: Neuropeptide Synthesis
What are Neurotransmitters?
Neurotransmitters are chemical molecules which facilitate the signals transmission through neurones. They can be a single amino acid, peptide, monoamine, purines trace amine or another type of molecule. They are produced at the axon terminal, inside the small sacs called synaptic vesicles which are enclosed by membranes. One synaptic vesicle carries many neurotransmitters. Neurotransmitters are released into a small space called synaptic cleft through a process called exocytosis as shown in figure 01. Exocytosis is an active transport method used by the cell membrane to transfer molecules from the interior to the outside, consuming the energy. Neurotransmitters will be available at the synaptic cleft till they are binding with the receptors, procured in the postsynaptic end of the adjacent neurone or the target cell. Some of the neurotransmitters reuptake while some bind with the correct receptors. Some are also subjected to hydrolysis by the enzymes.
Some examples of neurotransmitters include Acetylcholine, Glutamine, Glutamate, Serine, Glycine, Alanine, Aspartate, Dopamine, etc.
Figure_2: Synapse
What is the difference between Neuropeptides and Neurotransmitters?
Neuropeptides vs Neurotransmitters |
|
| Neuropeptides are larger molecules made up of 3 to 36 amino acids. | Neurotransmitters are smaller molecules composed of different compounds. |
| Return to the Nerve Cell | |
| Once secreted, they cannot reuptake to the cell. | They can reuptake by the cell after releasing to the synaptic cleft. |
| After Release | |
| Extracellular peptidases modify the neuropeptide | No modifications are done by extracellular peptidases. |
| Storage | |
| Neuropeptides are stored in the dense core vesicles. | Neurotransmitters are stored in the small synapse vesicles. |
| Location | |
| They can be found anywhere in the neurone. | They can be seen in the axon terminal at the presynaptic location. |
| Secretions | |
| Secretions are co-released with smaller neurotransmitters. | Secretions are co-released with neuropeptides. |
| Action | |
| Neuropeptides are slow-acting transmitters. | Neurotransmitters are fast-acting transmitters. |
| Synthesis | |
| Synthesis happens in the ribosomes, ER, Golgi bodies, etc. | They are synthesised in the cytoplasm of the presynaptic end. |
| Efficiency | |
| They are more efficient in transmitting the signal. | They are less efficient in signal transmission. |
| Concentrations | |
| Neuropeptides are present in lower concentrations than other neurotransmitters. | Neurotransmitters are present in high concentrations than neuropeptides. |
| Diffusion at the Release Site | |
| They can diffuse from the release point to a distance and act. | They can’t diffuse from the synapsis cleft. |
| Examples | |
| Examples include Vasopressin and Cholecystokinin. | Examples include Glycine, Glutamate, and Aspartate. |
Summary – Neuropeptides vs Neurotransmitters
Neurotransmitters are small chemical molecules, involve in the signal transmission through neurones. There are different types of neurotransmitters such as single amino acids, small peptides, purines, amines, etc. Neuropeptides are one type of neurotransmitters, and they are small proteins composed of peptides. Neurotransmitters and neuropeptides are packaged in separate vesicles called dense core vesicles, and synapsis vesicles respectively found in the interior of the neurone. Neuropeptides are more efficient than the conventional neurotransmitters. However, smaller neurotransmitters are fast in action while the larger neuropeptides are slow in the action. This is the difference between Neuropeptides and Neurotransmitters.
References;
Pol, Anthony N. van den. “Neuropeptide transmission in brain circuits.” NCBI. U.S. National Library of Medicine, 04 Oct. 2012. Web. 06 Feb. 2017
“Neurotransmitter.” Wikipedia. Wikimedia Foundation, n.d. Web. 06 Feb. 2017
Purves, Dale. “Neurotransmitter Synthesis.” Neuroscience. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 06 Feb. 2017
Vole, G. P., and K. D. Rainsford, eds. “Mechanism of action of neuropeptides: a group of naturally occurring (endogenous) anti-inflammatory analgesic compounds.” Side-Effects of Anti-Inflammatory Drugs. Vol. 2. N.p.: n.p., 1987. 449-50. Print.
Image Courtesy:
“Synapse Illustration2 tweaked” By Nrets – first upload on en.wikipedia.org, uploaded to Wikimedia Commons as Image:SynapseIllustration2.png, SVG version by User: Surachit. F.(CC BY-SA 3.0) via Commons Wikimedia
“Neuropeptide synthesis” By Pancrat – Own work (CC BY-SA 3.0) via Commons Wikimedia