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Home » Science » Biology » Difference Between Neuropeptides and Neurotransmitters
Difference Between Neuropeptides and
Neurotransmitters
June 2, 2017 •by Lakna •7 min read
1
Main Difference – Neuropeptides
vs Neurotransmitters
Neuropeptides and neurotransmitters are chemical substances
which act as mediators for the transmission of impulse from
one neuron to another neuron through the synapse. Both
neuropeptides and neurotransmitters are polypeptide
derivatives. The transmission of neuron signal across the
synapse occurs in several steps. First, the neurotransmitter is
released from the presynaptic neuron into the synapse. Then,
the neurotransmitter diffuses across the synaptic cleft and
binds to specific receptors. Neuropeptides are a type of neurotransmitters. Neuropeptides are large molecules but
neurotransmitters are small molecules. The main difference between neuropeptides and neurotransmitters is that
neuropeptides are slow-acting and produce a prolonged action whereas neurotransmitters are fast-acting and
produce a short-term response.
This article looks at,
1. What are Neuropeptides
– Definition, Characteristics, Function
2. What are Neurotransmitters
– Definition, Categorization, Characteristics, Function
3. What is the difference between Neuropeptides and Neurotransmitters
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What are Neuropeptides
Neuropeptides are neurotransmitters made up of amino acids, each connected by peptide bonds. They are relatively
large and are composed of 3 to 36 amino acids. They are released into the synaptic cleft along with another
neurotransmitter. Neuropeptides are derived from about 90 amino acids large, inactive precursors. The removal of the
signal sequence from the neuropeptide precursor produces the bioactive peptide. In some neuropeptide precursor
peptides, the same bioactive neuropeptide occurs in multiple copies. Neuropeptides are synthesized in the cell body of
the neuron. Then, they are sequestrated within the lumen and transported to the axon, while undergoing its processing
events like signal peptide cleavage. The bioactive neuropeptides are stored in large dense-core vesicles (LDCVs).
After the exocytosis of LDCVs, the membrane components of LDCVs are reinternalized. Therefore, no re-use of
neuropeptides occurs in the synapse. The release of neuropeptides occurs at low cytosolic Ca concentrations. But,
Ca ions usually stimulate the exocytosis of LDCVs. Thus, Ca ions from other sources like internal stores or
transmembrane current may be used for exocytosis. The synthesis of neuropeptides is shown in figure 1.
2+
2+ 2+
5/7/2018 Difference Between Neuropeptides and Neurotransmitters | Definition, Categorization, Characteristics, Function
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Figure 1: Neuropeptide synthesis
Table 1: Origins of Neuropeptides and Examples
Origin Example
Hypothalamic Releasing Hormones TRH, LHRH, GHIH (Somatostatin)
Pituitary Peptides ACTH, β-Endorphin, α-MSH, PRL, LH, TSH, GH,
Vasopressin, Oxytocin
Peptides Acting on Gut & Brain Leucin enkephalin, Methionine enkephalin, Subs P,
Gastrin, CCK, VIP, Nerve GF, Brain derived
neurotropic factors, Neurotrensin, Insulin,
Glucagon
From other Tissues Ag-II, Bradykinin, Carnosine, Sleep peptides,
Calcitonin
What are Neurotransmitters
5/7/2018 Difference Between Neuropeptides and Neurotransmitters | Definition, Categorization, Characteristics, Function
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Neurotransmitters are chemicals which transmit signals
from a neuron to a target cell across a synapse. They are
stored in synaptic vesicles, which are present at the
terminal of the presynaptic neuron cells. Once the
presynaptic neuron is stimulated by a nerve impulse,
neurotransmitters are released into the synapse from the
axon terminal. The released neurotransmitters diffuse
across the synapse and bind to the specific receptors on the
postsynaptic neuron. Hence, neurotransmitters are in the
direct apposition to their target cells.
Categorization of Neurotransmitters
Neurotransmitters are categorized into types based on the function; they are excitatory and inhibitory
neurotransmitters. Excitatory neurotransmitters increase the trans-membrane ion flow, allowing the postsynaptic
neuron to produce an action potential. In contrast, inhibitory neurotransmitters decrease the trans-membrane ion
flow, prohibiting the postsynaptic neuron to produce an action potential. However, the overall effect of excitatory and
inhibitory functions determines whether the postsynaptic neuron “fires” or not.
Acetylcholine, biogenic ammines, and amino acids are the three classes of neurotransmitters. Acetyl and choline are
involved in the production of acetylcholine, which acts on the neuromuscular junctions. Biogenic amines found in
the brain are involved in the emotional behavior of the animal. They include catecholamines like dopamine,
epinephrine, and norepinephrine (NE) and indolamines like serotonin and histamine. They also help to regulate the
biological clock. The function of biogenic amines depends on the type of receptor they bind to. Glutamate and
gamma-aminobutyric acid (GABA) are amino acid neurotransmitters. Glutamates act on the brain. Neuropeptides
like endorphins and Substance P are strings of amino acids, which mediate pain signals. A synapse with
neurotransmitters is shown in figure 2.
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Figure 2: A Synapse
Difference Between Neuropeptides and Neurotransmitters
Definition
Neuropeptides: Neuropeptides are short chains of amino acids which serve as neurotransmitters.
Neurotransmitters: Neurotransmitters are chemical substances which are released at the end of a nerve cell by the
arrival of a nerve impulse, transmitting the impulse into another neuron, muscle or some other structure.
Molecular Weight
Neuropeptides: Neuropeptides have high molecular weight.
Neurotransmitters: Neurotransmitters have low molecular weight.
Activity
Neuropeptides: Neuropeptides are slow-acting.
Neurotransmitters: Neurotransmitters are fast-acting.
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Response
Neuropeptides: Neuropeptides produce a slow response.
Neurotransmitters: Neurotransmitters produce acute response.
Duration
Neuropeptides: Neuropeptides produce a prolonged action.
Neurotransmitters: Neurotransmitters trigger short-term response.
Receptor Proteins
Neuropeptides: Neuropeptides act on a number of receptor proteins.
Neurotransmitters: Most of the neurotransmitters only act on a specific receptor.
Metabolic Machinery
Neuropeptides: Neuropeptides change metabolic machinery.
Neurotransmitters: Most of the neurotransmitters do not change the metabolic machinery.
Genes
Neuropeptides: Neuropeptides alter the expression of specific genes.
Neurotransmitters: Most of the neurotransmitters do not alter gene expression.
Synthesis
Neuropeptides: Neuropeptides are synthesized in rough endoplasmic reticulum and Golgi apparatus.
Neurotransmitters: Neurotransmitters are synthesized in the cytosol of presynaptic neuron terminals.
Concentration
Neuropeptides: Neuropeptides are synthesized in low concentrations.
Neurotransmitters: Neurotransmitters are synthesized in high concentrations.
Location
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Neuropeptides: Neuropeptides are found all over the neuron.
Neurotransmitters: Neurotransmitters are only found in the axon terminals of presynaptic neurons.
Stored in
Neuropeptides: Neuropeptides are stored in large dense-core vesicles (LDCVs).
Neurotransmitters: Neurotransmitters are stored in small secretory vesicles (SSVs).
Release
Neuropeptides: Axonal streaming of neurotransmitters occurs in few cm/day.
Neurotransmitters: Neurotransmitters are released within few milliseconds upon an arrival of an action potential.
Released with
Neuropeptides: Neuropeptides are released to the synaptic cleft along with another neurotransmitter.
Neurotransmitters: Neurotransmitters are released individually depending on the action potential.
Cytosolic Ca2+ Concentration
Neuropeptides: Neuropeptides are released at low cytosolic Ca concentrations.
Neurotransmitters: Neurotransmitters are released at high cytosolic Ca concentrations.
Site of Action
Neuropeptides: Neuropeptides have a different site of action than their origin.
Neurotransmitters: Neurotransmitters are released in direct apposition to their target cells.
Fate
Neuropeptides: Vesicles are autolysed without reusing. Once released, they do not undergo reuptake.
Neurotransmitters: Neurotransmitters are either destroyed by enzymes in the synaptic cleft or are reuptake by
presynaptic terminal or neuroglia by active transport.
Potency
2+
2+
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Neuropeptides: Neuropeptides are 1000 times potent than neurotransmitters.
Neurotransmitters: Neurotransmitters are less potent when compared to neuropeptides.
Examples
Neuropeptides: Oxytocin, vasopressin, TSH, LH, GH, insulin, and Glucagon are neuropeptides.
Neurotransmitters: Acetylcholine, Dopamine, Serotonin, and Histamine are neurotransmitters.
Conclusion
Neuropeptides and neurotransmitters are chemical mediators, which are involved in the transmission of neuron
impulses. Neuropeptides are a type of neurotransmitters. Neuropeptides are short-chain amino acids and
neurotransmitters are polypeptide molecules. The production of neuropeptides occurs in the cell body of the neuron
while the production of neurotransmitters occurs at the axon terminal of presynaptic neurons. Neuropeptides are
released at a distinct site to the site of action. Therefore, their diffusion to the active site takes time, making
neuropeptides to act slowly. But they produce a prolonged response. In contrast, neurotransmitters are released
directly apposition to their target, producing an acute response. Since neurotransmitters are destroyed at the
presynaptic cleft, their response lasts for a short time period. Therefore, the main difference between neuropeptides
and neurotransmitters is in their mechanism of action after releasing.
Reference:
1.”What are Neurotransmitters?” Neurogistics. N.p., n.d. Web. 29 May 2017. <http://www.neurogistics.com/the-
science/what-are-neurotransmitters>.
2.”Types of Neurotransmitters by Function – Boundless Open Textbook.” Boundless. N.p., 29 Sept. 2016. Web. 29
May 2017. <https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-
textbook/overview-of-the-nervous-system-11/neurophysiology-113/types-of-neurotransmitters-by-function-619-
3349/>.
3.”Synaptic Transmitters- Neurotransmitters & Neuropeptides.” HowMed. N.p., 18 May 2011. Web. 30 May 2017.
<http://howmed.net/physiology/synaptic-transmitters/>.
4. Mains, R. E., Eipper, B. A., “The Neuropeptides.” Basic Neurochemistry: Molecular, Cellular and Medical Aspects.
6th edition. U.S. National Library of Medicine, 01 Jan. 1999. Web. 30 May 2017.
<https://www.ncbi.nlm.nih.gov/books/NBK28247/>.
Image Courtesy:
1. “Neuropeptide synthesis” By Pancrat – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “1225 Chemical Synapse” By OpenStax – (CC BY 4.0) via Commons Wikimedia
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About the Author: Lakna
Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a
broad and keen interest in the discovery of nature related things
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