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Catnip Insect Repellent and the Function of TRPA1 Channels

Linda Crampton is a writer and former science teacher with an honors degree in biology. She enjoys writing about nature and science.

A Useful and Interesting Plant

The catnip plant has an intriguing effect on some domestic cats and on some of their wild relatives. The euphoria that the animals exhibit when they are exposed to the plant’s leaves can be impressive. Catnip is also known for its ability to repel insects, especially mosquitoes. Scientists have recently discovered the mechanism behind this ability. Understanding the mechanism in detail is important. If global warming continues and harmful insects expand their range, new and effective ways to repel the insects could become vital.

In mosquitoes, catnip exerts its effects via stimulating the TRPA1 channel in the cell membrane. We have the channel in our cell membranes, too, but catnip doesn’t hurt us. The plant doesn’t cause us to develop the euphoria that cats experience, either. The varying effects of the plant are puzzling as well as interesting. Investigating the herb could prove to be very useful.

The Catnip Plant

Catnip is a member of the mint family, or the Lamiaceae. It has the very appropriate scientific name Nepeta cataria. The chemical that triggers the interesting effect in cats and mosquitoes is called nepetalactone.

The plant is a perennial herb that is native to Europe and Asia. Like other members of the mint family, it has square stems. Its leaves are toothed and are attached to the stem in pairs. They have a roughly oval or triangular shape.

Catnip’s flowers are small and tubular. The tube has an upper and lower “lip“. Both of the lips are lobed. The flowers are white, white with pink or purple spots, or entirely pale pink or pale purple. They’re borne on a tall spike.

Catnip is considered to be edible. Some people use the plant’s leaves to make a tea. There are some concerns about the safety of ingesting large amounts of the plant or products made from it, however. It shouldn’t be ingested frequently or in large quantities.

Nepetalactone Facts

Catnip has had a reputation as a useful insect repellent for a long time. It’s known to be especially effective against mosquitoes. Some scientists say that it’s more effective at repelling mosquitoes than DEET ( N,N-diethyl-meta-toluamide), a popular insecticide. Researchers have recently discovered that the nepetalactone in catnip activates the TRPA1 in mosquitoes but doesn’t activate ours. Combined with its effectiveness, this could make it a great repellent.

Nepatalactone was discovered in 1941 by Samuel McElvain at the University of Wisconsin and is classified as an iridoid. The scientist was investigating the essential oil found in catnip plants. The plant makes nepetalactone from a chemical called geraniol. This chemical is present in other plants and is used by us to make perfume. Catnip oxidizes the geraniol molecules, or adds oxygen to them, during the process of making nepetalactone.

Nepatalactone is volatile. It’s released into the air and repels specific types of insect that are approaching the plant. The chemical exists in slightly different forms known as isomers. Some insects are attracted to one of the isomers, as stated in the quote below. Fortunately, mosquitoes aren’t.

The soybean aphid (Aphis glycines)...uses Z,E-nepetalactone as a pheromone component, and green lacewings (Neuroptera: Chrysopidae) are attracted to this compound, perhaps because their larvae feed on aphids.

— Nadia Melo et al, via Current Biology

Cell Membrane Structure

As shown in the illustration above, the cell or plasma membrane contains a double layer of phospholipid molecules, or a phospholipid bilayer. Proteins are dispersed throughout the membrane. Some are found only on the surface of the membrane, and others extend through it. The membrane also contains cholesterol molecules.

The TRPA1 channel is an integral protein in the membrane, or one that is permanently attached to it. It's also a transmembrane protein because it travels through the entire membrane. Peripheral proteins are also integral ones, but they are found on and near the surface of the membrane instead of extending through it.

Chains of carbohydrate molecules are attached to the outer surface of the membrane. If the chain is attached to a phospholipid, it’s called a glycolipid. If it’s attached to a protein, it’s called a glycoprotein. The proteins in the membrane fall into additional categories.

An Integral and Transmembrane Protein

A protein consists of one or more chains of amino acids. The chains can be very long. Depending on the location of the folds in an integral protein, a channel or pore can be created through the middle of the molecule. The channel allows substances to pass through the cell membrane if the protein extends through it, as the TRPA1 channel does.

The passageway through the protein isn’t a passive route that allows any particles of a suitable size to pass through the membrane. The channel is activated by specific factors and determines which substances can move through the protein. Studying the ways in which substances enter and leave cells via membrane proteins and other methods is very important with respect to health and disease.

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TRP Channels

Transient Receptor Potential (TRP) channels are proteins in the cell membrane that enable specific substances to pass through the membrane when conditions are right. The channels are also called TRP ion channels and TRP receptors.

The TRP family contains twenty-eight members that are grouped into six subfamilies. TRPA1 stands for “Transient receptor potential Ankyrin 1”. The channel is shown in the video above. It’s sometimes known as the wasabi receptor because in humans a chemical in wasabi stimulates it. It also referred to as simply TRPA1.

  • The T (Transient) in the receptor’s name means that once it’s stimulated by a particular substance, the change in its form doesn’t last for long.
  • The R (Receptor) refers to the fact that the protein receives or binds to a molecule from outside the cell.
  • The P (Potential) refers to the electric potential that appears as ions flow.
  • Ankyrin is a short segment of around thirty-three amino acids. There are often multiple ankyrins in proteins. They play a role in the interaction of one protein with another inside living things.

TRPA1 Ion Channels and Action Potentials

Researchers have discovered that TRPA1 channels are located on sensory neurons in humans (and on some other types of cells). A neuron is a nerve cell. Neurons grouped together form a nerve.

A sensory neuron receives a signal from a receptor that has detected a change in the environment and then transmits the signal to the central nervous system, which consists of the brain and spinal cord. The sequence of events involving the actions in the neuron is as follows. (Other receptors exist in addition to TRPA1 ones.)

  • The TRPA1 receptor is stimulated by its union with a particular molecule.
  • The ion channel responds by changing its shape in order to allow cations (ions that have a positive charge) to flow into the cell.
  • The influx of cations changes the cell’s internal environment.
  • If the change is sufficient, an action potential is generated in the neuron. An action potential is a rapid rise and fall in the membrane potential, or voltage. It’s caused by changes in the permeability of the membrane to specific ions.
  • Once an action potential has been produced, it triggers the creation of another one in the next section of the neuron. The process repeats, causing a wave of action potentials to travel along the neuron in the forward direction.
  • At the end of the sensory neuron, the action potential triggers processes that stimulate another structure, such as a neuron in the spinal cord or a cranial nerve.

TRPA1 Channel Stimulation in Humans

Although TRPA1 channels have been found in other types of cells besides sensory neurons, their role in the neurons seems to have been best studied. The neuron receptors respond to the presence of noxious chemicals.They seem to be involved in giving a warning signal in the form of an unpleasant sensation and thereby triggering avoidance behaviour when a harmful stimulus is present. TRPA1 is sometimes referred to as an irritant receptor.

Allyl isothiocyanate or AITC is one well-known agonist (stimulator) of human TRPA1. It’s sometimes called mustard oil but is found in wasabi as well as mustard. Mustard oil activates TRPA1 channels on our sensory neurons. Once a neuron is triggered by the channel, it sends a signal to a specific part the brain, causing us to feel pain or discomfort and encouraging us to try to avoid or neutralize it.

Scientists know that when signals originating in TRPA1 channels reach specific parts of our brain, they create the sensation of pain or irritation in the body part that was stimulated. As described above, nerve impulses consist of a flow of charged particles through and along a cell membrane. How this creates sensations of pain or discomfort in our mind is not fully understood.

Anopheles stephensi is one of the mosquitoes that transmits malaria.

Anopheles stephensi is one of the mosquitoes that transmits malaria.

TRPA1 Channels in Mosquitoes

Mosquitoes can cause some major diseases in humans and transmit some dangerous microorganisms. Problems caused by the insects include malaria, dengue, infection by the West Nile virus and the Zika virus, chikungunya, and other illnesses. People need protection from mosquito-borne illnesses, which are sometimes serious and even deadly. It’s important that the protection is effective without harming people, however. Catnip and nepatalactone might be very helpful in this respect.

As in us, in mosquitoes the TRPA1 channels act as nociceptors, which are receptors that detect potentially damaging stimuli. They may not work in exactly the same way as ours, but they do seem to be similar. Insects have receptors, neurons, nerves, and action potentials as we do. They also have a brain, though it’s a relatively simple one compared to ours. The structure of their nervous system means that we may be able to “persuade” the insects to leave an area by causing an unpleasant sensation via their TPRA1 receptors.

Researchers have discovered that nepetalactone from catnip stimulates TRPA1 receptors in mosquitoes but not in us. There are “at least” four forms of the receptors in insects, according to the scientists involved in the research described in the last referenced article below. Studies have shown that nepetalactone activates specific forms of the receptor in the mosquito Aedes aegypti and the fruit fly Drosophila melanogaster and can be a very effective repellent. It doesn’t activate all forms of the receptor in the insects, however.

If researchers learn more about the structure and behaviour of the insect receptors, they may be able to modify or design substances to stimulate the ones that nepetalactone misses. Even if this isn’t necessary for controlling mosquitoes, the increased knowledge might be useful in many ways.

A Potentially Important Insect Repellent

Some people love to use natural remedies for problems. It’s wonderful when science demonstrates that a particular plant like catnip could be beneficial for us. The plant and the nepetalactone that it contains might be very helpful in protecting us from harmful insects.

The study of TRPA1 and related receptors in insects and in humans could lead to important discoveries. The discoveries may be useful with respect to repelling insects. They may also be useful with respect to other aspects of our lives or of the lives of the animals that we care for. I hope this is the case.

References

  • Catnip facts from the Missouri Botanical Garden
  • Nepetalactone information from the John Innes Centre (a centre for studying plant science, genetics, and microbiology)
  • Information about membrane proteins (including integral ones) from the National Center for Biotechnology Information
  • Facts about transient receptor potential channels from the U.S. National Library of Medicine
  • TRPA1: A Sensory Channel of Many Talents from the NCBI Bookshelf
  • Information about the TRPA1 channel from Nature Scientific Reports
  • Effects of the receptors in mosquitoes from Nature Scientific Reports
  • The irritant receptor TRPA1 mediates the mosquito effect of catnip from Current Biology, Cell Press

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on March 17, 2021:

Hi, Vidya. It would be wonderful to use catnip or its components as an insect repellent. I think biology is fascinating, too!

VIDYA D SAGAR on March 17, 2021:

A very interesting article Alicia. Isn't it wonderful if insect repellents can be made naturally from plants like the catnip. So much safer for us humans and animals that we care for. We got to learn how the TRPA1 channels work. Biology is my favorite subject. It is so fascinating.

Linda Crampton (author) from British Columbia, Canada on March 17, 2021:

Thanks, Eman. I appreciate your visit and comment.

Linda Crampton (author) from British Columbia, Canada on March 17, 2021:

Hi, Mary. Summer is a lovely season, but it does have some disadvantages, such as the appearance of certain insects. I hope you have a good season at the cottage.

Eman Abdallah Kamel from Egypt on March 17, 2021:

Thank you, Linda, for this interesting article about the catnip plant and its effects on mosquitoes. I enjoyed reading the article so much.

Mary Norton from Ontario, Canada on March 17, 2021:

Summer soon will be here and we certainly need protection from mosquitoes. I will definitely look for catnip when I buy plants for the cottage.

Linda Crampton (author) from British Columbia, Canada on March 17, 2021:

Thank you very much for the comment, Devika. I appreciate your visit a great deal.

Devika Primić from Dubrovnik, Croatia on March 17, 2021:

AliciaC I know that nature has its way of healing us from ailments. Catnip is different it protects us from mosquitoes. You have put together a useful and most informative hub on this unique title. Your ideas and research are outstanding!

Linda Crampton (author) from British Columbia, Canada on March 17, 2021:

Thank you for such a kind and lovely comment, EK. I appreciate what you have said very much.

EK Jadoon from Abbottabad Pakistan on March 17, 2021:

I haven't seen this plant before. Thanks for adding in my knowledge, Alicia. I wanna tell you something; you are my most favourite author on hubpages and what I like the most is your kindness.

Keep up the good work.

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

Hi, Nithya. Thank you very much for the comment.

Nithya Venkat from Dubai on March 16, 2021:

An interesting and informative article about the catnip plant and the TRPA1 Channels. It is amazing how proteins form an integral part of the cell membrane and its functions. Thank you for sharing a detailed, easy-to-understand article with a wealth of information.

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

Hi, Chitrangada. Nature can certainly be helpful for us. Repelling insects is a great ability. Thank you very much for the visit and the comment.

Chitrangada Sharan from New Delhi, India on March 16, 2021:

Excellent information and well presented.

Catnip looks familiar, but I wasn't aware of such interesting details. Nature is full of such plants, which have different effects, on different creatures. I have heard about some other herbs, which repel insects.

Thank you for sharing this well researched and informative article.

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

Thank you very much for commenting, Misbah, especially at 2:45 am! I hope you sleep well for the rest of the night.

Misbah Sheikh from The World of Rebels. on March 16, 2021:

Hi Linda, I enjoyed the read

It’s 2:40 am here in Spain

I was putting an alarm on my phone

just thought to check HP notifications and saw your hub

Your beautiful article distracted me from sleeping...lol

A very well balanced and well presented article dear

I enjoyed it, very informative

I don’t like mosquitoes because they spread dengue virus

Blessings

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

My cats enjoy catnip, too. It’s interesting to watch their response to the herb. Thanks for the visit and the comment, Peggy.

Peggy Woods from Houston, Texas on March 16, 2021:

Our cats always enjoyed toys with powdered catnip in them. I did not realize catnip is a part of the mint family or that it repels mosquitoes. Thanks for another fascinating article from you, Linda.

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

Hi, Pamela. I like many insects, but not mosquitoes! They can be harmful for humans, especially in some areas. I appreciate your comment very much.

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

Thanks for the comment and for sharing the information, Manatita. I appreciate your visit.

Pamela Oglesby from Sunny Florida on March 16, 2021:

I would have never thought tht catnip was part of the mint family, This is a fascinating article, Linda. There is a wealth of facts in this article, which I apreciate. While I knew I didn't like mosquitoes I didn't realize they carried so many diseases. This is another excellent article.

manatita44 from london on March 16, 2021:

Excellent write and a little deep for me this time. As regards the plant, it resembles one that I used in the Caribbean. It has medicinal properties. The repellant effect is probably good in certain environments.

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

Thank you very much, Fran. I hope you do learn to love biology. I think it’s a fascinating topic.

fran rooks from Toledo, Ohio on March 16, 2021:

Linda, I do love all your very detailed scientific articles. And, always informative. I may learn to love biology yet. Thanks again.

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

Hi, Bill. We have sunshine here, too. The sun makes it nice to work outside. Thank you for the kind comment. I appreciate the fact that you read the article as soon as you found it.

Bill Holland from Olympia, WA on March 16, 2021:

I was heading outside to take advantage of the sunshine when this popped up. I figured I better catch it quick before it got lost in the feed.

I just loved the title; the article was a bonus. I've never heard of this, but you better believe I'll be trying it. Thank you, Linda!

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

Thanks, Ron. I enjoy exploring science literature.

Ron Hooft from Ottawa on March 16, 2021:

Great hub. You did your research. Always nice to see.

Linda Crampton (author) from British Columbia, Canada on March 16, 2021:

Thank you very much, Liz. Catnip is an interesting plant.

Liz Westwood from UK on March 16, 2021:

This is a very interesting and well-presented article. It is fascinating to read about a natural insect repellant and to discover how the TRPA1 channels work. I was interested too to read that catnip is in the mint family of plants as I could see similarities in the leaves.

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