A Tiny Surprise in Regards to Regeneration (A Guest Post)

A reposting of an original article by Jessica Klein in The Scorpion and the Frog.

The ability to regenerate limbs and tails is nothing new to reptiles and amphibians. Many lizards are able to drop their tails to escape an enemy, whereas salamanders have been known to grow back entire legs with muscle after being attacked by a predator. These regenerative characteristics have been seen to some extent in rabbits and pika before 2012, but were later discovered to occur extensively in, surprisingly enough, small African spiny mice.

One of the African spiny mouse species. Photo by Ashley Seifert and Tom Gawriluk.

In a study done by Ashley W. Seifert and Megan G. Seifert at the University of Kentucky, Todd M. Palmer and Malcolm Maden at the University of Florida, Stephen G. Kiama at the University of Nairobi, and Jacob R. Goheen at the University of Wyoming, African spiny mice were studied in order to view the extent of their regenerative properties, why they might occur, and the physiological processes that make it happen.

The rodents were captured in Kenya, where researchers learned that vigorous movement during handling caused the skin of African spiny mice to come apart. One mouse was reported to have an open wound that took up 60% of its back, just from being handled! Therefore, Dr. Seifert measured the amount of strength it took to tear the skin of spiny mice using something called a Hounsfield tensometer. He took the measurements from that tool and graphed them on a plot, creating something called a stress-strain curve which showed how much strength it took to tear the skin of the mouse.

The strength measurements revealed that the skin of these species was 77 times weaker than average mice, explaining why their skin tore so easily during the handling process. In order for the African spiny mice to survive such large injuries due to their extremely fragile skin, it would be beneficial to heal quickly or regenerate the skin. This is exactly what Dr. Seifert discovered.

An African spiny mouse shows
the regenerative process with
(1) being before the wound
(2) being after the wound and
(3) showing how the wound was
completely healed after 30 days.
Figure from Seifert, et al., 2012.

After the strength measurements were completed, the rodents were anaesthetized and had 4mm and 1.5cm wounds made on their skin, as well as 4mm holes punched in their ears in order to view the regeneration process. In an average rodent, the repair of a 4mm skin wound takes around 5 to 7 days and is accompanied by a significant amount of scarring. However, in the African spiny mouse it only took 1 to 2 days for scabbing of the skin wound to occur with new cells forming on the outside of the wound to repair it. After just 10 days, the ear of the mouse was fully healed. In the ear punches, there were no signs of scarring that would have been expected in a rodent, and healthy cartilage had formed. By the 21st day of the experiment, African spiny mice had developed new hair follicles and healthy new hair covering the once wounded area. In total, Dr. Seifert discovered that African spiny mice were capable of regenerating their skin, hair follicles, and sweat glands.

Dr. Seifert suggested the skin of African spiny mice is fragile because it allows them to escape predators. This would require a quick healing time to reduce the chance of infection and ultimately death in the mouse after escaping. This is why they may have gained the ability to regenerate their skin, but how exactly does this happen? Dr. Seifert and his research team recently showed that, in these species, it occurs through a process known as epimorphic regeneration. This is when a blastema (a mass of immature, unspecialized cells) forms where the wound once was. These cells are capable of turning into whatever type of tissue was present in that area. This particular method of regeneration is how salamanders are capable of regenerating their limbs. Again, more research would need to be done in order to confirm or deny this. However, one thing is true, and that is that more research into this could prove to be useful in the future of medicine when it comes to healing critical and invasive injuries. By discovering the physiological process behind this, and then being able to replicate it in a lab, researchers may discover ways to heal injuries faster.

Works Cited

Seifert, Ashley W., Stephen G. Kiama, Megan G. Seifert, Jacob R. Goheen, Todd M. Palmer, and Malcolm Maden. "Skin Shedding and Tissue Regeneration in African Spiny Mice (Acomys)." Nature 489 (2012): 561-65. doi:10.1038/nature11499

Gawriluk, Thomas R., Jennifer Simkin, Katherine L. Thompson, Shishir K. Biswas, Zak Clare-Salzler, John M. Kimani, Stephen G. Kiama, Jeramiah J. Smith, Vanessa O. Ezenwa & Ashley W. Seifert. "Comparative analysis of ear-hole closure identifies epimorphic regeneration as a discrete trait in mammals" Nature Communications 7.11164 (2016). doi:10.1038/ncomms11164

Nature Shapes Faithful and Unfaithful Brains

A reposting of an original article from January 22, 2017.

Among monogamous animals, some individuals are more faithful than others. Could these differences in fidelity be, in part, because of differences in our brains? And if so, why does this diversity in brain and behavior exist?

A snuggly prairie vole family. Photo from theNerdPatrol at Wikimedia Commons.

Prairie voles are small North American rodents that form monogamous pair bonds, share parental duties, and defend their homes. Although prairie voles form monogamous pairs, that does not mean they are sexually exclusive. About a quarter of prairie vole pups are conceived outside of their parents’ union.

Not all male prairie voles cheat on their partners at the same rates. In fact, some males are very sexually faithful. It turns out, there are both costs and benefits to being faithful and to cheating. Mariam Okhovat, Alejandro Berrio, Gerard Wallace, and Steve Phelps from the University of Texas at Austin, and Alex Ophir from Cornell University used radio-telemetry to track male prairie voles for several weeks to explore what some of these costs and benefits might be. Compared to males that only sired offspring with their own partner, unfaithful males had larger home ranges, intruded on more territories of other individuals, and encountered females more often. However, these unfaithful males were also more likely to be cheated on when they were away (probably because they were away more). I guess even rodents live by The Golden Rule.

Maps of how paired male voles in this study used space. The solid red/orange/yellow peaks show where a faithful male (in the left map) and unfaithful male (in the right map) spent their time in relation to where other paired males spent their time (showed by open blue peaks). Image from the Okhovat et al. Science paper (2015).

Vasopressin is a hormone that has been found to affect social behaviors such as aggression and pair bonding when it acts in the brain. Mariam, Alejandro, Gerard, Alex, and Steve all set out to determine how vasopressin in the brain may relate to sexual fidelity in prairie voles. They found that faithful males had lots of a particular type of vasopressin receptor (called V1aR) in certain brain areas involved in spatial memory. Surprisingly, faithful males did not have more V1aR in brain regions typically associated with pair bonding and aggression. A male that has more V1aR in spatial memory regions might better remember where his own mate is and where other males have been aggressive, which would decrease the chances that he would intrude on other territories in search of other females and increase the time that he spends home with his own mate. A male that has less V1aR in spatial memory regions might be less likely to learn from his negative experiences and more likely to sleep around.

Photos of a brain section from a faithful male (left) and unfaithful male (right). The dark shading shows the density of V1aR vasopressin receptors. The arrows show the location of the retrosplenial cortex (RSC), a brain area involved in spatial memory. Faithful males had significantly more V1aR receptors in the RSC compared to unfaithful males. Image from the Okhovat et al. Science paper (2015).

The research team then found genotype variations that related to having lots or not much V1aR in one of these spatial memory regions (called retrosplenial cortex … but we’ll just call it RSC). They confirmed these findings with a breeding study, in which they reared siblings that were genetically similar, but some had the genotype they predicted would result in lots of V1aR in RSC and some had the genotype they predicted would result in very little V1aR in RSC. They confirmed that these genetic variations correspond with the amount of vasopressin receptor in this specific spatial memory area.

The researchers then looked closer at the different versions of this vasopressin receptor gene in the RSC brain region to see if differences in the amount of vasopressin receptors in RSC may be caused by the epigenetic state of the gene (i.e. how active the gene is). They found that the genotype that results in very little V1aR in RSC had many more potential methylation sites, which can repress gene activity.

All of this data together tells a very interesting story. Male prairie voles that have the genotype for more V1aR vasopressin receptors in their RSC part of their brain are more likely to remember where their home and mate are and to remember where other aggressive prairie voles are, which will make them more likely to spend more time with their partner, to be sexually faithful and to have sexually faithful partners. Male prairie voles that have the genotype for less V1aR in their RSC are more likely to forget where their home and mate are and where other aggressive prairie voles are, which will make them more likely to cheat and to be cheated on. Overall, faithful and unfaithful male prairie voles have roughly the same number of offspring, but advantages may emerge with changes in population density. Prairie vole populations vary anywhere from 25 to 600 voles per hectare from year to year. When population densities are high, you (and your partner) are more likely to encounter more potential mates and it may benefit you to cheat (and have a “cheater’s brain”). When population densities are low, you (and your partner) are less likely to encounter more potential mates and it may benefit you to be faithful (and have a “faithful brain”). But when populations fluctuate between high and low densities, both faithful and unfaithful genotypes will get passed along from generation to generation.


Want to know more? Check this out:

Okhovat, M., Berrio, A., Wallace, G., Ophir, A., & Phelps, S. (2015). Sexual fidelity trade-offs promote regulatory variation in the prairie vole brain Science, 350 (6266), 1371-1374 DOI: 10.1126/science.aac5791

Mr. Nanny Makes Mr. Right

A reposting of an original article from November 28, 2012.

Quick! Introduce yourself to this guy before
his baby-high wears off! Photo by David
Castillo Dominici at FreeDigitalPhotos.net. 

What happens if you take a wrestler or action star and force him to babysit obnoxious but lovable kids? Well, if you’ve seen movies like The Pacifier with Vin Diesel, The Tooth Fairy with Dwayne ‘The Rock’ Johnson, Kindergarten Cop with Arnold Schwarzenegger, or The Spy Next Door with Jackie Chan, you know that he will fall madly in love both with his young charges and with the closest available woman. Hollywood is so sure of this phenomenon that they have based a whole genre of family movies on it. Now, scientists are finding that Hollywood may be on to something.

Prairie voles are one of the only 3-5% of mammals that are monogamous and in which both parents help take care of young. In females, maternal care is regulated in part by the hormones associated with pregnancy, birth and lactation. The fact that males don’t do those things and they still provide paternal care is curious. The fact that male prairie voles will often provide care to offspring that aren’t even their own is even more curious.

Will Kenkel, Jim Paredes, Jason Yee, Hossein Pournajafi-Nazarloo, Karen Bales, and Sue Carter at the University of Illinois at Chicago recently explored what happens to male prairie voles when they are exposed to unfamiliar vole pups. Male voles without any experience with females or pups were placed in a new clean cage. Then the researchers put either a pup (that was not related to the male), a dowel rod (an unfamiliar object), or nothing into the cage with them for 10 minutes. Afterwards, they measured oxytocin (a hormone associated with bonding between mothers and their offspring) and corticosterone (a stress hormone) in the males’ blood at different time points. In another study, they also looked at the activity of brain neurons associated with the production of these hormones.

A male prairie vole is startled to find a baby in his cage...

But then he takes care of it. Video by Will Kenkel.

Both adult and juvenile males exposed to a pup for 10 minutes had higher oxytocin and lower corticosterone compared to the males not exposed to a pup. But this effect was short-lived, as male hormone levels quickly evened out again. Most of these males that were exposed to a pup showed alloparental care (care of a baby that is not their own), like approaching the pup, cuddling with it and grooming it. Males with higher oxytocin and lower corticosterone levels were more attentive towards the pups. Additionally, alloparental males exposed to pups had more activity of oxytocin-producing neurons and less activity of neurons associated with corticosterone-production in a specific brain region called the paraventricular nucleus (or PVN for short).

Oxytocin is strongly associated with pair bonding in prairie voles, particularly in females, and corticosterone affects pair bonding too (generally increasing pair bonding in males and preventing it in females). If exposure to a pup affects these hormones, maybe it affects how the male would interact with adult females. To test this, the researchers put male voles in a new clean cage and put a pup, a dowel rod, or nothing into the cage with them for 20 minutes. Then they put the males with an unfamiliar adult female for 30 minutes. After getting acquainted with the female, the males were put in a “partner preference apparatus”, which has three connected chambers: a neutral center chamber, a connected chamber with the familiar female tethered into it, and a connected chamber with an unfamiliar female tethered into it. The researchers measured how much time the males spent in each of the three chambers and with each of the two females over the next 3 hours.



A prairie vole pair snuggles. Photo from Young,
Gobrogge, Liu and Wang paper in
Frontiers in Neuroendocrinology (2011)

Males that were exposed to a dowel rod or to nothing before they were introduced to a female spent equal amounts of time with each of the two females. But males that were exposed to a pup before they were introduced to a female spent nearly 4 times as much time with that female than with the unfamiliar one. In other words, hanging out with a random pup acted like Love Potion #9 on these bachelor males and made them fall for the next female they encountered! Interestingly, this effect was true not only for the males that acted in an alloparental way towards the pups, but it was also true of males that attacked the pups (The researchers quickly rescued the pups if this occurred). Perhaps, males that were alloparental with the pups had increased oxytocin and males that were aggressive with the pups had increased corticosterone, either of which would make it more likely for them to form a preference for the female they were with.

Hmm… Got your eye on a special someone? Try volunteering him to babysit before your next date.

Want to know more? Check this out:

Kenkel, W., Paredes, J., Yee, J., Pournajafi-Nazarloo, H., Bales, K., & Carter, C. (2012). Neuroendocrine and Behavioural Responses to Exposure to an Infant in Male Prairie Voles Journal of Neuroendocrinology, 24 (6), 874-886 DOI: 10.1111/j.1365-2826.2012.02301.x

Animal Mass Suicide and the Lemming Conspiracy

A repost of an original article from April 4, 2012.

Ticked off Norway lemming doesn't like gossip!
Photo from Wikimedia Commons by Frode Inge Helland 

We all know the story: Every few years, millions of lemmings, driven by a deep-seated urge, run and leap off a cliff only to be dashed on the rocks below and eventually drowned in the raging sea. Stupid lemmings. It’s a story with staying power: short, not-so-sweet, and to the rocky point.

But it is a LIE.

And who, you may ask, would tell us such a horrendous fabrication? Walt Disney! Well, technically not Walt Disney himself… Let me explain:

The Disney Studio first took interest in the lemming mass suicide story when, in 1955, they published an Uncle Scrooge adventure comic called “The Lemming with the Locket” illustrated by Carl Barks. In this story, Uncle Scrooge takes Huey, Dewey and Louie in search of a lemming that stole a locket containing the combination to his vault … but they have to catch the lemming before it leaps with all his buddies into the sea forever. Three years later, Disney further popularized this idea in the 1958 documentary White Wilderness, which won that year’s Academy Award for Best Documentary Feature. A scene in White Wilderness supposedly depicts a mass lemming migration in which the lemmings leap en masse into the Canadian Arctic Ocean in a futile attempt to cross it.

In 1982, the fifth estate, a television news magazine by the CBC (that’s the Canadian Broadcasting Corporation), broadcast a documentary about animal cruelty in Hollywood. They revealed that the now infamous White Wilderness lemming scene was filmed on a constructed set at the Bow River in Canmore, Alberta, nowhere near the Arctic Ocean. Lemmings are not native to the area where they filmed, so they imported them from Churchill after being purchased from Inuit children for 25 cents each. To give the illusion of a mass migration, they installed a rotating turntable and filmed the few lemmings they had from multiple angles over and over again. As it turns out, the lemming species filmed (collared lemmings) are not even known to migrate (unlike some Norwegian lemmings). Worst of all, the lemmings did not voluntarily leap into the water, but were pushed by the turntable and the film crew. Oh, Uncle Walt! How could you?!


Norway lemmings really do migrate en masse, but they don't commit mass suicide.
Drawing titled Lemmings in Migration, in Popular Science Monthly Volume 11, 1877.

As far as we know, there are no species that purposely hurl themselves off cliffs to die en masse for migration. But, strangely enough, North Pacific salmon do purposely hurl themselves up cliffs to die en masse for migration. And what, you may ask, is worth such a sacrifice? Sex, of course!


Migrating sockeye salmon thinking about sex.
Photo from Wikimedia Commons by Joe Mabel.

The six common North Pacific salmon species are all anadromous (meaning that they are born in fresh water, spend most of their lives in the sea and return to fresh water to breed) and semelparous (meaning they only have a single reproductive event before they die). After years at sea, salmon swim sometimes thousands of miles to get to the mouth of the very same stream in which they were born. Exactly how they do this is still a mystery. Once they enter their stream, they stop eating and their stomach even begins to disintegrate to leave room for the developing eggs or sperm. Their bodies change in other ways as well, both for reproduction and to help them adapt to fresh water. They then swim upstream, sometimes thousands of miles more, and sometimes having to leap over multiple waterfalls, using up their precious energy reserves. Only the most athletic individuals even survive the journey. Once they reach the breeding grounds, the males immediately start to fight each other over breeding territories. The females arrive and begin to dig a shallow nest (called a redd) in which she releases a few thousand eggs, which are then fertilized by the male. They then move on, and if they have energy and gametes left, repeat the process with other mates, until they are completely spent. If the females have any energy left after laying all their eggs, they spend it guarding their nests. Having spent the last of their energy, they die and are washed up onto the banks of the stream.

Now that’s parental commitment! So the next time your parents start laying on the guilt about everything they’ve given up for you, share this nugget with them and remind them it could be worse…


Want to know more? Check these out:

1. Learn more about semelparity here

2. Learn more about salmon reproduction at Marine Science

3. And learn even more about salmon reproduction with this awesome post by science blogger and Aquatic and Fishery Sciences graduate student, Iris. Her current blog posts can be found here.

4. Ramsden E, & Wilson D (2010). The nature of suicide: science and the self-destructive animal. Endeavour, 34 (1), 21-4 PMID: 20144484

The Love Chemical of 2018

Hello and welcome to the Love Chemical Pageant Results Show! The voting results are in, and today we get to crown the Love Chemical of 2018… Vasopressin! Now let’s get to know Vasopressin a little bit better.

Vasopressin (also known as Antidiuretic Hormone) is a molecule that is widely involved in the balance of water and ions (such as salts) in mammals. (Other taxonomic groups have variations of it as well). But this chemical has gone to our heads, influencing behavior as well.

In the brain, vasopressin acts on a specific receptor type, called vasopressin 1a receptor (V1aR). There are lots of V1aR receptors in brain areas that regulate social and emotional behaviors. When vasopressin binds to many of these receptors, it can result in aggression, territoriality, and fight-or-flight responses. It is also involved in the formation of memories that are necessary to avoid danger. Interestingly, males and females usually have different patterns of where in the brain these V1aR receptors are.

Although we often think of love and aggression as opposites, the life-preserving roles of vasopressin have made it well-suited to become an important chemical of love. In animals, pair bonding (the formation of a strong and unique connection between mates of a socially monogamous species) is often accompanied by an increase in aggression towards non-mates. This aggression can serve to protect the mate and family, but also to reject competitive suitors towards either partner.

Photo of a prairie vole pair from Young, Gobrogge, Liu and Wang paper
in Frontiers in Neuroendocrinology (2011)

Researchers often use several closely-related vole species to study how the brain regulates pair bonding; While prairie voles and pine voles are monogamous, raise their offspring with their partners, and defend their homes and families, montane voles and meadow voles are promiscuous and females raise their young by themselves. Oddly, giving monogamous vole species vasopressin increases their preference for spending time with their mate, their parental behaviors, and their selective aggression against outsiders, but giving promiscuous vole species vasopressin does not. Vasopressin is also more likely to increase these monogamous behaviors in males more than in females. Both males and females respond differently to vasopressin depending on their reproductive status.

It turns out, the pattern of V1aR receptors in the brain is similar between the monogamous prairie and pine voles, but different from the promiscuous montane and meadow voles. Genetic factors drive this difference, and if you alter the gene for the V1aR of a promiscuous species to be more like the prairie vole’s version of the gene, the previously promiscuous species behaves in a monogamous way! The reason promiscuous vole species don’t behave in a monogamous way when given vasopressin is because they don’t naturally have the V1aR receptors in certain brain regions to respond to it that way.

We are still learning about the role of vasopressin in pair bonding behaviors. Much of what we know has focused on these vole species, and we know much less about vasopressin’s involvement in pair bonding in other species. We also don’t know as much about the role of vasopressin in females across different reproductive stages. But one thing is for sure: Love wouldn’t be the same without Vasopressin!


Want to know more? Check these out:
Carter, C.S. (2017). The Oxytocin–vasopressin Pathway in the Context of Love and Fear. Frontiers in Endocrinology, 8(356): 1-12.

Phelps, S.M., Okhovat, M. and Berrio, A. (2017). Individual Differences in Social Behavior and Cortical Vasopressin Receptor: Genetics, Epigenetics, and Evolution. Frontiers in Endocrinology, 8(537): 1-12.

Tickerhoof, M.C. and Smith, A.S. (2017). Vasopressinergic Neurocircuitry Regulating Social Attachment in a Monogamous Species. Frontiers in Endocrinology, 8(265): 1-10.

The Love Chemical Pageant of 2018

A modified repost of an original article from February 15, 2012.

Hello and welcome to the Love Chemical Pageant of 2018! I’m your host, Miss Behavior, and YOU are the judges.

Since the beginning of…well, social animals, many hormones and neurotransmitters have been quietly working in their own ways to fill our world with love. Lately (over the last few decades), some of them have been brought out of the background and into the limelight, credited with every crush, passionate longing, parental hug, embrace among friends, and cuddle between spouses. But who truly deserves the title of The Love Chemical?

Let’s meet our contestants!

Let’s first meet our reining title-holder, Dopamine! Dopamine is a neurotransmitter produced in the brain. Sex increases dopamine levels in both males and females and blocking its effects during sex can prevent prairie voles (a monogamous species often used to test questions on pair bonding) from forming preferences for their own partner. Dopamine also plays a role in maternal and paternal behaviors.

But dopamine is not just involved in love. It has a wide range of known functions in the brain, involved in everything from voluntary movement, mood, motivation, punishment and reward, cognition, memory, learning, aggression, pain perception and sleep. Abnormally high levels of dopamine have been linked to schizophrenia and psychosis. And dopamine is especially well-known for its role in addiction... in fact, many researchers believe that we may even be addicted to our own romantic partners.

Now let’s meet Dopamine’s partner, Opioids! When natural opioids are released in the brain, they can cause a rewarding feeling that often cause us to seek more of it. When prairie voles are given drugs that prevent opioids from acting on a particular opioid receptor type (mu-opioid receptors) in a particular brain region (the caudate-putamen), they do not form pair bonds with sexual partners. Interestingly, people that see the faces of their loved ones experience lots of activity in the caudate-putamen region of the brain, especially if they rate their relationship with that person as very romantic and passionate. The caudate-putamen region of the brain also uses dopamine, so the two chemicals appear to work together there to promote the feelings of romantic love.

Please welcome Oxytocin! Oxytocin is a peptide hormone, most of which is made in the brain. Some of this oxytocin is released into the blood and affects body organs, such as the uterus and cervix during child birth and the mammary glands during breast feeding. But some of it stays in the brain and spinal cord, acting on neurons with oxytocin receptors to affect a number of behaviors. Released during child birth and nursing, oxytocin is important for helping mammalian mothers behave like moms and in species in which both parents raise young, it helps fathers behave like dads. Also released during sex, oxytocin plays an important role in pair bonding in prairie voles (particularly in the female of the pair). In humans, people given oxytocin nasal sprays have been reported to have less fear, more financial trust in strangers, increased generosity, improved memory for faces, improved recognition of social cues, and increased empathy.

But before you fall head-over-heels for oxytocin, you should know a few more things. For one thing, oxytocin isn’t exclusively linked with feel-good emotions; It has also been associated with territoriality, aggressive defense of offspring, and forming racist associations. Also, oxytocin doesn’t work alone. It has been shown to interact with vasopressin, dopamine, adrenaline and corticosterone and all these interactions affect pair bonding.

Next up is Vasopressin! Vasopressin is closely related to oxytocin. Like oxytocin receptors, vasopressin receptors are expressed in different patterns in the brains of monogamous vole species compared to promiscuous vole species. Released during sex, vasopressin plays an important role in pair bonding in monogamous prairie voles (particularly in the male of the pair). If you block vasopressin in the brain of a paired male prairie vole, he will be more likely to prefer spending time around a new female rather than his mate. On the flip side, if you increase vasopressin activity in specific brain regions of an unpaired male prairie vole or even a promiscuous male meadow vole and introduce him to a female, he will prefer spending time with her than other females. Vasopressin may also make male prairie voles more paternal.

But vasopressin does a lot of things. In the body, its primary function is to regulate water retention. In the brain, it plays a role in memory formation and territorial aggression. And even its role in monogamy is not exclusive: Vasopressin interacts with oxytocin and testosterone when working to regulate pair bonding and parental behavior.

Look out for Cortisol! Cortisol is produced by the adrenal glands (on top of the kidneys) and is involved in stress responses in humans and primates. Both men and women have increased cortisol levels when they report that they have recently fallen in love. Many studies have also found relationships between cortisol and maternal behavior in primates, but sometimes they show that cortisol increases maternal behavior and sometimes it prevents it. In rodents, where corticosterone is similar to cortisol, the story is also not very clear. Corticosterone appears to be necessary for male prairie voles to form pair bonds and it plays a role in maintaining pair bonds and promoting paternal behavior. But in female prairie voles, the opposite seems to be true! Corticosterone in females appears to prevent preference for spending time with their partner and pair bond formation.

Put your hands together for Testosterone! Testosterone is a steroid hormone and is primarily secreted from the gonads (testes in males and ovaries in females). Frequently referred to as “the male hormone”, both males and females have it and use it, although maybe a little differently. Testosterone is associated with sex drive in both men and women. But men who have recently fallen in love have lower testosterone levels than do single males, whereas women who have recently fallen in love have higher testosterone than single gals.

This is Estrogen! Estrogen is another steroid hormone, frequently referred to as “the female hormone”, although again, both males and females have it. Estrogen also seems to play a role in sex drive in both men and women. The combination of high estrogen levels and dropping progesterone levels (another steroid hormone) is critical for the development of maternal behavior in primates, sheep and rodents. But look closer and you will find that the activation of estrogen receptors in particular brain regions is associated with less sexual receptivity, parental behavior, and the preference for spending time with the mate.

So let’s have a round of applause for this year’s contenders in The Love Chemical Pageant! Now it is your turn to voice your opinion in the comments section below. Vote for the neurochemical you believe deserves the title The Love Chemical. Or suggest an alternative pageant result!


Want to know more? Check these out:

Burkett, J.P. and Young, L.J. (2012). The behavioral, anatomical and pharmacological parallels between social attachment, love and addiction. Psychopharmacology, 224:1-26.

Fisher, H.E. (1998). Lust, attraction, and attachment in mammalian reproduction. Human Nature, 9(1) 23-52.

Marazziti, D. and Canale, D. (2004). Hormonal changes when falling in love. Psychoneuroendocrinology, 29, 931-936.

Van Anders, S.M. and Watson, N.V. (2006). Social neuroendocrinology: Effects of social contexts and behaviors on sex steroids in humans. Human Nature, 17(2), 212-237.

Young, K.A., Gobrogge, K.L., Liu, Y. and Wang, Z. (2011). The neurobiology of pair bonding: Insights from a socially monogamous rodent. Frontiers in Neuroendocrinology, 32(2011), 53-69.

The Complexities of “The Love Hormone”

New York street art. Photo in
Wikimedia Commons posted by Pedroalmovar.

Oxytocin, commonly known as “the love hormone”, is a small chemical that is produced in the brain of mammals, but can both act as a neurotransmitter and enter the blood stream and act as a hormone. It has long been heralded for its role in both maternal and romantic love, but more recent research is showing us just how complicated the physiology of love can be.

Oxytocin is released in mammalian mothers after birth. It promotes nursing and bonding between a mother and her young. As children grow, oxytocin is involved in how both mothers and fathers “baby-talk” and mirror their children. It is involved in pro-social behaviors in both young and adults: trust, generosity, cooperation, hugging, and empathy. And of course, oxytocin promotes positive communication and pair bonding in romantic couples. Countless studies have found these relationships between affiliation and oxytocin in many mammalian species, giving oxytocin its commonly used nickname “the love hormone”.

But more recent studies show that it’s not so simple.

In a number of recent studies, people have been given oxytocin nasal sprays and tested for various behavioral effects in different contexts… and the context really seems to matter. Oxytocin increases trust, generosity, cooperation, and empathy towards people we already know and like. But it decreases trust, generosity, cooperation, and empathy towards strangers. When we play games with strangers, oxytocin makes us more jealous when we lose and it makes us gloat more when we win. It also seems to enhance many attributes relating to ethnocentrism: It increases our ability to read facially-expressed emotions in people of our own race while making it harder to read facial expressions of people of a different race. When forced to choose between being nice to a stranger of our own race versus a stranger of another race, oxytocin makes us more likely to choose the person of our own race. In studies of both people and rodents, oxytocin decreases aggression towards our families and friends, but increases aggression towards strangers.

Oxytocin is not the universal love hormone we once understood it to be. It helps us direct our positive support towards our “in-groups” (our family and friends) and defend them from our “out-groups” (individuals we don’t know). It is a delicate balance: Too little of it can cause social impairment and make it difficult to connect with loved-ones; Too much of it can increase our anxiety towards strangers and racist tendencies. And to make things more complicated, each of us has a slightly different oxytocin system: sex, gender, social history, history of childhood trauma or neglect, psychiatric illnesses and genetic variations all have profound effects on the oxytocin system.

There is much we don’t know about the role of oxytocin and love. But they are a good fit, because both, it seems, are complicated.


Want to know more? Check these out:

Shamay-Tsoory SG, & Abu-Akel A (2016). The Social Salience Hypothesis of Oxytocin. Biological psychiatry, 79 (3), 194-202 PMID: 26321019

Zik JB, & Roberts DL (2015). The many faces of oxytocin: implications for psychiatry. Psychiatry research, 226 (1), 31-7 PMID: 25619431

Nature Shapes Faithful and Unfaithful Brains

Among monogamous animals, some individuals are more faithful than others. Could these differences in fidelity be, in part, because of differences in our brains? And if so, why does this diversity in brain and behavior exist?

A snuggly prairie vole family. Photo from theNerdPatrol at Wikimedia Commons.

Prairie voles are small North American rodents that form monogamous pair bonds, share parental duties, and defend their homes. Although prairie voles form monogamous pairs, that does not mean they are sexually exclusive. About a quarter of prairie vole pups are conceived outside of their parents’ union.

Not all male prairie voles cheat on their partners at the same rates. In fact, some males are very sexually faithful. It turns out, there are both costs and benefits to being faithful and to cheating. Mariam Okhovat, Alejandro Berrio, Gerard Wallace, and Steve Phelps from the University of Texas at Austin, and Alex Ophir from Cornell University used radio-telemetry to track male prairie voles for several weeks to explore what some of these costs and benefits might be. Compared to males that only sired offspring with their own partner, unfaithful males had larger home ranges, intruded on more territories of other individuals, and encountered females more often. However, these unfaithful males were also more likely to be cheated on when they were away (probably because they were away more). I guess even rodents live by The Golden Rule.

Maps of how paired male voles in this study used space. The solid red/orange/yellow peaks show where a faithful male (in the left map) and unfaithful male (in the right map) spent their time in relation to where other paired males spent their time (showed by open blue peaks). Image from the Okhovat et al. Science paper (2015).

Vasopressin is a hormone that has been found to affect social behaviors such as aggression and pair bonding when it acts in the brain. Mariam, Alejandro, Gerard, Alex, and Steve all set out to determine how vasopressin in the brain may relate to sexual fidelity in prairie voles. They found that faithful males had lots of a particular type of vasopressin receptor (called V1aR) in certain brain areas involved in spatial memory. Surprisingly, faithful males did not have more V1aR in brain regions typically associated with pair bonding and aggression. A male that has more V1aR in spatial memory regions might better remember where his own mate is and where other males have been aggressive, which would decrease the chances that he would intrude on other territories in search of other females and increase the time that he spends home with his own mate. A male that has less V1aR in spatial memory regions might be less likely to learn from his negative experiences and more likely to sleep around.

Photos of a brain section from a faithful male (left) and unfaithful male (right). The dark shading shows the density of V1aR vasopressin receptors. The arrows show the location of the retrosplenial cortex (RSC), a brain area involved in spatial memory. Faithful males had significantly more V1aR receptors in the RSC compared to unfaithful males. Image from the Okhovat et al. Science paper (2015).

The research team then found genotype variations that related to having lots or not much V1aR in one of these spatial memory regions (called retrosplenial cortex … but we’ll just call it RSC). They confirmed these findings with a breeding study, in which they reared siblings that were genetically similar, but some had the genotype they predicted would result in lots of V1aR in RSC and some had the genotype they predicted would result in very little V1aR in RSC. They confirmed that these genetic variations correspond with the amount of vasopressin receptor in this specific spatial memory area.

The researchers then looked closer at the different versions of this vasopressin receptor gene in the RSC brain region to see if differences in the amount of vasopressin receptors in RSC may be caused by the epigenetic state of the gene (i.e. how active the gene is). They found that the genotype that results in very little V1aR in RSC had many more potential methylation sites, which can repress gene activity.

All of this data together tells a very interesting story. Male prairie voles that have the genotype for more V1aR vasopressin receptors in their RSC part of their brain are more likely to remember where their home and mate are and to remember where other aggressive prairie voles are, which will make them more likely to spend more time with their partner, to be sexually faithful and to have sexually faithful partners. Male prairie voles that have the genotype for less V1aR in their RSC are more likely to forget where their home and mate are and where other aggressive prairie voles are, which will make them more likely to cheat and to be cheated on. Overall, faithful and unfaithful male prairie voles have roughly the same number of offspring, but advantages may emerge with changes in population density. Prairie vole populations vary anywhere from 25 to 600 voles per hectare from year to year. When population densities are high, you (and your partner) are more likely to encounter more potential mates and it may benefit you to cheat (and have a “cheater’s brain”). When population densities are low, you (and your partner) are less likely to encounter more potential mates and it may benefit you to be faithful (and have a “faithful brain”). But when populations fluctuate between high and low densities, both faithful and unfaithful genotypes will get passed along from generation to generation.


Want to know more? Check this out:

Okhovat, M., Berrio, A., Wallace, G., Ophir, A., & Phelps, S. (2015). Sexual fidelity trade-offs promote regulatory variation in the prairie vole brain Science, 350 (6266), 1371-1374 DOI: 10.1126/science.aac5791

Cow Pies Can Make You Smarter and Less Stressed

A reposting of an article from August, 2015

It seems like everyone is running around buying school supplies and books, registering for classes, and fretting about how hard it is going to be to learn another whole year’s worth of stuff. The secret to success, it turns out, may lie in cow dung.

A cow pie. Photo taken by Jeff Vanuga at
the USDA available at Wikimedia Commons.

Recent research has highlighted the important role that microbes living in animal digestive tracts have on host animals’ health and behavior. This influence of our gut microbes on our behavior is called the microbiota-gut-brain axis. Many of these microbes have long-standing populations that reproduce and spend their whole lives in our guts. Because our digestive tracts do not have much oxygen, these species are anaerobic (do not require oxygen to live). However, our gut communities also have more transient aerobic members (species that do require oxygen to live) that come in when they are ingested and die or leave with the droppings. One of these transient aerobic intestinal citizens is Mycobacterium vaccae (or M. vaccae for short), an aerobic bacterium that naturally lives in soil, water, and yes, cow dung.

When mice are injected with heat-killed M. vaccae, they develop an immune response that activates their brain serotonin system and reduces signs of stress. Serotonin is a neurotransmitter that is found in the brain and is involved in regulating alertness, mood, learning and memory. In fact, many antidepressant drugs work by increasing the amount of available serotonin in the brain. Interestingly, serotonin is also found in the digestive system, where it plays a role in digestive health. Since M. vaccae can increase serotonin function, and serotonin reduces anxiety and improves learning, researchers Dorothy Matthews and Susan Jenks at The Sage Colleges in New York set out to test whether eating live M. vaccae could reduce anxiety and improve learning in mice.

A drawing of the mouse maze used by Dorothy and Susan.
This image is from their 2013 Behavioural Processes paper.

The researchers developed a Plexiglas mouse-maze with three difficulty levels, where each increase in difficulty was marked by more turns and a longer path. They encouraged the mice to run the maze by placing a tasty treat (a square of peanut butter on Wonder Bread™) at the end of the maze. Half of the mice were given live M. vaccae on the peanut butter and bread treat three weeks and one week before running the maze, and then again on each treat at the end of each maze run. The other half were given peanut butter and bread without the bacterial additive. The mice then ran the maze roughly every other day: four times at level 1, four times at level 2 and four times at level 3. Each maze run was video recorded and the researchers later watched the videos to count stress-related behaviors.

The mice that ingested M. vaccae on their peanut butter sandwiches completed the maze twice as fast as those that ate plain peanut butter sandwiches. They also had fewer stress-related behaviors, particularly at the first difficulty level of the maze when everything was new and scary. In general, the fewer stress behaviors a mouse did, the faster its maze-running time was. The mice that ate the M. vaccae also tended to make fewer mistakes.

The researchers then wanted to know how long the effects of M. vaccae lasted. They continued to test the mice in the same maze, again with four runs at level 1, four runs at level 2 and four runs at level 3, but for these maze runs no one was given the M. vaccae. The mice that had previously eaten the M. vaccae continued to complete the maze faster and with fewer mistakes and to show fewer stress-related behaviors for about the first week before the M. vaccae effects wore off.

What does this all mean? It means eating dirt isn’t all bad (although I don't recommend eating cow poop). Letting yourself get a bit dirty and ingesting some of nature's microbes could even help you learn better, remember more, and stay calm - especially in new situations. Just something to think about as the school year gets started.


Want to know more? Check these out:

1. Matthews, D., & Jenks, S. (2013). Ingestion of Mycobacterium vaccae decreases anxiety-related behavior and improves learning in mice Behavioural Processes, 96, 27-35 DOI: 10.1016/j.beproc.2013.02.007

2. Lowry, C., Hollis, J., de Vries, A., Pan, B., Brunet, L., Hunt, J., Paton, J., van Kampen, E., Knight, D., Evans, A., Rook, G., & Lightman, S. (2007). Identification of an immune-responsive mesolimbocortical serotonergic system: Potential role in regulation of emotional behavior Neuroscience, 146 (2), 756-772 DOI: 10.1016/j.neuroscience.2007.01.067

A Tiny Surprise in Regards to Regeneration (A Guest Post)

By Jessica Klein

The ability to regenerate limbs and tails is nothing new to reptiles and amphibians. Many lizards are able to drop their tails to escape an enemy, whereas salamanders have been known to grow back entire legs with muscle after being attacked by a predator. These regenerative characteristics have been seen to some extent in rabbits and pika before 2012, but were later discovered to occur extensively in, surprisingly enough, small African spiny mice.

One of the African spiny mouse species. Photo by Ashley Seifert and Tom Gawriluk.

In a study done by Ashley W. Seifert and Megan G. Seifert at the University of Kentucky, Todd M. Palmer and Malcolm Maden at the University of Florida, Stephen G. Kiama at the University of Nairobi, and Jacob R. Goheen at the University of Wyoming, African spiny mice were studied in order to view the extent of their regenerative properties, why they might occur, and the physiological processes that make it happen.

The rodents were captured in Kenya, where researchers learned that vigorous movement during handling caused the skin of African spiny mice to come apart. One mouse was reported to have an open wound that took up 60% of its back, just from being handled! Therefore, Dr. Seifert measured the amount of strength it took to tear the skin of spiny mice using something called a Hounsfield tensometer. He took the measurements from that tool and graphed them on a plot, creating something called a stress-strain curve which showed how much strength it took to tear the skin of the mouse.

The strength measurements revealed that the skin of these species was 77 times weaker than average mice, explaining why their skin tore so easily during the handling process. In order for the African spiny mice to survive such large injuries due to their extremely fragile skin, it would be beneficial to heal quickly or regenerate the skin. This is exactly what Dr. Seifert discovered.

An African spiny mouse shows
the regenerative process with
(1) being before the wound
(2) being after the wound and
(3) showing how the wound was
completely healed after 30 days.
Figure from Seifert, et al., 2012.

After the strength measurements were completed, the rodents were anaesthetized and had 4mm and 1.5cm wounds made on their skin, as well as 4mm holes punched in their ears in order to view the regeneration process. In an average rodent, the repair of a 4mm skin wound takes around 5 to 7 days and is accompanied by a significant amount of scarring. However, in the African spiny mouse it only took 1 to 2 days for scabbing of the skin wound to occur with new cells forming on the outside of the wound to repair it. After just 10 days, the ear of the mouse was fully healed. In the ear punches, there were no signs of scarring that would have been expected in a rodent, and healthy cartilage had formed. By the 21st day of the experiment, African spiny mice had developed new hair follicles and healthy new hair covering the once wounded area. In total, Dr. Seifert discovered that African spiny mice were capable of regenerating their skin, hair follicles, and sweat glands.

Dr. Seifert suggested the skin of African spiny mice is fragile because it allows them to escape predators. This would require a quick healing time to reduce the chance of infection and ultimately death in the mouse after escaping. This is why they may have gained the ability to regenerate their skin, but how exactly does this happen? Dr. Seifert and his research team recently showed that, in these species, it occurs through a process known as epimorphic regeneration. This is when a blastema (a mass of immature, unspecialized cells) forms where the wound once was. These cells are capable of turning into whatever type of tissue was present in that area. This particular method of regeneration is how salamanders are capable of regenerating their limbs. Again, more research would need to be done in order to confirm or deny this. However, one thing is true, and that is that more research into this could prove to be useful in the future of medicine when it comes to healing critical and invasive injuries. By discovering the physiological process behind this, and then being able to replicate it in a lab, researchers may discover ways to heal injuries faster.

Works Cited

Seifert, Ashley W., Stephen G. Kiama, Megan G. Seifert, Jacob R. Goheen, Todd M. Palmer, and Malcolm Maden. "Skin Shedding and Tissue Regeneration in African Spiny Mice (Acomys)." Nature 489 (2012): 561-65. doi:10.1038/nature11499

Gawriluk, Thomas R., Jennifer Simkin, Katherine L. Thompson, Shishir K. Biswas, Zak Clare-Salzler, John M. Kimani, Stephen G. Kiama, Jeramiah J. Smith, Vanessa O. Ezenwa & Ashley W. Seifert. "Comparative analysis of ear-hole closure identifies epimorphic regeneration as a discrete trait in mammals" Nature Communications 7.11164 (2016). doi:10.1038/ncomms11164

A True Underdog…or Undermouse (A Guest Post)

By Spencer Henkel

People love a good underdog story, and nowhere is that image more embodied than in the rodents that live in deserts. In the desert there are two main problems that animals must face: it is way too hot and way too dry. You would think that rodents, the smallest of mammals, would not have much difficulty surviving in this kind of habitat. You might think that they would need far less food and water than their larger neighbors like reptiles and birds. Unfortunately, this is not the case; in fact, rodents’ small size actually makes life harder for them in such harsh conditions. Rodents gain and lose body heat faster through surface exchange with their environment, their highly active lifestyle requires a lot of food and a high metabolism, which generates a lot of extra heat that must be dispersed, and the distance they can travel to find food and water is extremely limited. Desert rodents must find ways to deal with all these issues, a tremendous feat for such tiny creatures.


Photo of a Golden Spiny Mouse (Acomys russatus) in Israel
by Mickey Samuni-Blank at Wikimedia Commons.

The most pressing concern of any animal that lives in the desert is making sure its body has enough water to carry it through the day. Needless to say, water can be hard to come by in such arid lands, and what water is present is usually found in seeds, tubers, and other plant material. Rodents will find and take in this water, but they face another problem: the contents of their diet are very salty. The rodents must now find a way to get rid of this excess salt while still holding onto a fair amount of water, for they cannot afford to simply excrete a steady stream of urine like we can. They must call upon a chemical from their brain, vasopressin, to help them out with this process. Vasopressin is an antidiuretic hormone, what I like to call an “anti-makes-you-pee”. It is made in the hypothalamus part of the brain, and when called upon it exits the pituitary gland and travels by blood to the kidneys. Once there, vasopressin causes the tiny blood vessels in the kidneys to clench up, slowing the flow of blood and increasing the time water has to be reabsorbed before urine is produced. When Nature eventually does call, the rodents will have made a small amount of urine that rids them of a whole lot of salt.

Now the rodents must turn to the other issue at hand: keeping cool. Water plays an active role in cooling an animal’s body by evaporation through sweating, panting, urinating, and defecating. Unfortunately, as with the salt in their diet, rodents can’t afford to lose all that water if they want their insides to keep functioning. So instead, rodents will lower their metabolisms. This reduces the amount of heat generated inside the body, so their core temperatures will decrease. A lower metabolism will also reduce the amount of water the rodents need to cool themselves down. However, if this process keeps up, the animal could die of hypothermia, ironically. So to keep that from happening, these rodents increase the amount of heat generated by their brown fat, masses of fat found primarily in animals that hibernate. This tissue will keep the animal’s core body temperature stable even when their metabolism slows way down.

In spite of their size, rodents actually have a rather tough time surviving in the desert. Yet they have found efficient ways of dealing with such extreme challenges. They can conserve enough water to live while still filtering out a great deal of salt, and they can slow down their own heat production while maintaining stable body temperatures. It is indeed quite a feat when the smallest of mammals succeeds in living in one of the harshest places on earth!

Sources Cited

SCHWIMMER, H., & HAIM, A. (2009). Physiological adaptations of small mammals to desert ecosystems Integrative Zoology, 4 (4), 357-366 DOI: 10.1111/j.1749-4877.2009.00176.x

This Animal Looks Like a Penis With Teeth... But It's Even Stranger Than That

This is a naked mole rat.

Yes, this is arguably the freakiest-looking animal on Earth.
Photo by Roman Klementschitz at Wikimedia Commons.

Naked mole rats are rodents that live in underground tunnels under East African savannas and grasslands. There's nothing all that strange about that... but how they have adapted to this lifestyle is unique... and, quite frankly, amazing.

For one thing, to cope with the low oxygen levels of the subterranean environment, naked mole rats have very low metabolisms and breathing rates. One of the biggest uses of metabolic engines in mammals is to produce our own body heat. These little guys have cut this big expenditure by being what may be the only ectothermic mammals on the planet. Ectotherms are animals like most fish, amphibians and reptiles that get most of their body heat from their environment, rather than making it themselves. Because naked mole rats want to exchange heat with their environment, they want to eliminate insulation... giving them their hairless and fatless bodies. Now when they bask in the sun at their tunnel entrances or huddle with their family they can take in all that warmth without anything getting in the way.

There are some benefits to having low metabolisms and not using much oxygen: Naked mole rats live for nearly 30 years (compared to 1-3 years in regular rats). Oxygen creates free radicals, highly reactive chemicals that cause damage to DNA, leading to a wide range of diseases. Naked mole rats don't just use less oxygen, but they have special proteins that are resistant to these damaging chemicals. They also produce a specialized super-sugar that has essentially eliminated cancer in this long-living species. What's more, these elderly rodents have managed to avoid dementia and osteoporosis, traits we hope to learn more about through ongoing research.

Naked mole rats have also developed some unique sensory traits. Living with your entire extended family in underground burrows means that you live in high levels of carbon dioxide and walls saturated in pee. These little guys don't even have any body hair to protect their pink skin from all that burning ammonia. Their solution: get rid of pain. These guys have no pain receptors for noxious chemicals like acids or capsaicin (the stuff that makes hot peppers hot). Furthermore, they are lacking a specific neurotransmitter, called substance P, that other mammals use to send many pain signals. Since naked mole rats have less need for sensation in their skin, they have developed brains that have repurposed about 30% of the sematosensory cortex (the part of the brain that interprets touch sensations) to their digging teeth!

Perhaps the strangest quality of all for these animals is their behavior. Naked mole rats are one of only two known mammals that are eusocial (the other being the Damaraland mole rat). Eusociality is a social organization common among bees, wasps, ants and termites, in which the colony has castes that include queens, workers and soldiers. Among naked mole rats, there is a single queen in the colony that mates with a few dominant males; workers that dig the tunnels, gather food, and care for the young; and soldiers that protect the colony from predators. Workers and soldiers are all reproductively sterile with undeveloped gonads and low hormone levels. However, if the queen dies, one of the non-reproducing females will go through puberty and take on her role as the new queen.

Now that you know that naked mole rats are so much more than just a "freaky thing", enjoy this naked mole rat rap (or maybe even a whole episode of Disney's Kim Possible, which features Rufus, the naked mole rat):