Immigrants, they get the job done — eventually. Among dwarf mongooses, it takes newcomers a bit to settle into a pack. But once these immigrants become established residents, everyone in the pack profits, researchers from the University of Bristol in England report online December 4 in Current Biology.
Dwarf mongooses (Helogale parvula) live in groups of around 10, with a pecking order. The alphas — a top male and female — get breeding priority, while the others help with such group activities as babysitting and guard duty. But the road to the top of the social hierarchy is linear and sometimes crowded. So some individuals skip out on the group they were born into to find one with fewer members of their sex with which to compete —“effectively ‘skipping the queue,’” says ecologist Julie Kern. Kern and her colleague Andrew Radford tracked mongoose immigration among nine packs at Sorabi Rock Lodge Reserve in Limpopo, South Africa. The researchers focused on guard duty, in which sentinels watch for predators and warn foragers digging for food.
Dwarf mongoose packs gain about one member a year. Among pack animals, higher group numbers are thought to come with the benefit of better access to shared social information like the approach of prowling predators. But upon arrival, new individuals are less likely to pitch in and serve as sentinels, Kern and Radford found. One possible reason: Immigrants lose weight during their transition from one pack to another and may not have the energy required for guard duty. Pack residents don’t exactly put out a welcome mat for strangers, either. On the rare occasions when newcomers take a guard shift, residents tend to ignore their warning calls. Newbies may be seen as less reliable guards, or packs may have signature alarm calls that immigrants must learn. But after five months, these immigrants have come far. “Given time to recuperate following dispersal and a period of integration,” Kern says, “they contribute equally to their new group.”
Science came out of the lab and touched people’s lives in some awe-inspiring and alarming ways in 2017. Science enthusiasts gathered to celebrate a total solar eclipse, but also to march on behalf of evidence-based policy making. Meanwhile, deadly natural disasters revealed the strengths and limitations of science. Here’s a closer look at some of the top science events of the year.
Great American Eclipse On August 21, many Americans witnessed their first total solar eclipse, dubbed the “Great American Eclipse.” Its path of totality stretched across the United States, passing through 14 states — with other states seeing a partial eclipse. This was the first total solar eclipse visible from the mainland United States since 1979, and the first to pass from coast to coast since 1918 (SN: 8/20/16, p. 14). As people donned protective glasses to watch, scientists used telescopes, spectrometers, radio receivers and even cameras aboard balloons and research jets in hopes of answering lingering questions about the sun, Earth’s atmosphere and the solar system. One of the biggest: Why is the solar atmosphere so much hotter than the sun’s surface (SN Online: 8/20/17)? Data collected during the event may soon provide new insights.
March for Science On April 22, Earth Day, more than 1 million people in over 600 cities around the world marched to defend science’s role in society. Called the first-ever March for Science, the main event was in Washington, D.C. Featured speakers included Denis Hayes, coordinator of the first Earth Day in 1970, and science advocate Bill Nye (SN Online: 4/22/17). Attendees advocated for government funding for scientific research and acceptance of the scientific evidence on climate change.
The march came on the heels of the Trump administration’s first budget proposal, released in March, which called for cutting federal science spending in fiscal year 2018 (SN: 4/15/17, p. 15). Some scientists worried that being involved with the march painted science in a partisan light, but others said science has always been political since scientists are people with their own values and opinions (SN Online: 4/19/17).
Climate deal announcement On June 1, President Donald Trump announced that the United States would pull out of the Paris climate accord (SN Online: 6/1/17) — an agreement the United States and nearly 200 other countries signed in 2015 pledging to curb greenhouse gas emissions to combat global warming. With the announcement, Trump made good on one of his campaign promises. He said during a news conference that the agreement “is less about the climate and more about other countries gaining a financial advantage over the United States.”
Nicaragua and Syria signed on to the agreement in late 2017. A withdrawal from the United States would leave it as the only United Nations–recognized country to reject the global pact. President Trump left the door open for the United States to stay in the climate deal under revised terms. A U.S. climate assessment released in November by 13 federal agencies said it is “extremely likely” that humans are driving warming on Earth (SN Online: 11/3/17). Whether that report — the final version of which is due to be released in 2018 — will have an impact on U.S. involvement in the global accord remains to be seen.
North Korea nuclear test On September 3, North Korea reported testing a hydrogen bomb, its sixth confirmed nuclear detonation, within a mountain at Punggye-ri. That test, along with the launch of intercontinental ballistic missiles this year, increased hostilities between North Korea and other nations, raising fears of nuclear war. As a result of these tests, the United Nations Security Council passed a resolution strengthening sanctions against North Korea to discourage the country from more nuclear testing.
As the international community waits to see what’s next, scientists continue to study the seismic waves that result from underground explosions in North Korea. These studies can help reveal the location, depth and strength of a blast (SN: 8/5/17, p. 18).
Natural disasters The 2017 Atlantic hurricane season saw hurricanes Harvey, Irma and Maria devastate areas of Texas, Florida and the Caribbean. More than 200 people died from these three massive storms, and preliminary estimates of damage are as high as hundreds of billions of dollars. The National Oceanic and Atmospheric Administration had predicted that the 2017 season could be extreme, thanks to above-normal sea surface temperatures. The storms offered scientists an opportunity to test new technologies that might save lives by improving forecasting (SN Online: 9/21/17) and by determining the severity of flooding in affected regions (SN Online: 9/12/17).
In addition to these deadly storms, two major earthquakes rocked Mexico in September, killing more than 400 people. More than 500 died when a magnitude 7.3 earthquake shook Iran and Iraq in November. And wildfires raged across the western United States in late summer and fall. In California, fires spread quickly thanks to record summer heat and high winds. At least 40 people died and many more were hospitalized in California’s October fires. Rising global temperatures and worsening droughts are making wildfire seasons worldwide last longer on average than in the past, researchers have found (SN Online: 7/15/15).
Not so long ago, the lives of sea turtles were largely a mystery. From the time that hatchlings left the beaches where they were born to waddle into the ocean until females returned to lay their eggs, no one really knew where the turtles went or what they did.
Then researchers started attaching satellite trackers to young turtles. And that’s when scientists discovered that the turtles aren’t just passive ocean drifters; they actively swim at least some of the time. Now scientists have used tracking technology to get some clues about where South Atlantic loggerhead turtles go. And it turns out that those turtles are traveling to some unexpected places.
Katherine Mansfield, a marine scientist and turtle biologist at the University of Central Florida in Orlando, and colleagues put 19 solar-powered satellite tags on young (less than a year old), lab-reared loggerhead sea turtles. The turtles were then let loose into the ocean off the coast of Brazil at various times during the hatching season, between November 2011 and April 2012.
The tags get applied to the turtles in several steps. Turtle shells are made of keratin, like your fingernails, and this flakes off and changes shape as a turtle grows. Mansfield’s team had figured out, thanks to a handy tip from a manicurist, that a base layer of manicure acrylic deals with the flaking. And then some strips of neoprene along with aquarium silicone attach the tag to the shell. With all that prep, the tag can stay on for months. The tags transmit while a turtle is at the water’s surface. A loss of the signal indicates that either the tag has fallen off and sunken into the water, “or something ate the turtle,” Mansfield says. The trackers revealed that not all Brazilian loggerhead sea turtles stay in the South Atlantic. Turtles released in the early- to mid-hatching season stay in southern waters. But then the off-coast currents change direction, which brings later-season turtles north, across the equator. Their trajectories could take them as far as the Caribbean, the Gulf of Mexico or even farther north, which would explain genetic evidence of mixing between southern and northern loggerhead populations. And it may help to make the species, which is endangered, more resilient in the face of environmental and human threats, the researchers conclude December 6 in the Proceedings of the Royal Society B.
But, Mansfield cautions, “these are just a handful of satellite tracks for a handful of turtles off the coast of Brazil.” She and other scientists “are just starting to build a story” about what happens to these turtles out in the ocean. “There’s still so much we don’t know,” she says.
Mansfield hopes the tracking data will help researchers figure out where the young turtles can be found out in the open ocean so scientists can catch, tag and track wild turtles. And there’s a need for even tinier tags that can be attached to newly hatched turtles to see exactly where they go and how many actually survive those first vulnerable weeks and months at sea. Eventually, Mansfield would like to have enough data to make comparisons between sea turtle species.
“The more we’re tracking, the more we’re studying them, we’re starting to realize [the turtles] behave differently than we’ve historically assumed,” Mansfield says.
It’s like having “an elephant stand on your thumb.”
That’s how deep-sea physiologist and ecologist Mackenzie Gerringer describes the pressure squeezing down on the deepest known living fish, some 8 kilometers down. What may help these small, pale Mariana snailfish survive elephantine squashing, says Gerringer of the University of Washington’s Friday Harbor Labs, is a body bulked up, especially at the rump, with a watery goo.
The snailfish family gets its nickname from the way some shallow-water species in thundering tides grip a rock with a little suction cup on the belly and curl up. “Quite cute,” Gerringer says, and maybe, if you squint, somewhat like a snail. She and colleagues discovered the deepest fish in 2014 in the western Pacific Ocean’s Mariana Trench and described the newly named Psuedoliparis swirei November 28 in Zootaxa. To catch specimens, Gerringer and colleagues turned to extreme trapping. They weighted a boxy, mesh-sided trap with steel plates to sink it. It took about four hours to fall to the bottom.
The scientists baited traps with mackerel, which snailfish don’t eat. But the fish do eat the underwater amphipods that mob a mackerel feast. Remotely related to harmless garden pill bugs, trench amphipods clean mackerel to the bones, Gerringer says. “I certainly wouldn’t swallow a live amphipod after seeing what they can do.” A snailfish, however, has a second set of jaws at the back of its throat that render crustaceans safe to swallow.
Story continues below image For animals that live in such extreme pressures and temperatures (1° or 2° Celsius), snailfish don’t “look very robust … or very armored,” she says. “You can actually see the brain through the skull.”
Skimping on dense muscles and bones may improve snailfish buoyancy and save energy. These fish also lack air pockets that give a little lift to some other fishes, but that would get squashed to nothing so far down. Instead, the snailfish have inner deposits of a watery goo, more buoyant than muscles and bones and less compressible than air.
The goo also may aid swimming efficiency by offering a cheap shape improvement, Gerringer and colleagues proposed December 6 in Royal Society Open Science. To test the idea, she 3-D printed and motorized a robo-snailfish. Easier than catching a real one, Gerringer says.
A latex sleeve around the robot tail let her add or subtract water as an approximation of the gelatinous tissue. With an empty sleeve, the wide fish body pinches in to a thin tail, inviting vortices that cause drag. With this abrupt narrowing, robo-swimming proved a struggle. Filling the tail-sleeve to create a tapering rear let the robo-snailfish swim faster.
This goo is cheap tissue to grow, Gerringer says. It’s mostly water, one thing a fish living underneath eight kilometers of ocean has in abundance.
OXON HILL, Md. — Fast radio bursts could come from a turbulent home. At least one source of these bright, brief blasts of radio energy may be a young neutron star assisted by a nearby massive black hole, new research suggests.
“The biggest mystery around fast radio bursts is how such powerful and short-duration bursts are emitted,” says astronomer Daniele Michilli of the University of Amsterdam. The latest observations, reported online January 10 in Nature and at a meeting of the American Astronomical Society, suggest the bursts are coming from an environment with an unusually strong magnetic field. That field leaves a signature mark on the radio waves, twisting them into spirals, Michilli and his colleagues report. Only a few fast radio bursts have ever been detected, and most appear as one-off events. Few known processes in the universe can explain them. But one burst, FRB 121102, has been seen repeating over the past decade or so (SN Online: 12/21/16). That repetition let astronomers follow up on the burst, and track it to a dwarf galaxy some 2.5 billion light-years away (SN: 2/4/17, p. 10).
Now, Michilli and his colleagues have used the Arecibo radio telescope in Puerto Rico to show that the burst’s source is embedded in an extremely strong magnetic field, 200 times stronger than the average magnetic field in the Milky Way.
The team measured the radio waves from 16 distinct bursts over three two-hour observational runs spanning several months. The bursts were exceptionally brief, the shortest lasting just 30 microseconds. That means that whatever emitted it must be just 10 kilometers wide, Michilli says.
“To emit a short burst you need a small region,” he says. “Therefore compact objects such as neutron stars are strongly favored by this result.” The team also analyzed the radio waves in a new way, revealing that what looked like individual bursts were actually composed of many smaller sub-bursts, says astronomer Andrew Seymour of the Universities Space Research Association at Arecibo. That complicates the picture even further. The sub-bursts might be intrinsic to the object that creates them, or they might be the result of the waves passing through blobs of plasma, he says.
Finally, the observations showed that the waves were polarized, all oriented in the same direction. But something had twisted the waves, forcing them to rotate in corkscrews on their way from the dwarf galaxy to Earth. Follow-up observations with the Green Bank Telescope in West Virginia confirmed the twists were really there.
Story continues below image The only phenomenon that is known to create such a rotation is a strong magnetic field, Michilli says. There are two main hypotheses for the bursts’ behavior. One is that they are from a young, energetic neutron star called a magnetar that’s sitting inside a shell of magnetized gas, which the magnetar itself expelled in a supernova explosion. The magnetar emits radio waves, and the shell makes them rotate.
“If you have young magnetars that have just been born in supernova explosions, only a few decades old, they could be very bursty objects, have very violent youths, and that could give rise to repeating fast radio bursts,” says astronomer Brian Metzger of Columbia University, who was not involved in the new study.
But Michilli points out that in order to drive such strong magnetic fields, the supernova remnant would have to be a million times brighter than even the brightest remnant in the Milky Way, the Crab nebula (SN: 1/1/11, p. 11). Instead, the bursts could come from a young neutron star orbiting the dwarf galaxy’s dominant black hole, which probably has between 10,000 and 1 million times the mass of the sun, he says.
Such large black holes are already known to have strong magnetic fields and to make polarized light rotate. And a neutron star nestling up next to a black hole is a plausible setup: There’s one orbiting the supermassive black hole at the center of the Milky Way. Although this neutron star’s radio waves don’t come in brief bright bursts, they are also twisted, the researchers say.
If not for that neutron star, “this would seem very contrived to me,” Metzger says. “That combines two unlikely things.”
More exotic explanations remain possible, too, Michilli’s team says.
“The joke is there are far more theories than there are observed bursts,” said coauthor Jason Hessels of the University of Amsterdam in a news conference January 10. “In the coming weeks we expect that very creative theorists will come up with explanations for our observations we haven’t thought of yet.”
Questions remain about whether all fast radio bursts, including the ones that don’t repeat, come from such exciting neighborhoods. “We cannot say yet if there are two classes with different properties, or if it’s one class of fast radio bursts and they just happen to be seen in different configurations,” Michilli says.
It’s also still unknown whether any other bursts have twisted waves at high frequencies — the smoking gun for strong magnetic fields. Measuring the rotation of the waves in FRB 121102 required hacking Arecibo with new hardware that let it detect higher frequencies than before. “We weren’t able to do that until recently,” Seymour says. “I stayed up on Christmas evening [2016] and made these observations, and luckily it paid off.” Maybe other fast radio bursts that Arecibo observed didn’t show the same rotation signature because the telescope wasn’t ready to measure it yet.
Hessels thinks “the prospects are quite good” for figuring out what fast radio bursts are in the near future. Several new radio observatories around the world are due to come online in the next few years. “These are going to be FRB factories,” Hessels said. He expects to find other repeating bursts, if they exist. “Then we can see if this repeating source is really a complete oddball, or part of a distribution of sources.”
Lab-grade flight tracking has gone wild, creating a broad new way of studying some of the flashiest of natural acrobats, wild hummingbirds.
One of the findings: Bigger hummingbird species don’t seem handicapped by their size when it comes to agility. A battleship may not be as maneuverable as a kayak, but in a study of 25 species, larger hummingbirds outdid smaller species at revving or braking while turning. Measurements revealed these species have more muscle capacity and their wings tended to be proportionately larger for their body size than smaller species. Those boosts could help explain how these species could be so agile despite their size, researchers report in the Feb. 9 Science. Adapting a high-speed camera array and real-time tracking software to perform in field conditions let the researchers analyze more than 200 wild birds swerving and pivoting naturally. With over 330,000 bird maneuvers recorded, the researchers could compare the agility of the different species. It’s the first comparative study of natural flight moves in wild birds, says coauthor Roslyn Dakin, who is based in Ottawa with the Smithsonian Conservation Biology Institute.
“What makes this research a clear advance is the methods they used,” says Christopher J. Clark of the University of California, Riverside. His hummingbird studies have revealed how the birds’ feathers squeal during flight (SN: 4/4/15, p. 5), but he was not involved in the new research.
In the experimental setup, four cameras film a temporary flight chamber in the field. Customized computer software allows the team to track birds in 3-D as they explore the space in any way they choose. The project began almost a decade ago when coauthor Paolo Segre adapted and then hauled the flight-tracking system to Ecuador, Costa Rica and Peru — great places to find hummingbirds with different wing shapes and body sizes, but hard on equipment. At the time, he needed five computers, sometimes running just on solar panels and a generator in the Amazon. “We were in a thatched hut,” accessible only by several hours’ boat ride, he says. “Monkeys poked their heads in.” Since then, computers have improved, and one machine is enough to run the software.
The new paper uses some of this hard-won data to focus on two kinds of turning maneuvers — a simple flying arc and a pitch-and-roll move that Dakin calls “turning on a dime.” That involves the bird slanting its body and then pivoting in place.
Birds’ agility did not appear to be affected in field sites at higher elevations. In theory, less oxygen and lower air pressure should make athletic flying tougher. An earlier study by the same researchers found that Anna’s hummingbirds (Calypte anna) accelerated more slowly and had other performance falloffs at altitudes higher than the birds’ home range. Yet birds that call those higher elevations home had adapted to the conditions.
Studying how hummingbirds, or even birds in general, maneuver has been hard to do. Previous approaches to understanding bird motion were limited to capturing data on animals performing set tasks. “A ballerina has a number of different moves,” Clark says, but “so far we’ve just studied individual moves.” Now researchers are starting “to put together the entire dance.”
Fossilized footprints from an iguana-like reptile provide what could be the earliest evidence of a lizard running on two legs.
The 29 exceptionally well-preserved lizard tracks, found in a slab of rock from an abandoned quarry in Hadong County, South Korea, include back feet with curved digits and front feet with a slightly longer third digit. The back footprints outnumber the front ones, and digit impressions are more pronounced than those of the balls of the feet. The lizard’s stride length also increases across the slab. That’s what you’d expect to see in a transition from moseying along on four legs to scampering on two, says Yuong-Nam Lee, a paleontologist at Seoul National University who first came across the slab back in 2004. A closer examination two years ago revealed the telltale tracks.
Lee and his colleagues attribute the tracks to a previously unknown lizard ichnospecies, that is a species defined solely by trace evidence of its existence, rather than bones or tissue. Lee and his colleagues have dubbed the possible perpetrator Sauripes hadongensis and linked it to an order that includes today’s iguanas and chameleons in the Feb. 15 Scientific Reports. Bipedal running certainly would have come in handy when escaping predatory pterosaurs some 110 million to 128 million years ago, the age of the rock slab. Lizard tracks are pretty rare in the fossil record, due to the reptiles’ lightweight bodies and penchant for habitats that don’t make great fossils. Though tracks appear in older fossils from the Triassic Epoch, 200 million to 250 million years ago, those prints belong to more primitive lizardlike reptiles. The new find edges out another set from the same region as the oldest true lizard tracks in the world by a few million years, the researchers say. Plenty of modern lizards use two legs to scurry around. Some studies have linked similarities in ancient lizard bone structure to bipedal locomotion, but it is unclear exactly when lizards developed bipedalism. Lee’s team argues that these tracks represent the earliest and only direct evidence of bipedal running in an ancient lizard.
Martin Lockley, a paleontologist at the University of Colorado Denver who studies ancient animal tracks, points to alternative explanations. S. hadongensis might have trampled over front prints with its back feet, obscuring them and giving the appearance of two-legged running. Preservation can vary between back and front footprints. And the stride lengths aren’t quite as long as what Lockley says he’d expect to see in running. “Running or ‘leaping’ lizards make for a good story, but I am skeptical based on the evidence,” he adds.
So it may take the discovery of more fossilized lizard prints to determine whether S. hadongensis’ tracks truly represent running on two legs rather than simply scurrying on four.
Free-roaming Przewalski’s horses of Central Asia are often called the last of the wild horses, the only living equines never domesticated. But a new genetic analysis of ancient horse bones suggests that these horses have a tamed ancestor after all, making them feral rather than wild.
The findings also debunk the idea that these domesticated ancestors — known as Botai horses —gave rise to all other modern horses. That leaves the progenitors of today’s domesticated horses a mystery, researchers report online February 22 in Science.
The earliest known domesticated horses were those of the ancient Botai people in northern Kazakhstan (SN: 3/28/09, p. 15). Botai sites dating to around 5,500 years ago are scattered with remnants of harnesses and pots with horse-milk residue, suggesting the animals provided both transportation and food.
To see how Botai horses relate to today’s steeds, evolutionary geneticist Ludovic Orlando of the Natural History Museum of Denmark in Copenhagen and colleagues analyzed DNA from 88 horses spanning the last 5,000 years or so across Europe and Asia. Horses from the last 4,000 years had less than 3 percent Botai ancestry, suggesting that different and unknown horses founded today’s populations. But Botai horses are direct ancestors of Przewalski’s horses, the study found.
The moon might have formed from the filling during Earth’s jelly doughnut phase.
Around 4.5 billion years ago, something hit Earth, and the moon appeared shortly after. A new simulation of how the moon formed suggests it took shape in the midst of a hot cloud of rotating rock and vapor, which (in theory) forms when big planetary objects smash into each other at high speeds and energies. Planetary scientists Simon Lock of Harvard University and Sarah Stewart of the University of California, Davis proposed this doughnut-shaped planetary blob in 2017 and dubbed it a synestia (SN: 8/5/17, p. 5). Radiation at the surface of this swirling cloud of vaporized, mixed-together planet matter sent rocky rain inward toward bigger debris. The gooey seed of the moon grew from fragments in this hot, high-pressure environment, with a bit of iron solidifying into the lunar core. Some elements, such as potassium and sodium, remained aloft in vapor, accounting for their scarcity in moon rocks today.
After a few hundred years, the synestia shrank and cooled. Eventually, a nearly full-grown moon emerged from the cloud and condensed. While Earth ended up with most of the synestia material, the moon spent enough time in the doughnut filling to gain similar ingredients, Lock, Stewart and colleagues write February 28 in Journal of Geophysical Research: Planets . The simulation shakes up the prevailing explanation for the moon’s birth: A Mars-sized protoplanet called Theia collided with Earth, and the moon formed from distinct rubble pieces. If that’s true, moon rocks should have very different chemical compositions than Earth’s. But they don’t.
Other recent studies have wrestled with why rocks from the moon and Earth are so alike (SN: 4/15/17, p. 18). Having a synestia in the mix shifts the focus from the nature of the collision to what happened in its aftermath, potentially resolving the conundrum.
On the hormonal roller coaster of life, the ups and downs of childbirth are the Tower of Power. For nine long months, a woman’s body and brain absorb a slow upwelling of hormones, notably progesterone and estrogen. The ovaries and placenta produce these two chemicals in a gradual but relentless rise to support the developing fetus.
With the birth of a baby, and the immediate expulsion of the placenta, hormone levels plummet. No other physiological change comes close to this kind of free fall in both speed and intensity. For most women, the brain and body make a smooth landing, but more than 1 in 10 women in the United States may have trouble coping with the sudden crash. Those new mothers are left feeling depressed, isolated or anxious at a time society expects them to be deliriously happy. This has always been so. Mental struggles following childbirth have been recognized for as long as doctors have documented the experience of pregnancy. Hippocrates described a woman’s restlessness and insomnia after giving birth. In the 19th century, some doctors declared that mothers were suffering from “insanity of pregnancy” or “insanity of lactation.” Women were sent to mental hospitals.
Modern medicine recognizes psychiatric suffering in new mothers as an illness like any other, but the condition, known as postpartum depression, still bears stigma. Both depression and anxiety are thought to be woefully underdiagnosed in new mothers, given that many women are afraid to admit that a new baby is anything less than a bundle of joy. It’s not the feeling they expected when they were expecting.
Treatment — when offered — most commonly involves some combination of antidepression medication, hormone therapy, counseling and exercise. Still, a significant number of mothers find these options wanting. Untreated, postpartum depression can last for years, interfering with a mother’s ability to connect with and care for her baby.
Although postpartum depression entered official medical literature in the 1950s, decades have passed with few new options and little research. Even as brain imaging has become a common tool for looking at the innermost workings of the mind, its use to study postpartum depression has been sparse. A 2017 review in Trends in Neurosciences found only 17 human brain imaging studies of postpartum depression completed through 2016. For comparison, more than four times as many have been conducted on a problem called “internet gaming disorder” — an unofficial diagnosis acknowledged only five years ago. Now, however, more researchers are turning their attention to this long-neglected women’s health issue, peering into the brains of women to search for the root causes of the depression. At the same time, animal studies exploring the biochemistry of the postpartum brain are uncovering changes in neural circuitry and areas in need of repair.
And for the first time, researchers are testing an experimental drug designed specifically for postpartum depression. Early results have surprised even the scientists.
Women’s health experts hope that these recent developments signal a new era of research to help new moms who are hurting.
“I get this question all the time: Isn’t it just depression during the postpartum period? My answer is no,” says neuroscientist Benedetta Leuner of Ohio State University. “It’s occurring in the context of dramatic hormonal changes, and that has to be impacting the brain in a unique way. It occurs when you have an infant to care for. There’s no other time in a woman’s life when the stakes are quite as high.”
Brain drain Even though progesterone and estrogen changes create hormonal whiplash, pregnancy wouldn’t be possible without them. Progesterone, largely coming from the ovaries, helps orchestrate a woman’s monthly menstrual cycle. The hormone’s primary job is to help thicken the lining of the uterus so it will warmly welcome a fertilized egg. In months when conception doesn’t happen, progesterone levels fall and the uterine lining disintegrates. If a woman becomes pregnant, the fertilized egg implants in the uterine wall and progesterone production is eventually taken over by the placenta, which acts like an extra endocrine organ.
Like progesterone, estrogen is a normal part of the menstrual cycle that kicks into overdrive after conception. In addition to its usual duties in the female body, estrogen helps encourage the growth of the uterus and fetal development, particularly the formation of the hormone-producing endocrine system.
These surges in estrogen and progesterone, along with other physiological changes, are meant to support the fetus. But the hormones, or chemicals made from them, cross into the mother’s brain, which must constantly adapt. When it doesn’t, signs of trouble can appear even before childbirth, although they are often missed. Despite the name “postpartum,” about half of women who become ill are silently distressed in the later months of pregnancy.
Decades ago, controversy churned over whether postpartum depression was a consequence of fluctuating hormones alone or something else, says neuroscientist Joseph Lonstein of Michigan State University in East Lansing. He studies the neurochemistry of maternal caregiving and postpartum anxiety. Lonstein says many early studies measured hormone levels in women’s blood and tried to determine whether natural fluctuations were associated with the risk of postpartum depression. Those studies found “no clear correlations with [women’s] hormones and their susceptibility to symptoms,” he says. “While the hormone changes are certainly thought to be involved, not all women are equally susceptible. The question then became, what is it about their brains that makes particular women more susceptible?” Seeking answers, researchers have examined rodent brains and placed women into brain scanners to measure the women’s responses to pictures or videos of babies smiling, babbling or crying. Though hormones likely underlie the condition, many investigations have led to the amygdalae. These two, almond-shaped clumps of nerve cells deep in the brain are sometimes referred to as the emotional thermostat for their role in the processing of emotions, particularly fear.
The amygdalae are entangled with many structures that help make mothers feel like mothering, says neuroscientist Alison Fleming of the University of Toronto Mississauga. The amygdalae connect to the striatum, which is involved in experiencing reward, and to the hippocampus, a key player in memory and the body’s stress response. And more: They are wired to the hypothalamus, the interface between the brain and the endocrine system (when you are afraid, the endocrine system produces adrenaline and other chemicals that get your heart racing and palms sweating). The amygdalae are also connected to the prefrontal cortex and insula, involved in decision making, motivation and other functions intertwined with maternal instinct.
Fleming and colleagues have recently moved from studies in postpartum rodents to human mothers. In one investigation, reported in 2012 in Social Neuroscience, women were asked to look at pictures of smiling infants while in a functional MRI, which images brain activity. In mothers who were not depressed, the researchers found a higher amygdala response, more positive feelings and lower stress when women saw their own babies compared with unfamiliar infants.
But an unexpected pattern emerged in mothers with postpartum depression, as the researchers reported in 2016 in Social Neuroscience. While both depressed and not-depressed mothers showed elevated amygdala activity when viewing their own babies, the depressed mothers also showed heightened responses to happy, unknown babies, suggesting reactions to the women’s own children were blunted and not unique. This finding may mean that depressed women had less inclination to emotionally attach to their babies.
Mothers with postpartum depression also showed weaker connectivity between the amygdalae and the insula. Mothers with weaker connectivity in this area had greater symptoms of depression and anxiety. Women with stronger connectivity were more responsive to their newborns.
While there’s still no way to definitely know that the amygdalae are responding to postpartum chemical changes, “it’s very likely,” Lonstein says, pointing out that the amygdalae are influenced by the body’s reaction to hormones in other emotional settings.
Maternal rewards While important, the amygdalae are just part of the puzzle that seems to underlie postpartum depression. Among others is the nucleus accumbens, famous for its role in the brain’s reward system and in addiction, largely driven by the yin and yang of the neurotransmitters dopamine and serotonin. In studies, mothers who watched films of their infants (as opposed to watching unknown infants) experienced increased production of feel-good dopamine. The women also had a strengthening of the connection between the nucleus accumbens, the amygdalae and other structures, researchers from Harvard Medical School and their collaborators reported in February 2017 in Proceedings of the National Academy of Sciences.
That’s not entirely surprising given that rodent mothers find interacting with their newborn pups as neurologically rewarding as addictive drugs, says Ohio State’s Leuner. Rodent mothers that are separated from their offspring “will press a bar 100 times an hour to get to a pup. They will step across electrified grids to get to their pups. They’ve even been shown in some studies to choose the pups over cocaine.” Mothers find their offspring “highly, highly rewarding,” she says.
When there are postpartum glitches in the brain’s reward system, women may find their babies less satisfying, which could increase the risk for impaired mothering. Writing in 2014 in the European Journal of Neuroscience, Leuner and colleagues reported that in rats with symptoms of postpartum depression (induced by stress during pregnancy, a major risk factor for postpartum depression in women), nerve cells in the nucleus accumbens atrophied and showed fewer protrusions called dendritic spines — suggesting weaker connections to surrounding nerve cells compared with healthy rats. This is in contrast to other forms of depression, which show an increase in dendritic spines. Unpublished follow-up experiments conducted by Leuner’s team also point to a role for oxytocin, a hormone that spikes with the birth of a baby as estrogen and progesterone fall. Sometimes called the “cuddle chemical,” oxytocin is known for its role in maternal bonding (SN Online: 4/16/15). Leuner hypothesizes that maternal depression is associated with deficits in oxytocin receptors that enable the hormone to have its effects as part of the brain’s reward system.
If correct, the idea may help explain why oxytocin treatment failed women in some studies of postpartum depression. The hormone may simply not have the same potency in some women whose brains are short on receptors the chemical can latch on to. The next step is to test whether reversing the oxytocin receptor deficits in rodents’ brains relieves symptoms.
Leuner and other scientists emphasize that the oxytocin story is complex. In 2017, in a study reported in Depression & Anxiety, women without a history of depression who received oxytocin — which is often given to promote contractions or stem bleeding after delivery — had a 32 percent higher likelihood of developing postpartum depression than women who did not receive the hormone. In more than 46,000 births, 5 percent of women who did not receive the hormone were diagnosed with depression, compared with 7 percent who did.
“This was the opposite of what we predicted,” says Kristina Deligiannidis, a neuroscientist and perinatal psychiatrist at the Feinstein Institute for Medical Research in Manhasset, N.Y. After all, oxytocin is supposed to enhance brain circuits involved in mothering. “We had a whole group of statisticians reanalyze the data because we didn’t believe it,” she says. While the explanation is unknown, one theory is that perhaps the women who needed synthetic oxytocin during labor weren’t making enough on their own — and that could be why they are more prone to depression after childbirth.
But postpartum depression can’t be pinned to any single substance or brain malfunction — it doesn’t reside in one tidy nest of brain cells, or any one chemical process gone haywire. Maternal behavior is based on complex neurological circuitry. “Multiple parts of the brain are involved in any single function,” Deligiannidis says. “Just to have this conversation, I’m activating several different parts of my brain.” When any kind of depression occurs, she says, multiple regions of the brain are suffering from a communication breakdown.
Looking further, Deligiannidis has also examined the role of certain steroids synthesized from progesterone and other hormones and known to affect maternal brain circuitry. In a 2016 study in Psychoneuroendocrinology involving 32 new mothers at risk for postpartum depression and 24 healthy mothers, Deligiannidis and colleagues reported that concentrations of some steroids that affect the brain, also called neurosteroids, were higher in women at risk for developing depression (because of their past history or symptoms), compared with women who were not. The higher levels suggest a system out of balance — the brain is making too much of one neurosteroid and not enough of another, called allopregnanolone, which is thought to protect against postpartum depression and is being tested as a treatment. Treating pregnancy withdrawal Beyond mom
CASEZY IDEA/SHUTTERSTOCK Postpartum depression doesn’t weigh down just mom. Research suggests it might have negative effects on her offspring that can last for years. Risks include:
Newborns Higher levels of cortisol and other stress hormones More time fussing and crying More “indeterminate sleep,” hovering between deep and active sleep Infants and children Increased risk of developmental problems Slower growth Lower cognitive function Elevated cortisol levels Adolescents Higher risk of depression Tufts University neuroscientist Jamie Maguire, based in Boston, got interested in neurosteroids during her postgraduate studies in the lab of Istvan Mody at UCLA. Maguire and Mody reported in 2008 in Neuron that during pregnancy, the hippocampus has fewer receptors for neurosteroids, presumably to protect the brain from the massive levels of progesterone and estrogen circulating at that time. When progesterone drops after birth, the receptors repopulate.
But in mice genetically engineered to lack those receptors, something else happened: The animals were less interested in tending to their offspring, failing to make nests for them.
“We started investigating. Why are these animals having these abnormal postpartum behaviors?” Maguire recalls. Was an inability to recover these receptors making some women susceptible? Interestingly, similar receptors are responsible for the mood-altering and addictive effects of some antianxiety drugs, suggesting that the sudden progesterone drop after childbirth could be leaving some women with a kind of withdrawal effect.
Further experiments demonstrated that giving the mice a progesterone-derived neurosteroid — producing levels close to what the mice had in pregnancy — alleviated the symptoms.
Today, Maguire is on the scientific advisory board of Boston area–based Sage Therapeutics, which is testing a formulation of allopregnanolone called brexanolone. Results of an early clinical trial published last July in The Lancet assessed whether brexanolone would alleviate postpartum symptoms in women with severe postpartum depression. The study involved 21 women randomly assigned to receive a 60-hour infusion of the drug or a placebo within six months after delivery.
At the end of treatment, the women who received the drug reported a 21-point reduction on a standard scale of depression symptoms, compared with about 9 points for the women on a placebo. “These women got better in about a day,” says Deligiannidis, who is on the study’s research team. “The results were astonishing.”
In November, Sage Therapeutics announced the results of two larger studies, although neither has been published. Combined, the trials involved 226 women with severe or moderate postpartum depression. Both groups showed similar improvements that lasted for the month the women were followed. The company has announced plans to request approval from the U.S. Food and Drug Administration to market brexanolone in the United States. This is an important first step, researchers say, toward better treatments.
“We are just touching on one small piece of a bigger puzzle,” says Jodi Pawluski, a neuroscientist at the Université de Rennes 1 in France who coauthored the 2017 review in Trends in Neurosciences. She was surprised at the dearth of research, given how common postpartum depression is. “This is not the end, it’s the beginning.”
