Ow! These cells might help brains remember pain and fear
WASHINGTON, D.C — War, pain and other traumatic events can sear themselves into our memories. Now, a study in rats offers clues to how the brain appears to form those memories. It gets a hand from cells called astrocytes. Scientists used to think these cells only provided food and comfort to more important nerve cells. It now turns out that astrocytes may play a key role in how we learn from tough times.
Fear and pain are not pleasant. But they can help us to learn how to anticipate it — or avoid what triggers it — in the future. That’s a benefit. But when an event is truly terrible, such memories can become a source of post-traumatic stress disorder, or PTSD.
This is a severe condition that can occur after someone has a terrible experience, such as a terrorist attack, kidnapping or battlefield firefight. People with PTSD may become anxious, even when there’s no danger. They also may have flashbacks, where they remember a traumatic event, replaying the details over and over in their mind.
Meghan Jones is a brain scientist at the University of North Carolina in Chapel Hill. She wants to know where fear crosses the line from learning to trauma. It’s difficult to study memory or PTSD in people. After all, everyone’s experience is different. So Jones and her colleagues work in rats.
To make sure their animals had a powerful bad memory, the scientists gave these rats a short series of foot shocks. These did not injure the animals. Indeed, Jones tested the shocks on herself. They were painful and scary, she recalls — “painful enough to make you curse.”
Rats are no fools when it comes to fear. A week after the first, painful experience, they remained jumpy when given a second, milder shock (about as strong as the static-electricity shock one might get from a metal doorknob in winter).
The point of the research was not to make rats miserable. Jones and her team wanted to figure out what was going on in their brains. To do this, the scientists focused on the hippocampus. It’s an area of the brain important for learning and memory.
After the first painful experience, the rat’s hippocampus released a chemical called interleukin 1 beta (IL-1 beta). This chemical is important in inflammation — or how the body responds to stress or injury.
More than 90 percent of this IL-1 beta was coming from astrocytes, the researchers found. And this surprised them.
Not just support
Scientists used to think of astrocytes and other non-nerve cells in the brain as mere support cells. They did the dirty work, cleaning up messes and providing food to the neurons — nerve cells that are the stars of the nervous system and that conduct electrical signals. Astrocytes were just the backup dancers. But now, it appears astrocytes have their own important roles to play.
The scientists treated the animals’ brains with a drug designed to turn on a signal in their brains’ astrocyte cells. That signal was inhibitory — meaning that it reduced the activity of the astrocytes. With this treatment, the scientist were able to change how the rats learned fear. Instead of getting jumpy, the animals stayed calm in the face of later shocks.
This could mean the animals need IL-1 beta from the astrocytes to remember scary times. Jones and her group haven’t specifically figured out how IL-1 beta from astrocytes does this. But they are running more tests to find out.
On November 15, they presented their initial results here at the annual meeting of the Society for Neuroscience.
Rebecca Shansky is a brain researcher at Northeastern University in Boston, Mass. She says the rat tests may offer only a rough gauge of what to expect in people with PTSD. Why? The rats here were tested only one week after they went through their painful experience. People, in contrast, don’t get diagnosed with PTSD until at least a month has passed since their trauma.
But the study does show how animals learn and make memories from stressful experiences. As such, Shansky notes, “it’s pretty cool.” What’s more, she says, “The idea that there are inflammatory mechanisms involved in the way these experiences are processed makes sense.”
Where those inflammatory signals come from is important, notes Georgia Hodes. She’s a brain scientist at Virginia Tech in Blacksburg. “Everyone’s been focused on what neurons are doing,” she says. This is “showing an important effect of cells we thought of as only being supportive.”
Studies like these are “changing how we think about the circuitry that’s involved in depression and post-traumatic stress disorder,” Hodes says. Understanding more about how memories form could eventually help scientists find the line between PTSD and helpful — if painful — memories.
astrocyte A type of non-nerve cell found in the brain.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
colleague Someone who works with another; a co-worker or team member.
depression (in medicine) A mental illness characterized by persistent sadness and apathy. Although these feelings can be triggered by events, such as the death of a loved one or the move to a new city, that isn’t typically considered an “illness” — unless the symptoms are prolonged and harm an individual’s ability to perform normal daily tasks (such as working, sleeping or interacting with others). People suffering from depression often feel they lack the energy needed to get anything done. They may have difficulty concentrating on things or showing an interest in normal events. Many times, these feelings seem to be triggered by nothing; they can appear out of nowhere.
disorder (in medicine) A condition where the body does not work appropriately, leading to what might be viewed as an illness. This term can sometimes be used interchangeably with disease.
hippocampus (pl. hippocampi) A seahorse-shaped region of the brain. It is thought to be the center of emotion, memory and the involuntary nervous system.
immune (adj.) Having to do with the immunity. (v.) Able to ward off a particular infection. Alternatively, this term can be used to mean an organism shows no impacts from exposure to a particular poison or process. More generally, the term may signal that something cannot be hurt by a particular drug, disease or chemical.
immune system The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.
inflammation (adj. inflammatory) The body’s response to cellular injury and obesity; it often involves swelling, redness, heat and pain. It also is an underlying feature responsible for the development and aggravation of many diseases, especially heart disease and diabetes.
interleukin 1 beta A chemical that plays a signaling role in the body and brain. It is especially important in inflammation — one process by which the body responds to injury.
mechanism The steps or process by which something happens or “works.” It may be the spring that pops something from one hole into another. It could be the squeezing of the heart muscle that pumps blood throughout the body. It could be the friction (with the road and air) that slows down the speed of a coasting car. Researchers often look for the mechanism behind actions and reactions to understand how something functions.
microglia A type of cell found in the brain and spinal cord. It can move from place to place, and serve as part of the immune system, protecting the brain from infection.
nerve A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.
neuron An impulse-conducting cell. Such cells are found in the brain, spinal column and nervous system.
neuroscience The field of science that deals with the structure or function of the brain and other parts of the nervous system. Researchers in this field are known as neuroscientists.
neuroscientist Someone who studies the structure or function of the brain and other parts of the nervous system.
post-traumatic stress disorder , or PTSD A severe condition that may develop after a person is exposed to a traumatic injury or severe psychological shock. Recalling the event can bring on anxiety and other problems in the victim.
stress (in biology) A factor — such as unusual temperatures, movements, moisture or pollution — that affects the health of a species or ecosystem. (in psychology) A mental, physical, emotional or behavioral reaction to an event or circumstance (stressor) that disturbs a person or animal’s usual state of being or places increased demands on a person or animal; psychological stress can be either positive or negative. (in physics) Pressure or tension exerted on a material object.
Meeting: M.E. Jones et al. Neuroimmune signaling in stress-enhanced fear learning, an animal model of post-traumatic stress disorder. Society for Neuroscience annual meeting, Washington, D.C., November 13, 2017.