A common bladder infection may make memory and thinking problems worse after a traumatic brain injury, according to new research in mice.
The findings suggest that infections outside the brain could have a bigger effect on recovery than doctors have realized.
Traumatic brain injury, or TBI, happens when a sudden blow or jolt damages the brain. Falls are one of the most common causes, especially among older adults, and even people who survive a moderate injury can experience lasting problems with memory, concentration, mood and daily activities.
People recovering from TBI are also more likely to develop infections. Lung infections are well known, but urinary tract infections, or UTIs, are also common and may be responsible for a significant number of hospital visits after a brain injury.
A UTI usually happens when bacteria enter the urinary system and multiply in the bladder. The most common cause is E. coli, a type of bacteria that normally lives in the digestive system but can cause infection when it reaches the urinary tract.
UTIs can cause pain or burning during urination, frequent trips to the bathroom and lower abdominal discomfort. In medically vulnerable or older people, they may also occur alongside sudden confusion or changes in thinking.
Researchers at The Ohio State University wanted to know whether a bladder infection could interfere with the brain’s recovery after an injury. Their study is among the first to directly examine how a UTI after TBI affects both memory and the body’s immune response in an animal model.
The researchers studied four groups of female mice. Some received a moderate brain injury under anesthesia, while others underwent a similar procedure without the brain injury.
Three days later, some of the mice were given E. coli bacteria that cause UTIs, while the remaining animals received a control treatment. The scientists then tested the animals’ behavior and examined changes in the brain, blood and bladder.
Six days after the brain injury, mice with TBI already showed poorer spatial memory, which is the ability to remember locations and surroundings. But mice that developed a UTI after the brain injury had much greater memory problems.
The researchers also found signs that the immune system was reacting differently when the two conditions occurred together. Certain inflammation-related substances increased later in several parts of the injured brain, suggesting that brain immune cells were responding to the bladder infection as well as the original injury.
Another surprising finding appeared in the bladder. Brain injury alone changed the number or activity of some immune cells there, even before a UTI was added.
This raises the possibility that a brain injury may somehow change the bladder’s defenses and make infection more likely. Researchers do not yet know exactly how this happens, but the brain and bladder communicate through nerves, and the new findings suggest the connection may also involve the immune system.
The team also examined IL-6, a substance involved in inflammation. Its levels increased in the blood after brain injury but changed when a UTI was present, providing another clue that the body’s response to infection may be altered after TBI.
Senior author Olga Kokiko-Cochran said common infections should not automatically be considered minor in people recovering from brain injuries. Understanding and preventing UTIs could potentially become another way to support recovery and reduce additional problems with thinking and memory.
The first study used female mice because UTIs are much more common in females. Future experiments will include both sexes and investigate more closely how signals travel between the injured brain and the bladder.
The research was led by scientists at The Ohio State University and published in the Journal of Neurotrauma. Because the findings come from mice, studies in people will be needed to determine whether UTIs have the same effects on the human brain after TBI.
