To urinate or not to urinate? That’s a question for the bladder and the brain.

You’re driving somewhere, staring at the road, when you start to feel a tingling sensation in your lower abdomen. That extra large Coke you drank an hour ago has made its way through your kidneys to your bladder. “It’s time to stop,” she thinks, looking for an exit ramp.

For most people, stopping at a rest stop on the highway is a deeply mundane experience. But not for neuroscientist Rita Valentino, who has studied how the brain detects, interprets and acts on signals from the bladder. She is fascinated by the brain’s ability to capture sensations from the bladder, combine them with signals outside the body, such as the sights and sounds of the road, and then use that information to act; in this scenario, to find a safe and socially secure place. appropriate place to urinate. “To me, it’s really an example of one of the beautiful things the brain does,” she says.

Scientists used to think our bladders were governed by a relatively simple reflex: an “on-off” switch between storing urine and letting it go. “Now we realize it’s much more complex than that,” says Valentino, now director of the division of neuroscience and behavior at the National Institute on Drug Abuse. An intricate network of brain regions participates in making the call that contributes to functions such as decision making, social interactions and awareness of the internal state of our body, also called interoception.

In addition to being astonishingly complex, the system is also delicate. Scientists estimate, for example, that more than 1 in 10 adults suffer from overactive bladder syndrome, a common constellation of symptoms that includes urinary urgency (the feeling of needing to urinate even when the bladder is not full), nocturia (the need to urinate frequently) nighttime visits to the bathroom) and incontinence. Although existing treatments can improve symptoms in some people, they don’t work for many people, says Martin Michel, a pharmacologist at Johannes Gutenberg University in Mainz, Germany, who researches therapies for bladder disorders. Developing better drugs has proven so difficult that all the major pharmaceutical companies have abandoned the effort, he adds.

Recently, however, a wave of new research is opening the field to new hypotheses and treatment approaches. Although therapies for bladder disorders have historically focused on the bladder itself, new studies point to the brain as another potential target, Valentino says. Combined with studies aimed at explaining why certain groups, such as postmenopausal women, are more likely to suffer from bladder problems, the research suggests we shouldn’t simply accept symptoms like incontinence as inevitable, says Indira Mysorekar, a microbiologist at Baylor College of Medicine. In Houston. We are often told that these problems are simply part of aging, especially for women, “and that is true to a certain extent,” she says. But many common problems can be avoided and treated successfully, she says: “We don’t have to live with pain or discomfort.”

A delicate balance

The human bladder is, at the most basic level, an elastic bag. To fill its capacity (a volume of 400 to 500 milliliters (about 2 cups) of urine in most healthy adults) it must undergo one of the most extreme expansions of any organ in the human body, expanding approximately six times from its shriveled state. and empty. .

To stretch that much, the smooth muscle wall surrounding the bladder, called the detrusor, must relax. At the same time, the sphincter muscles surrounding the lower opening of the bladder, or urethra, must contract, in what scientists call the guard reflex.

It's not just the sensory neurons (purple) that can detect stretch, pressure, pain and other sensations in the bladder.  Other cell types, such as the umbrella-shaped cells that form the urothelial barrier to urine, can also sense and respond to mechanical forces (for example, by releasing chemical signaling molecules such as adenosine triphosphate (ATP) as they move. The organ expands to fill with urine.
Enlarge / It’s not just the sensory neurons (purple) that can detect stretch, pressure, pain and other sensations in the bladder. Other cell types, such as the umbrella-shaped cells that form the urothelial barrier to urine, can also sense and respond to mechanical forces (for example, by releasing chemical signaling molecules such as adenosine triphosphate (ATP) as they move. The organ expands to fill with urine.

Full or full, the bladder spends more than 95 percent of its time in storage mode, allowing us to go about our daily activities without leaking. At some point (ideally, when we decide it’s time to urinate), the organ switches from storage mode to release mode. To do this, the detrusor muscle must contract strongly to expel urine, while the sphincter muscles surrounding the urethra simultaneously relax to release urine.

For a century, physiologists have wondered how the body coordinates the switch between storage and release. In the 1920s, a surgeon named Frederick Barrington at University College London looked for the on-off switch in the brainstem, the lowest part of the brain that connects to the spinal cord.

Working with sedated cats, Barrington used an electrified needle to damage slightly different areas of the pons, part of the brain stem that handles vital functions like sleeping and breathing. When the cats recovered, Barrington noticed that some showed a desire to urinate (by scratching, rolling, or bending over) but were unable to do so voluntarily. Meanwhile, cats with lesions on a different part of the bump appeared to have lost awareness of the need to urinate, urinated at random times, and appeared frightened each time it occurred. Clearly, the pons served as an important command center for urinary function, telling the bladder when to release urine.

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