We鈥檝e all been there 鈥� desperately holding on until reaching a toilet. Now researchers have discovered the brain cells that help mammals do this 鈥� a finding that may聽lead to new treatments for incontinence.
Just like humans, mice learn to control when and where they urinate. To attract mates, males intentionally leave dabs of urine wherever they pick up the scent of females. of the Scripps Research Institute in La Jolla, California, and her colleagues聽used聽this behaviour to identify the brain cells involved in this voluntary urination.
The team had previously identified neurons in the brainstem region 鈥� the part of the brain that extends downward into the spinal cord 鈥� that control bladder muscles. But these alone are not enough for a mouse to urinate 鈥� muscles that constrict the urethra, the tube that empties the bladder, need to relax too.
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Analysing slices of cells from this region of the brain, they identified around 200 neurons that didn鈥檛 behave the same way as the other bladder-relaxing cells.
Urinating at will
When the team artificially stimulated these neurons, the mice urinated on demand. Measurements made using implanted pressure recorders showed that activation of these neurons relaxes the muscles that normally hold the urethra closed. Chemically blocking these neurons stopped mice from urinating when they were exposed to female scents.
鈥淚dentifying these neurons now opens the door for new ways of understanding and treating incontinence,鈥� says Stowers.
She thinks these brain cells might also have a role in other bodily functions, such as defecation, giving birth, orgasm and ejaculation during sex. Like peeing, these depend on relaxation of . 鈥淭hese muscles stay contracted your whole life, and only relax briefly during a handful of behaviours: urination, defecation, sex and childbirth,鈥� she says.
Nature Neuroscience
