Joseph Garner, Purdue University associate professor of animal sciences, fed mice a diet high in sugar and tryptophan that was expected to reduce abnormal hair-pulling, the journal Nutritional Neuroscience reported.
Instead, mice that were already ill worsened or started scratching themselves. The seemingly healthy mice also developed the same abnormal behaviour, according to a Purdue release.
“This strain of mouse is predisposed to being either a scratcher or a hair-puller. Giving them this diet brought out those predispositions,” Garner said.
Garner studies trichotillomania, a disorder in which people pull out their hair. The disorder, which disproportionately occurs in women, is thought to affect 2-4 percent of the population.
Mice that pull their hair out have been shown to have low levels of serotonin activity in the brain. Serotonin is a neurotransmitter that affects mood and impulses and is made from the amino acid tryptophan, which is found in diets.
Garner hypothesised that increasing serotonin activity in the brain might cure or reduce trichotillomania.
The problem is that tryptophan often doesn’t cross the barrier between blood and the brain because other amino acids essentially block the door for tryptophan.
Garner modified a mouse diet to increase simple carbohydrates, or sugars, and tryptophan. The sugars trigger a release of insulin, which causes muscles to absorb those other amino acids and gives tryptophan a chance to make it to the brain.
Using eight times as much sugar and four times as much tryptophan, Garner observed a doubling of serotonin activity in the brain. But the mice that barbered did not get better.
“We put them on this diet, and it made them much, much worse,” Garner said.
