TOKYO -- Drugs that stimulate the secretion of histamine in the brain can enable people to smoothly recall vague memories, Japanese researchers found in a recent experiment on mice and people.
The research team, including members of Hokkaido University, published their discovery Jan. 8 in the electronic edition of American medical journal Biological Psychiatry. Researchers said that the drugs had a profound effect especially on those with poor memory, and say their findings may lead to the development of new therapeutic drugs to treat cognitive impairment like Alzheimer's disease.
The team focused on the fact that histamine functions as a neurotransmitter and is relevant to memory. Researchers used the nature of mice to identify objects they came across in the past by using their sense of smell and touch, and to show interest in new items. They observed the mice by placing two toys in their operant conditioning chamber and replacing one with a new toy. Although the mice could distinguish and favor the new toy over the old one within a short time after introducing the objects, they showed interest in both toys after three days due to memory loss.
But the mice were able to identify and favor the new toy again when they were given the drug -- even after a month.
With the experiment on humans, researchers used over-the-counter drugs that prompt the release of histamine, and placebos. The team members showed about 100 photos to a total of 38 men and women in their 20s to 40s and tested if participants remembered them a week later. The correct answer rate for those who took the over-the-counter drugs was 46 percent and 43 percent for those who took the placebos.
When the group of people who had the worst results after taking the placebos was given the drugs, their correct answer rate rose from roughly 25 percent to about 50 percent. However, when the group of people taking the placebos who had the highest correct answer rate of about 60 percent took the drugs, their figure decreased to about 40 percent.
The research team analyzed that all the nerve cells in the brain were activated due to the release of histamine and increased sensitivity to recall fragments of memory. But they concluded that too much activation of nerve cells created "noise" that hindered memory recall of those who already had vivid memories. "It's an accomplishment that can lead to a breakthrough discovery in the mechanism of memory," commented team member Hiroshi Nomura, a professor of neuroscience at Hokkaido University.
(Japanese original by Yuka Saito, Science & Environment News Department)