U.S. and Israeli scientists - led by Gene E. Robinson of the University of Illinois - report that forager bees, which work outside the hive collecting nectar and pollen, have lower activity levels of the acetylcholingesterase (AChE) protein in their brains than do younger nurse bees.
AChE is an enzyme that breaks down a primary neurotransmitter known as acetylcholine (ACh). Neurons use ACh to communicate with one another. In the human body, ACh signals muscle movement, and, in the brain, it is linked to learning and memory. In many Alzheimer's patients, researchers have noted a loss of neurons that secrete ACh. One treatment is the use of an AChE inhibitor. The scientists, reporting in a recent issue of the Journal of Molecular Neuroscience, showed that the reduction of AChE protein activity is the result of the down regulation of the AChE gene.
"A reduction in AChE activity might mean that foragers, which among honeybees lead the most challenging life, have enhanced ACh neurotransmission," said Robinson, a professor of entomology and neuroscience. He speculated that enhanced ACh neurotransmission in foragers, as in humans, may improve cognitive performance.
Honeybees live in a social world known for its distinct division of labor based on age-specific tasks. They begin their adult life working inside the hive as sanitation workers and nursemaids, among other roles. They then shift to foraging outside the hive when they are about 3 weeks old. The shift to foraging requires the learning of new skills, many revolving around vision and smell.
AChE accounts for almost all of the cholinesterase activity in the brain of a honeybee, suggesting that this particular protein may regulate major aspects of cholinergetic activity, Robinson said. While the biochemical makeup of AChE was the same in nurses and foragers, the decline of catalytic activity of AChE ranged from 20 percent to 65 percent in the foragers. Other experiments showed that the drop in AChE activity was probably "due to aging or experience as a forager" and not associated with the transition from working in the hive to foraging.
When researchers used an inhibitor, metrifonate, to reduce AChE activity, the treated foragers consistently outscored the control foragers in a laboratory learning test. "Although it is not clear whether foragers have higher cognitive capacities than nurses, our findings provide a possible explanation if that is the case," Robinson said.
Co-authors were Robinson and C.K. Thompson, a Howard Hughes Research Fellow in the UI department of entomology, and M. Shapira and H. Soreq, both of the Hebrew University of Jerusalem. The research was funded in part by the U.S. National Institutes of Health, U.S. Army Medical Research and Development Command, and the Israeli Ministry of Science.